Molecular dynamics simulations of acoustic absorption by a carbon nanotube

NASA Astrophysics Data System (ADS)

Ayub, M.; Zander, A. C.; Huang, D. M.; Howard, C. Q.; Cazzolato, B. S.

2018-06-01

Acoustic absorption by a carbon nanotube (CNT) was studied using molecular dynamics (MD) simulations in a molecular domain containing a monatomic gas driven by a time-varying periodic force to simulate acoustic wave propagation. Attenuation of the sound wave and the characteristics of the sound field due to interactions with the CNT were studied by evaluating the behavior of various acoustic parameters and comparing the behavior with that of the domain without the CNT present. A standing wave model was developed for the CNT-containing system to predict sound attenuation by the CNT and the results were verified against estimates of attenuation using the thermodynamic concept of exergy. This study demonstrates acoustic absorption effects of a CNT in a thermostatted MD simulation, quantifies the acoustic losses induced by the CNT, and illustrates their effects on the CNT. Overall, a platform was developed for MD simulations that can model acoustic damping induced by nanostructured materials such as CNTs, which can be used for further understanding of nanoscale acoustic loss mechanisms associated with molecular interactions between acoustic waves and nanomaterials.

Enhanced field emission properties of carbon nanotube bundles confined in SiO2 pits

NASA Astrophysics Data System (ADS)

Lim, Yu Dian; Grapov, Dmitry; Hu, Liangxing; Kong, Qinyu; Tay, Beng Kang; Labunov, Vladimir; Miao, Jianmin; Coquet, Philippe; Aditya, Sheel

2018-02-01

It has been widely reported that carbon nanotubes (CNTs) exhibit superior field emission (FE) properties due to their high aspect ratios and unique structural properties. Among the various types of CNTs, random growth CNTs exhibit promising FE properties due to their reduced inter-tube screening effect. However, growing random growth CNTs on individual catalyst islands often results in spread out CNT bundles, which reduces overall field enhancement. In this study, significant improvement in FE properties in CNT bundles is demonstrated by confining them in microfabricated SiO2 pits. Growing CNT bundles in narrow (0.5 μm diameter and 2 μm height) SiO2 pits achieves FE current density of 1-1.4 A cm-2, which is much higher than for freestanding CNT bundles (76.9 mA cm-2). From the Fowler Nordheim plots, confined CNT bundles show a higher field enhancement factor. This improvement can be attributed to the reduced bundle diameter by SiO2 pit confinement, which yields bundles with higher aspect ratios. Combining the obtained outcomes, it can be conclusively summarized that confining CNTs in SiO2 pits yields higher FE current density due to the higher field enhancement of confined CNTs.

Longitudinal waves in carbon nanotubes in the presence of transverse magnetic field and elastic medium

NASA Astrophysics Data System (ADS)

Liu, Hu; Liu, Hua; Yang, Jialing

2017-09-01

In the present paper, the coupling effect of transverse magnetic field and elastic medium on the longitudinal wave propagation along a carbon nanotube (CNT) is studied. Based on the nonlocal elasticity theory and Hamilton's principle, a unified nonlocal rod theory which takes into account the effects of small size scale, lateral inertia and radial deformation is proposed. The existing rod theories including the classic rod theory, the Rayleigh-Love theory and Rayleigh-Bishop theory for macro solids can be treated as the special cases of the present model. A two-parameter foundation model (Pasternak-type model) is used to represent the elastic medium. The influence of transverse magnetic field, Pasternak-type elastic medium and small size scale on the longitudinal wave propagation behavior of the CNT is investigated in detail. It is shown that the influences of lateral inertia and radial deformation cannot be neglected in analyzing the longitudinal wave propagation characteristics of the CNT. The results also show that the elastic medium and the transverse magnetic field will also affect the longitudinal wave dispersion behavior of the CNT significantly. The results obtained in this paper are helpful for understanding the mechanical behaviors of nanostructures embedded in an elastic medium.

Disabling CNT Electronic Devices by Use of Electron Beams

NASA Technical Reports Server (NTRS)

Petkov, Mihail

2008-01-01

Bombardment with tightly focused electron beams has been suggested as a means of electrically disabling selected individual carbon-nanotubes (CNTs) in electronic devices. Evidence in support of the suggestion was obtained in an experiment in which a CNT field-effect transistor was disabled (see figure) by focusing a 1-keV electron beam on a CNT that served as the active channel of a field-effect transistor (FET). Such bombardment could be useful in the manufacture of nonvolatile-memory circuits containing CNT FETs. Ultimately, in order to obtain the best electronic performances in CNT FETs and other electronic devices, it will be necessary to fabricate the devices such that each one contains only a single CNT as an active element. At present, this is difficult because there is no way to grow a single CNT at a specific location and with a specific orientation. Instead, the common practice is to build CNTs into electronic devices by relying on spatial distribution to bridge contacts. This practice results in some devices containing no CNTs and some devices containing more than one CNT. Thus, CNT FETs have statistically distributed electronic characteristics (including switching voltages, gains, and mixtures of metallic and semiconducting CNTs). According to the suggestion, by using a 1-keV electron beam (e.g., a beam from a scanning electron microscope), a particular nanotube could be rendered electrically dysfunctional. This procedure could be repeated as many times as necessary on different CNTs in a device until all of the excess CNTs in the device had been disabled, leaving only one CNT as an active element (e.g., as FET channel). The physical mechanism through which a CNT becomes electrically disabled is not yet understood. On one hand, data in the literature show that electron kinetic energy >86 keV is needed to cause displacement damage in a CNT. On the other hand, inasmuch as a 1-keV beam focused on a small spot (typically a few tens of nanometers wide) deposits a significant amount of energy in a small volume, the energy density may suffice to thermally induce structural and/or electronic changes that disable the CNT. Research may be warranted to investigate this effect in detail.

Linear increases in carbon nanotube density through multiple transfer technique.

PubMed

Shulaker, Max M; Wei, Hai; Patil, Nishant; Provine, J; Chen, Hong-Yu; Wong, H-S P; Mitra, Subhasish

2011-05-11

We present a technique to increase carbon nanotube (CNT) density beyond the as-grown CNT density. We perform multiple transfers, whereby we transfer CNTs from several growth wafers onto the same target surface, thereby linearly increasing CNT density on the target substrate. This process, called transfer of nanotubes through multiple sacrificial layers, is highly scalable, and we demonstrate linear CNT density scaling up to 5 transfers. We also demonstrate that this linear CNT density increase results in an ideal linear increase in drain-source currents of carbon nanotube field effect transistors (CNFETs). Experimental results demonstrate that CNT density can be improved from 2 to 8 CNTs/μm, accompanied by an increase in drain-source CNFET current from 4.3 to 17.4 μA/μm.

The effects of ferrocene concentration on CNT growth on micron silica gel

NASA Astrophysics Data System (ADS)

Othman, Raja N.; Wilkinson, Arthur N.

2017-12-01

The growth of CNT on micron size spherical silica gel of high porosity was performed in this work. The CNT was grown via floating catalyst chemical vapor deposition method (FCCVD). The reaction temperature and time were kept at 760 °C and 3 hours, respectively. The concentration of the catalyst used, which was ferrocene, was varied from 1 wt. % to 9.6 wt. %, with respect to toluene. Striking difference in the morphology of the synthesized tubes was observed using Field Emission Scanning Electron Microscope (FESEM) and Transmission Electron Microscope (TEM) images. The quality and quantity of the CNT were further characterized via Raman Spectroscopy and Thermogravimetric Analysis. Based on these characterizations, it was found that the ferrocene concentration greatly affects the morphology of the obtained CNT; with 1 wt.% and 9.6 wt.% ferrocene concentrations yield CNT of bigger outer diameters, compared to the CNT obtained from 5 wt.% ferrocene concentrations.

Advances in mechanisms and signaling pathways of carbon nanotube toxicity

PubMed Central

Dong, Jie; Ma, Qiang

2015-01-01

Carbon nanotubes (CNT) have been developed into new materials with a variety of industrial and commercial applications. In contrast, the physicochemical properties of CNT at the nanoscale render them the potency to generate toxic effects. Indeed, the potential health impacts of CNT have drawn a great deal of attention in recent years, owing to their identified toxicological and pathological consequences including cytotoxicity, inflammation, fibrosis, genotoxicity, tumorigenesis, and immunotoxicity. Understanding the mechanisms by which CNT induce toxicity and pathology is thus urgently needed for accurate risk assessment of CNT exposure in humans, and for safe and responsible development and commercialization of nanotechnology. Here, we summarize and discuss recent advances in this area with a focus on the molecular interactions between CNT and mammalian systems, and the signaling pathways important for the development of CNT toxicity such as the NF-κB, NLRP3 inflammasome, TGF-β1, MAPK, and p53 signaling cascades. With the current mechanistic evidence summarized in this review, we expect to provide new insights into CNT toxicology at the molecular level and offer new clues to the prevention of health effects resulting from CNT exposure. Moreover, we disclose questions and issues that remain in this rapidly advancing field of nanotoxicology, which would facilitate ascertaining future research directions. PMID:25676622

Highly anisotropic magneto-transport and field orientation dependent oscillations in aligned carbon nanotube/epoxy composites

NASA Astrophysics Data System (ADS)

Wells, Brian; Kumar, Raj; Reynolds, C. Lewis; Peters, Kara; Bradford, Philip D.

2017-12-01

Carbon nanotubes (CNTs) have been widely investigated as additive materials for composites with potential applications in electronic devices due to their extremely large electrical conductivity and current density. Here, highly aligned CNT composite films were created using a sequential layering fabrication technique. The degree of CNT alignment leads to anisotropic resistance values which varies >400× in orthogonal directions. Similarly, the magnetoresistance (MR) of the CNT composite differs depending upon the relative direction of current and the applied magnetic field. A suppression of negative to positive MR crossover was also observed. More importantly, an overall positive magnetoresistance behavior with localized +/- oscillations was discovered at low fields which persists up to room temperature when the current (I) and in-plane magnetic field (B) were parallel to the axis of CNT (B∥I∥CNT), which is consistent with Aharonov-Bohm oscillations in our CNT/epoxy composites. When the current, applied magnetic field, and nanotube axis are aligned, the in-plane MR is positive instead of negative as observed for all other field, current, and tube orientations. Here, we provide in-depth analysis of the conduction mechanism and anisotropy in the magneto-transport properties of these aligned CNT-epoxy composites.

Label-free electrical detection using carbon nanotube-based biosensors.

PubMed

Maehashi, Kenzo; Matsumoto, Kazuhiko

2009-01-01

Label-free detections of biomolecules have attracted great attention in a lot of life science fields such as genomics, clinical diagnosis and practical pharmacy. In this article, we reviewed amperometric and potentiometric biosensors based on carbon nanotubes (CNTs). In amperometric detections, CNT-modified electrodes were used as working electrodes to significantly enhance electroactive surface area. In contrast, the potentiometric biosensors were based on aptamer-modified CNT field-effect transistors (CNTFETs). Since aptamers are artificial oligonucleotides and thus are smaller than the Debye length, proteins can be detected with high sensitivity. In this review, we discussed on the technology, characteristics and developments for commercialization in label-free CNT-based biosensors.

Improved field emission properties of carbon nanotubes grown on stainless steel substrate and its application in ionization gauge

NASA Astrophysics Data System (ADS)

Li, Detian; Cheng, Yongjun; Wang, Yongjun; Zhang, Huzhong; Dong, Changkun; Li, Da

2016-03-01

Vertically aligned carbon nanotube (CNT) arrays were fabricated by chemical vapor deposition (CVD) technique on different substrates. Microstructures and field emission characteristics of the as-grown CNT arrays were investigated systematically, and its application in ionization gauge was also evaluated preliminarily. The results indicate that the as-grown CNT arrays are vertically well-aligned relating to the substrate surfaces, but the CNTs grown on stainless steel substrate are longer and more crystalline than the ones grown on silicon wafer substrate. The field emission behaviors of the as-grown CNT arrays are strongly dependent upon substrate properties. Namely, the CNT array grown on stainless steel substrate has better field emission properties, including lower turn on and threshold fields, better emission stability and repeatability, compared with the one grown on silicon wafer substrate. The superior field emission properties of the CNT array grown on stainless steel substrate are mainly attributed to low contact resistance, high thermal conductivity, good adhesion strength, etc. In addition, the metrological behaviors of ionization gauge with the CNT array grown on stainless steel substrate as an electron source were investigated, and this novel cathode ionization gauge extends the lower limit of linear pressure measurement to 10-8 Pa, which is one order of magnitude lower than the result reported for the same of gauge with CNT cathode.

Field emission properties of SiO2-wrapped CNT field emitter.

PubMed

Lim, Yu Dian; Hu, Liangxing; Xia, Xin; Ali, Zishan; Wang, Shaomeng; Tay, Beng Kang; Aditya, Sheel; Miao, Jianmin

2018-01-05

Carbon nanotubes (CNTs) exhibit unstable field emission (FE) behavior with low reliability due to uneven heights of as-grown CNTs. It has been reported that a mechanically polished SiO 2 -wrapped CNT field emitter gives consistent FE performance due to its uniform CNT heights. However, there are still a lack of studies on the comparison between the FE properties of freestanding and SiO 2 -wrapped CNTs. In this study, we have performed a comparative study on the FE properties of freestanding and SiO 2 -wrapped CNT field emitters. From the FE measurements, freestanding CNT field emitter requires lower applied voltage of 5.5 V μm -1 to achieve FE current density of 22 mA cm -2 ; whereas SiO 2 -wrapped field emitter requires 8.5 V μm -1 to achieve the same current density. This can be attributed to the lower CNT tip electric field of CNTs embedded in SiO 2 , as obtained from the electric field simulation. Nevertheless, SiO 2 -wrapped CNTs show higher consistency in FE current than freestanding CNTs. Under repeated FE measurement, SiO 2 -wrapped CNT field emitter achieves consistent FE behavior from the 1st voltage sweep, whereas freestanding field emitter only achieved consistent FE performance after 3rd voltage sweep. At the same time, SiO 2 -wrapped CNTs exhibit better emission stability than freestanding CNTs over 4000 s continuous emission.

Field emission properties of SiO2-wrapped CNT field emitter

NASA Astrophysics Data System (ADS)

Lim, Yu Dian; Hu, Liangxing; Xia, Xin; Ali, Zishan; Wang, Shaomeng; Tay, Beng Kang; Aditya, Sheel; Miao, Jianmin

2018-01-01

Carbon nanotubes (CNTs) exhibit unstable field emission (FE) behavior with low reliability due to uneven heights of as-grown CNTs. It has been reported that a mechanically polished SiO2-wrapped CNT field emitter gives consistent FE performance due to its uniform CNT heights. However, there are still a lack of studies on the comparison between the FE properties of freestanding and SiO2-wrapped CNTs. In this study, we have performed a comparative study on the FE properties of freestanding and SiO2-wrapped CNT field emitters. From the FE measurements, freestanding CNT field emitter requires lower applied voltage of 5.5 V μm-1 to achieve FE current density of 22 mA cm-2 whereas SiO2-wrapped field emitter requires 8.5 V μm-1 to achieve the same current density. This can be attributed to the lower CNT tip electric field of CNTs embedded in SiO2, as obtained from the electric field simulation. Nevertheless, SiO2-wrapped CNTs show higher consistency in FE current than freestanding CNTs. Under repeated FE measurement, SiO2-wrapped CNT field emitter achieves consistent FE behavior from the 1st voltage sweep, whereas freestanding field emitter only achieved consistent FE performance after 3rd voltage sweep. At the same time, SiO2-wrapped CNTs exhibit better emission stability than freestanding CNTs over 4000 s continuous emission.

Polymer-based doping control for performance enhancement of wet-processed short-channel CNTFETs

NASA Astrophysics Data System (ADS)

Hartmann, Martin; Schubel, René; Claus, Martin; Jordan, Rainer; Schulz, Stefan E.; Hermann, Sascha

2018-01-01

The electrical transport properties of short-channel transistors based on single-walled carbon nanotubes (CNT) are significantly affected by bundling along with solution processing. We report that especially high off currents of CNT transistors are not only related to the incorporation of metallic CNTs but also to the incorporation of CNT bundles. By applying device passivation with poly(4-vinylpyridine), the impact of CNT bundling on the device performance can be strongly reduced due to increased gate efficiency as well as reduced oxygen and water-induced p-type doping, boosting essential field-effect transistor performance parameters by several orders of magnitude. Moreover, this passivation approach allows the hysteresis and threshold voltage of CNT transistors to be tuned.

Carbon nanotubes within polymer matrix can synergistically enhance mechanical energy dissipation

NASA Astrophysics Data System (ADS)

Ashraf, Taimoor; Ranaiefar, Meelad; Khatri, Sumit; Kavosi, Jamshid; Gardea, Frank; Glaz, Bryan; Naraghi, Mohammad

2018-03-01

Safe operation and health of structures relies on their ability to effectively dissipate undesired vibrations, which could otherwise significantly reduce the life-time of a structure due to fatigue loads or large deformations. To address this issue, nanoscale fillers, such as carbon nanotubes (CNTs), have been utilized to dissipate mechanical energy in polymer-based nanocomposites through filler-matrix interfacial friction by benefitting from their large interface area with the matrix. In this manuscript, for the first time, we experimentally investigate the effect of CNT alignment with respect to reach other and their orientation with respect to the loading direction on vibrational damping in nanocomposites. The matrix was polystyrene (PS). A new technique was developed to fabricate PS-CNT nanocomposites which allows for controlling the angle of CNTs with respect to the far-field loading direction (misalignment angle). Samples were subjected to dynamic mechanical analysis, and the damping of the samples were measured as the ratio of the loss to storage moduli versus CNT misalignment angle. Our results defied a notion that randomly oriented CNT nanocomposites can be approximated as a combination of matrix-CNT representative volume elements with randomly aligned CNTs. Instead, our results points to major contributions of stress concentration induced by each CNT in the matrix in proximity of other CNTs on vibrational damping. The stress fields around CNTs in PS-CNT nanocomposites were studied via finite element analysis. Our findings provide significant new insights not only on vibrational damping nanocomposites, but also on their failure modes and toughness, in relation to interface phenomena.

Ferromagnetic CNT suspended H2O+Cu nanofluid analysis through composite stenosed arteries with permeable wall

NASA Astrophysics Data System (ADS)

Akbar, Noreen Sher

2015-08-01

In the present article magnetic field effects for CNT suspended copper nanoparticles for blood flow through composite stenosed arteries with permeable wall are discussed. The CNT suspended copper nanoparticles for the blood flow with water as base fluid is not explored yet. The equations for the CNT suspended Cu-water nanofluid are developed first time in the literature and simplified using long wavelength and low Reynolds number assumptions. Exact solutions have been evaluated for velocity, pressure gradient, the solid volume fraction of the nanoparticles and temperature profile. Effect of various flow parameters on the flow and heat transfer characteristics is utilized. It is also observed that with the increase in slip parameter blood flows slowly in arteries and trapped bolus increases.

An evaluation of UO2-CNT composites made by SPS as an accident tolerant nuclear fuel pellet and the feasibility of SPS as an economical fabrication process for the nuclear fuel cycle

NASA Astrophysics Data System (ADS)

Cartas, Andrew R.

The innovative and advanced purpose of this study is to understand and establish proper sintering procedures for Spark Plasma Sintering process in order to fabricate high density, high thermal conductivity UO2 -CNT pellets. Mixing quality and chemical reactions have been investigated by field emission scanning electron microscopy (FESEM), wavelength dispersive spectroscopy (WDS), and X-ray diffraction (XRD). The effect of various types of CNTs on the mixing and sintering quality of UO2-CNT pellets with SPS processing have been examined. The Archimedes Immersion Method, laser flash method, and FE-SEM will be used to investigate the density, thermal conductivity, grain size, pinning effects, and CNT dispersion of fabricated UO2-CNT pellets. Pre-fabricated CNT's were added to UO 2 powder and dispersed via sonication and/or ball milling and then made into composite nuclear pellets. An investigation of the economic impact of SPS on the nuclear fuel cycle for producing pure and composite UO2 fuels was conducted.

A statistical-based material and process guidelines for design of carbon nanotube field-effect transistors in gigascale integrated circuits.

PubMed

Ghavami, Behnam; Raji, Mohsen; Pedram, Hossein

2011-08-26

Carbon nanotube field-effect transistors (CNFETs) show great promise as building blocks of future integrated circuits. However, synthesizing single-walled carbon nanotubes (CNTs) with accurate chirality and exact positioning control has been widely acknowledged as an exceedingly complex task. Indeed, density and chirality variations in CNT growth can compromise the reliability of CNFET-based circuits. In this paper, we present a novel statistical compact model to estimate the failure probability of CNFETs to provide some material and process guidelines for the design of CNFETs in gigascale integrated circuits. We use measured CNT spacing distributions within the framework of detailed failure analysis to demonstrate that both the CNT density and the ratio of metallic to semiconducting CNTs play dominant roles in defining the failure probability of CNFETs. Besides, it is argued that the large-scale integration of these devices within an integrated circuit will be feasible only if a specific range of CNT density with an acceptable ratio of semiconducting to metallic CNTs can be adjusted in a typical synthesis process.

Field Emission Properties of Carbon Nanotube Fibers and Sheets for a High Current Electron Source

NASA Astrophysics Data System (ADS)

Christy, Larry

Field emission (FE) properties of carbon nanotube (CNT) fibers from Rice University and the University of Cambridge have been studied for use within a high current electron source for a directed energy weapon. Upon reviewing the performance of these two prevalent CNT fibers, cathodes were designed with CNT fibers from the University of Cincinnati Nanoworld Laboratory. Cathodes composed of a single CNT fiber, an array of three CNT fibers, and a nonwoven CNT sheet were investigated for FE properties; the goal was to design a cathode with emission current in excess of 10 mA. Once the design phase was complete, the cathode samples were fabricated, characterized, and then analyzed to determine FE properties. Electrical conductivity of the CNT fibers was characterized with a 4-probe technique. FE characteristics were measured in an ultra-high vacuum chamber at Wright-Patterson Air Force Base. The arrayed CNT fiber and the enhanced nonwoven CNT sheet emitter design demonstrated the most promising FE properties. Future work will include further analysis and cathode design using this nonwoven CNT sheet material to increase peak current performance during electron emission.

Field emission luminescence of nanodiamonds deposited on the aligned carbon nanotube array

NASA Astrophysics Data System (ADS)

Fedoseeva, Yu. V.; Bulusheva, L. G.; Okotrub, A. V.; Kanygin, M. A.; Gorodetskiy, D. V.; Asanov, I. P.; Vyalikh, D. V.; Puzyr, A. P.; Bondar, V. S.

2015-03-01

Detonation nanodiamonds (NDs) were deposited on the surface of aligned carbon nanotubes (CNTs) by immersing a CNT array in an aqueous suspension of NDs in dimethylsulfoxide (DMSO). The structure and electronic state of the obtained CNT-ND hybrid material were studied using optical and electron microscopy and Infrared, Raman, X-ray photoelectron and near-edge X-ray absorption fine structure spectroscopy. A non-covalent interaction between NDs and CNT and preservation of vertical orientation of CNTs in the hybrid were revealed. We showed that current-voltage characteristics of the CNT-ND cathode are changed depending on the applied field; below ~3 V/µm they are similar to those of the initial CNT array and at the higher field they are close to the ND behavior. Involvement of the NDs in field emission process resulted in blue luminescence of the hybrid surface at an electric field higher than 3.5 V/µm. Photoluminescence measurements showed that the NDs emit blue-green light, while blue luminescence prevails in the CNT-ND hybrid. The quenching of green luminescence was attributed to a partial removal of oxygen-containing groups from the ND surface as the result of the hybrid synthesis.

Observable consequences of zero-point energy

NASA Astrophysics Data System (ADS)

Sen, Siddhartha; Gupta, Kumar S.

2017-12-01

Spectral line widths, the Lamb shift and the Casimir effect are generally accepted to be observable consequences of the zero-point electromagnetic (ZPEM) fields. A new class of observable consequences of ZPEM field at the mesoscopic scale were recently proposed and observed. Here, we extend this class of observable effects and predict that mesoscopic water layers should have a high value for its solid-liquid phase transition temperature, as illustrated by water inside a single-walled carbon nanotube (CNT). For this case, our analysis predicts that the phase transition temperature scales inversely with the square of the effective radius available for the water flow within the CNT.

Aligned Carbon Nanotube Tape for Sensor Applications

NASA Technical Reports Server (NTRS)

Tucker, Dennis S.

2013-01-01

For this effort, will concentrate on three applications: Vibration Gyroscope utilizes piezoelectric properties of the tape and Coriolis effect Accelerometer utilizes the piezoresistive property Strain Gauge utilizes piezoresistive property Accelerometer and Strain Gauge can also utilize piezoelectric effect Test piezoelectric properties using facilities at the Microfabrication Laboratory (AMRDEC) . Enhance piezoelectric effect using polyvinylidine fluoride and P(VDF ]TrFE) which is readily polarizable .Spray matrix solution while winding fiber; Sandwich of CNT tape and PVDF film (DOE .Two Level) . Construct and test prototype vibration gyroscope . Construct and test prototype accelerometer using cantilever design . Test strain sensitivity of CNT tape against industrial strain gauge . Embed CNT tape in composite samples as well as on surface and test to failure (4 ]point bend) A piezoelectric device exhibits an electrical response from a mechanical applied stress. . A piezoelectric device has both capacitance and resistance properties in which by applying an electric field from a waveform will exert a mechanical stress that can be monitored for a response. . The typical waveform applied is a sinusoidal waveform of a defined voltage for a defined period. The defined voltage is driven from 0 volts to the positive defined volts then back to 0 and driven to negative defined volts then back to 0. . Example. Vmax set to 10V and period set to 10 ms. . Voltage will start at zero, go to 10 volts, return to zero, go to ]10 volts and return to zero during 10 ms. . Applying this electrical field to a DUT, the capacitance response and resistance response can be observed. CNT tape is easier to manufacture and cheaper than micromachining silicon or other ceramic piezoelectric used in gyroscopes and accelerometers CNT tape properties can be modified during manufacture for specific application CNT tape has enhanced mechanical and thermal properties in addition to unique electrical properties CNT tape as a strain gauge in Structural Health Monitoring will provide an excellent material to embed within composite structures

Effect of Aspect Ratio on Electrical, Rheological and Glass Transition Properties of PC/MWCNT Nanocomposites.

PubMed

Cruz, Heidy; Son, Younggon

2018-02-01

Since the discovery of carbon nanotubes (CNT), significant research works have focused on the application of CNT as conductive filler to polymer nanocomposites which can be used in several fields such as electrostatic dissipation (ESD), electrostatic painting and electromagnetic interference shielding (EMI-shielding). However, the main challenge in the large-scale manufacturing of this technology is the poor electrical conductivity of polymer nanocomposites produced by injection molding process. This study aims to investigate the effect of CNT aspect ratio in improving the electrical conductivity of injection molded nanocomposites. In this work, three types of multiwall carbon nanotubes with different lengths were melt-mixed with polycarbonate in a twin screw extruder followed by injection and compression molding. Results show that nanocomposites with higher CNT aspect ratio exhibit higher electrical conductivity. Longer nanotubes form a stronger conductive network during secondary agglomeration which can withstand the high shear forces during injection molding. Higher melt viscosity and storage modulus were observed in nanocomposites with higher CNT aspect ratio which is attributed to the effective constriction of polymer chains by longer nanotubes. It was also found that Tg of the composites increased with nanotube aspect ratio and the addition of CNT causes degradation which leads to the general Tg depression of polycarbonate.

High Current Emission from Patterned Aligned Carbon Nanotubes Fabricated by Plasma-Enhanced Chemical Vapor Deposition

NASA Astrophysics Data System (ADS)

Cui, Linfan; Chen, Jiangtao; Yang, Bingjun; Jiao, Tifeng

2015-12-01

Vertically, carbon nanotube (CNT) arrays were successfully fabricated on hexagon patterned Si substrates through radio frequency plasma-enhanced chemical vapor deposition using gas mixtures of acetylene (C2H2) and hydrogen (H2) with Fe/Al2O3 catalysts. The CNTs were found to be graphitized with multi-walled structures. Different H2/C2H2 gas flow rate ratio was used to investigate the effect on CNT growth, and the field emission properties were optimized. The CNT emitters exhibited excellent field emission performance (the turn-on and threshold fields were 2.1 and 2.4 V/μm, respectively). The largest emission current could reach 70 mA/cm2. The emission current was stable, and no obvious deterioration was observed during the long-term stability test of 50 h. The results were relevant for practical applications based on CNTs.

Investigation of the environmental implications of the CNT switch through its life cycle

NASA Astrophysics Data System (ADS)

Dahlben, Lindsay Johanna

Carbon nanotubes (CNTs) are unique allotropes of carbon that have high tensile strength, a high Young's modulus, good thermal conductivity, and depending on the CNT chirality can be metallic or semiconducting. These mechanical, thermal, and electrical properties make CNTs an attractive element in electronic applications such as conductive films, photovoltaics, non-volatile memory devices, batteries, sensors, and displays. Although commercialization of CNT-enabled products is increasing, there remains a significant lack of information regarding the health effects and environmental impacts of CNTs. Some studies have even shown that the behavior, toxicity, and persistence of CNTs may differ from bulk heterogeneous carbon. Given these uncertainties, it is prudent to assess the environmental attributes of CNT products and processes now to discover and potentially prevent adverse effects. This study investigates the environmental implications of a non-volatile bi-stable electromechanical CNT switch through its life cycle. Life cycle assessment (LCA) methodology is used to track the environmental impacts of the CNT switch through its fabrication and expected use and end-of-life (EOL) stages. Process parameters, energy consumption, input materials, output emissions, and yield efficiencies are determined for the laboratory and full-scale manufacture environments. The Ecoinvent(TM) inventory database and Eco-indicator 1999(TM) method are utilized for the impact assessment. Results for the fabrication stage are reported for highest contributions to environmental impact such as airborne inorganics, land use, and fossil fuels due to Au refining processes and electricity consumption. Extension of the LCA scope is evaluated for the potential replacement of CNT switches to current field-effect transistors (FETs) in flash memory for a cellular phone application. First-order predictions are made for the functionality and performance of the CNT switch during the use stage through an environmental perspective. Existing cellular phone EOL management options including recycling and direct disposal to landfill and incineration are evaluated for potential limitations, concerns, and environmental releases that may occur from the assimilation of CNT switch-enabled phones into the waste stream. In this manner, potential environmental effects of the CNT switch throughout its life cycle stages can be addressed alongside its technological development to ensure safe, sustainable, and successful CNT products.

Ice-assisted transfer of carbon nanotube arrays.

PubMed

Wei, Haoming; Wei, Yang; Lin, Xiaoyang; Liu, Peng; Fan, Shoushan; Jiang, Kaili

2015-03-11

Decoupling the growth and the application of nanomaterials by transfer is an important issue in nanotechnology. Here, we developed an efficient transfer technique for carbon nanotube (CNT) arrays by using ice as a binder to temporarily bond the CNT array and the target substrate. Ice makes it an ultraclean transfer because the evaporation of ice ensures that no contaminants are introduced. The transferred superaligned carbon nanotube (SACNT) arrays not only keep their original appearance and initial alignment but also inherit their spinnability, which is the most desirable feature. The transfer-then-spin strategy can be employed to fabricate patterned CNT arrays, which can act as 3-dimensional electrodes in CNT thermoacoustic chips. Besides, the flip-chipped CNTs are promising field electron emitters. Furthermore, the ice-assisted transfer technique provides a cost-effective solution for mass production of SACNTs, giving CNT technologies a competitive edge, and this method may inspire new ways to transfer other nanomaterials.

Aligning Solution-Derived Carbon Nanotube Film with Full Surface Coverage for High-Performance Electronics Applications.

PubMed

Zhu, Ma-Guang; Si, Jia; Zhang, Zhiyong; Peng, Lian-Mao

2018-06-01

The main challenge for application of solution-derived carbon nanotubes (CNTs) in high performance field-effect transistor (FET) is how to align CNTs into an array with high density and full surface coverage. A directional shrinking transfer method is developed to realize high density aligned array based on randomly orientated CNT network film. Through transferring a solution-derived CNT network film onto a stretched retractable film followed by a shrinking process, alignment degree and density of CNT film increase with the shrinking multiple. The quadruply shrunk CNT films present well alignment, which is identified by the polarized Raman spectroscopy and electrical transport measurements. Based on the high quality and high density aligned CNT array, the fabricated FETs with channel length of 300 nm present ultrahigh performance including on-state current I on of 290 µA µm -1 (V ds = -1.5 V and V gs = -2 V) and peak transconductance g m of 150 µS µm -1 , which are, respectively, among the highest corresponding values in the reported CNT array FETs. High quality and high semiconducting purity CNT arrays with high density and full coverage obtained through this method promote the development of high performance CNT-based electronics. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Highly reliable field electron emitters produced from reproducible damage-free carbon nanotube composite pastes with optimal inorganic fillers.

PubMed

Kim, Jae-Woo; Jeong, Jin-Woo; Kang, Jun-Tae; Choi, Sungyoul; Ahn, Seungjoon; Song, Yoon-Ho

2014-02-14

Highly reliable field electron emitters were developed using a formulation for reproducible damage-free carbon nanotube (CNT) composite pastes with optimal inorganic fillers and a ball-milling method. We carefully controlled the ball-milling sequence and time to avoid any damage to the CNTs, which incorporated fillers that were fully dispersed as paste constituents. The field electron emitters fabricated by printing the CNT pastes were found to exhibit almost perfect adhesion of the CNT emitters to the cathode, along with good uniformity and reproducibility. A high field enhancement factor of around 10,000 was achieved from the CNT field emitters developed. By selecting nano-sized metal alloys and oxides and using the same formulation sequence, we also developed reliable field emitters that could survive high-temperature post processing. These field emitters had high durability to post vacuum annealing at 950 °C, guaranteeing survival of the brazing process used in the sealing of field emission x-ray tubes. We evaluated the field emitters in a triode configuration in the harsh environment of a tiny vacuum-sealed vessel and observed very reliable operation for 30 h at a high current density of 350 mA cm(-2). The CNT pastes and related field emitters that were developed could be usefully applied in reliable field emission devices.

Highly reliable field electron emitters produced from reproducible damage-free carbon nanotube composite pastes with optimal inorganic fillers

NASA Astrophysics Data System (ADS)

Kim, Jae-Woo; Jeong, Jin-Woo; Kang, Jun-Tae; Choi, Sungyoul; Ahn, Seungjoon; Song, Yoon-Ho

2014-02-01

Highly reliable field electron emitters were developed using a formulation for reproducible damage-free carbon nanotube (CNT) composite pastes with optimal inorganic fillers and a ball-milling method. We carefully controlled the ball-milling sequence and time to avoid any damage to the CNTs, which incorporated fillers that were fully dispersed as paste constituents. The field electron emitters fabricated by printing the CNT pastes were found to exhibit almost perfect adhesion of the CNT emitters to the cathode, along with good uniformity and reproducibility. A high field enhancement factor of around 10 000 was achieved from the CNT field emitters developed. By selecting nano-sized metal alloys and oxides and using the same formulation sequence, we also developed reliable field emitters that could survive high-temperature post processing. These field emitters had high durability to post vacuum annealing at 950 °C, guaranteeing survival of the brazing process used in the sealing of field emission x-ray tubes. We evaluated the field emitters in a triode configuration in the harsh environment of a tiny vacuum-sealed vessel and observed very reliable operation for 30 h at a high current density of 350 mA cm-2. The CNT pastes and related field emitters that were developed could be usefully applied in reliable field emission devices.

Electrostatic capacitance and Faraday cage behavior of carbon nanotube forests

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ya'akobovitz, A.; Department of Mechanical Engineering, Faculty of Engineering Sciences, Ben-Gurion University, Beer-Sheva; Bedewy, M.

2015-02-02

Understanding of the electrostatic properties of carbon nanotube (CNT) forests is essential to enable their integration in microelectronic and micromechanical devices. In this study, we sought to understand how the hierarchical geometry and morphology of CNT forests determines their capacitance. First, we find that at small gaps, solid micropillars have greater capacitance, yet at larger gaps the capacitance of the CNT forests is greater. The surface area of the CNT forest accessible to the electrostatic field was extracted by analysis of the measured capacitance, and, by relating the capacitance to the average density of CNTs in the forest, we findmore » that the penetration depth of the electrostatic field is on the order of several microns. Therefore, CNT forests can behave as a miniature Faraday cage. The unique electrostatic properties of CNT forests could therefore enable their use as long-range proximity sensors and as shielding elements for miniature electronic devices.« less

Electrostatic capacitance and Faraday cage behavior of carbon nanotube forests

NASA Astrophysics Data System (ADS)

Ya'akobovitz, A.; Bedewy, M.; Hart, A. J.

2015-02-01

Understanding of the electrostatic properties of carbon nanotube (CNT) forests is essential to enable their integration in microelectronic and micromechanical devices. In this study, we sought to understand how the hierarchical geometry and morphology of CNT forests determines their capacitance. First, we find that at small gaps, solid micropillars have greater capacitance, yet at larger gaps the capacitance of the CNT forests is greater. The surface area of the CNT forest accessible to the electrostatic field was extracted by analysis of the measured capacitance, and, by relating the capacitance to the average density of CNTs in the forest, we find that the penetration depth of the electrostatic field is on the order of several microns. Therefore, CNT forests can behave as a miniature Faraday cage. The unique electrostatic properties of CNT forests could therefore enable their use as long-range proximity sensors and as shielding elements for miniature electronic devices.

Field emission from carbon nanotube fibers in varying anode-cathode gap with the consideration of contact resistance

NASA Astrophysics Data System (ADS)

Zhang, Peng; Fairchild, S. B.; Back, T. C.; Luo, Yi

2017-12-01

This paper studies field emission (FE) from a single carbon nanotube (CNT) fiber with different anode-cathode (AK) gap distances. It is found that the field enhancement factor depends strongly on the finite AK gap distance, due to the combination of geometrical effects and possible fiber morphology change. The geometrical effects of AK gap distance on the field enhancement factor are confirmed using COMSOL simulations. The slope drop in the Fowler-Northeim (FN) plot of the FE data in the high voltage is related to the electrical contact resistance between the CNT fiber and the substrate. It is found that even a small series resistance to the field emitter (<30% of the emission gap impedance) can strongly modify the FE characteristics in the high voltage regime, inducing a strong deviation from the linear FN plot.

Device and circuit-level performance of carbon nanotube field-effect transistor with benchmarking against a nano-MOSFET.

PubMed

Tan, Michael Loong Peng; Lentaris, Georgios; Amaratunga Aj, Gehan

2012-08-19

The performance of a semiconducting carbon nanotube (CNT) is assessed and tabulated for parameters against those of a metal-oxide-semiconductor field-effect transistor (MOSFET). Both CNT and MOSFET models considered agree well with the trends in the available experimental data. The results obtained show that nanotubes can significantly reduce the drain-induced barrier lowering effect and subthreshold swing in silicon channel replacement while sustaining smaller channel area at higher current density. Performance metrics of both devices such as current drive strength, current on-off ratio (Ion/Ioff), energy-delay product, and power-delay product for logic gates, namely NAND and NOR, are presented. Design rules used for carbon nanotube field-effect transistors (CNTFETs) are compatible with the 45-nm MOSFET technology. The parasitics associated with interconnects are also incorporated in the model. Interconnects can affect the propagation delay in a CNTFET. Smaller length interconnects result in higher cutoff frequency.

Theoretical Investigation of Light Transmission in a Slab Cavity via Kerr Nonlinearity of Carbon Nanotube Quantum Dot Nanostructure

NASA Astrophysics Data System (ADS)

Solookinejad, Gh.; Jabbari, M.; Sangachin, E. Ahmadi; Asadpour, S. H.

2018-01-01

In this paper, we discuss the transmission properties of weak probe laser field propagate through slab cavity with defect layer of carbon-nanotube quantum dot (CNT-QD) nanostructure. We show that due to spin-orbit coupling, the double electromagnetically induced transparency (EIT) windows appear and the giant Kerr nonlinearity of the intracavity medium can lead to manipulating of transmission coefficient of weak probe light. The thickness effect of defect layer medium has also been analyzed on transmission properties of probe laser field. Our proposed model may be useful for integrated photonics devices based on CNT-QD for applications in all-optical systems which require multiple EIT effect.

Modeling of Gate Bias Modulation in Carbon Nanotube Field-Effect-Transistor

NASA Technical Reports Server (NTRS)

Toshishige, Yamada; Biegel, Bryan A. (Technical Monitor)

2002-01-01

The threshold voltages of a carbon-nanotube (CNT) field-effect transistor (FET) are studied. The CNT channel is so thin that there is no voltage drop perpendicular to the gate electrode plane, and this makes the device characteristics quite unique. The relation between the voltage and the electrochemical potentials, and the mass action law for electrons and holes are examined in the context of CNTs, and inversion and accumulation threshold voltages (V(sub Ti), and V(sub Ta)) are derived. V(sub Ti) of the CNTFETs has a much stronger doping dependence than that of the metal-oxide- semiconductor FETs, while V(sub Ta) of both devices depends weakly on doping with the same functional form.

Characterization of Multifunctional Carbon Nanotube Yarns: In-situ Strain Sensing and Composite Reinforcement

NASA Astrophysics Data System (ADS)

Page, Christian David

A large body of scientific research and development worldwide has focused on the unprecedented structural/functional properties of carbon nanotubes (CNT), yet translation of these unique properties of CNTs to macroscopic materials has been slow to develop. CNT yarns are an appealing application for CNTs; their lightweight and small diameter can allow for them to be embedded into composite materials. Since the individual nanotubes have shown to have incredibly high strength, stiffness, and strain sensitivity, CNT yarns have the potential to be highly effective for in-situ structural health monitoring of advanced materials and structures. This work identifies the sources for losses in strength and electromechanical sensitivity. This is done by first understanding the physics involved with a CNT yarn under axial strain. Since this material is not a Newtonian solid, the stress-strain relationships are dissimilar to conventional materials, exhibiting a three zone behavior. This is present in both the stress-strain and resistance-strain relationships. A tensile test performed in-situ within a scanning electron microscope showed that the diameter of the yarn reduced greatly during tension, which indicates that the volume is not constant; therefore, the intratube/intrabundle load transfer efficiency and electrical conductivity change significantly under strain. Observation of this phenomenon helps elucidate the source for loss in the translation from nanoscopic CNTs to the macroscopic CNT yarns. Following the observation that the CNT yarn is not a solid body mechanics system, investigation into the long-standing field of textile engineering helped to identify that the CNT yarn structural hierarchy should be re-evaluated. Literary review reveals that the predominant base morphology of CNT yarns is bundles of CNTs as opposed to individual CNTs. Furthermore, in conventional textiles, it is well known that the base morphology (in textiles this is the "fiber") will bundle together during twisting. For CNT yarns, this level is referred to as packs since the title "bundle" has already been widely used as the grouping of individual CNTs. The utilization of conventional textile mechanics is supported by the congruent stress strain curves of cotton/wool yarns and CNT yarns. With this new perspective, sources of strength losses can be identified and, in most cases, quantified. Deterministic and statistical textile models are used to enumerate three top-level parameters which affect the yarn's strength. This approach offers guidance for future work to be done in the field of CNT yarns, including the growth of raw CNT forests, the spinning procedures involved, and any post-processing steps that may arise that can mitigate these losses that are extremely degrading to the CNT yarn mechanical strength. The strength of the yarn is a direct reflection of the quality of the yarn's structure. These morphological properties across the nano, meso, and macro scales have an effect on other physical properties such as electromechanical sensitivity. Improving the strength will also improve the yarn's ability to serve as a strain gage. Coupled with its appealing size, these yarns will be an effective in-situ embedded strain sensor. In conclusion, high quality CNT yarns with minimized strength losses show promise for structural health monitoring of advanced materials and structures since they can be both strongly reinforcing and electromechanically sensitive.

Carbon Nanotubes as FET Channel: Analog Design Optimization considering CNT Parameter Variability

NASA Astrophysics Data System (ADS)

Samar Ansari, Mohd.; Tripathi, S. K.

2017-08-01

Carbon nanotubes (CNTs), both single-walled as well as multi-walled, have been employed in a plethora of applications pertinent to semiconductor materials and devices including, but not limited to, biotechnology, material science, nanoelectronics and nano-electro mechanical systems (NEMS). The Carbon Nanotube Field Effect Transistor (CNFET) is one such electronic device which effectively utilizes CNTs to achieve a boost in the channel conduction thereby yielding superior performance over standard MOSFETs. This paper explores the effects of variability in CNT physical parameters viz. nanotube diameter, pitch, and number of CNT in the transistor channel, on the performance of a chosen analog circuit. It is further shown that from the analyses performed, an optimal design of the CNFETs can be derived for optimizing the performance of the analog circuit as per a given specification set.

Effect of cleaning procedures on the electrical properties of carbon nanotube transistors—A statistical study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tittmann-Otto, J., E-mail: jana.tittmann-otto@zfm.tu-chemnitz.de; Hermann, S.; Hartmann, M.

The interface between a carbon nanotube (CNT) and its environment can dramatically affect the electrical properties of CNT-based field-effect transistors (FETs). For such devices, the channel environment plays a significant role inducing doping or charge traps giving rise to hysteresis in the transistor characteristics. Thereby the fabrication process strongly determines the extent of those effects and the final device performance. In CNT-based devices obtained from dispersions, a proper individualization of the nanotubes is mandatory. This is generally realized by an ultrasonic treatment combined with surfactant molecules, which enwrap nanotubes forming micelle aggregates. To minimize impact on device performance, it ismore » of vital importance to consider post-deposition treatments for removal of surfactant molecules and other impurities. In this context, we investigated the effect of several wet chemical cleaning and thermal post treatments on the electrical characteristics as well as physical properties of more than 600 devices fabricated only by wafer-level compatible technologies. We observed that nitric acid and water treatments improved the maximum-current of devices. Additionally, we found that the ethanol treatment successfully lowered hysteresis in the transfer characteristics. The effect of the chemical cleaning procedures was found to be more significant on CNT-metal contacts than for the FET channels. Moreover, we investigated the effect of an additional thermal cleaning step under vacuum after the chemical cleaning, which had an exceptional impact on the hysteresis behavior including hysteresis reversal. The presence of surfactant molecules on CNT was evidenced by X-ray photoelectron and Raman spectroscopies. By identifying the role of surfactant molecules and assessing the enhancement of device performance as a direct consequence of several cleaning procedures, these results are important for the development of CNT-based electronics at the wafer-level.« less

Effect of cleaning procedures on the electrical properties of carbon nanotube transistors—A statistical study

NASA Astrophysics Data System (ADS)

Tittmann-Otto, J.; Hermann, S.; Kalbacova, J.; Hartmann, M.; Toader, M.; Rodriguez, R. D.; Schulz, S. E.; Zahn, D. R. T.; Gessner, T.

2016-03-01

The interface between a carbon nanotube (CNT) and its environment can dramatically affect the electrical properties of CNT-based field-effect transistors (FETs). For such devices, the channel environment plays a significant role inducing doping or charge traps giving rise to hysteresis in the transistor characteristics. Thereby the fabrication process strongly determines the extent of those effects and the final device performance. In CNT-based devices obtained from dispersions, a proper individualization of the nanotubes is mandatory. This is generally realized by an ultrasonic treatment combined with surfactant molecules, which enwrap nanotubes forming micelle aggregates. To minimize impact on device performance, it is of vital importance to consider post-deposition treatments for removal of surfactant molecules and other impurities. In this context, we investigated the effect of several wet chemical cleaning and thermal post treatments on the electrical characteristics as well as physical properties of more than 600 devices fabricated only by wafer-level compatible technologies. We observed that nitric acid and water treatments improved the maximum-current of devices. Additionally, we found that the ethanol treatment successfully lowered hysteresis in the transfer characteristics. The effect of the chemical cleaning procedures was found to be more significant on CNT-metal contacts than for the FET channels. Moreover, we investigated the effect of an additional thermal cleaning step under vacuum after the chemical cleaning, which had an exceptional impact on the hysteresis behavior including hysteresis reversal. The presence of surfactant molecules on CNT was evidenced by X-ray photoelectron and Raman spectroscopies. By identifying the role of surfactant molecules and assessing the enhancement of device performance as a direct consequence of several cleaning procedures, these results are important for the development of CNT-based electronics at the wafer-level.

Improved Photoresist Coating for Making CNT Field Emitters

NASA Technical Reports Server (NTRS)

Toda, Risaku; Manohara, Harish

2009-01-01

An improved photoresist-coating technique has been developed for use in the fabrication of carbon-nanotube- (CNT) based field emitters is described. The improved photoresist coating technique overcomes what, heretofore, has been a major difficulty in the fabrication process.

Controlled Growth of Carbon Nanotubes on Micropatterned Au/Cr Composite Film and Field Emission from Their Arrays

NASA Astrophysics Data System (ADS)

Kamide, Koichi; Araki, Hisashi; Yoshino, Katsumi

2003-12-01

Carbon nanotube (CNT) arrays with a controlled density are prepared on a micropatterned Au/Cr composite film formed on a quartz glass plate by pyrolysis of Ni-phthalocyanine at 800°C. It is clarified from characteristic X-ray analyses for those samples that a catalytic Ni nanoparticle is not contained within the base of the whisker-like CNT in contrast to that of the bamboo-like CNT, suggesting that the growth process of the present novel CNT is incompatible with that of the bamboo-like CNT. In the Au/Cr composite film, both the Cr atomic content of approximately 30% and the presence of the Ni catalyst devoid of a particle-like shape are important factors for the growth of CNTs. Field emission from the novel CNT arrays exhibits a lower turn-on voltage and a higher current density compared with that from the bamboo-like arrays formed on a quartz plate.

Toward Quantifying the Electrostatic Transduction Mechanism in Carbon Nanotube Biomolecular Sensors

NASA Astrophysics Data System (ADS)

Lerner, Mitchell; Kybert, Nicholas; Mendoza, Ryan; Dailey, Jennifer; Johnson, A. T. Charlie

2013-03-01

Despite the great promise of carbon nanotube field-effect transistors (CNT FETs) for applications in chemical and biochemical detection, a quantitative understanding of sensor responses is lacking. To explore the role of electrostatics in sensor transduction, experiments were conducted with a set of similar compounds designed to adsorb onto the CNT FET via a pyrene linker group and take on a set of known charge states under ambient conditions. Acidic and basic species were observed to induce threshold voltage shifts of opposite sign, consistent with gating of the CNT FET by local charges due to protonation or deprotonation of the pyrene compounds by interfacial water. The magnitude of the gate voltage shift was controlled by the distance between the charged group and the CNT. Additionally, functionalization with an uncharged pyrene compound showed a threshold shift ascribed to its molecular dipole moment. This work illustrates a method for producing CNT FETs with controlled values of the turnoff gate voltage, and more generally, these results will inform the development of quantitative models for the response of CNT FET chemical and biochemical sensors. As an example, the results of an experiment detecting biomarkers of Lyme disease will be discussed in the context of this model.

Microinjection moulding of polymeric composites with functionalized carbon nanotubes =

NASA Astrophysics Data System (ADS)

Ferreira, Tania Sofia Araujo Figueiras

Microinjection moulding of polymeric composites with functionalized carbon nanotubes The unique electronic, mechanical, and structural properties of carbon nanotubes (CNT) make them suitable for applications in the fields of electronics, sensors, medical devices, aerospace and automotive industries. The preparation of CNT/polymer nanocomposites presents particular interest among the various possible applications. However, the long entangled nanotubes form agglomerates that poses serious obstacles to further development of nanocomposites with the target properties. One of the approaches to overcome the CNT chemical inertness, enhance the compatibility with the matrix and improve homogeneous dispersion through the matrix is through its covalent functionalization. This is expected to improve the CNT interface with the polymer matrix, thus improving the mechanical properties of the nanocomposites at very low content. One of the purposes of this thesis was to implement the covalent modification of the CNT surface using a simple functionalization method, to increase the CNT surface reactivity and possibly help their dispersion into the polyamide matrix without inducing structural damage on the CNT. The functionalization of CNT was carried out through the 1,3-dipolar cycloaddition reaction of azomethine ylides using a solvent-free reaction route. CNT were successful functionalized with pyrrolidine groups through a simple and fast procedure that was scaled up, and may be compatible with current industrial processes. Another objective was to disperse the CNT in polyamide 6 (PA6) using melt mixing, and to produce PA6/CNT nanocomposites by microinjection molding (plM). Finally, the morphological and physical properties of the mouldings produced were evaluated. The plM process is becoming of greater importance for the manufacturing of polymeric micro- components considering its low cost and short cycle times, useful for mass production. The as-received and functionalized CNT were dispersed in PA6 at various contents (1, 1.5, 3 and 4.5 w.%) by twin-screw extrusion and then processed by pllVl. The same procedure was carried out for PA6 without CNT. To study the influence of the specific thermo-mechanical conditions generated during pllVl, the morphology and structure of PA6 and PA6/CNT samples produced by melt extrusion and plM were compared. The specimens of PA6 and PA6/CNT nanocomposites were analyzed by polarized light microscopy, differential scanning calorimetry, and wide-angle X-ray diffraction. The effect of the processing method upon the development of crystallinity in PA6 and PA6/CNT samples was studied. The contribution of the two crystalline phases, oi and y, on the PA6 with and without CNT was measured. The degree of crystallinity of the plM PA6 sample was lower compared to the extruded material, and was not affected by the CNT content. The plM samples of PA6 presented a considerable molecular orientation at the skin region that decreased towards the sample core, with larger contribution of y-phase compared to extruded samples. The orientation exhibited by plM parts of PA6, mainly at the skin region, is not detectable after CNT addition. The dispersion of the CNT agglomerates was quantified in all PA6/CNT samples using optical microscopy and image analysis. The effect of functionalization on the PA6/CNT interface, the nanocomposite morphology and the mechanical and electrical properties were studied. It was observed that the microinjected composites with functionalized CNT presented improved dispersion, with smaller CNT agglomerate area ratio compared to the composites with pure nanotubes. The functionalized nanotubes showed better adhesion to PA6 compared to pure nanotubes, as observed by scanning electron microscopy. The incorporation of CNT considerably improved the mechanical properties. The effect of high shear rate of the polymer melt on carbon nanotube alignment during plM was assessed by comparing the electrical resistivity of the composite after extrusion and after pllVl, through the thickness and along the flow direction. The experiments showed that the moulding geometry design and processing conditions significantly affected electrical resistivity. This thesis provides an insight into the joint effect of CNT chemical functionalization and the specific conditions of plM on PA6 morphology and on CNT dispersion, and its influence on the electrical, mechanical and thermal properties of the resulting composites.

3D magneto-convective heat transfer in CNT-nanofluid filled cavity under partially active magnetic field

NASA Astrophysics Data System (ADS)

Al-Rashed, Abdullah A. A. A.; Kolsi, Lioua; Oztop, Hakan F.; Aydi, Abdelkarim; Malekshah, Emad Hasani; Abu-Hamdeh, Nidal; Borjini, Mohamed Naceur

2018-05-01

A computational study has been performed to investigate the effects of partially active magnetic field on natural convection heat transfer in CNT-nanofluid filled and three-dimensional differentially heated closed space. Two cases are considered to see this effect as magnetic field is applied to upper half (Case I) and lower half (Case II) while remaining walls are insulated. The finite volume method is used to solve governing equations and results are obtained for different governing parameters as Hartmann number (0 ≤ Ha ≤ 100), nanoparticle volume fraction (0 ≤ φ ≤ 0.05) and height of the active zone (0 ≤ LB ≤ 1). It is found that location of magnetic field plays an important role even at the same Hartmann number. Thus, it can be a good parameter to control heat and fluid flow inside the closed space.

Carbon nanotube growth density control

NASA Technical Reports Server (NTRS)

Delzeit, Lance D. (Inventor); Schipper, John F. (Inventor)

2010-01-01

Method and system for combined coarse scale control and fine scale control of growth density of a carbon nanotube (CNT) array on a substrate, using a selected electrical field adjacent to a substrate surface for coarse scale density control (by one or more orders of magnitude) and a selected CNT growth temperature range for fine scale density control (by multiplicative factors of less than an order of magnitude) of CNT growth density. Two spaced apart regions on a substrate may have different CNT growth densities and/or may use different feed gases for CNT growth.

Piezoelectric effect in non-uniform strained carbon nanotubes

NASA Astrophysics Data System (ADS)

Ilina, M. V.; Blinov, Yu F.; Ilin, O. I.; Rudyk, N. N.; Ageev, O. A.

2017-10-01

The piezoelectric effect in non-uniform strained carbon nanotubes (CNTs) has been studied. It is shown that the magnitude of strained CNTs surface potential depends on a strain value. It is established that the resistance of CNT also depends on the strain and internal electric field, which leads to the hysteresis in the current-voltage characteristics. Analysis of experimental studies of the non-uniform strained CNT with a diameter of 92 nm and a height of 2.1 μm allowed us to estimate the piezoelectric coefficient 0.107 ± 0.032 C/m2.

Plasma-induced field emission study of carbon nanotube cathode

NASA Astrophysics Data System (ADS)

Shen, Yi; Xia, Liansheng; Zhang, Huang; Liu, Xingguang; Yang, Anmin; Shi, Jinshui; Zhang, Linwen; Liao, Qingliang; Zhang, Yue

2011-10-01

An investigation on the plasma-induced field emission (PFE) properties of a large area carbon nanotube (CNT) cathode on a 2 MeV linear induction accelerator injector is presented. Experimental results show that the cathode is able to emit intense electron beams. Intense electron beams of 14.9-127.8A/cm2 are obtained from the cathode. The CNT cathode desorbs gases from the CNTs during the PFE process. The fast cathode plasma expansion affects the diode perveance. The amount of outgassing is estimated to be 0.06-0.49Pa·L, and the ratio of outgassing and electron are roughly calculated to be within the range of 170-350 atoms per electron. The effect of the outgassing is analyzed, and the outgassing mass spectrum of the CNT cathode has been studied during the PFE. There is a significant desorption of CO2, N2(CO), and H2 gases, which plays an important role during the PFE process. All the experiments demonstrate that the outgassing plays an important role in the formation of the cathode plasma. Moreover, the characteristic turn-on time of the CNT cathode was measured to be 39 ns.

A literature review of connectedness to nature and its potential for environmental management.

PubMed

Restall, Brian; Conrad, Elisabeth

2015-08-15

Understanding how people's relationships with nature form, how they influence personal values and attitudes, and what behavioural implications they may have could provide more insight into how connectedness to nature (CNT) can effectively contribute to environmental management goals. This paper undertakes a review of literature published over the past decade (2002-2011) on SCOPUS; and describes the current state of knowledge regarding CNT, assesses any efforts towards the spatial mapping of CNT for environmental management, and identifies measures of CNT defined in the broader literature. This review suggests that there is quite some overlap in the literature on CNT concepts, and that more effort needs to be made towards multi-disciplinary research which explores how CNT can be useful to environmental planning and conservation research on the field. It also further corroborates the need and relevance of applying more social and affective strategies to promote conservation behaviour. The main progress in CNT theory seems to have been made in the development of measurement tools, and it is clear that there is a strong convergent validity amongst the different measures due to their similarity, and functional associations. Further efforts towards the exploration of multi-dimensional measures is recommended since they consistently stand out as showing better results. The geographic visualisation of CNT constructs is another area of research that deserves attention since it can provide a unique point of view towards guiding participatory protected area planning and management. Copyright © 2015 Elsevier Ltd. All rights reserved.

Band-to-band tunneling in a carbon nanotube metal-oxide-semiconductor field-effect transistor is dominated by phonon-assisted tunneling.

PubMed

Koswatta, Siyuranga O; Lundstrom, Mark S; Nikonov, Dmitri E

2007-05-01

Band-to-band tunneling (BTBT) devices have recently gained a lot of interest due to their potential for reducing power dissipation in integrated circuits. We have performed extensive simulations for the BTBT operation of carbon nanotube metal-oxide-semiconductor field-effect transistors (CNT-MOSFETs) using the nonequilibrium Green's function formalism for both ballistic and dissipative quantum transport. In comparison with recently reported experimental data (J. Am. Chem. Soc. 2006, 128, 3518-3519), we have obtained strong evidence that BTBT in CNT-MOSFETs is dominated by optical phonon assisted inelastic transport, which can have important implications on the transistor characteristics. It is shown that, under large biasing conditions, two-phonon scattering may also become important.

Specificity Bio-identification of CNT-Based Transistor

NASA Astrophysics Data System (ADS)

Wang, Sheng-Yu; Wu, Hue-Min

2017-12-01

In this research, we report a simple and general approach to π-π stacking functionalization of the sidewalls of CNTs by 1-pyrenebutanoic acid, succinimidyl ester (PSE), and subsequent immobilization of insulin-like growth factor 1 receptor (IGF1R) onto SWNTs with a high degree of control and specificity. The selection of PSE provides visualization and characterization of individual CNTs based on its strong luminescence. In addition, we designed a simple and efficient electrode with a staggered pattern to increase the effect of electrophoresis by using electric field for the macroscopic alignment of CNTs to complete a field-effect device for CNT-based biosensors. Scanning Electron Microscopy (SEM) was used to investigate the morphology of the biosensors. The results of four-point probe method demonstrated high selectivity and sensitivity of detection. The functionalization of SWNTs was investigated by Fourier transform infrared spectroscopy (FTIR). Experimental results imply that specific binding between IGF1R and its specific mAb results in a dramatic change in electrical current of CNT-based devices, and suggest that the devices are very promising biosensor candidates to detect circulating cancer cells.

Control of unidirectional transport of single-file water molecules through carbon nanotubes in an electric field.

PubMed

Su, Jiaye; Guo, Hongxia

2011-01-25

The transport of water molecules through nanopores is not only crucial to biological activities but also useful for designing novel nanofluidic devices. Despite considerable effort and progress that has been made, a controllable and unidirectional water flow is still difficult to achieve and the underlying mechanism is far from being understood. In this paper, using molecular dynamics simulations, we systematically investigate the effects of an external electric field on the transport of single-file water molecules through a carbon nanotube (CNT). We find that the orientation of water molecules inside the CNT can be well-tuned by the electric field and is strongly coupled to the water flux. This orientation-induced water flux is energetically due to the asymmetrical water-water interaction along the CNT axis. The wavelike water density profiles are disturbed under strong field strengths. The frequency of flipping for the water dipoles will decrease as the field strength is increased, and the flipping events vanish completely for the relatively large field strengths. Most importantly, a critical field strength E(c) related to the water flux is found. The water flux is increased as E is increased for E ≤ E(c), while it is almost unchanged for E > E(c). Thus, the electric field offers a level of governing for unidirectional water flow, which may have some biological applications and provides a route for designing efficient nanopumps.

Study of adhesion of vertically aligned carbon nanotubes to a substrate by atomic-force microscopy

NASA Astrophysics Data System (ADS)

Ageev, O. A.; Blinov, Yu. F.; Il'ina, M. V.; Il'in, O. I.; Smirnov, V. A.; Tsukanova, O. G.

2016-02-01

The adhesion to a substrate of vertically aligned carbon nanotubes (VA CNT) produced by plasmaenhanced chemical vapor deposition has been experimentally studied by atomic-force microscopy in the current spectroscopy mode. The longitudinal deformation of VA CNT by applying an external electric field has been simulated. Based on the results, a technique of determining VA CNT adhesion to a substrate has been developed that is used to measure the adhesion strength of connecting VA CNT to a substrate. The adhesion to a substrate of VA CNT 70-120 nm in diameter varies from 0.55 to 1.19 mJ/m2, and the adhesion force from 92.5 to 226.1 nN. When applying a mechanical load, the adhesion strength of the connecting VA CNT to a substrate is 714.1 ± 138.4 MPa, and the corresponding detachment force increases from 1.93 to 10.33 μN with an increase in the VA CNT diameter. As an external electric field is applied, the adhesion strength is almost doubled and is 1.43 ± 0.29 GPa, and the corresponding detachment force is changed from 3.83 to 20.02 μN. The results can be used in the design of technological processes of formation of emission structures, VA CNT-based elements for vacuum microelectronics and micro- and nanosystem engineering, and also the methods of probe nanodiagnostics of VA CNT.

Novel planar field emission of ultra-thin individual carbon nanotubes.

PubMed

Song, Xuefeng; Gao, Jingyun; Fu, Qiang; Xu, Jun; Zhao, Qing; Yu, Dapeng

2009-10-07

In this work, we proposed and realized a new prototype of planar field emission device based on as-grown individual carbon nanotubes (CNTs) on the surface of a Si-SiO2 substrate. The anode, cathode and the CNT tip all lie on the same surface, so the electron emission is reduced from three-dimensional to two-dimensional. The benefits of such a design include usage of thinner CNT emitters, integrity with planar technology, stable construction, better heat dissipation, etc. A tip-to-tip field emission device was presented besides the tip-to-electrode one. Real-time, in situ observation of the planar field emission was realized in a scanning electron microscope (SEM). Measurements showed that the minimum voltage for 10 nA field emission current was only 8.0 V and the maximum emission current density in an individual CNT emitter (1.0 nm in diameter) exceeded 5.7 x 10(8) A cm(-2). These results stand out in the comparison with recent works on individual CNT field emission, indicating that the planar devices based on ultra-thin individual CNTs are more competitive candidates for next-generation electron field emitters.

Electron transfer from a carbon nanotube into vacuum under high electric fields

NASA Astrophysics Data System (ADS)

Filip, L. D.; Smith, R. C.; Carey, J. D.; Silva, S. R. P.

2009-05-01

The transfer of an electron from a carbon nanotube (CNT) tip into vacuum under a high electric field is considered beyond the usual one-dimensional semi-classical approach. A model of the potential energy outside the CNT cap is proposed in order to show the importance of the intrinsic CNT parameters such as radius, length and vacuum barrier height. This model also takes into account set-up parameters such as the shape of the anode and the anode-to-cathode distance, which are generically portable to any modelling study of electron emission from a tip emitter. Results obtained within our model compare well to experimental data. Moreover, in contrast to the usual one-dimensional Wentzel-Kramers-Brillouin description, our model retains the ability to explain non-standard features of the process of electron field emission from CNTs that arise as a result of the quantum behaviour of electrons on the surface of the CNT.

Device and circuit-level performance of carbon nanotube field-effect transistor with benchmarking against a nano-MOSFET

PubMed Central

2012-01-01

The performance of a semiconducting carbon nanotube (CNT) is assessed and tabulated for parameters against those of a metal-oxide-semiconductor field-effect transistor (MOSFET). Both CNT and MOSFET models considered agree well with the trends in the available experimental data. The results obtained show that nanotubes can significantly reduce the drain-induced barrier lowering effect and subthreshold swing in silicon channel replacement while sustaining smaller channel area at higher current density. Performance metrics of both devices such as current drive strength, current on-off ratio (Ion/Ioff), energy-delay product, and power-delay product for logic gates, namely NAND and NOR, are presented. Design rules used for carbon nanotube field-effect transistors (CNTFETs) are compatible with the 45-nm MOSFET technology. The parasitics associated with interconnects are also incorporated in the model. Interconnects can affect the propagation delay in a CNTFET. Smaller length interconnects result in higher cutoff frequency. PMID:22901374

Quasi-ballistic carbon nanotube array transistors with current density exceeding Si and GaAs

PubMed Central

Brady, Gerald J.; Way, Austin J.; Safron, Nathaniel S.; Evensen, Harold T.; Gopalan, Padma; Arnold, Michael S.

2016-01-01

Carbon nanotubes (CNTs) are tantalizing candidates for semiconductor electronics because of their exceptional charge transport properties and one-dimensional electrostatics. Ballistic transport approaching the quantum conductance limit of 2G0 = 4e2/h has been achieved in field-effect transistors (FETs) containing one CNT. However, constraints in CNT sorting, processing, alignment, and contacts give rise to nonidealities when CNTs are implemented in densely packed parallel arrays such as those needed for technology, resulting in a conductance per CNT far from 2G0. The consequence has been that, whereas CNTs are ultimately expected to yield FETs that are more conductive than conventional semiconductors, CNTs, instead, have underperformed channel materials, such as Si, by sixfold or more. We report quasi-ballistic CNT array FETs at a density of 47 CNTs μm−1, fabricated through a combination of CNT purification, solution-based assembly, and CNT treatment. The conductance is as high as 0.46 G0 per CNT. In parallel, the conductance of the arrays reaches 1.7 mS μm−1, which is seven times higher than the previous state-of-the-art CNT array FETs made by other methods. The saturated on-state current density is as high as 900 μA μm−1 and is similar to or exceeds that of Si FETs when compared at and equivalent gate oxide thickness and at the same off-state current density. The on-state current density exceeds that of GaAs FETs as well. This breakthrough in CNT array performance is a critical advance toward the exploitation of CNTs in logic, high-speed communications, and other semiconductor electronics technologies. PMID:27617293

Quasi-ballistic carbon nanotube array transistors with current density exceeding Si and GaAs.

PubMed

Brady, Gerald J; Way, Austin J; Safron, Nathaniel S; Evensen, Harold T; Gopalan, Padma; Arnold, Michael S

2016-09-01

Carbon nanotubes (CNTs) are tantalizing candidates for semiconductor electronics because of their exceptional charge transport properties and one-dimensional electrostatics. Ballistic transport approaching the quantum conductance limit of 2G 0 = 4e (2)/h has been achieved in field-effect transistors (FETs) containing one CNT. However, constraints in CNT sorting, processing, alignment, and contacts give rise to nonidealities when CNTs are implemented in densely packed parallel arrays such as those needed for technology, resulting in a conductance per CNT far from 2G 0. The consequence has been that, whereas CNTs are ultimately expected to yield FETs that are more conductive than conventional semiconductors, CNTs, instead, have underperformed channel materials, such as Si, by sixfold or more. We report quasi-ballistic CNT array FETs at a density of 47 CNTs μm(-1), fabricated through a combination of CNT purification, solution-based assembly, and CNT treatment. The conductance is as high as 0.46 G 0 per CNT. In parallel, the conductance of the arrays reaches 1.7 mS μm(-1), which is seven times higher than the previous state-of-the-art CNT array FETs made by other methods. The saturated on-state current density is as high as 900 μA μm(-1) and is similar to or exceeds that of Si FETs when compared at and equivalent gate oxide thickness and at the same off-state current density. The on-state current density exceeds that of GaAs FETs as well. This breakthrough in CNT array performance is a critical advance toward the exploitation of CNTs in logic, high-speed communications, and other semiconductor electronics technologies.

Two-component spin-coated Ag/CNT composite films based on a silver heterogeneous nucleation mechanism adhesion-enhanced by mechanical interlocking and chemical grafting.

PubMed

Zhang, Yang; Kang, Zhixin; Bessho, Takeshi

2017-03-10

In this paper, a new method for the synthesis of silver carbon nanotube (Ag/CNT) composite films as conductive connection units for flexible electronic devices is presented. This method is about a two-component solution process by spin coating with an after-treatment annealing process. In this method, multi-walled carbon nanotubes (MWCNTs) act as the core of silver heterogeneous nucleation, which can be observed and analyzed by a field-emission scanning electron microscope. With the effects of mechanical interlocking, chemical grafting, and annealing, the interfacial adhesive strength between films and PET sheets was enhanced to 12 N cm -1 . The tensile strength of the Ag/CNT composite films was observed to increase by 38% by adding 5 g l -1 MWCNTs. In the four-probe method, the resistivity of Ag/CNT-5 declined by 78.2% compared with pristine Ag films. The anti-fatigue performance of the Ag/CNT composite films was monitored by cyclic bending deformation and the results revealed that the growth rate of electrical resistance during the deformation was obviously retarded. As for industrial application, this method provides an efficient low-cost way to prepare Ag/CNT composite films and can be further applied to other coating systems.

The Dependence of CNT Aerogel Synthesis on Sulfur-driven Catalyst Nucleation Processes and a Critical Catalyst Particle Mass Concentration.

PubMed

Hoecker, Christian; Smail, Fiona; Pick, Martin; Weller, Lee; Boies, Adam M

2017-11-06

The floating catalyst chemical vapor deposition (FC-CVD) process permits macro-scale assembly of nanoscale materials, enabling continuous production of carbon nanotube (CNT) aerogels. Despite the intensive research in the field, fundamental uncertainties remain regarding how catalyst particle dynamics within the system influence the CNT aerogel formation, thus limiting effective scale-up. While aerogel formation in FC-CVD reactors requires a catalyst (typically iron, Fe) and a promotor (typically sulfur, S), their synergistic roles are not fully understood. This paper presents a paradigm shift in the understanding of the role of S in the process with new experimental studies identifying that S lowers the nucleation barrier of the catalyst nanoparticles. Furthermore, CNT aerogel formation requires a critical threshold of Fe x C y  > 160 mg/m 3 , but is surprisingly independent of the initial catalyst diameter or number concentration. The robustness of the critical catalyst mass concentration principle is proved further by producing CNTs using alternative catalyst systems; Fe nanoparticles from a plasma spark generator and cobaltocene and nickelocene precursors. This finding provides evidence that low-cost and high throughput CNT aerogel routes may be achieved by decoupled and enhanced catalyst production and control, opening up new possibilities for large-scale CNT synthesis.

Synergistic effects from graphene and carbon nanotubes endow ordered hierarchical structure foams with a combination of compressibility, super-elasticity and stability and potential application as pressure sensors

NASA Astrophysics Data System (ADS)

Kuang, Jun; Dai, Zhaohe; Liu, Luqi; Yang, Zhou; Jin, Ming; Zhang, Zhong

2015-05-01

Nanostructured carbon material based three-dimensional porous architectures have been increasingly developed for various applications, e.g. sensors, elastomer conductors, and energy storage devices. Maintaining architectures with good mechanical performance, including elasticity, load-bearing capacity, fatigue resistance and mechanical stability, is prerequisite for realizing these functions. Though graphene and CNT offer opportunities as nanoscale building blocks, it still remains a great challenge to achieve good mechanical performance in their microarchitectures because of the need to precisely control the structure at different scales. Herein, we fabricate a hierarchical honeycomb-like structured hybrid foam based on both graphene and CNT. The resulting materials possess excellent properties of combined high specific strength, elasticity and mechanical stability, which cannot be achieved in neat CNT and graphene foams. The improved mechanical properties are attributed to the synergistic-effect-induced highly organized, multi-scaled hierarchical architectures. Moreover, with their excellent electrical conductivity, we demonstrated that the hybrid foams could be used as pressure sensors in the fields related to artificial skin.Nanostructured carbon material based three-dimensional porous architectures have been increasingly developed for various applications, e.g. sensors, elastomer conductors, and energy storage devices. Maintaining architectures with good mechanical performance, including elasticity, load-bearing capacity, fatigue resistance and mechanical stability, is prerequisite for realizing these functions. Though graphene and CNT offer opportunities as nanoscale building blocks, it still remains a great challenge to achieve good mechanical performance in their microarchitectures because of the need to precisely control the structure at different scales. Herein, we fabricate a hierarchical honeycomb-like structured hybrid foam based on both graphene and CNT. The resulting materials possess excellent properties of combined high specific strength, elasticity and mechanical stability, which cannot be achieved in neat CNT and graphene foams. The improved mechanical properties are attributed to the synergistic-effect-induced highly organized, multi-scaled hierarchical architectures. Moreover, with their excellent electrical conductivity, we demonstrated that the hybrid foams could be used as pressure sensors in the fields related to artificial skin. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr00841g

Simulations of Field-Emission Electron Beams from CNT Cathodes in RF Photoinjectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mihalcea, Daniel; Faillace, Luigi; Panuganti, Harsha

2015-06-01

Average field emission currents of up to 700 mA were produced by Carbon Nano Tube (CNT) cathodes in a 1.3 GHz RF gun at Fermilab High Brightness Electron Source Lab. (HBESL). The CNT cathodes were manufactured at Xintek and tested under DC conditions at RadiaBeam. The electron beam intensity as well as the other beam properties are directly related to the time-dependent electric field at the cathode and the geometry of the RF gun. This report focuses on simulations of the electron beam generated through field-emission and the results are compared with experimental measurements. These simulations were performed with themore » time-dependent Particle In Cell (PIC) code WARP.« less

Performance of a carbon nanotube field emission electron gun

NASA Astrophysics Data System (ADS)

Getty, Stephanie A.; King, Todd T.; Bis, Rachael A.; Jones, Hollis H.; Herrero, Federico; Lynch, Bernard A.; Roman, Patrick; Mahaffy, Paul

2007-04-01

A cold cathode field emission electron gun (e-gun) based on a patterned carbon nanotube (CNT) film has been fabricated for use in a miniaturized reflectron time-of-flight mass spectrometer (RTOF MS), with future applications in other charged particle spectrometers, and performance of the CNT e-gun has been evaluated. A thermionic electron gun has also been fabricated and evaluated in parallel and its performance is used as a benchmark in the evaluation of our CNT e-gun. Implications for future improvements and integration into the RTOF MS are discussed.

A Fully-Sealed Carbon-Nanotube Cold-Cathode Terahertz Gyrotron

PubMed Central

Yuan, Xuesong; Zhu, Weiwei; Zhang, Yu; Xu, Ningsheng; Yan, Yang; Wu, Jianqiang; Shen, Yan; Chen, Jun; She, Juncong; Deng, Shaozhi

2016-01-01

Gigahertz to terahertz radiation sources based on cold-cathode vacuum electron technology are pursued, because its unique characteristics of instant switch-on and power saving are important to military and space applications. Gigahertz gyrotron was reported using carbon nanotube (CNT) cold-cathode. It is reported here in first time that a fully-sealed CNT cold-cathode 0.22 THz-gyrotron is realized, typically with output power of 500 mW. To achieve this, we have studied mechanisms responsible for CNTs growth on curved shape metal surface, field emission from the sidewall of a CNT, and crystallized interface junction between CNT and substrate material. We have obtained uniform growth of CNTs on and direct growth from cone-cylinder stainless-steel electrode surface, and field emission from both tips and sidewalls of CNTs. It is essential for the success of a CNT terahertz gyrotron to have such high quality, high emitting performance CNTs. Also, we have developed a magnetic injection electron gun using CNT cold-cathode to exploit the advantages of such a conventional gun design, so that a large area emitting surface is utilized to deliver large current for electron beam. The results indicate that higher output power and higher radiation frequency terahertz gyrotron may be made using CNT cold-cathode electron gun. PMID:27609247

A Fully-Sealed Carbon-Nanotube Cold-Cathode Terahertz Gyrotron.

PubMed

Yuan, Xuesong; Zhu, Weiwei; Zhang, Yu; Xu, Ningsheng; Yan, Yang; Wu, Jianqiang; Shen, Yan; Chen, Jun; She, Juncong; Deng, Shaozhi

2016-09-09

Gigahertz to terahertz radiation sources based on cold-cathode vacuum electron technology are pursued, because its unique characteristics of instant switch-on and power saving are important to military and space applications. Gigahertz gyrotron was reported using carbon nanotube (CNT) cold-cathode. It is reported here in first time that a fully-sealed CNT cold-cathode 0.22 THz-gyrotron is realized, typically with output power of 500 mW. To achieve this, we have studied mechanisms responsible for CNTs growth on curved shape metal surface, field emission from the sidewall of a CNT, and crystallized interface junction between CNT and substrate material. We have obtained uniform growth of CNTs on and direct growth from cone-cylinder stainless-steel electrode surface, and field emission from both tips and sidewalls of CNTs. It is essential for the success of a CNT terahertz gyrotron to have such high quality, high emitting performance CNTs. Also, we have developed a magnetic injection electron gun using CNT cold-cathode to exploit the advantages of such a conventional gun design, so that a large area emitting surface is utilized to deliver large current for electron beam. The results indicate that higher output power and higher radiation frequency terahertz gyrotron may be made using CNT cold-cathode electron gun.

Controlled Deposition and Alignment of Carbon Nanotubes

NASA Technical Reports Server (NTRS)

Smits, Jan M. (Inventor); Wincheski, Russell A. (Inventor); Ingram, JoAnne L. (Inventor); Watkins, Anthony Neal (Inventor); Jordan, Jeffrey D. (Inventor)

2009-01-01

A carbon nanotube (CNT) attraction material is deposited on a substrate in the gap region between two electrodes on the . substrate. An electric potential is applied to the two electrodes. The CNT attraction material is wetted with a solution defined by a carver liquid having carbon nanotubes (CNTs) suspended therein. A portion of the CNTs align with the electric field and adhere to The CNT attraction material. The carrier liquid and any CNTs not adhered to the CNT attraction material are then removed.

Controlled Deposition and Alignment of Carbon Nanotubes

NASA Technical Reports Server (NTRS)

Patry, JoAnne L. (Inventor); Smits, Jan M. (Inventor); Watkins, Anthony Neal (Inventor); Jordan, Jeffrey D. (Inventor); Wincheski, Russell A. (Inventor)

2012-01-01

A carbon nanotube (CNT) attraction material is deposited on a substrate in the gap region between two electrodes on the substrate. An electric potential is applied to the two electrodes. The CNT attraction material is wetted with a solution defined by a carrier liquid having carbon nanotubes (CNTs) suspended therein. A portion of the CNTs align with the electric field and adhere to the CNT attraction material. The carrier liquid and any CNTs not adhered to the CNT attraction material are then removed.

Carbon Nanotube Field Emitters Synthesized on Metal Alloy Substrate by PECVD for Customized Compact Field Emission Devices to Be Used in X-Ray Source Applications.

PubMed

Park, Sangjun; Gupta, Amar Prasad; Yeo, Seung Jun; Jung, Jaeik; Paik, Sang Hyun; Mativenga, Mallory; Kim, Seung Hoon; Shin, Ji Hoon; Ahn, Jeung Sun; Ryu, Jehwang

2018-05-29

In this study, a simple, efficient, and economical process is reported for the direct synthesis of carbon nanotube (CNT) field emitters on metal alloy. Given that CNT field emitters can be customized with ease for compact and cold field emission devices, they are promising replacements for thermionic emitters in widely accessible X-ray source electron guns. High performance CNT emitter samples were prepared in optimized plasma conditions through the plasma-enhanced chemical vapor deposition (PECVD) process and subsequently characterized by using a scanning electron microscope, tunneling electron microscope, and Raman spectroscopy. For the cathode current, field emission (FE) characteristics with respective turn on (1 μA/cm²) and threshold (1 mA/cm²) field of 2.84 and 4.05 V/μm were obtained. For a field of 5.24 V/μm, maximum current density of 7 mA/cm² was achieved and a field enhancement factor β of 2838 was calculated. In addition, the CNT emitters sustained a current density of 6.7 mA/cm² for 420 min under a field of 5.2 V/μm, confirming good operational stability. Finally, an X-ray generated image of an integrated circuit was taken using the compact field emission device developed herein.

Mechanics of Carbon Nanotubes and their Polymer Composites

NASA Technical Reports Server (NTRS)

Wei, Chenyu; Cho, K. J.; Srivastava, Deepak; Tang, Harry (Technical Monitor)

2002-01-01

Contents include the folloving: carbon nanotube (CNT): structures, application of carbon nanotubes, simulation method, Elastic properties of carbon nanotubes, yield strain of CNT, yielding under tensile stress, yielding: strain-rate and temperature dependence, yield strain under tension, yielding at realistic conditions, nano fibers, polymer CNT composite, force field, density dependency on temperature, diffusion coefficients, young modulus, and conclusions.

Novel strategy for diameter-selective separation and functionalization of single-wall carbon nanotubes.

PubMed

Tromp, R M; Afzali, A; Freitag, M; Mitzi, D B; Chen, Zh

2008-02-01

The problem of separating single-wall carbon nanotubes (CNTs) by diameter and/or chirality is one of the greatest impediments toward the widespread application of these promising materials in nanoelectronics. In this paper, we describe a novel physical-chemical method for diameter-selective CNT separation that is both simple and effective and that allows up-scaling to large volumes at modest cost. Separation is based on size-selective noncovalent matching of an appropriate anchor molecule to the wall of the CNT, enabling suspension of the CNTs in solvents in which they would otherwise not be soluble. We demonstrate size-selective separation in the 1-2 nm diameter range using easily synthesized oligo-acene adducts as a diameter-selective molecular anchor. CNT field effect transistors fabricated from diameter-selected CNTs show markedly improved electrical properties as compared to nonselected CNTs.

Upgrading non-oxidized carbon nanotubes by thermally decomposed hydrazine

NASA Astrophysics Data System (ADS)

Wang, Pen-Cheng; Liao, Yu-Chun; Liu, Li-Hung; Lai, Yu-Ling; Lin, Ying-Chang; Hsu, Yao-Jane

2014-06-01

We found that the electrical properties of conductive thin films based on non-oxidized carbon nanotubes (CNTs) could be further improved when the CNTs consecutively underwent a mild hydrazine adsorption treatment and then a sufficiently effective thermal desorption treatment. We also found that, after several rounds of vapor-phase hydrazine treatments and baking treatments were applied to an inferior single-CNT field-effect transistor device, the device showed improvement in Ion/Ioff ratio and reduction in the extent of gate-sweeping hysteresis. Our experimental results indicate that, even though hydrazine is a well-known reducing agent, the characteristics of our hydrazine-exposed CNT samples subject to certain treatment conditions could become more graphenic than graphanic, suggesting that the improvement in the electrical and electronic properties of CNT samples could be related to the transient bonding and chemical scavenging of thermally decomposed hydrazine on the surface of CNTs.

Parametrically Optimized Carbon Nanotube-Coated Cold Cathode Spindt Arrays

PubMed Central

Yuan, Xuesong; Cole, Matthew T.; Zhang, Yu; Wu, Jianqiang; Milne, William I.; Yan, Yang

2017-01-01

Here, we investigate, through parametrically optimized macroscale simulations, the field electron emission from arrays of carbon nanotube (CNT)-coated Spindts towards the development of an emerging class of novel vacuum electron devices. The present study builds on empirical data gleaned from our recent experimental findings on the room temperature electron emission from large area CNT electron sources. We determine the field emission current of the present microstructures directly using particle in cell (PIC) software and present a new CNT cold cathode array variant which has been geometrically optimized to provide maximal emission current density, with current densities of up to 11.5 A/cm2 at low operational electric fields of 5.0 V/μm. PMID:28336845

Curvature induced L-defects in water conduction in carbon nanotubes.

PubMed

Zimmerli, Urs; Gonnet, Pedro G; Walther, Jens H; Koumoutsakos, Petros

2005-06-01

We conduct molecular dynamics simulations to study the effect of the curvature induced static dipole moment of small open-ended single-walled carbon nanotubes (CNTs) immersed in water. This dipole moment generates a nonuniform electric field, changing the energy landscape in the CNT and altering the water conduction process. The CNT remains practically filled with water at all times, whereas intermittent filling is observed when the dipole term is not included. In addition, the dipole moment induces a preferential orientation of the water molecules near the end regions of the nanotube, which in turn causes a reorientation of the water chain in the middle of the nanotube. The most prominent feature of this reorientation is an L-defect in the chain of water molecules inside the CNT. The analysis of the water energetics and structural characteristics inside and in the vicinity of the CNT helps to identify the role of the dipole moment and to suggest possible mechanisms for controlled water and proton transport at the nanoscale.

Transport properties of CNT/oligosilane/CNT heterojunctions

NASA Astrophysics Data System (ADS)

Yu, J.; Zhang, G. L.; Shang, Y.; Wang, K. D.; Zhang, H.; Sun, M.; Liu, B.; Zeng, T.

2013-02-01

Combining the non-equilibrium Green's function formalism with density functional theory, the transport properties of nine CNT/oligosilane/CNT heterojunctions were systematically studied. We have found that the incorporation of oligosilane linkage to the carbon nanotube mouth could significantly tune the transport properties compared with the pure oligosilane and pure CNT. The P- and B-dopings upon the oligosilane moiety could not only enhance the conductivity but also give rise to multiple negative differential resistance behavior for the CNT/oligosilane/CNT heterojunctions. The concentration of heteroatom plays an important role in the transport properties of the CNT/oligosilane/CNT heterojunctions, while the number of the oligosilane linkage exerts little effect on the conductivity. The B-doped CNT/oligosilane/CNT heterojunctions show higher conductivity than those of the P-doped ones. The p-n junction caused by B- and P-codopings exhibits a rectifying effect and the rectification ratio is up to 7.19.

Design and simulation of nanoscale double-gate TFET/tunnel CNTFET

NASA Astrophysics Data System (ADS)

Bala, Shashi; Khosla, Mamta

2018-04-01

A double-gate tunnel field-effect transistor (DG tunnel FET) has been designed and investigated for various channel materials such as silicon (Si), gallium arsenide (GaAs), alminium gallium arsenide (Al x Ga1‑x As) and CNT using a nano ViDES Device and TCAD SILVACO ATLAS simulator. The proposed devices are compared on the basis of inverse subthreshold slope (SS), I ON/I OFF current ratio and leakage current. Using Si as the channel material limits the property to reduce leakage current with scaling of channel, whereas the Al x Ga1‑x As based DG tunnel FET provides a better I ON/I OFF current ratio (2.51 × 106) as compared to other devices keeping the leakage current within permissible limits. The performed silmulation of the CNT based channel in the double-gate tunnel field-effect transistor using the nano ViDES shows better performace for a sub-threshold slope of 29.4 mV/dec as the channel is scaled down. The proposed work shows the potential of the CNT channel based DG tunnel FET as a futuristic device for better switching and high retention time, which makes it suitable for memory based circuits.

Design, simulation and comparative analysis of CNT based cascode operational transconductance amplifiers

NASA Astrophysics Data System (ADS)

Nizamuddin, M.; Loan, Sajad A.; Alamoud, Abdul R.; Abbassi, Shuja A.

2015-10-01

In this work, design and calibrated simulation of carbon nanotube field effect transistor (CNTFET)-based cascode operational transconductance amplifiers (COTA) have been performed. Three structures of CNTFET-based COTAs have been designed using HSPICE and have been compared with the conventional CMOS-based COTAs. The proposed COTAs include one using pure CNTFETs and two others that employ CNTFETs, as well as the conventional MOSFETs. The simulation study has revealed that the CNTFET-based COTAs have significantly outperformed the conventional MOSFET-based COTAs. A significant increase in dc gain, output resistance and slew rate of 81.4%, 25% and 13.2%, respectively, have been achieved in the proposed pure CNT-based COTA in comparison to the conventional CMOS-based COTA. The power consumption in the pure CNT-COTA is 324 times less in comparison to the conventional CMOS-COTA. Further, the phase margin (PM), gain margin (GM), common mode and power supply rejection ratios have been significantly increased in the proposed CNT-based COTAs in comparison to the conventional CMOS-based COTAs. Furthermore, to see the advantage of cascoding, the proposed CNT-based cascode OTAs have been compared with the CNT-based OTAs. It has been observed that by incorporating the concept of cascode in the CNTFET-based OTAs, significant increases in gain (12.5%) and output resistance (13.07%) have been achieved. The performance of the proposed COTAs has been further observed by changing the number of CNTs (N), CNT pitch (S) and CNT diameter (DCNT) in the CNTFETs used. It has been observed that the performance of the proposed COTAs can be significantly improved by using optimum values of N, S and DCNT.

Dielectrophoresis-Assisted Integration of 1024 Carbon Nanotube Sensors into a CMOS Microsystem.

PubMed

Seichepine, Florent; Rothe, Jörg; Dudina, Alexandra; Hierlemann, Andreas; Frey, Urs

2017-05-01

Carbon-nanotube (CNT)-based sensors offer the potential to detect single-molecule events and picomolar analyte concentrations. An important step toward applications of such nanosensors is their integration in large arrays. The availability of large arrays would enable multiplexed and parallel sensing, and the simultaneously obtained sensor signals would facilitate statistical analysis. A reliable method to fabricate an array of 1024 CNT-based sensors on a fully processed complementary-metal-oxide-semiconductor microsystem is presented. A high-yield process for the deposition of CNTs from a suspension by means of liquid-coupled floating-electrode dielectrophoresis (DEP), which yielded 80% of the sensor devices featuring between one and five CNTs, is developed. The mechanism of floating-electrode DEP on full arrays and individual devices to understand its self-limiting behavior is studied. The resistance distributions across the array of CNT devices with respect to different DEP parameters are characterized. The CNT devices are then operated as liquid-gated CNT field-effect-transistors (LG-CNTFET) in liquid environment. Current dependency to the gate voltage of up to two orders of magnitude is recorded. Finally, the sensors are validated by studying the pH dependency of the LG-CNTFET conductance and it is demonstrated that 73% of the CNT sensors of a given microsystem show a resistance decrease upon increasing the pH value. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

High-Performance Complementary Transistors and Medium-Scale Integrated Circuits Based on Carbon Nanotube Thin Films.

PubMed

Yang, Yingjun; Ding, Li; Han, Jie; Zhang, Zhiyong; Peng, Lian-Mao

2017-04-25

Solution-derived carbon nanotube (CNT) network films with high semiconducting purity are suitable materials for the wafer-scale fabrication of field-effect transistors (FETs) and integrated circuits (ICs). However, it is challenging to realize high-performance complementary metal-oxide semiconductor (CMOS) FETs with high yield and stability on such CNT network films, and this difficulty hinders the development of CNT-film-based ICs. In this work, we developed a doping-free process for the fabrication of CMOS FETs based on solution-processed CNT network films, in which the polarity of the FETs was controlled using Sc or Pd as the source/drain contacts to selectively inject carriers into the channels. The fabricated top-gated CMOS FETs showed high symmetry between the characteristics of n- and p-type devices and exhibited high-performance uniformity and excellent scalability down to a gate length of 1 μm. Many common types of CMOS ICs, including typical logic gates, sequential circuits, and arithmetic units, were constructed based on CNT films, and the fabricated ICs exhibited rail-to-rail outputs because of the high noise margin of CMOS circuits. In particular, 4-bit full adders consisting of 132 CMOS FETs were realized with 100% yield, thereby demonstrating that this CMOS technology shows the potential to advance the development of medium-scale CNT-network-film-based ICs.

Effect of Pre-Ozonation and UF Membrane Modification with CNT on Fouling Control

NASA Astrophysics Data System (ADS)

Wang, Kailun; Guan, Yuqi; Zhu, Xuedong; Dong, Dan; Guo, Jin

2018-01-01

The effect of carbon nanotubes (CNT) modification on ultrafiltration membrane fouling control was explored. Three kinds of base membrane were chosen in the study: 20 kDa polysulfone (PS) membrane, 20 kDa and 100 kDa polyethersulfone (PES) membrane. Besides, the effect of pre-ozonation on the three CNT modified membranes for fouling alleviation was further studied. CNT modification presented antifouling properties at the beginning of filtration, while the recoverability of the CNT modified membranes are relatively lower as for the blocking of CNT layer by foulants. Pre-ozonation with a lower ozone concentration (0.25 mgO3/mgDOC) did not efficiently alleviate the fouling of CNT modified membranes. With the ozone concentration increased to 0.81 mgO3/mgDOC, the CNT modified membranes exhibited their higher antifouling properties. Water quality analysis results showed that CNT modification presented a higher capture ability for the humic-like and protein-like substances. After pre-ozonation, more organic materials could be retained in the interior of CNT layer, which decreased the fouling of base membranes and increased the permeate quality as well. Base membrane with large molecular size cut-off is more helpful for the synergistic effect of pre-ozonation and CNT modification.

Advances and prospects on biomolecules functionalized carbon nanotubes.

PubMed

Cui, Daxiang

2007-01-01

In recent years, functionalization of carbon nanotubes (CNTs) with biomolecules such as nucleotide acids, proteins, and polymers as well as cells have emerged as a new exciting field. Theoretical and experimental studies of structure and function of bio-inspired CNT composites have made great advances. The importance of nucleic acids, proteins, and polymers to the fundamental developments in CNT-based bio-nano-composites or devices has been recognized. In particular, biomechanics, biochemistry, thermodynamics, electronic, optical, and magnetic properties of the bio-inspired CNT composites have become a new interdisciplinary frontier in life science and nanomaterial science. Here we review some of the main advances in this field over the past few years, explore the application prospects, and discuss the issues, approaches, and challenges, with the aim of stimulating a broader interest in developing CNT-based bio-nanotechnology.

Efficient 2-Nitrophenol Chemical Sensor Development Based on Ce2O3 Nanoparticles Decorated CNT Nanocomposites for Environmental Safety

PubMed Central

Hussain, Mohammad M.; Rahman, Mohammed M.; Asiri, Abdullah M.

2016-01-01

Ce2O3 nanoparticle decorated CNT nanocomposites (Ce2O3.CNT NCs) were prepared by a wet-chemical method in basic medium. The Ce2O3.CNT NCs were examined using FTIR, UV/Vis, Field-Emission Scanning Electron Microscopy (FESEM), X-ray electron dispersive spectroscopy (XEDS), X-ray photoelectron spectroscopy (XPS), and powder X-ray diffraction (XRD). A selective 2-nitrophenol (2-NP) sensor was developed by fabricating a thin-layer of NCs onto a flat glassy carbon electrode (GCE, surface area = 0.0316 cm2). Higher sensitivity including linear dynamic range (LDR), long-term stability, and enhanced electrochemical performances towards 2-NP were achieved by a reliable current-voltage (I-V) method. The calibration curve was found linear (R2 = 0.9030) over a wide range of 2-NP concentration (100 pM ~ 100.0 mM). Limit of detection (LOD) and sensor sensitivity were calculated based on noise to signal ratio (~3N/S) as 60 ± 0.02 pM and 1.6×10−3 μAμM-1cm-2 respectively. The Ce2O3.CNT NCs synthesized by a wet-chemical process is an excellent way of establishing nanomaterial decorated carbon materials for chemical sensor development in favor of detecting hazardous compounds in health-care and environmental fields at broad-scales. Finally, the efficiency of the proposed chemical sensors can be applied and utilized in effectively for the selective detection of toxic 2-NP component in environmental real samples with acceptable and reasonable results. PMID:27973600

Efficient 2-Nitrophenol Chemical Sensor Development Based on Ce2O3 Nanoparticles Decorated CNT Nanocomposites for Environmental Safety.

PubMed

Hussain, Mohammad M; Rahman, Mohammed M; Asiri, Abdullah M

2016-01-01

Ce2O3 nanoparticle decorated CNT nanocomposites (Ce2O3.CNT NCs) were prepared by a wet-chemical method in basic medium. The Ce2O3.CNT NCs were examined using FTIR, UV/Vis, Field-Emission Scanning Electron Microscopy (FESEM), X-ray electron dispersive spectroscopy (XEDS), X-ray photoelectron spectroscopy (XPS), and powder X-ray diffraction (XRD). A selective 2-nitrophenol (2-NP) sensor was developed by fabricating a thin-layer of NCs onto a flat glassy carbon electrode (GCE, surface area = 0.0316 cm2). Higher sensitivity including linear dynamic range (LDR), long-term stability, and enhanced electrochemical performances towards 2-NP were achieved by a reliable current-voltage (I-V) method. The calibration curve was found linear (R2 = 0.9030) over a wide range of 2-NP concentration (100 pM ~ 100.0 mM). Limit of detection (LOD) and sensor sensitivity were calculated based on noise to signal ratio (~3N/S) as 60 ± 0.02 pM and 1.6×10-3 μAμM-1cm-2 respectively. The Ce2O3.CNT NCs synthesized by a wet-chemical process is an excellent way of establishing nanomaterial decorated carbon materials for chemical sensor development in favor of detecting hazardous compounds in health-care and environmental fields at broad-scales. Finally, the efficiency of the proposed chemical sensors can be applied and utilized in effectively for the selective detection of toxic 2-NP component in environmental real samples with acceptable and reasonable results.

Self aligned hysteresis free carbon nanotube field-effect transistors

NASA Astrophysics Data System (ADS)

Shlafman, M.; Tabachnik, T.; Shtempluk, O.; Razin, A.; Kochetkov, V.; Yaish, Y. E.

2016-04-01

Hysteresis phenomenon in the transfer characteristics of carbon nanotube field effect transistor (CNT FET) is being considered as the main obstacle for successful realization of electronic devices based on CNTs. In this study, we prepare four kinds of CNTFETs and explore their hysteretic behavior. Two kinds of devices comprise on-surface CNTs (type I) and suspended CNTs (type II) with thin insulating layer underneath and a single global gate which modulates the CNT conductance. The third and fourth types (types III and IV) consist of suspended CNT over a metallic local gate underneath, where for type IV the local gate was patterned self aligned with the source and drain electrodes. The first two types of devices, i.e., type I and II, exhibit substantial hysteresis which increases with scanning range and sweeping time. Under high vacuum conditions and moderate electric fields ( |E |>4 ×106 V /cm ), the hysteresis for on-surface devices cannot be eliminated, as opposed to suspended devices. Interestingly, type IV devices exhibit no hysteresis at all at ambient conditions, and from the different roles which the global and local gates play for the four types of devices, we could learn about the hysteresis mechanism of this system. We believe that these self aligned hysteresis free FETs will enable the realization of different electronic devices and sensors based on CNTs.

The fabrication of vertically aligned and periodically distributed carbon nanotube bundles and periodically porous carbon nanotube films through a combination of laser interference ablation and metal-catalyzed chemical vapor deposition.

PubMed

Yuan, Dajun; Lin, Wei; Guo, Rui; Wong, C P; Das, Suman

2012-06-01

Scalable fabrication of carbon nanotube (CNT) bundles is essential to future advances in several applications. Here, we report on the development of a simple, two-step method for fabricating vertically aligned and periodically distributed CNT bundles and periodically porous CNT films at the sub-micron scale. The method involves laser interference ablation (LIA) of an iron film followed by CNT growth via iron-catalyzed chemical vapor deposition. CNT bundles with square widths ranging from 0.5 to 1.5 µm in width, and 50-200 µm in length, are grown atop the patterned catalyst over areas spanning 8 cm(2). The CNT bundles exhibit a high degree of control over square width, orientation, uniformity, and periodicity. This simple scalable method of producing well-placed and oriented CNT bundles demonstrates a high application potential for wafer-scale integration of CNT structures into various device applications, including IC interconnects, field emitters, sensors, batteries, and optoelectronics, etc.

Carbon-nanotube probes for three-dimensional critical-dimension metrology

NASA Astrophysics Data System (ADS)

Park, B. C.; Ahn, S. J.; Choi, J.; Jung, K. Y.; Song, W. Y.

2006-03-01

We fabricate three kinds of carbon nanotube (CNT) probes to be employed in critical dimension atomic force microscope (CD-AFM). Despite unique advantages in its size and hardness, use of nanotube tip has been limited due to the lack of reproducible control of CNT orientation and its shape. We proposed that CNT alignment issues can be addressed based on the ion beam bending process, where a CNT free-standing on the apex of an AFM tip aligns itself in parallel to the FIB direction so that its free end is directed toward the ion source, with no external electric or magnetic field involved. The process allowed us to embody cylindrical probes of CNT diameters, and subsequently two additional types of CNT tips. One is ball-ended CNT tip which has, at the end of CNT tip, side-protrusions of tungsten/amorphous carbon in the horizontal dithering direction. The other is 'bent' CNT tip where the end of CNT is bent to a side direction. Using the former type of CNT tip, both sides of trench/line sidewall can be measured except for bottom corners, while the corners can be reached with the latter type, but the only one sidewall can be measured at a tip setting. The three types of tips appear to satisfy the requirements in both the size and accessibility to the re-entrant sidewall, and are awaiting actual test in CD-AFM.

A power system design and analysis of carbon nano-tubes field emission displays

NASA Astrophysics Data System (ADS)

Wang, Jong C.; Yao, W. C.

2006-01-01

In new generation Flat Panel Displays(FPD), a lot of design methods are being deployed, including OLED, PDP, TFT-LCD, Back Projection and Field Emission Display(FED) etc. These new generation FPDs have their respective pluses and minuses. Each has its selling points and market attractions. But among them, FED principles are most close to that of CRT displays. Not only FEDs are advantageous in their good degree of saturation of color, but also they have excellent contrast, luminance and electricity consumption etc. It has been considered as the main products of future generation FPDs. Japan and countries all over the world are successively proposing and launching related FED products in the fields. This will not only drive the FEDs into a wave of new trends, but also it will be able to replace most of the current FPD products within a short time. In this paper, based on these solid trends, we are determined to put into our resources and efforts to perform research on these important FEDs technologies and products, particularly in Carbon Nano-Tubes FEDs(CNT-FED). Our research group has already performed research on CNT-FED subjects for almost three years. During the course of our research, we have run into a lot of issues and problems. We have made every effort to overcome some of them. This paper performs comparative analysis of three power option for small size (4-inch) CNT-FEDs to drive the FED effects such as the direct current power, pulsed power and sinusoidal power respectively. This paper performs comparative analysis of three power options for small sized CNT-FEDs. It was concluded that the pulsed power option will produce the best results overall among the three power options. It is felt that these data presented can then be referenced and used to design a power system circuit to get an optimum design for better luminance and least power consumption for small sized commercial CNT-FED products.

Carbon nanotubes gathered onto silica particles lose their biomimetic properties with the cytoskeleton becoming biocompatible.

PubMed

González-Domínguez, Elena; Iturrioz-Rodríguez, Nerea; Padín-González, Esperanza; Villegas, Juan; García-Hevia, Lorena; Pérez-Lorenzo, Moisés; Parak, Wolfgang J; Correa-Duarte, Miguel A; Fanarraga, Mónica L

2017-01-01

Carbon nanotubes (CNTs) are likely to transform the therapeutic and diagnostic fields in biomedicine during the coming years. However, the fragmented vision of their side effects and toxicity in humans has proscribed their use as nanomedicines. Most studies agree that biocompatibility depends on the state of aggregation/dispersion of CNTs under physiological conditions, but conclusions are confusing so far. This study designs an experimental setup to investigate the cytotoxic effect of individualized multiwalled CNTs compared to that of identical nanotubes assembled on submicrometric structures. Our results demonstrate how CNT cytotoxicity is directly dependent on the nanotube dispersion at a given dosage. When CNTs are gathered onto silica templates, they do not interfere with cell proliferation or survival becoming highly compatible. These results support the hypothesis that CNT cytotoxicity is due to the biomimetics of these nanomaterials with the intracellular nanofilaments. These findings provide major clues for the development of innocuous CNT-containing nanodevices and nanomedicines.

Immobilization of natural anti-oxidants on carbon nanotubes and aging behavior of ultra-high molecular weight polyethylene-based nanocomposites

NASA Astrophysics Data System (ADS)

Dintcheva, Nadka Tzankova; Arrigo, Rossella; Gambarotti, Cristian; Guenzi, Monica; Carroccio, Sabrina; Cicogna, Francesca; Filippone, Giovanni

2014-05-01

The use of natural antioxidants is an attractive way to formulate nanocomposites with extended durability and with potential applications in bio-medical field. In this work, Vitamin E (VE) in the form of α-tocopherol and Quercetin (Q) are physically immobilized on the outer surface of multi-walled carbon nanotubes (CNTs). Afterward, the CNTs-VE and CNTs-Q are used to formulate thermally stable ultra high molecular weight polyethylene based nanocomposites. The obtained results in the study of the thermo-oxidation behavior suggest a beneficial effect of the natural anti-oxidant carbon nanotubes systems. The unexpected excellent thermo-resistance of the nanocomposites seems to be due to a synergistic effect of the natural anti-oxidant and carbon nanotubes, i.e. strong interaction between CNT surface and anti-oxidant molecules. Particularly, these interactions cause the formation of structural defects onto outer CNT surfaces, which, in turn, increase the CNT radical scavenging activity.

Nanoscale discharge electrode for minimizing ozone emission from indoor corona devices.

PubMed

Bo, Zheng; Yu, Kehan; Lu, Ganhua; Mao, Shun; Chen, Junhong; Fan, Fa-Gung

2010-08-15

Ground-level ozone emitted from indoor corona devices poses serious health risks to the human respiratory system and the lung function. Federal regulations call for effective techniques to minimize the indoor ozone production. In this work, stable atmospheric corona discharges from nanomaterials are demonstrated using horizontally suspended carbon nanotubes (CNTs) as the discharge electrode. Compared with the conventional discharges employing micro- or macroscale electrodes, the corona discharge from CNTs could initiate and operate at a much lower voltage due to the small electrode diameter, and is thus energy-efficient. Most importantly, the reported discharge is environmentally friendly since no ozone (below the detection limit of 0.5 ppb) was detected for area current densities up to 0.744 A/m(2) due to the significantly reduced number of electrons and plasma volume generated by CNT discharges. The resulting discharge current density depends on the CNT loading. Contrary to the conventional wisdom, negative CNT discharges should be used to enhance the current density owing to the efficient field emission of electrons from the CNT surface.

Evaluating the environmental impacts of a nano-enhanced field emission display using life cycle assessment: a screening-level study.

PubMed

Upadhyayula, Venkata K K; Meyer, David E; Curran, Mary Ann; Gonzalez, Michael A

2014-01-21

Carbon nanotube (CNT) field emission displays (FEDs) are currently in the product development stage and are expected to be commercialized in the near future because they offer image quality and viewing angles comparable to a cathode ray tube (CRT) while using a thinner structure, similar to a liquid crystal display (LCD), and enable more efficient power consumption during use. To address concerns regarding the environmental performance of CNT-FEDs, a screening-level, cradle-to-grave life cycle assessment (LCA) was conducted based on a functional unit of 10,000 viewing hours, the viewing lifespan of a CNT-FED. Contribution analysis suggests the impacts for material acquisition and manufacturing are greater than the combined impacts for use and end-of-life. A scenario analysis of the CNT paste composition identifies the metal components used in the paste are key contributors to the impacts of the upstream stages due to the impacts associated with metal preparation. Further improvement of the manufacturing impacts is possible by considering the use of plant-based oils, such as rapeseed oil, as alternatives to organic solvents for dispersion of CNTs. Given the differences in viewing lifespan, the impacts of the CNT-FED were compared with a LCD and a CRT display to provide more insight on how to improve the CNT-FED to make it a viable product alternative. When compared with CRT technology, CNT-FEDs show better environmental performance, whereas a comparison with LCD technology indicates the environmental impacts are roughly the same. Based on the results, the enhanced viewing capabilities of CNT-FEDs will be a more viable display option if manufacturers can increase the product's expected viewing lifespan.

Carbon Nanotube Emissions from Arc Discharge Production: Classification of Particle Types with Electron Microscopy and Comparison with Direct Reading Techniques.

PubMed

Ludvigsson, Linus; Isaxon, Christina; Nilsson, Patrik T; Tinnerberg, Hakan; Messing, Maria E; Rissler, Jenny; Skaug, Vidar; Gudmundsson, Anders; Bohgard, Mats; Hedmer, Maria; Pagels, Joakim

2016-05-01

An increased production and use of carbon nanotubes (CNTs) is occurring worldwide. In parallel, a growing concern is emerging on the adverse effects the unintentional inhalation of CNTs can have on humans. There is currently a debate regarding which exposure metrics and measurement strategies are the most relevant to investigate workplace exposures to CNTs. This study investigated workplace CNT emissions using a combination of time-integrated filter sampling for scanning electron microscopy (SEM) and direct reading aerosol instruments (DRIs). Field measurements were performed during small-scale manufacturing of multiwalled carbon nanotubes using the arc discharge technique. Measurements with highly time- and size-resolved DRI techniques were carried out both in the emission and background (far-field) zones. Novel classifications and counting criteria were set up for the SEM method. Three classes of CNT-containing particles were defined: type 1: particles with aspect ratio length:width >3:1 (fibrous particles); type 2: particles without fibre characteristics but with high CNT content; and type 3: particles with visible embedded CNTs. Offline sampling using SEM showed emissions of CNT-containing particles in 5 out of 11 work tasks. The particles were classified into the three classes, of which type 1, fibrous CNT particles contributed 37%. The concentration of all CNT-containing particles and the occurrence of the particle classes varied strongly between work tasks. Based on the emission measurements, it was assessed that more than 85% of the exposure originated from open handling of CNT powder during the Sieving, mechanical work-up, and packaging work task. The DRI measurements provided complementary information, which combined with SEM provided information on: (i) the background adjusted emission concentration from each work task in different particle size ranges, (ii) identification of the key procedures in each work task that lead to emission peaks, (iii) identification of emission events that affect the background, thereby leading to far-field exposure risks for workers other than the operator of the work task, and (iv) the fraction of particles emitted from each source that contains CNTs. There is an urgent need for a standardized/harmonized method for electron microscopy (EM) analysis of CNTs. The SEM method developed in this study can form the basis for such a harmonized protocol for the counting of CNTs. The size-resolved DRI techniques are commonly not specific enough to selective analysis of CNT-containing particles and thus cannot yet replace offline time-integrated filter sampling followed by SEM. A combination of EM and DRI techniques offers the most complete characterization of workplace emissions of CNTs today. © The Author 2016. Published by Oxford University Press on behalf of the British Occupational Hygiene Society.

Photothermal therapy of melanoma tumor using multiwalled carbon nanotubes.

PubMed

Sobhani, Zahra; Behnam, Mohammad Ali; Emami, Farzin; Dehghanian, Amirreza; Jamhiri, Iman

2017-01-01

Photothermal therapy (PTT) is a therapeutic method in which photon energy is transformed into heat rapidly via different operations to extirpate cancer. Nanoparticles, such as carbon nanotubes (CNTs) have exceptional optical absorbance in visible and near infrared spectra. Therefore, they could be a good converter to induce hyperthermia in PTT technique. In our study, for improving the dispersibility of multiwalled CNTs in water, the CNTs were oxidized (O-CNTs) and then polyethylene glycol (PEG) was used for wrapping the surface of nanotubes. The formation of a thin layer of PEG around the nanotubes was confirmed through Fourier transform infrared, thermogravimetric analysis, and field emission scanning electron microscopy techniques. Results of thermogravimetric analysis showed that the amount of PEG component in the O-CNT-PEG was approximately 80% (w/w). Cell cytotoxicity study showed that O-CNT was less cytotoxic than pristine multiwalled nanotubes, and O-CNT-PEG had the lowest toxicity against HeLa and HepG2 cell lines. The effect of O-CNT-PEG in reduction of melanoma tumor size after PTT was evaluated. Cancerous mice were exposed to a continuous-wave near infrared laser diode (λ=808 nm, P =2 W and I =8 W/cm 2 ) for 10 minutes once in the period of the treatment. The average size of tumor in mice receiving O-CNT-PEG decreased sharply in comparison with those that received laser therapy alone. Results of animal studies indicate that O-CNT-PEG is a powerful candidate for eradicating solid tumors in PTT technique.

A pH sensor based on electric properties of nanotubes on a glass substrate

PubMed Central

Nakamura, Motonori; Ishii, Atsushi; Subagyo, Agus; Hosoi, Hirotaka; Sueoka, Kazuhisa; Mukasa, Koichi

2007-01-01

We fabricated a pH-sensitive device on a glass substrate based on properties of carbon nanotubes. Nanotubes were immobilized specifically on chemically modified areas on a substrate followed by deposition of metallic source and drain electrodes on the area. Some nanotubes connected the source and drain electrodes. A top gate electrode was fabricated on an insulating layer of silane coupling agent on the nanotube. The device showed properties of ann-type field effect transistor when a potential was applied to the nanotube from the top gate electrode. Before fabrication of the insulating layer, the device showed that thep-type field effect transistor and the current through the source and drain electrodes depend on the buffer pH. The current increases with decreasing pH of the CNT solution. This device, which can detect pH, is applicable for use as a biosensor through modification of the CNT surface. PMID:21806848

Water desalination by electrical resonance inside carbon nanotubes.

PubMed

Feng, Jia-Wei; Ding, Hong-Ming; Ma, Yu-Qiang

2016-10-12

Although previous studies have indicated that the carbon nanotube (CNT) can be used for directed transportation of water and ions, it is still a challenging problem to design a CNT-based device for high performance water desalination. In this study, by using molecular dynamics simulations, we successfully design one type of CNT as a highly efficient desalination membrane through electrical resonance. By decorating the two ends of the CNT with vibrational charges, an alternating electric field is created inside the CNT. When the amplitude of the vibrational charge is 0.05 e, and the vibrational frequency is between 10 THz and 20 THz, the CNT can completely block the transportation of ions. The decrease of the amplitude or the deviation of the frequency in an appropriate range will gradually increase the ion flow. Besides, we also reveal the underlying molecular mechanism of ion blockage, i.e., the electric resonance can disrupt the water structure inside the CNT and then alter the hydration energy of ions inside the CNT. More importantly, we further demonstrate that this mechanism is universal, which is independent of the type of ions and the size of CNT. The present work could be useful for designing water desalination membranes with lower energy consumption and higher fresh water production.

Universal model of bias-stress-induced instability in inkjet-printed carbon nanotube networks field-effect transistors

NASA Astrophysics Data System (ADS)

Jung, Haesun; Choi, Sungju; Jang, Jun Tae; Yoon, Jinsu; Lee, Juhee; Lee, Yongwoo; Rhee, Jihyun; Ahn, Geumho; Yu, Hye Ri; Kim, Dong Myong; Choi, Sung-Jin; Kim, Dae Hwan

2018-02-01

We propose a universal model for bias-stress (BS)-induced instability in the inkjet-printed carbon nanotube (CNT) networks used in field-effect transistors (FETs). By combining two experimental methods, i.e., a comparison between air and vacuum BS tests and interface trap extraction, BS instability is explained regardless of either the BS polarity or ambient condition, using a single platform constituted by four key factors: OH- adsorption/desorption followed by a change in carrier concentration, electron concentration in CNT channel corroborated with H2O/O2 molecules in ambient, charge trapping/detrapping, and interface trap generation. Under negative BS (NBS), the negative threshold voltage shift (ΔVT) is dominated by OH- desorption, which is followed by hole trapping in the interface and/or gate insulator. Under positive BS (PBS), the positive ΔVT is dominated by OH- adsorption, which is followed by electron trapping in the interface and/or gate insulator. This instability is compensated by interface trap extraction; PBS instability is slightly more complicated than NBS instability. Furthermore, our model is verified using device simulation, which gives insights on how much each mechanism contributes to BS instability. Our result is potentially useful for the design of highly stable CNT-based flexible circuits in the Internet of Things wearable healthcare era.

Length separation of single-walled carbon nanotubes and its impact on structural and electrical properties of wafer-level fabricated carbon nanotube-field-effect transistors

NASA Astrophysics Data System (ADS)

Böttger, Simon; Hermann, Sascha; Schulz, Stefan E.; Gessner, Thomas

2016-10-01

For an industrial realization of devices based on single-walled carbon nanotube (SWCNTs) such as field-effect transistors (FETs) it becomes increasingly important to consider technological aspects such as intrinsic device structure, integration process controllability as well as yield. From the perspective of a wafer-level integration technology, the influence of SWCNT length on the performance of short-channel CNT-FETs is demonstrated by means of a statistical and comparative study. Therefore, a methodological development of a length separation process based on size-exclusion chromatography was conducted in order to extract well-separated SWCNT dispersions with narrowed length distribution. It could be shown that short SWCNTs adversely affect integrability and reproducibility, underlined by a 25% decline of the integration yield with respect to long SWCNTs. Furthermore, it turns out that the significant changes in electrical performance are directly linked to a SWCNT chain formation in the transistor channel. In particular, CNT-FETs with long SWCNTs outperform reference and short SWCNTs with respect to hole mobility and subthreshold controllability by up to 300% and up to 140%, respectively. As a whole, this study provides a statistical and comparative analysis towards chain-less CNT-FETs fabricated with a wafer-level technology.

Study of electron transport in the functionalized nanotubes and their impact on the electron transfer in the active site of horseradish peroxidase

NASA Astrophysics Data System (ADS)

Feizabadi, Mina; Ajloo, Davood; Soleymanpour, Ahmad; Faridnouri, Hassan

2018-05-01

Electrochemical characterization of functionalized carbon nanotubes (f-CNT) including carboxyl (CNT-COOH), amine (CNT-NH2) and hydroxyl (CNT-OH) functional groups were studied using differential pulse voltammetry (DPV). The current-voltage (I-V) curves were obtained from each system and the effect of f-CNT on redox interaction of horseradish peroxidase (HRP) immobilized on the electrode surface was investigated. The non-equilibrium Green's function (NEGF) combined with density functional theory (DFT) were used to study the transport properties of f-CNT. Additionally, the effect of the number of functional groups on transport properties of CNT, I-V characteristics, electronic transmission coefficients and spatial distribution of f-CNTs have been calculated and analyzed. The results showed that the carboxyl derivative has larger transmission coefficients and current value than other f-CNTs. Then, the effect of functional groups on the electron transport in heme group of HRP is discussed. Finally, the effect of a covalent bond between active site amino acids and amine functional group of CNT was investigated and discussed.

Improvement of the relaxation time and the order parameter of nematic liquid crystal using a hybrid alignment mixture of carbon nanotube and polyimide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Hyojin; Yang, Seungbin; Lee, Ji-Hoon, E-mail: jihoonlee@jbnu.ac.kr

2014-05-12

We examined the electrooptical properties of a nematic liquid crystal (LC) sample whose substrates were coated with a mixture of carbon nanotube (CNT) and polyimide (PI). The relaxation time of the sample coated with 1.5 wt. % CNT mixture was about 35% reduced compared to the pure polyimide sample. The elastic constant and the order parameter of the CNT-mixture sample were increased and the fast relaxation of LC could be approximated to the mean-field theory. We found the CNT-mixed polyimide formed more smooth surface than the pure PI from atomic force microscopy images, indicating the increased order parameter is related to themore » smooth surface topology of the CNT-polyimide mixture.« less

Hysteresis-Free Carbon Nanotube Field-Effect Transistors.

PubMed

Park, Rebecca S; Hills, Gage; Sohn, Joon; Mitra, Subhasish; Shulaker, Max M; Wong, H-S Philip

2017-05-23

While carbon nanotube (CNT) field-effect transistors (CNFETs) promise high-performance and energy-efficient digital systems, large hysteresis degrades these potential CNFET benefits. As hysteresis is caused by traps surrounding the CNTs, previous works have shown that clean interfaces that are free of traps are important to minimize hysteresis. Our previous findings on the sources and physics of hysteresis in CNFETs enabled us to understand the influence of gate dielectric scaling on hysteresis. To begin with, we validate through simulations how scaling the gate dielectric thickness results in greater-than-expected benefits in reducing hysteresis. Leveraging this insight, we experimentally demonstrate reducing hysteresis to <0.5% of the gate-source voltage sweep range using a very large-scale integration compatible and solid-state technology, simply by fabricating CNFETs with a thin effective oxide thickness of 1.6 nm. However, even with negligible hysteresis, large subthreshold swing is still observed in the CNFETs with multiple CNTs per transistor. We show that the cause of large subthreshold swing is due to threshold voltage variation between individual CNTs. We also show that the source of this threshold voltage variation is not explained solely by variations in CNT diameters (as is often ascribed). Rather, other factors unrelated to the CNTs themselves (i.e., process variations, random fixed charges at interfaces) are a significant factor in CNT threshold voltage variations and thus need to be further improved.

Mass transport through vertically aligned large diameter MWCNT embedded in parylene

PubMed Central

Krishnakumar, P; Tiwari, P B; Staples, S; Luo, T; Darici, Y; He, J; Lindsay, SM

2013-01-01

We have fabricated porous membranes using a parylene encapsulated vertically aligned forest of multi-walled carbon nanotube (MWCNT, about 7nm inner diameter). The transport of charged particles in electrolyte through these membranes was studied by applying electric field and pressure. Under an electric field in the range of 4.4×104 V/m, electrophoresis instead of electroomosis is found to be the main mechanism for ion transport. Small molecules and 5 nm gold nanoparticles can be driven through the membranes by an electric field. However, small biomolecules, like DNA oligomers, cannot. Due to the weak electric driving force, the interactions between charged particles and the hydrophobic CNT inner surface play important roles in the transport, leading to enhanced selectivity for small molecules. Simple chemical modification on the CNT ends also induces an obvious effect on the translocation of single strand DNA oligomer and gold nanoparticle under a modest pressure (<294 Pa). PMID:23064678

Photonic crystal wave guide for non-cryogenic cooled carbon nanotube based middle wave infrared sensors

NASA Astrophysics Data System (ADS)

Fung, Carmen Kar Man; Xi, Ning; Lou, Jianyong; Lai, King Wai Chiu; Chen, Hongzhi

2010-10-01

We report high sensitivity carbon nanotube (CNT) based middle wave infrared (MWIR) sensors with a two-dimensional photonic crystal waveguide. MWIR sensors are of great importance in a variety of current military applications including ballistic missile defense, surveillance and target detection. Unlike other existing MWIR sensing materials, CNTs exhibit low noise level and can be used as new nano sensing materials for MWIR detection where cryogenic cooling is not required. However, the quantum efficiency of the CNT based infrared sensor is still limited by the small sensing area and low incoming electric field. Here, a photonic nanostructure is used as a resonant cavity for boosting the electric field intensity at the position of the CNT sensing element. A two-dimensional photonic crystal with periodic holes in a polymer thin film is fabricated and a resonant cavity is formed by removing holes from the array of the photonic crystal. Based on the design of the photonic crystal topologies, we theoretically study the electric field distribution to predict the resonant behavior of the structure. Numerical simulations reveal the field is enhanced and almost fully confined to the defect region of the photonic crystal. To verify the electric field enhancement effect, experiments are also performed to measure the photocurrent response of the sensor with and without the photonic crystal resonant cavity. Experimental results show that the photocurrent increases ~3 times after adding the photonic crystal resonant cavity.

A digital miniature x-ray tube with a high-density triode carbon nanotube field emitter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jeong, Jin-Woo; Kang, Jun-Tae; Choi, Sungyoul

2013-01-14

We have fabricated a digital miniature x-ray tube (6 mm in diameter and 32 mm in length) with a high-density triode carbon nanotube (CNT) field emitter for special x-ray applications. The triode CNT emitter was densely formed within a diameter of below 4 mm with the focusing-functional gate. The brazing process enables us to obtain and maintain a desired vacuum level for the reliable electron emission from the CNT emitters after the vacuum packaging. The miniature x-ray tube exhibited a stable and reliable operation over 250 h in a pulse mode at an anode voltage of above 25 kV.

Enhanced photocatalytic activity of graphitic carbon nitride/carbon nanotube/Bi2WO6 ternary Z-scheme heterojunction with carbon nanotube as efficient electron mediator.

PubMed

Jiang, Deli; Ma, Wanxia; Xiao, Peng; Shao, Leqiang; Li, Di; Chen, Min

2018-02-15

All-solid-state Z-scheme heterojunction has attracted much attention in photocatalytic field because of its strong ability in charge separation and transfer. In the present study, all-solid-state ternary Z-scheme heterojunction constructed by graphitic carbon nitride (CN) nanosheet, carbon nanotube (CNT), and Bi 2 WO 6 (BWO) nanosheet, in which CNT was employed as the electron mediator. The CN/CNT/BWO ternary Z-scheme heterojunction shows the enhanced photocatalytic activity towards the degradation of tetracycline hydrochloride (TC) as compared to the pristine g-C 3 N 4 , Bi 2 WO 6 , CNT/BWO, CNT/CN, and CN/BWO. The significantly improved photocatalytic activity can be mainly ascribed to the formed CNT-mediated Z-scheme heterojunction, which facilitates the separation and transfer of photogenerated electron-hole pairs. Our work provides a rational design of all-solid-state Z-scheme heterojunction with CNT as the electron mediator for highly efficient photocatalysis. Copyright © 2017 Elsevier Inc. All rights reserved.

Integrating carbon nanotube forests into polysilicon MEMS: Growth kinetics, mechanisms, and adhesion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ubnoske, Stephen M.; Radauscher, Erich J.; Meshot, Eric R.

The growth of carbon nanotubes (CNTs) on polycrystalline silicon substrates was studied to improve the design of CNT field emission sources for microelectromechanical systems (MEMS) applications and vacuum microelectronic devices (VMDs). Microwave plasma-enhanced chemical vapor deposition (PECVD) was used for CNT growth, resulting in CNTs that incorporate the catalyst particle at their base. The kinetics of CNT growth on polysilicon were compared to growth on Si (100) using the model of Deal and Grove, finding activation energies of 1.61 and 1.54 eV for the nucleation phase of growth and 1.90 and 3.69 eV for the diffusion-limited phase on Si (100)more » and polysilicon, respectively. Diffusivity values for growth on polysilicon were notably lower than the corresponding values on Si (100) and the growth process became diffusion-limited earlier. Evidence favors a surface diffusion growth mechanism involving diffusion of carbon precursor species along the length of the CNT forest to the catalyst at the base. Explanations for the differences in activation energies and diffusivities were elucidated by SEM analysis of the catalyst nanoparticle arrays and through wide-angle X-ray scattering (WAXS) of CNT forests. As a result, methods are presented to improve adhesion of CNT films during operation as field emitters, resulting in a 2.5× improvement.« less

Integrating carbon nanotube forests into polysilicon MEMS: Growth kinetics, mechanisms, and adhesion

DOE PAGES

Ubnoske, Stephen M.; Radauscher, Erich J.; Meshot, Eric R.; ...

2016-11-19

The growth of carbon nanotubes (CNTs) on polycrystalline silicon substrates was studied to improve the design of CNT field emission sources for microelectromechanical systems (MEMS) applications and vacuum microelectronic devices (VMDs). Microwave plasma-enhanced chemical vapor deposition (PECVD) was used for CNT growth, resulting in CNTs that incorporate the catalyst particle at their base. The kinetics of CNT growth on polysilicon were compared to growth on Si (100) using the model of Deal and Grove, finding activation energies of 1.61 and 1.54 eV for the nucleation phase of growth and 1.90 and 3.69 eV for the diffusion-limited phase on Si (100)more » and polysilicon, respectively. Diffusivity values for growth on polysilicon were notably lower than the corresponding values on Si (100) and the growth process became diffusion-limited earlier. Evidence favors a surface diffusion growth mechanism involving diffusion of carbon precursor species along the length of the CNT forest to the catalyst at the base. Explanations for the differences in activation energies and diffusivities were elucidated by SEM analysis of the catalyst nanoparticle arrays and through wide-angle X-ray scattering (WAXS) of CNT forests. As a result, methods are presented to improve adhesion of CNT films during operation as field emitters, resulting in a 2.5× improvement.« less

Hybridizing CNT/PMMA/PVDF towards high-performance piezoelectric nanofibers

NASA Astrophysics Data System (ADS)

Fang, K. Y.; Fang, F.; Wang, S. W.; Yang, W.; Sun, W.; Li, J. F.

2018-07-01

Piezoelectric nanofibers are of great importance in their potential applications as smart fibers and textiles to bring changes to daily lives. By employing the technique of electrospinning, polyvinylidene fluoride (PVDF) nanofibers modified with polymethyl methacrylate (PMMA) and single-wall carbon nanotubes (CNTs) (referred to as CNT/PMMA/PVDF) are prepared. The electric field induced displacement of the as-prepared nanofibers is characterized by piezoresponse force microscopy. Compared with the pure PVDF nanofibers, the CNT/PMMA/PVDF nanofibers exhibit a great enhancement of about 196% for the electric field induced displacement, while increments of about 104% and 78% are obtained for the PMMA/PVDF and CNT/PVDF nanofibers, respectively. A structural analysis indicates that the hydrogen bonding between the O atom in the carbonyl group of PMMA and the hydrogen atom in the CH2 groups of PVDF, the promotion of the nucleation of crystallites by CNTs, work synergistically to produce the high electroactive response of the CNT/PMMA/PVDF nanofibers. Based on the high-performance nanofibers, a prototype of a flexible nanofiber generator is fabricated, which exhibits a typical electrical output of 3.11 V upon a repeated impact-release loading at a frequency of 50 Hz.

Ionic Adsorption and Desorption of CNT Nanoropes

PubMed Central

Shang, Jun-Jun; Yang, Qing-Sheng; Yan, Xiao-Hui; He, Xiao-Qiao; Liew, Kim-Meow

2016-01-01

A nanorope is comprised of several carbon nanotubes (CNTs) with different chiralities. A molecular dynamic model is built to investigate the ionic adsorption and desorption of the CNT nanoropes. The charge distribution on the nanorope is obtained by using a modified gradient method based on classical electrostatic theory. The electrostatic interactions among charged carbon atoms are calculated by using the Coulomb law. It was found here that the charged nanorope can adsorb heavy metal ions, and the adsorption and desorption can be realized by controlling the strength of applied electric field. The distance between the ions and the nanorope as well as the amount of ions have an effect on the adsorption capacity of the nanorope. The desorption process takes less time than that of adsorption. The study indicates that the CNT nanorope can be used as a core element of devices for sewage treatment. PMID:28335306

Ionic Adsorption and Desorption of CNT Nanoropes.

PubMed

Shang, Jun-Jun; Yang, Qing-Sheng; Yan, Xiao-Hui; He, Xiao-Qiao; Liew, Kim-Meow

2016-09-28

A nanorope is comprised of several carbon nanotubes (CNTs) with different chiralities. A molecular dynamic model is built to investigate the ionic adsorption and desorption of the CNT nanoropes. The charge distribution on the nanorope is obtained by using a modified gradient method based on classical electrostatic theory. The electrostatic interactions among charged carbon atoms are calculated by using the Coulomb law. It was found here that the charged nanorope can adsorb heavy metal ions, and the adsorption and desorption can be realized by controlling the strength of applied electric field. The distance between the ions and the nanorope as well as the amount of ions have an effect on the adsorption capacity of the nanorope. The desorption process takes less time than that of adsorption. The study indicates that the CNT nanorope can be used as a core element of devices for sewage treatment.

Effects of CNT size on the desalination performance of an outer-wall CNT slit membrane.

PubMed

Ang, Elisa Y M; Ng, Teng Yong; Yeo, Jingjie; Lin, Rongming; Liu, Zishun; Geethalakshmi, K R

2018-05-23

We investigate the effect of varying carbon nanotube (CNT) size on the desalination performance through slit confinements formed by horizontally aligned CNTs stacked on top of one another. By increasing the CNT size, the results obtained from this study indicate a corresponding increase in the water flow rate, accompanied by a slight reduction in salt rejection performance. However, due to the increase in the membrane area with CNT size, the permeability performance is observed to reduce as the CNT size increases. Nevertheless, a comparison with nanoporous 2D membranes shows that the permeability of an outer-wall CNT slit membrane remains significantly higher for all CNT sizes considered. This indicates that precise dimensions of the CNTs are not highly crucial for achieving ultra-high permeability performance in such membranes, as long as the critical slit size is maintained. In-depth analytical studies were further conducted to correlate the influence of curvature effects due to increasing CNT size on the flow characteristcis of the outer-wall CNT membrane. These include the analysis of the measured velocity profiles, oxygen density mapping, potential of mean force profile and friction profile. The present numerical results demonstrate the superb desalination performance of the outer-wall CNT slit membrane, regardless of the size of CNTs used. In addition, an extensive analysis conducted provides detailed characterization of how the curvature affects flow across outer-wall CNTs, and can be used to guide future design and fabrication for experimental testing.

Bioaccumulation and ecotoxicity of carbon nanotubes

PubMed Central

2013-01-01

Carbon nanotubes (CNT) have numerous industrial applications and may be released to the environment. In the aquatic environment, pristine or functionalized CNT have different dispersion behavior, potentially leading to different risks of exposure along the water column. Data included in this review indicate that CNT do not cross biological barriers readily. When internalized, only a minimal fraction of CNT translocate into organism body compartments. The reported CNT toxicity depends on exposure conditions, model organism, CNT-type, dispersion state and concentration. In the ecotoxicological tests, the aquatic organisms were generally found to be more sensitive than terrestrial organisms. Invertebrates were more sensitive than vertebrates. Single-walled CNT were found to be more toxic than double-/multi-walled CNT. Generally, the effect concentrations documented in literature were above current modeled average environmental concentrations. Measurement data are needed for estimation of environmental no-effect concentrations. Future studies with benchmark materials are needed to generate comparable results. Studies have to include better characterization of the starting materials, of the dispersions and of the biological fate, to obtain better knowledge of the exposure/effect relationships. PMID:24034413

Classical nucleation theory in the phase-field crystal model

NASA Astrophysics Data System (ADS)

Jreidini, Paul; Kocher, Gabriel; Provatas, Nikolas

2018-04-01

A full understanding of polycrystalline materials requires studying the process of nucleation, a thermally activated phase transition that typically occurs at atomistic scales. The numerical modeling of this process is problematic for traditional numerical techniques: commonly used phase-field methods' resolution does not extend to the atomic scales at which nucleation takes places, while atomistic methods such as molecular dynamics are incapable of scaling to the mesoscale regime where late-stage growth and structure formation takes place following earlier nucleation. Consequently, it is of interest to examine nucleation in the more recently proposed phase-field crystal (PFC) model, which attempts to bridge the atomic and mesoscale regimes in microstructure simulations. In this work, we numerically calculate homogeneous liquid-to-solid nucleation rates and incubation times in the simplest version of the PFC model, for various parameter choices. We show that the model naturally exhibits qualitative agreement with the predictions of classical nucleation theory (CNT) despite a lack of some explicit atomistic features presumed in CNT. We also examine the early appearance of lattice structure in nucleating grains, finding disagreement with some basic assumptions of CNT. We then argue that a quantitatively correct nucleation theory for the PFC model would require extending CNT to a multivariable theory.

Classical nucleation theory in the phase-field crystal model.

PubMed

Jreidini, Paul; Kocher, Gabriel; Provatas, Nikolas

2018-04-01

A full understanding of polycrystalline materials requires studying the process of nucleation, a thermally activated phase transition that typically occurs at atomistic scales. The numerical modeling of this process is problematic for traditional numerical techniques: commonly used phase-field methods' resolution does not extend to the atomic scales at which nucleation takes places, while atomistic methods such as molecular dynamics are incapable of scaling to the mesoscale regime where late-stage growth and structure formation takes place following earlier nucleation. Consequently, it is of interest to examine nucleation in the more recently proposed phase-field crystal (PFC) model, which attempts to bridge the atomic and mesoscale regimes in microstructure simulations. In this work, we numerically calculate homogeneous liquid-to-solid nucleation rates and incubation times in the simplest version of the PFC model, for various parameter choices. We show that the model naturally exhibits qualitative agreement with the predictions of classical nucleation theory (CNT) despite a lack of some explicit atomistic features presumed in CNT. We also examine the early appearance of lattice structure in nucleating grains, finding disagreement with some basic assumptions of CNT. We then argue that a quantitatively correct nucleation theory for the PFC model would require extending CNT to a multivariable theory.

Modeling and simulations of carbon nanotube (CNT) dispersion in water/surfactant/polymer systems

NASA Astrophysics Data System (ADS)

Uddin, Nasir Mohammad

An innovative multiscale (atomistic to mesoscale) model capable of predicting carbon nanotube (CNT) interactions and dispersion in water/surfactant/polymer systems was developed. The model was verified qualitatively with available experimental data in the literature. It can be used to computationally screen potential surfactants, solvents, polymers, and CNT with appropriate diameter and length to obtain improved CNT dispersion in aqueous medium. Thus the model would facilitate the reduction of time and cost required to produce CNT dispersed homogeneous solutions and CNT reinforced materials. CNT dispersion in any water/surfactant/polymer system depends on interactions between CNTs and surrounding molecules. Central to the study was the atomistic scale model which used the atomic structure of the surfactant, solvent, polymer, and CNT. The model was capable of predicting the CNT interactions in terms of potential of mean force (PMF) between CNTs under the influence of surrounding molecules in an aqueous solution. On the atomistic scale, molecular dynamics method was used to compute the PMF as a function of CNT separation and CNT alignment. An adaptive biasing force (ABF) method was used to speed up the calculations. Correlations were developed to determine the effective interactions between CNTs as a function of their any inter-atomic distance and orientation angle in water as well as in water/surfactant by fitting the calculated PMF data. On the mesoscale, the fitted PMF correlations were used as input in the Monte Carlo simulations to determine the degree of dispersion of CNTs in water and water/surfactant system. The distribution of CNT cluster size was determined for the CNTs dispersed in water with and without surfactant addition. The entropie and enthalpie contributions to the CNT interactions in water were determined to understand the dispersion mechanism of CNTs in water. The effects of CNT orientation, length, diameter, chirality and surfactant concentrations and structures on CNT interactions in water were investigated at room conditions. CNT interactions in polymer solution were also investigated with polyethylene oxide (PEO) polymer and water as a solvent. In all cases, the atomic arrangement of molecules was discussed in detailed. Simulations revealed that CNT orientation, length, diameter, and addition of surfactant and its structures can significantly affect CNT interactions (i.e., PMFs varied significantly) and in-turn the degree of CNT dispersion in aqueous solution. For all simulation cases, a uniform sampling was achieved by using the ABF method to calculate the governing PMF between CNTs indicating the effectiveness and convergence of the adaptive sampling scheme. The surfactant molecules were shown to adsorb at the CNT surface and contribute to weaker interactions between CNTs which resulted less CNT aggregate size at the mesoscale. Surfactant consisting with a benzene ring contributed much weaker interactions between CNTs as compared with that of without benzene ring. The increase in CNT length contributed the stronger CNT interactions where the increase in CNT diameter caused weaker CNT interactions in water. The interfacial characteristics between the CNT, surfactant and the polymer were also predicted and discussed. The model can be expanded for more solvents, surfactants, and polymers.

Extreme Magneto-transport of Bulk Carbon Nanotubes in Sorted Electronic Concentrations and Aligned High Performance Fiber

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bulmer, John S.; Lekawa-Raus, Agnieszka; Rickel, Dwight G.

We explored high-field (60 T) magneto-resistance (MR) with two carbon nanotube (CNT) material classes: (1) unaligned single-wall CNTs (SWCNT) films with controlled metallic SWCNT concentrations and doping degree and (2) CNT fiber with aligned, long-length microstructure. All unaligned SWCNT films showed localized hopping transport where high-field MR saturation definitively supports spin polarization instead of a more prevalent wave function shrinking mechanism. Nitric acid exposure induced an insulator to metal transition and reduced the positive MR component. Aligned CNT fiber, already on the metal side of the insulator to metal transition, had positive MR without saturation and was assigned to classicalmore » MR involving electronic mobility. Subtracting high-field fits from the aligned fiber’s MR yielded an unconfounded negative MR, which was assigned to weak localization. It is concluded that fluctuation induced tunnelling, an extrinsic transport model accounting for most of the aligned fiber’s room temperature resistance, appears to lack MR field dependence.« less

Extreme Magneto-transport of Bulk Carbon Nanotubes in Sorted Electronic Concentrations and Aligned High Performance Fiber.

PubMed

Bulmer, John S; Lekawa-Raus, Agnieszka; Rickel, Dwight G; Balakirev, Fedor F; Koziol, Krzysztof K

2017-09-22

We explored high-field (60 T) magneto-resistance (MR) with two carbon nanotube (CNT) material classes: (1) unaligned single-wall CNTs (SWCNT) films with controlled metallic SWCNT concentrations and doping degree and (2) CNT fiber with aligned, long-length microstructure. All unaligned SWCNT films showed localized hopping transport where high-field MR saturation definitively supports spin polarization instead of a more prevalent wave function shrinking mechanism. Nitric acid exposure induced an insulator to metal transition and reduced the positive MR component. Aligned CNT fiber, already on the metal side of the insulator to metal transition, had positive MR without saturation and was assigned to classical MR involving electronic mobility. Subtracting high-field fits from the aligned fiber's MR yielded an unconfounded negative MR, which was assigned to weak localization. It is concluded that fluctuation induced tunnelling, an extrinsic transport model accounting for most of the aligned fiber's room temperature resistance, appears to lack MR field dependence.

Extreme Magneto-transport of Bulk Carbon Nanotubes in Sorted Electronic Concentrations and Aligned High Performance Fiber

DOE PAGES

Bulmer, John S.; Lekawa-Raus, Agnieszka; Rickel, Dwight G.; ...

2017-09-22

We explored high-field (60 T) magneto-resistance (MR) with two carbon nanotube (CNT) material classes: (1) unaligned single-wall CNTs (SWCNT) films with controlled metallic SWCNT concentrations and doping degree and (2) CNT fiber with aligned, long-length microstructure. All unaligned SWCNT films showed localized hopping transport where high-field MR saturation definitively supports spin polarization instead of a more prevalent wave function shrinking mechanism. Nitric acid exposure induced an insulator to metal transition and reduced the positive MR component. Aligned CNT fiber, already on the metal side of the insulator to metal transition, had positive MR without saturation and was assigned to classicalmore » MR involving electronic mobility. Subtracting high-field fits from the aligned fiber’s MR yielded an unconfounded negative MR, which was assigned to weak localization. It is concluded that fluctuation induced tunnelling, an extrinsic transport model accounting for most of the aligned fiber’s room temperature resistance, appears to lack MR field dependence.« less

Development of a glucose oxidase-based biocatalyst adopting both physical entrapment and crosslinking, and its use in biofuel cells

NASA Astrophysics Data System (ADS)

Chung, Yongjin; Ahn, Yeonjoo; Christwardana, Marcelinus; Kim, Hansung; Kwon, Yongchai

2016-04-01

New enzymatic catalysts prepared using physical entrapment and chemical bonding were used as anodic catalysts to enhance the performance of enzymatic biofuel cells (EBCs). For estimating the physical entrapment effect, the best glucose oxidase (GOx) concentration immobilized on polyethyleneimine (PEI) and carbon nanotube (CNT) (GOx/PEI/CNT) was determined, while for inspecting the chemical bonding effect, terephthalaldehyde (TPA) and glutaraldehyde (GA) crosslinkers were employed. According to the enzyme activity and XPS measurements, when the GOx concentration is 4 mg mL-1, they are most effectively immobilized (via the physical entrapment effect) and TPA-crosslinked GOx/PEI/CNT(TPA/[GOx/PEI/CNT]) forms π conjugated bonds via chemical bonding, inducing the promotion of electron transfer by delocalization of electrons. Due to the optimized GOx concentration and π conjugated bonds, TPA/[GOx/PEI/CNT], including 4 mg mL-1 GOx displays a high electron transfer rate, followed by excellent catalytic activity and EBC performance.New enzymatic catalysts prepared using physical entrapment and chemical bonding were used as anodic catalysts to enhance the performance of enzymatic biofuel cells (EBCs). For estimating the physical entrapment effect, the best glucose oxidase (GOx) concentration immobilized on polyethyleneimine (PEI) and carbon nanotube (CNT) (GOx/PEI/CNT) was determined, while for inspecting the chemical bonding effect, terephthalaldehyde (TPA) and glutaraldehyde (GA) crosslinkers were employed. According to the enzyme activity and XPS measurements, when the GOx concentration is 4 mg mL-1, they are most effectively immobilized (via the physical entrapment effect) and TPA-crosslinked GOx/PEI/CNT(TPA/[GOx/PEI/CNT]) forms π conjugated bonds via chemical bonding, inducing the promotion of electron transfer by delocalization of electrons. Due to the optimized GOx concentration and π conjugated bonds, TPA/[GOx/PEI/CNT], including 4 mg mL-1 GOx displays a high electron transfer rate, followed by excellent catalytic activity and EBC performance. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr00902f

Investigation of thermal energy transport interface of hybrid graphene-carbon nanotube/polyethylene nanocomposites.

PubMed

Liu, Feng; Liu, Xuyang; Hu, Ning; Ning, Huiming; Atobe, Satoshi; Yan, Cheng; Mo, Fuhao; Fu, Shaoyun; Zhang, Jianyu; Wang, Yu; Mu, Xiaojing

2017-10-31

It is well known the thermal properties of three-dimensional (3-D) hybrid graphene (GR)-carbon nanotube (CNT) structures are not superior to that of the individual GR and CNT, however, the 3-D hybrid GR-CNT structures can effectively improve the thermal properties of polymer matrix. Therefore, understanding the thermal energy transport in the interface between polymer matrix and 3-D hybrid GR-CNT structure is essential. Here, the enhancement mechanism of interfacial thermal transport of hybrid GR-CNT structure was explored by applying non-equilibrium molecular dynamics (NEMD) simulations. Three different types of hybrid GR-CNT structures were built. The influences of CNT radius and CNT type for the hybrid GR-CNT on the interfacial thermal properties were also analyzed. Computational results show that among the three different types of hybrid GR-CNT structures, the Model-I, i.e., the covalent bond hybrid GR-CNT structures are of the best interfacial thermal properties. Meanwhile, the CNT radius of hybrid GR-CNT structure has a great influence on the interfacial thermal properties.

About the relevance of waviness, agglomeration, and strain on the electrical behavior of polymer composites filled with carbon nanotubes evaluated by a Monte-Carlo simulation

NASA Astrophysics Data System (ADS)

Román, Sebastián; Lund, Fernando; Bustos, Javier; Palza, Humberto

2018-01-01

In several technological applications, carbon nanotubes (CNT) are added to a polymer matrix in order to develop electrically conductive composite materials upon percolation of the CNT network. This percolation state depends on several parameters such as particle characteristics, degree of dispersion, and filler orientation. For instance, CNT aggregation is currently avoided because it is thought that it will have a negative effect on the electrical behavior despite some experimental evidence showing the contrary. In this study, the effect of CNT waviness, degree of agglomeration, and external strain, on the electrical percolation of polymer composites is studied by a three dimensional Monte-Carlo simulation. The simulation shows that the percolation threshold of CNT depends on the particle waviness, with rigid particles displaying the lowest values. Regarding the effect of CNT dispersion, our numerical results confirm that low levels of agglomeration reduce the percolation threshold of the composite. However, the threshold is shifted to larger values at high agglomeration states because of the appearance of isolated areas of high CNT concentrations. These results imply, therefore, an optimum of agglomeration that further depends on the waviness and concentration of CNT. Significantly, CNT agglomeration can further explain the broad percolation transition found in these systems. When an external strain is applied to the composites, the percolation concentration shifts to higher values because CNT alignment increases the inter-particle distances. The strain sensitivity of the composites is affected by the percolation state of CNT showing a maximum value at certain filler concentration. These results open up the discussion about the relevance in polymer composites of the dispersion state of CNT and filler flexibility towards electrically conductive composites.

Self-supporting activated carbon/carbon nanotube/reduced graphene oxide flexible electrode for high performance supercapacitor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Xing; Tang, Yao; Song, Junhua

A self-supporting and flexible activated carbon/carbon nanotube/reduced graphene oxide (AC/CNT/RGO) film has been rationally designed for constructing high- performance supercapacitor. The AC/CNT/RGO film is prepared by anchoring the AC particles with a 3D and porous framework built by hierarchically weaving the 1 D CNT and 2D RGO using their intrinsic van der Waals force. The CNT network is beneficial for improving the electronic conductivity of the electrode, while the AC particles could effectively suppress the aggregation of RGO and CNT due to their blocking effect. The synergistic effects among the AC, CNT and RGO validate the AC/CNT/RGO as a promisingmore » electrode for supercapacitor, exhibiting greatly enhanced electrochemical performances in comparison with the pure RGO film, pure CNT film and AC electrode. The AC/CNT/RGO electrode delivers a high specific capacitance of 101 F g-1 at the current density of 0.2 A g-1, offering a maximum energy density of 30.0 W h kg-1 in organic electrolyte at the cut-off voltage range of 0.001~3.0 V. The findings of this work open a new avenue for the design of self-supporting electrodes for the development of flexible and light weight energy storage supercapacitor.« less

Carbon nanotubes part II: a remarkable carrier for drug and gene delivery

PubMed Central

Karimi, Mahdi; Solati, Navid; Ghasemi, Amir; Estiar, Mehrdad Asghari; Hashemkhani, Mahshid; Kiani, Parnian; Mohamed, Elmira; Saeidi, Ahad; Taheri, Mahdiar; Avci, Pinar; Aref, Amir R; Amiri, Mohammad; Baniasadi, Fazel; Hamblin, Michael R

2015-01-01

Introduction Carbon nanotubes (CNT) have recently been studied as novel and versatile drug and gene delivery vehicles. When CNT are suitably functionalized, they can interact with various cell types and are taken up by endocytosis. Areas covered Anti-cancer drugs cisplatin and doxorubicin have been delivered by CNT, as well as methotrexate, taxol and gemcitabine. The delivery of the antifungal compound amphotericin B and the oral administration of erythropoietin have both been assisted using CNT. Frequently, targeting moieties such as folic acid, epidermal growth factor or various antibodies are attached to the CNT-drug nanovehicle. Different kinds of functionalization (e.g., polycations) have been used to allow CNT to act as gene delivery vectors. Plasmid DNA, small interfering RNA and micro-RNA have all been delivered by CNT vehicles. Significant concerns are raised about the nanotoxicology of the CNT and their potentially damaging effects on the environment. Expert opinion CNT-mediated drug delivery has been studied for over a decade, and both in vitro and in vivo studies have been reported. The future success of CNTs as vectors in vivo and in clinical application will depend on achievement of efficacious therapy with minimal adverse effects and avoidance of possible toxic and environmentally damaging effects. PMID:25613837

Carbon Nanotube-Reinforced Thermotropic Liquid Crystal Polymer Nanocomposites

PubMed Central

Kim, Jun Young

2009-01-01

This paper focuses on the fabrication via simple melt blending of thermotropic liquid crystal polyester (TLCP) nanocomposites reinforced with a very small quantity of modified carbon nanotube (CNT) and the unique effects of the modified CNT on the physical properties of the nanocomposites. The thermal, mechanical, and rheological properties of modified CNT-reinforced TLCP nanocomposites are highly dependent on the uniform dispersion of CNT and the interactions between the CNT and TLCP, which can be enhanced by chemical modification of the CNT, providing a design guide of CNT-reinforced TLCP nanocomposites with great potential for industrial uses.

Binder-free 2D titanium carbide (MXene)/carbon nanotube composites for high-performance lithium-ion capacitors.

PubMed

Yu, Peng; Cao, Gejin; Yi, Sha; Zhang, Xiong; Li, Chen; Sun, Xianzhong; Wang, Kai; Ma, Yanwei

2018-03-29

Two-dimensional (2D) MXenes have a very good application prospect in the field of electrochemical energy storage due to their metallic conductivity, high volumetric capacity, mechanical and thermal stability. Herein, we report the preparation of titanium carbide (Ti3C2Tx)/carbon nanotube (CNT) flexible self-supporting composite films by vacuum filtration. The CNTs can effectively prevent Ti3C2Tx from stacking and improve the electrochemical performance. The as-fabricated Ti3C2Tx/CNT film shows a high reversible capacity of 489 mA h g-1 at a current density of 50 mA g-1 together with good cycling performance. The full-cell lithium-ion capacitor (LIC) is assembled using the Ti3C2Tx/CNT film as the anode and activated carbon as the cathode. The LIC exhibits a high energy density of 67 Wh kg-1 (based on the total weight of the anode and the cathode), and a good capacity retention of 81.3% after 5000 cycles. These results suggest that Ti3C2Tx-CNT films are promising as anode materials for lithium ion capacitors.

Carbon nanotube and graphene device modeling and simulation

NASA Astrophysics Data System (ADS)

Yoon, Young Ki

The performance of the semiconductors has been improved and the price has gone down for decades. It has been continuously scaled down in size year by year, and now it encounters the fundamental scaling limit. We, therefore, should prepare a new era beyond the conventional semiconductor technologies. One of the most promising devices is possible by carbon nanotube (CNT) or graphene nanoribbon (GNR) in terms of its excellent charge transport properties. Their fundamental material properties and device physics are totally different to those of the conventional devices. In this nano-regime, more sophisticated device modeling and simulation are really needed to elucidate nano-device operation and to save our resources from errors. The numerical simulation works in this dissertation will provide novel view points on the emerging devices. In this dissertation, CNT and GNR devices are numerically studied. The first part of this work is on CNT devices, and a common structure of CNT device has CNT channel, metal source and drain contacts, and gate electrode. We investigate the strain, geometry, and scattering effects on the device performance of CNT field-effect transistors (FETs). It is shown that even a small amount of strain can result in a large effect on the performance of CNTFETs due to the variation of the bandgap and band-structure-limited velocity. A type of strain which produces a larger bandgap results in increased Schottky barrier (SB) height and decreased band-structure-limited velocity, and hence a smaller minimum leakage current, smaller on current, larger maximum achievable Ion/Ioff, and larger intrinsic delay. We also examine geometry effect of partial gate CNTFETs. In the growth process of vertical CNT, underlap between the gate and the bottom electrode is advantageous for transistor operation because it suppresses ambipolar conduction of SBFETs. Both n-type and p-type transistor operations with balanced performance metrics can be achieved on a single partial gate FET by using proper bias schemes. The effect of phonon scattering on the intrinsic delay and cut-off frequency of Schottky barrier CNTFETs is also examined. Carriers are mostly scattered by optical and zone boundary phonons beyond the beginning of the channel. The scattering has a small direct effect on the DC on current of the CNTFET, but it results in significant decrease of intrinsic cut-off frequency and increase of intrinsic delay. Semiconducting CNT is useful for the channel in CNTFETs, whereas metallic CNT can be used as an electrode. If a porous CNT film is used as a source electrode, vertical thin-film transistors (TFTs) can be constructed. Vertical organic FET (OFET) shows clear transistor switching behavior allowing orders of magnitude modulation of the source-drain current even in the presence of electrostatic screening by the source electrode. The channel length should be carefully engineered due to the trade-off between device characteristics in the subthreshold and above-threshold regions. The second subject is device simulations of GNRFETs. Even though GNR is also graphene-based quasi-1D nanostructure like CNT, the differences in shape, boundary condition, and existence of edges and dangling bonds make it operate in a different way. Atomistic 3D simulation study of the performance of GNR SBFETs is presented. The impacts of non-idealities on device performance have been investigated. The edges of GNR, which do not exist in CNT, can be advantages or disadvantages. If an appropriate control by different edge atoms is possible, it would be definitely positive. Totally new electronic band structure is obtained by different edge-termination atoms. In addition, only a fraction of impurity atom can also much affect on the material properties of GNR. In order to perform device simulations of non-uniform GNR devices, multiscale simulation scheme can be used in non-equilibrium Green's function (NEGF) formalism and density-functional method.

Electrocatalyzed O2 response of myoglobin immobilized on multi-walled carbon nanotube forest electrodes.

PubMed

Pacios, M; del Valle, M; Bartroli, J; Esplandiu, M J

2009-10-01

Direct electrochemistry and activity of myoglobin (Mb) immobilized on carbon nanotube (CNT) forest electrodes were investigated by probing mainly its electrocatalytical response towards oxygen. The protein was anchored on the CNT electrodes through carbodiimide coupling, which was shown to provide long term stability. The electrochemical response was monitored as a function of oxygen concentration and pH. Conformational changes together with the consequent loss of oxygen affinity were recorded at low pH, which delimits the operative range of the Mb/CNT electrodes for sensing purposes. In general, it can be concluded that CNT forests constitute suitable platforms for Mb attachment without compromising the protein bioactivity and by keeping at the same time the direct electron exchange with the heme core. All these characteristics confer to the protein modified CNT system promising properties for the implementation of (bio)sensor devices with impact in the clinical and environmental field.

Development of end-selective functionalized carbon nanotubes for biomedical applications

NASA Astrophysics Data System (ADS)

Lee, Seung Ho; Kim, Wan Sun; Lee, Ha Rim; Park, Kyu Chang; Lee, Chang Hoon; Park, Hun Kuk; Kim, Kyung Sook

2015-12-01

Carbon nanotube (CNT) is a type of carbon allotrope with excellent physical and electrical properties, including high thermal conductivity, mechanical strength, and thermal stability. Therefore, applications of CNT have been considered for a variety of fields, including biosensors, molecular electronics, X-ray, and fuel cells. However, the application of CNT to biomedicine is limited because this material is cytotoxic and inhomogeneous. In particular, the irregularity in the structural properties of paste or bundle-type CNTs causes an uncontrolled modification in biomolecules. Therefore, using CNT as biosensors to obtain quantitative analyses is difficult. In this study, we developed a new method to perform end-selective functionalization of CNT in order to enable quantitative analysis for biomedical applications. The process was as follows: (1) etching the tip of vertically-aligned CNTs under optimum conditions, (2) oxidation of exposed CNTs, and (3) end-selective linkage of functionalized CNTs with biomolecules (dsDNA).

Synergistic effects from graphene and carbon nanotubes endow ordered hierarchical structure foams with a combination of compressibility, super-elasticity and stability and potential application as pressure sensors.

PubMed

Kuang, Jun; Dai, Zhaohe; Liu, Luqi; Yang, Zhou; Jin, Ming; Zhang, Zhong

2015-01-01

Nanostructured carbon material based three-dimensional porous architectures have been increasingly developed for various applications, e.g. sensors, elastomer conductors, and energy storage devices. Maintaining architectures with good mechanical performance, including elasticity, load-bearing capacity, fatigue resistance and mechanical stability, is prerequisite for realizing these functions. Though graphene and CNT offer opportunities as nanoscale building blocks, it still remains a great challenge to achieve good mechanical performance in their microarchitectures because of the need to precisely control the structure at different scales. Herein, we fabricate a hierarchical honeycomb-like structured hybrid foam based on both graphene and CNT. The resulting materials possess excellent properties of combined high specific strength, elasticity and mechanical stability, which cannot be achieved in neat CNT and graphene foams. The improved mechanical properties are attributed to the synergistic-effect-induced highly organized, multi-scaled hierarchical architectures. Moreover, with their excellent electrical conductivity, we demonstrated that the hybrid foams could be used as pressure sensors in the fields related to artificial skin.

The effect of carbon nanotubes functionalization on the band-gap energy of TiO2-CNT nanocomposite

NASA Astrophysics Data System (ADS)

Shahbazi, Hessam; Shafei, Alireza; Sheibani, Saeed

2018-01-01

In this paper the morphology and structure of TiO2-CNT nanocomposite powder obtained by an in situ sol-gel process were investigated. The synthesized nanocomposite powders were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and diffuse reflectance spectroscopy (DRS). The effect of functionalizing of CNT on the properties was studied. XRD results showed amorphous structure before calcination. Also, anatase phase TiO2 was formed after calcination at 400 °C. The SEM results indicate different distributions of TiO2 on CNTs. As a result, well dispersed TiO2 microstructure on the surface of CNTs was observed after functionalizing, while compact and large aggregated particles were found without functionalizing. The average thickness of uniform and well-defined coated TiO2 layer was in the range of 30-40 nm. The DRS results have determined the reflective properties and band gap energies of nanocomposite powders and have shown that functionalizing of CNTs caused the change of band-gap energy from 2.98 to 2.87 eV.

Modeling of Gate Bias Modulation in Carbon Nanotube Field-Effect-Transistors

NASA Technical Reports Server (NTRS)

Yamada, Toshishige; Biegel, Bryan (Technical Monitor)

2002-01-01

The threshold voltages of a carbon nanotube (CNT) field-effect transistor (FET) are derived and compared with those of the metal oxide-semiconductor (MOS) FETs. The CNT channel is so thin that there is no voltage drop perpendicular to the gate electrode plane, which is the CNT diameter direction, and this makes the CNTFET characteristics quite different from those in MOSFETs. The relation between the voltage and the electrochemical potentials, and the mass action law for electrons and holes are examined in the context of CNTs, and it is shown that the familiar relations are still valid because of the macroscopic number of states available in the CNTs. This is in sharp contrast to the cases of quantum dots. Using these relations, we derive an inversion threshold voltage V(sub Ti) and an accumulation threshold voltage V(sub Ta) as a function of the Fermi level E(sub F) in the channel, where E(sub F) is a measure of channel doping. V(sub Ti) of the CNTFETs has a much stronger dependence than that of MOSFETs, while V(sub Ta)s of both CNTFETs and MOSFETs depend quite weakly on E(sub F) with the same functional form. This means the transition from normally-off mode to normally-on mode is much sharper in CNTFETs as the doping increases, and this property has to be taken into account in circuit design.

Highly Stretchable Fully-Printed CNT-Based Electrochemical Sensors and Biofuel Cells: Combining Intrinsic and Design-Induced Stretchability.

PubMed

Bandodkar, Amay J; Jeerapan, Itthipon; You, Jung-Min; Nuñez-Flores, Rogelio; Wang, Joseph

2016-01-13

We present the first example of an all-printed, inexpensive, highly stretchable CNT-based electrochemical sensor and biofuel cell array. The synergistic effect of utilizing specially tailored screen printable stretchable inks that combine the attractive electrical and mechanical properties of CNTs with the elastomeric properties of polyurethane as a binder along with a judiciously designed free-standing serpentine pattern enables the printed device to possess two degrees of stretchability. Owing to these synergistic design and nanomaterial-based ink effects, the device withstands extremely large levels of strains (up to 500% strain) with negligible effect on its structural integrity and performance. This represents the highest stretchability offered by a printed device reported to date. Extensive electrochemical characterization of the printed device reveal that repeated stretching, torsional twisting, and indenting stress has negligible impact on its electrochemical properties. The wide-range applicability of this platform to realize highly stretchable CNT-based electrochemical sensors and biofuel cells has been demonstrated by fabricating and characterizing potentiometric ammonium sensor, amperometric enzyme-based glucose sensor, enzymatic glucose biofuel cell, and self-powered biosensor. Highly stretchable printable multianalyte sensor, multifuel biofuel cell, or any combination thereof can thus be realized using the printed CNT array. Such combination of intrinsically stretchable printed nanomaterial-based electrodes and strain-enduring design patterns holds considerable promise for creating an attractive class of inexpensive multifunctional, highly stretchable printed devices that satisfy the requirements of diverse healthcare and energy fields wherein resilience toward extreme mechanical deformations is mandatory.

Effects of vacancy defects on the interfacial shear strength of carbon nanotube reinforced polymer composite.

PubMed

Chowdhury, Sanjib Chandra; Okabe, Tomonaga; Nishikawa, Masaaki

2010-02-01

We investigate the effects of the vacancy defects (i.e., missing atoms) in carbon nanotubes (CNTs) on the interfacial shear strength (ISS) of the CNT-polyethylene composite with the molecular dynamics simulation. In the simulation, the crystalline polyethylene matrix is set up in a hexagonal array with the polymer chains parallel to the CNT axis. Vacancy defects in the CNT are introduced by removing the corresponding atoms from the pristine CNT (i.e., CNT without any defect). Three patterns of vacancy defects with three different sizes are considered. Two types of interfaces, with and without cross-links between the CNT and the matrix are also considered here. Polyethylene chains are used as cross-links between the CNT and the matrix. The Brenner potential is used for the carbon-carbon interaction in the CNT, while the polymer is modeled by a united-atom potential. The nonbonded van der Waals interaction between the CNT and the polymer matrix and within the polymer matrix itself is modeled with the Lennard-Jones potential. To determine the ISS, we conduct the CNT pull-out from the polymer matrix and the ISS has been estimated with the change of total potential energy of the CNT-polymer system. The simulation results reveal that the vacancy defects significantly influence the ISS. Moreover, the simulation clarifies that CNT breakage occurs during the pull-out process for large size vacancy defect which ultimately reduces the reinforcement.

Detection of the Odor Signature of Ovarian Cancer using DNA-Decorated Carbon Nanotube Field Effect Transistor Arrays

NASA Astrophysics Data System (ADS)

Kehayias, Christopher; Kybert, Nicholas; Yodh, Jeremy; Johnson, A. T. Charlie

Carbon nanotubes are low-dimensional materials that exhibit remarkable chemical and bio-sensing properties and have excellent compatibility with electronic systems. Here, we present a study that uses an electronic olfaction system based on a large array of DNA-carbon nanotube field effect transistors vapor sensors to analyze the VOCs of blood plasma samples collected from patients with malignant ovarian cancer, patients with benign ovarian lesions, and age-matched healthy subjects. Initial investigations involved coating each CNT sensor with single-stranded DNA of a particular base sequence. 10 distinct DNA oligomers were used to functionalize the carbon nanotube field effect transistors, providing a 10-dimensional sensor array output response. Upon performing a statistical analysis of the 10-dimensional sensor array responses, we showed that blood samples from patients with malignant cancer can be reliably differentiated from those of healthy control subjects with a p-value of 3 x 10-5. The results provide preliminary evidence that the blood of ovarian cancer patients contains a discernable volatile chemical signature that can be detected using DNA-CNT nanoelectronic vapor sensors, a first step towards a minimally invasive electronic diagnostic technology for ovarian cancer.

Design, Fabrication, and Characterization of Carbon Nanotube Field Emission Devices for Advanced Applications

NASA Astrophysics Data System (ADS)

Radauscher, Erich Justin

Carbon nanotubes (CNTs) have recently emerged as promising candidates for electron field emission (FE) cathodes in integrated FE devices. These nanostructured carbon materials possess exceptional properties and their synthesis can be thoroughly controlled. Their integration into advanced electronic devices, including not only FE cathodes, but sensors, energy storage devices, and circuit components, has seen rapid growth in recent years. The results of the studies presented here demonstrate that the CNT field emitter is an excellent candidate for next generation vacuum microelectronics and related electron emission devices in several advanced applications. The work presented in this study addresses determining factors that currently confine the performance and application of CNT-FE devices. Characterization studies and improvements to the FE properties of CNTs, along with Micro-Electro-Mechanical Systems (MEMS) design and fabrication, were utilized in achieving these goals. Important performance limiting parameters, including emitter lifetime and failure from poor substrate adhesion, are examined. The compatibility and integration of CNT emitters with the governing MEMS substrate (i.e., polycrystalline silicon), and its impact on these performance limiting parameters, are reported. CNT growth mechanisms and kinetics were investigated and compared to silicon (100) to improve the design of CNT emitter integrated MEMS based electronic devices, specifically in vacuum microelectronic device (VMD) applications. Improved growth allowed for design and development of novel cold-cathode FE devices utilizing CNT field emitters. A chemical ionization (CI) source based on a CNT-FE electron source was developed and evaluated in a commercial desktop mass spectrometer for explosives trace detection. This work demonstrated the first reported use of a CNT-based ion source capable of collecting CI mass spectra. The CNT-FE source demonstrated low power requirements, pulsing capabilities, and average lifetimes of over 320 hours when operated in constant emission mode under elevated pressures, without sacrificing performance. Additionally, a novel packaged ion source for miniature mass spectrometer applications using CNT emitters, a MEMS based Nier-type geometry, and a Low Temperature Cofired Ceramic (LTCC) 3D scaffold with integrated ion optics were developed and characterized. While previous research has shown other devices capable of collecting ion currents on chip, this LTCC packaged MEMS micro-ion source demonstrated improvements in energy and angular dispersion as well as the ability to direct the ions out of the packaged source and towards a mass analyzer. Simulations and experimental design, fabrication, and characterization were used to make these improvements. Finally, novel CNT-FE devices were developed to investigate their potential to perform as active circuit elements in VMD circuits. Difficulty integrating devices at micron-scales has hindered the use of vacuum electronic devices in integrated circuits, despite the unique advantages they offer in select applications. Using a combination of particle trajectory simulation and experimental characterization, device performance in an integrated platform was investigated. Solutions to the difficulties in operating multiple devices in close proximity and enhancing electron transmission (i.e., reducing grid loss) are explored in detail. A systematic and iterative process was used to develop isolation structures that reduced crosstalk between neighboring devices from 15% on average, to nearly zero. Innovative geometries and a new operational mode reduced grid loss by nearly threefold, thereby improving transmission of the emitted cathode current to the anode from 25% in initial designs to 70% on average. These performance enhancements are important enablers for larger scale integration and for the realization of complex vacuum microelectronic circuits.

Forces, energetics, and dynamics of conjugated-carbon ring tethers adhered to CNTs: a computational investigation.

PubMed

Filla, Nicholas; Ramasamy, Ramaraja; Wang, Xianqiao

2018-04-25

The strength and nature of the interactions between carbon nanotubes (CNTs) and molecular tethers plays a vital role in technology such as CNT-enzyme sensors. Tethers that attach noncovalently to CNTs are ideal for retaining the electrical properties of the CNTs since they do not degrade the CNT surface and effect its electrical conductivity. However, leaching due to weak CNT-tether attachment is very common when using noncovalent tethers, and this has limited their use in commercial products including biosensors. Thus, understanding the fundamental mechanics governing the strength of CNT-tether adhesion is crucial for the design of highly sensitive, viable sensors. Here, we computationally investigate the adhesion strength of CNT-tether complexes with 8 different tethering molecules designed to adhere noncovalently to the CNT surface. We study the effects of CNT diameter, CNT chirality, and the size/geometry of the tethering molecule on the adhesion energy and force. Our results show an asymptotic relationship between adhesion strength and CNT diameter. Calculations show that noncovalent tethers tested here can reach adhesion forces and energies that are up to 21% and 54% of the strength of the carbon-carbon single bond force and bond energy respectively. We anticipate our results will help guide CNT-enzyme sensor design to produce sensors with high sensitivity and minimal leaching.

Electron spin relaxation in carbon nanotubes: Dyakonov-Perel mechanism

NASA Astrophysics Data System (ADS)

Semenov, Yuriy; Zavada, John; Kim, Ki Wook

2010-03-01

The long standing problem of unaccountable short spin relaxation in carbon nanotubes (CNT) meets a disclosure in terms of curvature-mediated spin-orbital interaction that leads to spin fluctuating precession analogous to Dyakonov-Perel mechanism. Strong anisotropy imposed by arbitrary directed magnetic field has been taken into account in terms of extended Bloch equations. Especially, stationary spin current through CNT can be controlled by spin-flip processes with relaxation time as less as 150 ps, the rate of transversal polarization (i.e. decoherence) runs up to 1/(70 ps) at room temperature while spin interference of the electrons related to different valleys can be responsible for shorter spin dephasing. Dependencies of spin-relaxation parameters on magnetic field strength and orientation, CNT curvature and chirality have been analyzed.

Improving the fracture toughness and the strength of epoxy using nanomaterials--a review of the current status.

PubMed

Domun, N; Hadavinia, H; Zhang, T; Sainsbury, T; Liaghat, G H; Vahid, S

2015-06-21

The incorporation of nanomaterials in the polymer matrix is considered to be a highly effective technique to improve the mechanical properties of resins. In this paper the effects of the addition of different nanoparticles such as single-walled CNT (SWCNT), double-walled CNT (DWCNT), multi-walled CNT (MWCNT), graphene, nanoclay and nanosilica on fracture toughness, strength and stiffness of the epoxy matrix have been reviewed. The Young's modulus (E), ultimate tensile strength (UTS), mode I (GIC) and mode II (GIIC) fracture toughness of the various nanocomposites at different nanoparticle loadings are compared. The review shows that, depending on the type of nanoparticles, the integration of the nanoparticles has a substantial effect on mode I and mode II fracture toughness, strength and stiffness. The critical factors such as maintaining a homogeneous dispersion and good adhesion between the matrix and the nanoparticles are highlighted. The effect of surface functionalization, its relevancy and toughening mechanism are also scrutinized and discussed. A large variety of data comprised of the mechanical properties of nanomaterial toughened composites reported to date has thus been compiled to facilitate the evolution of this emerging field, and the results are presented in maps showing the effect of nanoparticle loading on mode I fracture toughness, stiffness and strength.

Anisotropic D-EAP Electrodes and their Application in Spring Roll Actuators

NASA Astrophysics Data System (ADS)

Fang, Xiaomeng

Electroactive polymers (EAPs) exhibit shape change when subjected to an electric field. They are lightweight, soft, and inexpensive, while they are easy to process, shape, and tune to offer a broad range of mechanical and electrical properties. Dielectric electroactive polymers (DEAP) constitute a class of EAPs with great potential. D-EAPs consist of physically or chemically cross-linked macromolecular networks and are mechanically isotopic. Therefore, in most actuator applications that require directional electromechanical response, it is necessary to use other complex means to direct the stress/strain in the preferred direction. In this work, a simple carbon nanotube (CNT) based electrode for D-EAP actuators is demonstrated that vastly improves directional strain response originating from the mechanical anisotropy of the electrode material. Using this novel approach, the mechanical anisotropy, defined as the ratio of initial modulus in fiber direction and that in cross-fiber direction, of the CNT electroded VHB actuators, ranges from 7.9 to 11.2. Hence, the CNT-VHB flat film actuators show high directed linear actuation strain in cross-fiber direction of greater than 25% meanwhile almost no strain in fiber direction at a relatively low electric field (120 V mum-1). The morphology of the CNT sheets has critical influence on their mechanical properties and resultant actuator performance. The results demonstrate the efficacy of microcombing and selective laser etching processes to improve the CNT fiber alignment to produce pure unidirectional strain of 33% at a relatively moderate electric field. Unidirectional D-EAP composite laminates using polyurethane and polyamide monofilaments are also employed in spring roll actuators to investigate their directional mechanical and electromechanical properties. While CNT electroded D-EAP spring roll actuators were found to have about the same performance as actuators with carbon grease electrodes (6.5% strain in CNT electroded spring roll actuators and 8.2% for carbon grease electroded actuators at 5kV), spring roll actuator made of fiber reinforced VHB composites with carbon grease electrodes showed marginal improvement in actuation strain (9.9%-11% strain in longitudinal direction at 5kV).

Self-supporting activated carbon/carbon nanotube/reduced graphene oxide flexible electrode for high performance supercapacitor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Xing; Tang, Yao; Song, Junhua

A self-supporting and flexible activated carbon/carbon nanotube/reduced graphene oxide (AC/CNT/RGO) film has been rationally designed for constructing high-performance supercapacitor. We prepared the AC/CNT/RGO film by anchoring the AC particles with a 3D and porous framework built by hierarchically weaving the 1 D CNT and 2D RGO using their intrinsic van der Waals force. The CNT network is beneficial for improving the electronic conductivity of the electrode, while the AC particles could effectively suppress the aggregation of RGO and CNT due to their blocking effect. The synergistic effects among the AC, CNT and RGO validate the AC/CNT/RGO as a promising electrodemore » for supercapacitor, exhibiting greatly enhanced electrochemical performances in comparison with the pure RGO film, pure CNT film and AC electrode. Furthermore, the AC/CNT/RGO electrode delivers a high specific capacitance of 101 F g -1 at the current density of 0.2 A g -1 offering a maximum energy density of 30.0 W h kg -1 in organic electrolyte at the cut-off voltage range of 0.001–3.0 V. The findings of this work open a new avenue for the design of self-supporting electrodes for the development of flexible and light weight energy storage supercapacitor.« less

Self-supporting activated carbon/carbon nanotube/reduced graphene oxide flexible electrode for high performance supercapacitor

DOE PAGES

Li, Xing; Tang, Yao; Song, Junhua; ...

2017-12-06

A self-supporting and flexible activated carbon/carbon nanotube/reduced graphene oxide (AC/CNT/RGO) film has been rationally designed for constructing high-performance supercapacitor. We prepared the AC/CNT/RGO film by anchoring the AC particles with a 3D and porous framework built by hierarchically weaving the 1 D CNT and 2D RGO using their intrinsic van der Waals force. The CNT network is beneficial for improving the electronic conductivity of the electrode, while the AC particles could effectively suppress the aggregation of RGO and CNT due to their blocking effect. The synergistic effects among the AC, CNT and RGO validate the AC/CNT/RGO as a promising electrodemore » for supercapacitor, exhibiting greatly enhanced electrochemical performances in comparison with the pure RGO film, pure CNT film and AC electrode. Furthermore, the AC/CNT/RGO electrode delivers a high specific capacitance of 101 F g -1 at the current density of 0.2 A g -1 offering a maximum energy density of 30.0 W h kg -1 in organic electrolyte at the cut-off voltage range of 0.001–3.0 V. The findings of this work open a new avenue for the design of self-supporting electrodes for the development of flexible and light weight energy storage supercapacitor.« less

Effect of acidification conditions on the properties of carbon nanotube fibers

NASA Astrophysics Data System (ADS)

Wang, Kun; Li, Min; Liu, Ya-Nan; Gu, Yizhuo; Li, Qingwen; Zhang, Zuoguang

2014-02-01

Carbon nanotube (CNT) fibers prepared by dry-spun method were functionalized by mixture of nitric and sulfuric acids. The effects of acidification conditions on the electrical conductivity and tensile properties of CNT fibers were investigated. A strong, high conductive CNT fiber was obtained under the optimal mixture ratio and processing time, with a electrical conductivity and tensile strength up to 3.2 × 104 S/m and 1103 MPa, respectively. It showed that the acids densified the surface of the CNT fiber and introduced functional groups onto the tubes, both of which contributed to the conductivity improvement of the CNT fiber. The infrared spectroscopy, Raman and fracture analysis indicated that acidification process resulted in two competitive effects on the tensile properties of CNT fibers, one was the positive contribution by the enhancement of interactions between CNTs through the densification and functional groups, and the other was the negative effect due to the structural destruction of the tubes.

Thermal conductivity enhancements and viscosity properties of water based Nanofluid containing carbon nanotubes decorated with ag nanoparticles

NASA Astrophysics Data System (ADS)

Gu, Yanni; Xu, Sheng; Wu, Xiaoshan

2018-01-01

The water based nanofluid containing carbon nanotube (CNT) decorated with Ag nanoparticles (Ag/CNT) is prepared. Its thermal conductivity (k) enhancement increases with the thermal filler loading and the decoration quantity of Ag nanoparticles. The low absolute CNT content will decrease the tangles or aggregations among the CNTs, and it will be good at the Brownian motion of CNTs in the water. It has positive effects on the thermal conductivity of nanofluid. With the increase of Ag loading, the average size of Ag nanoparticles increased, and further results in the decrease of dispersing amount of Ag/CNT as the weight of Ag/CNT is fixed. Little dispersing quantity of Ag/CNT makes it possible that the Ag/CNT particles disperse well in the fluid. So it is not easy for CNTs to form aggregation. The high intrinsic k of CNT and the effective thermal conductive networks forming by CNTs and Ag nanoparticles are good at the k enhancement. With temperature increase the k of Ag/CNT nanofluid appears improvement. The study results make it possible to develop high-efficiency nanofluid for advanced thermal management regions.

Thermal conductivity enhancements and viscosity properties of water based Nanofluid containing carbon nanotubes decorated with ag nanoparticles

NASA Astrophysics Data System (ADS)

Gu, Yanni; Xu, Sheng; Wu, Xiaoshan

2018-06-01

The water based nanofluid containing carbon nanotube (CNT) decorated with Ag nanoparticles (Ag/CNT) is prepared. Its thermal conductivity ( k) enhancement increases with the thermal filler loading and the decoration quantity of Ag nanoparticles. The low absolute CNT content will decrease the tangles or aggregations among the CNTs, and it will be good at the Brownian motion of CNTs in the water. It has positive effects on the thermal conductivity of nanofluid. With the increase of Ag loading, the average size of Ag nanoparticles increased, and further results in the decrease of dispersing amount of Ag/CNT as the weight of Ag/CNT is fixed. Little dispersing quantity of Ag/CNT makes it possible that the Ag/CNT particles disperse well in the fluid. So it is not easy for CNTs to form aggregation. The high intrinsic k of CNT and the effective thermal conductive networks forming by CNTs and Ag nanoparticles are good at the k enhancement. With temperature increase the k of Ag/CNT nanofluid appears improvement. The study results make it possible to develop high-efficiency nanofluid for advanced thermal management regions.

Mechanical properties of functionalised CNT filled kenaf reinforced epoxy composites

NASA Astrophysics Data System (ADS)

Sapiai, Napisah; Jumahat, Aidah; Mahmud, Jamaluddin

2018-04-01

This paper aims to study the effect of functionalised carbon nanotubes (CNT) on mechanical properties of kenaf fibre reinforced polymer composites. The CNT was functionalised using acid mixtures of H2SO4:HNO3 and 3-Aminopropyl Triethoxysilane before it was incorporated into epoxy resin. Three different types of CNT were used, i.e. pristine (PCNT), acid-treated (ACNT) and acid-silane treated (SCNT), to fabricate kenaf composite. Three different filler contents were mixed in each composite system, i.e. 0.5, 0.75 and 1.0 wt%. The functionalised CNT was characterized using x-ray Diffraction (XRD), Fourier Transform Infrared (FTIR) and Transmission Electron Microscopy (TEM). Tensile, flexural and Izod impact tests were conducted in order to evaluate the effect of CNT contents and surface treatment of mechanical properties of kenaf composites. It was observed that the inclusion of 1 wt% acid-silane treated CNT improved the tensile, flexural and impact strengths of kenaf/epoxy composite by 43.30%, 21.10%, and 130%, respectively. Silane modification had been proven to be beneficial in enhancing the dispersibility and reducing agglomeration of CNT in the epoxy matrix.

Carbon Nanotube Composite Ampacity and Metallic CNT Buckypaper Conductivity

NASA Technical Reports Server (NTRS)

De Groh, Henry C., III

2016-01-01

NASA is currently working on developing motors for hybrid electric propulsion applications in aviation. To make electric power more feasible in airplanes higher power to weight ratios are sought for electric motors. One facet to these efforts is to improve (increase) the conductivity and (lower) density of the magnet wire used in motors. Carbon nanotubes (CNT) and composites containing CNT are being explored as a possible way to increase wire conductivity and lower density. Presented here are measurements of the current carrying capacity (ampacity) of a composite made from CNT and copper. The ability of CNT to improve the conductivity of such composites is hindered by the presence of semiconductive CNT (s-CNT) that exist in CNT supplies naturally, and currently, unavoidably. To solve this problem, and avoid s-CNT, various preferential growth and sorting methods are being explored. A supply of sorted 95 metallic CNT (m-CNT) was acquired in the form of thick film Buckypaper (BP) as part of this work and characterized using Raman spectroscopy, resistivity, and density measurements. The ampacity (Acm2) of the Cu-5volCNT composite was 3.8 lower than the same gauge pure Cu wire similarly tested. The lower ampacity in the composite wire is believed to be due to the presence of s-CNT in the composite and the relatively low (proper) level of longitudinal cooling employed in the test method. Although Raman spectroscopy can be used to characterize CNT, a strong relation between the ratios of the primary peaks GGand the relative amounts of m-CNT and s-CNT was not observed. The average effective conductivity of the CNT in the sorted, 95 m-CNT BP was 2.5 times higher than the CNT in the similar but un-sorted BP. This is an indication that improvements in the conductivity of CNT composites can be made by the use of sorted, highly conductive m-CNT.

Highly Conductive Wire: Cu Carbon Nanotube Composite Ampacity and Metallic CNT Buckypaper Conductivity

NASA Technical Reports Server (NTRS)

de Groh, Henry C.

2017-01-01

NASA is currently working on developing motors for hybrid electric propulsion applications in aviation. To make electric power more feasible in airplanes higher power to weight ratios are sought for electric motors. One facet to these efforts is to improve (increase) the conductivity and (lower) density of the magnet wire used in motors. Carbon nanotubes (CNT) and composites containing CNT are being explored as a possible way to increase wire conductivity and lower density. Presented here are measurements of the current carrying capacity (ampacity) of a composite made from CNT and copper. The ability of CNT to improve the conductivity of such composites is hindered by the presence of semiconductive CNT (s-CNT) that exist in CNT supplies naturally, and currently, unavoidably. To solve this problem, and avoid s-CNT, various preferential growth and sorting methods are being explored. A supply of sorted 95 metallic CNT (m-CNT) was acquired in the form of thick film Buckypaper (BP) as part of this work and characterized using Raman spectroscopy, resistivity, and density measurements. The ampacity (Acm2) of the Cu-5volCNT composite was 3.8 lower than the same gauge pure Cu wire similarly tested. The lower ampacity in the composite wire is believed to be due to the presence of s-CNT in the composite and the relatively low (proper) level of longitudinal cooling employed in the test method. Although Raman spectroscopy can be used to characterize CNT, a strong relation between the ratios of the primary peaks GGand the relative amounts of m-CNT and s-CNT was not observed. The average effective conductivity of the CNT in the sorted, 95 m-CNT BP was 2.5 times higher than the CNT in the similar but un-sorted BP. This is an indication that improvements in the conductivity of CNT composites can be made by the use of sorted, highly conductive m-CNT.

Structures of water molecules in carbon nanotubes under electric fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Winarto,; Takaiwa, Daisuke; Yamamoto, Eiji

2015-03-28

Carbon nanotubes (CNTs) are promising for water transport through membranes and for use as nano-pumps. The development of CNT-based nanofluidic devices, however, requires a better understanding of the properties of water molecules in CNTs because they can be very different from those in the bulk. Using all-atom molecular dynamics simulations, we investigate the effect of axial electric fields on the structure of water molecules in CNTs having diameters ranging from (7,7) to (10,10). The water dipole moments were aligned parallel to the electric field, which increases the density of water inside the CNTs and forms ordered ice-like structures. The electricmore » field induces the transition from liquid to ice nanotubes in a wide range of CNT diameters. Moreover, we found an increase in the lifetime of hydrogen bonds for water structures in the CNTs. Fast librational motion breaks some hydrogen bonds, but the molecular pairs do not separate and the hydrogen bonds reform. Thus, hydrogen bonds maintain the water structure in the CNTs, and the water molecules move collectively, decreasing the axial diffusion coefficient and permeation rate.« less

A vacuum-sealed compact x-ray tube based on focused carbon nanotube field-emission electrons

NASA Astrophysics Data System (ADS)

Jeong, Jin-Woo; Kim, Jae-Woo; Kang, Jun-Tae; Choi, Sungyoul; Ahn, Seungjoon; Song, Yoon-Ho

2013-03-01

We report on a fully vacuum-sealed compact x-ray tube based on focused carbon nanotube (CNT) field-emission electrons for various radiography applications. The specially designed two-step brazing process enabled us to accomplish a good vacuum level for the stable and reliable operation of the x-ray tube without any active vacuum pump. Also, the integrated focusing electrodes in the field-emission electron gun focused electron beams from the CNT emitters onto the anode target effectively, giving a small focal spot of around 0.3 mm with a large current of above 50 mA. The active-current control through the cathode electrode of the x-ray tube led a fast digital modulation of x-ray dose with a low voltage of below 5 V. The fabricated compact x-ray tube showed a stable and reliable operation, indicating good maintenance of a vacuum level of below 5 × 10-6 Torr and the possibility of field-emission x-ray tubes in a stand-alone device without an active pumping system.

Comparative Studies on Thermal, Mechanical, and Flame Retardant Properties of PBT Nanocomposites via Different Oxidation State Phosphorus-Containing Agents Modified Amino-CNTs.

PubMed

Zhu, San-E; Wang, Li-Li; Chen, Hao; Yang, Wei; Yuen, Anthony Chun-Yin; Chen, Timothy Bo-Yuan; Luo, Cheng; Bi, Wen-Mei; Hu, En-Zhu; Zhang, Jian; Si, Jing-Yu; Lu, Hong-Dian; Hu, Kun-Hong; Chan, Qing Nian; Yeoh, Guan Heng

2018-01-26

High-performance poly(1,4-butylene terephthalate) (PBT) nanocomposites have been developed via the consideration of phosphorus-containing agents and amino-carbon nanotube (A-CNT). One-pot functionalization method has been adopted to prepare functionalized CNTs via the reaction between A-CNT and different oxidation state phosphorus-containing agents, including chlorodiphenylphosphine (DPP-Cl), diphenylphosphinic chloride (DPP(O)-Cl), and diphenyl phosphoryl chloride (DPP(O₃)-Cl). These functionalized CNTs, DPP(O x )-A-CNTs ( x = 0, 1, 3), were, respectively, mixed with PBT to obtain the CNT-based polymer nanocomposites through a melt blending method. Scanning electron microscope observations demonstrated that DPP(O x )-A-CNT nanoadditives were homogeneously distributed within PBT matrix compared to A-CNT. The incorporation of DPP(O x )-A-CNT improved the thermal stability of PBT. Moreover, PBT/DPP(O₃)-A-CNT showed the highest crystallization temperature and tensile strength, due to the superior dispersion and interfacial interactions between DPP(O₃)-A-CNT and PBT. PBT/DPP(O)-A-CNT exhibited the best flame retardancy resulting from the excellent carbonization effect. The radicals generated from decomposed polymer were effectively trapped by DPP(O)-A-CNT, leading to the reduction of heat release rate, smoke production rate, carbon dioxide and carbon monoxide release during cone calorimeter tests.

Piezoresistive Strain Sensors Made from Carbon Nanotubes Based Polymer Nanocomposites

PubMed Central

Alamusi; Hu, Ning; Fukunaga, Hisao; Atobe, Satoshi; Liu, Yaolu; Li, Jinhua

2011-01-01

In recent years, nanocomposites based on various nano-scale carbon fillers, such as carbon nanotubes (CNTs), are increasingly being thought of as a realistic alternative to conventional smart materials, largely due to their superior electrical properties. Great interest has been generated in building highly sensitive strain sensors with these new nanocomposites. This article reviews the recent significant developments in the field of highly sensitive strain sensors made from CNT/polymer nanocomposites. We focus on the following two topics: electrical conductivity and piezoresistivity of CNT/polymer nanocomposites, and the relationship between them by considering the internal conductive network formed by CNTs, tunneling effect, aspect ratio and piezoresistivity of CNTs themselves, etc. Many recent experimental, theoretical and numerical studies in this field are described in detail to uncover the working mechanisms of this new type of strain sensors and to demonstrate some possible key factors for improving the sensor sensitivity. PMID:22346667

Detection of α-fetoprotein in human serum using carbon nanotube transistor

NASA Astrophysics Data System (ADS)

So, Hye-Mi; Park, Dong-Won; Lee, Seong-Kyu; Kim, Beom Soo; Chang, Hyunju; Lee, Jeong-O.

2009-03-01

We have fabricated antibody-coated carbon nanotube field effect transistor (CNT-FET) sensor for the detection of α-fetoprotein (AFP), single chain glycoprotein of 70 kDa that is normally expressed in the fetal liver, in human serum. The AFP-specific antibodies were immobilized on CNT with linker molecule such as pyrenebutyric acid N-hydroxysuccinimide ester. To prevent nonspecific adsorption of antigen, we performed blocking procedure using bovine serum albumin (BSA). Antibody-antigen binding was determined by measuring electrical conductance change of FET and took an average of thereshold voltage change before and after binding. Also we checked concentration-dependent conductance change in human serum using both p-type SWNT-FETs and n-type SWNT-FETs.

Epoxy composite dusts with and without carbon nanotubes cause similar pulmonary responses, but differences in liver histology in mice following pulmonary deposition.

PubMed

Saber, Anne Thoustrup; Mortensen, Alicja; Szarek, Józef; Koponen, Ismo Kalevi; Levin, Marcus; Jacobsen, Nicklas Raun; Pozzebon, Maria Elena; Mucelli, Stefano Pozzi; Rickerby, David George; Kling, Kirsten; Atluri, Rambabu; Madsen, Anne Mette; Jackson, Petra; Kyjovska, Zdenka Orabi; Vogel, Ulla; Jensen, Keld Alstrup; Wallin, Håkan

2016-06-29

The toxicity of dusts from mechanical abrasion of multi-walled carbon nanotube (CNT) epoxy nanocomposites is unknown. We compared the toxic effects of dusts generated by sanding of epoxy composites with and without CNT. The used CNT type was included for comparison. Mice received a single intratracheal instillation of 18, 54 and 162 μg of CNT or 54, 162 and 486 μg of the sanding dust from epoxy composite with and without CNT. DNA damage in lung and liver, lung inflammation and liver histology were evaluated 1, 3 and 28 days after intratracheal instillation. Furthermore, the mRNA expression of interleukin 6 and heme oxygenase 1 was measured in the lungs and serum amyloid A1 in the liver. Printex 90 carbon black was included as a reference particle. Pulmonary exposure to CNT and all dusts obtained by sanding epoxy composite boards resulted in recruitment of inflammatory cells into lung lumen: On day 1 after instillation these cells were primarily neutrophils but on day 3, eosinophils contributed significantly to the cell population. There were still increased numbers of neutrophils 28 days after intratracheal instillation of the highest dose of the epoxy dusts. Both CNT and epoxy dusts induced DNA damage in lung tissue up to 3 days after intratracheal instillation but not in liver tissue. There was no additive effect of adding CNT to epoxy resins for any of the pulmonary endpoints. In livers of mice instilled with CNT and epoxy dust with CNTs inflammatory and necrotic histological changes were observed, however, not in mice instilled with epoxy dust without CNT. Pulmonary deposition of epoxy dusts with and without CNT induced inflammation and DNA damage in lung tissue. There was no additive effect of adding CNT to epoxies for any of the pulmonary endpoints. However, hepatic inflammatory and necrotic histopathological changes were seen in mice instilled with sanding dust from CNT-containing epoxy but not in mice instilled with reference epoxy.

Water confined in carbon nanotubes: Magnetic response and proton chemical shieldings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, P; Schwegler, E; Galli, G

2008-11-14

We study the proton nuclear magnetic resonance ({sup 1}H-NMR) of a model system consisting of liquid water in infinite carbon nanotubes (CNT). Chemical shieldings are evaluated from linear response theory, where the electronic structure is derived from density functional theory (DFT) with plane-wave basis sets and periodic boundary conditions. The shieldings are sampled from trajectories generated via first-principles molecular dynamics simulations at ambient conditions, for water confined in (14,0) and (19,0) CNTs with diameters d = 11 {angstrom} and 14.9 {angstrom}, respectively. We find that confinement within the CNT leads to a large ({approx} -23 ppm) upfield shift relative tomore » bulk liquid water. This shift is a consequence of strongly anisotropic magnetic fields induced in the CNT by an applied magnetic field.« less

Effect of Electron Beam Irradiation on the Tensile Properties of Carbon Nanotubes Sheets and Yarns

NASA Technical Reports Server (NTRS)

Williams, Tiffany S.; Miller, Sandi G.; Baker, James S.; McCorkle, Linda S.; Meador, Michael A.

2013-01-01

Carbon nanotube sheets and yarns were irradiated using electron beam (e-beam) energy to determine the effect of irradiation dose on the tensile properties. Results showed that a slight change in tensile strength occurred after irradiating as-received CNT sheets for 20 minutes, and a slight decrease in tensile strength as the irradiation time approached 90 minutes. On the other hand, the addition of small molecules to the CNT sheet surface had a greater effect on the tensile properties of e-beam irradiated CNT sheets. Some functionalized CNT sheets displayed up to a 57% increase in tensile strength following 90 minutes of e-beam exposure. In addition, as-received CNT yarns showed a significant increase in tensile strength as the irradiation time increased.

On the behavior of isolated and embedded carbon nano-tubes in a polymeric matrix

NASA Astrophysics Data System (ADS)

Rahimian-Koloor, Seyed Mostafa; Moshrefzadeh-Sani, Hadi; Mehrdad Shokrieh, Mahmood; Majid Hashemianzadeh, Seyed

2018-02-01

In the classical micro-mechanical method, the moduli of the reinforcement and the matrix are used to predict the stiffness of composites. However, using the classical micro-mechanical method to predict the stiffness of CNT/epoxy nanocomposites leads to overestimated results. One of the main reasons for this overestimation is using the stiffness of the isolated CNT and ignoring the CNT nanoscale effect by the method. In the present study the non-equilibrium molecular dynamics simulation was used to consider the influence of CNT length on the stiffness of the nanocomposites through the isothermal-isobaric ensemble. The results indicated that, due to the nanoscale effects, the reinforcing efficiency of the embedded CNT is not constant and decreases with decreasing its length. Based on the results, a relationship was derived, which predicts the effective stiffness of an embedded CNT in terms of its length. It was shown that using this relationship leads to predict more accurate elastic modulus of nanocomposite, which was validated by some experimental counterparts.

Carbon Nanotube-Multilayered Graphene Edge Plane Core-Shell Hybrid Foams for Ultrahigh-Performance Electromagnetic-Interference Shielding.

PubMed

Song, Qiang; Ye, Fang; Yin, Xiaowei; Li, Wei; Li, Hejun; Liu, Yongsheng; Li, Kezhi; Xie, Keyu; Li, Xuanhua; Fu, Qiangang; Cheng, Laifei; Zhang, Litong; Wei, Bingqing

2017-08-01

Materials with an ultralow density and ultrahigh electromagnetic-interference (EMI)-shielding performance are highly desirable in fields of aerospace, portable electronics, and so on. Theoretical work predicts that 3D carbon nanotube (CNT)/graphene hybrids are one of the most promising lightweight EMI shielding materials, owing to their unique nanostructures and extraordinary electronic properties. Herein, for the first time, a lightweight, flexible, and conductive CNT-multilayered graphene edge plane (MLGEP) core-shell hybrid foam is fabricated using chemical vapor deposition. MLGEPs are seamlessly grown on the CNTs, and the hybrid foam exhibits excellent EMI shielding effectiveness which exceeds 38.4 or 47.5 dB in X-band at 1.6 mm, while the density is merely 0.0058 or 0.0089 g cm -3 , respectively, which far surpasses the best values of reported carbon-based composite materials. The grafted MLGEPs on CNTs can obviously enhance the penetration losses of microwaves in foams, leading to a greatly improved EMI shielding performance. In addition, the CNT-MLGEP hybrids also exhibit a great potential as nano-reinforcements for fabricating high-strength polymer-based composites. The results provide an alternative approach to fully explore the potentials of CNT and graphene, for developing advanced multifunctional materials. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Batch Fabrication of Ultrasensitive Carbon Nanotube Hydrogen Sensors with Sub-ppm Detection Limit.

PubMed

Xiao, Mengmeng; Liang, Shibo; Han, Jie; Zhong, Donglai; Liu, Jingxia; Zhang, Zhiyong; Peng, Lianmao

2018-04-27

Carbon nanotube (CNT) has been considered as an ideal channel material for building highly sensitive gas sensors. However, the reported H 2 sensors based on CNT always suffered from the low sensitivity or low production. We developed the technology to massively fabricate ultra-highly sensitive H 2 sensors based on solution derived CNT network through comprehensive optimization of the CNT material, device structure, and fabrication process. In the H 2 sensors, high semiconducting purity solution-derived CNT film sorted by poly[9-(1-octylonoyl)-9 H-carbazole-2,7-diyl](PCz) is used as the main channel, which is decorated with Pd nanoparticles as functionalization for capturing H 2 . Meanwhile, Ti contacts are used to form a Schottky barrier for enhancing transferred charge-induced resistance change, and then a response of resistance change by 3 orders of magnitude is achieved at room temperature under the concentration of ∼311 ppm with a very fast response time of approximately 7 s and a detection limit of 890 ppb, which is the highest response to date for CNT H 2 sensors and the very first time to show the sub-ppm detection for H 2 at room temperature. Furthermore, the detection limit concentration can be improved to 89 ppb at 100 °C. The batch fabrication of CNT film H 2 sensors with ultra-high sensitivity and high uniformity is ready to promote CNT devices to application for the first time in some specialized field.

3D assembly of carbon nanotubes for fabrication of field-effect transistors through nanomanipulation and electron-beam-induced deposition

NASA Astrophysics Data System (ADS)

Yu, Ning; Shi, Qing; Nakajima, Masahiro; Wang, Huaping; Yang, Zhan; Sun, Lining; Huang, Qiang; Fukuda, Toshio

2017-10-01

Three-dimensional carbon nanotube field-effect transistors (3D CNTFETs) possess predictable characteristics that rival those of planar CNTFETs and Si-based MOSFETs. However, due to the lack of a reliable assembly technology, they are rarely reported on, despite the amount of attention they receive. To address this problem, we propose the novel concept of a 3D CNTFET and develop its assembly strategy based on nanomanipulation and the electron-beam-induced deposition (EBID) technique inside a scanning electron microscope (SEM). In particular, the electrodes in our transistor design are three metallic cuboids of the same size, and their front, top and back surfaces are all wrapped up in CNTs. The assembly strategy is employed to build the structure through a repeated basic process of pick-up, placement, fixing and cutting of CNTs. The pick-up and placement is performed through one nanomanipulator with four degrees of freedom. Fixing is carried out through the EBID technique so as to improve the mechanical and electrical characteristics of the CNT/electrodes connection. CNT cutting is undertaken using the typical method of electrical breakdown. Experimental results showed that two CNTs were successfully assembled on the front sides of the cubic electrodes. This validates our assembly method for the 3D CNTFET. Also, when contact resistance was measured, tens of kilohms of resistance was observed at the CNT-EBID deposition-FET electrodes junction.. This manifests the electrical reliability of our assembly strategy.

Modification of carbon nanotube's dispersion using cetyltrimethyl ammonium bromide (CTAB) as cancer drug delivery

NASA Astrophysics Data System (ADS)

Wulan, Praswati PDK.; Wulandari, Hanifia; Ulwan, Sekar H.; Purwanto, Widodo W.; Mulia, Kamarza

2018-02-01

Cancer is a disease that causes many deaths globally. Cancer treatments have side effects that can danger the human body. Carbon nanotube (CNT) becomes drug (anti-cancer) delivery towards cancer cells that have been targeted. Yet, CNT tends to aggregate. It could be overcome by functionalization (modification) of CNT using Cetyltrimethyl Ammonium Bromide (CTAB). The variations we use were CNT-CTAB with a dose of CNT 100 mg and CTAB varied between 80, 90, 100, 110, and 120 mg. There were several stages of CNT modification process: dispersion, filtration, washing, and drying. The optimum condition obtained was on CNT-110 mg CTAB because it could be dispersed up to 70 hours better than pure CNT, Zeta Potential (ZP) ≥16 mV, and absorbance Uv-vis 1.05. Both the ZP value and the absorbance of Uv-vis showed the CNT dispersion modified to be better than the pure CNT. Furthermore, SEM-EDX did not produce structural damage to CNT modified surfaces, the percentage of the mass of Oxygen (O) elements as characteristic of increased hydrophilic properties, and Ni elements as toxic impurities become reduced. FTIR spectrum results showed the highest intensity occurred at CTAB CNT-110mg at 1221 m-1. This strong C-N vibration interaction suggests that CNTs CNT modification become readily dispersed in water.

The effect of hydrochloric acid addition to increase carbon nanotubes dispersibility as drug delivery system by covalent functionalization

NASA Astrophysics Data System (ADS)

Wulan, P. P. D. K.; Ulwani, S. H.; Wulandari, H.; Purwanto, W. W.; Mulia, K.

2018-03-01

This study is to obtain the effect of adding hydrochloric acid (HCl) to the mixture of sulfuric acid (H2SO4) and HNO3 in CNT covalent functionalization. HCl expected to increase the dispersibility of functionalized CNT by improving the dispersion time period done with H2SO4 or HNO3. Functionalization used mixture of H2SO4 and HNO3 with volume ratio of 3:1. Covalent functionalization used 0.5 grams of MWCNT ultra sonicated in 50mL HNO3 with and mixture of H2SO4 and HNO3. Additions of 200 mL HCl used variation of molarity from 1M, 2M, 3M, 4M, 5M to 6M. CNT were oxidized to form carboxylic and hydroxyl bonds on the surface that increase dispersibility of CNT. FTIR spectrums showed the existences of carboxyl and hydroxyl group on spectra of 2600-3700 cm-1 and 900-1400 cm-1. Dispersion tests, which showed functionalized CNT (f-CNT) dispersion capabilities, were done by dissolving f-CNT in water. The study resulted that 6M f-CNT (NSC6) gave the best dispersion with zeta potential value of -37.1mV. NSC6 gave the longest dispersion time which was 20 days until f-CNT settle again. SEM-EDS micrographs showed the surface structure of 6M f-CNT without significant damage and no longer contain impurities of Fe, Ni, and Cl.

Carbon nanotube balls and their application in supercapacitors.

PubMed

Kang, Da-Young; Moon, Jun Hyuk

2014-01-08

We have provided a design of the macroscopic morphology of carbon nanotubes (CNTs) using emulsion droplet confinement. The evaporation of CNT-dispersed aqueous emulsion droplets in oil produces spherical CNT assemblies, i.e., CNT balls. In this emulsion-assisted method, compact packing of CNT was obtained by the presence of capillary pressure during droplet evaporation. The size of the CNT balls could be controlled by changing the concentration of the CNT dispersion solution; typically, CNT balls with an average size in the range of 8-12 μm were obtained with a Brunauer-Emmett-Teller (BET) specific area of 200 m(2)/g. Heat treatment of the CNT balls, which was required to remove residual solvent, and cement CNTs was followed, and their effect has been characterized; the heat treatment at high temperature desorbed surface oxygenated groups of CNTs and created defective carbon structures, but did not change pore structure. The dispersion of CNT balls was applied to form CNT ball-assembled film for a supercapacitor electrode. The specific capacitance of 80 F/g was obtained at 500 °C heat treatment, but the CNT balls prepared at a higher temperature actually decreased the capacitance, because of the removal of surface oxygenated groups, thereby decreasing the pseudo-capacitance. The capacitive properties of CNT ball-assembled electrodes were compared to CNT films; the CNT ball electrodes showed 40% higher specific electrochemical capacitance and higher rate performance, which is attributed to the compact packing of CNTs in the CNT ball and the hierarchical porous structures in the ball assemblies.

Effects of Atomic-Scale Structure on the Fracture Properties of Amorphous Carbon - Carbon Nanotube Composites

NASA Technical Reports Server (NTRS)

Jensen, Benjamin D.; Wise, Kristopher E.; Odegard, Gregory M.

2015-01-01

The fracture of carbon materials is a complex process, the understanding of which is critical to the development of next generation high performance materials. While quantum mechanical (QM) calculations are the most accurate way to model fracture, the fracture behavior of many carbon-based composite engineering materials, such as carbon nanotube (CNT) composites, is a multi-scale process that occurs on time and length scales beyond the practical limitations of QM methods. The Reax Force Field (ReaxFF) is capable of predicting mechanical properties involving strong deformation, bond breaking and bond formation in the classical molecular dynamics framework. This has been achieved by adding to the potential energy function a bond-order term that varies continuously with distance. The use of an empirical bond order potential, such as ReaxFF, enables the simulation of failure in molecular systems that are several orders of magnitude larger than would be possible in QM techniques. In this work, the fracture behavior of an amorphous carbon (AC) matrix reinforced with CNTs was modeled using molecular dynamics with the ReaxFF reactive forcefield. Care was taken to select the appropriate simulation parameters, which can be different from those required when using traditional fixed-bond force fields. The effect of CNT arrangement was investigated with three systems: a single-wall nanotube (SWNT) array, a multi-wall nanotube (MWNT) array, and a SWNT bundle system. For each arrangement, covalent bonds are added between the CNTs and AC, with crosslink fractions ranging from 0-25% of the interfacial CNT atoms. The SWNT and MWNT array systems represent ideal cases with evenly spaced CNTs; the SWNT bundle system represents a more realistic case because, in practice, van der Waals interactions lead to the agglomeration of CNTs into bundles. The simulation results will serve as guidance in setting experimental processing conditions to optimize the mechanical properties of CNT composites.

Fabricating and strengthening the carbon nanotube/copper composite fibers with high strength and high electrical conductivity

NASA Astrophysics Data System (ADS)

Han, Baoshuai; Guo, Enyu; Xue, Xiang; Zhao, Zhiyong; Li, Tiejun; Xu, Yanjin; Luo, Liangshun; Hou, Hongliang

2018-05-01

Combining the excellent properties of carbon nanotube (CNT) and copper, CNT/Cu composite fibers were fabricated by physical vapor deposition (PVD) and rolling treatment. Dense and continuous copper film (∼2 μm) was coated on the surface of the CNT fibers by PVD, and rolling treatment was adopt to strengthen the CNT/Cu composite fibers. After the rolling treatment, the defects between the Cu grains and the CNT bundles were eliminated, and the structure of both the copper film and the core CNT fibers were optimized. The rolled CNT/Cu composite fibers possess high tensile effective strength (1.01 ± 0.13 GPa) and high electrical conductivity ((2.6 ± 0.3) × 107 S/m), and thus, this material may become a promising wire material.

Carbon Nanotube-Based Structural Health Monitoring Sensors

NASA Technical Reports Server (NTRS)

Wincheski, Russell; Jordan, Jeffrey; Oglesby, Donald; Watkins, Anthony; Patry, JoAnne; Smits, Jan; Williams, Phillip

2011-01-01

Carbon nanotube (CNT)-based sensors for structural health monitoring (SHM) can be embedded in structures of all geometries to monitor conditions both inside and at the surface of the structure to continuously sense changes. These CNTs can be manipulated into specific orientations to create small, powerful, and flexible sensors. One of the sensors is a highly flexible sensor for crack growth detection and strain field mapping that features a very dense and highly ordered array of single-walled CNTs. CNT structural health sensors can be mass-produced, are inexpensive, can be packaged in small sizes (0.5 micron(sup 2)), require less power than electronic or piezoelectric transducers, and produce less waste heat per square centimeter than electronic or piezoelectric transducers. Chemically functionalized lithographic patterns are used to deposit and align the CNTs onto metallic electrodes. This method consistently produces aligned CNTs in the defined locations. Using photo- and electron-beam lithography, simple Cr/Au thin-film circuits are patterned onto oxidized silicon substrates. The samples are then re-patterned with a CNT-attracting, self-assembled monolayer of 3-aminopropyltriethoxysilane (APTES) to delineate the desired CNT locations between electrodes. During the deposition of the solution-suspended single- wall CNTs, the application of an electric field to the metallic contacts causes alignment of the CNTs along the field direction. This innovation is a prime candidate for smart skin technologies with applications ranging from military, to aerospace, to private industry.

Mechanically Robust Magnetic Carbon Nanotube Papers Prepared with CoFe2O4 Nanoparticles for Electromagnetic Interference Shielding and Magnetomechanical Actuation.

PubMed

Lim, Guh-Hwan; Woo, Seongwon; Lee, Hoyoung; Moon, Kyoung-Seok; Sohn, Hiesang; Lee, Sang-Eui; Lim, Byungkwon

2017-11-22

The introduction of inorganic nanoparticles into carbon nanotube (CNT) papers can provide a versatile route to the fabrication of CNT papers with diverse functionalities, but it may lead to a reduction in their mechanical properties. Here, we describe a simple and effective strategy for the fabrication of mechanically robust magnetic CNT papers for electromagnetic interference (EMI) shielding and magnetomechanical actuation applications. The magnetic CNT papers were produced by vacuum filtration of an aqueous suspension of CNTs, CoFe 2 O 4 nanoparticles, and poly(vinyl alcohol) (PVA). PVA plays a critical role in enhancing the mechanical strength of CNT papers. The magnetic CNT papers containing 73 wt % of CoFe 2 O 4 nanoparticles exhibited high mechanical properties with Young's modulus of 3.2 GPa and tensile strength of 30.0 MPa. This magnetic CNT paper was successfully demonstrated as EMI shielding paper with shielding effectiveness of ∼30 dB (99.9%) in 0.5-1.0 GHz, and also as a magnetomechanical actuator in an audible frequency range from 200 to 20 000 Hz.

Evaluations of carbon nanotube field emitters for electron microscopy

NASA Astrophysics Data System (ADS)

Nakahara, Hitoshi; Kusano, Yoshikazu; Kono, Takumi; Saito, Yahachi

2009-11-01

Brightness of carbon nanotube (CNT) emitters was already reported elsewhere. However, brightness of electron emitter is affected by a virtual source size of the emitter, which strongly depends on electron optical configuration around the emitter. In this work, I- V characteristics and brightness of a CNT emitter are measured under a practical field emission electron gun (e-gun) configuration to investigate availability of CNT for electron microscopy. As a result, it is obtained that an emission area of MWNT is smaller than its tip surface area, and the emission area corresponds to a five-membered-ring with 2nd nearest six-membered-rings on the MWNT cap surface. Reduced brightness of MWNT is measured as at least 2.6×109 A/m 2 sr V. It is concluded that even a thick MWNT has enough brightness under a practical e-gun electrode configuration and suitable for electron microscopy.

Overdense microwave plasma heating in the CNT stellarator

NASA Astrophysics Data System (ADS)

Hammond, K. C.; Diaz-Pacheco, R. R.; Köhn, A.; Volpe, F. A.; Wei, Y.

2018-02-01

Overdense plasmas have been attained with 2.45 GHz microwave heating in the low-field, low-aspect-ratio CNT stellarator. Densities higher than four times the ordinary (O) mode cutoff density were measured with 8 kW of power injected in the O-mode and, alternatively, with 6.5 kW in the extraordinary (X) mode. The temperature profiles peak at the plasma edge. This was ascribed to collisional damping of the X-mode at the upper hybrid resonant layer. The X-mode reaches that location by tunneling, mode-conversions or after polarization-scrambling reflections off the wall and in-vessel coils, regardless of the initial launch being in O- or X-mode. This interpretation was confirmed by full-wave numerical simulations. Also, as the CNT plasma is not completely ionized at these low microwave power levels, electron density was shown to increase with power. A dependence on magnetic field strength was also observed, for O-mode launch.

Computational Investigation of Graphene-Carbon Nanotube-Polymer Composite

NASA Astrophysics Data System (ADS)

Jha, Sanjiv; Roth, Michael; Todde, Guido; Subramanian, Gopinath; Shukla, Manoj; Univ of Southern Mississippi Collaboration; US Army Engineer Research; Development Center 3909 Halls Ferry Road Vicksburg, MS 39180, USA Collaboration

Graphene is a single atom thick two dimensional carbon sheet where sp2 -hybridized carbon atoms are arranged in a honeycomb structure. The functionalization of graphene and carbon nanotubes (CNTs) with polymer is a route for developing high performance nanocomposite materials. We study the interfacial interactions among graphene, CNT, and Nylon 6 polymer using computational methods based on density functional theory (DFT) and empirical force-field. Our DFT calculations are carried out using Quantum-ESPRESSO electronic structure code with van der Waals functional (vdW-DF2), whereas the empirical calculations are performed using LAMMPS with the COMPASS force-field. Our results demonstrated that the interactions between (8,8) CNT and graphene, and between CNT/graphene and Nylon 6 consist mostly of van der Waals type. The computed Young's moduli indicated that the mechanical properties of carbon nanostructures are enhanced by their interactions with polymer. The presence of Stone-Wales (SW) defects lowered the Young's moduli of carbon nanostructures.

Fullerene-like MoSe2 nanoparticles-embedded CNT balls with excellent structural stability for highly reversible sodium-ion storage

NASA Astrophysics Data System (ADS)

Choi, Seung Ho; Kang, Yun Chan

2016-02-01

Three-dimensional (3D) porous-structured carbon nanotube (CNT) balls embedded with fullerene-like MoSe2 nanocrystals were successfully prepared by the spray pyrolysis process and subsequent selenization process. The MoO2-CNT composite balls prepared by spray pyrolysis transformed into the fullerene-like MoSe2/CNT (F-MoSe2/CNT) composite balls by the selenization process. The F-MoSe2/CNT composite balls exhibited superior sodium-ion storage properties to bare MoSe2 and MoSe2/CNT with a filled structure (N-MoSe2/CNT), both of which were prepared as comparison samples. The 250th discharge capacities of bare MoSe2, N-MoSe2/CNT composite balls, and F-MoSe2/CNT composite balls were 144, 200, and 296 mA h g-1, respectively, at a high current density of 1.0 A g-1, and their capacity retentions measured from the second cycle were 37%, 66%, and 83%, respectively. The 10th discharge capacities of the F-MoSe2/CNT composite balls were 382, 346, 310, 280, and 255 mA h g-1 at current densities of 0.2, 0.5, 1.5, 3.0, and 5.0 A g-1, respectively. The synergetic effect of the fullerene-like MoSe2 nanocrystals with ultrafine sizes and the CNT balls with a tangled and 3D porous structure and high electrical conductivity resulted in excellent sodium-ion storage properties of the F-MoSe2/CNT composite balls.Three-dimensional (3D) porous-structured carbon nanotube (CNT) balls embedded with fullerene-like MoSe2 nanocrystals were successfully prepared by the spray pyrolysis process and subsequent selenization process. The MoO2-CNT composite balls prepared by spray pyrolysis transformed into the fullerene-like MoSe2/CNT (F-MoSe2/CNT) composite balls by the selenization process. The F-MoSe2/CNT composite balls exhibited superior sodium-ion storage properties to bare MoSe2 and MoSe2/CNT with a filled structure (N-MoSe2/CNT), both of which were prepared as comparison samples. The 250th discharge capacities of bare MoSe2, N-MoSe2/CNT composite balls, and F-MoSe2/CNT composite balls were 144, 200, and 296 mA h g-1, respectively, at a high current density of 1.0 A g-1, and their capacity retentions measured from the second cycle were 37%, 66%, and 83%, respectively. The 10th discharge capacities of the F-MoSe2/CNT composite balls were 382, 346, 310, 280, and 255 mA h g-1 at current densities of 0.2, 0.5, 1.5, 3.0, and 5.0 A g-1, respectively. The synergetic effect of the fullerene-like MoSe2 nanocrystals with ultrafine sizes and the CNT balls with a tangled and 3D porous structure and high electrical conductivity resulted in excellent sodium-ion storage properties of the F-MoSe2/CNT composite balls. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr07733h

Thermal effects on nonlinear vibration of a carbon nanotube-based mass sensor using finite element analysis

NASA Astrophysics Data System (ADS)

Kang, Dong-Keun; Kim, Chang-Wan; Yang, Hyun-Ik

2017-01-01

In the present study we carried out a dynamic analysis of a CNT-based mass sensor by using a finite element method (FEM)-based nonlinear analysis model of the CNT resonator to elucidate the combined effects of thermal effects and nonlinear oscillation behavior upon the overall mass detection sensitivity. Mass sensors using carbon nanotube (CNT) resonators provide very high sensing performance. Because CNT-based resonators can have high aspect ratios, they can easily exhibit nonlinear oscillation behavior due to large displacements. Also, CNT-based devices may experience high temperatures during their manufacture and operation. These geometrical nonlinearities and temperature changes affect the sensing performance of CNT-based mass sensors. However, it is very hard to find previous literature addressing the detection sensitivity of CNT-based mass sensors including considerations of both these nonlinear behaviors and thermal effects. We modeled the nonlinear equation of motion by using the von Karman nonlinear strain-displacement relation, taking into account the additional axial force associated with the thermal effect. The FEM was employed to solve the nonlinear equation of motion because it can effortlessly handle the more complex geometries and boundary conditions. A doubly clamped CNT resonator actuated by distributed electrostatic force was the configuration subjected to the numerical experiments. Thermal effects upon the fundamental resonance behavior and the shift of resonance frequency due to attached mass, i.e., the mass detection sensitivity, were examined in environments of both high and low (or room) temperature. The fundamental resonance frequency increased with decreasing temperature in the high temperature environment, and increased with increasing temperature in the low temperature environment. The magnitude of the shift in resonance frequency caused by an attached mass represents the sensing performance of a mass sensor, i.e., its mass detection sensitivity, and it can be seen that this shift is affected by the temperature change and the amount of electrostatic force. The thermal effects on the mass detection sensitivity are intensified in the linear oscillation regime and increase with increasing CNT length; this intensification can either improve or worsen the detection sensitivity.

Biological response to purification and acid functionalization of carbon nanotubes

NASA Astrophysics Data System (ADS)

Figarol, Agathe; Pourchez, Jérémie; Boudard, Delphine; Forest, Valérie; Tulliani, Jean-Marc; Lecompte, Jean-Pierre; Cottier, Michèle; Bernache-Assollant, Didier; Grosseau, Philippe

2014-07-01

Acid functionalization has been considered as an easy way to enhance the dispersion and biodegradation of carbon nanotubes (CNT). However, inconsistencies between toxicity studies of acid functionalized CNT remain unexplained. This could be due to a joint effect of the main physicochemical modifications resulting from an acid functionalization: addition of surface acid groups and purification from catalytic metallic impurities. In this study, the impact on CNT biotoxicity of these two physiochemical features was assessed separately. The in vitro biological response of RAW 264.7 macrophages was evaluated after exposure to 15-240 µg mL-1 of two types of multi-walled CNT. For each type of CNT (small: 20 nm diameter, and big: 90 nm diameter), three different surface chemical properties were studied (total of six CNT samples): pristine, acid functionalized and desorbed. Desorbed CNT were purified by the acid functionalization but presented a very low amount of surface acid groups due to a thermal treatment under vacuum. A Janus effect of acid functionalization with two opposite impacts is highlighted. The CNT purification decreased the overall toxicity, while the surface acid groups intensified it when present at a specific threshold. These acid groups especially amplified the pro-inflammatory response. The threshold mechanism which seemed to regulate the impact of acid groups should be further studied to determine its value and potential link to the other physicochemical state of the CNT. The results suggest that, for a safer-design approach, the benefit-risk balance of an acid functionalization has to be considered, depending on the CNT primary state of purification. Further research should be conducted in this direction.

Carbon nanotube feedback-gate field-effect transistor: suppressing current leakage and increasing on/off ratio.

PubMed

Qiu, Chenguang; Zhang, Zhiyong; Zhong, Donglai; Si, Jia; Yang, Yingjun; Peng, Lian-Mao

2015-01-27

Field-effect transistors (FETs) based on moderate or large diameter carbon nanotubes (CNTs) usually suffer from ambipolar behavior, large off-state current and small current on/off ratio, which are highly undesirable for digital electronics. To overcome these problems, a feedback-gate (FBG) FET structure is designed and tested. This FBG FET differs from normal top-gate FET by an extra feedback-gate, which is connected directly to the drain electrode of the FET. It is demonstrated that a FBG FET based on a semiconducting CNT with a diameter of 1.5 nm may exhibit low off-state current of about 1 × 10(-13) A, high current on/off ratio of larger than 1 × 10(8), negligible drain-induced off-state leakage current, and good subthreshold swing of 75 mV/DEC even at large source-drain bias and room temperature. The FBG structure is promising for CNT FETs to meet the standard for low-static-power logic electronics applications, and could also be utilized for building FETs using other small band gap semiconductors to suppress leakage current.

Nanoneedle transistor-based sensors for the selective detection of intracellular calcium ions.

PubMed

Son, Donghee; Park, Sung Young; Kim, Byeongju; Koh, Jun Tae; Kim, Tae Hyun; An, Sangmin; Jang, Doyoung; Kim, Gyu Tae; Jhe, Wonho; Hong, Seunghun

2011-05-24

We developed a nanoneedle transistor-based sensor (NTS) for the selective detection of calcium ions inside a living cell. In this work, a single-walled carbon nanotube-based field effect transistor (swCNT-FET) was first fabricated at the end of a glass nanopipette and functionalized with Fluo-4-AM probe dye. The selective binding of calcium ions onto the dye molecules altered the charge state of the dye molecules, resulting in the change of the source-drain current of the swCNT-FET as well as the fluorescence intensity from the dye. We demonstrated the electrical and fluorescence detection of the concentration change of intracellular calcium ions inside a HeLa cell using the NTS.

Facile fabrication of CNT-based chemical sensor operating at room temperature

NASA Astrophysics Data System (ADS)

Sheng, Jiadong; Zeng, Xian; Zhu, Qi; Yang, Zhaohui; Zhang, Xiaohua

2017-12-01

This paper describes a simple, low cost and effective route to fabricate CNT-based chemical sensors, which operate at room temperature. Firstly, the incorporation of silk fibroin in vertically aligned CNT arrays (CNTA) obtained through a thermal chemical vapor deposition (CVD) method makes the direct removal of CNT arrays from substrates without any rigorous acid or sonication treatment feasible. Through a simple one-step in situ polymerization of anilines, the functionalization of CNT arrays with polyaniline (PANI) significantly improves the sensing performance of CNT-based chemical sensors in detecting ammonia (NH3) and hydrogen chloride (HCl) vapors. Chemically modified CNT arrays also show responses to organic vapors like menthol, ethyl acetate and acetone. Although the detection limits of chemically modified CNT-based chemical sensors are of the same orders of magnitudes reported in previous studies, these CNT-based chemical sensors show advantages of simplicity, low cost and energy efficiency in preparation and fabrication of devices. Additionally, a linear relationship between the relative sensitivity and concentration of analyte makes precise estimations on the concentrations of trace chemical vapors possible.

Method to fabricate portable electron source based on nitrogen incorporated ultrananocrystalline diamond (N-UNCD)

DOEpatents

Sumant, Anirudha V.; Divan, Ralu; Posada, Chrystian M.; Castano, Carlos H.; Grant, Edwin J.; Lee, Hyoung K.

2016-03-29

A source cold cathode field emission array (FEA) source based on ultra-nanocrystalline diamond (UNCD) field emitters. This system was constructed as an alternative for detection of obscured objects and material. Depending on the geometry of the given situation a flat-panel source can be used in tomography, radiography, or tomosynthesis. Furthermore, the unit can be used as a portable electron or X-ray scanner or an integral part of an existing detection system. UNCD field emitters show great field emission output and can be deposited over large areas as the case with carbon nanotube "forest" (CNT) cathodes. Furthermore, UNCDs have better mechanical and thermal properties as compared to CNT tips which further extend the lifetime of UNCD based FEA.

Mechanical properties of hollow and water-filled graphyne nanotube and carbon nanotube hybrid structure.

PubMed

Lei, Guangping; Zhang, Yayun; Liu, Hantao; Song, Fenhong

2018-05-11

By performing molecular dynamics simulations, a GNT/CNT hybrid structure constructed via combing (6, 6) graphyne nanotube (GNT) with (6, 6) carbon nanotube (CNT) has been designed and investigated. The mechanical properties induced by the percentage of GNT, water content and electric field were examined. Calculation results reveal that the fracture strain and strength of hollow hybrid structure are remarkably smaller than that of perfect (6, 6) CNT. In addition, the Young's modulus decreases monotonously with the increase of percentage of GNT. More importantly, the tunable mechanical properties of hybrid structure can be achieved through filling with water molecules and applying an electric field along tensile direction. Specifically, increasing water content from 0.0 to 8.70 mmol g -1 in the absence of electric field could result in fracture strain and strength reducing by 15.09% and 12.87%, respectively. Besides, enhancing fracture strain and strength of water-filled hybrid structure with water content of 8.70 mmol g -1 can also be obtained with rising electric field intensity. These findings would provide a valuable theoretical basis for designing and fabricating a nanodevice with controllable mechanical performances.

Mechanical properties of hollow and water-filled graphyne nanotube and carbon nanotube hybrid structure

NASA Astrophysics Data System (ADS)

Lei, Guangping; Zhang, Yayun; Liu, Hantao; Song, Fenhong

2018-05-01

By performing molecular dynamics simulations, a GNT/CNT hybrid structure constructed via combing (6, 6) graphyne nanotube (GNT) with (6, 6) carbon nanotube (CNT) has been designed and investigated. The mechanical properties induced by the percentage of GNT, water content and electric field were examined. Calculation results reveal that the fracture strain and strength of hollow hybrid structure are remarkably smaller than that of perfect (6, 6) CNT. In addition, the Young’s modulus decreases monotonously with the increase of percentage of GNT. More importantly, the tunable mechanical properties of hybrid structure can be achieved through filling with water molecules and applying an electric field along tensile direction. Specifically, increasing water content from 0.0 to 8.70 mmol g-1 in the absence of electric field could result in fracture strain and strength reducing by 15.09% and 12.87%, respectively. Besides, enhancing fracture strain and strength of water-filled hybrid structure with water content of 8.70 mmol g-1 can also be obtained with rising electric field intensity. These findings would provide a valuable theoretical basis for designing and fabricating a nanodevice with controllable mechanical performances.

Magneto-transport of highly conductive carbon nanotube assemblies under high-field

NASA Astrophysics Data System (ADS)

Bulmer, John; Lekawa-Raus, Agnieszka; Koziol, Krzysztof; ECNM Group Team

2014-03-01

The magneto-transport response of carbon nanotube (CNT) assemblies has a resistance decrease with magnetic field, which is typically followed by a resistance increase with higher field. These negative and positive components of the magneto-resistance are from, respectively, suppression of weak localization and suppression of inter-tube coupling brought on by the magnetic restriction of the electron wave function. Recently, highly conductive CNT films, which were either doped or enriched with metallic chiralities, showed only a decrease in resistance with field and indicate that the extent of carrier delocalization is beyond individual CNTs. These magneto-transport measurements, however, were no greater then approximately 12 T and it is not clear when or if the magneto-resistance will go positive. In this study we prepared highly conductive single wall CNT films that have been either heavily doped, enriched with metallic chiralities, highly aligned, or a combination of these three. The magneto-resistance was measured up to 65 T with temperatures down to 2 K. The most metallic-like samples had the greatest delay in the positive magneto-resistance upturn. Fluctuation induced tunneling, variable range hopping, and weak localization models were each considered to quantitatively evaluate the transport behavior. http://www.kkoziol.org/index.html

Active vacuum brazing of CNT films to metal substrates for superior electron field emission performance

NASA Astrophysics Data System (ADS)

Longtin, Rémi; Sanchez-Valencia, Juan Ramon; Shorubalko, Ivan; Furrer, Roman; Hack, Erwin; Elsener, Hansrudolf; Gröning, Oliver; Greenwood, Paul; Rupesinghe, Nalin; Teo, Kenneth; Leinenbach, Christian; Gröning, Pierangelo

2015-02-01

The joining of macroscopic films of vertically aligned multiwalled carbon nanotubes (CNTs) to titanium substrates is demonstrated by active vacuum brazing at 820 °C with a Ag-Cu-Ti alloy and at 880 °C with a Cu-Sn-Ti-Zr alloy. The brazing methodology was elaborated in order to enable the production of highly electrically and thermally conductive CNT/metal substrate contacts. The interfacial electrical resistances of the joints were measured to be as low as 0.35 Ω. The improved interfacial transport properties in the brazed films lead to superior electron field-emission properties when compared to the as-grown films. An emission current of 150 μA was drawn from the brazed nanotubes at an applied electric field of 0.6 V μm-1. The improvement in electron field-emission is mainly attributed to the reduction of the contact resistance between the nanotubes and the substrate. The joints have high re-melting temperatures up to the solidus temperatures of the alloys; far greater than what is achievable with standard solders, thus expanding the application potential of CNT films to high-current and high-power applications where substantial frictional or resistive heating is expected.

Active vacuum brazing of CNT films to metal substrates for superior electron field emission performance

PubMed Central

Longtin, Rémi; Ramon Sanchez-Valencia, Juan; Shorubalko, Ivan; Furrer, Roman; Hack, Erwin; Elsener, Hansrudolf; Gröning, Oliver; Greenwood, Paul; Rupesinghe, Nalin; Teo, Kenneth; Leinenbach, Christian; Gröning, Pierangelo

2015-01-01

The joining of macroscopic films of vertically aligned multiwalled carbon nanotubes (CNTs) to titanium substrates is demonstrated by active vacuum brazing at 820 °C with a Ag–Cu–Ti alloy and at 880 °C with a Cu–Sn–Ti–Zr alloy. The brazing methodology was elaborated in order to enable the production of highly electrically and thermally conductive CNT/metal substrate contacts. The interfacial electrical resistances of the joints were measured to be as low as 0.35 Ω. The improved interfacial transport properties in the brazed films lead to superior electron field-emission properties when compared to the as-grown films. An emission current of 150 μA was drawn from the brazed nanotubes at an applied electric field of 0.6 V μm−1. The improvement in electron field-emission is mainly attributed to the reduction of the contact resistance between the nanotubes and the substrate. The joints have high re-melting temperatures up to the solidus temperatures of the alloys; far greater than what is achievable with standard solders, thus expanding the application potential of CNT films to high-current and high-power applications where substantial frictional or resistive heating is expected. PMID:27877755

Atomic Layer Deposition on Carbon Nanotubes and their Assemblies

NASA Astrophysics Data System (ADS)

Stano, Kelly Lynn

Global issues related to energy and the environment have motivated development of advanced material solutions outside of traditional metals ceramics, and polymers. Taking inspiration from composites, where the combination of two or more materials often yields superior properties, the field of organic-inorganic hybrids has recently emerged. Carbon nanotube (CNT)-inorganic hybrids have drawn widespread and increasing interest in recent years due to their multifunctionality and potential impact across several technologically important application areas. Before the impacts of CNT-inorganic hybrids can be realized however, processing techniques must be developed for their scalable production. Optimization in chemical vapor deposition (CVD) methods for synthesis of CNTs and vertically aligned CNT arrays has created production routes both high throughput and economically feasible. Additionally, control of CVD parameters has allowed for growth of CNT arrays that are able to be drawn into aligned sheets and further processed to form a variety of aligned 1, 2, and 3-dimensional bulk assemblies including ribbons, yarns, and foams. To date, there have only been a few studies on utilizing these bulk assemblies for the production of CNT-inorganic hybrids. Wet chemical methods traditionally used for fabricating CNT-inorganic hybrids are largely incompatible with CNT assemblies, since wetting and drying the delicate structures with solvents can destroy their structure. It is therefore necessary to investigate alternative processing strategies in order to advance the field of CNT-inorganic hybrids. In this dissertation, atomic layer deposition (ALD) is evaluated as a synthetic route for the production of large-scale CNT-metal oxide hybrids as well as pure metal oxide architectures utilizing CNT arrays, ribbons, and ultralow density foams as deposition templates. Nucleation and growth behavior of alumina was evaluated as a function of CNT surface chemistry. While highly graphitic and defect-free CNTs were shown to produce alumina beads on their surfaces, plasma-treated CNTs with a high concentration of oxygen- containing functional groups on their surface promoted conformal film formation. Furthermore, it was determined that ultrahigh aspect ratio CNT assemblies could be uniformly coated throughout the cross-section by orienting the CNT axes parallel to the direction of precursor flow, as well as by removing any barriers to the pump/purge process such as growth substrates or non-porous sample holders. Heat treatment of CNT-alumina hybrids in air not only led to the crystallization of alumina, but also oxidative removal of CNTs from the core-shell structure. In the case of CNT arrays, this resulted in a weak array of alumina nanotubes. When the same process was applied to alumina-coated CNT foams (CNTFs) however, a robust and resilient aerogel-like material remained post-calcination. Further inspection of this novel material revealed that the foam was made up of a three-dimensional network of interconnect alumina nanotubes resulting from the direct templating of alumina on the CNTF structure. With an average density of 1.2 mg cm-3, it is an order of magnitude lower than the lowest density alumina aerogel reported to date, and is among the lowest density for any inorganic aerogel reported to date as well. The structure, and therefore, properties of these novel foams could be easily tuned by varying the thickness of the alumina coating. Evaluation of the compressive behavior of all foams revealed that their mechanical properties exceed those of various foams with similar densities. This was found to be a result of efficient load transfer through the structure due to good connectivity among nanotube ligaments. This connectivity also provided unprecedented elastic recoverability following compression, particularly for thin-walled samples with CNTFs still intact. Structural stability to liquid infiltration and drying increased with the number of ALD cycles, as well as thermal insulation ability.

Carbon nanotube multilayered nanocomposites as multifunctional substrates for actuating neuronal differentiation and functions of neural stem cells.

PubMed

Shao, Han; Li, Tingting; Zhu, Rong; Xu, Xiaoting; Yu, Jiandong; Chen, Shengfeng; Song, Li; Ramakrishna, Seeram; Lei, Zhigang; Ruan, Yiwen; He, Liumin

2018-08-01

Carbon nanotubes (CNTs) have shown potential applications in neuroscience as growth substrates owing to their numerous unique properties. However, a key concern in the fabrication of homogeneous composites is the serious aggregation of CNTs during incorporation into the biomaterial matrix. Moreover, the regulation mechanism of CNT-based substrates on neural differentiation remains unclear. Here, a novel strategy was introduced for the construction of CNT nanocomposites via layer-by-layer assembly of negatively charged multi-walled CNTs and positively charged poly(dimethyldiallylammonium chloride). Results demonstrated that the CNT-multilayered nanocomposites provided a potent regulatory signal over neural stem cells (NSCs), including cell adhesion, viability, differentiation, neurite outgrowth, and electrophysiological maturation of NSC-derived neurons. Importantly, the dynamic molecular mechanisms in the NSC differentiation involved the integrin-mediated interactions between NSCs and CNT multilayers, thereby activating focal adhesion kinase, subsequently triggering downstream signaling events to regulate neuronal differentiation and synapse formation. This study provided insights for future applications of CNT-multilayered nanomaterials in neural fields as potent modulators of stem cell behavior. Copyright © 2018 Elsevier Ltd. All rights reserved.

Extension of coarse-grained UNRES force field to treat carbon nanotubes.

PubMed

Sieradzan, Adam K; Mozolewska, Magdalena A

2018-04-26

Carbon nanotubes (CNTs) have recently received considerable attention because of their possible applications in various branches of nanotechnology. For their cogent application, knowledge of their interactions with biological macromolecules, especially proteins, is essential and computer simulations are very useful for such studies. Classical all-atom force fields limit simulation time scale and size of the systems significantly. Therefore, in this work, we implemented CNTs into the coarse-grained UNited RESidue (UNRES) force field. A CNT is represented as a rigid infinite-length cylinder which interacts with a protein through the Kihara potential. Energy conservation in microcanonical coarse-grained molecular dynamics simulations and temperature conservation in canonical simulations with UNRES containing the CNT component have been verified. Subsequently, studies of three proteins, bovine serum albumin (BSA), soybean peroxidase (SBP), and α-chymotrypsin (CT), with and without CNTs, were performed to examine the influence of CNTs on the structure and dynamics of these proteins. It was found that nanotubes bind to these proteins and influence their structure. Our results show that the UNRES force field can be used for further studies of CNT-protein systems with 3-4 order of magnitude larger timescale than using regular all-atom force fields. Graphical abstract Bovine serum albumin (BSA), soybean peroxidase (SBP), and α-chymotrypsin (CT), with and without CNTsᅟ.

Electroconductive PET/SWNT Films by Solution Casting

NASA Technical Reports Server (NTRS)

Steinert, Brian W.; Dean, Derrick R.

2008-01-01

The market for electrically conductive polymers is rapidly growing, and an emerging pathway for attaining these materials is via polymer-carbon nanotube (CNT) nanocomposites, because of the superior properties of CNTs. Due to their excellent electrical properties and anisotropic magnetic susceptibility, we expect CNTs could be easily aligned to maximize their effectiveness in imparting electrical conductivity to the polymer matrix. Single-walled carbon nanotubes (SWNT) were dispersed in a polyethylene terephthalate (PET) matrix by solution blending then cast onto a glass substrate to create thin, flexible films. Various SWNT loading concentrations were implemented (0.5, 1.0, and 3.0 wt.%) to study the effect of additive density. The processing method was repeated to produce films in the presence of magnetic fields (3 and 9.4 Tesla). The SWNTs showed a high susceptibility to the magnetic field and were effectively aligned in the PET matrix. The alignment was characterized with Raman spectroscopy. Impedance spectroscopy was utilized to study the electrical behavior of the films. Concentration and dispersion seemed to play very important roles in improving electrical conductivity, while alignment played a secondary and less significant role. The most interesting result proved to be the effect of a magnetic field during processing. It appears that a magnetic field may improve dispersion of unmodified SWNTs, which seems to be more important than alignment. It was concluded that SWNTs offer a good option as conductive, nucleating filler for electroconductive polymer applications, and the utilization of a magnetic field may prove to be a novel method for CNT dispersion that could lead to improved nanocomposite materials.

Carbon nanotube and nanofiber exposure and sputum and blood biomarkers of early effect among U.S. workers.

PubMed

Beard, John D; Erdely, Aaron; Dahm, Matthew M; de Perio, Marie A; Birch, M Eileen; Evans, Douglas E; Fernback, Joseph E; Eye, Tracy; Kodali, Vamsi; Mercer, Robert R; Bertke, Stephen J; Schubauer-Berigan, Mary K

2018-07-01

Carbon nanotubes and nanofibers (CNT/F) are increasingly used for diverse applications. Although animal studies suggest CNT/F exposure may cause deleterious health effects, human epidemiological studies have typically been small, confined to single workplaces, and limited in exposure assessment. We conducted an industrywide cross-sectional epidemiological study of 108 workers from 12 U.S. sites to evaluate associations between occupational CNT/F exposure and sputum and blood biomarkers of early effect. We assessed CNT/F exposure via personal breathing zone, filter-based air sampling to measure background-corrected elemental carbon (EC) (a CNT/F marker) mass and microscopy-based CNT/F structure count concentrations. We measured 36 sputum and 37 blood biomarkers. We used factor analyses with varimax rotation to derive factors among sputum and blood biomarkers separately. We used linear, Tobit, and unconditional logistic regression models to adjust for potential confounders and evaluate associations between CNT/F exposure and individual biomarkers and derived factors. We derived three sputum and nine blood biomarker factors that explained 78% and 67%, respectively, of the variation. After adjusting for potential confounders, inhalable EC and total inhalable CNT/F structures were associated with the most sputum and blood biomarkers, respectively. Biomarkers associated with at least three CNT/F metrics were 72 kDa type IV collagenase/matrix metalloproteinase-2 (MMP-2), interleukin-18, glutathione peroxidase (GPx), myeloperoxidase, and superoxide dismutase (SOD) in sputum and MMP-2, matrix metalloproteinase-9, metalloproteinase inhibitor 1/tissue inhibitor of metalloproteinases 1, 8-hydroxy-2'-deoxyguanosine, GPx, SOD, endothelin-1, fibrinogen, intercellular adhesion molecule 1, vascular cell adhesion protein 1, and von Willebrand factor in blood, although directions of associations were not always as expected. Inhalable rather than respirable CNT/F was more consistently associated with fibrosis, inflammation, oxidative stress, and cardiovascular biomarkers. Published by Elsevier Ltd.

Biodegradability of carbon nanotube/polymer nanocomposites under aerobic mixed culture conditions.

PubMed

Phan, Duc C; Goodwin, David G; Frank, Benjamin P; Bouwer, Edward J; Fairbrother, D Howard

2018-10-15

The properties and commercial viability of biodegradable polymers can be significantly enhanced by the incorporation of carbon nanotubes (CNTs). The environmental impact and persistence of these carbon nanotube/polymer nanocomposites (CNT/PNCs) after disposal will be strongly influenced by their microbial interactions, including their biodegradation rates. At the end of consumer use, CNT/PNCs will encounter diverse communities of microorganisms in landfills, surface waters, and wastewater treatment plants. To explore CNT/PNC biodegradation under realistic environmental conditions, the effect of multi-wall CNT (MWCNT) incorporation on the biodegradation of polyhydroxyalkanoates (PHA) was investigated using a mixed culture of microorganisms from wastewater. Relative to unfilled PHA (0% w/w), the MWCNT loading (0.5-10% w/w) had no statistically significant effect on the rate of PHA matrix biodegradation. Independent of the MWCNT loading, the extent of CNT/PNC mass remaining closely corresponded to the initial mass of CNTs in the matrix suggesting a lack of CNT release. CNT/PNC biodegradation was complete in approximately 20 days and resulted in the formation of a compressed CNT mat that retained the shape of the initial CNT/PNC. This study suggests that although CNTs have been shown to be cytotoxic towards a range of different microorganisms, this does not necessarily impact the biodegradation of the surrounding polymer matrix in mixed culture, particularly in situations where the polymer type and/or microbial population favor rapid polymer biodegradation. Copyright © 2018 Elsevier B.V. All rights reserved.

Adsorption of insulin peptide on charged single-walled carbon nanotubes: significant role of ordered water molecules.

PubMed

Shen, Jia-Wei; Wu, Tao; Wang, Qi; Kang, Yu; Chen, Xin

2009-06-02

Ordered hydration shells: The more ordered hydration shells outside the charged CNT surfaces prevent more compact adsorption of the peptide in the charged CNT systems [picture: see text], but peptide binding strengths on the charged CNT surfaces are stronger due to the electrostatic interaction.Studies of adsorption dynamics and stability for peptides/proteins on single-walled carbon nanotubes (SWNTs) are of great importance for a better understanding of the properties and nature of nanotube-based biosystems. Herein, the dynamics and mechanism of the adsorption of the insulin chain B peptide on different charged SWNTs are investigated by explicit solvent molecular dynamics simulations. The results show that all types of surfaces effectively attract the model peptide. Water molecules play a significant role in peptide adsorption on the surfaces of charged carbon nanotubes (CNTs). Compared to peptide adsorption on neutral CNT surfaces, the more ordered hydration shells outside the tube prevent more compact adsorption of the peptide in charged CNT systems. This shield effect leads to a smaller conformational change and van der Waals interaction between the peptide and surfaces, but peptide binding strengths on charged CNT surfaces are stronger than those on the neutral CNT surface due to the strong electrostatic interaction. The result of these simulations implies the possibility of improving the binding strength of peptides/proteins on CNT surfaces, as well as keeping the integrity of the peptide/protein conformation in peptide/protein-CNT complexes by charging the CNTs.

Effect of the mechanical deformation on the electrical properties of the polymer/CNT fiber

NASA Astrophysics Data System (ADS)

Cho, Hyun Woo; Sung, Bong June; Nano-Bio Computational Chemistry Laboratory Team

2014-03-01

We elucidate the effect of the mechanical deformation on the electrical properties of the polymer/CNT fiber. The conductive polymer fiber has drawn a great attention for its potential application to a stretchable electronics such as wearable devices and artificial muscles, etc. However, the electrical conductivity of the polymer-based stretchable electronics decreases significantly during the deformation, which may limit the applicability of the polymer/CNT fiber for the stretchable electronics. Moreover, its physical origin for the decrease in electrical conductivity has not been explained clearly. In this work, we employ a coarse-grained model for the polymer/CNT fiber, and we calculate the electric conductivity using global tunneling network (GTN) model. We show that the electric conductivity decreases during the elongation of the polymer/CNT fiber. We also find using critical path approximation (CPA) that the structure of the electrical network of the CNTs changes collectively during the elongation of the fiber, which is strongly responsible for the reduction of the electrical conductivity of the polymer/CNT fiber.

Unveiling Stability Criteria of DNA-Carbon Nanotubes Constructs by Scanning Tunneling Microscopy and Computational Modeling

DOE PAGES

Kilina, Svetlana; Yarotski, Dzmitry A.; Talin, A. Alec; ...

2011-01-01

We present a combined approach that relies on computational simulations and scanning tunneling microscopy (STM) measurements to reveal morphological properties and stability criteria of carbon nanotube-DNA (CNT-DNA) constructs. Application of STM allows direct observation of very stable CNT-DNA hybrid structures with the well-defined DNA wrapping angle of 63.4 ° and a coiling period of 3.3 nm. Using force field simulations, we determine how the DNA-CNT binding energy depends on the sequence and binding geometry of a single strand DNA. This dependence allows us to quantitatively characterize the stability of a hybrid structure with an optimal π-stacking between DNA nucleotides and themore » tube surface and better interpret STM data. Our simulations clearly demonstrate the existence of a very stable DNA binding geometry for (6,5) CNT as evidenced by the presence of a well-defined minimum in the binding energy as a function of an angle between DNA strand and the nanotube chiral vector. This novel approach demonstrates the feasibility of CNT-DNA geometry studies with subnanometer resolution and paves the way towards complete characterization of the structural and electronic properties of drug-delivering systems based on DNA-CNT hybrids as a function of DNA sequence and a nanotube chirality.« less

Electron transport in extended carbon-nanotube/metal contacts: Ab initio based Green function method

NASA Astrophysics Data System (ADS)

Fediai, Artem; Ryndyk, Dmitry A.; Cuniberti, Gianaurelio

2015-04-01

We have developed a new method that is able to predict the electrical properties of the source and drain contacts in realistic carbon nanotube field effect transistors (CNTFETs). It is based on large-scale ab initio calculations combined with a Green function approach. For the first time, both internal and external parts of a realistic CNT-metal contact are taken into account at the ab initio level. We have developed the procedure allowing direct calculation of the self-energy for an extended contact. Within the method, it is possible to calculate the transmission coefficient through a contact of both finite and infinite length; the local density of states can be determined in both free and embedded CNT segments. We found perfect agreement with the experimental data for Pd and Al contacts. We have explained why CNTFETs with Pd electrodes are p -type FETs with ohmic contacts, which can carry current close to the ballistic limit (provided contact length is large enough), whereas in CNT-Al contacts transmission is suppressed to a significant extent, especially for holes.

Analytical Calculation of Sensing Parameters on Carbon Nanotube Based Gas Sensors

PubMed Central

Akbari, Elnaz; Buntat, Zolkafle; Ahmad, Mohd Hafizi; Enzevaee, Aria; Yousof, Rubiyah; Iqbal, Syed Muhammad Zafar; Ahmadi, Mohammad Taghi.; Sidik, Muhammad Abu Bakar; Karimi, Hediyeh

2014-01-01

Carbon Nanotubes (CNTs) are generally nano-scale tubes comprising a network of carbon atoms in a cylindrical setting that compared with silicon counterparts present outstanding characteristics such as high mechanical strength, high sensing capability and large surface-to-volume ratio. These characteristics, in addition to the fact that CNTs experience changes in their electrical conductance when exposed to different gases, make them appropriate candidates for use in sensing/measuring applications such as gas detection devices. In this research, a model for a Field Effect Transistor (FET)-based structure has been developed as a platform for a gas detection sensor in which the CNT conductance change resulting from the chemical reaction between NH3 and CNT has been employed to model the sensing mechanism with proposed sensing parameters. The research implements the same FET-based structure as in the work of Peng et al. on nanotube-based NH3 gas detection. With respect to this conductance change, the I–V characteristic of the CNT is investigated. Finally, a comparative study shows satisfactory agreement between the proposed model and the experimental data from the mentioned research. PMID:24658617

Fullerene-like MoSe2 nanoparticles-embedded CNT balls with excellent structural stability for highly reversible sodium-ion storage.

PubMed

Choi, Seung Ho; Kang, Yun Chan

2016-02-21

Three-dimensional (3D) porous-structured carbon nanotube (CNT) balls embedded with fullerene-like MoSe2 nanocrystals were successfully prepared by the spray pyrolysis process and subsequent selenization process. The MoO2-CNT composite balls prepared by spray pyrolysis transformed into the fullerene-like MoSe2/CNT (F-MoSe2/CNT) composite balls by the selenization process. The F-MoSe2/CNT composite balls exhibited superior sodium-ion storage properties to bare MoSe2 and MoSe2/CNT with a filled structure (N-MoSe2/CNT), both of which were prepared as comparison samples. The 250(th) discharge capacities of bare MoSe2, N-MoSe2/CNT composite balls, and F-MoSe2/CNT composite balls were 144, 200, and 296 mA h g(-1), respectively, at a high current density of 1.0 A g(-1), and their capacity retentions measured from the second cycle were 37%, 66%, and 83%, respectively. The 10(th) discharge capacities of the F-MoSe2/CNT composite balls were 382, 346, 310, 280, and 255 mA h g(-1) at current densities of 0.2, 0.5, 1.5, 3.0, and 5.0 A g(-1), respectively. The synergetic effect of the fullerene-like MoSe2 nanocrystals with ultrafine sizes and the CNT balls with a tangled and 3D porous structure and high electrical conductivity resulted in excellent sodium-ion storage properties of the F-MoSe2/CNT composite balls.

Effects of carbon nanotube (CNT) dispersion and interface condition on thermo-mechanical behavior of CNT-reinforced vinyl ester

NASA Astrophysics Data System (ADS)

Sabet, Seyed Morteza

In fabrication of nanoparticle-reinforced polymers, two critical factors need to be taken into account to control properties of the final product; nanoparticle dispersion/distribution in the matrix; and interfacial interactions between nanoparticles and their surrounding matrix. The focus of this thesis was to examine the role of these two factors through experimental methodologies and molecular-level simulations. Carbon nanotubes (CNTs) and vinyl ester (VE) resin were used as nanoparticles and matrix, respectively. In a parametric study, a series of CNT/VE nanocomposites with different CNT dispersion conditions were fabricated using the ultrasonication mixing method. Thermomechanical properties of nanocomposites and quality of CNT dispersion were evaluated. By correlation between nanocomposite behavior and CNT dispersion, a thermomechanical model was suggested; at a certain threshold level of sonication energy, CNT dispersion would be optimal and result in maximum enhancement in properties. This threshold energy level is also related to particle concentration. Sonication above this threshold level, leads to destruction of nanotubes and renders a negative effect on the properties of nanocomposites. In an attempt to examine the interface condition, a novel process was developed to modify CNT surface with polyhedral oligomeric silsesquioxane (POSS). In this process, a chemical reaction was allowed to occur between CNTs and POSS in the presence of an effective catalyst. The functionalized CNTs were characterized using TEM, SEM-EDS, AFM, TGA, FTIR and Raman spectroscopy techniques. Formation of amide bonds between POSS and nanotubes was established and verified. Surface modification of CNTs with POSS resulted in significant improvement in nanotube dispersion. In-depth SEM analysis revealed formation of a 3D network of well-dispersed CNTs with POSS connections to the polymer. In parallel, molecular dynamics simulation of CNT-POSS/VE system showed an effective load transfer from polymer chains to the CNT due to POSS linkages at the interface. The rigid and flexible network of CNTs is found to be responsible for enhancement in elastic modulus, strength, fracture toughness and glass transition temperature (Tg) of the final nanocomposites.

Photodegradation of ibuprofen by TiO2 co-doping with urea and functionalized CNT irradiated with visible light - Effect of doping content and pH.

PubMed

Yuan, Ching; Hung, Chung-Hsuang; Li, Huei-Wen; Chang, Wei-Hsian

2016-07-01

Ibuprofen (IBP) is one kind of non-steroidal anti-inflammatory drugs (NSAIDs), which are classified as Pharmaceuticals and Personal Care Products (PPCPs). IBP possesses bioactive property and the substantial use of IBP results in a harmful impact on bioreceptors even in small concentrations. Accordingly, the treatment of these wastewaters is important before discharging them into the ecosystem. The photodegradation of IBP with TiO2 co-doped with functionalized CNTs (CNT-COOH and CNT-COCl) and urea, named as N-doping CNT/TiO2, irradiated with visible light of 410 nm was investigated in this study. The titanium tetrachloride was used as the precursor of Ti. The N-doping CNT-COCl/TiO2 photocatalysts exhibited a better crystalline structure and smaller crystal size than the N-doping CNT-COOH/TiO2 photocatalyst. It might largely ascribe to strong binding between acyl chloride functional group and TiO2. About 85.0%-86.0% of IBP was degraded with N-doping CNT/TiO2 within 120 min at natural condition, which obeyed the pseudo first order reaction and the rate constant was 4.45 × 10(-3)-1.22 × 10(-2) min(-1) and 5.03 × 10(-3)-1.47 × 10(-2) min(-1) for N-doping CNT-COOH/TiO2 and N-doping CNT-COCl/TiO2, respectively. The best IBP degradation of 87.9%-89.0% was found at pH 5, which indicated superoxide radicals (O2(-)) played a key role. The optimal pH was majorly dominated by the nature of IBP and N-doping CNT/TiO2. A successful synergy effect of TiO2 and dopants was exhibited and this mainly attributed to the strong binding strength by functional group of acyl chloride (COCl) and carboxylic acid (COOH). In summary, IBP could be effectively photodegraded by the fabricated N-doping CNT/TiO2 photocatalysts. Copyright © 2016 Elsevier Ltd. All rights reserved.

Polyaniline/Carbon nanotube Electrochromic Films: Electrochemical Polymerization and characterization

NASA Astrophysics Data System (ADS)

Li, Xiao-Xia; Zhao, Liang; Ma, De-Yue; Zeng, Yu-Run

2018-02-01

Polyaniline/Carbon nanotube (PANI/CNT) composite films doped with dodecyl-benzene sulfonic acid were synthesized by cyclic voltammetry on an ITO-coated glass substrate. FTIR, XRD and electrochemical analyzer were used to characterize the micro-morphology, chemical structure, crystallinity and electrochromic behavior of the films, respectively. The effect of CNT content on the properties of the films was investigated. Results show that the introducing CNTs make aniline polymerize easier than before. Within a range, the conductivity and crystallinity of PANI/CNT composites improves with CNT content increasing. The electrochromic device made from the PAN/CNT film with a CNT content of 2.5wt% presents a reflectance contrast of 38.8%, a mean response time of 2.3s and a coloration efficiency of 386.4cm2/C at 540nm. The PAN/CNT film shows better electrochromic behaviors due to some interaction between CNTs and the PANI backbones than PANI film.

Ce-Doped NiFe-Layered Double Hydroxide Ultrathin Nanosheets/Nanocarbon Hierarchical Nanocomposite as an Efficient Oxygen Evolution Catalyst.

PubMed

Xu, Huajie; Wang, Bingkai; Shan, Changfu; Xi, Pinxian; Liu, Weisheng; Tang, Yu

2018-02-21

Developing convenient doping to build highly active oxygen evolution reaction (OER) electrocatalysts is a practical process for solving the energy crisis. Herein, a facile and low-cost in situ self-assembly strategy for preparing a Ce-doped NiFe-LDH nanosheets/nanocarbon (denoted as NiFeCe-LDH/CNT, LDH = layered double hydroxide and CNT = carbon nanotube) hierarchical nanocomposite is established for enhanced OER, in which the novel material provides its overall advantageous structural features, including high intrinsic catalytic activity, rich redox properties, high, flexible coordination number of Ce 3+ , and strongly coupled interface. Further experimental results indicate that doped Ce into NiFe-LDH/CNT nanoarrays brings about the reinforced specific surface area, electrochemical surface area, lattice defects, and the electron transport between the LDH nanolayered structure and the framework of CNTs. The effective synergy prompts the NiFeCe-LDH/CNT nanocomposite to possess superior OER electrocatalytic activity with a low onset potential (227 mV) and Tafel slope (33 mV dec -1 ), better than the most non-noble metal-based OER electrocatalysts reported. Therefore, the combination of the remarkable catalytic ability and the facile normal temperature synthesis conditions endows the Ce-doped LDH nanocomposite as a promising catalyst to expand the field of lanthanide-doped layered materials for efficient water-splitting electrocatalysis with scale-up potential.

Towards an optimal contact metal for CNTFETs.

PubMed

Fediai, Artem; Ryndyk, Dmitry A; Seifert, Gotthard; Mothes, Sven; Claus, Martin; Schröter, Michael; Cuniberti, Gianaurelio

2016-05-21

Downscaling of the contact length Lc of a side-contacted carbon nanotube field-effect transistor (CNTFET) is challenging because of the rapidly increasing contact resistance as Lc falls below 20-50 nm. If in agreement with existing experimental results, theoretical work might answer the question, which metals yield the lowest CNT-metal contact resistance and what physical mechanisms govern the geometry dependence of the contact resistance. However, at the scale of 10 nm, parameter-free models of electron transport become computationally prohibitively expensive. In our work we used a dedicated combination of the Green function formalism and density functional theory to perform an overall ab initio simulation of extended CNT-metal contacts of an arbitrary length (including infinite), a previously not achievable level of simulations. We provide a systematic and comprehensive discussion of metal-CNT contact properties as a function of the metal type and the contact length. We have found and been able to explain very uncommon relations between chemical, physical and electrical properties observed in CNT-metal contacts. The calculated electrical characteristics are in reasonable quantitative agreement and exhibit similar trends as the latest experimental data in terms of: (i) contact resistance for Lc = ∞, (ii) scaling of contact resistance Rc(Lc); (iii) metal-defined polarity of a CNTFET. Our results can guide technology development and contact material selection for downscaling the length of side-contacts below 10 nm.

Effect of CNT addition on cure kinetics of glass fiber/epoxy composite

NASA Astrophysics Data System (ADS)

Fulmali, A. O.; Kattaguri, R.; Mahato, K. K.; Prusty, R. K.; Ray, B. C.

2018-03-01

In present time, developments in reinforced polymer composites have acquired preferential attention for high performance and high precision applications like aerospace, marine and transportation. Fibre reinforced polymer (FRP) composites are being substituted because of their low density, higher strength, stiffness, impact resistance, and improved corrosion resistance. Further laminated composites exhibit superior in-plane mechanical properties that are mostly governed by the fibers. However, laminated FRP composites suffer from poor out of plane properties in some applications. These properties can further be improved by the addition of Nano fillers like carbon nanotube (CNT), graphene and so on. Curing cycle plays a very important role in drawing out the optimum property of glass fiber/epoxy (GE) composite. It is expected that the cure kinetics can further be altered by addition of CNT due to its higher aspect ratio. The main objective of this work is to study the effect of CNT addition on cure kinetics of GE composite as multi-segment adsorption of polymer takes place on the CNT surface. In this study effects of curing parameters on mechanical properties and glass transition temperature of CNT embedded glass fiber/epoxy composite (CNT-GE) has been evaluated. For this study control GE and CNT-GE (with 0.1 wt. %) laminates were fabricated using hand lay-up technique followed by hot compression. The curing parameters that were considered in the present investigation were temperature (80°C, 110°C, and 140°C) and time (0.5 hr, 3 hr and 6 hr). For different combination of above mentioned temperature and time, samples of GE and CNT-GE composites were post cured. Mechanical properties were determined by flexural testing using 3 point bending fixture on INSTRON-5967 and thermal properties i.e. glass transition temperature (Tg) determined by Differential Scanning Calorimeter (DSC) to evaluate the effects of curing parameters. For CNT-GE samples, No much variation observed in flexural modulus with increase in post curing temperature and time, but swift increment was observed in flexural strength at 140°C with increase in post cure time. Elevation in Tg observed with increase in temperature and time duration of post curing; highest Tg noted at 140°C-6hr. Optimum post curing parameters for CNT-GE composite observed to be 140°C-6hr.

Do Membranes Dream of Electric Tubes? Advanced Membranes Using Carbon Nanotube - Polymer Nanocomposites

NASA Astrophysics Data System (ADS)

de Lannoy, Charles-Francois Pedro Claude Karolek Ghislain

Membrane technologies represent an energy efficient, effective solution for treating municipal and commercial waters/wastewaters. Membranes are predominantly polymer-based and despite steady advances in polymeric materials, they continue to suffer from operational problems including biofouling and breakages. This work addresses these two disparate problems by developing novel CNT-polymer nanocomposite materials that contain variously functionalized carbon nanotubes (fCNTs) in low quantities (<0.5wt%). Several strategies have been employed to achieve highly functional CNT-polymer nanocomposite membranes including blend mixing, ionic charge association, and covalent cross-linking with monomer and oligomer constituents. These CNT-polymer nanocomposite membranes were compared to traditional polymer membranes across various properties including increased Young's Modulus, changes in surface hydrophilicity, fine control over molecular weight cut-off and flux, and surface electrical conductivity. Membranes with high surface electrical conductivity were further tested for their anti-biofouling properties. Finally, CNT stability and polymer compatibility were evaluated throughout membrane manufacture, use, and cleaning. The incorporation of CNTs mixed in bulk phase and linked through ionic associations in polymer matrices showed significant (50%) increases in Young's modulus for certain CNT functionalizations and derivatization percent. Membranes formed with high surface electrical conductivity demonstrated almost complete resistance to biofouling (> 95%) in long-term bacterially challenged experiments. CNTs and polymer mixtures that lacked covalent or ionic bonds were susceptible to significant (up to 10%) loss of CNTs during membrane non-solvent gelation and aggressive chemical cleaning treatment. Functionalized carbon nanotubes endow polymer membranes with their unique strength and electrically conductive properties. These added properties were demonstrated to greatly improve membrane operational efficiency and membrane longevity. CNT-polymer nanocomposite membranes offer low-energy, high-efficiency, and long-lifetime alternatives to traditional polymer membranes. With further advances in polymeric nanomaterials, membrane technology has the potential for wide applicability across many fields outside of water filtration and desalination.

Fabrication and characterization of a CNT forest integrated micromechanical resonator for a rarefied gas analyzer in a medium vacuum atmosphere

NASA Astrophysics Data System (ADS)

Sugano, Koji; Matsumoto, Ryu; Tsutsui, Ryota; Kishihara, Hiroyuki; Matsuzuka, Naoki; Yamashita, Ichiro; Uraoka, Yukiharu; Isono, Yoshitada

2016-07-01

This study focuses on the development of a multi-walled carbon nanotube (MWCNT) forest integrated micromechanical resonator working as a rarefied gas analyzer for nitrogen (N2) and hydrogen (H2) gases in a medium vacuum atmosphere. The resonant response is detected in the form of changes in the resonant frequency or damping effects, depending on the rarefied gas species. The carbon nanotube (CNT) forest on the resonator enhances the effective specific surface area of the resonator, such that the variation of the resonant frequency and the damping effect based on the gas species increase significantly. We developed the fabrication process for the proposed resonator, which consists of standard micro-electro-mechanical systems (MEMS) processes and high-density CNT synthesis on the resonator mass. The high-density CNT synthesis was realized using multistep alternate coating of two types of ferritin proteins that act as catalytic iron particles. Two devices with different CNT densities were fabricated and characterized to evaluate the effect of the surface area of the CNT forest on the resonant response as a function of gas pressures ranging from 0.011 to 1 Pa for N2 and H2. Considering the damping effect, we found that the device with higher density was able to distinguish N2 and H2 clearly, whereas the device with lower density showed no difference between N2 and H2. We confirmed that a larger surface area showed a higher damping effect. These results were explained based on the kinetic theory of gases. In the case of resonant frequency, the relative resonant frequency shift increased with gas pressure and surface area because of the adsorption of gas molecules on the resonator surfaces. Higher density CNT forest adsorbed more gas molecules on the surfaces. The developed CNT forest integrated micromechanical resonator could successfully detect N2 and H2 gases and distinguish between them under pressures of 1 Pa.

Size effects of single-walled carbon nanotubes on in vivo and in vitro pulmonary toxicity

PubMed Central

Fujita, Katsuhide; Fukuda, Makiko; Endoh, Shigehisa; Maru, Junko; Kato, Haruhisa; Nakamura, Ayako; Shinohara, Naohide; Uchino, Kanako; Honda, Kazumasa

2015-01-01

Abstract To elucidate the effect of size on the pulmonary toxicity of single-wall carbon nanotubes (SWCNTs), we prepared two types of dispersed SWCNTs, namely relatively thin bundles with short linear shapes (CNT-1) and thick bundles with long linear shapes (CNT-2), and conducted rat intratracheal instillation tests and in vitro cell-based assays using NR8383 rat alveolar macrophages. Total protein levels, MIP-1α expression, cell counts in BALF, and histopathological examinations revealed that CNT-1 caused pulmonary inflammation and slower recovery and that CNT-2 elicited acute lung inflammation shortly after their instillation. Comprehensive gene expression analysis confirmed that CNT-1-induced genes were strongly associated with inflammatory responses, cell proliferation, and immune system processes at 7 or 30 d post-instillation. Numerous genes were significantly upregulated or downregulated by CNT-2 at 1 d post-instillation. In vitro assays demonstrated that CNT-1 and CNT-2 SWCNTs were phagocytized by NR8383 cells. CNT-2 treatment induced cell growth inhibition, reactive oxygen species production, MIP-1α expression, and several genes involved in response to stimulus, whereas CNT-1 treatment did not exert a significant impact in these regards. These results suggest that SWCNTs formed as relatively thin bundles with short linear shapes elicited delayed pulmonary inflammation with slower recovery. In contrast, SWCNTs with a relatively thick bundle and long linear shapes sensitively induced cellular responses in alveolar macrophages and elicited acute lung inflammation shortly after inhalation. We conclude that the pulmonary toxicity of SWCNTs is closely associated with the size of the bundles. These physical parameters are useful for risk assessment and management of SWCNTs. PMID:25865113

Multiscale mechanics of the lateral pressure effect on enhancing the load transfer between polymer coated CNTs.

PubMed

Yazdandoost, Fatemeh; Mirzaeifar, Reza; Qin, Zhao; Buehler, Markus J

2017-05-04

While individual carbon nanotubes (CNTs) are known as one of the strongest fibers ever known, even the strongest fabricated macroscale CNT yarns and fibers are still significantly weaker than individual nanotubes. The loss in mechanical properties is mainly because the deformation mechanism of CNT fibers is highly governed by the weak shear strength corresponding to sliding of nanotubes on each other. Adding polymer coating to the bundles, and twisting the CNT yarns to enhance the intertube interactions are both efficient methods to improve the mechanical properties of macroscale yarns. Here, we perform molecular dynamics (MD) simulations to unravel the unknown deformation mechanism in the intertube polymer chains and also local deformations of the CNTs at the atomistic scale. Our results show that the lateral pressure can have both beneficial and adverse effects on shear strength of polymer coated CNTs, depending on the local deformations at the atomistic scale. In this paper we also introduce a bottom-up bridging strategy between a full atomistic model and a coarse-grained (CG) model. Our trained CG model is capable of incorporating the atomistic scale local deformations of each CNT to the larger scale collect behavior of bundles, which enables the model to accurately predict the effect of lateral pressure on larger CNT bundles and yarns. The developed multiscale CG model is implemented to study the effect of lateral pressure on the shear strength of straight polymer coated CNT yarns, and also the effect of twisting on the pull-out force of bundles in spun CNT yarns.

Nonhomogeneous morphology and the elastic modulus of aligned carbon nanotube films

NASA Astrophysics Data System (ADS)

Won, Yoonjin; Gao, Yuan; Guzman de Villoria, Roberto; Wardle, Brian L.; Xiang, Rong; Maruyama, Shigeo; Kenny, Thomas W.; Goodson, Kenneth E.

2015-11-01

Carbon nanotube (CNT) arrays offer the potential to develop nanostructured materials that leverage their outstanding physical properties. Vertically aligned carbon nanotubes (VACNTs), also named CNT forests, CNT arrays, or CNT turfs, can provide high heat conductivity and sufficient mechanical compliance to accommodate thermal expansion mismatch for use as thermal interface materials (TIMs). This paper reports measurements of the in-plane moduli of vertically aligned, single-walled CNT (SWCNT) and multi-walled CNT (MWCNT) films. The mechanical response of these films is related to the nonhomogeneous morphology of the grown nanotubes, such as entangled nanotubes of a top crust layer, aligned CNTs in the middle region, and CNTs in the bottom layer. To investigate how the entanglements govern the overall mechanical moduli of CNT films, we remove the crust layer consisting of CNT entanglements by etching the CNT films from the top. A microfabricated cantilever technique shows that crust removal reduces the resulting moduli of the etched SWCNT films by as much as 40%, whereas the moduli of the etched MWCNT films do not change significantly, suggesting a minimal crust effect on the film modulus for thick MWCNT films (>90 μm). This improved understanding will allow us to engineer the mechanical moduli of CNT films for TIMs or packaging applications.

Structural CNT Composites Part II: Assessment of CNT Yarns as Reinforcement for Composite Overwrapped Pressure Vessels

NASA Technical Reports Server (NTRS)

Kim, Jae-Woo; Sauti, Godfrey; Cano, Roberto J.; Wincheski, Russell A.; Ratcliffe, James G.; Czabaj, Michael; Siochi, Emilie J.

2015-01-01

Carbon nanotubes (CNTs) are one-dimensional nanomaterials with outstanding electrical and thermal conductivities and mechanical properties. This combination of properties offers routes to enable lightweight structural aerospace components. Recent advances in the manufacturing of CNTs have made bulk forms such as yarns, tapes and sheets available in commercial quantities to permit the evaluation of these materials for aerospace use, where the superior tensile properties of CNT composites can be exploited in tension dominated applications such as composite overwrapped pressure vessels (COPVs). To investigate their utility in this application, aluminum rings were overwrapped with thermoset/CNT yarn composite and their mechanical properties measured. CNT composite overwrap characteristics such as processing method, CNT/resin ratio, and applied tension during CNT yarn winding were varied to determine their effects on the mechanical performance of the CNT composite overwrapped Al rings (CCOARs). Mechanical properties of the CCOARs were measured under static and cyclic loads at room, elevated, and cryogenic temperatures to evaluate their mechanical performance relative to bare Al rings. At room temperature, the breaking load of CCOARs with a 10.8% additional weight due to the CNT yarn/thermoset overwrap increased by over 200% compared to the bare Al ring. The quality of the wound CNT composites was also investigated using x-ray computed tomography.

Identification of Complex Carbon Nanotube Structures

NASA Technical Reports Server (NTRS)

Han, Jie; Saini, Subhash (Technical Monitor)

1998-01-01

A variety of complex carbon nanotube (CNT) structures have been observed experimentally. These include sharp bends, branches, tori, and helices. They are believed to be formed by using topological defects such as pentagons and heptagons to connect different CNT. The effects of type, number, and arrangement (separation and orientation) of defects on atomic structures and energetics of complex CNT are investigated using topology, quantum mechanics and molecular mechanics calculations. Energetically stable models are derived for identification of observed complex CNT structures.

Interaction of cholesterol with carbon nanotubes: A density functional theory study

NASA Astrophysics Data System (ADS)

Ciani, Anthony J.; Gupta, Bikash C.; Batra, Inder P.

2008-07-01

Carbon nanotubes (CNT) are being presented as medical devices at an increasing rate. To date, they have been suggested as targets for the thermal ablation of cancers, as delivery systems for pharmaceuticals, and as bio-sensors. A common thread amongst these applications is that CNTs are used as a delivery vector for some pharmaceutical into the body. We consider here the possibility that CNTs might be used as a device to trap and remove chemicals, particularly cholesterol, from a living organism. We have performed ab-initio calculations to determine how cholesterol might interact with CNTs placed inside the body. We have found that cholesterol exhibits no particular affinity for or effect on a bare CNT; however, its binding energy can be increased by functionalizing the CNT with a Ca adatom. We found that a Ca adatom on the wall of a CNT increases the binding energy of cholesterol to a CNT by around 1.5 eV, regardless of the nanotube's diameter. The presence of the cholesterol does not affect the band structure of the CNT, but the Ca atom does have an effect near the Fermi level. This indicates that a CNT based detector could function by detecting the alteration to the electronic structure caused by the induced adsorption of an adatom in the trinary system of CNT + cholesterol + adatom.

Foldable Thermoelectric Materials: Improvement of the Thermoelectric Performance of Directly Spun CNT Webs by Individual Control of Electrical and Thermal Conductivity.

PubMed

An, Cheng Jin; Kang, Young Hun; Lee, A-Young; Jang, Kwang-Suk; Jeong, Youngjin; Cho, Song Yun

2016-08-31

We suggest the fabrication of foldable thermoelectric (TE) materials by embedding conducting polymers into Au-doped CNT webs. The CNT bundles, which are interconnected by a direct spinning method to form 3D networks without interfacial contact resistance, provide both high electrical conductivity and high carrier mobility. The ZT value of the spun CNT web is significantly enhanced through two simple processes. Decorating the porous CNT webs with Au nanoparticles increases the electrical conductivity, resulting in an optimal ZT of 0.163, which represents a more than 2-fold improvement compared to the ZT of pristine CNT webs (0.079). After decoration, polyaniline (PANI) is integrated into the Au-doped CNT webs both to improve the Seebeck coefficient by an energy-filtering effect and to decrease the thermal conductivity by the phonon-scattering effect. This leads to a ZT of 0.203, which is one of the highest ZT values reported for organic TE materials. Moreover, Au-doped CNT/PANI web is ultralightweight, free-standing, thermally stable, and mechanically robust, which makes it a viable candidate for a hybrid TE conversion device for wearable electronics. When a 20 K temperature gradient is applied to the TE module consisting of seven p-n couples, 1.74 μW of power is generated.

Molecular transport properties through carbon nanotube membrane

NASA Astrophysics Data System (ADS)

Majumder, Mainak

Molecular transport through hollow cores of crystalline carbon nanotubes (CNTs) are of considerable interest from the fundamental and application point of view. This dissertation focuses on understanding molecular transport through a membrane platform consisting of open ended CNTs with ˜ 7 nm core diameter and ˜ 1010 CNTs/cm2 encapsulated in an inert polymer matrix. While ionic diffusion through the membrane is close to bulk diffusion expectations, gases and liquids were respectively observed to be transported ˜ 10 times faster than Knudsen diffusion and ˜ 10000--100000 times faster than hydrodynamic flow predictions. This phenomenon has been attributed to the non-interactive and frictionless graphitic interface. Functionalization of the CNT tips was observed to change selectivity and flux through the CNT membranes with analogy to 'gate-keeper' functionality in biological membranes. An electro-chemical diazonium grafting chemistry was utilized for enhancing the functional density on the CNT membranes. A strategy to confine the reactions at the CNT tips by a fast flowing liquid column was also designed. Characterization using electrochemical impedance spectroscopy and dye assay indicated ˜ 5--6 times increase in functional density. Electrochemical impedance spectroscopy experiments on CNT membrane/electrode functionalized with charged macro-molecules showed voltage-controlled conformational change. Similar chemistry has been applied for realizing 'voltage-gated' transport channels with potential application in trans-dermal drug delivery. Electrically-facilitated transport (a geometry in which an electric field gradient acts across the membrane) through the CNT and functionalized CNT membranes was observed to be electrosmotically controlled. Finally, a simulation framework based on continuum electrostatics and finite elements has been developed to further the understanding of transport through the CNT membranes. KEYWORDS: carbon nanotube membrane, nano-scale hydrodynamics, diazonium grafting, voltage-gated membrane, finite element analysis

Stable iodide doping induced by photonic curing for carbon nanotube transparent conductive films

NASA Astrophysics Data System (ADS)

Wachi, Atsushi; Nishikawa, Hiroyuki; Zhou, Ying; Azumi, Reiko

2018-06-01

Doping has become crucial for achieving stable and high-performance conductive transparent carbon nanotube (CNT) films. In this study, we systematically investigate the doping effects of a few materials including alkali metal iodides, nonmetal iodide, and metals. We demonstrate that photonic curing can enhance the doping effects, and correspondingly improve the conductivity of CNT films, and that such iodides have better doping effects than metals. In particular, doping with a nonmetal compound (NH4I) shows the largest potential to improve the conductivity of CNT films. Typically, doping with metal iodides reduces the sheet resistance (R S) of CNT films with 70–80% optical transmittances at λ = 550 nm from 600–2400 to 250–440 Ω/square, whereas doping with NH4I reduces R S to 57 and 84 Ω/square at 74 and 84% optical transmittances, respectively. Interestingly, such a doped CNT film exhibits only a slight increase in sheet resistance under an extreme environment of high temperature (85 °C) and high relative humidity (85%) for 350 h. The results suggest that photonic-curing-induced iodide doping is a promising approach to producing high-performance conductive transparent CNT films.

Photoflash thermal diffusivity measurement of carbon nanotube-filled PVDF composite at low temperature

NASA Astrophysics Data System (ADS)

Moksin, M. M.; Haydari, M.; Husin, M. S.; Yahya, N.; Azmi, B. Z.

2013-09-01

The suitability of a simple photoflash technique was further examined in the measurement of thermal diffusivity of nanotube-filled polyvinylidene difluoride (PVDF) film composites at low temperature. The effect of temperature and carbon nanotube (CNT) composition in PVDF composite on its thermal diffusivity is presented as equivalent to the effect of changing thermal phonon mean free path. It is done by assuming no other thermal carrier effects other than from phonons detected during measurement by using photoflash technique. The results show that thermal diffusivity of CNT-filled PVDF film composites was found to have consistently increased with increasing the CNT concentration or decreasing temperature, as in the case of insulators with dominant phonon thermal carriers. At any particular temperature, a dramatic increase in thermal diffusivity was noticed at the beginning as the CNT concentration was systematically increased up to a 1% turning point, from which the thermal diffusivity increased further at a much smaller rate with the CNT addition up to 10%. The thermal diffusivity of the samples was in the range of about (10-35) × 10- 8 m2/s depending on the temperature and the CNT concentration of the composites.

Influence of composite processing on the properties of CNT grown on carbon surfaces

NASA Astrophysics Data System (ADS)

Guignier, Claire; Bueno, Marie-Ange; Camillieri, Brigitte; Durand, Bernard

2018-01-01

Carbon nanotubes (CNT) grafted on carbon fibres (CF) are the subject of more and more studies on the reinforcement of composite materials thanks to the CNT' mechanical properties. This study concerns the growth of CNT directly on CF by the flame method, which is an assembly-line process. However the industrial-scale use of this method and of the composite processing leads to stresses on the CNT-grafted fabrics, such as friction and pulling-out. The aim of this study is to determine the behaviour of the CNT under these kinds of stresses and to study theirs consequences in composite processing. For this purpose, adhesion tests and friction tests were performed as well as analysis of the surface by Scanning Electron Microscopy (SEM), Raman spectroscopy, and energy-dispersive X-ray spectroscopy (EDX). In friction tests, CNT formed a transfer film, and its effect on the wettability of the fabric with epoxy resin is determined. Finally, the wear of the CNT does not influence the wettability of the fabric. Furthermore, it is proven that the nature of the catalyst needed to grow the CNT modifies the behaviour of the surface.

Reinforced carbon nanotubes as electrically conducting and flexible films for space applications.

PubMed

Atar, Nurit; Grossman, Eitan; Gouzman, Irina; Bolker, Asaf; Hanein, Yael

2014-11-26

Chemical vapor deposition (CVD)-grown entangled carbon nanotube (CNT) sheets are characterized by high electrical conductivity and durability to bending and folding. However, since freestanding CNT sheets are mechanically weak, they cannot be used as stand-alone flexible films. In this work, polyimide (PI) infiltration into entangled cup-stacked CNT (CSCNT) sheets was studied to form electrically conducting, robust, and flexible films for space applications. The infiltration process preserved CNTs' advantageous properties (i.e., conductivity and flexibility), prevented CNT agglomeration, and enabled CNT patterning. In particular, the CNT-PI films exhibited ohmic electrical conductance in both the lateral and vertical directions, with a sheet resistivity as low as 122 Ω/□, similar to that of as-grown CNT sheets, with minimal effect of the insulating matrix. Moreover, this high conductivity was preserved under mechanical and thermal manipulations. These properties make the reported CNT-PI films excellent candidates for applications where flexibility, thermal stability, and electrical conductivity are required. Particularly, the developed CNT-PI films were found to be durable in space environment hazards such as high vacuum, thermal cycling, and ionizing radiation, and hence they are suggested as an alternative for the electrostatic discharge (ESD) protection layer in spacecraft thermal blankets.

Photocatalytic performance of electrospun CNT/TiO2 nanofibers in a simulated air purifier under visible light irradiation.

PubMed

Wongaree, Mathana; Chiarakorn, Siriluk; Chuangchote, Surawut; Sagawa, Takashi

2016-11-01

The photocatalytic treatment of gaseous benzene under visible light irradiation was developed using electrospun carbon nanotube/titanium dioxide (CNT/TiO 2 ) nanofibers as visible light active photocatalysts. The CNT/TiO 2 nanofibers were fabricated by electrospinning CNT/poly(vinyl pyrrolidone) (PVP) solution followed by the removal of PVP by calcination at 450 °C. The molar ratio of CNT/TiO 2 was fixed at 0.05:1 by weight, and the quantity of CNT/TiO 2 loaded in PVP solution varied between 30 and 60 % wt. CNT/TiO 2 nanofibers have high specific surface area (116 m 2 /g), significantly higher than that of TiO 2 nanofibers (44 m 2 /g). The photocatalytic performance of the CNT/TiO 2 nanofibers was investigated by decolorization of 1 × 10 -5  M methylene blue (MB) dye (in water solution) and degradation of 100 ppm gaseous benzene under visible light irradiation. The 50-CNT/TiO 2 nanofibers (calcined CNT/TiO 2 nanofibers fabricated from a spinning solution of 50 % wt CNT/TiO 2 based on PVP) had higher MB degradation efficiency (58 %) than did other CNT/TiO 2 nanofibers and pristine TiO 2 nanofibers (15 %) under visible light irradiation. The photocatalytic degradation of gaseous benzene under visible light irradiation on filters made of 50-CNT/TiO 2 nanofibers was carried out in a simulated air purifier system. Similar to MB results, the degradation efficiency of gaseous benzene by 50-CNT/TiO 2 nanofibers (52 %) was higher than by other CNT/TiO 2 nanofibers and pristine TiO 2 nanofibers (18 %). The synergistic effects of the larger surface area and lower band gap energy of CNT/TiO 2 nanofibers were presented as strong adsorption ability and greater visible light adsorption. The CNT/TiO 2 nanofiber prepared in this study has potential for use in air purifiers to improve air treatment efficiency with less energy.

Thermal and mechanical analysis of PVA / sulfonated carbon nanotubes composite

NASA Astrophysics Data System (ADS)

Yadav, Vikrant; Sharma, Prem P.; Rajput, Abhishek; Kulshrestha, Vaibhav

2018-04-01

Nanocomposites of polyvinyl alcohol (PVA) and sulfonated carbon nanotubes (s-CNT) with enhanced properties were synthesized successfully. Effect of different amount of sulfonated nanotubes on thermal and mechanical properties of resultant nanocomposites derived from s-CNT and PVA were studied. Structural analysis for functionalization of CNT was done by using FTIR spectra. Thermal and mechanical analysis were done by using TGA, DSC and UTM. Nanocomposite containing s-CNT shows higher elastic moduli, higher melting temperature in consort with lower weight loss at same temperature, compared with pristine PVA. The novelty of this work is to use PVA/s-CNT based composites with improved thermomechanical properties in different nanotechnologies.

Electrochemical supramolecular recognition of hemin-carbon composites

NASA Astrophysics Data System (ADS)

Le, Hien Thi Ngoc; Jeong, Hae Kyung

2018-04-01

Hemin-graphite oxide-carbon nanotube (hemin-GO-CNT) and hemin-thermally reduced graphite oxide-carbon nanotube (hemin-TRGO-CNT) composites are synthesized and investigated for the electrochemical supramolecular recognition by electron transfer between biomolecules (dopamine and hydrogen peroxide) and the composite electrodes. Redox reaction mechanisms of two composites with dopamine and hydrogen peroxide are explained in detail by using cyclic voltammetry and differential pulse voltammetry. Hemin-TRGO-CNT displays higher electrochemical detection for dopamine and hydrogen peroxide than that of hemin-GO-CNT, exhibiting enhancement of the electron transfer due to the effective immobilization of redox couple of hemin (Fe2+/Fe3+) on the TRGO-CNT surface.

Dramatic nano-fluidic properties of carbon nanotube membranes as a platform for protein channel mimetics

NASA Astrophysics Data System (ADS)

Hinds, Bruce

2013-03-01

Carbon nanotubes have three key attributes that make them of great interest for novel membrane applications: 1) atomically flat graphite surface allows for ideal fluid slip boundary conditions and extremely fast flow rates 2) the cutting process to open CNTs inherently places functional chemistry at CNT core entrance for chemical selectivity and 3) CNT are electrically conductive allowing for electrochemical reactions and application of electric fields gradients at CNT tips. Pressure driven flux of a variety of solvents (H2O, hexane, decane ethanol, methanol) are 4-5 orders of magnitude higher than conventional Newtonian flow [Nature 2005, 438, 44] due to atomically flat graphite planes inducing nearly ideal slip conditions. However this is eliminated with selective chemical functionalization [ACS Nano 2011 5(5) 3867-3877] needed to give chemical selectivity. These unique properties allow us to explore the hypothesis of producing ``Gatekeeper'' membranes that mimic natural protein channels to actively pump through rapid nm-scale channels. With anionic tip functionality strong electroosmotic flow is induced by unimpeded cation flow with similar 10,000 fold enhancements [Nature Nano 2012 7(2) 133-39]. With enhanced power efficiency, carbon nanotube membranes were employed as the active element of a switchable transdermal drug delivery device that can facilitate more effective treatments of drug abuse and addiction. Recently methods to deposit Pt monolayers on CNT surface have been developed making for highly efficient catalytic platforms. Discussed are other applications of CNT protein channel mimetics, for large area robust engineering platforms, including water purification, flow battery energy storage, and biochemical/biomass separations. DOE EPSCoR (DE-FG02-07ER46375) and DARPA, W911NF-09-1-0267

Evaluation of Pd Nanoparticle-Decorated CeO2-MWCNT Nanocomposite as an Electrocatalyst for Formic Acid Fuel Cells

NASA Astrophysics Data System (ADS)

Saleem, Junaid; Safdar Hossain, SK.; Al-Ahmed, Amir; Rahman, Ateequr; McKay, Gordon; Hossain, Mohammed M.

2018-04-01

In this work, CeO2-modified Pd/CeO2-carbon nanotube (CNT) electrocatalyst for the electro-oxidation of formic acid has been investigated. The support CNT was first modified with different amounts (5-30 wt.%) of CeO2 using a precipitation-deposition method. The electrocatalysts were developed by dispersing Pd on the CeO2-CNT supports using the borohydride reduction method. The synthesized electrocatalysts were analyzed for composition, morphology and electronic structure using x-ray diffraction (XRD), scanning electron microscopy with energy-dispersive x-ray spectroscopy (SEM/EDX), transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA) techniques. The formation of Pd nanoparticles on the CeO2-CNT support was confirmed using TEM. The activity of Pd/CeO2-CNT and of Pd-CNT samples upon oxidation of formic acid was evaluated by using carbon monoxide stripping voltammetry, cyclic voltammetry, and chronoamperometry. The addition of moderate amounts of cerium oxide (up to 10 wt.%) significantly improved the activity of Pd/CeO2-CNT compared to the unmodified Pd-CNT. Pd/10 wt.% CeO2-CNT showed a current density of 2 A mg-1, which is ten times higher than that of the unmodified Pd-CNT (0.2 A mg-1). Similarly, the power density obtained for Pd/10 wt.% CeO2-CNT in an air-breathing formic acid fuel cell was 6.8 mW/cm2 which is two times higher than Pd-CNT (3.2 mW/cm2), thus exhibiting the promotional effects of CeO2 to Pd/CeO2-CNT. A plausible justification for the improved catalytic performance and stability is provided in the light of the physical characterization results.

Carbon nanotubes as carriers of Panax ginseng metabolites and enhancers of ginsenosides Rb1 and Rg1 anti-cancer activity

NASA Astrophysics Data System (ADS)

Lahiani, Mohamed H.; Eassa, Souzan; Parnell, Charlette; Nima, Zeid; Ghosh, Anindya; Biris, Alexandru S.; Khodakovskaya, Mariya V.

2017-01-01

A major benefit to nanomaterial based-medicine is the ability to provide nanosized vehicles for sporadic metabolites. Here, we describe how the conjugation of valuable ginseng secondary metabolites (ginsenoside Rb1 or Rg1) with carbon nanotubes (CNT) can enhance their anti-proliferative and anti-cancer effects. Ginsenoside-CNT conjugate (Rb-CNT or Rg-CNT) permitted the ginsenosides to be used at a low dose, yet achieve a higher incidence of cancer killing. We were able to demonstrate that the ginsenoside-CNT conjugate can decrease cell viability up to 62% in breast cancer cells (MCF-7) and enhance antiproliferation of drug-resistant pancreatic cancer cells (PANC-1) by 61%. The interaction of the ginsenoside-CNT conjugate with breast cancer cells was studied using Raman Spectroscopy mapping. Total transcriptome profiling (Affymetrix platform) of MCF-7 cells treated with the ginsenoside-CNT conjugate shows that a number of cellular, apoptotic and response to stimulus processes were affected. Therefore, our data confirmed the potential use of CNT as a drug delivery system.

Toxicity study of complex CNT-PEG(-NH2)-DOX synthesis on neuroblastoma cells

NASA Astrophysics Data System (ADS)

Nurulhuda, I.; Mazatulikhma, M. Z.; Alrokayan, S.; Khan, H.; Rusop, M.

2018-05-01

The synthesized carbon nanotubes was functionalized with PEG and drug (doxorubicin) was tested on neuroblastoma cells. The treatment was done for 24 and 48 h. The concentration of CNT and doxorubicin were at 2.5, 5, 10 µg/ml and 0.5, 0.1, 0.05 µM, respectively. The result showed the longer time treatment do have effect on the cells viability and the complex functionalized CNT have high cells viability rather than the drug and CNT treatment alone.

Effects of propagational factors on quantum wires in close parallel proximity

NASA Astrophysics Data System (ADS)

Wilson, David A.

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Amino acid analogues bind to carbon nanotube via π-π interactions: Comparison of molecular mechanical and quantum mechanical calculations

NASA Astrophysics Data System (ADS)

Yang, Zaixing; Wang, Zhigang; Tian, Xingling; Xiu, Peng; Zhou, Ruhong

2012-01-01

Understanding the interaction between carbon nanotubes (CNTs) and biomolecules is essential to the CNT-based nanotechnology and biotechnology. Some recent experiments have suggested that the π-π stacking interactions between protein's aromatic residues and CNTs might play a key role in their binding, which raises interest in large scale modeling of protein-CNT complexes and associated π-π interactions at atomic detail. However, there is concern on the accuracy of classical fixed-charge molecular force fields due to their classical treatments and lack of polarizability. Here, we study the binding of three aromatic residue analogues (mimicking phenylalanine, tyrosine, and tryptophan) and benzene to a single-walled CNT, and compare the molecular mechanical (MM) calculations using three popular fixed-charge force fields (OPLSAA, AMBER, and CHARMM), with quantum mechanical (QM) calculations using the density-functional tight-binding method with the inclusion of dispersion correction (DFTB-D). Two typical configurations commonly found in π-π interactions are used, one with the aromatic rings parallel to the CNT surface (flat), and the other perpendicular (edge). Our calculations reveal that compared to the QM results the MM approaches can appropriately reproduce the strength of π-π interactions for both configurations, and more importantly, the energy difference between them, indicating that the various contributions to π-π interactions have been implicitly included in the van der Waals parameters of the standard MM force fields. Meanwhile, these MM models are less accurate in predicting the exact structural binding patterns (matching surface), meaning there are still rooms to be improved. In addition, we have provided a comprehensive and reliable QM picture for the π-π interactions of aromatic molecules with CNTs in gas phase, which might be used as a benchmark for future force field developments.

Amino acid analogues bind to carbon nanotube via π-π interactions: comparison of molecular mechanical and quantum mechanical calculations.

PubMed

Yang, Zaixing; Wang, Zhigang; Tian, Xingling; Xiu, Peng; Zhou, Ruhong

2012-01-14

Understanding the interaction between carbon nanotubes (CNTs) and biomolecules is essential to the CNT-based nanotechnology and biotechnology. Some recent experiments have suggested that the π-π stacking interactions between protein's aromatic residues and CNTs might play a key role in their binding, which raises interest in large scale modeling of protein-CNT complexes and associated π-π interactions at atomic detail. However, there is concern on the accuracy of classical fixed-charge molecular force fields due to their classical treatments and lack of polarizability. Here, we study the binding of three aromatic residue analogues (mimicking phenylalanine, tyrosine, and tryptophan) and benzene to a single-walled CNT, and compare the molecular mechanical (MM) calculations using three popular fixed-charge force fields (OPLSAA, AMBER, and CHARMM), with quantum mechanical (QM) calculations using the density-functional tight-binding method with the inclusion of dispersion correction (DFTB-D). Two typical configurations commonly found in π-π interactions are used, one with the aromatic rings parallel to the CNT surface (flat), and the other perpendicular (edge). Our calculations reveal that compared to the QM results the MM approaches can appropriately reproduce the strength of π-π interactions for both configurations, and more importantly, the energy difference between them, indicating that the various contributions to π-π interactions have been implicitly included in the van der Waals parameters of the standard MM force fields. Meanwhile, these MM models are less accurate in predicting the exact structural binding patterns (matching surface), meaning there are still rooms to be improved. In addition, we have provided a comprehensive and reliable QM picture for the π-π interactions of aromatic molecules with CNTs in gas phase, which might be used as a benchmark for future force field developments.

Investigation of phonon transport and thermal boundary conductance at the interface of functionalized SWCNT and poly (ether-ketone)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Haoxiang; Kumar, Satish, E-mail: satish.kumar@me.gatech.edu; Chen, Liang

2016-09-07

Carbon nanostructures such as carbon nanotube (CNT), graphene, and carbon fibers can be used as fillers in amorphous polymers to improve their thermal properties. In this study, the effect of covalent bonding of CNT with poly(ether ketone) (PEK) on interfacial thermal interactions is investigated using non-equilibrium molecular dynamics simulations. The number of covalent bonds between (20, 20) CNT and PEK is varied in the range of 0–80 (0%–6.25%), and the thermal boundary conductance is computed. The analysis reveals that covalent functionalization of CNT atoms can enhance the thermal boundary conductance by an order of magnitude compared to the non-functionalized CNT-PEKmore » interface at a high degree of CNT functionalization. Besides strengthening the thermal coupling, covalent functionalization is also shown to modify the phonon spectra of CNT. The transient spectral energy analysis shows that the crosslinks cause faster energy exchange from CNT to PEK in different frequency bands. The oxygen atom of hydroxyl group of PEK contributes energy transfer in the low frequency band, while aromatic and carbonyl carbon atoms play a more significant role in high frequency bands. In addition, by analyzing the relaxation time of the spectral temperature of different frequency bands of CNT, it is revealed that with increasing number of bonds, both lower frequency vibrational modes and higher frequency modes efficiently couple across the CNT-PEK interface and contribute in thermal energy transfer from CNT to the matrix.« less

Imaging of soft material with carbon nanotube tip using near-field scanning microwave microscopy.

PubMed

Wu, Zhe; Sun, Wei-Qiang; Feng, Tao; Tang, Shawn Wenjie; Li, Gang; Jiang, Kai-Li; Xu, Sheng-Yong; Ong, Chong Kim

2015-01-01

In this manuscript, a near-field scanning microwave microscope (NSMM) of our own design is introduced while using a multi-walled carbon nanotube (MWCNT) bundle as the tip (referred to as 'CNT tip'). Clear images of gold-patterned numbers, photoresist stripes and corneal endothelial cells (cell line B4G12) were obtained by mapping the resonant frequency fr and S11 amplitude of a given area while the NSMM is operating in tapping mode. The CNT tip helps to improve image quality and reveals more information about the sample as compared to a traditional metallic tip. The CNT tip is flexible and does not scratch the surface of the sample during the scan, which is useful for imaging soft material in biological science. In the imaging of the B4G12 endothelial cells, the nuclei and cytoplasm can be clearly distinguished from the rest of the cell and its surrounding medium. Copyright © 2014 Elsevier B.V. All rights reserved.

Plasma-Sprayed Titania and Alumina Coatings Obtained from Feedstocks Prepared by Heterocoagulation with 1 wt.% Carbon Nanotube

NASA Astrophysics Data System (ADS)

Jambagi, Sudhakar C.; Agarwal, Anish; Sarkar, Nilmoni; Bandyopadhyay, P. P.

2018-05-01

Properties of plasma-sprayed ceramic coatings can be improved significantly by reinforcing such coatings with carbon nanotube (CNT). However, it is difficult to disperse CNT in the plasma spray feedstock owing to its tendency to form agglomerate. A colloidal processing technique, namely heterocoagulation, is effective in bringing about unbundling of CNT, followed by its homogeneous dispersion in the ceramic powder. This report deals with the mixing of micro-sized crushed titania and agglomerated alumina powders with CNT using the heterocoagulation technique. Heterocoagulation of titania was attempted with both cationic and anionic surfactants, and the latter was found to be more effective. Mixing of the oxides and carbon nanotube was also accomplished in a ball mill either in a dry condition or in alcohol, and powders thus obtained were compared with the heterocoagulated powder. The heterocoagulated powder has shown a more homogeneous dispersion of CNT in the oxide. The coatings produced from the heterocoagulated powder demonstrated improvement in hardness, porosity, indentation fracture toughness and elastic modulus. This is attributed to CNT reinforcement.

Interaction Between New Anti-cancer Drug Syndros and CNT(6,6-6) Nanotube for Medical Applications: Geometry Optimization, Molecular Structure, Spectroscopic (NMR, UV/Vis, Excited state), FMO, MEP and HOMO-LUMO Investigation

NASA Astrophysics Data System (ADS)

Sheikhi, Masoome; Shahab, Siyamak; Khaleghian, Mehrnoosh; Kumar, Rakesh

2018-03-01

In the present work, Density Functional Theory (DFT) was first time employed to investigate the interaction between new drug (6aR,10aR)-6,6,9-trimethyl-3-pentyl-6a,7,8,10a-tetrahydrobenzo[c]chromen-1-ol (Syndros) and the CNT(6,6-6) Nanotube in the gaseous phase. The interaction effects of compounds Syndros and CNT (6,6-6) nanotube on the electronic properties, chemical shift tensors and natural charge was also determined and discussed. The electronic spectra of the Syndros and the complex CNT(6,6-6)/Syndros in the gas phase were calculated by Time Dependent Density Functional Theory (TD-DFT) for the formation of adsorption effect on maximum wavelength of the Syndros. Nucleus-Independent Chemical Shifts (NICS) calculations have also been carried out for the compound Syndors and the complex CNT(6,6-6)/Syndros and the aromaticity of the compound Syndors before and after interaction with the CNT(6,6-6) Nanotube was investigated.

Ni Nanobuffer Layer Provides Light-Weight CNT/Cu Fibers with Superior Robustness, Conductivity, and Ampacity.

PubMed

Zou, Jingyun; Liu, Dandan; Zhao, Jingna; Hou, Ligan; Liu, Tong; Zhang, Xiaohua; Zhao, Yonghao; Zhu, Yuntian T; Li, Qingwen

2018-03-07

Carbon nanotube (CNT) fiber has not shown its advantage as next-generation light-weight conductor due to the large contact resistance between CNTs, as reflected by its low conductivity and ampacity. Coating CNT fiber with a metal layer like Cu has become an effective solution to this problem. However, the weak CNT-Cu interfacial bonding significantly limits the mechanical and electrical performances. Here, we report that a strong CNT-Cu interface can be formed by introducing a Ni nanobuffer layer before depositing the Cu layer. The Ni nanobuffer layer remarkably promotes the load and heat transfer efficiencies between the CNT fiber and Cu layer and improves the quality of the deposited Cu layer. As a result, the new composite fiber with a 2 μm thick Cu layer can exhibit a superhigh effective strength >800 MPa, electrical conductivity >2 × 10 7 S/m, and ampacity >1 × 10 5 A/cm 2 . The composite fiber can also sustain 10 000 times of bending and continuously work for 100 h at 90% ampacity.

Nanoscale Structure-Property Relationships of Polyacrylonitrile/CNT Composites as a Function of Polymer Crystallinity and CNT Diameter.

PubMed

Gissinger, Jacob R; Pramanik, Chandrani; Newcomb, Bradley; Kumar, Satish; Heinz, Hendrik

2018-01-10

Polyacrylonitrile (PAN)/carbon nanotube (CNT) composites are used as precursors for ultrastrong and lightweight carbon fibers. However, insights into the structure at the nanoscale and the relationships to mechanical and thermal properties have remained difficult to obtain. In this study, molecular dynamics simulation with accurate potentials and available experimental data were used to describe the influence of different degrees of PAN preorientation and CNT diameter on the atomic-scale structure and properties of the composites. The inclusion of CNTs in the polymer matrix is favored for an intermediate degree of PAN orientation and small CNT diameter whereas high PAN crystallinity and larger CNT diameter disfavor CNT inclusion. The glass transition at the CNT/PAN interface involves the release of rotational degrees of freedom of the polymer backbone and increased mobility of the protruding nitrile side groups in contact with the carbon nanotubes. The glass-transition temperature of the composite increases in correlation with the amount of CNT/polymer interfacial area per unit volume, i.e., in the presence of CNTs, for higher CNT volume fraction,  and inversely with CNT diameter. The increase in glass-transition temperature upon CNT addition is larger for PAN of lower crystallinity than for PAN of higher crystallinity. Interfacial shear strengths of the composites are higher for CNTs of smaller diameter and for PAN with preorientation, in correlation with more favorable CNT inclusion energies. The lowest interfacial shear strength was observed in amorphous PAN for the same CNT diameter. PAN with ∼75% crystallinity exhibited hexagonal patterns of nitrile groups near and far from the CNT interface which could influence carbonization into regular graphitic structures. The results illustrate the feasibility of near-quantitative insights into macroscale properties of polymer/CNT composites from simulations of nanometer-scale composite domains. Guidance is most effective when key assumptions in experiment and simulation are closely aligned, such as exfoliation versus bundling of CNTs, size, type, potential defects of CNTs, and precise measures for polymer crystallinity.

Lambertian white top-emitting organic light emitting device with carbon nanotube cathode

NASA Astrophysics Data System (ADS)

Freitag, P.; Zakhidov, Al. A.; Luessem, B.; Zakhidov, A. A.; Leo, K.

2012-12-01

We demonstrate that white organic light emitting devices (OLEDs) with top carbon nanotube (CNT) electrodes show almost no microcavity effect and exhibit essentially Lambertian emission. CNT top electrodes were applied by direct lamination of multiwall CNT sheets onto white small molecule OLED stack. The devices show an external quantum efficiency of 1.5% and high color rendering index of 70. Due to elimination of the cavity effect, the devices show good color stability for different viewing angles. Thus, CNT electrodes are a viable alternative to thin semitransparent metallic films, where the strong cavity effect causes spectral shift and non-Lambertian angular dependence. Our method of the device fabrication is simple yet effective and compatible with virtually any small molecule organic semiconductor stack. It is also compatible with flexible substrates and roll-to-roll fabrication.

Carbon nanotube/metal-sulfide composite flexible electrodes for high-performance quantum dot-sensitized solar cells and supercapacitors

NASA Astrophysics Data System (ADS)

Muralee Gopi, Chandu V. V.; Ravi, Seenu; Rao, S. Srinivasa; Eswar Reddy, Araveeti; Kim, Hee-Je

2017-04-01

Carbon nanotubes (CNT) and metal sulfides have attracted considerable attention owing to their outstanding properties and multiple application areas, such as electrochemical energy conversion and energy storage. Here we describes a cost-effective and facile solution approach to the preparation of metal sulfides (PbS, CuS, CoS, and NiS) grown directly on CNTs, such as CNT/PbS, CNT/CuS, CNT/CoS, and CNT/NiS flexible electrodes for quantum dot-sensitized solar cells (QDSSCs) and supercapacitors (SCs). X-ray photoelectron spectroscopy, X-ray diffraction, and transmission electron microscopy confirmed that the CNT network was covered with high-purity metal sulfide compounds. QDSSCs equipped with the CNT/NiS counter electrode (CE) showed an impressive energy conversion efficiency (η) of 6.41% and remarkable stability. Interestingly, the assembled symmetric CNT/NiS-based polysulfide SC device exhibited a maximal energy density of 35.39 W h kg-1 and superior cycling durability with 98.39% retention after 1,000 cycles compared to the other CNT/metal-sulfides. The elevated performance of the composites was attributed mainly to the good conductivity, high surface area with mesoporous structures and stability of the CNTs and the high electrocatalytic activity of the metal sulfides. Overall, the designed composite CNT/metal-sulfide electrodes offer an important guideline for the development of next level energy conversion and energy storage devices.

Carbon nanotube/metal-sulfide composite flexible electrodes for high-performance quantum dot-sensitized solar cells and supercapacitors.

PubMed

Muralee Gopi, Chandu V V; Ravi, Seenu; Rao, S Srinivasa; Eswar Reddy, Araveeti; Kim, Hee-Je

2017-04-19

Carbon nanotubes (CNT) and metal sulfides have attracted considerable attention owing to their outstanding properties and multiple application areas, such as electrochemical energy conversion and energy storage. Here we describes a cost-effective and facile solution approach to the preparation of metal sulfides (PbS, CuS, CoS, and NiS) grown directly on CNTs, such as CNT/PbS, CNT/CuS, CNT/CoS, and CNT/NiS flexible electrodes for quantum dot-sensitized solar cells (QDSSCs) and supercapacitors (SCs). X-ray photoelectron spectroscopy, X-ray diffraction, and transmission electron microscopy confirmed that the CNT network was covered with high-purity metal sulfide compounds. QDSSCs equipped with the CNT/NiS counter electrode (CE) showed an impressive energy conversion efficiency (η) of 6.41% and remarkable stability. Interestingly, the assembled symmetric CNT/NiS-based polysulfide SC device exhibited a maximal energy density of 35.39 W h kg -1 and superior cycling durability with 98.39% retention after 1,000 cycles compared to the other CNT/metal-sulfides. The elevated performance of the composites was attributed mainly to the good conductivity, high surface area with mesoporous structures and stability of the CNTs and the high electrocatalytic activity of the metal sulfides. Overall, the designed composite CNT/metal-sulfide electrodes offer an important guideline for the development of next level energy conversion and energy storage devices.

Carbon nanotube epoxy nanocomposites: the effects of interfacial modifications on the dynamic mechanical properties of the nanocomposites.

PubMed

Yoonessi, Mitra; Lebrón-Colón, Marisabel; Scheiman, Daniel; Meador, Michael A

2014-10-08

Surface functionalization of pretreated carbon nanotubes (CNT) using aromatic, aliphatic, and aliphatic ether diamines was performed. The pretreatment of the CNT consisted of either acid- or photo-oxidation. The acid treated CNT had a higher initial oxygen content compared to the photo-oxidized CNT and this resulted in a higher density of functionalization. X-ray photoelectron spectroscopy (XPS) and thermal gravimetric analysis (TGA) were used to verify the presence of the oxygenated and amine moieties on the CNT surfaces. Epoxy/0.1 wt % CNT nanocomposites were prepared using the functionalized CNT and the bulk properties of the nanocomposites were examined. Macroscale correlations between the interfacial modification and bulk dynamic mechanical and thermal properties were observed. The amine modified epoxy/CNT nanocomposites exhibited up to a 1.9-fold improvement in storage modulus (G') below the glass transition (Tg) and up to an almost 4-fold increase above the Tg. They also exhibited a 3-10 °C increase in the glass transition temperature. The aromatic diamine surface modified epoxy/CNT nanocomposites resulted in the largest increase in shear moduli below and above the Tg and the largest increase in the Tg. Surface examination of the nanocomposites with scanning electron microscopy (SEM) revealed indications of a greater adhesion of the epoxy resin matrix to the CNT, most likely due to the covalent bonding.

Carbon nanotube macrofilm-based nanocomposite electrodes for energy applications

NASA Astrophysics Data System (ADS)

Cao, Zeyuan

Finding new electrode materials for energy conversion and storage devices have been the focus of recent research in the fields of science and engineering. Suffering from poor electronic conductivity, chemical and mechanical stability, active electrode materials are usually coupled with different carbon nanostructured materials to form nanocomposite electrodes, showing promising electrochemical performance. Among the carbon nanostructured materials, carbon nanotube (CNT) macrofilms draw great attention owing to their extraordinary properties, such as a large specific surface area, exceptionally high conductivity, porous structure, flexibility, mechanical robustness, and adhesion. They could effectively enhance the electrochemical performance of the incorporated active materials in the nanocomposites. In this dissertation, CNT macrofilm-based nanocomposites are investigated for rechargeable lithium-ion batteries, supercapacitors, and electrocatalysts of fuel cells. The progressive research developed various nanocomposites from cathode materials to anode materials followed by a general nanocomposite solution due to the unique adhesive property of the fragmented CNT macrofilms. The in-situ synthesis strategy are explored to in-situ deposit unlithiated cathode materials V2O5 and lithiated cathode materials LiMn2O4 nanocrystals in the matrix of the CNT macrofilms as nanocomposites to be paired with metallic lithium in half cells. The presence of oxygen-containing functional groups on the surface of the CNT macrofilms after purification can enhance the association with the active materials to enable the facilitated transport of solvated ions to the electrolyte/electrode interfaces and increase the diffusion kinetics, consequently enhancing the battery performance in terms of high specific capacity, rate capability, and cycling stability. It is also significant to demonstrate a reliable, low-cost, and effective route to synthesize the family of metal oxides (MxOy (M=Fe, Co, Ni)) with CNT macofilms as high performance anodes for rechargeable lithium-ion batteries and as catalysts for oxygen reduction/evolution (ORR/OER). All MxOy-CNT macrofilm nanocomposites inherit the high specific capacity and cycling stability for lithium-ion batteries. NiO/SWNT and Co3O4/SWNT (200 °C) have their specialized high catalytic activities for ORR and OER in alkaline solutions, respectively. NiO/SWNT also exhibits an excellent electrochemical performance in asymmetric supercapacitors with a high power and energy density. Experimental measurements on electrochemical kinetics such as potentiostatic/galvanostatic intermittent titration techniques (PITT/GITT) are depended to understand the underlying improved Li+ diffusion behavior of nanocomposites. Critical effects of the film thickness have been identified. The CNT macrofilm with a thickness that is comparable to the characteristic diffusion length of 300~500 nm enables the nanocomposite with the highest Li+ chemical diffusion coefficient and thus an optimal electrochemical performance. The adhesive characteristic of CNT macrofilms is noticed for the first time after fragmentation by ultrasound that origins from irregular structures of laterally 2-D distributed CNT segments. The fragmented CNT macrofilms (FCNT) as "bifunctional" adhesive conductors promote a general approach to construct nanocomposite electrodes with both cathode and anode materials for lithium-ion batteries. An in-situ tribology method combining the wear track imaging and force measurement is employed to evaluate the adhesion strength of the adhesive FCNT conductors. The results show that the FCNT macrofilms have a higher adhesion strength than the conventional polymer binder polyvinylidene fluoride (PVDF). It is confirmed that the fabricated nanocomposite electrodes exhibit high rate and retention capabilities, superior to the electrodes using PVDF and carbon black. Thus, FCNT is recognized to be a competent substitute for polymer binders to maintain mechanical integrity and meanwhile to improve electrical connectivity of active materials in the nanocomposite electrodes. In addition, this new electrode manufacturing technique avoids the utilization of toxic organic solvents and could provide a revolution to traditional battery industry.

The effect of titanium nickel nitride decorated carbon nanotubes-reduced graphene oxide hybrid support for methanol oxidation

NASA Astrophysics Data System (ADS)

Liu, Gen; Pan, Zhanchang; Li, Wuyi; Yu, Ke; Xia, Guowei; Zhao, Qixiang; Shi, Shikun; Hu, Guanghui; Xiao, Chumin; Wei, Zhigang

2017-07-01

Titanium nickel nitride (TiNiN) decorated three-dimensional (3D) carbon nanotubes-reduced graphene oxide (CNT-rGO), a fancy 3D platinum (Pt)-based catalyst hybrid support, is prepared by a solvothermal process followed by a nitriding process, which is tested as anodic catalyst support for the methanol oxidation reaction (MOR). The structure, morphology and composition of the synthesized TiNiN/CNT-rGO exhibits a uniform particle dispersion with high purity and interpenetrating 3D network structure. Notably, Pt/TiNiN/CNT-rGO catalyst exhibits significantly improved catalytic activity and durability for methanol oxidation in comparison with Pt/CNT-rGO and conventional Pt/C (JM). The outstanding electrochemical performance was attributed to structure and properties. That is, the 3D CNT-rGO provided a fast transport network for charge-transfer and mass-transfer as well as TiNiN NPs with good synergistic effect and the strong electronic coupling between different domains in TiNiN/CNT-rGO, thus the catalytic activity of the novel catalyst is greatly improved. These results evidences 3D TiNiN/CNT-rGO as a promising catalyst support for a wide range of applications in fuel cells.

Synthesis and characterization of Au-MWCNT/PEDOT: PSS composite film for optoelectronic applications

NASA Astrophysics Data System (ADS)

Jasna, M.; Anjana, R.; Jayaraj, M. K.

2017-08-01

Recently, flexible organic optoelectronics have got great attention because of their light weight, mechanical flexibility and cost effective fabrication process. Conjugated polymers like PEDOT: PSS are widely used for the transparent electrode applications due to its chemical stability, high conductivity, flexibility and optical transparency in the visible region. Conductivity of the PEDOT: PSS polymer can be enhanced by adding organic solvents or conducting nano fillers like CNT, graphene, etc. Carbon nanotubes are good nano fillers to enhance the conductivity and mechanical strength of PEDOT: PSS composite film. Inthe present work, the effect of gold nano particles in PEDOT: PSS/CNT composite is studied. The conductivity enhancement in PEDOT: PSS/CNT thin films can be attributed to the formation of CNT network in the polymer matrix and conformational change of the PEDOT from benzoid to quinoid structure. Even though the conductivity was enhanced, the transparency of the composite thin films decreased with increase in CNT concentration. To overcome this problem, gold nano particles were attached to CNT walls via chemical route. AuMWCNT/PEDOT: PSS composite films were prepared by spin coating method. TEM images confirmed the decoration of gold nano particles on CNT walls. Electrical and optical properties of the composite films were studied. This simple solution processed conducting films are suitable for optoelectronic applications

Crystalline multiwall carbon nanotubes and their application as a field emission electron source.

PubMed

Liu, Peng; Zhou, Duanliang; Zhang, Chunhai; Wei, Haoming; Yang, Xinhe; Wu, Yang; Li, Qingwei; Liu, Changhong; Du, Bingchu; Liu, Liang; Jiang, Kaili; Fan, Shoushan

2018-05-18

Using super-aligned carbon nanotube (CNT) film, we have fabricated van der Waals crystalline multiwall CNTs (MWCNT) by adopting high pressure and high temperature processing. The CNTs keep parallel to each other and are distributed uniformly. X-ray diffraction characterization shows peaks at the small angle range, which can be assigned to the spacing of the MWCNT crystals. The mechanical, electrical and thermal properties are all greatly improved compared with the original CNT film. The field emission properties of van der Waals crystalline MWCNTs are tested and they show a better surface morphology stability for the large emission current. We have further fabricated a field emission x-ray tube and demonstrated a precise resolution imaging ability.

Polyaniline modified graphene and carbon nanotube composite electrode for asymmetric supercapacitors of high energy density

NASA Astrophysics Data System (ADS)

Cheng, Qian; Tang, Jie; Shinya, Norio; Qin, Lu-Chang

2013-11-01

Graphene and single-walled carbon nanotube (CNT) composites are explored as the electrodes for supercapacitors by coating polyaniline (PANI) nano-cones onto the graphene/CNT composite to obtain graphene/CNT-PANI composite electrode. The graphene/CNT-PANI electrode is assembled with a graphene/CNT electrode into an asymmetric pseudocapacitor and a highest energy density of 188 Wh kg-1 and maximum power density of 200 kW kg-1 are achieved. The structure and morphology of the graphene/CNT composite and the PANI nano-cone coatings are characterized by both scanning electron microscopy and transmission electron microscopy. The excellent performance of the assembled supercapacitors is also discussed and it is attributed to (i) effective utilization of the large surface area of the three-dimensional network structure of graphene-based composite, (ii) the presence of CNT in the composite preventing graphene from re-stacking, and (ii) uniform and vertically aligned PANI coating on graphene offering increased electrical conductivity.

Positive temperature coefficient thermistors based on carbon nanotube/polymer composites

PubMed Central

Zeng, You; Lu, Guixia; Wang, Han; Du, Jinhong; Ying, Zhe; Liu, Chang

2014-01-01

In order to explore availability of carbon nanotube (CNT)-based positive temperature coefficient (PTC) thermistors in practical application, we prepared carbon nanotube (CNT) filled high density polyethylene (HDPE) composites by using conventional melt-mixing methods, and investigated their PTC effects in details. The CNT-based thermistors exhibit much larger hold current and higher hold voltage, increasing by 129% in comparison with the commercial carbon black (CB) filled HDPE thermistors. Such high current-bearing and voltage-bearing capacity for the CNT/HDPE thermistors is mainly attributed to high thermal conductivity and heat dissipation of entangled CNT networks. Moreover, the CNT/HDPE thermistors exhibit rapid electrical response to applied voltages, comparable to commercial CB-based thermistors. In light of their high current-bearing capacity and quick response, the CNT-based thermistors have great potential to be used as high-performance thermistors in practical application, especially in some critical circumstances of high temperature, large applied currents, and high applied voltages. PMID:25327951

Effects of cashew nut testa levels as an alternative to wheat bran in gestating sow diets.

PubMed

Fang, Lin Hu; Hong, Young Gi; Hong, Jin Su; Jeong, Jae Hark; Han, Young Geol; Kwon, In Hyuk; Kim, Yoo Yong

2018-06-01

This study was conducted to evaluate the effects of dietary cashew nut testa (CNT) as an alternative feed ingredient to wheat bran on reproductive performance, litter performance, milk composition, and blood profiles of gestating sows. Forth multiparous sows (Yorkshire×Landrace) were fed experimental diets starting at 35 days of pregnancy and an initial average body weight (BW) of 211.53±8.86 kg. Each sow was assigned to a treatment based on BW, backfat thickness (BF) and parity with 10 sows per treatment. Treatments were as follows: i) corn-soybean meal based diet with 6% of wheat bran (C0); ii) basal diet with 2% of CNT and 4% of wheat bran (C2); iii) basal diet with 4% of CNT and 2% of wheat bran (C4); and iv) basal diet with 6% of CNT (C6). There were no statistically significant differences in BW and BF of gestating sows throughout the experimental period. However, changes in BF (p = 0.09) and the daily feed intake of sows (p = 0.09) tended to linearly increase during the lactation period. The weaning to estrus interval (WEI) showed a quadratic response to CNT treatment (p = 0.02), and the C2 diet showed the shortest WEI. Litter birth weight (p = 0.04) and piglet birth weight (p = 0.06) were linearly decreased with increase in CNT. Furthermore, there had no significant differences in piglet weight and litter weight in 21 day. Insulin concentration at day 70 of gestation was linearly reduced with increasing CNT level in diets (p = 0.03). When 6% CNT replaced wheat bran in gestating sow diets, there were no negative effects on sow performance, but litter birth weight and piglet birth weight were decreased when CNT level increased in gestating sow diets.

Release of (14)C-labelled carbon nanotubes from polycarbonate composites.

PubMed

Rhiem, Stefan; Barthel, Anne-Kathrin; Meyer-Plath, Asmus; Hennig, Michael P; Wachtendorf, Volker; Sturm, Heinz; Schäffer, Andreas; Maes, Hanna M

2016-08-01

Waste disposal of carbon nanotube (CNT) containing products is expected to be the most important pathway for release of CNTs into the environment. In the present work, the use of radiolabelled CNTs ((14)C-CNT) for polycarbonate polymer nanocomposites with 1 wt% (14)C-CNT content allowed for the first time to quantify and differentiate the CNT release according to the type of impact along the materials' ageing history. After an initial exposure of the nanocomposite by solar-like irradiation, further environmental impacts were applied to composite material. They aimed at mimicking disposal site conditions that may induce further ageing effects and CNT release. This study included shaking in water, rapid temperature changes, soaking in humic acid solution as well as waste water effluent, and, finally, gentle mechanical abrasion. All ageing impacts were applied sequentially, both on pristine (control) and on solar-irradiated nanocomposites. All experiments were accompanied by absolute quantification of radioactive release as well as chemical and morphological analyses of the nanocomposite surfaces using infra-red (IR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The morphological analysis showed that spectral irradiation can uncover CNT networks on the outer nanocomposite surface layers by polymer degradation. After having subjected the solar-irradiated nanocomposite to all studied disposal site effect, the total radioactive release was quantified to amount to 64 mg CNT/m(2), whereas only 0.8 mg CNT/m(2) were found for the un-irradiated control sample. Solar degradation of polymers was thus found to significantly increase the propensity of the studied polymer nanocomposites to release CNTs during ageing effects at the product's end-of-life typical for disposal sites. Copyright © 2016. Published by Elsevier Ltd.

Controlled growth of aligned carbon nanotube using pulsed glow barrier discharge

NASA Astrophysics Data System (ADS)

Nozaki, Tomohiro; Kimura, Yoshihito; Okazaki, Ken

2002-10-01

We first achieved a catalytic growth of aligned carbon nanotube (CNT) using atmospheric pressure pulsed glow barrier discharge combined with DC bias (1000 V). Aligned CNT can grow with the directional electric field, and this is a big challenge in barrier discharges since dielectric barrier does not allow DC bias and forces to use AC voltage to maintain stable plasma conditions. To overcome this, we developed a power source generating Gaussian-shape pulses at 20 kpps with 4% duty, and DC bias was applied to the GND electrode where Ni-, Fe-coated substrate existed. With positive pulse, i.e. substrate was the cathode, random growth of CNT was observed at about 10^9 cm-2. Growth rate significantly reduced when applied negative pulse; Negative glow formation near substrate is essential for sufficient supply of radical species to the catalyst. If -DC was biased, aligned CNT with 20 nm was synthesized because negative bias enhanced negative glow formation. Interestingly, 2 to 3 CNTs stuck each other with +DC bias, resulting in 50-70 nm and non-aligned CNT. Atmospheric pressure glow barrier discharges can be highly controlled and be a potential alternative to vacuum plasmas for CVD, micro-scale, nano-scale fabrication.

Growth of Carbon Nanostructure Materials Using Laser Vaporization

NASA Technical Reports Server (NTRS)

Zhu, Shen; Su, Ching-Hua; Lehozeky, S.

2000-01-01

Since the potential applications of carbon nanotubes (CNT) was discovered in many fields, such as non-structure electronics, lightweight composite structure, and drug delivery, CNT has been grown by many techniques in which high yield single wall CNT has been produced by physical processes including arc vaporization and laser vaporization. In this presentation, the growth mechanism of the carbon nanostructure materials by laser vaporization is to be discussed. Carbon nanoparticles and nanotubes have been synthesized using pulsed laser vaporization on Si substrates in various temperatures and pressures. Two kinds of targets were used to grow the nanostructure materials. One was a pure graphite target and the other one contained Ni and Co catalysts. The growth temperatures were 600-1000 C and the pressures varied from several torr to 500 torr. Carbon nanoparticles were observed when a graphite target was used, although catalysts were deposited on substrates before growing carbon films. When the target contains catalysts, carbon nanotubes (CNT) are obtained. The CNT were characterized by scanning electron microscopy, x-ray diffraction, optical absorption and transmission, and Raman spectroscopy. The temperature-and pressure-dependencies of carbon nanotubes' growth rate and size were investigated.

Adsorption mechanism of SF6 decomposed species on pyridine-like PtN3 embedded CNT: A DFT study

NASA Astrophysics Data System (ADS)

Cui, Hao; Zhang, Xiaoxing; Chen, Dachang; Tang, Ju

2018-07-01

Metal-Nx embedded CNT have aroused considerable attention in the field of gas interaction due to their strong catalytic behavior, which provides prospective scopes for gas adsorption and sensing. Detecting SF6 decomposed species in certain devices is essential to guarantee their safe operation. In this work, we performed DFT method and simulated the adsorption of three SF6 decomposed gases (SO2, SOF2 and SO2F2) onto the PtN3 embedded CNT surface, in order to shed light on its adsorption ability and sensing mechanism. Results suggest that the CNT embedded with PtN3 center has strong interaction with these gas molecules, leading to high hybridization between Pt dopant and active atoms inner gas molecules. These interactions are assumed to be chemisorption due to the remarkable Ead and QT, thus resulting in dramatic deformations in electronic structure of PtN3-CNT near the Fermi level. Furthermore, the electronic redistribution cause the conductivity increase of proposed material in three systems, based on frontier molecular orbital theory. Our calculations attempt to suggest novel sensing material that are potentially employed in detection of SF6 decomposed components.

Comment on "Water-processed carbon nanotube/graphene hybrids with enhanced field emission properties" [AIP Advances 5, 097130 (2015)

NASA Astrophysics Data System (ADS)

Rani, Reena; Bhatia, Ravi

2018-03-01

In their research paper, M. Song et al. [AIP ADVANCES 5, 097130 (2015)] have claimed to have achieved enhanced field emission (FE) characteristics of carbon nanotubes (CNT)/graphene hybrids experimentally, exhibiting improved FE parameters e.g. turn-on electric field of 0.79 V/μm, threshold electric field of 1.05 V/μm, maximum emission current density (Jmax) of 5.76 mA/cm2, and field enhancement factor (β) of ˜1.3 × 104. The authors have emphasized on the surprisingly high value of β to be the basis of their claim of achieving superior FE performance which is further attributed to the optimized mass ratio CNT/ graphene, which is 5:1 in the present case. However, the claim based upon high value of β is misleading because it does not corroborate with the obtained Jmax parameter. Also, the obtained value of J is quite low in the mentioned study as compared to the reported values. For an instance, Sameera et al. [J. Appl. Phys. 111, 044307 (2012) & Appl. Phys. Lett. 102, 033102 (2013)] have reported FE properties of CNT composites and reduced graphene oxide with Jmax and β values of the order of ˜102 mA/cm2 and 6 × 103, respectively. Therefore, the conclusions drawn by M. Song et al. [AIP ADVANCES 5, 097130 (2015)] in their paper do no hold.

Effects of multiple polyaniline layers immobilized on carbon nanotube and glutaraldehyde on performance and stability of biofuel cell

NASA Astrophysics Data System (ADS)

Christwardana, Marcelinus; Kwon, Yongchai

2015-12-01

Enzymatic biofuel cell (EBC) employing new catalyst for anode electrode is fabricated. The new catalyst consists of glucose oxidase (GOx), polyaniline (PANI) and carbon nanotube (CNT) that are multiply stacked together and finally the stack layer is surrounded by glutaraldehyde (GA) (GA/[GOx/PANI/CNT]n). To evaluate how the GA/[GOx/PANI/CNT]n layer affects EBC performance and stability, electrochemical characterizations are implemented. Regarding optimization, GA/[GOx/PANI/CNT]3 is determined. For elucidating reaction mechanism between glucose and flavin adenine dinucleotide (FAD) of GA/[GOx/PANI/CNT]3, associated investigations are performed. In the evaluations, drop in reduction current peak of FAD is observed with provisions of glucose and O2, while glucose does not influence FAD reaction without O2, confirming O2 makes mediator role. When the GA/[GOx/PANI/CNT]3 layer is adopted, superior catalytic activity and EBC performance are gained (electron transfer rate constant of 5.1 s-1, glucose sensitivity of 150 ìA mM-1 cm-2, and EBC maximum power density (MPD) of 0.29 mW cm-2). Regarding EBC stability, MPD of EBC adopting GA/[GOx/PANI/CNT]3 maintains up to 93% of their initial value even after four weeks. Although GA is little effective for improving EBC performance, EBC stability is helped by GA due to its adhesion promotion capability with [GOx/PANI/CNT]n layer.

Angular dependent anisotropic terahertz response of vertically aligned multi-walled carbon nanotube arrays with spatial dispersion.

PubMed

Zhou, Yixuan; E, Yiwen; Xu, Xinlong; Li, Weilong; Wang, Huan; Zhu, Lipeng; Bai, Jintao; Ren, Zhaoyu; Wang, Li

2016-12-14

Spatial dispersion effect of aligned carbon nanotubes (CNTs) in the terahertz (THz) region has significance for both theoretical and applied consideration due to the unique intrinsically anisotropic physical properties of CNTs. Herein, we report the angular dependent reflection of p-polarized THz wave from vertically aligned multi-walled CNT arrays in both experiment and theory. The spectra indicate that the reflection depends on the film thickness of vertically aligned CNTs, the incident angle, and the frequency. The calculation model is based on the spatial dispersion effect of aligned CNTs and performed with effective impedance method and the Maxwell-Garnett approximation. The results fit well with the experiment when the thickness of CNT film is thin, which reveals a coherent superposition mechanism of the CNT surface reflection and CNTs/Si interface reflection. For thick CNT films, the CNTs/Si interface response determines the reflection at small incident angles, while the CNTs surface effect dominates at large incident angles. This work investigates the spatial dispersion effect of vertically aligned CNT arrays in the THz region, and paves a way for potential anisotropic THz applications based on CNTs with oblique incidence requirements.

Angular dependent anisotropic terahertz response of vertically aligned multi-walled carbon nanotube arrays with spatial dispersion

NASA Astrophysics Data System (ADS)

Zhou, Yixuan; Yiwen, E.; Xu, Xinlong; Li, Weilong; Wang, Huan; Zhu, Lipeng; Bai, Jintao; Ren, Zhaoyu; Wang, Li

2016-12-01

Spatial dispersion effect of aligned carbon nanotubes (CNTs) in the terahertz (THz) region has significance for both theoretical and applied consideration due to the unique intrinsically anisotropic physical properties of CNTs. Herein, we report the angular dependent reflection of p-polarized THz wave from vertically aligned multi-walled CNT arrays in both experiment and theory. The spectra indicate that the reflection depends on the film thickness of vertically aligned CNTs, the incident angle, and the frequency. The calculation model is based on the spatial dispersion effect of aligned CNTs and performed with effective impedance method and the Maxwell-Garnett approximation. The results fit well with the experiment when the thickness of CNT film is thin, which reveals a coherent superposition mechanism of the CNT surface reflection and CNTs/Si interface reflection. For thick CNT films, the CNTs/Si interface response determines the reflection at small incident angles, while the CNTs surface effect dominates at large incident angles. This work investigates the spatial dispersion effect of vertically aligned CNT arrays in the THz region, and paves a way for potential anisotropic THz applications based on CNTs with oblique incidence requirements.

Electrocatalytic water treatment using carbon nanotube filters modified with metal oxides.

PubMed

Yang, So Young; Vecitis, Chad D; Park, Hyunwoong

2017-01-28

This study examined the electrocatalytic activity of multi-walled carbon nanotube (CNT) filters for remediation of aqueous phenol in a sodium sulfate electrolyte. CNT filters were loaded with antimony-doped tin oxide (Sb-SnO 2 ; SS) and bismuth- and antimony-codoped tin oxide (Bi-Sb-SnO 2 ; BSS) via electrosorption at 2 V for 1 h and then assembled into a flow-through batch reactor as anode-cathode couples with perforated titanium foils. The as-synthesized pristine CNT filters were composed of 50-60-nm-thick tubular carbons with smooth surfaces, whereas the tubes composing the SS-CNT and BSS-CNT filters were slightly thicker and bumpy, because they were coated with SS and BSS particles ~50 nm in size. Electrochemical characterization of the samples indicated a positive shift in the onset potential and a decrease in the current magnitude in the modified CNT filters due to passivation and oxidation inhibition of the bare CNT filters. These filters exhibited a similar adsorption capacity for phenol (5-8%), whereas loadings of SS and BSS enhanced the degradation rate of phenol by ~1.5 and 2.1 times, respectively. In particular, the total organic carbon removal performance and mineralization efficiency of the BSS-CNT filters were approximately twice those of the bare CNT filters. The BSS-CNT filters also exhibited an enhanced oxidation of ferrocyanide [Fe II (CN) 6 4- ], which was not adsorbed onto the CNT filters. The enhanced electrocatalytic performance of the modified CNT filters was attributed to an effective generation of OH radicals. The surfaces of the filters were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy.

Water-processed carbon nanotube/graphene hybrids with enhanced field emission properties

NASA Astrophysics Data System (ADS)

Song, Meng; Xu, Peng; Song, Yenan; Wang, Xu; Li, Zhenhua; Shang, Xuefu; Wu, Huizhen; Zhao, Pei; Wang, Miao

2015-09-01

Integrating carbon nanotubes (CNTs) and graphene into hybrid structures provides a novel approach to three dimensional (3D) materials with advantageous properties. Here we present a water-processing method to create integrated CNT/graphene hybrids and test their field emission properties. With an optimized mass ratio of CNTs to graphene, the hybrid shows a significantly enhanced field emission performance, such as turn-on electric field of 0.79 V/μm, threshold electric field of 1.05 V/μm, maximum current density of 0.1 mA/cm2, and field enhancement factor of ˜1.3 × 104. The optimized mass ratio for field emission emphasizes the importance of both CNTs and graphene in the hybrid. We also hypothesize a possible mechanism for this enhanced field emission performance from the CNT/graphene hybrid. During the solution treatment, graphene oxide behaves as surfactant sheets for CNTs to form a well dispersed solution, which leads to a better organized 3D structure with more conducting channels for electron transport.

Density controlled carbon nanotube array electrodes

DOEpatents

Ren, Zhifeng F [Newton, MA; Tu, Yi [Belmont, MA

2008-12-16

CNT materials comprising aligned carbon nanotubes (CNTs) with pre-determined site densities, catalyst substrate materials for obtaining them and methods for forming aligned CNTs with controllable densities on such catalyst substrate materials are described. The fabrication of films comprising site-density controlled vertically aligned CNT arrays of the invention with variable field emission characteristics, whereby the field emission properties of the films are controlled by independently varying the length of CNTs in the aligned array within the film or by independently varying inter-tubule spacing of the CNTs within the array (site density) are disclosed. The fabrication of microelectrode arrays (MEAs) formed utilizing the carbon nanotube material of the invention is also described.

Intracerebral CpG Immunotherapy with Carbon Nanotubes Abrogates Growth of Subcutaneous Melanomas in Mice

PubMed Central

Fan, Haitao; Zhang, Ian; Chen, Xuebo; Zhang, Leying; Wang, Huaqing; Fonseca, Anna Da; Manuel, Edwin R.; Diamond, Don J.; Raubitschek, Andrew; Badie, Behnam

2012-01-01

Purpose Recently, we showed that intratumoral delivery of low-dose, immunostimulatory CpG oligodeoxynucleotides conjugated with carbon nanotubes (CNT-CpG) was more effective than free CpG and not only eradicated intracranial (i.c.) gliomas, but also induced antitumor immunity that protected mice from subsequent i.c. or systemic tumor rechallenge. Here, we examined if the same “intracerebral immunotherapy” strategy could be applied to the treatment of metastatic brain tumors. Experimental Design Mice with both i.c. and subcutaneous (s.c.) melanomas were injected intratumorally with CNT-CpG into either location. Antitumor responses were assessed by flow cytometry, bioluminescent imaging, and animal survival. Results When given s.c., CNT-CpG response was mostly local, and it only modestly inhibited the growth of i.c. melanomas. However, i.c. CNT-CpG abrogated the growth of not only brain, but also s.c. tumors. Furthermore, compared to s.c. injections, i.c. CNT-CpG elicited a stronger inflammatory response that resulted in more potent antitumor cytotoxicity and improved in vivo trafficking of effector cells into both i.c. and s.c. tumors. To investigate factors that accounted for these observations, CNT-CpG biodistribution and cellular inflammatory responses were examined in both tumor locations. Intracranial melanomas retained the CNT-CpG particles longer and were infiltrated by TLR-9-positive microglia. In contrast, myeloid-derived suppressive cells were more abundant in s.c. tumors. Although depletion of these cells prior to s.c. CNT-CpG therapy enhanced its cytotoxic responses, antitumor responses to brain melanomas were unchanged. Conclusions These findings suggest that intracerebral CNT-CpG immunotherapy is more effective than systemic therapy in generating antitumor responses that target both brain and systemic melanomas. PMID:22904105

Intracerebral CpG immunotherapy with carbon nanotubes abrogates growth of subcutaneous melanomas in mice.

PubMed

Fan, Haitao; Zhang, Ian; Chen, Xuebo; Zhang, Leying; Wang, Huaqing; Da Fonseca, Anna; Manuel, Edwin R; Diamond, Don J; Raubitschek, Andrew; Badie, Behnam

2012-10-15

Recently, we showed that intratumoral delivery of low-dose, immunostimulatory CpG oligodeoxynucleotides conjugated with carbon nanotubes (CNT-CpG) was more effective than free CpG and not only eradicated intracranial (i.c.) gliomas but also induced antitumor immunity that protected mice from subsequent i.c. or systemic tumor rechallenge. Here, we examined whether the same "intracerebral immunotherapy" strategy could be applied to the treatment of metastatic brain tumors. Mice with both i.c. and s.c. melanomas were injected intratumorally with CNT-CpG into either location. Antitumor responses were assessed by flow cytometry, bioluminescent imaging, and animal survival. When given s.c., CNT-CpG response was mostly local, and it only modestly inhibited the growth of i.c. melanomas. However, i.c. CNT-CpG abrogated the growth of not only brain but also s.c. tumors. Furthermore, compared with s.c. injections, i.c. CNT-CpG elicited a stronger inflammatory response that resulted in more potent antitumor cytotoxicity and improved in vivo trafficking of effector cells into both i.c. and s.c. tumors. To investigate factors that accounted for these observations, CNT-CpG biodistribution and cellular inflammatory responses were examined in both tumor locations. Intracranial melanomas retained the CNT-CpG particles longer and were infiltrated by Toll-like receptor (TLR-9)-positive microglia. In contrast, myeloid-derived suppressive cells were more abundant in s.c. tumors. Although depletion of these cells before s.c. CNT-CpG therapy enhanced its cytotoxic responses, antitumor responses to brain melanomas were unchanged. These findings suggest that intracerebral CNT-CpG immunotherapy is more effective than systemic therapy in generating antitumor responses that target both brain and systemic melanomas. ©2012 AACR

Optoelectronic properties and interfacial durability of CNT and ITO on boro-silicate glass and PET substrates with nano- and heterostructural aspects

NASA Astrophysics Data System (ADS)

Park, Joung-Man; Wang, Zuo-Jia; Kwon, Dong-Jun; DeVries, Lawrence

2011-02-01

Nano- and hetero-structures of carbon nanotube (CNT) and indium tin oxide (ITO) can control significantly piezoelectric and optoelectronic properties in Microelectromechanical Systems (MEMS) as sensing and actuator under cyclic loading. Optimized preparing conditions were obtained for multi-functional purpose of the specimen by obtaining the best dispersion and turbidity in the solution. Optical transmittance and electrical properties were investigated for CNT and ITO dipping and spraying coating on boro-silicate glass and polyethylene terephthalate (PET) substrates by electrical resistance measurement under cyclic loading and wettability test. Uniform dip-coating was performed using Wilhelmy plate method due to its simple and convenience. Spraying coating was applied to the specimen additionally. The change in the electrical resistance and optical properties of coated layer were mainly dependent upon the number of dip-coating, the concentration of CNT and ITO solutions, and the surface treatment condition. Electric properties of coating layers were measured using four-point probe method, and surface resistance was calculated using a dual configuration method. Optical transmittance of CNT and ITO coated PET film was also evaluated using UV spectrum. Surface energy and their hydrophilic and hydrophobic properties of CNT and ITO coated substrates were investigated by wettability test via static and dynamic contact angle measurements. As the elapsing time of cyclic loading passed, the stability of surface resistance and thus comparative interfacial adhesion between coated layer and substrates was evaluated to compare the thermodynamic work of adhesion, Wa. As dip-coating number increased, surface resistance of coated CNT decreased, whereas the transmittance decreased step-by-step due to the thicker CNT and ITO networked layer. Nano- and heterostructural effects of CNT and ITO solution on the optical and electrical effects have been studied continuously.

Solid state carbon nanotube device for controllable trion electroluminescence emission

NASA Astrophysics Data System (ADS)

Liang, Shuang; Ma, Ze; Wei, Nan; Liu, Huaping; Wang, Sheng; Peng, Lian-Mao

2016-03-01

Semiconducting carbon nanotubes (CNTs) have a direct chirality-dependent bandgap and reduced dimensionality-related quantum confinement effects, which are closely related to the performance of optoelectronic devices. Here, taking advantage of the large energy separations between neutral singlet excitons and charged excitons, i.e. trions in CNTs, we have achieved for the first time all trion electroluminescence (EL) emission from chirality-sorted (8,3) and (8,4) CNT-based solid state devices. We showed that strong trion emission can be obtained as a result of localized impact excitation and electrically injected holes, with an estimated efficiency of ~5 × 10-4 photons per injected hole. The importance of contact-controlled carrier injection (including symmetric and asymmetric contact configurations) and EL spectral stability for gradually increasing bias were also investigated. The realization of electrically induced pure trion emission opens up a new opportunity for CNT film-based optoelectronic devices, providing a new degree of freedom in controlling the devices to extend potential applications in spin or magnetic optoelectronics fields.Semiconducting carbon nanotubes (CNTs) have a direct chirality-dependent bandgap and reduced dimensionality-related quantum confinement effects, which are closely related to the performance of optoelectronic devices. Here, taking advantage of the large energy separations between neutral singlet excitons and charged excitons, i.e. trions in CNTs, we have achieved for the first time all trion electroluminescence (EL) emission from chirality-sorted (8,3) and (8,4) CNT-based solid state devices. We showed that strong trion emission can be obtained as a result of localized impact excitation and electrically injected holes, with an estimated efficiency of ~5 × 10-4 photons per injected hole. The importance of contact-controlled carrier injection (including symmetric and asymmetric contact configurations) and EL spectral stability for gradually increasing bias were also investigated. The realization of electrically induced pure trion emission opens up a new opportunity for CNT film-based optoelectronic devices, providing a new degree of freedom in controlling the devices to extend potential applications in spin or magnetic optoelectronics fields. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr07468a

Super-strengthening and stabilizing with carbon nanotube harnessed high density nanotwins in metals by shock loading

PubMed Central

Lin, Dong; Saei, Mojib; Suslov, Sergey; Jin, Shengyu; Cheng, Gary J.

2015-01-01

CNTs reinforced metal composites has great potential due to their superior properties, such as light weight, high strength, low thermal expansion and high thermal conductivity. The current strengthening mechanisms of CNT/metal composite mainly rely on CNTs’ interaction with dislocations and CNT’s intrinsic high strength. Here we demonstrated that laser shock loading the CNT/metal composite results in high density nanotwins, stacking fault, dislocation around the CNT/metal interface. The composites exhibit enhanced strength with excellent stability. The results are interpreted by both molecular dynamics simulation and experiments. It is found the shock wave interaction with CNTs induces a stress field, much higher than the applied shock pressure, surrounding the CNT/metal interface. As a result, nanotwins were nucleated under a shock pressure much lower than the critical values to generate twins in metals. This hybrid unique nanostructure not only enhances the strength, but also stabilize the strength, as the nanotwin boundaries around the CNTs help pin the dislocation movement. PMID:26493533

Molecular Dynamics Modeling of Carbon Nanotube Composite Fracture Using ReaxFF

NASA Technical Reports Server (NTRS)

Jensen, Benjamin D.; Wise, Kristopher E.; Odegard, Gregory M.

2016-01-01

Carbon nanotube (CNT) fiber reinforced composites with specific tensile strengths and moduli approaching those of aerospace grade carbon fiber composites have recently been reported. This achievement was enabled by the emerging availability of high N/tex yarns in kilometer-scale quantities. While the production of this yarn is an impressive advance, its strength is still much lower than that of the individual CNTs comprising the yarn. Closing this gap requires understanding load transfer between CNTs at the nanometer dimensional scale. This work uses reactive molecular dynamics simulations to gain an understanding at the nanometer scale of the key factors that determine CNT nanocomposite mechanical performance, and to place more realistic upper bounds on the target properties. While molecular dynamics simulations using conventional force fields can predict elastic properties, the ReaxFF reactive forcefield can also model fracture behavior because of its ability to accurately describe bond breaking and formation during a simulation. The upper and lower bounds of CNT composite properties are investigated by comparing systems composed of CNTs continuously connected across the periodic boundary with systems composed of finite length CNTs. These lengths, effectively infinite for the continuous tubes and an aspect ratio of 13 for the finite length case, result from practical limitations on the number of atoms that can be included in a simulation. Experimentally measured aspect ratios are typically on the order of 100,000, so the calculated results should represent upper and lower limits on experimental mechanical properties. Finally, the effect of various degrees of covalent crosslinking between the CNTs and amorphous carbon matrix is considered to identify the amount of CNT-matrix covalent bonding that maximizes overall composite properties.

Solution Deposition Methods for Carbon Nanotube Field-Effect Transistors

DTIC Science & Technology

2009-06-01

authorized documents. Citation of manufacturer’s or trade names does not constitute an official endorsement or approval of the use thereof. Destroy...processed into FETs using standard microelectronics processing techniques. The resulting devices were characterized using a semiconductor parameter...method will help to determine which conditions are useful for producing CNT devices for chemical sensing and electronic applications. 15. SUBJECT TERMS

Fabrication of a biofuel cell improved by the π-conjugated electron pathway effect induced from a new enzyme catalyst employing terephthalaldehyde

NASA Astrophysics Data System (ADS)

Chung, Yongjin; Hyun, Kyu Hwan; Kwon, Yongchai

2015-12-01

A model explaining the π-conjugated electron pathway effect induced by a novel cross-linker adopted enzyme catalyst is suggested and the performance and stability of an enzymatic biofuel cell (EBC) adopting the new catalyst are evaluated. For this purpose, new terephthalaldehyde (TPA) and conventional glutaraldehyde (GA) cross-linkers are adopted on a glucose oxidase (GOx), polyethyleneimine (PEI) and carbon nanotube (CNT)(GOx/PEI/CNT) structure. GOx/PEI/CNT cross-linked by TPA (TPA/[GOx/PEI/CNT]) results in a superior EBC performance and stability to other catalysts. It is attributed to the π bonds conjugated between the aldehyde of TPA and amine of the GOx/PEI molecules. By π conjugation, electrons bonded with carbon and nitrogen are delocalized, promoting the electron transfer and catalytic activity with an excellent EBC performance. The maximum power density (MPD) of an EBC adopting TPA/[GOx/PEI/CNT] (0.66 mW cm-2) is far better than that of the other EBCs (the MPD of EBC adopting GOx/PEI/CNT is 0.40 mW cm-2). Regarding stability, the covalent bonding formed between TPA and GOx/PEI plays a critical role in preventing the denaturation of GOx molecules, leading to an excellent stability. By repeated measurements of the catalytic activity, TPA/[GOx/PEI/CNT] maintains its activity to 92% of its initial value even after five weeks.A model explaining the π-conjugated electron pathway effect induced by a novel cross-linker adopted enzyme catalyst is suggested and the performance and stability of an enzymatic biofuel cell (EBC) adopting the new catalyst are evaluated. For this purpose, new terephthalaldehyde (TPA) and conventional glutaraldehyde (GA) cross-linkers are adopted on a glucose oxidase (GOx), polyethyleneimine (PEI) and carbon nanotube (CNT)(GOx/PEI/CNT) structure. GOx/PEI/CNT cross-linked by TPA (TPA/[GOx/PEI/CNT]) results in a superior EBC performance and stability to other catalysts. It is attributed to the π bonds conjugated between the aldehyde of TPA and amine of the GOx/PEI molecules. By π conjugation, electrons bonded with carbon and nitrogen are delocalized, promoting the electron transfer and catalytic activity with an excellent EBC performance. The maximum power density (MPD) of an EBC adopting TPA/[GOx/PEI/CNT] (0.66 mW cm-2) is far better than that of the other EBCs (the MPD of EBC adopting GOx/PEI/CNT is 0.40 mW cm-2). Regarding stability, the covalent bonding formed between TPA and GOx/PEI plays a critical role in preventing the denaturation of GOx molecules, leading to an excellent stability. By repeated measurements of the catalytic activity, TPA/[GOx/PEI/CNT] maintains its activity to 92% of its initial value even after five weeks. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr06703k

The impact of different multi-walled carbon nanotubes on the X-band microwave absorption of their epoxy nanocomposites.

PubMed

Che, Bien Dong; Nguyen, Bao Quoc; Nguyen, Le-Thu T; Nguyen, Ha Tran; Nguyen, Viet Quoc; Van Le, Thang; Nguyen, Nieu Huu

2015-01-01

Carbon nanotube (CNT) characteristics, besides the processing conditions, can change significantly the microwave absorption behavior of CNT/polymer composites. In this study, we investigated the influence of three commercial multi-walled CNT materials with various diameters and length-to-diameter aspect ratios on the X-band microwave absorption of epoxy nanocomposites with CNT contents from 0.125 to 2 wt%, prepared by two dispersion methods, i.e. in solution with surfactant-aiding and via ball-milling. The laser diffraction particle size and TEM analysis showed that both methods produced good dispersions at the microscopic level of CNTs. Both a high aspect ratio resulting in nanotube alignment trend and good infiltration of the matrix in the individual nanotubes, which was indicated by high Brookfield viscosities at low CNT contents of CNT/epoxy dispersions, are important factors to achieve composites with high microwave absorption characteristics. The multi-walled carbon nanotube (MWCNT) with the largest aspect ratio resulted in composites with the best X-band microwave absorption performance, which is considerably better than that of reported pristine CNT/polymer composites with similar or lower thicknesses and CNT loadings below 4 wt%. A high aspect ratio of CNTs resulting in microscopic alignment trend of nanotubes as well as a good level of micro-scale CNT dispersion resulting from good CNT-matrix interactions are crucial to obtain effective microwave absorption performance. This study demonstrated that effective radar absorbing MWCNT/epoxy nanocomposites having small matching thicknesses of 2-3 mm and very low filler contents of 0.25-0.5 wt%, with microwave energy absorption in the X-band region above 90% and maximum absorption peak values above 97%, could be obtained via simple processing methods, which is promising for mass production in industrial applications. Graphical AbstractComparison of the X-band microwave reflection loss of epoxy composites of various commercial multi-walled carbon nanotube materials.

A novel multi-wall CNT synthesis technique using conventional CVD with controlled pressure

NASA Astrophysics Data System (ADS)

Kara, M. H. S.; Amir, M. H.; Teh, A. A.; Ahmad, R.; Mahmood, M. R.; Awang, Z.

2012-09-01

In this paper we have demonstrated successfully for the first time, a simple but efficient and reliable approach for the growth of multi walled carbon nanotubes (MWCNTs) with high degree of crystallinity, purity and density under a wide range of growth parameters. Multi-walled carbon nanotubes (MWCNTs) were synthesized at 800 - 950°C by thermal chemical vapor deposition (TCVD) method using a thin nickel film as catalyst and methane gas as carbon source. In this process, two substrates were placed in a long alumina boat inside a double-heater TCVD. One of the substrates was covered with a short upside down alumina boat. The prepared nanotubes were characterized by scanning electron microscopy (SEM) and field emission scanning electron microscopy (FESEM) and it was found that, CNT growth on the covered substrate was improved in terms of quality and density compared to the other uncovered substrate. In addition, the nanotube diameter is reduced more than half. Results also revealed that the temperature gradient played a key factor for growth efficiency and purity of nanotubes. In addition, the diameter of CNT can be influenced by growth temperature too. The catalyst thickness and gas flow rate were found to influence the diameter and density of tubes, whereas the effect of synthesis time was on the CNT length. This growth technique is unique because of its simplicity, high efficiency and its ability to yield CNTs of high purity and density. This finding is supported by Raman spectrometry analysis.

Impact of Silicon Nanocrystal Oxidation on the Nonmetallic Growth of Carbon Nanotubes.

PubMed

Rocks, Conor; Mitra, Somak; Macias-Montero, Manuel; Maguire, Paul; Svrcek, Vladimir; Levchenko, Igor; Ostrikov, Kostya; Mariotti, Davide

2016-07-27

Carbon nanotube (CNT) growth has been demonstrated recently using a number of nonmetallic semiconducting and metal oxide nanoparticles, opening up pathways for direct CNT synthesis from a number of more desirable templates without the need for metallic catalysts. However, CNT growth mechanisms using these nonconventional catalysts has been shown to largely differ and reamins a challenging synthesis route. In this contribution we show CNT growth from partially oxidized silicon nanocrystals (Si NCs) that exhibit quantum confinement effects using a microwave plasma enhanced chemical vapor deposition (PECVD) method. On the basis of solvent and a postsynthesis frgamentation process, we show that oxidation of our Si NCs can be easily controlled. We determine experimentally and explain with theoretical simulations that the Si NCs morphology together with a necessary shell oxide of ∼1 nm is vital to allow for the nonmetallic growth of CNTs. On the basis of chemical analysis post-CNT-growth, we give insight into possible mechanisms for CNT nucleation and growth from our partially oxidized Si NCs. This contribution is of significant importance to the improvement of nonmetallic catalysts for CNT growth and the development of Si NC/CNT interfaces.

Electrical passivation of nonselective bio molecules in carbon nanotubes: Effect of pulse train in serum

NASA Astrophysics Data System (ADS)

Kim, Seok Hyang; Woo, Jun-Myung; Choi, Seongwook; Park, Young June

2015-06-01

We present an experimental and simulation study about a desorption of albumin, a representative nonselective molecules in serum, on carbon nanotube (CNT) surface as an electrical bio sensing channel under the pulse train condition. The motivation of the study on binding kinetics between CNT surface and albumin is to suppress the adsorption of nonselective proteins in blood such as albumin, thereby enhancing the selectivity of the electrical biosensor. To theoretically model the behavior of molecules and ions under the step pulse bias, the physics on the reaction rate, mass transport, and the resulting surface pH-value are considered using the Poisson and drift-diffusion equations. For the simulation model, the phosphate buffered saline is considered as the electrolyte solution and albumin is considered as a representative charged molecule for nonspecific binding in serum. Both the transient simulation and experimental result indicate that the suppression of the nonspecific binding under the pulse train is due to the unsymmetrical field force experienced by the protein during the pulse transitions (high to low and low to high) and the non-symmetry is caused by the different transient times between the electric field and the charge/discharge of the protein according to the surface pH modulation in serum. The experimental and simulation results clearly indicate that the pulse bias suppresses the nonselective bio molecules adsorption at the CNT surface so that the selectivity of the electrical biosensor for detecting the target molecules can be enhanced.

Molecular Modeling of Aerospace Polymer Matrices Including Carbon Nanotube-Enhanced Epoxy

NASA Astrophysics Data System (ADS)

Radue, Matthew S.

Carbon fiber (CF) composites are increasingly replacing metals used in major structural parts of aircraft, spacecraft, and automobiles. The current limitations of carbon fiber composites are addressed through computational material design by modeling the salient aerospace matrix materials. Molecular Dynamics (MD) models of epoxies with and without carbon nanotube (CNT) reinforcement and models of pure bismaleimides (BMIs) were developed to elucidate structure-property relationships for improved selection and tailoring of matrices. The influence of monomer functionality on the mechanical properties of epoxies is studied using the Reax Force Field (ReaxFF). From deformation simulations, the Young's modulus, yield point, and Poisson's ratio are calculated and analyzed. The results demonstrate an increase in stiffness and yield strength with increasing resin functionality. Comparison between the network structures of distinct epoxies is further advanced by the Monomeric Degree Index (MDI). Experimental validation demonstrates the MD results correctly predict the relationship in Young's moduli for all epoxies modeled. Therefore, the ReaxFF is confirmed to be a useful tool for studying the mechanical behavior of epoxies. While epoxies have been well-studied using MD, there has been no concerted effort to model cured BMI polymers due to the complexity of the network-forming reactions. A novel, adaptable crosslinking framework is developed for implementing 5 distinct cure reactions of Matrimid-5292 (a BMI resin) and investigating the network structure using MD simulations. The influence of different cure reactions and extent of curing are analyzed on the several thermo-mechanical properties such as mass density, glass transition temperature, coefficient of thermal expansion, elastic moduli, and thermal conductivity. The developed crosslinked models correctly predict experimentally observed trends for various properties. Finally, the epoxies modeled (di-, tri-, and tetra-functionalresins) are simulated with embedded CNT to understand how the affinity to nanoparticles affects the mechanical response. Multiscale modeling techniques are then employed to translate the molecular phenomena observed to predict the behavior of realistic composites. The effective stiffness of hybrid composites are predicted for CNT/epoxy composites with randomly oriented CNTs, for CF/CNT/epoxy systems with aligned CFs and randomly oriented CNTs, and for woven CF/CNT/epoxy fabric with randomly oriented CNTs. The results indicate that in the CNT/epoxy systems the epoxy type has a significant influence on the elastic properties. For the CF/CNT/epoxy hybrid composites, the axial modulus is highly influenced by CF concentration, while the transverse modulus is primarily affected by the CNT weight fraction.

Structural Polymer-Based Carbon Nanotube Composite Fibers: Understanding the Processing–Structure–Performance Relationship

PubMed Central

Song, Kenan; Zhang, Yiying; Meng, Jiangsha; Green, Emily C.; Tajaddod, Navid; Li, Heng; Minus, Marilyn L.

2013-01-01

Among the many potential applications of carbon nanotubes (CNT), its usage to strengthen polymers has been paid considerable attention due to the exceptional stiffness, excellent strength, and the low density of CNT. This has provided numerous opportunities for the invention of new material systems for applications requiring high strength and high modulus. Precise control over processing factors, including preserving intact CNT structure, uniform dispersion of CNT within the polymer matrix, effective filler–matrix interfacial interactions, and alignment/orientation of polymer chains/CNT, contribute to the composite fibers’ superior properties. For this reason, fabrication methods play an important role in determining the composite fibers’ microstructure and ultimate mechanical behavior. The current state-of-the-art polymer/CNT high-performance composite fibers, especially in regards to processing–structure–performance, are reviewed in this contribution. Future needs for material by design approaches for processing these nano-composite systems are also discussed. PMID:28809290

Capillary assisted deposition of carbon nanotube film for strain sensing

NASA Astrophysics Data System (ADS)

Li, Zida; Xue, Xufeng; Lin, Feng; Wang, Yize; Ward, Kevin; Fu, Jianping

2017-10-01

Advances in stretchable electronics offer the possibility of developing skin-like motion sensors. Carbon nanotubes (CNTs), owing to their superior electrical properties, have great potential for applications in such sensors. In this paper, we report a method for deposition and patterning of CNTs on soft, elastic polydimethylsiloxane (PDMS) substrates using capillary action. Micropillar arrays were generated on PDMS surfaces before treatment with plasma to render them hydrophilic. Capillary force enabled by the micropillar array spreads CNT solution evenly on PDMS surfaces. Solvent evaporation leaves a uniform deposition and patterning of CNTs on PDMS surfaces. We studied the effect of the CNT concentration and micropillar gap size on CNT coating uniformity, film conductivity, and piezoresistivity. Leveraging the piezoresistivity of deposited CNT films, we further designed and characterized a device for the contraction force measurement. Our capillary assisted deposition method of CNT films showed great application potential in fabrication of flexible CNT thin films for strain sensing.

Tunable and label-free virus enrichment for ultrasensitive virus detection using carbon nanotube arrays

PubMed Central

Yeh, Yin-Ting; Tang, Yi; Sebastian, Aswathy; Dasgupta, Archi; Perea-Lopez, Nestor; Albert, Istvan; Lu, Huaguang; Terrones, Mauricio; Zheng, Si-Yang

2016-01-01

Viral infectious diseases can erupt unpredictably, spread rapidly, and ravage mass populations. Although established methods, such as polymerase chain reaction, virus isolation, and next-generation sequencing have been used to detect viruses, field samples with low virus count pose major challenges in virus surveillance and discovery. We report a unique carbon nanotube size-tunable enrichment microdevice (CNT-STEM) that efficiently enriches and concentrates viruses collected from field samples. The channel sidewall in the microdevice was made by growing arrays of vertically aligned nitrogen-doped multiwalled CNTs, where the intertubular distance between CNTs could be engineered in the range of 17 to 325 nm to accurately match the size of different viruses. The CNT-STEM significantly improves detection limits and virus isolation rates by at least 100 times. Using this device, we successfully identified an emerging avian influenza virus strain [A/duck/PA/02099/2012(H11N9)] and a novel virus strain (IBDV/turkey/PA/00924/14). Our unique method demonstrates the early detection of emerging viruses and the discovery of new viruses directly from field samples, thus creating a universal platform for effectively remediating viral infectious diseases. PMID:27730213

Mechanical coupling limits the density and quality of self-organized carbon nanotube growth

NASA Astrophysics Data System (ADS)

Bedewy, Mostafa; Hart, A. John

2013-03-01

Aligned carbon nanotube (CNT) structures are promising for many applications; however, as-grown CNT "forests" synthesized by chemical vapor deposition (CVD) are typically low-density and mostly comprise tortuous defective CNTs. Here, we present evidence that the density and alignment of self-organized CNT growth is limited by mechanical coupling among CNTs in contact, in combination with their diameter-dependent growth rates. This study is enabled by comprehensive X-ray characterization of the spatially and temporally-varying internal morphology of CNT forests. Based on this data, we model the time evolution and diameter-dependent scaling of the ensuing mechanical forces on catalyst nanoparticles during CNT growth, which arise from the mismatch between the collective lengthening rate of the forest and the diameter-dependent growth rates of individual CNTs. In addition to enabling self-organization of CNTs into forests, time-varying forces between CNTs in contact dictate the hierarchical tortuous morphology of CNT forests, and may be sufficient to influence the structural quality of CNTs. These forces reach a maximum that is coincident with the maximum density observed in our growth process, and are proportional to CNT diameter. Therefore, we propose that improved manufacturing strategies for self-organized CNTs should consider both chemical and mechanical effects. This may be especially necessary to achieve high density CNT forests with low defect density, such as for improved thermal interfaces and high-permeability membranes.Aligned carbon nanotube (CNT) structures are promising for many applications; however, as-grown CNT "forests" synthesized by chemical vapor deposition (CVD) are typically low-density and mostly comprise tortuous defective CNTs. Here, we present evidence that the density and alignment of self-organized CNT growth is limited by mechanical coupling among CNTs in contact, in combination with their diameter-dependent growth rates. This study is enabled by comprehensive X-ray characterization of the spatially and temporally-varying internal morphology of CNT forests. Based on this data, we model the time evolution and diameter-dependent scaling of the ensuing mechanical forces on catalyst nanoparticles during CNT growth, which arise from the mismatch between the collective lengthening rate of the forest and the diameter-dependent growth rates of individual CNTs. In addition to enabling self-organization of CNTs into forests, time-varying forces between CNTs in contact dictate the hierarchical tortuous morphology of CNT forests, and may be sufficient to influence the structural quality of CNTs. These forces reach a maximum that is coincident with the maximum density observed in our growth process, and are proportional to CNT diameter. Therefore, we propose that improved manufacturing strategies for self-organized CNTs should consider both chemical and mechanical effects. This may be especially necessary to achieve high density CNT forests with low defect density, such as for improved thermal interfaces and high-permeability membranes. Electronic supplementary information (ESI) available: Detailed description of the cold-wall CVD reactor used for growing CNTs; fitting the diameter-dependent model-predicted CNT growth kinetics; time evolution of compressive stresses as a function of CNT diameter; time evolution of the diameter dependent variations in CNT number density; cumulative forest mass kinetics normalized to the number of CNTs. See DOI: 10.1039/c3nr34067h

Carbon nanotube/metal-sulfide composite flexible electrodes for high-performance quantum dot-sensitized solar cells and supercapacitors

PubMed Central

Muralee Gopi, Chandu V. V.; Ravi, Seenu; Rao, S. Srinivasa; Eswar Reddy, Araveeti; Kim, Hee-Je

2017-01-01

Carbon nanotubes (CNT) and metal sulfides have attracted considerable attention owing to their outstanding properties and multiple application areas, such as electrochemical energy conversion and energy storage. Here we describes a cost-effective and facile solution approach to the preparation of metal sulfides (PbS, CuS, CoS, and NiS) grown directly on CNTs, such as CNT/PbS, CNT/CuS, CNT/CoS, and CNT/NiS flexible electrodes for quantum dot-sensitized solar cells (QDSSCs) and supercapacitors (SCs). X-ray photoelectron spectroscopy, X-ray diffraction, and transmission electron microscopy confirmed that the CNT network was covered with high-purity metal sulfide compounds. QDSSCs equipped with the CNT/NiS counter electrode (CE) showed an impressive energy conversion efficiency (η) of 6.41% and remarkable stability. Interestingly, the assembled symmetric CNT/NiS-based polysulfide SC device exhibited a maximal energy density of 35.39 W h kg−1 and superior cycling durability with 98.39% retention after 1,000 cycles compared to the other CNT/metal-sulfides. The elevated performance of the composites was attributed mainly to the good conductivity, high surface area with mesoporous structures and stability of the CNTs and the high electrocatalytic activity of the metal sulfides. Overall, the designed composite CNT/metal-sulfide electrodes offer an important guideline for the development of next level energy conversion and energy storage devices. PMID:28422182

Study on the effect of carbon nanotube coating on the refractive index sensing sensitivity of fiber modal interferometer

NASA Astrophysics Data System (ADS)

Zhang, Ya-nan; Xie, Wen-ge; Wang, Jianzhang; Wang, Pengzhao

2018-01-01

Refractive index sensing of liquid is important in the domain of chemistry and biology. Fiber optical sensors provide an excellent way to measure the refractive index due to their feasible integration to other fiber optics components, high sensitivity, small size, and distributed sensing. However, conventional optical sensors have different shortages. To find a practical way to measure the refractive index of liquid, this paper intended to combine Carbon Nanotube (CNT) with non-core fiber (NCF) to prepare a kind of modal interferometer sensor and to explore the effect of CNT coating on refractive index sensing properties of the modal interferometer. Firstly, a structure of single mode non-core single mode (SNS) fiber with a CNT film coating was proposed and simulated. The simulation results showed that the CNT coating could improve the refractive index sensitivity of the interferometer sensor. Then in the experiment part, the CNT solution was fabricated and deposited onto the NCF, and a refractive index sensing system was built to examine the property of the CNT-coated SNS interferometer sensor. During the experiment, the influence factors of sensitivity were summarized by testing the sensing performance under different conditions, and it was demonstrated that the CNT coating could improve the contrast of the interference spectrum, and also had the possibility to increase the refractive index sensitivity of the interferometer sensor.

Effect of carbon nanotube addition on the thermite reaction in the Al/CuO energetic nanocomposite

NASA Astrophysics Data System (ADS)

Sharma, Manjula; Sharma, Vimal

2017-08-01

In this work, the Al/CNT/CuO nano-thermite samples are prepared by ultrasonic mixing with variable CNT content. The morphology of nano-thermites analysed by electron microscopy revealed that the CNTs are dispersed and there are intimate contacts between fuels (Al and CNT) and oxidiser (CuO) constituents of the nano-thermite. Raman spectroscopy technique is used to analyse the structural integrity of the CNTs in the nano-thermite. The thermite reaction characteristics are evaluated by simultaneous thermogravimetric analysis/differential scanning calorimetry technique. The exothermic enthalpy of the Al/CNT/CuO nano-thermite samples increased with increasing CNT content. The effect of Al particle size and Al/Cu molar ratio variation on the thermite reaction enthalpy is also analysed. The ignition temperature of the thermite reaction is also lowered by 71 °C than that of Al/CuO nano-thermite. The activation energy for thermite reaction of Al/CNT/CuO nano-thermite is also lowered by 23% to that of pure Al/CuO. The residues of the nano-thermites after the thermite reaction at 1010 °C are collected and analysed by the X-ray diffraction.

Impact of non-functionalized and amino-functionalized multiwall carbon nanotubes on pesticide uptake by lettuce (Lactuca sativa L.).

PubMed

Hamdi, Helmi; De La Torre-Roche, Roberto; Hawthorne, Joseph; White, Jason C

2015-03-01

The effect of non-functionalized and amino-functionalized multiwall carbon nanotube (CNT) exposure, as well as the impact of CNT presence on coexistent pesticide accumulation, was investigated in lettuce (Lactuca sativa L.). Lettuce seeds were sown directly into CNT-amended vermiculite (1000 mg L(-1)) to monitor phytotoxicity during germination and growth. During growth, lettuce seedlings were subsequently exposed to chlordane (cis-chlordane [CS], trans-chlordane [TC] and trans-nonachlor [TN]) and p,p'-DDE (all at 100 ng/L) in the irrigation solution for a 19-d growth period. CNT exposure did not significantly influence seed germination (82-96%) or plant growth. Similarly, pesticide exposure had no impact on plant growth, total pigment production or tissue lipid peroxidation. After 19 d, the root content of total chlordane and p,p'-DDE was 390 and 73.8 µg g(-1), respectively; in plants not exposed to CNTs, the shoot levels were 1.58 and 0.40 µg g(-1), respectively. The presence and type of CNT significantly influenced pesticide availability to lettuce seedlings. Non-functionalized CNT decreased the root and shoot pesticide content by 88% and 78%, respectively, but amino-functionalized CNT effects were significantly more modest, with decreases of 57% in the roots and 23% in the shoots, respectively. The presence of humic acid completely reversed the reduced accumulation of pesticides induced by amino-functionalized CNT, likely due to strong competition over adsorption sites on the nanomaterial (NM). These findings have implications for food safety and for the use of engineered NMs in agriculture, especially with leafy vegetables.

Coating carbon nanotubes with a polystyrene-based polymer protects against pulmonary toxicity.

PubMed

Tabet, Lyes; Bussy, Cyrill; Setyan, Ari; Simon-Deckers, Angélique; Rossi, Michel J; Boczkowski, Jorge; Lanone, Sophie

2011-01-21

carbon nanotubes (CNT) can have adverse effects on health. Therefore, minimizing the risk associated with CNT exposure is of crucial importance. The aim of this work was to evaluate if coating multi-walled CNT (MWCNT) with polymers could modify their toxicity, thus representing a useful strategy to decrease adverse health effects of CNT. We used industrially-produced MWCNT uncoated (NT1) or coated (50/50 wt%) with acid-based (NT2) or polystyrene-based (NT3) polymer, and exposed murine macrophages (RAW 264.7 cell line) or Balb/c mice by intratracheal administration. Biological experiments were performed both in vitro and in vivo, examining time- and dose-dependent effects of CNT, in terms of cytotoxicity, expression of genes and proteins related to oxidative stress, inflammation and tissue remodeling, cell and lung tissue morphology (optical and transmission electron microscopy), and bronchoalveolar lavage fluid content analysis. extensive physico-chemical characterization of MWCNT was performed, and showed, although similar dimensions for the 3 MWCNT, a much smaller specific surface area for NT2 and NT3 as compared to NT1 (54.1, 34 and 227.54 m(2)/g respectively), along with different surface characteristics. MWCNT-induced cytotoxicity, oxidative stress, and inflammation were increased by acid-based and decreased by polystyrene-based polymer coating both in vitro in murine macrophages and in vivo in lung of mice monitored for 6 months. these results demonstrate that coating CNT with polymers, without affecting their intrinsic structure, may constitute a useful strategy for decreasing CNT toxicity, and may hold promise for improving occupational safety and that of general the user.

Effect of Length, Diameter, Chirality, Deformation, and Strain on Contact Thermal Conductance between Single Wall Carbon Nanotubes

NASA Astrophysics Data System (ADS)

Varshney, Vikas; Lee, Jonghoon; Brown, Joshua S.; Farmer, Barry L.; Voevodin, Andrey A.; Roy, Ajit K.

2018-04-01

Thermal energy transfer across physically interacting single-wall carbon nanotube (SWCNT) interconnects has been investigated using non-equilibrium molecular dynamics simulations. The role of various geometrical and structural (length, diameter, chirality) as well as external (deformation and strain) carbon nanotube (CNT) parameters has been explored to estimate total as well as area-normalized thermal conductance across cross-contact interconnects. It is shown that the CNT aspect ratio and degree of lateral as well as tensile deformation play a significant role in determining the extent of thermal energy exchange across CNT contacts, while CNT chirality has a negligible influence on thermal transport. Depending on the CNT diameter, aspect ratio, and degree of deformation at the contact interface, the thermal conductance values can vary significantly –by more than an order of magnitude for total conductance and a factor of 3 to 4 for area-normalized conductance. The observed trends are discussed from the perspective of modulation in number of low frequency out-of-plane (transverse, flexural, and radial) phonons that transmit thermal energy across the contact and govern the conductance across the interface. The established general dependencies for phonon governed thermal transport at CNT contacts are anticipated to help design and performance prediction of CNT-based flexible nanoelectronic devices, where CNT-CNT contact deformation and strain are routinely encountered during device operations.

Synthesis of TiO2-CNT hybrid nanocatalyst and its application in direct oxidation of H2S to S

NASA Astrophysics Data System (ADS)

Daraee, Maryam; Baniadam, Majid; Rashidi, Alimorad; Maghrebi, Morteza

2018-07-01

In this study, a TiO2-CNT hybrid catalyst has been synthesized and its catalytic activity in the oxidation of H2S to S has been investigated and compared with those of TiO2 nanoparticles and pyrolyzed TiO2-CNT hybrid (P-TiO2-CNT). The optimum catalyst amount was determined using central composite design (CCD) method. Catalysts were characterized by various analytical techniques. The H2S conversion, sulfur selectivity and yield at the optimal temperature of 200 °C and O2/H2S ratio of 0.5 were 98.3, 99.5 and 97%, respectively. TiO2-CNT16% catalyst has a higher surface area than TiO2 nanoparticles and P-TiO2-CNT. In addition, the former catalyst gives a high conversion of H2S and sulfur selectivity at 200 °C and O2/H2S ratio of 0.5 compared with the latter two catalysts. The superior conversion (over 10%) of TiO2-CNT16% hybrid compared to TiO2 nanoparticles can be attributed to the synergistic effects of TiO2 and CNT, the reduced band gap of TiO2-CNT16% hybrid and high specific surface area of the catalyst.

Carbon Nanotubes and Carbon Nanotube Fiber Sensors: Growth, Processing and Characterization

NASA Astrophysics Data System (ADS)

Zhao, Haibo

With multiple outstanding properties, such as high Young's modulus, high strength, good thermal conductivity and electrical conductivity, carbon nanotube (CNT) has been considered as a new generation of material that has many potential applications in many fields. One obstacle that stands in the way of applying CNTs in the real world is the limited growth length. Catalyst instability is one of the many factors that cause the stops of CNT growth. In this research, intermetalic Fe-Zr catalyst was used to grow millimeter long CNT arrays. The Fe-Zr particles enabled the growth of 1.7 millimeter long carbon nanotube arrays in 45 minutes. A comparison with pure Fe catalyst indicated that adding Zr to iron can stabilize the Fe catalyst at the CNT growth temperature and moderate its reactivity. In future, when CNTs are largely used in industrial, mass production of CNTs at a low cost is vital for market competition. In many current CNT growth methods, a process of depositing a thin catalyst film on top of Al 2O3 film on a piece of silicon wafer is required. Thus the size of CNT samples is limited by the size of the largest silicon wafer currently available, which is 8 inch in diameter. In this study, FeCl2 powders were used as the catalyst to grow CNT arrays not only on traditional silicon substrates but also on quartz substrates and carbon sheets. This unique method does not require the thin film deposition step, which shortens the time used for each batch of CNT growth. The simplicity of this method allows an easy scale-up for mass production of CNTs with a low cost. In order to improve this method, HCl was used to assist the CNT growth. HCl was added via flowing a small amount of C2H2 thorough a bubbuler where HCl solution was contained. With the assistance of HCl, CNT growth could be extended to 1 hour. 3 mm tall non-spinnable arrays and 2 mm tall spinnable arrays were produced using this method. With the increasing use of composite materials, real time health monitoring of composite structures becomes vital for maintenance purpose as well as prevention of catastrophic failure. In this research, a novel prototype of CNT fiber sensor with excellent repeatability and stability was applied for in-situ structural health monitoring. The CNT fiber was spun directly from CNT arrays, and its electrical resistance increases linearly with tensile strain, which makes it an ideal strain sensor. Importantly, it shows consistent piezoresistive behavior under repetitive straining and unloading, and good stability at temperatures ranging from 77K to 373K. CNT fiber sensors can be easily embedded into composite structures with minimal invasiveness and weight penalty due to the lightweight and good mechanical properties of fibers. With multiple fibers aligned in the composite, crack initiation and propagation could be monitored in situ.

High-performance, lightweight coaxial cable from carbon nanotube conductors.

PubMed

Jarosz, Paul R; Shaukat, Aalyia; Schauerman, Christopher M; Cress, Cory D; Kladitis, Paul E; Ridgley, Richard D; Landi, Brian J

2012-02-01

Coaxial cables have been constructed with carbon nanotube (CNT) materials serving as both the inner and outer conductors. Treatment of the CNT outer and inner conductors with KAuBr(4) was found to significantly reduce the attenuation of these cables, which demonstrates that chemical agents can be used to improve power transmission through CNT networks at high frequencies (150 kHz-3 GHz). For cables constructed with a KAuBr(4)-treated CNT outer conductor, power attenuation per length approaches parity with cables constructed from metallic conductors at significantly lower weight per length (i.e., 7.1 g/m for CNT designs compared to 38.8 g/m for an RG-58 design). A relationship between the thickness of the CNT outer conductor and the cable attenuation was observed and used to estimate the effective skin depth at high frequency. These results establish reliable, reproducible methods for the construction of coaxial cables from CNT materials that can facilitate further investigation of their performance in high-frequency transmission structures, and highlight a specific opportunity for significant reduction in coaxial cable mass.

Electron percolation in realistic models of carbon nanotube networks

NASA Astrophysics Data System (ADS)

Simoneau, Louis-Philippe; Villeneuve, Jérémie; Rochefort, Alain

2015-09-01

The influence of penetrable and curved carbon nanotubes (CNT) on the charge percolation in three-dimensional disordered CNT networks have been studied with Monte-Carlo simulations. By considering carbon nanotubes as solid objects but where the overlap between their electron cloud can be controlled, we observed that the structural characteristics of networks containing lower aspect ratio CNT are highly sensitive to the degree of penetration between crossed nanotubes. Following our efficient strategy to displace CNT to different positions to create more realistic statistical models, we conclude that the connectivity between objects increases with the hard-core/soft-shell radii ratio. In contrast, the presence of curved CNT in the random networks leads to an increasing percolation threshold and to a decreasing electrical conductivity at saturation. The waviness of CNT decreases the effective distance between the nanotube extremities, hence reducing their connectivity and degrading their electrical properties. We present the results of our simulation in terms of thickness of the CNT network from which simple structural parameters such as the volume fraction or the carbon nanotube density can be accurately evaluated with our more realistic models.

Carbon nanotube multi-electrode array chips for noninvasive real-time measurement of dopamine, action potentials, and postsynaptic potentials.

PubMed

Suzuki, Ikuro; Fukuda, Mao; Shirakawa, Keiichi; Jiko, Hideyasu; Gotoh, Masao

2013-11-15

Multi-electrode arrays (MEAs) can be used for noninvasive, real-time, and long-term recording of electrophysiological activity and changes in the extracellular chemical microenvironment. Neural network organization, neuronal excitability, synaptic and phenotypic plasticity, and drug responses may be monitored by MEAs, but it is still difficult to measure presynaptic activity, such as neurotransmitter release, from the presynaptic bouton. In this study, we describe the development of planar carbon nanotube (CNT)-MEA chips that can measure both the release of the neurotransmitter dopamine as well as electrophysiological responses such as field postsynaptic potentials (fPSPs) and action potentials (APs). These CNT-MEA chips were fabricated by electroplating the indium-tin oxide (ITO) microelectrode surfaces. The CNT-plated ITO electrode exhibited electrochemical response, having much higher current density compared with the bare ITO electrode. Chronoamperometric measurements using these CNT-MEA chips detected dopamine at nanomolar concentrations. By placing mouse striatal brain slices on the CNT-MEA chip, we successfully measured synaptic dopamine release from spontaneous firings with a high S/N ratio of 62. Furthermore, APs and fPSPs were measured from cultured hippocampal neurons and slices with high temporal resolution and a 100-fold greater S/N ratio. Our CNT-MEA chips made it possible to measure neurotransmitter dopamine (presynaptic activities), postsynaptic potentials, and action potentials, which have a central role in information processing in the neuronal network. CNT-MEA chips could prove useful for in vitro studies of stem cell differentiation, drug screening and toxicity, synaptic plasticity, and pathogenic processes involved in epilepsy, stroke, and neurodegenerative diseases. Copyright © 2013 Elsevier B.V. All rights reserved.

Plasma and cold sprayed aluminum carbon nanotube composites: Quantification of nanotube distribution and multi-scale mechanical properties

NASA Astrophysics Data System (ADS)

Bakshi, Srinivasa Rao

Carbon nanotubes (CNT) could serve as potential reinforcement for metal matrix composites for improved mechanical properties. However dispersion of carbon nanotubes (CNT) in the matrix has been a longstanding problem, since they tend to form clusters to minimize their surface area. The aim of this study was to use plasma and cold spraying techniques to synthesize CNT reinforced aluminum composite with improved dispersion and to quantify the degree of CNT dispersion as it influences the mechanical properties. Novel method of spray drying was used to disperse CNTs in Al-12 wt.% Si prealloyed powder, which was used as feedstock for plasma and cold spraying. A new method for quantification of CNT distribution was developed. Two parameters for CNT dispersion quantification, namely Dispersion parameter (DP) and Clustering Parameter (CP) have been proposed based on the image analysis and distance between the centers of CNTs. Nanomechanical properties were correlated with the dispersion of CNTs in the microstructure. Coating microstructure evolution has been discussed in terms of splat formation, deformation and damage of CNTs and CNT/matrix interface. Effect of Si and CNT content on the reaction at CNT/matrix interface was thermodynamically and kinetically studied. A pseudo phase diagram was computed which predicts the interfacial carbide for reaction between CNT and Al-Si alloy at processing temperature. Kinetic aspects showed that Al4C3 forms with Al-12 wt.% Si alloy while SiC forms with Al-23wt.% Si alloy. Mechanical properties at nano, micro and macro-scale were evaluated using nanoindentation and nanoscratch, microindentation and bulk tensile testing respectively. Nano and micro-scale mechanical properties (elastic modulus, hardness and yield strength) displayed improvement whereas macro-scale mechanical properties were poor. The inversion of the mechanical properties at different scale length was attributed to the porosity, CNT clustering, CNT-splat adhesion and Al 4C3 formation at the CNT/matrix interface. The Dispersion parameter (DP) was more sensitive than Clustering parameter (CP) in measuring degree of CNT distribution in the matrix.

Probing the structure and function of biopolymer-carbon nanotube hybrids with molecular dynamics

NASA Astrophysics Data System (ADS)

Johnson, Robert R.

2009-12-01

Nanoscience deals with the characterization and manipulation of matter on the atomic/molecular size scale in order to deepen our understanding of condensed matter and develop revolutionary technology. Meeting the demands of the rapidly advancing nanotechnological frontier requires novel, multifunctional nanoscale materials. Among the most promising nanomaterials to fulfill this need are biopolymer-carbon nanotube hybrids (Bio-CNT). Bio-CNT consists of a single-walled carbon nanotube (CNT) coated with a self-assembled layer of biopolymers such as DNA or protein. Experiments have demonstrated that these nanomaterials possess a wide range of technologically useful properties with applications in nanoelectronics, medicine, homeland security, environmental safety and microbiology. However, a fundamental understanding of the self-assembly mechanics, structure and energetics of Bio-CNT is lacking. The objective of this thesis is to address this deficiency through molecular dynamics (MD) simulation, which provides an atomic-scale window into the behavior of this unique nanomaterial. MD shows that Bio-CNT composed of single-stranded DNA (ssDNA) self-assembles via the formation of high affinity contacts between DNA bases and the CNT sidewall. Calculation of the base-CNT binding free energy by thermodynamic integration reveals that these contacts result from the attractive pi--pi stacking interaction. Binding affinities follow the trend G > A > T > C. MD reveals that long ssDNA sequences are driven into a helical wrapping about CNT with a sub-10 nm pitch by electrostatic and torsional interactions in the backbone. A large-scale replica exchange molecular dynamics simulation reveals that ssDNA-CNT hybrids are disordered. At room temperature, ssDNA can reside in several low-energy conformations that contain a sequence-specific arrangement of bases detached from CNT surface. MD demonstrates that protein-CNT hybrids composed of the Coxsackie-adenovirus receptor are biologically active and function as a nanobiosensor with specific recognition of Knob proteins from the adenovirus capsid. Simulation also shows that the rigid CNT damps structural fluctuations in bound proteins, which may have important ramifications for biosensing devices composed of protein-CNT hybrids. These results expand current knowledge of Bio-CNT and demonstrate the effectiveness of MD for investigations of nanobiomolecular systems.

Calculation of the figure of merit for carbon nanotubes based devices

NASA Astrophysics Data System (ADS)

Vaseashta, Ashok

2004-03-01

The dimensionality of a system has a profound influence on its physical behavior. With advances in technology over the past few decades, it has become possible to fabricate and study reduced-dimensional systems in which electrons are strongly confined in one or more dimensions. In the case of 1-D electron systems, most of the results, such as conductance quantization, have been explained in terms of non-interacting electrons. In contrast to the cases of 2D and 3D systems, the question of what roles electron-electron interactions play in real 1-D systems has been difficult to address, because of the difficulty in obtaining long, relatively disorder free 1-D wires. Since their first discovery and fabrication in 1991, carbon nanotubes (CNTs) have received considerable attention because of the prospect of new fundamental science and many potential applications. Hence, it has been possible to conduct studies of the electrons in 1-D. Carbon nanotubes are of considerable technological importance due to their excellent mechanical, electrical, and chemical characteristics. The potential technological applications include electronics, opto-electronics and biomedical sensors. The applications of carbon nanotubes include quantum wire interconnects, diodes and transistors for computing, capacitors, data storage devices, field emitters, flat panel displays and terahertz oscillators. One of the most remarkable characteristics is the possibility of bandgap engineering by controlling the microstructure. Hence, a pentagon-heptagon defect in the hexagonal network can connect a metallic to a semiconductor nanotube, providing an Angstrom-scale hetero-junction with a device density approximately 10^4 times greater than present day microelectronics. Also, successfully contacted carbon nanotubes have exhibited a large number of useful quantum electronic and low dimensional transport phenomena, such as true quantum wire behaviors, room temperature field effect transistors, room temperature single electron transistors, Luttinger-liquid behavior, the Aharonov Bohm effect, and Fabry-Perot interference effects. Hence it is evident that CNT can be used for a variety of applications. To use CNT based devices, it is critical to know the relative advantage of using CNTs over other known electronic materials. The figure of merit for CNT based devices is not reported so far. It is the objective of this investigation to calculate the figure of merit and present such results. Such calculations will enable researchers to focus their research for specific device designs where CNT based devices show a marked improvement over conventional semiconductor devices.

A comprehensive theoretical investigation about the bio-functionalization capability of single walled CNT, BNNT and SiCNT using DNA/RNA nucleobases

NASA Astrophysics Data System (ADS)

Alinezhad, Heshmatollah; Ganji, Masoud Darvish; Soleymani, Elham; Tajbakhsh, Mahmood

2017-11-01

By means of Density Functional Theory (DFT) based calculations, we have elucidated the interactions between five nucleobases and three nanotubes, namely: CNT, BNNT and SiCNT. The energetics and equilibrium geometries have been calculated within the framework of revPBE method in combination with third version of Grimme's atom pair-wise dispersion corrections with Becke-Johnson damping (D3BJ). The obtained results in terms of adsorption energy values and geometrical parameters suggest that the overall interactions are divided into two parts: non-covalently and covalently bonded systems as the nucleobases are physisorbed onto the surface of CNT and BNNT (Eads ranges from -0.57 to -0.76 eV and -0.54 to -0.78 eV for CNT and BNNT complexes, respectively) while the type of interactions between nucleobase molecules and SiCNT has been found to be of covalent type with the Eads ranging from -0.61 to -1.8 eV. Moreover, the empirical dispersion corrections have been found to play crucial roles in obtaining reliable geometries and adsorption energy values for the non-covalently bonded systems. The role of solvation on the overall interactions has also been explored using the COSMO model within a media with dielectric constant of 78.39 which resembles the water environment and the results revealed that the interaction strength showed a decreasing trend with increasing the polarity of the system. Considering the adsorption energy differences between each nucleobase and the nanotubes, the SiCNT showed promising performance in differentiating between the nucleobase molecules and exhibited the highest affinity to be biofunctionalized in comparison to other nanotubes. The findings of the present work would be very useful for understanding the underlying phenomena behind the interface interactions and would aid future experimental investigations in the fields of biotechnology and materials science.

Ventilation via Cut Nasotracheal Tube During General Anesthesia

PubMed Central

Asahi, Yoshinao; Omichi, Shiro; Adachi, Seita; Kagamiuchi, Hajime; Kotani, Junichiro

2013-01-01

Many patients with disabilities need recurrent dental treatment under general anesthesia because of high caries prevalence and the nature of dental treatment. We evaluated the use of a nasal device as a possible substitute for flexible laryngeal mask airway to reduce the risk of unexpected failure accompanying intubation; we succeeded in ventilating the lungs with a cut nasotracheal tube (CNT) with its tip placed in the pharynx. We hypothesized that this technique would be useful during dental treatment under general anesthesia and investigated its usefulness as part of a minimally invasive technique. A prospective study was designed using general anesthesia in 37 dental patients with disabilities such as intellectual impairment, autism, and cerebral palsy. CNT ventilation was compared with mask ventilation with the patient in 3 positions: the neck in flexion, horizontal position, and in extension. The effect of mouth gags was also recorded during CNT ventilation. The percentages of cases with effective ventilation were similar for the 2 techniques in the neck extension and horizontal positions (89.2–97.3%). However, CNT ventilation was significantly more effective than mask ventilation in the neck flexion position (94.6 vs 45.9%; P < .0001). Mouth gags slightly reduced the rate of effective ventilation in the neck flexion position. Most dental treatments involving minor oral surgeries were performed using mouth gags during CNT ventilation. CNT ventilation was shown to be superior to mask ventilation and is useful during dental treatment under general anesthesia. PMID:23506278

Electron Beam Irradiated Intercalated CNT Yarns For Aerospace Applications

NASA Technical Reports Server (NTRS)

Waters, Deborah L.; Gaier, James R.; Williams, Tiffany S.; Lopez Calero, Johnny E.; Ramirez, Christopher; Meador, Michael A.

2015-01-01

Multi-walled CNT yarns have been experimentally and commercially created to yield lightweight, high conductivity fibers with good tensile properties for application as electrical wiring and multifunctional tendons. Multifunctional tendons are needed as the cable structures in tensegrity robots for use in planetary exploration. These lightweight robust tendons can provide mechanical strength for movement of the robot in addition to power distribution and data transmission. In aerospace vehicles, such as Orion, electrical wiring and harnessing mass can approach half of the avionics mass. Use of CNT yarns as electrical power and data cables could reduce mass of the wiring by thirty to seventy percent. These fibers have been intercalated with mixed halogens to increase their specific electrical conductivity to that near copper. This conductivity, combined with the superior strength and fatigue resistance makes it an attractive alternative to copper for wiring and multifunctional tendon applications. Electron beam irradiation has been shown to increase mechanical strength in pristine CNT fibers through increased cross-linking. Both pristine and intercalated CNT yarns have been irradiated using a 5-megavolt electron beam for various durations and the conductivities and tensile properties will be discussed. Structural information obtained using a field emission scanning electron microscope, energy dispersive X-ray spectroscopy (EDS), and Raman spectroscopy will correlate microstructural details with bulk properties.

Compressive Sampling Based Interior Reconstruction for Dynamic Carbon Nanotube Micro-CT

PubMed Central

Yu, Hengyong; Cao, Guohua; Burk, Laurel; Lee, Yueh; Lu, Jianping; Santago, Pete; Zhou, Otto; Wang, Ge

2010-01-01

In the computed tomography (CT) field, one recent invention is the so-called carbon nanotube (CNT) based field emission x-ray technology. On the other hand, compressive sampling (CS) based interior tomography is a new innovation. Combining the strengths of these two novel subjects, we apply the interior tomography technique to local mouse cardiac imaging using respiration and cardiac gating with a CNT based micro-CT scanner. The major features of our method are: (1) it does not need exact prior knowledge inside an ROI; and (2) two orthogonal scout projections are employed to regularize the reconstruction. Both numerical simulations and in vivo mouse studies are performed to demonstrate the feasibility of our methodology. PMID:19923686

High-sensitivity visualization of localized electric fields using low-energy electron beam deflection

NASA Astrophysics Data System (ADS)

Jeong, Samuel; Ito, Yoshikazu; Edwards, Gary; Fujita, Jun-ichi

2018-06-01

The visualization of localized electronic charges on nanocatalysts is expected to yield fundamental information about catalytic reaction mechanisms. We have developed a high-sensitivity detection technique for the visualization of localized charges on a catalyst and their corresponding electric field distribution, using a low-energy beam of 1 to 5 keV electrons and a high-sensitivity scanning transmission electron microscope (STEM) detector. The highest sensitivity for visualizing a localized electric field was ∼0.08 V/µm at a distance of ∼17 µm from a localized charge at 1 keV of the primary electron energy, and a weak local electric field produced by 200 electrons accumulated on the carbon nanotube (CNT) apex can be visualized. We also observed that Au nanoparticles distributed on a CNT forest tended to accumulate a certain amount of charges, about 150 electrons, at a ‑2 V bias.

Tailoring Interfacial Properties by Controlling Carbon Nanotube Coating Thickness on Glass Fibers Using Electrophoretic Deposition.

PubMed

Tamrakar, Sandeep; An, Qi; Thostenson, Erik T; Rider, Andrew N; Haque, Bazle Z Gama; Gillespie, John W

2016-01-20

The electrophoretic deposition (EPD) method was used to deposit polyethylenimine (PEI) functionalized multiwall carbon nanotube (CNT) films onto the surface of individual S-2 glass fibers. By varying the processing parameters of EPD following Hamaker's equation, the thickness of the CNT film was controlled over a wide range from 200 nm to 2 μm. The films exhibited low electrical resistance, providing evidence of coating uniformity and consolidation. The effect of the CNT coating on fiber matrix interfacial properties was investigated through microdroplet experiments. Changes in interfacial properties due to application of CNT coatings onto the fiber surface with and without a CNT-modified matrix were studied. A glass fiber with a 2 μm thick CNT coating and the unmodified epoxy matrix showed the highest increase (58%) in interfacial shear strength (IFSS) compared to the baseline. The increase in the IFSS was proportional to CNT film thickness. Failure analysis of the microdroplet specimens indicated higher IFSS was related to fracture morphologies with higher levels of surface roughness. EPD enables the thickness of the CNT coating to be adjusted, facilitating control of fiber/matrix interfacial resistivity. The electrical sensitivity provides the opportunity to fabricate a new class of sizing with tailored interfacial properties and the ability to detect damage initiation.

Enhanced Defluoridation Capacity From Aqueous Media via Hydroxyapatite Decorated With Carbon Nanotube.

PubMed

Tang, Qingzi; Duan, Tongdan; Li, Peng; Zhang, Ping; Wu, Daishe

2018-01-01

In this work, the potential of a novel hydroxyapatite decorated with carbon nanotube composite (CNT-HAP) for fluoride removal was investigated. The synthesized CNT-HAP composite was systematically characterized by X-ray diffraction(XRD), Fourier Transform infrared spectroscopy(FTIR), scanning electron microscope (SEM) and Brunauer-Emmett-Teller(BET). Batch adsorption experiments were conducted to investigate the defluorination capacity of CNT-HAP. The CNT-HAP composite has a maximum adsorption capacity of 11.05 mg·g -1 for fluoride, and the isothermal adsorption data were fitted by the Freundlich model to calculate the thermodynamic parameters. Thermodynamic analysis implies that the adsorption of fluoride on CNT-HAP is a spontaneous process. Furthermore, the adsorption of fluoride follows pseudo-second-order model. The effects of solution pH, co-existing anions and reaction temperature on defluorination efficiency were examined to optimize the operation conditions for fluoride adsorption. It is found that the optimized pH-value for fluoride removal by CNT-HAP composite is 6. In addition, among five common anions studied in this work, the presence of [Formula: see text] and [Formula: see text] could considerably affect the fluoride removal by CNT-HPA in aqueous media. Finally, the underlying mechanism for the fluoride removal by CNT-HAP is analyzed, and an anion exchange process is proposed.

Enhanced defluoridation capacity from aqueous media via hydroxyapatite decorated with carbon nanotube

NASA Astrophysics Data System (ADS)

Tang, Qingzi; Duan, Tongdan; Li, Peng; Zhang, Ping; Wu, Daishe

2018-04-01

In this work, the potential of a novel carbon nanotube-doped hydroxyapatite composite (CNT-HAP) for fluoride removal was investigated. The synthesized CNT-HAP composite was systematically characterized by X-ray diffraction(XRD), Fourier Transform infrared spectroscopy(FTIR), scanning electron microscope (SEM) and Brunauer–Emmett–Teller(BET). Batch adsorption experiments were conducted to investigate the defluorination capacity of CNT-HAP. The CNT-HAP composite has a maximum adsorption capacity of 11.05 mg·g-1 for fluoride, and the isothermal adsorption data were fitted by the Freundlich model to calculate the thermodynamic parameters. Thermodynamic analysis implies that the adsorption of fluoride on CNT-HAP is a spontaneous process. Furthermore, the adsorption of fluoride follows pseudo-second-order model. The effects of solution pH, co-existing anions and reaction temperature on defluorination efficiency were examined to optimize the operation conditions for fluoride adsorption. It is found that the optimized pH value for fluoride removal by CNT-HAP composite is 6. In addition, among five common anions studied in this work, the presence of HCO3- and PO43- could considerably affect the fluoride removal by CNT-HPA in aqueous media. Finally, the underlying mechanism for the fluoride removal by CNT-HAP is analysed, and an anion exchange process is proposed.

Enhanced Defluoridation Capacity From Aqueous Media via Hydroxyapatite Decorated With Carbon Nanotube

PubMed Central

Tang, Qingzi; Duan, Tongdan; Li, Peng; Zhang, Ping; Wu, Daishe

2018-01-01

In this work, the potential of a novel hydroxyapatite decorated with carbon nanotube composite (CNT-HAP) for fluoride removal was investigated. The synthesized CNT-HAP composite was systematically characterized by X-ray diffraction(XRD), Fourier Transform infrared spectroscopy(FTIR), scanning electron microscope (SEM) and Brunauer–Emmett–Teller(BET). Batch adsorption experiments were conducted to investigate the defluorination capacity of CNT-HAP. The CNT-HAP composite has a maximum adsorption capacity of 11.05 mg·g−1 for fluoride, and the isothermal adsorption data were fitted by the Freundlich model to calculate the thermodynamic parameters. Thermodynamic analysis implies that the adsorption of fluoride on CNT-HAP is a spontaneous process. Furthermore, the adsorption of fluoride follows pseudo-second-order model. The effects of solution pH, co-existing anions and reaction temperature on defluorination efficiency were examined to optimize the operation conditions for fluoride adsorption. It is found that the optimized pH-value for fluoride removal by CNT-HAP composite is 6. In addition, among five common anions studied in this work, the presence of HCO3- and PO43- could considerably affect the fluoride removal by CNT-HPA in aqueous media. Finally, the underlying mechanism for the fluoride removal by CNT-HAP is analyzed, and an anion exchange process is proposed. PMID:29696138

Nanostructured Composites of Bi1-xSbx Nanoparticles and Carbon Nanotubes and the Characterization of Their Thermoelectric Properties.

PubMed

Güneş, Ekrem; Gundlach, Felix; Elm, Matthias T; Klar, Peter J; Schlecht, Sabine; Wickleder, Mathias S; Müller, Eckhard

2017-12-27

The impact of inclusions of carbon nanotubes (CNT) on the thermoelectric properties of nanostructured Bi 1-x Sb x alloys with an Sb content between 10 and 20% was investigated for varying amounts of CNT. Three series of Bi 1-x Sb x pellets with 0, 0.3, and 0.5 wt % CNT were synthesized by mechanical alloying followed by uniaxial pressing. The resistivity was investigated in the temperature range from 30 to 500 K, revealing an enlargement of the band gap due to nanostructuring of the Bi 1- x Sb x alloy, which is even more pronounced for alloys including CNT. This enlargement is attributed to a modification of the interface between the Bi 1-x Sb x nanoparticles by a graphene-like coating, which is formed during the fabrication process due to the addition of CNT. Measurements of the Seebeck coefficient and the thermal conductivity were also performed to determine the thermoelectric properties. In total, the CNT-containing samples show a significant improvement of the figure of merit up to 250% for the Bi 0.88 Sb 0.12 composition with 0.3 wt % CNT due to the interface modification between the nanoparticles, demonstrating the beneficial effect of CNT on the thermoelectric properties.

Technical feasibility and economical viability of remote hybrid power systems in Northern Ontario

NASA Astrophysics Data System (ADS)

Gubbels, Jason Matthew

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Evaluation of remotely sensed wetland mapping

NASA Astrophysics Data System (ADS)

Gluck, Michael J.

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Tectonic magnetic fabrics in pure and simple shear: Experimental investigations

NASA Astrophysics Data System (ADS)

Alford, Craig Steven

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Use of a single epiphyte lichen species Hypogymnia physodes as an indicator of air quality in northern Ontario

NASA Astrophysics Data System (ADS)

Pfeiffer, Helmut Nickolaus

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Gravity study of an Archaen crustal segment near Thunder Bay, Ontario

NASA Astrophysics Data System (ADS)

Cheadle, Scott Philip

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Northern lights: A history of Thunder Bay Hydro

NASA Astrophysics Data System (ADS)

Black, David Leo

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Static dielectric properties of an ensemble of restricted one-dimensional oscillators

NASA Astrophysics Data System (ADS)

Tjipto Margo, Broto

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Photoluminescence and Raman characterization of PLEE and MBE grown semiconductor epilayers

NASA Astrophysics Data System (ADS)

Harrison, Dale A.

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Development of nonlinear 3-D, and novel 2-D optical microscope imaging systems for time-lapse imaging

NASA Astrophysics Data System (ADS)

Girardin, Robert Joseph

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Simple route to new palladium-carbonyl-bis(diphenylphosphino)methane complexes

NASA Astrophysics Data System (ADS)

Krysa, Elizabeth

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Impurity band conduction in reduced samples of bismuth iron molybdate

NASA Astrophysics Data System (ADS)

McIntyre, Shawn M.

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Photon number density operator

NASA Astrophysics Data System (ADS)

Melde, Thomas

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Dielectric and infrared studies of radio frequency processes in some alcohols

NASA Astrophysics Data System (ADS)

Mandal, Humayun

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Real-time implementation of some attitude estimation algorithms on a quadrotor UAV

NASA Astrophysics Data System (ADS)

Nayak, Siddhant

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Aligned Carbon Nanotubes for High-Performance Films and Composites

NASA Astrophysics Data System (ADS)

Zhang, Liwen

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Ordered supramolecular oligothiophene structures on passivated silicon surfaces

NASA Astrophysics Data System (ADS)

Liu, Renjie

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Synthesis and electrochemical study of PtIr and PtRu nanomaterials

NASA Astrophysics Data System (ADS)

Alammari, Walaa S.

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

P-type gallium nitride semiconductor development and characterization for LEDs and other devices

NASA Astrophysics Data System (ADS)

Togtema, Gregorey L.

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Association of pulmonary, cardiovascular, and hematologic metrics with carbon nanotube and nanofiber exposure among U.S. workers: a cross-sectional study.

PubMed

Schubauer-Berigan, Mary K; Dahm, Matthew M; Erdely, Aaron; Beard, John D; Eileen Birch, M; Evans, Douglas E; Fernback, Joseph E; Mercer, Robert R; Bertke, Stephen J; Eye, Tracy; de Perio, Marie A

2018-05-16

Commercial use of carbon nanotubes and nanofibers (CNT/F) in composites and electronics is increasing; however, little is known about health effects among workers. We conducted a cross-sectional study among 108 workers at 12 U.S. CNT/F facilities. We evaluated chest symptoms or respiratory allergies since starting work with CNT/F, lung function, resting blood pressure (BP), resting heart rate (RHR), and complete blood count (CBC) components. We conducted multi-day, full-shift sampling to measure background-corrected elemental carbon (EC) and CNT/F structure count concentrations, and collected induced sputum to measure CNT/F in the respiratory tract. We measured (nonspecific) fine and ultrafine particulate matter mass and count concentrations. Concurrently, we conducted physical examinations, BP measurement, and spirometry, and collected whole blood. We evaluated associations between exposures and health measures, adjusting for confounders related to lifestyle and other occupational exposures. CNT/F air concentrations were generally low, while 18% of participants had evidence of CNT/F in sputum. Respiratory allergy development was positively associated with inhalable EC (p=0.040) and number of years worked with CNT/F (p=0.008). No exposures were associated with spirometry-based metrics or pulmonary symptoms, nor were CNT/F-specific metrics related to BP or most CBC components. Systolic BP was positively associated with fine particulate matter (p-values: 0.015-0.054). RHR was positively associated with EC, at both the respirable (p=0.0074) and inhalable (p=0.0026) size fractions. Hematocrit was positively associated with the log of CNT/F structure counts (p=0.043). Most health measures were not associated with CNT/F. The positive associations between CNT/F exposure and respiratory allergies, RHR, and hematocrit counts may not be causal and require examination in other studies.

DFT computational study on the phosphate functionalized SWCNTs as efficient drug delivery systems for anti-osteoporosis zolendronate and risedronate drugs

NASA Astrophysics Data System (ADS)

Nikfar, Zahra; Shariatinia, Zahra

2017-07-01

The pristine (4,4)-armchair SWCNT as well as its three phosphate functionalized (CNT-nH2PO4, n=1-3) forms were studied as novel drug delivery systems for the two commercially famous anti-osteoporosis drugs including risedronate (RIS) and zolendronate (ZOL) using the density functional theory (DFT) computations at both B3LYP and B3PW91 levels. Results revealed that the binding energy was increased by increasing number of H2PO4 moieties attached on the CNT with the most negative binding energy was measured for the CNT-3H2PO4 carrier. The dipole moments of all phosphate containing CNTs were much greater ( 1.5-4.5 D) than that of pristine CNT ( 0 D). The contour maps verified that when the CNT was functionalized by H2PO4 groups, the symmetric distribution of electric charge was vanished so that the highest and the lowest asymmetric charge distributions were achieved for the CNT-2H2PO4 and CNT-3H2PO4, respectively, leading to the greatest and the smallest dipole moments for the CNT-2H2PO4 (4.177 D) and the CNT-3H2PO4 (1.614 D). The compounds RIS-CNT-3H2PO4 and ZOL-CNT-3H2PO4 displayed the greatest electronegativity and electrophilicity index which were appropriate for the binding of drugs onto the bone surface (having partial positive charge due to the presence of Ca2+) and therefore effectively inhibiting the osteoporosis. Consequently, it was proposed that the drug-CNT-3H2PO4 was the most appropriate drug-carrier system for both of the RIS and ZOL drugs which could be employed as the most efficient vehicle.

Fabrication of Nanocarbon Composites Using In Situ Chemical Vapor Deposition and Their Applications.

PubMed

He, Chunnian; Zhao, Naiqin; Shi, Chunsheng; Liu, Enzuo; Li, Jiajun

2015-09-23

Nanocarbon (carbon nanotubes (CNTs) and graphene (GN)) composites attract considerable research interest due to their fascinating applications in many fields. Here, recent developments in the field of in situ chemical vapor deposition (CVD) for the design and controlled preparation of advanced nanocarbon composites are highlighted, specifically, CNT-reinforced bulk structural composites, as well as CNT, GN, and CNT/GN functional composites, together with their practical and potential applications. In situ CVD is a very attractive approach for the fabrication of composites because of its engaging features, such as its simplicity, low-cost, versatility, and tunability. The morphologies, structures, dispersion, and interface of the resulting nanocarbon composites can be easily modulated by varying the experimental parameters (such as temperature, catalysts, carbon sources, templates or template catalysts, etc.), which enables a great potential for the in situ synthesis of high-quality nanocarbons with tailored size and dimension for constructing high-performance composites, which has not yet been achieved by conventional methods. In addition, new trends of the in situ CVD toward nanocarbon composites are discussed. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Comparison between Single-Walled CNT, Multi-Walled CNT, and Carbon Nanotube-Fiber Pyrograf III

NASA Astrophysics Data System (ADS)

Mousa, Marwan S.

2018-02-01

Single-Walled CNT (SWCNTs), Multi-walled Carbon Nanotubes (MWCNTs), and Carbon Nanotube-Fibers Pyrograf III PR-1 (CNTFs) were deposited by chemical vapor deposition under vacuum pressure value of (10-7mbar). Their structures were investigated by field emission microscopy. Carbon Nano-Fibers Pyrograf III PR-1 showed an average fiber diameter within the range of 100-200 nm and a length of (30-100) μm. Single-walled Carbon Nanotubes were produced by high-pressure Carbon Monoxide process with an average diameter ranging between (1-4) nm and a length of (1-3) μm. Thin Multiwall Carbon Nanotube of carbon purity (90%) showed an average diameter tube (9.5 nm) with a high-aspect-ratio (>150). The research work reported here includes the field electron emission current-voltage (I-V) characteristics and presented as Fowler-Nordheim (FN) plots and the spatial emission current distributions (electron emission images) obtained and analyzed in terms of electron source features. For the three types of emitters, a single spot pattern for the electron spatial; distributions were observed, with emission current fluctuations in some voltage region.

Ab initio study of aspirin adsorption on single-walled carbon and carbon nitride nanotubes

NASA Astrophysics Data System (ADS)

Lee, Yongju; Kwon, Dae-Gyeon; Kim, Gunn; Kwon, Young-Kyun

We use ab intio density functional theory to investigate the adsorption properties of acetylsalicylic acid or aspirin on a (10, 0) carbon nanotube (CNT) and a (8, 0) triazine-based graphitic carbon nitride nanotube (CNNT). It is found that an aspirin molecule binds stronger to the CNNT with its adsorption energy of 0.67 eV than to the CNT with 0.51 eV. The stronger adsorption energy on the CNNT is ascribed to the high reactivity of its N atoms with high electron affinity. The CNNT exhibits local electric dipole moments, which cause strong charge redistribution in the aspirin molecule adsorbed on the CNNT than on the CNT. We also explore the influence of an external electric field on the adsorption properties of aspirin on these nanotubes by examining the modifications in their electronic band structures, partial densities of states, and charge distributions. It is found that an electric field applied along a particular direction induces aspirin molecular states in the in-gap region of the CNNT implying a potential application of aspirin detection.

Carbon nanotube-based multi electrode arrays for neuronal interfacing: progress and prospects

PubMed Central

Bareket-Keren, Lilach; Hanein, Yael

2013-01-01

Carbon nanotube (CNT) coatings have been demonstrated over the past several years as a promising material for neuronal interfacing applications. In particular, in the realm of neuronal implants, CNTs have major advantages owing to their unique mechanical and electrical properties. Here we review recent investigations utilizing CNTs in neuro-interfacing applications. Cell adhesion, neuronal engineering and multi electrode recordings with CNTs are described. We also highlight prospective advances in this field, in particular, progress toward flexible, bio-compatible CNT-based technology. PMID:23316141

Characterization of the Field Emission Properties of Carbon Nanotubes Formed on Silicon Carbide Substrates by Surface Decomposition

DTIC Science & Technology

2006-03-01

chemical vapor deposition (CVD) with methane as the feed gas . CNT growth specifics included using iron nitrate in an isopropanol solution as the...with residual oxygen gas in the chamber used for growth ([24], [25], [13]). Specific conditions for producing CNTs through the decomposition of...resulting in CNT formation is given by (2.30), (2.31), and (2.32) [24]. The oxygen gas acting as a catalyst to the chemical reaction is purported to be

Transparent Carbon Nanotube layers as cathodes in OLEDs

NASA Astrophysics Data System (ADS)

Papadimitratos, Alexios; Nasibulin, Albert; Kauppinen, Esko; Zakhidov, Anvar; Solarno Inc Collaboration; Aalto University Collaboration; UT Dallas Collaboration

2011-03-01

Organic Light Emitting diodes (OLEDs) have attracted high interest in recent years due to their potential use in future lighting and display applications. Reported work on OLEDs traditionally utilizes low work function materials as cathodes that are expensive to fabricate because of the high vacuum processing. Transparent carbon nanotube (CNT) sheets have excellent mechanical and electrical properties. We have already shown earlier that multi-wall (MWCNT) as well as single CNT (SWCNT) sheets can be used as effective anodes in bright OLEDs [,]. The true advantage of using the CNT sheets lies in flexible devices and new architectures with CNT sheet as layers in tandem devices with parallel connection. In this work, we are investigating the possibility of using SWCNT as cathodes in OLEDs. SWCNT sheets have been reported to show lower work function compared to MWCNT. Our work attempts to demonstrate transparent OLED devices with CNT anodes and cathodes. In the process, OLEDs with CNT cathodes have been fabricated in normal and inverted configurations using inorganic oxides (MoO3,ZnO) as invertion layers.

Improvement of thermal radiation characteristic of AC servomotor using Al-CNT composite material

NASA Astrophysics Data System (ADS)

Kikuchi, Y.; Wakiwaka, H.; Yanagihara, M.

2018-02-01

This study deals with a high thermal conductivity material of aluminum-carbon nanotube (CNT) composite with carbon fiber (CF) and the high radiation performance of AC servomotor using a stator made of nanotube composite material. The composite fabrication process was performed by melting a mixture of granular aluminum of less than 200 μm and CNT under conditions of pressed atmosphere at the same time. Two kinds of motors made using aluminum and the composite were evaluated to confirm the effect of thermal conductivity as the motor stator. A test rod of the composite with 14 wt% CF-7 wt% CNT-aluminum indicated the excellent thermal conductivity of 169 W/(mK) in the radial direction and 173 W/(mK) in the lengthwise direction. According to the obtained temperature radiation characteristic of the AC servomotor, the composite stator using CNT decreased the consumption energy to 16% compared to the conventional one. As a result, the highly efficient motor improved the radiation characteristic using the CNT composite stator.

Effect of carbon nano tube working electrode thickness on charge transport kinetics and photo-electrochemical characteristics of dye-sensitized solar cells

NASA Astrophysics Data System (ADS)

Gacemi, Yahia; Cheknane, Ali; Hilal, Hikmat S.

2018-02-01

Physiochemical processes at the photo-electrode and the counter electrode of dye sensitized solar cells (DSSCs) involving having carbon nanotubes (CNTs) instead of the TiO2 layer, within the working electrode, are simulated in this work. Attention is paid to find the effect of CNT layer thickness on photo-electrochemical (PEC) characteristics of the CNT-DSSCs. Comparison with other conventional TiO2-DSSC systems, taking into account the working electrode film thickness, is also described here. To achieve these goals, a model is presented to explain charge transport and electron recombination which involve electron photo-excitation in dye molecules, injection of electrons from the excited dye to CNT working electrode conduction band, diffusion of electrons inside the CNT electrode, charge transfer between oxidized dye and (I-) and recombination of electrons. The simulation is based on solving non-linear equations using the Newton-Raphson numerical method. This concept is proposed for modelling numerical Faradaic impedance at the photo-electrode and the platinum counter electrode. It then simulates the cell impedance spectrum describing the locus of the three semicircles in the Nyquist diagram. The transient equivalent circuit model is also presented based on optimizing current-voltage curves of CNT-DSSCs so as to optimize the fill factor (FF) and conversion efficiency (η). The results show that the simulated characteristics of CNT-DSSCs, with different active CNT layer thicknesses, are superior to conventional TiO2-DSSCs.

Coating carbon nanotubes with a polystyrene-based polymer protects against pulmonary toxicity

PubMed Central

2011-01-01

Background carbon nanotubes (CNT) can have adverse effects on health. Therefore, minimizing the risk associated with CNT exposure is of crucial importance. The aim of this work was to evaluate if coating multi-walled CNT (MWCNT) with polymers could modify their toxicity, thus representing a useful strategy to decrease adverse health effects of CNT. We used industrially-produced MWCNT uncoated (NT1) or coated (50/50 wt%) with acid-based (NT2) or polystyrene-based (NT3) polymer, and exposed murine macrophages (RAW 264.7 cell line) or Balb/c mice by intratracheal administration. Biological experiments were performed both in vitro and in vivo, examining time- and dose-dependent effects of CNT, in terms of cytotoxicity, expression of genes and proteins related to oxidative stress, inflammation and tissue remodeling, cell and lung tissue morphology (optical and transmission electron microscopy), and bronchoalveolar lavage fluid content analysis. Results extensive physico-chemical characterization of MWCNT was performed, and showed, although similar dimensions for the 3 MWCNT, a much smaller specific surface area for NT2 and NT3 as compared to NT1 (54.1, 34 and 227.54 m2/g respectively), along with different surface characteristics. MWCNT-induced cytotoxicity, oxidative stress, and inflammation were increased by acid-based and decreased by polystyrene-based polymer coating both in vitro in murine macrophages and in vivo in lung of mice monitored for 6 months. Conclusions these results demonstrate that coating CNT with polymers, without affecting their intrinsic structure, may constitute a useful strategy for decreasing CNT toxicity, and may hold promise for improving occupational safety and that of general the user. PMID:21255417

Determination of the effective diffusivity of water in a poly (methyl methacrylate) membrane containing carbon nanotubes using kinetic Monte Carlo simulations.

PubMed

Mermigkis, Panagiotis G; Tsalikis, Dimitrios G; Mavrantzas, Vlasis G

2015-10-28

A kinetic Monte Carlo (kMC) simulation algorithm is developed for computing the effective diffusivity of water molecules in a poly(methyl methacrylate) (PMMA) matrix containing carbon nanotubes (CNTs) at several loadings. The simulations are conducted on a cubic lattice to the bonds of which rate constants are assigned governing the elementary jump events of water molecules from one lattice site to another. Lattice sites belonging to PMMA domains of the membrane are assigned different rates than lattice sites belonging to CNT domains. Values of these two rate constants are extracted from available numerical data for water diffusivity within a PMMA matrix and a CNT pre-computed on the basis of independent atomistic molecular dynamics simulations, which show that water diffusivity in CNTs is 3 orders of magnitude faster than in PMMA. Our discrete-space, continuum-time kMC simulation results for several PMMA-CNT nanocomposite membranes (characterized by different values of CNT length L and diameter D and by different loadings of the matrix in CNTs) demonstrate that the overall or effective diffusivity, D(eff), of water in the entire polymeric membrane is of the same order of magnitude as its diffusivity in PMMA domains and increases only linearly with the concentration C (vol. %) in nanotubes. For a constant value of the concentration C, D(eff) is found to vary practically linearly also with the CNT aspect ratio L/D. The kMC data allow us to propose a simple bilinear expression for D(eff) as a function of C and L/D that can describe the numerical data for water mobility in the membrane extremely accurately. Additional simulations with two different CNT configurations (completely random versus aligned) show that CNT orientation in the polymeric matrix has only a minor effect on D(eff) (as long as CNTs do not fully penetrate the membrane). We have also extensively analyzed and quantified sublinear (anomalous) diffusive phenomena over small to moderate times and correlated them with the time needed for penetrant water molecules to explore the available large, fast-diffusing CNT pores before Fickian diffusion is reached.

Determination of the effective diffusivity of water in a poly (methyl methacrylate) membrane containing carbon nanotubes using kinetic Monte Carlo simulations

NASA Astrophysics Data System (ADS)

Mermigkis, Panagiotis G.; Tsalikis, Dimitrios G.; Mavrantzas, Vlasis G.

2015-10-01

A kinetic Monte Carlo (kMC) simulation algorithm is developed for computing the effective diffusivity of water molecules in a poly(methyl methacrylate) (PMMA) matrix containing carbon nanotubes (CNTs) at several loadings. The simulations are conducted on a cubic lattice to the bonds of which rate constants are assigned governing the elementary jump events of water molecules from one lattice site to another. Lattice sites belonging to PMMA domains of the membrane are assigned different rates than lattice sites belonging to CNT domains. Values of these two rate constants are extracted from available numerical data for water diffusivity within a PMMA matrix and a CNT pre-computed on the basis of independent atomistic molecular dynamics simulations, which show that water diffusivity in CNTs is 3 orders of magnitude faster than in PMMA. Our discrete-space, continuum-time kMC simulation results for several PMMA-CNT nanocomposite membranes (characterized by different values of CNT length L and diameter D and by different loadings of the matrix in CNTs) demonstrate that the overall or effective diffusivity, Deff, of water in the entire polymeric membrane is of the same order of magnitude as its diffusivity in PMMA domains and increases only linearly with the concentration C (vol. %) in nanotubes. For a constant value of the concentration C, Deff is found to vary practically linearly also with the CNT aspect ratio L/D. The kMC data allow us to propose a simple bilinear expression for Deff as a function of C and L/D that can describe the numerical data for water mobility in the membrane extremely accurately. Additional simulations with two different CNT configurations (completely random versus aligned) show that CNT orientation in the polymeric matrix has only a minor effect on Deff (as long as CNTs do not fully penetrate the membrane). We have also extensively analyzed and quantified sublinear (anomalous) diffusive phenomena over small to moderate times and correlated them with the time needed for penetrant water molecules to explore the available large, fast-diffusing CNT pores before Fickian diffusion is reached.

Thermal transport of carbon nanotubes and graphene under optical and electrical heating measured by Raman spectroscopy

NASA Astrophysics Data System (ADS)

Hsu, I.-Kai

This thesis presents systematic studies of thermal transport in individual single walled carbon nanotubes (SWCNTs) and graphene by optical and electrical approaches using Raman spectroscopy. In the work presented from Chapter 2 to Chapter 6, individual suspended CNTs are preferentially measured in order to explore their intrinsic thermal properties. Moreover, the Raman thermometry is developed to detect the temperature of the carbon nanotube (CNT). A parabolic temperature profile is observed in the suspended region of the CNT while a heating laser scans across it, providing a direct evidence of diffusive thermal transport in an individual suspended CNT. Based on the curvature of the temperature profile, we can solve for the ratio of thermal contact resistance to the thermal resistance of the CNT, which spans the range from 0.02 to 17. The influence of thermal contact resistance on the thermal transport in an individual suspended CNT is also studied. The Raman thermometry is carried out in the center of a CNT, while its contact length is successively shortened by an atomic force microscope (AFM) tip cutting technique. By investigating the dependence of the CNT temperature on its thermal contact length, the temperature of a CNT is found to increase dramatically as the contact length is made shorter. This work reveals the importance of manipulating the CNT thermal contact length when adopting CNT as a thermal management material. In using a focused laser to induce heating in a suspended CNT, one open question that remains unanswered is how many of the incident photons are absorbed by the CNT of interest. To address this question, micro-fabricated platinum thermometers, together with micro-Raman spectroscopy are used to quantify the optical absorption of an individual CNT. The absorbed power in the CNT is equal to the power detected by two thermometers at the end of the CNT. Our result shows that the optical absorption lies in the range between 0.03 to 0.44%. In addition, the temperature gradient from the heating location to both ends of the suspended CNT, together with absorbed power and diameter of the CNT can be used to solve for the thermal conductivity of the CNT, which is found to span the range from 0.51nW/K to 2.28nW/K. We also conduct Raman measurements to explore the effect of gas molecules on thermal transport in electrically- or optically-heated suspended carbon nanotubes. Under the same electric heating power, the temperature increase of the CNT in gaseous environments is found to be considerably less than in vacuum, indicating non-negligible heat dissipation to the surrounding gas molecules. The result shows the approximately 50 to 60% of the heat is taken away by the surrounding gas molecules in a 5 microm long electrically-heated CNT. Following the electrical heating technique, a two-laser, purely optical measurement technique is utilized to observe heat dissipation in an ultra-long suspended CNT. Exponentially decaying temperature profiles with the heat decay lengths shorter than 7 microm are found in all samples measured. These relatively short heat decay lengths are attributed to the strong thermal coupling of carbon nanotubes' surface to air molecules. Moreover, the previously unmeasured heat transfer coefficient between CNT and air molecules is determined to be on the order of 104 W/m2·K.

Electrical properties of carbon nanotubes modified GaSe glassy system

NASA Astrophysics Data System (ADS)

Khan, Hana; Khan, Zubair M. S. H.; Islam, Shama; Rahman, Raja Saifu; Husain, M.; Zulfequar, M.

2018-05-01

In this paper we report the investigation of the effect of Carbon Nanotubes (CNT) addition on the electrical properties of GaSe Glassy system. Dielectric constant and dielectric loss of GaSe glassy system are found to increase on CNT addition. The conductivity of GaSe glasy systems is also found to increase on CNT addition. This behavior is attributed to the excellent conduction properties of Carbon Nanotube.

Multifunctional Shear Pressed CNT Sheets for Strain Sensing and Composite Joint Toughening

DTIC Science & Technology

2015-09-30

overall delamination fracture mechanism shows highly variable from sample to sample and very sensitive to such factors as CNT functionalization, epoxy...fibers). The overall delamination fracture mechanism becomes highly variable from sample to sample and very sensitive to the effects of CNT... Mechanics Reviews, 1994, 47, No. 11, 517-544. 13. Sela, N.; Ishai, O. “Interlaminar Fracture Toughness and Toughening of Laminated Composite

Piezoelectric Response of Aligned Electrospun Polyvinylidene Fluoride/Carbon Nanotube Nanofibrous Membranes.

PubMed

Wu, Chang-Mou; Chou, Min-Hui; Zeng, Wun-Yuan

2018-06-10

Polyvinylidene fluoride (PVDF) shows piezoelectricity related to its β-phase content and mechanical and electrical properties influenced by its morphology and crystallinity. Electrospinning (ES) can produce ultrafine and well-aligned PVDF nanofibers. In this study, the effects of the presence of carbon nanotubes (CNT) and optimized ES parameters on the crystal structures and piezoelectric properties of aligned PVDF/CNT nanofibrous membranes were examined. The optimal β content and piezoelectric coefficient (d 33 ) of the aligned electrospun PVDF reached 88% and 27.4 pC/N; CNT addition increased the β-phase content to 89% and d 33 to 31.3 pC/N. The output voltages of piezoelectric units with aligned electrospun PVDF/CNT membranes increased linearly with applied loading and showed good stability during cyclic dynamic compression and tension. The sensitivities of the piezoelectric units with the membranes under dynamic compression and tension were 2.26 mV/N and 4.29 mV/%, respectively. In bending tests, the output voltage increased nonlinearly with bending angle because complicated forces were involved. The output of the aligned membrane-based piezoelectric unit with CNT was 1.89 V at the bending angle of 100°. The high electric outputs indicate that the aligned electrospun PVDF/CNT membranes are potentially effective for flexible wearable sensor application with high sensitivity.

Development of plenoptic infrared camera using low dimensional material based photodetectors

NASA Astrophysics Data System (ADS)

Chen, Liangliang

Infrared (IR) sensor has extended imaging from submicron visible spectrum to tens of microns wavelength, which has been widely used for military and civilian application. The conventional bulk semiconductor materials based IR cameras suffer from low frame rate, low resolution, temperature dependent and highly cost, while the unusual Carbon Nanotube (CNT), low dimensional material based nanotechnology has been made much progress in research and industry. The unique properties of CNT lead to investigate CNT based IR photodetectors and imaging system, resolving the sensitivity, speed and cooling difficulties in state of the art IR imagings. The reliability and stability is critical to the transition from nano science to nano engineering especially for infrared sensing. It is not only for the fundamental understanding of CNT photoresponse induced processes, but also for the development of a novel infrared sensitive material with unique optical and electrical features. In the proposed research, the sandwich-structured sensor was fabricated within two polymer layers. The substrate polyimide provided sensor with isolation to background noise, and top parylene packing blocked humid environmental factors. At the same time, the fabrication process was optimized by real time electrical detection dielectrophoresis and multiple annealing to improve fabrication yield and sensor performance. The nanoscale infrared photodetector was characterized by digital microscopy and precise linear stage in order for fully understanding it. Besides, the low noise, high gain readout system was designed together with CNT photodetector to make the nano sensor IR camera available. To explore more of infrared light, we employ compressive sensing algorithm into light field sampling, 3-D camera and compressive video sensing. The redundant of whole light field, including angular images for light field, binocular images for 3-D camera and temporal information of video streams, are extracted and expressed in compressive approach. The following computational algorithms are applied to reconstruct images beyond 2D static information. The super resolution signal processing was then used to enhance and improve the image spatial resolution. The whole camera system brings a deeply detailed content for infrared spectrum sensing.

Dramatic improvement in water retention and proton conductivity in electrically aligned functionalized CNT/SPEEK nanohybrid PEM.

PubMed

Gahlot, Swati; Kulshrestha, Vaibhav

2015-01-14

Nanohybrid membranes of electrically aligned functionalized carbon nanotube f CNT with sulfonated poly ether ether ketone (SPEEK) have been successfully prepared by solution casting. Functionalization of CNTs was done through a carboxylation and sulfonation route. Further, a constant electric field (500 V·cm(-2)) has been applied to align CNTs in the same direction during the membrane drying process. All the membranes are characterized chemically, thermally, and mechanically by the means of FTIR, DSC, DMA, UTM, SEM, TEM, and AFM techniques. Intermolecular interactions between the components in hybrid membranes are established by FTIR. Physicochemical measurements were done to analyze membrane stability. Membranes are evaluated for proton conductivity (30-90 °C) and methanol crossover resistance to reveal their potential for direct methanol fuel cell application. Incorporation of f CNT reasonably increases the ion-exchange capacity, water retention, and proton conductivity while it reduces the methanol permeability. The maximum proton conductivity has been found in the S-sCNT-5 nanohybrid PEM with higher methanol crossover resistance. The prepared membranes can be also used for electrode material for fuel cells and batteries.

Separation of Bacteria, Protozoa and Carbon Nanotubes by Density Gradient Centrifugation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mortimer, Monika; Petersen, Elijah; Buchholz, Bruce

Sustainable production and use of carbon nanotube (CNT)-enabled materials require efficient assessment of CNT environmental hazards, including the potential for CNT bioaccumulation and biomagnification in environmental receptors. Microbes, as abundant organisms responsible for nutrient cycling in soil and water, are important ecological receptors for studying the effects of CNTs. Quantification of CNT association with microbial cells requires efficient separation of CNT-associated cells from individually dispersed CNTs and CNT agglomerates. Here in this paper, we designed, optimized, and demonstrated procedures for separating bacteria (Pseudomonas aeruginosa) from unbound multiwall carbon nanotubes (MWCNTs) and MWCNT agglomerates using sucrose density gradient centrifugation. We demonstratemore » separation of protozoa (Tetrahymena thermophila) from MWCNTs, bacterial agglomerates, and protozoan fecal pellets by centrifugation in an iodixanol solution. The presence of MWCNTs in the density gradients after centrifugation was determined by quantification of 14C-labeled MWCNTs; the recovery of microbes from the density gradient media was confirmed by optical microscopy. Protozoan intracellular contents of MWCNTs and of bacteria were also unaffected by the designed separation process. Lastly, the optimized methods contribute to improved efficiency and accuracy in quantifying MWCNT association with bacteria and MWCNT accumulation in protozoan cells, thus supporting improved assessment of CNT bioaccumulation.« less

Separation of Bacteria, Protozoa and Carbon Nanotubes by Density Gradient Centrifugation

DOE PAGES

Mortimer, Monika; Petersen, Elijah; Buchholz, Bruce; ...

2016-10-12

Sustainable production and use of carbon nanotube (CNT)-enabled materials require efficient assessment of CNT environmental hazards, including the potential for CNT bioaccumulation and biomagnification in environmental receptors. Microbes, as abundant organisms responsible for nutrient cycling in soil and water, are important ecological receptors for studying the effects of CNTs. Quantification of CNT association with microbial cells requires efficient separation of CNT-associated cells from individually dispersed CNTs and CNT agglomerates. Here in this paper, we designed, optimized, and demonstrated procedures for separating bacteria (Pseudomonas aeruginosa) from unbound multiwall carbon nanotubes (MWCNTs) and MWCNT agglomerates using sucrose density gradient centrifugation. We demonstratemore » separation of protozoa (Tetrahymena thermophila) from MWCNTs, bacterial agglomerates, and protozoan fecal pellets by centrifugation in an iodixanol solution. The presence of MWCNTs in the density gradients after centrifugation was determined by quantification of 14C-labeled MWCNTs; the recovery of microbes from the density gradient media was confirmed by optical microscopy. Protozoan intracellular contents of MWCNTs and of bacteria were also unaffected by the designed separation process. Lastly, the optimized methods contribute to improved efficiency and accuracy in quantifying MWCNT association with bacteria and MWCNT accumulation in protozoan cells, thus supporting improved assessment of CNT bioaccumulation.« less

Microcontact printing for patterning carbon nanotube/polymer composite films with electrical conductivity.

PubMed

Ogihara, Hitoshi; Kibayashi, Hiro; Saji, Tetsuo

2012-09-26

Patterned carbon nanotube (CNT)/acrylic resin composite films were prepared using microcontact printing (μCP). To prepare ink for μCP, CNTs were dispersed into propylene glycol monomethyl ether acetate (PGMEA) solution in which acrylic resin and a commercially available dispersant (Disperbyk-2001) dissolved. The resulting ink were spin-coated onto poly(dimethylsiloxane) (PDMS) stamps. By drying solvent components from the ink, CNT/polymer composite films were prepared over PDMS stamps. Contact between the stamps and glass substrates provided CNT/polymer composite patternings on the substrates. The transfer behavior of the CNT/polymer composite films depended on the thermal-treatment temperature during μCP; thermal treatment at temperatures near the glass-transition temperature (T(g)) of the acrylic resin was effective to form uniform patternings on substrates. Moreover, contact area between polymer and substrates also affect the transfer behavior. The CNT/polymer composite films showed high electrical conductivity, despite the nonconductivity of polymer components, because CNTs in the films were interconnected. The electrical conductivity of the composite films increased as CNT content in the film became higher; as a result, the composite patternings showed almost as high electrical conductivity as previously reported CNT/polymer bulk composites.

Separation of Bacteria, Protozoa and Carbon Nanotubes by Density Gradient Centrifugation

PubMed Central

Mortimer, Monika; Petersen, Elijah J.; Buchholz, Bruce A.; Holden, Patricia A.

2016-01-01

Sustainable production and use of carbon nanotube (CNT)-enabled materials require efficient assessment of CNT environmental hazards, including the potential for CNT bioaccumulation and biomagnification in environmental receptors. Microbes, as abundant organisms responsible for nutrient cycling in soil and water, are important ecological receptors for studying the effects of CNTs. Quantification of CNT association with microbial cells requires efficient separation of CNT-associated cells from individually dispersed CNTs and CNT agglomerates. Here, we designed, optimized, and demonstrated procedures for separating bacteria (Pseudomonas aeruginosa) from unbound multiwall carbon nanotubes (MWCNTs) and MWCNT agglomerates using sucrose density gradient centrifugation. We demonstrate separation of protozoa (Tetrahymena thermophila) from MWCNTs, bacterial agglomerates, and protozoan fecal pellets by centrifugation in an iodixanol solution. The presence of MWCNTs in the density gradients after centrifugation was determined by quantification of 14C-labeled MWCNTs; the recovery of microbes from the density gradient media was confirmed by optical microscopy. Protozoan intracellular contents of MWCNTs and of bacteria were also unaffected by the designed separation process. The optimized methods contribute to improved efficiency and accuracy in quantifying MWCNT association with bacteria and MWCNT accumulation in protozoan cells, thus supporting improved assessment of CNT bioaccumulation. PMID:27917301

Domination of volumetric toughening by silver nanoparticles over interfacial strengthening of carbon nanotubes in bactericidal hydroxyapatite biocomposite.

PubMed

Herkendell, Katharina; Shukla, Vishnu Raj; Patel, Anup Kumar; Balani, Kantesh

2014-01-01

In order to address the problem of bacterial infections in bone-substitution surgery, it is essential that bone replacement biomaterials are equipped with bactericidal components. This research aims to optimize the content of silver (Ag), a well-known antibacterial metal, in a multiwalled carbon nanotube (CNT) reinforced hydroxyapatite (HA) composite, to yield a bioceramic which can be used as an antibacterial and tough surface of bone replacement prosthesis. The bactericidal properties evaluated using Escherichia coli and Staphylococcus epidermidis indicate that CNT reinforcement supports growth of Gram negative E. coli bacteria (~8.5% more adhesion than pure HA); but showed a strong decrease of Gram positive S. epidermidis bacteria (~diminished to 66%) compared to that of pure HA. Small amounts of silver (2-5wt.%) already show a severe bactericidal effect when compared to that of HA-CNT (by 30% and ~60% respectively). MTT assay confirmed enhanced biocompatibility of L929 cells on HA-4wt.% CNT (~121%), HA-4wt.% CNT-1wt.% Ag (~124%) sample and HA-4wt.% CNT-2wt.% Ag (~100%) when compared to that of pure HA. The samples with higher silver content showed decreased biocompatibility (77% for HA-4wt.% CNT-5wt.% Ag sample and 73% for HA-4wt.% CNT-10wt.% Ag). Though reinforcement of 4wt.% CNT has shown an increase of fracture toughness by ~62%, silver reinforcement has shown enhancement of up to 244% (i.e. 3.43 times). Accordingly, isolation of toughening contribution indicates that volumetric toughening by silver dominates over interfacial strengthening contributed by CNTs towards enhanced fracture toughness of potential HA-Ag-CNT biocomposites. © 2013.

Mechanical deformation of carbon nanotube nano-rings on flat substrate

NASA Astrophysics Data System (ADS)

Zheng, Meng; Ke, Changhong

2011-04-01

We present a numerical analysis of the mechanical deformation of carbon nanotube (CNT) nano-rings on flat graphite substrates, which is motivated by our recent experimental findings on the elastic deformation of CNT nano-rings. Our analysis considers a perfectly circular CNT ring formed by bending a straight individual or bundled single-walled nanotube to connect its two ends. The seamless CNT ring is placed vertically on a flat graphite substrate and its respective deformation curvatures under zero external force, compressive, and tensile forces are determined using a continuum model based on nonlinear elastica theory. Our results show that the van der Waals interaction between the CNT ring and the substrate has profound effects on the deformation of the CNT ring, and that the interfacial binding interaction between the CNT ring and the substrate is strongly modulated by the ring deformation. Our results demonstrate that the CNT ring in force-free conditions has a flat ring segment in contact with the substrate if the ring radius R ≥√EI/2Wvdw , in which EI is the flexural rigidity of the nanotube and Wvdw is the per-unit-length van der Waals energy between the flat ring segment and the substrate. Our results reveal that the load-deformation profiles of the CNT ring under tensile loadings exhibit bifurcation behavior, which is ascribed to its van der Waals interaction with the substrate and is dependent on its relaxed conformation on the substrate. Our work suggests that CNT nano-rings are promising for a number of applications, such as ultrasensitive force sensors and stretchable and flexible structural components in nanoscale mechanical and electromechanical systems.

Carbon and metal nanotube hybrid structures on graphene as efficient electron field emitters

NASA Astrophysics Data System (ADS)

Heo, Kwang; Lee, Byung Yang; Lee, Hyungwoo; Cho, Dong-guk; Arif, Muhammad; Kim, Kyu Young; Choi, Young Jin; Hong, Seunghun

2016-07-01

We report a facile and efficient method for the fabrication of highly-flexible field emission devices by forming tubular hybrid structures based on carbon nanotubes (CNTs) and nickel nanotubes (Ni NTs) on graphene-based flexible substrates. By employing an infiltration process in anodic alumina oxide (AAO) templates followed by Ni electrodeposition, we could fabricate CNT-wrapped Ni NT/graphene hybrid structures. During the electrodeposition process, the CNTs served as Ni nucleation sites, resulting in a large-area array of high aspect-ratio field emitters composed of CNT-wrapped Ni NT hybrid structures. As a proof of concepts, we demonstrate that high-quality flexible field emission devices can be simply fabricated using our method. Remarkably, our proto-type field emission devices exhibited a current density higher by two orders of magnitude compared to other devices fabricated by previous methods, while maintaining its structural integrity in various bending deformations. This novel fabrication strategy can be utilized in various applications such as optoelectronic devices, sensors and energy storage devices.

Carbon and metal nanotube hybrid structures on graphene as efficient electron field emitters.

PubMed

Heo, Kwang; Lee, Byung Yang; Lee, Hyungwoo; Cho, Dong-Guk; Arif, Muhammad; Kim, Kyu Young; Choi, Young Jin; Hong, Seunghun

2016-07-08

We report a facile and efficient method for the fabrication of highly-flexible field emission devices by forming tubular hybrid structures based on carbon nanotubes (CNTs) and nickel nanotubes (Ni NTs) on graphene-based flexible substrates. By employing an infiltration process in anodic alumina oxide (AAO) templates followed by Ni electrodeposition, we could fabricate CNT-wrapped Ni NT/graphene hybrid structures. During the electrodeposition process, the CNTs served as Ni nucleation sites, resulting in a large-area array of high aspect-ratio field emitters composed of CNT-wrapped Ni NT hybrid structures. As a proof of concepts, we demonstrate that high-quality flexible field emission devices can be simply fabricated using our method. Remarkably, our proto-type field emission devices exhibited a current density higher by two orders of magnitude compared to other devices fabricated by previous methods, while maintaining its structural integrity in various bending deformations. This novel fabrication strategy can be utilized in various applications such as optoelectronic devices, sensors and energy storage devices.

Immobilization of carbon nanotubes on functionalized graphene film grown by chemical vapor deposition and characterization of the hybrid material.

PubMed

Adhikari, Prashanta Dhoj; Jeon, Seunghan; Cha, Myoung-Jun; Jung, Dae Sung; Kim, Yooseok; Park, Chong-Yun

2014-02-01

We report the surface functionalization of graphene films grown by chemical vapor deposition and fabrication of a hybrid material combining multi-walled carbon nanotubes and graphene (CNT-G). Amine-terminated self-assembled monolayers were prepared on graphene by the UV-modification of oxidized groups introduced onto the film surface. Amine-termination led to effective interaction with functionalized CNTs to assemble a CNT-G hybrid through covalent bonding. Characterization clearly showed no defects of the graphene film after the immobilization reaction with CNT. In addition, the hybrid graphene material revealed a distinctive CNT-G structure and p-n type electrical properties. The introduction of functional groups on the graphene film surface and fabrication of CNT-G hybrids with the present technique could provide an efficient, novel route to device fabrication.

Synergistic effect of non-covalent interaction in colloidal nematic liquid crystal doped with magnetic functionalized single-walled carbon nanotubes

NASA Astrophysics Data System (ADS)

Dalir, Nima; Javadian, Soheila

2018-03-01

Single-walled carbon nanotubes (SWCNTs), CNT@Fe3O4, and Fe3O4 nanocomposites were doped to eutectic uniaxial nematic liquid crystal (NLC's) (E5CN7) to improve physiochemical properties such as phase transition temperature, activation energy (Ea), dielectric anisotropy, and electro-optical properties. The thermal study of nematic phase shows a decrease in the nematic to isotropic phase transition temperature as CNT is doped. However, higher doping concentration of CNTs leads to the further increase in transition temperature. The anchoring effect or π-π interaction plays a key role in N-I phase transition. The functionalization of SWCNTs with Fe3O4 diminishes the CNT aggregation while the magnetic susceptibility is increased. The functionalized CNT doping to NLC's decrease significantly the phase transition temperature compared to doping of non-functionalized CNTs. Attractive interaction between guest and host molecules by magnetic and geometry effect increased the enthalpy and entropy of phase transition in the SWCNT@Fe3O4 sample compared to non-functionalized CNT doped system. Also, the Ea values are decreased as SWCNT@Fe3O4 is doped to pure E5CN7. The difference of N-I phase transition temperature was observed in Fe3O4 and CNT@Fe3O4 compared to SWCNT doped systems. Finally, dielectric anisotropy was increased in the doped system compared to pure NLC.

Functional characteristics, wettability properties and cytotoxic effect of starch film incorporated with multi-walled and hydroxylated multi-walled carbon nanotubes.

PubMed

Shahbazi, Mahdiyar; Rajabzadeh, Ghadir; Sotoodeh, Shahnaz

2017-11-01

Two types of multi-walled carbon nanotubes (CNT and CNT-OH) at different levels (0.1-0.9wt%) were introduced into starch matrix in order to modify its functional properties. The optimum concentration of each nanotube was selected based on the results of water solubility, water permeability and mechanical experiments. The physico-mechanical data showed that CNT up to 0.7wt% led to a notable increase in water resistance, water barrier property and tensile strength, whilst regarding CNT-OH, these improvements found at 0.9wt%. Therefore, effects of optimized level of each nanotube on the starch film were evaluated by XRD, surface hydrophobicity, wettability and surface energy tests. XRD revealed that the position of starch characteristic peak shifted to higher degree after nanotubes introducing. The hydrophobic character of the film was greatly increased with incorporation of nanoparticles, as evidenced by increased contact angle with greatest value regarding CNT-OH. Moreover, CNT-OH notably decreased the surface free energy of the starch film. Finally, the conformity of both nanocomposites with actual food regulations on biodegradable materials was tested by cytotoxicity assay to evaluate the possibility of application in food packaging sector. Both nanocomposite films had potential of cytotoxic effects, since they could increase cytoplasmic lactate dehydrogenase release from L-929 fibroblast cells in contact with their surface. Copyright © 2017 Elsevier B.V. All rights reserved.

Modeling the interaction Between Ethylene Diamine and Water Films on the Surface of a Carbon Nanotube

NASA Technical Reports Server (NTRS)

Jaffe, Richard L.; Walther, Jens H.; Zimmerli, Urs; Koumoutsakos, Petros

2004-01-01

It has been observed that a carbon nanotube (CNT) AFM tip coated with ethylene diamine (EDA) penetrates the liquid water-air interface more easily than an uncoated nanotube tip. The EDA coating remains intact through repeated cycles of dipping and removal. In order to understand the physical basis for this observation, we use ab initio quantum chemistry calculations to study the EDA-CNT-water interaction and to parameterize a force field describing this system. Molecular dynamics (MD) simulations are carried out for EDA-water mixtures and an EDA-coated carbon nanotube immmed in water. These simulations are similar to our earlier MD study that characterized the CNT-water interface. The attractive CNT-EDA and CNT-water interactions arise primarily from van der Waals forces, and the EDA-EDA, EDA-water and water-water interactions are mainly due to hydrogen bond formation. The binding energ of single EDA molecule to the nanotube is nearly three times larger than the corresponding value found for water (4.3 versus 1.5 kcal mol, respectively). The EDA molecules readily stick to and diffuse along the CNT surface. As a resulf mixing of the EDA and water films does not occur on the timescale of the MD simulations. The EDA film reduces the hydrophobicity of the nanotube surface and acts like a prototypical surfactant in stabilizing the suspension of carbon nanotubes in water. For this presentation, we use the MD simulations to determine how the presence of the carbon nanotube surface perturbs the properties of EDA-water mixtures.

Hierarchical multifunctional composites by conformally coating aligned carbon nanotube arrays with conducting polymer.

PubMed

Vaddiraju, Sreeram; Cebeci, Hülya; Gleason, Karen K; Wardle, Brian L

2009-11-01

A novel method for the fabrication of carbon nanotube (CNT)-conducting polymer composites is demonstrated by conformally coating extremely high aspect ratio vertically aligned-CNT (A-CNT) arrays with conducting polymer via oxidative chemical vapor deposition (oCVD). A mechanical densification technique is employed that allows the spacing of the A-CNTs to be controlled, yielding a range of inter-CNT distances between 20 and 70 nm. Using this morphology control, oCVD is shown to conformally coat 8-nm-diameter CNTs having array heights up to 1 mm (an aspect ratio of 10(5)) at all inter-CNT spacings. Three phase CNT-conducting polymer nanocomposites are then fabricated by introducing an insulating epoxy via capillary-driven wetting. CNT morphology is maintained during processing, allowing quantification of direction-dependent (nonisotropic) composite properties. Electrical conductivity occurs primarily along the CNT axial direction, such that the conformal conducting polymer has little effect on the activation energy required for charge conduction. In contrast, the conducting polymer coating enhanced the conductivity in the radial direction by lowering the activation energy required for the creation of mobile charge carriers, in agreement with variable-range-hopping models. The fabrication strategy introduced here can be used to create many multifunctional materials and devices (e.g., direction-tailorable hydrophobic and highly conducting materials), including a new four-phase advanced fiber composite architecture.

Mechanisms of connecting tubule glomerular feedback enhancement by aldosterone

PubMed Central

Ren, YiLin; Janic, Branislava; Kutskill, Kristopher; Peterson, Edward L.

2016-01-01

Connecting tubule glomerular feedback (CTGF) is a mechanism where an increase in sodium (Na) concentration in the connecting tubule (CNT) causes the afferent arteriole (Af-Art) to dilate. We recently reported that aldosterone within the CNT lumen enhances CTGF via a nongenomic effect involving GPR30 receptors and sodium/hydrogen exchanger (NHE), but the signaling pathways of this mechanism are unknown. We hypothesize that aldosterone enhances CTGF via cAMP/protein kinase A (PKA) pathway that activates protein kinase C (PKC) and stimulates superoxide (O2−) production. Rabbit Af-Arts and their adherent CNTs were microdissected and simultaneously perfused. Two consecutive CTGF curves were elicited by increasing the CNT luminal NaCl. We found that the main effect of aldosterone was to sensitize CTGF and we analyzed data by comparing NaCl concentration in the CNT perfusate needed to achieve half of the maximal response (EC50). During the control period, the NaCl concentration that elicited a half-maximal response (EC50) was 37.0 ± 2.0 mmol/l; addition of aldosterone (10−8 mol/l) to the CNT lumen decreased EC50 to 19.3 ± 1.3 mmol/l (P ≤ 0.001 vs. Control). The specific adenylyl cyclase inhibitor 2′,3′-dideoxyadenosine (ddA; 2 × 10−4 mol/l) and the PKA inhibitor H-89 dihydrochloride hydrate (H-89; 2 × 10−6 mol/l) prevented the aldosterone effect. The selective PKC inhibitor GF109203X (10−8 mol/l) also prevented EC50 reduction caused by aldosterone. CNT intraluminal addition of O2− scavenger tempol (10−4 mol/l) blocked the aldosterone effect. We conclude that aldosterone inside the CNT lumen enhances CTGF via a cAMP/PKA/PKC pathway and stimulates O2− generation and this process may contribute to renal damage by increasing glomerular capillary pressure. PMID:27413197

Structure and magnetic fabric of the Quetico metasedimentary rocks in the Calm Lake - Perch Lake area, near Atikokan, Northwestern Ontario

NASA Astrophysics Data System (ADS)

Sarvas, Perry

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Fire disturbance mapping in a northern boreal forest using AVHRR/NDVI imagery: Comparing techniques of change detection and substrate correction

NASA Astrophysics Data System (ADS)

Remmel, Tarmo Kaarel

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Bioelectronic Nose Using Odorant Binding Protein-Derived Peptide and Carbon Nanotube Field-Effect Transistor for the Assessment of Salmonella Contamination in Food.

PubMed

Son, Manki; Kim, Daesan; Kang, Jinkyung; Lim, Jong Hyun; Lee, Seung Hwan; Ko, Hwi Jin; Hong, Seunghun; Park, Tai Hyun

2016-12-06

Salmonella infection is the one of the major causes of food borne illnesses including fever, abdominal pain, diarrhea, and nausea. Thus, early detection of Salmonella contamination is important for our healthy life. Conventional detection methods for the food contamination have limitations in sensitivity and rapidity; thus, the early detection has been difficult. Herein, we developed a bioelectronic nose using a carbon nanotube (CNT) field-effect transistor (FET) functionalized with Drosophila odorant binding protein (OBP)-derived peptide for easy and rapid detection of Salmonella contamination in ham. 3-Methyl-1-butanol is known as a specific volatile organic compound, generated from the ham contaminated with Salmonella. We designed and synthesized the peptide based on the sequence of the Drosophila OBP, LUSH, which specifically binds to alcohols. The C-terminus of the synthetic peptide was modified with three phenylalanine residues and directly immobilized onto CNT channels using the π-π interaction. The p-type properties of FET were clearly maintained after the functionalization using the peptide. The biosensor detected 1 fM of 3-methyl-1-butanol with high selectivity and successfully assessed Salmonella contamination in ham. These results indicate that the bioelectronic nose can be used for the rapid detection of Salmonella contamination in food.

Fabrication and characterization of vertically aligned carbon-nanotube membranes

NASA Astrophysics Data System (ADS)

Castellano, Richard; Akin, Cevat; Purri, Matt; Shan, Jerry; Kim, Sangil; Fornasiero, Francesco

2015-11-01

Membranes having vertically-aligned carbon-nanotube (VACNT) pores offer promise as highly efficient and permeable membranes for use as breathable thin films, or in filtration and separation applications, among others. However, current membrane-fabrication techniques utilizing chemical-vapor-deposition-grown VACNT arrays are costly and difficult to scale up. We have developed a solution-based, electric-field-assisted approach as a cost-effective and scalable method to produce large-area VACNT membranes. Nanotubes are dispersed in a liquid polymer, and aligned and electrodeposited with the aid of an electric field prior to crosslinking the polymer to create VACNT membranes. We experimentally examine the electrodeposition process, focusing on parameters including the electric field, composition of the solution, and CNT functionalization that can affect the nanotube number density in the resulting membrane. We characterize the CNT pore size and number density and investigate the transport properties of the membrane. Size-exclusion tests are used to check for defects and infer the pore size of the VACNT membranes. Dry-gas membrane permeability is measured with a pressurized nitrogen-flow system, while moisture-vapor-transfer rate is measured with the ASTM-E96 upright-cup test. We discuss the measured transport properties of the solution-based, electric-field-fabricated VACNT membranes in reference to their application as breathable thin films. We would like to acknowledge DTRA for their funding and support of our research.

Highly Selective and Sensitive Detection of Acetylcholine Using Receptor-Modified Single-Walled Carbon Nanotube Sensors

NASA Astrophysics Data System (ADS)

Xu, Shihong; Kim, Byeongju; Song, Hyun Seok; Jin, Hye Jun; Park, Eun Jin; Lee, Sang Hun; Lee, Byung Yang; Park, Tai Hyun; Hong, Seunghun

2015-03-01

Acetylcholine (ACh) is a neurotransmitter in a human central nervous system and is related to various neural functions such as memory, learning and muscle contractions. Dysfunctional ACh regulations in a brain can induce several neuropsychiatric diseases such as Alzheimer's disease, Parkinson's disease and myasthenia gravis. In researching such diseases, it is important to measure the concentration of ACh in the extracellular fluid of the brain. Herein, we developed a highly sensitive and selective ACh sensor based on single-walled carbon nanotube-field effect transistors (swCNT-FETs). In our work, M1 mAChR protein, an ACh receptor, was expressed in E.coli and coated on swCNT-FETs with lipid membranes. Here, the binding of ACh onto the receptors could be detected by monitoring the change of electrical currents in the underlying swCNT-FETs, allowing the real-time detection of ACh at a 100 pM concentration. Furthermore, our sensor could selectively detect ACh from other neurotransmitters. This is the first report of the real-time sensing of ACh utilizing specific binding between the ACh and M1 mAChR, and it may lead to breakthroughs in various biomedical applications such as drug screening and disease diagnosis.

Modularized construction of general integrated circuits on individual carbon nanotubes.

PubMed

Pei, Tian; Zhang, Panpan; Zhang, Zhiyong; Qiu, Chenguang; Liang, Shibo; Yang, Yingjun; Wang, Sheng; Peng, Lian-Mao

2014-06-11

While constructing general integrated circuits (ICs) with field-effect transistors (FETs) built on individual CNTs is among few viable ways to build ICs with small dimension and high performance that can be compared with that of state-of-the-art Si based ICs, this has not been demonstrated owing to the absence of valid and well-tolerant fabrication method. Here we demonstrate a modularized method for constructing general ICs on individual CNTs with different electric properties. A pass-transistor-logic style 8-transistor (8-T) unit is built, demonstrated as a multifunctional function generator with good tolerance to inhomogeneity in the CNTs used and used as a building block for constructing general ICs. As an example, an 8-bits BUS system that is widely used to transfer data between different systems in a computer is constructed. This is the most complicated IC fabricated on individual CNTs to date, containing 46 FETs built on six individual semiconducting CNTs. The 8-T unit provides a good basis for constructing complex ICs to explore the potential and limits of CNT ICs given the current imperfection in available CNT materials and may also be developed into a universal and efficient way for constructing general ICs on ideal CNT materials in the future.

SU-C-BRE-04: Microbeam-Radiation-Therapy (MRT): Characterizing a Novel MRT Device Using High Resolution 3D Dosimetry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Q; Juang, T; Bache, S

2014-06-15

Purpose: The feasibility of MRT has recently been demonstrated utilizing a new technology of Carbon-Nano-Tube(CNT) field emission x-ray sources.This approach can deliver very high dose(10's of Gy) in narrow stripes(sub-mm) of radiation which enables the study of novel radiation treatment approaches. Here we investigate the application of highresolution (50um isotropic) PRESAGE/Optical-CT 3D dosimetry techniques to characterize the radiation delivered in this extremely dosimetrically challenging scenario. Methods: The CNT field emission x-ray source irradiator comprises of a linear cathode array and a novel collimator alignment system. This allows a precise delivery of high-energy small beams up to 160 kVp. A cylindricalmore » dosimeter (∼2.2cm in height ∼2.5cm in diameter) was irradiated by CNT MRT delivering 3 strips of radiation with a nominal entrance dose of 32 Gy.A second dosimeter was irradiated with similar entrance dose, with a regular x-ray irradiator collimated to microscopical strip-beams. 50um (isotropic) 3D dosimetry was performed using an in-house optical-CT system designed and optimized for high resolution imaging (including a stray light deconvolution correction).The percentage depth dose (PDD), peak-to-valley ratio (PVR) and beam width (FWHM) data were obtained and analyzed in both cases. Results: High resolution 3D images were successfully achieved with the prototype system, enabling extraction of PDD and dose profiles. The PDDs for the CNT irradiation showed pronounced attenuation, but less build-up effect than that from the multibeam irradiation. The beam spacing between the three strips has an average value of 0.9mm while that for the 13 strips is 1.5 mm at a depth of 16.5 mm. The stray light corrected image shows line profiles with reduced noise and consistent PVR values. Conclusion: MRT dosimetry is extremely challenging due to the ultra small fields involved.This preliminary application of a novel, ultra-high resolution, optical-CT 3D dosimetry system shows promise, but further work is required to validate and investigate accuracy and artifacts. This work was supported by NIH R01CA100835.« less

CNT-Confinement Effects on the Menshutkin SN2 Reaction: The Role of Nonbonded Interactions.

PubMed

Giacinto, Pietro; Zerbetto, Francesco; Bottoni, Andrea; Calvaresi, Matteo

2016-08-09

We investigated the effects of CNT confinement ((6,6) tube) on the model Menshutkin reaction H3N + H3CCl = H3NCH3((+)) + Cl((-)), which is representative of chemical processes involving developing of charge separation along the reaction pathway. We used either a full QM approach or a hybrid QM/MM approach. We found that the CNT significantly lowers the activation barrier with respect to the hypothetical gas-phase reaction: The activation barrier Ea varies from 34.6 to 25.7 kcal mol(-1) (a value similar to that found in a nonpolar solvent) and the endothermicity ΔE from 31.2 to 13.5 kcal mol(-1). A complex interplay between C-H···π, N-H···π, and Cl···π nonbonded interactions of the endohedral system with the CNT wall explains the lower barrier and lower endothermicity. The hybrid QM/MM approach (MM = UFF force field) does not reproduce satisfactorily the QM energy ΔE (18.1 vs 13.5 kcal mol(-1)), while optimum agreement is found in the barrier Ea (25.8 vs 25.7 kcal mol(-1)). These results suggest that the simple Qeq formalism (included in the MM potential) does not describe properly the effect of CNT polarization in the presence of the net charge separation featuring the final product. A more accurate estimate of the tube polarization was obtained with single-point QM/MM computations including PCM corrections (using the benzene dielectric constant) on the QM/MM optimized structures. After PCM corrections, Ea changes slightly (from 25.8 to 24.5 kcal mol(-1)), but a more significant variation is observed for ΔE that becomes 13.1 kcal mol(-1), in rather good agreement with the full QM. This level of theory (QM/MM with PCM correction, MM = UFF) represents a more general approach suitable for describing CNT-confined chemical processes involving significant charge separation. QM/MM computations were extended to CNTs of different radii: (4,4), (5,5), (7,7), (8,8), (9,9), (10,10), (12,12), (14,14) CNTs and, as a limit case, a graphene sheet. The lack of space available in the small tube (4,4) causes a strong structural distortion and a consequent increase in Ea and ΔE (40.8 and 44.0 kcal mol(-1), respectively). These quantities suddenly decrease with the augmented volume inside the (5,5) tube. For larger tubes, different structural arrangements of the endohedral system are possible, and Ea and ΔE remain almost constant until the limiting case of graphene.

Carbon nanotubes grown on metal microelectrodes for the detection of dopamine

DOE PAGES

Yang, Cheng; Jacobs, Christopher B.; Nguyen, Michael; ...

2015-12-07

Microelectrodes modified with carbon nanotubes (CNTs) are useful for the detection of neurotransmitters because the CNTs enhance sensitivity and have electrocatalytic effects. CNTs can be grown on carbon fiber microelectrodes (CFMEs) but the intrinsic electrochemical activity of carbon fibers makes evaluating the effect of CNT enhancement difficult. Metal wires are highly conductive and many metals have no intrinsic electrochemical activity for dopamine, so we investigated CNTs grown on metal wires as microelectrodes for neurotransmitter detection. In this work, we successfully grew CNTs on niobium substrates for the first time. Instead of planar metal surfaces, metal wires with a diameter ofmore » only 25 μm were used as CNT substrates; these have potential in tissue applications due to their minimal tissue damage and high spatial resolution. Scanning electron microscopy shows that aligned CNTs are grown on metal wires after chemical vapor deposition. By use of fast-scan cyclic voltammetry, CNT-coated niobium (CNT-Nb) microelectrodes exhibit higher sensitivity and lower ΔE p value compared to CNTs grown on carbon fibers or other metal wires. The limit of detection for dopamine at CNT-Nb microelectrodes is 11 ± 1 nM, which is approximately 2-fold lower than that of bare CFMEs. Adsorption processes were modeled with a Langmuir isotherm, and detection of other neurochemicals was also characterized, including ascorbic acid, 3,4-dihydroxyphenylacetic acid, serotonin, adenosine, and histamine. CNT-Nb microelectrodes were used to monitor stimulated dopamine release in anesthetized rats with high sensitivity. This research demonstrates that CNT-grown metal microelectrodes, especially CNTs grown on Nb microelectrodes, are useful for monitoring neurotransmitters.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Cheng; Jacobs, Christopher B.; Nguyen, Michael

Microelectrodes modified with carbon nanotubes (CNTs) are useful for the detection of neurotransmitters because the CNTs enhance sensitivity and have electrocatalytic effects. CNTs can be grown on carbon fiber microelectrodes (CFMEs) but the intrinsic electrochemical activity of carbon fibers makes evaluating the effect of CNT enhancement difficult. Metal wires are highly conductive and many metals have no intrinsic electrochemical activity for dopamine, so we investigated CNTs grown on metal wires as microelectrodes for neurotransmitter detection. In this work, we successfully grew CNTs on niobium substrates for the first time. Instead of planar metal surfaces, metal wires with a diameter ofmore » only 25 μm were used as CNT substrates; these have potential in tissue applications due to their minimal tissue damage and high spatial resolution. Scanning electron microscopy shows that aligned CNTs are grown on metal wires after chemical vapor deposition. By use of fast-scan cyclic voltammetry, CNT-coated niobium (CNT-Nb) microelectrodes exhibit higher sensitivity and lower ΔE p value compared to CNTs grown on carbon fibers or other metal wires. The limit of detection for dopamine at CNT-Nb microelectrodes is 11 ± 1 nM, which is approximately 2-fold lower than that of bare CFMEs. Adsorption processes were modeled with a Langmuir isotherm, and detection of other neurochemicals was also characterized, including ascorbic acid, 3,4-dihydroxyphenylacetic acid, serotonin, adenosine, and histamine. CNT-Nb microelectrodes were used to monitor stimulated dopamine release in anesthetized rats with high sensitivity. This research demonstrates that CNT-grown metal microelectrodes, especially CNTs grown on Nb microelectrodes, are useful for monitoring neurotransmitters.« less

Geometrical influence of a deposited particle on the performance of bridged carbon nanotube-based mass detectors

NASA Astrophysics Data System (ADS)

Ali-Akbari, H. R.; Ceballes, S.; Abdelkefi, A.

2017-10-01

A nonlocal continuum-based model is derived to simulate the dynamic behavior of bridged carbon nanotube-based nano-scale mass detectors. The carbon nanotube (CNT) is modeled as an elastic Euler-Bernoulli beam considering von-Kármán type geometric nonlinearity. In order to achieve better accuracy in characterization of the CNTs, the geometrical properties of an attached nano-scale particle are introduced into the model by its moment of inertia with respect to the central axis of the beam. The inter-atomic long-range interactions within the structure of the CNT are incorporated into the model using Eringen's nonlocal elastic field theory. In this model, the mass can be deposited along an arbitrary length of the CNT. After deriving the full nonlinear equations of motion, the natural frequencies and corresponding mode shapes are extracted based on a linear eigenvalue problem analysis. The results show that the geometry of the attached particle has a significant impact on the dynamic behavior of the CNT-based mechanical resonator, especially, for those with small aspect ratios. The developed model and analysis are beneficial for nano-scale mass identification when a CNT-based mechanical resonator is utilized as a small-scale bio-mass sensor and the deposited particles are those, such as proteins, enzymes, cancer cells, DNA and other nano-scale biological objects with different and complex shapes.

Adsorption properties of the molecule resveratrol on CNT(8,0-10) nanotube: Geometry optimization, molecular structure, spectroscopic (NMR, UV/Vis, excited state), FMO, MEP and HOMO-LUMO investigations

NASA Astrophysics Data System (ADS)

Sheikhi, Masoome; Shahab, Siyamak; Khaleghian, Mehrnoosh; Hajikolaee, Fatemeh Haji; Balakhanava, Iryna; Alnajjar, Radwan

2018-05-01

In the present work the adsorption properties of the molecule Resveratrol (RSV) (trans-3,5,4‧-Trihydroxystilbene) on CNT(8,0-10) nanotube was investigated by Density Functional Theory (DFT) in the gaseous phase for the first time. The non-bonded interaction effects of compounds RSV and CNT(8,0-10) nanotube on the electronic properties, chemical shift tensors and natural charge were determined and discussed. The electronic spectra of the RSV and the complex CNT(8,0-10)/RSV in the gaseous phase were calculated by Time Dependent Density Functional Theory (TD-DFT) for investigation of the maximum wavelength value of the RSV before and after the non-bonded interaction with the CNT(8,0-10) nanotube and molecular orbitals involved in the formation of absorption spectrum of the complex RSV at maximum wavelength.

Effect of platelet-shaped graphene additives on actuating response of carbon nanotube/ionic liquid/polymer composite actuators

NASA Astrophysics Data System (ADS)

Monobe, Hirosato; Tsuchiya, Nobuyuki; Yamamura, Masahiro; Mukai, Ken; Sugino, Takushi; Asaka, Kinji

2018-03-01

In this study, the platelet-shaped graphene was used as a conductive additive in porous electrodes of a dry-type polymer actuator consisting of carbon nanotube (CNT), ionic liquid, and a base polymer to improve actuation properties. The generated strain was estimated from the bending motion of the actuator in the frequency range from 0.005 to 10 Hz. Ten different types of electrode film were prepared by changing the mixing amounts and surface areas of the platelet-shaped graphene. When a small amount of graphene (30 mg) relative to CNT (50 mg) was added to the CNT electrode, the strain was increased to be almost twice larger than that of CNT (50 mg) without any additives. The strain coefficient of the three-layered actuator with CNT electrodes with graphene additives is positively correlated with the capacitance per volume of such electrodes.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arman, B.; An, Q.; Luo, S. N.

We investigate with nonreactive molecular dynamics simulations the dynamic response of phenolic resin and its carbon-nanotube (CNT) composites to shock wave compression. For phenolic resin, our simulations yield shock states in agreement with experiments on similar polymers except the “phase change” observed in experiments, indicating that such phase change is chemical in nature. The elastic–plastic transition is characterized by shear stress relaxation and atomic-level slip, and phenolic resin shows strong strain hardening. Shock loading of the CNT-resin composites is applied parallel or perpendicular to the CNT axis, and the composites demonstrate anisotropy in wave propagation, yield and CNT deformation. Themore » CNTs induce stress concentrations in the composites and may increase the yield strength. Our simulations indicate that the bulk shock response of the composites depends on the volume fraction, length ratio, impact cross-section, and geometry of the CNT components; the short CNTs in current simulations have insignificant effect on the bulk response of resin polymer.« less

Production and characterization of a novel carbon nanotube/titanium nitride nanocomposite

NASA Astrophysics Data System (ADS)

Baddour, Carole Emilie; Das, Kaushik; Vengallatore, Srikar; Meunier, Jean-Luc

2016-12-01

A novel titanium nitride (TiN)/carbon nanotube (CNT) nanocomposite is produced with the purpose to mechanically, structurally and chemically stabilize a ‘felt-like’ CNT growth structure. The CNTs are grown on stainless steel (SS) 304 by chemical vapor deposition using the direct growth method previously developed, which does not require the use of an additional catalyst precursor. The TiN coating is achieved by physical vapor deposition and is shown here to generate a nanocomposite with a porous three-dimensional architecture. The contact stiffness is evaluated using nanoindentation, and wetting properties of the TiN/CNT nanocomposites are determined from contact angle measurements. An increase in contact stiffness and effective elastic modulus with TiN coating time was observed. The TiN coating on the non-wetting CNT felt results in a wetting nanocomposite surface. The wetting property is found to be a function of the TiN coating thickness on the CNT structure.

Thermal property tuning in aligned carbon nanotube films and random entangled carbon nanotube films by ion irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Jing; Chen, Di; Wang, Xuemei

2015-10-12

Ion irradiation effects on thermal property changes are compared between aligned carbon nanotube (A-CNT) films and randomly entangled carbon nanotube (R-CNT) films. After H, C, and Fe ion irradiation, a focusing ion beam with sub-mm diameter is used as a heating source, and an infrared signal is recorded to extract thermal conductivity. Ion irradiation decreases thermal conductivity of A-CNT films, but increases that of R-CNT films. We explain the opposite trends by the fact that neighboring CNT bundles are loosely bonded in A-CNT films, which makes it difficult to create inter-tube linkage/bonding upon ion irradiation. In a comparison, in R-CNTmore » films, which have dense tube networking, carbon displacements are easily trapped between touching tubes and act as inter-tube linkage to promote off-axial phonon transport. The enhancement overcomes the phonon transport loss due to phonon-defect scattering along the axial direction. A model is established to explain the dependence of thermal conductivity changes on ion irradiation parameters including ion species, energies, and current.« less

Field emission from optimized structure of carbon nanotube field emitter array

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chouhan, V., E-mail: vchouhan@post.kek.jp, E-mail: vijaychouhan84@gmail.com; Noguchi, T.; Kato, S.

The authors report a detail study on the emission properties of field emitter array (FEA) of micro-circular emitters of multiwall carbon nanotubes (CNTs). The FEAs were fabricated on patterned substrates prepared with an array of circular titanium (Ti) islands on titanium nitride coated tantalum substrates. CNTs were rooted into these Ti islands to prepare an array of circular emitters. The circular emitters were prepared in different diameters and pitches in order to optimize their structure for acquiring a high emission current. The pitch was varied from 0 to 600 μm, while a diameter of circular emitters was kept constant to bemore » 50 μm in order to optimize a pitch. For diameter optimization, a diameter was changed from 50 to 200 μm while keeping a constant edge-to-edge distance of 150 μm between the circular emitters. The FEA with a diameter of 50 μm and a pitch of 120 μm was found to be the best to achieve an emission current of 47 mA corresponding to an effective current density of 30.5 A/cm{sup 2} at 7 V/μm. The excellent emission current was attributed to good quality of CNT rooting into the substrate and optimized FEA structure, which provided a high electric field on a whole circular emitter of 50 μm and the best combination of the strong edge effect and CNT coverage. The experimental results were confirmed with computer simulation.« less

Porous carbon nanotube/graphene composites for high-performance supercapacitors

NASA Astrophysics Data System (ADS)

Li, Jing; Tang, Jie; Yuan, Jinshi; Zhang, Kun; Yu, Xiaoliang; Sun, Yige; Zhang, Han; Qin, Lu-Chang

2018-02-01

Carbon nanotubes (CNTs) are an effective spacer to prevent the re-stacking of graphene layers. However, the aggregation of CNTs always reduces the specific surface area of resulting CNT/graphene composites. Meanwhile, different pores always have different contributions to the specific capacitance. In this study, CNT/graphene composites with different porous structures are synthesized by co-reduction of oxidized CNTs and graphene oxide with different mixing ratios. With an optimized CNT content of 20%, the CNT/graphene composite shows 206 F g-1 in 1-ethyl-3-methylimidazolium tetrafluoroborate electrolyte. It is found that pores larger than twice the size of electrolyte ions can make greater contributions to the specific capacitance.

A molybdenum disulfide/carbon nanotube heterogeneous complementary inverter.

PubMed

Huang, Jun; Somu, Sivasubramanian; Busnaina, Ahmed

2012-08-24

We report a simple, bottom-up/top-down approach for integrating drastically different nanoscale building blocks to form a heterogeneous complementary inverter circuit based on layered molybdenum disulfide and carbon nanotube (CNT) bundles. The fabricated CNT/MoS(2) inverter is composed of n-type molybdenum disulfide (MOS(2)) and p-type CNT transistors, with a high voltage gain of 1.3. The CNT channels are fabricated using directed assembly while the layered molybdenum disulfide channels are fabricated by mechanical exfoliation. This bottom-up fabrication approach for integrating various nanoscale elements with unique characteristics provides an alternative cost-effective methodology to complementary metal-oxide-semiconductors, laying the foundation for the realization of high performance logic circuits.

Crack Formation in Powder Metallurgy Carbon Nanotube (CNT)/Al Composites During Post Heat-Treatment

NASA Astrophysics Data System (ADS)

Chen, Biao; Imai, Hisashi; Li, Shufeng; Jia, Lei; Umeda, Junko; Kondoh, Katsuyoshi

2015-12-01

After the post heat-treatment (PHT) process of powder metallurgy carbon nanotubes (CNT)/Al composites, micro-cracks were observed in the composites, leading to greatly degraded mechanical properties. To understand and suppress the crack formation, an in situ observation of CNT/Al composites was performed at elevated temperatures. PHT was also applied to various bulk pure Al and CNT/Al composites fabricated under different processes. It was observed that the composites consolidated by hot-extrusion might form micro-cracks, but those consolidated by spark plasma sintering (SPS) showed no crack after PHT. A high-temperature SPS process before hot-extrusion was effective to prevent crack formation. The release of residual stress in severe plastic deformed (SPD) materials was responsible for the cracking phenomena during the PHT process. Furthermore, a good particle bonding was essential and effective to suppress cracks for SPD materials in the PHT process.

Catalytic oxidation of 1,2-DCBz over V2O5/TiO2-CNTs: effect of CNT diameter and surface functional groups.

PubMed

Du, Cuicui; Wang, Qiulin; Peng, Yaqi; Lu, Shengyong; Ji, Longjie; Ni, Mingjiang

2017-02-01

A series of V 2 O 5 /TiO 2 -carbon nanotube (CNT) catalysts were prepared and tested to decompose gaseous 1,2-dichlorobenzene (1,2-DCBz). Several physicochemical methods, including nitrogen adsorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and H 2 temperature-programmed reduction (TPR) were employed to characterise their physicochemical properties. To better understand the effect of CNT properties on the reactivity of V 2 O 5 /TiO 2 -CNT catalysts, the 1,2-DCBz residue remaining in the off-gas and on the catalyst surface were both collected and analysed. The results indicate that the outer diameter and the surface functional groups (hydroxide radical and carboxyl) of CNTs significantly influence upon the catalytic activity of CNT-containing V 2 O 5 /TiO 2 catalysts: the CNT outer diameter mainly affects the aggregation of CNTs and the π-π interaction between the benzene ring and CNTs, while the introduction of -OH and -COOH groups by acid treatment can further enlarge specific surface area (SSA) and contribute to a higher average oxidation state of vanadium (V aos ) and supplemental surface chemisorbed oxygen (O ads ). In addition, the enhanced mobility of lattice oxygen (O latt) also improves the oxidation ability of the catalysts.

Regulation of transport in the connecting tubule and cortical collecting duct

PubMed Central

Staruschenko, Alexander

2012-01-01

The central goal of this overview article is to summarize recent findings in renal epithelial transport, focusing chiefly on the connecting tubule (CNT) and the cortical collecting duct (CCD). Mammalian CCD and CNT are involved in fine tuning of electrolyte and fluid balance through reabsorption and secretion. Specific transporters and channels mediate vectorial movements of water and solutes in these segments. Although only a small percent of the glomerular filtrate reaches the CNT and CCD, these segments are critical for water and electrolyte homeostasis since several hormones, e.g. aldosterone and arginine vasopressin, exert their main effects in these nephron sites. Importantly, hormones regulate the function of the entire nephron and kidney by affecting channels and transporters in the CNT and CCD. Knowledge about the physiological and pathophysiological regulation of transport in the CNT and CCD and particular roles of specific channels/transporters has increased tremendously over the last two decades. Recent studies shed new light on several key questions concerning the regulation of renal transport. Precise distribution patterns of transport proteins in the CCD and CNT will be reviewed, and their physiological roles and mechanisms mediating ion transport in these segments will be also covered. Special emphasis will be given to pathophysiological conditions appearing as a result of abnormalities in renal transport in the CNT and CCD. PMID:23227301

Velcro-Inspired SiC Fuzzy Fibers for Aerospace Applications.

PubMed

Hart, Amelia H C; Koizumi, Ryota; Hamel, John; Owuor, Peter Samora; Ito, Yusuke; Ozden, Sehmus; Bhowmick, Sanjit; Syed Amanulla, Syed Asif; Tsafack, Thierry; Keyshar, Kunttal; Mital, Rahul; Hurst, Janet; Vajtai, Robert; Tiwary, Chandra Sekhar; Ajayan, Pulickel M

2017-04-19

The most recent and innovative silicon carbide (SiC) fiber ceramic matrix composites, used for lightweight high-heat engine parts in aerospace applications, are woven, layered, and then surrounded by a SiC ceramic matrix composite (CMC). To further improve both the mechanical properties and thermal and oxidative resistance abilities of this material, SiC nanotubes and nanowires (SiCNT/NWs) are grown on the surface of the SiC fiber via carbon nanotube conversion. This conversion utilizes the shape memory synthesis (SMS) method, starting with carbon nanotube (CNT) growth on the SiC fiber surface, to capitalize on the ease of dense surface morphology optimization and the ability to effectively engineer the CNT-SiC fiber interface to create a secure nanotube-fiber attachment. Then, by converting the CNTs to SiCNT/NWs, the relative morphology, advantageous mechanical properties, and secure connection of the initial CNT-SiC fiber architecture are retained, with the addition of high temperature and oxidation resistance. The resultant SiCNT/NW-SiC fiber can be used inside the SiC ceramic matrix composite for a high-heat turbo engine part with longer fatigue life and higher temperature resistance. The differing sides of the woven SiCNT/NWs act as the "hook and loop" mechanism of Velcro but in much smaller scale.

Breaking the electrical barrier between copper and carbon nanotubes.

PubMed

Milowska, Karolina Z; Ghorbani-Asl, Mahdi; Burda, Marek; Wolanicka, Lidia; Ćatić, Nordin; Bristowe, Paul D; Koziol, Krzysztof K K

2017-06-22

Improving the interface between copper and carbon nanotubes (CNTs) offers a straightforward strategy for the effective manufacturing and utilisation of Cu-CNT composite material that could be used in various industries including microelectronics, aerospace and transportation. Motivated by a combination of structural and electrical measurements on Cu-M-CNT bimetal systems (M = Ni, Cr) we show, using first principles calculations, that the conductance of this composite can exceed that of a pure Cu-CNT system and that the current density can even reach 10 11 A cm -2 . The results show that the proper choice of alloying element (M) and type of contact facilitate the fabrication of ultra-conductive Cu-M-CNT systems by creating a favourable interface geometry, increasing the interface electronic density of states and reducing the contact resistance. In particular, a small concentration of Ni between the Cu matrix and the CNT using either an "end contact" and or a "dot contact" can significantly improve the electrical performance of the composite. Furthermore the predicted conductance of Ni-doped Cu-CNT "carpets" exceeds that of an undoped system by ∼200%. Cr is shown to improve CNT integration and composite conductance over a wide temperature range while Al, at low voltages, can enhance the conductance beyond that of Cr.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mermigkis, Panagiotis G.; Tsalikis, Dimitrios G.; Institute of Chemical Engineering and High Temperature Chemical Processes, GR 26500 Patras

A kinetic Monte Carlo (kMC) simulation algorithm is developed for computing the effective diffusivity of water molecules in a poly(methyl methacrylate) (PMMA) matrix containing carbon nanotubes (CNTs) at several loadings. The simulations are conducted on a cubic lattice to the bonds of which rate constants are assigned governing the elementary jump events of water molecules from one lattice site to another. Lattice sites belonging to PMMA domains of the membrane are assigned different rates than lattice sites belonging to CNT domains. Values of these two rate constants are extracted from available numerical data for water diffusivity within a PMMA matrixmore » and a CNT pre-computed on the basis of independent atomistic molecular dynamics simulations, which show that water diffusivity in CNTs is 3 orders of magnitude faster than in PMMA. Our discrete-space, continuum-time kMC simulation results for several PMMA-CNT nanocomposite membranes (characterized by different values of CNT length L and diameter D and by different loadings of the matrix in CNTs) demonstrate that the overall or effective diffusivity, D{sub eff}, of water in the entire polymeric membrane is of the same order of magnitude as its diffusivity in PMMA domains and increases only linearly with the concentration C (vol. %) in nanotubes. For a constant value of the concentration C, D{sub eff} is found to vary practically linearly also with the CNT aspect ratio L/D. The kMC data allow us to propose a simple bilinear expression for D{sub eff} as a function of C and L/D that can describe the numerical data for water mobility in the membrane extremely accurately. Additional simulations with two different CNT configurations (completely random versus aligned) show that CNT orientation in the polymeric matrix has only a minor effect on D{sub eff} (as long as CNTs do not fully penetrate the membrane). We have also extensively analyzed and quantified sublinear (anomalous) diffusive phenomena over small to moderate times and correlated them with the time needed for penetrant water molecules to explore the available large, fast-diffusing CNT pores before Fickian diffusion is reached.« less

The effects of carbon nanotubes on lung and dermal cellular behaviors

PubMed Central

Luanpitpong, Sudjit; Wang, Liying; Rojanasakul, Yon

2016-01-01

Carbon nanotubes (CNTs) hold great promise to create new and better products, but their adverse health effect is a major concern. Human exposure to CNTs is primarily through inhalation and dermal contact, especially during the manufacturing and handling processes. Numerous animal studies have demonstrated the potential pulmonary and dermal hazards associated with CNT exposure, while in vitro studies have assessed the effects of CNT exposure on various cellular behaviors and have been used to perform mechanistic studies. In this review, we provide an overview of the pathological effects of CNTs and examine the acute and chronic effects of CNT exposure on lung and dermal cellular behaviors, beyond the generally discussed cytotoxicity. We then examine the linkage of cellular behaviors and disease pathogenesis, and discuss the pertinent mechanisms. PMID:24981653

Electrical Conductance Tuning and Bistable Switching in Poly(N-vinylcarbazole)-Carbon Nanotube Composite Films.

PubMed

Liu, Gang; Ling, Qi-Dan; Teo, Eric Yeow Hwee; Zhu, Chun-Xiang; Chan, D Siu-Hung; Neoh, Koon-Gee; Kang, En-Tang

2009-07-28

By varying the carbon nanotube (CNT) content in poly(N-vinylcarbazole) (PVK) composite thin films, the electrical conductance behavior of an indium-tin oxide/PVK-CNT/aluminum (ITO/PVK-CNT/Al) sandwich structure can be tuned in a controlled manner. Distinctly different electrical conductance behaviors, such as (i) insulator behavior, (ii) bistable electrical conductance switching effects (write-once read-many-times (WORM) memory effect and rewritable memory effect), and (iii) conductor behavior, are discernible from the current density-voltage characteristics of the composite films. The turn-on voltage of the two bistable conductance switching devices decreases and the ON/OFF state current ratio of the WORM device increases with the increase in CNT content of the composite film. Both the WORM and rewritable devices are stable under a constant voltage stress or a continuous pulse voltage stress, with an ON/OFF state current ratio in excess of 10(3). The conductance switching effects of the composite films have been attributed to electron trapping in the CNTs of the electron-donating/hole-transporting PVK matrix.

Novel high potential visible-light-active photocatalyst of CNT/Mo, S-codoped TiO2 hetero-nanostructure

NASA Astrophysics Data System (ADS)

Hamadanian, M.; Shamshiri, M.; Jabbari, V.

2014-10-01

The current study deals with synthesize of novel nanophotocatalysts of CNT/Mo,S-codoped TiO2 by reacting between titanium isopropoxide (Ti(OC3H7)4) and CNT in aqueous ammonia and subsequent calcining of hydrolysis of the products. The prepared catalysts were characterized by N2 adsorption-desorption measurements, XRD, SEM, TEM, EDX, FT-IR, and UV-vis DRS spectroscopy. SEM and TEM images exhibited uniform coverage of CNT with anatase TiO2 nanoclusters. It was also demonstrated that the presence of S and Mo within the TiO2 acts as electrons traps and prevents the charge recombination and also enables the TiO2 photocatalyst to be active in visible-light region. Moreover, the CNT/Mo,S-doped TiO2 nanohybrids has been proven to has a excellent photocatalytic performance in photodecomposition of Congored (CR), at which the rate of decomposition reaches 100% in only 20 and 30 min under UV and visible-light irradiation, respectively. The enhanced photocatalytic activity was ascribed to the synergetic effects of excellent electrical property of CNT and metal-non-metal codoping. Finally, which to best of our knowledge is done for the first time, we have demonstrated that Mo- and S-doped TiO2 decorated over CNT, or CNT/Mo,S-codoped TiO2, may have high potential applications in photocatalysis and environmental protection with superior catalytic activity under visible-light illumination.

Nonlinear behaviour of cantilevered carbon nanotube resonators based on a new nonlinear electrostatic load model

NASA Astrophysics Data System (ADS)

Farokhi, Hamed; Païdoussis, Michael P.; Misra, Arun K.

2018-04-01

The present study examines the nonlinear behaviour of a cantilevered carbon nanotube (CNT) resonator and its mass detection sensitivity, employing a new nonlinear electrostatic load model. More specifically, a 3D finite element model is developed in order to obtain the electrostatic load distribution on cantilevered CNT resonators. A new nonlinear electrostatic load model is then proposed accounting for the end effects due to finite length. Additionally, a new nonlinear size-dependent continuum model is developed for the cantilevered CNT resonator, employing the modified couple stress theory (to account for size-effects) together with the Kelvin-Voigt model (to account for nonlinear damping); the size-dependent model takes into account all sources of nonlinearity, i.e. geometrical and inertial nonlinearities as well as nonlinearities associated with damping, small-scale, and electrostatic load. The nonlinear equation of motion of the cantilevered CNT resonator is obtained based on the new models developed for the CNT resonator and the electrostatic load. The Galerkin method is then applied to the nonlinear equation of motion, resulting in a set of nonlinear ordinary differential equations, consisting of geometrical, inertial, electrical, damping, and size-dependent nonlinear terms. This high-dimensional nonlinear discretized model is solved numerically utilizing the pseudo-arclength continuation technique. The nonlinear static and dynamic responses of the system are examined for various cases, investigating the effect of DC and AC voltages, length-scale parameter, nonlinear damping, and electrostatic load. Moreover, the mass detection sensitivity of the system is examined for possible application of the CNT resonator as a nanosensor.

Texture design for microwave dielectric (Ca0.7Nd0.3)0.87TiO3 ceramics through reactive-templated grain growth.

PubMed

Tani, Toshihiko; Takeuchi, Tsuguto

2015-06-01

Plate-like Ca 3 Ti 2 O 7 (CT) and Nd 2 Ti 2 O 7 (NT) particles were synthesized in molten salts and used as reactive templates for the preparation of highly textured (Ca 0.7 Nd 0.3 ) 0.87 TiO 3 bulk ceramics (CNT) with preferred pseudocubic 〈100〉 and 〈110〉 orientations, respectively. During flux growth CT and NT particles developed facets parallel to the pseudocubic {100} and {110} planes, respectively, in a perovskite unit cell, since those planes correspond to the interlayers of the layered perovskite-type crystal structures. Complementary reactants for the CNT stoichiometry were wet-mixed with the reactive templates and the slurries were tape-cast. Then stacked tapes were heat-treated for dense single-phase CNT ceramics with a distorted and A-site deficient regular perovskite-type structure. The CNT ceramics prepared with CT and NT reactive templates exhibited strong pseudocubic 100- and 110-family x-ray diffraction peaks, respectively, with other peaks drastically suppressed when non-perovskite sources were used as complementary reactants. The textured ceramics possess unique microstructures; as either parallel or obliquely stacked block structures with a pseudocubic {100} plane faceted. The pseudocubic {100}-and {110}-textured CNT ceramics exhibited ∼10 and ∼20% higher products of the dielectric quality factor and frequency, Q · f , respectively, than conventional ceramic sintered at the same temperature. When Q · f is compared based on the same grain size, the {100}-textured CNT exhibited 27% higher values than non-textured while relative permittivity and temperature coefficient of resonant frequency were of similar values. Simple geometrical relationships between electric field and penetrated pseudocubic { hk 0}-type grain boundaries must lead to the reduced scattering and dielectric loss.

A study on carbon nanotube bridge as a electromechanical memory device

NASA Astrophysics Data System (ADS)

Kang, Jeong Won; Ha Lee, Jun; Joo Lee, Hoong; Hwang, Ho Jung

2005-04-01

A nanoelectromechanical (NEM) nanotube random access memory (NRAM) device based on carbon nanotube (CNT) was investigated using atomistic simulations. For the CNT-based NEM memory, the mechanical properties of the CNT-bridge and van der Waals interactions between the CNT-bridge and substrate were very important. The critical amplitude of the CNT-bridge was 16% of the length of the CNT-bridge. As molecular dynamics time increased, the CNT-bridge went to the steady state under the electrostatic force with the damping of the potential and the kinetic energies of the CNT-bridge. The interatomic interaction between the CNT-bridge and substrate, value of the CNT-bridge slack, and damping rate of the CNT-bridge were very important for the operation of the NEM memory device as a nonvolatile memory.

Carbon Nanotube Electron Gun

NASA Technical Reports Server (NTRS)

Ribaya, Bryan P. (Inventor); Nguyen, Cattien V. (Inventor)

2013-01-01

An electron gun, an electron source for an electron gun, an extractor for an electron gun, and a respective method for producing the electron gun, the electron source and the extractor are disclosed. Embodiments provide an electron source utilizing a carbon nanotube (CNT) bonded to a substrate for increased stability, reliability, and durability. An extractor with an aperture in a conductive material is used to extract electrons from the electron source, where the aperture may substantially align with the CNT of the electron source when the extractor and electron source are mated to form the electron gun. The electron source and extractor may have alignment features for aligning the electron source and the extractor, thereby bringing the aperture and CNT into substantial alignment when assembled. The alignment features may provide and maintain this alignment during operation to improve the field emission characteristics and overall system stability of the electron gun.

The rapid growth of vertically aligned carbon nanotubes using laser heating.

PubMed

Park, J B; Jeong, S H; Jeong, M S; Lim, S C; Lee, I H; Lee, Y H

2009-05-06

Growth of densely packed vertically aligned carbon nanotubes (VA-CNTs) using laser-induced chemical vapor deposition with visible laser (lambda = 532 nm) irradiation at room temperature is reported. Using a multiple-catalyst layer (Fe/Al/Cr) on quartz as the substrate and an acetylene-hydrogen mixture as the precursor gas, VA-CNT pillars with 60 microm height and 4 microm diameter were grown at a high rate of around 1 microm s(-1) with good reproducibility. It is demonstrated that the fabrication of uniform pillar arrays of VA-CNTs can be achieved with a single irradiation for each pillar using LCVD with no annealing or preprocessing of the substrate. Here, laser fast heating is considered the primary mechanism facilitating the growth of VA-CNT pillars. Field emission characteristics of an array of VA-CNT pillars were then examined to investigate their potential application in vacuum electronic devices.

Carbon nanotube electron gun

NASA Technical Reports Server (NTRS)

Nguyen, Cattien V. (Inventor); Ribaya, Bryan P. (Inventor)

2010-01-01

An electron gun, an electron source for an electron gun, an extractor for an electron gun, and a respective method for producing the electron gun, the electron source and the extractor are disclosed. Embodiments provide an electron source utilizing a carbon nanotube (CNT) bonded to a substrate for increased stability, reliability, and durability. An extractor with an aperture in a conductive material is used to extract electrons from the electron source, where the aperture may substantially align with the CNT of the electron source when the extractor and electron source are mated to form the electron gun. The electron source and extractor may have alignment features for aligning the electron source and the extractor, thereby bringing the aperture and CNT into substantial alignment when assembled. The alignment features may provide and maintain this alignment during operation to improve the field emission characteristics and overall system stability of the electron gun.

A novel PFIB sample preparation protocol for correlative 3D X-ray CNT and FIB-TOF-SIMS tomography.

PubMed

Priebe, Agnieszka; Audoit, Guillaume; Barnes, Jean-Paul

2017-02-01

We present a novel sample preparation method that allows correlative 3D X-ray Computed Nano-Tomography (CNT) and Focused Ion Beam Time-Of-Flight Secondary Ion Mass Spectrometry (FIB-TOF-SIMS) tomography to be performed on the same sample. In addition, our invention ensures that samples stay unmodified structurally and chemically between the subsequent experiments. The main principle is based on modifying the topography of the X-ray CNT experimental setup before FIB-TOF-SIMS measurements by incorporating a square washer around the sample. This affects the distribution of extraction field lines and therefore influences the trajectories of secondary ions that are now guided more efficiently towards the detector. As the result, secondary ion detection is significantly improved and higher, i.e. statistically better, signals are obtained. Copyright © 2016 Elsevier B.V. All rights reserved.

Programmable and functional electrothermal bimorph actuators based on large-area anisotropic carbon nanotube paper

NASA Astrophysics Data System (ADS)

Li, Qingwei; Liu, Changhong; Fan, Shoushan

2018-04-01

Electro-active polymer (EAP) actuators, such as electronic, ionic and electrothermal (ET) actuators, have become an important branch of next-generation soft actuators in bionic robotics. However, most reported EAP actuators could realize only simple movements, being restricted by the small area of flexible electrodes and simple designs. We prepared large-area flexible electrodes of high anisotropy, made of oriented carbon nanotube (CNT) paper, and carried out artful graphic designs and processing on the electrodes to make functional ET bimorph actuators which can realize large bending deformations (over 220°, curvature > 1.5 cm-1) and bionic movements driven by electricity. The anisotropy of CNT paper benefits electrode designs and multiform actuations for complex actuators. Based on the large-area CNT paper, more interesting and functional actuators can be designed and prepared which will have practical applications in the fields of artificial muscles, complicated actuations, and soft and bionic robotics.

Dielectric and electric modulus study of PPy/TiO2/CNT/SLS composite with temperature

NASA Astrophysics Data System (ADS)

Tiwari, D. C.; Atri, Priyanka; Sharma, Rishi

2013-02-01

Here we report the preparation and electrical characterization of nanocomposite of PPy/TiO2/CNT/SLS synthesized by in situ oxidative polymerization of pyrrole in the presence of TiO2 nanofibers, CNT and surfactant sodium lauryl sulfate. The surface morphology and elemental analysis is studied by SEM and EDAX. Dielectric and modulas studies were carried out in frequency range of 1 KHz to 2 MHz which provides quantitative description of grain and grain boundary effect in nanocomposite material.

High Interfacial Barriers at Narrow Carbon Nanotube-Water Interfaces.

PubMed

Varanasi, Srinivasa Rao; Subramanian, Yashonath; Bhatia, Suresh K

2018-06-26

Water displays anomalous fast diffusion in narrow carbon nanotubes (CNTs), a behavior that has been reproduced in both experimental and simulation studies. However, little is reported on the effect of bulk water-CNT interfaces, which is critical to exploiting the fast transport of water across narrow carbon nanotubes in actual applications. Using molecular dynamics simulations, we investigate here the effect of such interfaces on the transport of water across arm-chair CNTs of different diameters. Our results demonstrate that diffusion of water is significantly retarded in narrow CNTs due to bulk regions near the pore entrance. The slowdown of dynamics can be attributed to the presence of large energy barriers at bulk water-CNT interfaces. The presence of such intense barriers at the bulk-CNT interface arises due to the entropy contrast between the bulk and confined regions, with water molecules undergoing high translational and rotational entropy gain on entering from the bulk to the CNT interior. The intensity of such energy barriers decreases with increase in CNT diameter. These results are very important for emerging technological applications of CNTs and other nanoscale materials, such as in nanofluidics, water purification, nanofiltration, and desalination, as well as for biological transport processes.

Visibility and oxidation stability of hybrid-type copper mesh electrodes with combined nickel-carbon nanotube coating

NASA Astrophysics Data System (ADS)

Kim, Bu-Jong; Hwang, Young-Jin; Park, Jin-Seok

2017-04-01

Hybrid-type transparent conductive electrodes (TCEs) were fabricated by coating copper (Cu) meshes with carbon nanotube (CNT) via electrophoretic deposition, and with nickel (Ni) via electroplating. For the fabricated electrodes, the effects of the coating with CNT and Ni on their transmittance and reflectance in the visible-light range, electrical sheet resistance, and chromatic parameters (e.g., redness and yellowness) were characterized. Also, an oxidation stability test was performed by exposing the electrodes to air for 20 d at 85 °C and 85% temperature and humidity conditions, respectively. It was discovered that the CNT coating considerably reduced the reflectance of the Cu meshes, and that the Ni coating effectively protected the Cu meshes against oxidation. Furthermore, after the coating with CNT, both the redness and yellowness of the Cu mesh regardless of the Ni coating approached almost zero, indicating a natural color. The experiment results confirmed that the hybrid-type Cu meshes with combined Ni-CNT coating improved characteristics in terms of reflectance, sheet resistance, oxidation stability, and color, superior to those of the primitive Cu mesh, and also simultaneously satisfied most of the requirements for TCEs.

Self-assembled dopamine nanolayers wrapped carbon nanotubes as carbon-carbon bi-functional nanocatalyst for highly efficient oxygen reduction reaction and antiviral drug monitoring

NASA Astrophysics Data System (ADS)

Khalafallah, Diab; Akhtar, Naeem; Alothman, Othman Y.; Fouad, H.; Abdelrazek khalil, Khalil

2017-09-01

Oxygen reduction reaction (ORR) catalysts are the heart of eco-friendly energy resources particularly low temperature fuel cells. Although valuable efforts have been devoted to synthesize high performance catalysts for ORR, considerable challenges are extremely desirable in the development of energy technologies. Herein, we report a simple self-polymerization method to build a thin film of dopamine along the tubular nanostructures of multi-walled carbon nanotubes (CNT) in a weak alkaline solution. The dopamine@CNT hybrid (denoted as DA@CNT) reveals an enhanced electrocatalytic activity towards ORR with highly positive onset potential and cathodic current as a result of their outstanding features of longitudinal mesoporous structure, high surface area, and ornamentation of DA layers with nitrogen moieties, which enable fast electron transport and fully exposed electroactive sites. Impressively, the as-obtained hybrid afford remarkable electrochemical durability for prolonged test time of 60,000 s compared to benchmark Pt/C (20 wt%) catalyst. Furthermore, the developed DA@CNT electrode was successfully applied to access the quality of antiviral drug named Valacyclovir (VCR). The DA@CNT electrode shows enhanced sensing performance in terms of large linear range (3-75 nM), low limit of detection (2.55 nM) than CNT based electrode, indicating the effectiveness of the DA coating. Interestingly, the synergetic effect of nanostructured DA and CNT can significantly boost the electronic configuration and exposure level of active species for ORR and biomolecule recognition. Therefore, the existing carbon-based porous electrocatalyst may find numerous translational applications as attractive alternative to noble metals in polymer electrolyte membrane fuel cells and quality control assessment of pharmaceutical and therapeutic drugs.

Electronic and magneto-transport in chirality sorted carbon nanotube films

NASA Astrophysics Data System (ADS)

Janas, Dawid; Czechowski, Nikodem; Adamus, Zbigniew; GiŻewski, Tomasz

2018-01-01

This research details electronic and magneto-transport in unsorted and chirality-enriched carbon nanotube (CNT) films. By measuring the electrical conductivity from 4 K to 297 K, we were able to assign the governing mechanism of electronic transport. Fluctuation-induced tunnelling was in accordance with the obtained data and very well matched the underlying physics. We demonstrated how a change in the type of CNT to make the film affects its electrical performance. As the temperature was decreased down to cryogenic conditions, up to a 56-fold increase in resistance was noted. Moreover, the measurement of magnetoresistance (MR) revealed a non-monotonic dependence on the applied magnetic field. The initial negative component of MR was eventually overpowered by the positive MR component as the field strength was increased beyond a certain threshold.

An update on carbon nanotube-enabled X-ray sources for biomedical imaging.

PubMed

Puett, Connor; Inscoe, Christina; Hartman, Allison; Calliste, Jabari; Franceschi, Dora K; Lu, Jianping; Zhou, Otto; Lee, Yueh Z

2018-01-01

A new imaging technology has emerged that uses carbon nanotubes (CNT) as the electron emitter (cathode) for the X-ray tube. Since the performance of the CNT cathode is controlled by simple voltage manipulation, CNT-enabled X-ray sources are ideal for the repetitive imaging steps needed to capture three-dimensional information. As such, they have allowed the development of a gated micro-computed tomography (CT) scanner for small animal research as well as stationary tomosynthesis, an experimental technology for large field-of-view human imaging. The small animal CT can acquire images at specific points in the respiratory and cardiac cycles. Longitudinal imaging therefore becomes possible and has been applied to many research questions, ranging from tumor response to the noninvasive assessment of cardiac output. Digital tomosynthesis (DT) is a low-dose and low-cost human imaging tool that captures some depth information. Known as three-dimensional mammography, DT is now used clinically for breast imaging. However, the resolution of currently-approved DT is limited by the need to swing the X-ray source through space to collect a series of projection views. An array of fixed and distributed CNT-enabled sources provides the solution and has been used to construct stationary DT devices for breast, lung, and dental imaging. To date, over 100 patients have been imaged on Institutional Review Board-approved study protocols. Early experience is promising, showing an excellent conspicuity of soft-tissue features, while also highlighting technical and post-acquisition processing limitations that are guiding continued research and development. Additionally, CNT-enabled sources are being tested in miniature X-ray tubes that are capable of generating adequate photon energies and tube currents for clinical imaging. Although there are many potential applications for these small field-of-view devices, initial experience has been with an X-ray source that can be inserted into the mouth for dental imaging. Conceived less than 20 years ago, CNT-enabled X-ray sources are now being manufactured on a commercial scale and are powering both research tools and experimental human imaging devices. WIREs Nanomed Nanobiotechnol 2018, 10:e1475. doi: 10.1002/wnan.1475 This article is categorized under: Diagnostic Tools > Diagnostic Nanodevices Diagnostic Tools > In Vivo Nanodiagnostics and Imaging. © 2017 Wiley Periodicals, Inc.

Transport of ions through a (6,6) carbon nanotube under electric fields

NASA Astrophysics Data System (ADS)

Shen, Li; Xu, Zhen; Zhou, Zhe-Wei; Hu, Guo-Hui

2014-11-01

The transport of water and ions through carbon nanotubes (CNTs) is crucial in nanotechnology and biotechnology. Previous investigation indicated that the ions can hardly pass through (6,6) CNTs due to their hydrated shells. In the present study, utilizing molecular dynamics simulation, it is shown that the energy barrier mainly originating from the hydrated water molecules could be overcome by applying an electric field large enough in the CNT axis direction. Potential of mean force is calculated to show the reduction of energy barrier when the electric field is present for (Na+, K+, Cl-) ions. Consequently, ionic flux through (6,6) CNTs can be found once the electric field becomes larger than a threshold value. The variation of the coordination numbers of ions at different locations from the bulk to the center of the CNT is also explored to elaborate this dynamic process. The thresholds of the electric field are different for Na+, K+, and Cl- due to their characteristics. This consequence might be potentially applied in ion selectivity in the future.

Quantitative Interaction Effects of Carbon Dioxide, Sodium Chloride, and Sodium Nitrite on Neurotoxin Gene Expression in Nonproteolytic Clostridium botulinum Type B

PubMed Central

Lövenklev, Maria; Artin, Ingrid; Hagberg, Oskar; Borch, Elisabeth; Holst, Elisabet; Rådström, Peter

2004-01-01

The effects of carbon dioxide, sodium chloride, and sodium nitrite on type B botulinum neurotoxin (BoNT/B) gene (cntB) expression in nonproteolytic Clostridium botulinum were investigated in a tryptone-peptone-yeast extract (TPY) medium. Various concentrations of these selected food preservatives were studied by using a complete factorial design in order to quantitatively study interaction effects, as well as main effects, on the following responses: lag phase duration (LPD), growth rate, relative cntB expression, and extracellular BoNT/B production. Multiple linear regression was used to set up six statistical models to quantify and predict these responses. All combinations of NaCl and NaNO2 in the growth medium resulted in a prolonged lag phase duration and in a reduction in the specific growth rate. In contrast, the relative BoNT/B gene expression was unchanged, as determined by the cntB-specific quantitative reverse transcription-PCR method. This was confirmed when we measured the extracellular BoNT/B concentration by an enzyme-linked immunosorbent assay. CO2 was found to have a major effect on gene expression when the cntB mRNA levels were monitored in the mid-exponential, late exponential, and late stationary growth phases. The expression of cntB relative to the expression of the 16S rRNA gene was stimulated by an elevated CO2 concentration; the cntB mRNA level was fivefold greater in a 70% CO2 atmosphere than in a 10% CO2 atmosphere. These findings were also confirmed when we analyzed the extracellular BoNT/B concentration; we found that the concentrations were 27 ng · ml−1 · unit of optical density−1 in the 10% CO2 atmosphere and 126 ng · ml−1 · unit of optical density−1 in the 70% CO2 atmosphere. PMID:15128553

Thermal formation effect of g-C3N4 structure on the visible light driven photocatalysis of g-C3N4/NiTiO3 Z-scheme composite photocatalysts

NASA Astrophysics Data System (ADS)

Pham, Thanh-Truc; Shin, Eun Woo

2018-07-01

The development of efficient visible-light driven photocatalysts has attracted considerable attention in environmental protection and remediation. In this study, the facile thermal polymerization of dicyandiamide (DCDA) to graphitic carbon nitride (g-C3N4) in the presence of nickel titanium trioxide (NiTiO3) was investigated for fabricating g-C3N4 and NiTiO3 composite (CNT) photocatalysts to understand the influence of the presence of NiTiO3 on the thermal formation of g-C3N4 layers from DCDA and to find an optimal processing temperature for fabricating CNT photocatalysts. To examine the effect of NiTiO3 on the fabrication of CNT photocatalysts, a gas phase environment (flowing air or nitrogen) and different processing temperatures were employed as preparation variables to control the properties of the CNT photocatalysts. In addition, the CNT photocatalysts were applied for the visible light driven photocatalytic degradation of methylene blue to evaluate their photocatalytic performances. The CNT photocatalyst prepared at T = 500 °C showed the highest photocatalytic activity, which was caused by the optimal morphology of g-C3N4 in the composite photocatalysts. The NiTiO3 inorganic phase in the composite photocatalysts acted as a catalyst to accelerate the thermal polymerization to form the g-C3N4 structure and as a promoter to increase the photocatalytic activity during photodegradation.

Surface analysis and mechanical behaviour mapping of vertically aligned CNT forest array through nanoindentation

NASA Astrophysics Data System (ADS)

Koumoulos, Elias P.; Charitidis, C. A.

2017-02-01

Carbon nanotube (CNT) based architectures have increased the scientific interest owning to their exceptional performance rendering them promising candidates for advanced industrial applications in the nanotechnology field. Despite individual CNTs being considered as one of the most known strong materials, much less is known about other CNT forms, such as CNT arrays, in terms of their mechanical performance (integrity). In this work, thermal chemical vapor deposition (CVD) method is employed to produce vertically aligned multiwall (VA-MW) CNT carpets. Their structural properties were studied by means of scanning electron microscopy (SEM), X-Ray diffraction (XRD) and Raman spectroscopy, while their hydrophobic behavior was investigated via contact angle measurements. The resistance to indentation deformation of VA-MWCNT carpets was investigated through nanoindentation technique. The synthesized VA-MWCNTs carpets consisted of well-aligned MWCNTs. Static contact angle measurements were performed with water and glycerol, revealing a rather super-hydrophobic behavior. The structural analysis, hydrophobic behavior and indentation response of VA-MWCNTs carpets synthesized via CVD method are clearly demonstrated. Additionally, cycle indentation load-depth curve was applied and hysteresis loops were observed in the indenter loading-unloading cycle due to the local stress distribution. Hardness (as resistance to applied load) and modulus mapping, at 200 nm of displacement for a grid of 70 μm2 is presented. Through trajection, the resistance is clearly divided in 2 regions, namely the MWCNT probing and the in-between area MWCNT - MWCNT interface.

High- β equilibrium and ballooning stability of the low aspect ratio CNT stellarator

DOE PAGES

Hammond, K. C.; Lazerson, S. A.; Volpe, F. A.

2017-04-07

In the paper, the existence and ballooning-stability of low aspect ratio stellarator equilibria is predicted for the Columbia Neutral Torus (CNT) with the aid of 3D numerical tools. In addition to having a low aspect ratio, CNT is characterized by a low magnetic field and small plasma volume. Also, highly overdense plasmas were recently heated in CNT by means of microwaves. These characteristics suggest that CNT might attain relatively high values of plasma beta and thus be of use in the experimental study of stellarator stability to high-beta instabilities such as ballooning modes. As a first step in that direction,more » here the ballooning stability limit is found numerically. Depending on the particular magnetic configuration we expect volume-averaged β limits in the range 0.9%–3.0%, and possibly higher, and observe indications of a second region of ballooning stability. As the aspect ratio is reduced, stability is found to increase in some configurations and decrease in others. Energy-balance estimates using stellarator scaling laws indicate that the lower β limit may be attainable with overdense heating at powers of 40 to 100 kW. The present study serves the additional purpose of testing VMEC and other stellarator codes at high values of β and at low aspect ratios. For this reason, the study was carried out both for free boundary, for maximum fidelity to experiment, as well as with a fixed boundary, as a numerical test.« less

Carbon nanotubes accelerate methane production in pure cultures of methanogens and in a syntrophic coculture.

PubMed

Salvador, Andreia F; Martins, Gilberto; Melle-Franco, Manuel; Serpa, Ricardo; Stams, Alfons J M; Cavaleiro, Ana J; Pereira, M Alcina; Alves, M Madalena

2017-07-01

Carbon materials have been reported to facilitate direct interspecies electron transfer (DIET) between bacteria and methanogens improving methane production in anaerobic processes. In this work, the effect of increasing concentrations of carbon nanotubes (CNT) on the activity of pure cultures of methanogens and on typical fatty acid-degrading syntrophic methanogenic coculture was evaluated. CNT affected methane production by methanogenic cultures, although acceleration was higher for hydrogenotrophic methanogens than for acetoclastic methanogens or syntrophic coculture. Interestingly, the initial methane production rate (IMPR) by Methanobacterium formicicum cultures increased 17 times with 5 g·L -1 CNT. Butyrate conversion to methane by Syntrophomonas wolfei and Methanospirillum hungatei was enhanced (∼1.5 times) in the presence of CNT (5 g·L -1 ), but indications of DIET were not obtained. Increasing CNT concentrations resulted in more negative redox potentials in the anaerobic microcosms. Remarkably, without a reducing agent but in the presence of CNT, the IMPR was higher than in incubations with reducing agent. No growth was observed without reducing agent and without CNT. This finding is important to re-frame discussions and re-interpret data on the role of conductive materials as mediators of DIET in anaerobic communities. It also opens new challenges to improve methane production in engineered methanogenic processes. © 2017 The Authors. Environmental Microbiology published by Society for Applied Microbiology and John Wiley & Sons Ltd.

Regulation of transport in the connecting tubule and cortical collecting duct.

PubMed

Staruschenko, Alexander

2012-04-01

The central goal of this overview article is to summarize recent findings in renal epithelial transport,focusing chiefly on the connecting tubule (CNT) and the cortical collecting duct (CCD).Mammalian CCD and CNT are involved in fine-tuning of electrolyte and fluid balance through reabsorption and secretion. Specific transporters and channels mediate vectorial movements of water and solutes in these segments. Although only a small percent of the glomerular filtrate reaches the CNT and CCD, these segments are critical for water and electrolyte homeostasis since several hormones, for example, aldosterone and arginine vasopressin, exert their main effects in these nephron sites. Importantly, hormones regulate the function of the entire nephron and kidney by affecting channels and transporters in the CNT and CCD. Knowledge about the physiological and pathophysiological regulation of transport in the CNT and CCD and particular roles of specific channels/transporters has increased tremendously over the last two decades.Recent studies shed new light on several key questions concerning the regulation of renal transport.Precise distribution patterns of transport proteins in the CCD and CNT will be reviewed, and their physiological roles and mechanisms mediating ion transport in these segments will also be covered. Special emphasis will be given to pathophysiological conditions appearing as a result of abnormalities in renal transport in the CNT and CCD. © 2012 American Physiological Society. Compr Physiol 2:1491-1539, 2012.

In-situ determination of amine/epoxy and carboxylic/epoxy exothermic heat of reaction on surface of modified carbon nanotubes and structural verification of covalent bond formation

NASA Astrophysics Data System (ADS)

Neves, Juliana C.; de Castro, Vinícius G.; Assis, Ana L. S.; Veiga, Amanda G.; Rocco, Maria Luiza M.; Silva, Glaura G.

2018-04-01

An effective nanofiller-matrix interaction is considered crucial to produce enhanced nanocomposites. Nevertheless, there is lack of experiments focused in the direct measurement of possible filler-matrix covalent linkage, which was the main goal of this work for a carbon nanotube (CNT)/epoxy system. CNT were functionalized with oxygenated (ox) functions and further with triethylenetetramine (TETA). An in-situ determination methodology of epoxy-CNTs heat of reaction was developed by Differential Scanning Calorimetry (DSC). Values of -(8.7 ± 0.4) and -(6.0 ± 0.6) J/g were observed for epoxy with CNT-ox and CNT-TETA, respectively. These results confirm the occurrence of covalent bonds for both functionalized CNTs, a very important information due to the literature generally disregard this possibility for oxygenated functions. The higher value obtained for CNT-ox can be attributed to a not complete amidation and to steric impediments in the CNT-TETA structure. The modified CNTs produced by DSC experiments were then characterized by X-Ray Photoelectron Spectroscopy, Transmission Electron Microscopy and Thermogravimetry, which confirmed the covalent linkage. This characterization methodology can be used to verify the occurrence of covalent bonds in various nanocomposites with a quantitative evaluation, providing data for better understanding of the role of CNT functional groups and for tailoring its interface with polymers.

Enhanced performance of lithium-sulfur batteries with an ultrathin and lightweight MoS2/carbon nanotube interlayer

NASA Astrophysics Data System (ADS)

Yan, Lingjia; Luo, Nannan; Kong, Weibang; Luo, Shu; Wu, Hengcai; Jiang, Kaili; Li, Qunqing; Fan, Shoushan; Duan, Wenhui; Wang, Jiaping

2018-06-01

Ultrathin and lightweight MoS2/carbon nanotube (CNT) interlayers are developed to effectively trap polysulfides in high-performance lithium-sulfur (Li-S) batteries. The MoS2/CNT interlayer is constructed by loading MoS2 nanosheets onto a cross-stacked CNT film. The CNT film with excellent conductivity and superior mechanical properties provides the Li-S batteries with a uniform conductive network, a supporting skeleton for the MoS2 nanosheets, as well as a physical barrier for the polysulfides. Moreover, chemical interactions and bonding between the MoS2 nanosheets and the polysulfides are evident. The electrode with the MoS2/CNT interlayer delivers an attractive specific capacity of 784 mA h g-1 at a high capacity rate of 10 C. In addition, the electrode demonstrates a high initial capacity of 1237 mA h g-1 and a capacity fade as low as -0.061% per cycle over 500 charge/discharge cycles at 0.2 C. The problem of self-discharge can also be suppressed with the introduction of the MoS2/CNT interlayer. The simple fabrication procedure, which is suitable for commercialization, and the outstanding electrochemical performance of the cells with the MoS2/CNT interlayer demonstrate a great potential for the development of high-performance Li-S batteries.

Understanding physicochemical properties changes from multi-scale structures of starch/CNT nanocomposite films.

PubMed

Liu, Siyuan; Li, Xiaoxi; Chen, Ling; Li, Lin; Li, Bing; Zhu, Jie

2017-11-01

From the view of multi-scale structures of hydroxypropyl starch (HPS)/carbon nanotube (CNT) nanocomposite films, the film physicochemical properties were affected by comprehensive factors including molecular interaction, short range molecular conformation, crystalline structure and aggregated structure. The less original HPS hydrogen bonding that was broken, less decreased order of HPS short range molecular conformation, lower film crystallinity and larger size of micro-ordered regions contributed to higher tensile strength and Young's modulus of the film with CNT content of 0.5% (g/g, CNT in HPS). The higher film overall crystallinity and larger size of micro-ordered regions of the film with CNT content of 0.05%-0.3% compared with those of control contributed to better film barrier property. The addition of CNT with the content of 0.05%-0.5% broke the original HPS hydrogen bonding and decreased the order of starch short range molecular conformation, which counteracted the positive effect of CNT on the thermal stability of the material, thus thermal degradation temperature of these nanocomposite films did not increase. But the sharp increase of film crystallinity increased film thermal degradation temperature. This study provided a better understanding of film physicochemical properties changes which guides to rational design of starch-based nanocomposite films for packaging and coating application. Copyright © 2017. Published by Elsevier B.V.

Identifying the Nonradical Mechanism in the Peroxymonosulfate Activation Process: Singlet Oxygenation Versus Mediated Electron Transfer.

PubMed

Yun, Eun-Tae; Lee, Jeong Hoon; Kim, Jaesung; Park, Hee-Deung; Lee, Jaesang

2018-06-01

Select persulfate activation processes were demonstrated to initiate oxidation not reliant on sulfate radicals, although the underlying mechanism has yet to be identified. This study explored singlet oxygenation and mediated electron transfer as plausible nonradical mechanisms for organic degradation by carbon nanotube (CNT)-activated peroxymonosulfate (PMS). The degradation of furfuryl alcohol (FFA) as a singlet oxygen ( 1 O 2 ) indicator and the kinetic retardation of FFA oxidation in the presence of l-histidine and azide as 1 O 2 quenchers apparently supported a role of 1 O 2 in the CNT/PMS system. However, the 1 O 2 scavenging effect was ascribed to a rapid PMS depletion by l-histidine and azide. A comparison of CNT/PMS and photoexcited Rose Bengal (RB) excluded the possibility of singlet oxygenation during heterogeneous persulfate activation. In contrast to the case of excited RB, solvent exchange (H 2 O to D 2 O) did not enhance FFA degradation by CNT/PMS and the pH- and substrate-dependent reactivity of CNT/PMS did not reflect the selective nature of 1 O 2 . Alternatively, concomitant PMS reduction and trichlorophenol oxidation were achieved when PMS and trichlorophenol were physically separated in two chambers using a conductive vertically aligned CNT membrane. This result suggested that CNT-mediated electron transfer from organics to persulfate was primarily responsible for the nonradical degradative route.

Carbon nanotubes functionalized with sodium hyaluronate restore bone repair in diabetic rat sockets.

PubMed

Sá, M A; Andrade, V B; Mendes, R M; Caliari, M V; Ladeira, L O; Silva, E E; Silva, G A B; Corrêa-Júnior, J D; Ferreira, A J

2013-07-01

We evaluated the effects of sodium hyaluronate (HY) and carbon nanotubes functionalized with HY (HY-CNT) on bone repair in the tooth sockets of diabetic rats. Diabetes was induced by streptozotocin (50 mg kg(-1) i.v.), and the sockets were divided into normal control, diabetic control, diabetic treated with HY (1%), and diabetic treated with HY-CNT (100 μg ml(-1)) groups. The sockets were analyzed according to the percentage of bone formation and the number of cell nuclei. The percentage of bone trabeculae was lower in diabetic control animals (11.16 ± 5.10% vs 41.92 ± 6.34% in normal animals) after 14 days. Treating diabetic animals with HY or HY-CNT significantly increased the percentage of neoformed trabeculae (HY: 29.43 ± 3.29%; HY-CNT: 36.90 ± 3.07%). Moreover, the sockets of diabetic animals had an increased number of cell nuclei and HY or HY-CNT reduced this parameter. Our results indicate that HY and HY-CNT restore bone repair in the tooth sockets of diabetic rats, suggesting that these biomaterials are potential adjuvant therapies for the management of diabetes. © 2012 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Influence of Different Defects in Vertically Aligned Carbon Nanotubes on TiO2 Nanoparticle Formation through Atomic Layer Deposition.

PubMed

Acauan, Luiz; Dias, Anna C; Pereira, Marcelo B; Horowitz, Flavio; Bergmann, Carlos P

2016-06-29

The chemical inertness of carbon nanotubes (CNT) requires some degree of "defect engineering" for controlled deposition of metal oxides through atomic layer deposition (ALD). The type, quantity, and distribution of such defects rules the deposition rate and defines the growth behavior. In this work, we employed ALD to grow titanium oxide (TiO2) on vertically aligned carbon nanotubes (VACNT). The effects of nitrogen doping and oxygen plasma pretreatment of the CNT on the morphology and total amount of TiO2 were systematically studied using transmission electron microscopy, Raman spectroscopy, and thermogravimetric analysis. The induced chemical changes for each functionalization route were identified by X-ray photoelectron and Raman spectroscopies. The TiO2 mass fraction deposited with the same number of cycles for the pristine CNT, nitrogen-doped CNT, and plasma-treated CNT were 8, 47, and 80%, respectively. We demonstrate that TiO2 nucleation is dependent mainly on surface incorporation of heteroatoms and their distribution rather than structural defects that govern the growth behavior. Therefore, selecting the best way to functionalize CNT will allow us to tailor TiO2 distribution and hence fabricate complex heterostructures.

Enhanced electrochemical capacitance of polyimidazole coated covellite CuS dispersed CNT composite materials for application in supercapacitors.

PubMed

Ravi, Seenu; Gopi, Chandu V V M; Kim, Hee Je

2016-08-02

Great attention has been paid to the design and synthesis of distinct core/shell heterostructures for high-performance supercapacitors. We have prepared unique heterostructures consisting of polyimidazole-coated copper sulphide over a carbon nanotube network (CuS@CNT) on nickel foam, which was accomplished through a facile and cost-effective solvothermal method combined with a dip coating process. Hexagonal covellite CuS nanoparticles were dispersed on CNTs using a solvothermal method where dimethylformamide and distilled water were used as solvents. The synthesized CuS and CuS@CNT supercapacitor electrode materials were thoroughly characterized. The polymer supported electrode (PIM/CuS@CNT) shows a high areal capacitance of 1.51 F cm(-2) at a current density of 1.2 A g(-1), which is higher than the CuS@CNT electrode and many other previously reported CuS electrode materials. After 1000 cycles at a high current density of 1.2 A g(-1), the retention rate is 92%, indicating good long-term cycling stability. These results indicate that the PIM/CuS@CNT electrode is promising for high-performance supercapacitor applications.

Processing and Characterization of Carbon Nanotube Composites

NASA Technical Reports Server (NTRS)

Can, Roberto J.; Grimsley, Brian W.; Czabaj, Michael W.; Siochi, Emilie J.; Hull, Brandon

2014-01-01

Recent advances in the synthesis of large-scale quantities of carbon nanotubes (CNT) have provided the opportunity to study the mechanical properties of polymer matrix composites using these novel materials as reinforcement. Nanocomp Technologies, Inc. currently supplies large sheets with dimensions up to 122 cm x 244 cm containing both single-wall and few-wall CNTs. The tubes are approximately 1 mm in length with diameters ranging from 8 to 12 nm. In the present study being conducted at NASA Langley Research Center (LaRC), single and multiple layers of CNT sheets were infused or coated with various polymer solutions that included commercial toughened-epoxies and bismaleimides, as well as a LaRC developed polyimide. The resulting CNT composites were tested in tension using a modified version of ASTM D882-12 to determine their strength and modulus values. The effects of solvent treatment and mechanical elongation/alignment of the CNT sheets on the tensile performance of the composite were determined. Thin composites (around 50 wt% CNT) fabricated from acetone condensed and elongated CNT sheets with either a BMI or polyimide resin solution exhibited specific tensile moduli approaching that of toughened epoxy/ IM7 carbon fiber unidirectional composites.

Superabsorbent hydrogel composite based on copolymer cellulose/poly (vinyl alcohol)/CNT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khoerunnisa, Fitri, E-mail: fitri.khoerunnisa@gmail.com; Hendrawan,; Sonjaya, Yaya

2016-04-19

Superabsorbent hydrogels are cross-linked hydrophilic polymers that can absorb and retain a large volume of water, saline solution, or physiological fluids. A distinctive superabsorbent hydrogel composite based on cellulose/ poly (vinyl alcohol)/ carbon nanotubes was successfully synthesized via the graft bio-copolymerization in an aqueous medium with glutaraldehide as a crosslinking agent. The effect of carbon nanotubes (CNT) on water absorption capacity and mechanical properties of superabsorbent composite were particularly investigated. The Fourier transform infrared spectra showed the evidence of copolymerization of hydrogel precursors as well as the interaction of CNT filler with the hydrogel matrices, as indicated by the shiftingmore » of peak intensity and position of several functional groups (O-H, C-H sp{sup 3}, C=O, C-N, C-O). The modification of hydrogel surface morphology and porosity owing to CNT insertion was also confirmed by scanning electron microscopy images. The CNT insertion improved the mechanical strength of superabsorbent hydrogel composites. Moreover, insertion of CNT into hydrogel matrix remarkably increased the swelling capacity of superabsorbent composites up to 840%. This huge water absorption capacity of hydrogel composites offers promising applications in development of superabsorbent polymers.« less

Electroactive Shape Memory Property of a Cu-decorated CNT Dispersed PLA/ESO Nanocomposite

PubMed Central

Alam, Javed; Khan, Aslam; Alam, Manawwer; Mohan, Raja

2015-01-01

Shape memory polymer (SMP) nanocomposites with a fast electro-actuation speed were prepared by dispersing Cu-decorated carbon nanotubes (CNTs) (Cu-CNTs, 1 wt %, 2 wt %, and 3 wt %) in a polylactic acid (PLA)/epoxidized soybean oil (ESO) blend matrix. The shape memory effect (SME) induced by an electrical current was investigated by a fold-deploy “U”-shape bending test. In addition, the Cu-CNT dispersed PLA/ESO nanocomposite was characterized by atomic force microscopy (AFM), dynamic mechanical analysis (DMA) and tensile and electrical measurements. The results demonstrated that the SME was dependent on the Cu-CNT content in the nanocomposites. When comparing the SMEs of the nanocomposite specimens with different Cu-CNT contents, the 2 wt % Cu-CNT dispersed system exhibited a shape recovery as high as 98% within 35 s due to its higher electrical conductivity that results from uniform Cu-CNT dispersion. However, the nanocomposites that contained 1 wt % and 3 wt % Cu-CNTs required 75 s and 63 s, respectively, to reach a maximum recovery level. In addition, the specimens exhibited better mechanical properties after the addition of Cu-CNTs. PMID:28793570

Facilitation of NADH Electrooxidation at Treated Carbon Nanotubes

PubMed Central

Wooten, Marilyn; Gorski, Waldemar

2010-01-01

The relationship between the state of the surface of carbon nanotubes (CNT) and their electrochemical activity was investigated using the enzyme cofactor dihydronicotinamide adenine dinucleotide (NADH) as a redox probe. The boiling of CNT in water, while nondestructive, activated them toward the oxidation of NADH as indicated by a shift in the anodic peak potential of NADH (ENADH) from 0.4 to 0.0 V. The shift in ENADH was due to the redox mediation of NADH oxidation by traces of quinone species that were formed on the surface of treated CNT. The harsher treatment that comprised of microwaving of CNT in concentrated nitric acid had a similar effect on the ENADH and, additionally, it increased the anodic peak current of NADH. The latter correlated with the formation of defects on the surface of acid-microwaved CNT as indicated by their Raman spectra. The increase in current was discussed considering a role of surface mediators on the buckled graphene sheets of acid-microwaved CNT. The other carbon allotropes including the edge plane pyrolytic graphite, graphite powder, and glassy carbon did not display a comparable activation toward the oxidation of NADH. PMID:20088562

High-fidelity Characterization on Anisotropic Thermal Conductivity of Carbon Nanotube Sheets and on their effects of Thermal Enhancement of Nanocomposites.

PubMed

Zhang, Xiao; Tan, Wei; Smail, Fiona; De Volder, Michael; Fleck, Norman; Boies, Adam

2018-06-19

Some assemblies of nanomaterials, like carbon nanotube (CNT) sheet or film, always show outstanding and anisotropic thermal properties. However, there is still a lack of comprehensive thermal conductivity (κ) characterizations on CNT sheets, as well as lack of estimations of their true contributions on thermal enhancement of polymer composites when used as additives. Always, these characterizations were hindered by the low heat capacity, anisotropic thermal properties or low electrical conductivity of assemblies and their nanocomposites. And the transient κ measurement and calculations were also hampered by accurate determination of parameters, like specific heat capacity, density and cross-section, which could be difficult and controversial for nanomaterials, like CNT sheets. Here, to measure anisotropic κ of CNT sheets directly with high fidelity, we modified the conventional steady-state method by measuring under vacuum and by infrared camera, and then comparing temperature profiles on both reference standard material and a CNT sheet sample. The highly anisotropic thermal conductivities of CNT sheets were characterized comprehensively, with κ/ρ in alignment direction as ~95 mW·m^2/(K·kg). Furthermore, by comparing the measured thermal properties of different CNT-epoxy resin composites, the heat conduction pathway created by the CNT hierarchical network was demonstrated to remain intact after the in-situ polymerization and curing process. The reliable and direct κ measurement rituals used here, dedicated to nanomaterials, will be also essential to assist in assemblies' application to heat dissipation and composite thermal enhancement. © 2018 IOP Publishing Ltd.

Theoretical analysis of hydrogen spillover mechanism on carbon nanotubes

PubMed Central

Juarez-Mosqueda, Rosalba; Mavrandonakis, Andreas; Kuc, Agnieszka B.; Pettersson, Lars G. M.; Heine, Thomas

2015-01-01

The spillover mechanism of molecular hydrogen on carbon nanotubes in the presence of catalytically active platinum clusters was critically and systematically investigated by using density-functional theory. Our simulation model includes a Pt4 cluster for the catalyst nanoparticle and curved and planar circumcoronene for two exemplary single-walled carbon nanotubes (CNT), the (10,10) CNT and one of large diameter, respectively. Our results show that the H2 molecule dissociates spontaneously on the Pt4 cluster. However, the dissociated H atoms have to overcome a barrier of more than 2 eV to migrate from the catalyst to the CNT, even if the Pt4 cluster is at full saturation with six adsorbed and dissociated hydrogen molecules. Previous investigations have shown that the mobility of hydrogen atoms on the CNT surface is hindered by a barrier. We find that instead the Pt4 catalyst may move along the outer surface of the CNT with activation energy of only 0.16 eV, and that this effect offers the possibility of full hydrogenation of the CNT. Thus, although we have not found a low-energy pathway to spillover onto the CNT, we suggest, based on our calculations and calculated data reported in the literature, that in the hydrogen-spillover process the observed saturation of the CNT at hydrogen background pressure occurs through mobile Pt nanoclusters, which move on the substrate more easily than the substrate-chemisorbed hydrogens, and deposit or reattach hydrogens in the process. Initial hydrogenation of the carbon substrate, however, is thermodynamically unfavoured, suggesting that defects should play a significant role. PMID:25699250

Molecular insight into the enhancement of benzene-carbon nanotube interactions by surface modification for drug delivery systems (DDS)

NASA Astrophysics Data System (ADS)

Zhao, Jianghao; Liu, Xiaoshan; Zhu, Zhu; Wang, Ning; Sun, Wenjing; Chen, Congmei; He, Zhiwei

2017-09-01

Anthracyclines are effective anticancer drugs but have drawbacks including systemic toxicity and drug resistance. Delivering them directly to the tumor may improve therapeutic efficacy and reduce adverse effects. Carbon nanotubes (CNTs) can act as excellent drug delivery systems (DDS), but pristine CNTs have inert surfaces, which contributes poor drug loading capacity and limits dispersion. In this study, we designed a series of functionalized CNTs (f-CNTs) with anchored hydrophilic groups (OH, COOH, and NH2) by substitutional doping of the CNT lattice (DNT) using N or B atoms or the combination of both. The aromatic compound benzene (Ben) was selected as a model for anthracycline drugs. The effect of CNT curvature, chemical groups (CGs), and doping on the Ben-CNTs interactions was studied using quantum chemistry calculations. Our results show that π-π interactions between Ben and CNTs are influenced by CNT curvature. When the CNTs were functionalized only with CGs and not doped, the system was unstable, resulting in weak Ben-CNT interactions. However, anchoring CGs on DNTs greatly enhanced the Ben-CNT interactions. CNTs with good affinity for drug molecules, improved solubility, and lower tendency to aggregate have potential as DDS for enhancing the efficacy of medicines. We believe that these studies have general applicability and anticipate that our findings will motivate additional theoretical and experimental studies on the biology and chemistry of CNTs as DDS.

Surface modification of carbon nanotubes using 3-aminopropyltriethoxysilane to improve mechanical properties of nanocomposite based polymer matrix: Experimental and Density functional theory study

NASA Astrophysics Data System (ADS)

Hamed Mashhadzadeh, A.; Fereidoon, Ab.; Ghorbanzadeh Ahangari, M.

2017-10-01

In current study we combined theoretical and experimental studies to evaluate the effect of functionalization and silanization on mechanical behavior of polymer-based/CNT nanocomposites. Epoxy was selected as thermoset polymer, polypropylene and poly vinyl chloride were selected as thermoplastic polymers. The whole procedure is divided to two sections . At first we applied density functional theory (DFT) to analyze the effect of functionalization on equilibrium distance and adsorption energy of unmodified, functionalized by sbnd OH group and silanized epoxy/CNT, PP/CNT and PVC/CNT nanocomposites and the results showed that functionalization increased adsorption energy and reduced the equilibrium distance in all studied nanocomposites and silanization had higher effect comparing to OH functionalizing. Then we prepared experimental samples of all mentioned nanocomposites and tested their tensile and flexural strength properties. The obtained results showed that functionalization increased the studied mechanical properties in all evaluated nanocomposites. Finally we compared the results of experimental and theoretical sections with each other and estimated a suitable agreement between these parts.

Modifying the morphology and properties of aligned CNT foams through secondary CNT growth.

PubMed

Faraji, Shaghayegh; Stano, Kelly; Akyildiz, Halil; Yildiz, Ozkan; Jur, Jesse S; Bradford, Philip D

2018-07-20

In this work, we report for the first time, growth of secondary carbon nanotubes (CNTs) throughout a three-dimensional assembly of CNTs. The assembly of nanotubes was in the form of aligned CNT/carbon (ACNT/C) foams. These low-density CNT foams were conformally coated with an alumina buffer layer using atomic layer deposition. Chemical vapor deposition was further used to grow new CNTs. The CNT foam's extremely high porosity allowed for growth of secondary CNTs inside the bulk of the foams. Due to the heavy growth of new nanotubes, density of the foams increased more than 2.5 times. Secondary nanotubes had the same graphitic quality as the primary CNTs. Microscopy and chemical analysis revealed that the thickness of the buffer layer affected the diameter, nucleation density as well as growth uniformity across the thickness of the foams. The effects of secondary nanotubes on the compressive mechanical properties of the foams was also investigated.

Modifying the morphology and properties of aligned CNT foams through secondary CNT growth

NASA Astrophysics Data System (ADS)

Faraji, Shaghayegh; Stano, Kelly; Akyildiz, Halil; Yildiz, Ozkan; Jur, Jesse S.; Bradford, Philip D.

2018-07-01

In this work, we report for the first time, growth of secondary carbon nanotubes (CNTs) throughout a three-dimensional assembly of CNTs. The assembly of nanotubes was in the form of aligned CNT/carbon (ACNT/C) foams. These low-density CNT foams were conformally coated with an alumina buffer layer using atomic layer deposition. Chemical vapor deposition was further used to grow new CNTs. The CNT foam’s extremely high porosity allowed for growth of secondary CNTs inside the bulk of the foams. Due to the heavy growth of new nanotubes, density of the foams increased more than 2.5 times. Secondary nanotubes had the same graphitic quality as the primary CNTs. Microscopy and chemical analysis revealed that the thickness of the buffer layer affected the diameter, nucleation density as well as growth uniformity across the thickness of the foams. The effects of secondary nanotubes on the compressive mechanical properties of the foams was also investigated.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Srivastava, Ashish Kumar, E-mail: ashish.memech@gmail.com; Singh, Akhileshwar; Mokhalingam, A.

Atomistic simulations were conducted to estimate the effect of the carbon nanotube (CNT) reinforcement on the mechanical behavior of CNT-reinforced aluminum (Al) nanocomposite. The periodic system of CNT-Al nanocomposite was built and simulated using molecular dynamics (MD) software LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator). The mechanical properties of the nanocomposite were investigated by the application of uniaxial load on one end of the representative volume element (RVE) and fixing the other end. The interactions between the atoms of Al were modeled using embedded atom method (EAM) potentials, whereas Adaptive Intermolecular Reactive Empirical Bond Order (AIREBO) potential was used for themore » interactions among carbon atoms and these pair potentials are coupled with the Lennard-Jones (LJ) potential. The results show that the incorporation of CNT into the Al matrix can increase the Young’s modulus of the nanocomposite substantially. In the present case, i.e. for approximately 9 with % reinforcement of CNT can increase the axial Young’s modulus of the Al matrix up to 77 % as compared to pure Al.« less

Dynamic response of phenolic resin and its carbon-nanotube composites to shock wave loading

DOE PAGES

Arman, B.; An, Q.; Luo, S. N.; ...

2011-01-04

We investigate with nonreactive molecular dynamics simulations the dynamic response of phenolic resin and its carbon-nanotube (CNT) composites to shock wave compression. For phenolic resin, our simulations yield shock states in agreement with experiments on similar polymers except the “phase change” observed in experiments, indicating that such phase change is chemical in nature. The elastic–plastic transition is characterized by shear stress relaxation and atomic-level slip, and phenolic resin shows strong strain hardening. Shock loading of the CNT-resin composites is applied parallel or perpendicular to the CNT axis, and the composites demonstrate anisotropy in wave propagation, yield and CNT deformation. Themore » CNTs induce stress concentrations in the composites and may increase the yield strength. Our simulations indicate that the bulk shock response of the composites depends on the volume fraction, length ratio, impact cross-section, and geometry of the CNT components; the short CNTs in current simulations have insignificant effect on the bulk response of resin polymer.« less

Enhancement of the in-plane shear properties of carbon fiber composites containing carbon nanotube mats

NASA Astrophysics Data System (ADS)

Kim, Hansang

2015-01-01

The in-plane shear property of carbon fiber laminates is one of the most important structural features of aerospace and marine structures. Fiber-matrix debonding caused by in-plane shear loading is the major failure mode of carbon fiber composites because of the stress concentration at the interfaces. In this study, carbon nanotube mats (CNT mat) were incorporated in two different types of carbon fiber composites. For the case of woven fabric composites, mechanical interlocking between the CNTs and the carbon fibers increased resistance to shear failure. However, not much improvement was observed for the prepreg composites as a result of incorporation of the CNT mats. The reinforcement mechanism of the CNT mat layer was investigated by a fractographic study using scanning electron microscopy. In addition, the CNT mat was functionalized by three different methods and the effectiveness of the functionalization methods was determined and the most appropriate functionalization method for the CNT mat was air oxidation.

Pillared graphene on the basis of zigzag carbon nanotubes for adsorption in medicine: mechanical properties

NASA Astrophysics Data System (ADS)

Kolesnikova, Anna S.; Mazepa, Margarita M.

2018-02-01

In nowadays the nanoscale materials are actively used in medicine, based on the properties of adsorption. One of the main problems of this field of medicine is the increase in specific surface of sorbent. We proposed to use carbon composites consisting of an extended in its directions graphene sheet with attached to it by chemical bonds zigzag carbon nanotubes (CNT). This paper presents the results of a theoretical study of the mechanical properties of graphene based on the CNT zigzag depending on the geometric dimensions of the composite (length and diameter of CNTs).

Control of Wettability of Carbon Nanotube Array by Reversible Dry Oxidation for Superhydrophobic Coating and Supercapacitor Applications

NASA Astrophysics Data System (ADS)

Aria, Adrianus Indrat

In this thesis, dry chemical modification methods involving UV/ozone, oxygen plasma, and vacuum annealing treatments are explored to precisely control the wettability of CNT arrays. The effect of oxidation using UV/ozone and oxygen plasma treatments is highly reversible as long as the O/C ratio of the CNT arrays is kept below 18%. At O/C ratios higher than 18%, the effect of oxidation is no longer reversible. This irreversible oxidation is caused by irreversible changes to the CNT atomic structure during the oxidation process. During the oxidation process, CNT arrays undergo three different processes. For CNT arrays with O/C ratios lower than 40%, the oxidation process results in the functionalization of CNT outer walls by oxygenated groups. Although this functionalization process introduces defects, vacancies and micropores opening, the graphitic structure of the CNT is still largely intact. For CNT arrays with O/C ratios between 40% and 45%, the oxidation process results in the etching of CNT outer walls. This etching process introduces large scale defects and holes that can be obviously seen under TEM at high magnification. Most of these holes are found to be several layers deep and, in some cases, a large portion of the CNT side walls are cut open. For CNT arrays with O/C ratios higher than 45%, the oxidation process results in the exfoliation of the CNT walls and amorphization of the remaining CNT structure. This amorphization process can be implied from the disappearance of C-C sp2 peak in the XPS spectra associated with the pi-bond network. The impact behavior of water droplet impinging on superhydrophobic CNT arrays in a low viscosity regime is investigated for the first time. Here, the experimental data are presented in the form of several important impact behavior characteristics including critical Weber number, volume ratio, restitution coefficient, and maximum spreading diameter. As observed experimentally, three different impact regimes are identified while another impact regime is proposed. These regimes are partitioned by three critical Weber numbers, two of which are experimentally observed. The volume ratio between the primary and the secondary droplets is found to decrease with the increase of Weber number in all impact regimes other than the first one. In the first impact regime, this is found to be independent of Weber number since the droplet remains intact during and subsequent to the impingement. Experimental data show that the coefficient of restitution decreases with the increase of Weber number in all impact regimes. The rate of decrease of the coefficient of restitution in the high Weber number regime is found to be higher than that in the low and moderate Weber number. Experimental data also show that the maximum spreading factor increases with the increase of Weber number in all impact regimes. The rate of increase of the maximum spreading factor in the high Weber number regime is found to be higher than that in the low and moderate Weber number. Phenomenological approximations and interpretations of the experimental data, as well as brief comparisons to the previously proposed scaling laws, are shown here. Dry oxidation methods are used for the first time to characterize the influence of oxidation on the capacitive behavior of CNT array EDLCs. The capacitive behavior of CNT array EDLCs can be tailored by varying their oxygen content, represented by their O/C ratio. The specific capacitance of these CNT arrays increases with the increase of their oxygen content in both KOH and Et4NBF4/PC electrolytes. As a result, their gravimetric energy density increases with the increase of their oxygen content. However, their gravimetric power density decreases with the increase of their oxygen content. The optimally oxidized CNT arrays are able to withstand more than 35,000 charge/discharge cycles in Et4NBF4/PC at a current density of 5 A/g while only losing 10% of their original capacitance. (Abstract shortened by UMI.)

In-Situ Welding Carbon Nanotubes into a Porous Solid with Super-High Compressive Strength and Fatigue Resistance

PubMed Central

Lin, Zhiqiang; Gui, Xuchun; Gan, Qiming; Chen, Wenjun; Cheng, Xiaoping; Liu, Ming; Zhu, Yuan; Yang, Yanbing; Cao, Anyuan; Tang, Zikang

2015-01-01

Carbon nanotube (CNT) and graphene-based sponges and aerogels have an isotropic porous structure and their mechanical strength and stability are relatively lower. Here, we present a junction-welding approach to fabricate porous CNT solids in which all CNTs are coated and welded in situ by an amorphous carbon layer, forming an integral three-dimensional scaffold with fixed joints. The resulting CNT solids are robust, yet still highly porous and compressible, with compressive strengths up to 72 MPa, flexural strengths up to 33 MPa, and fatigue resistance (recovery after 100,000 large-strain compression cycles at high frequency). Significant enhancement of mechanical properties is attributed to the welding-induced interconnection and reinforcement of structural units, and synergistic effects stemming from the core-shell microstructures consisting of a flexible CNT framework and a rigid amorphous carbon shell. Our results provide a simple and effective method to manufacture high-strength porous materials by nanoscale welding. PMID:26067176

In-Situ Welding Carbon Nanotubes into a Porous Solid with Super-High Compressive Strength and Fatigue Resistance.

PubMed

Lin, Zhiqiang; Gui, Xuchun; Gan, Qiming; Chen, Wenjun; Cheng, Xiaoping; Liu, Ming; Zhu, Yuan; Yang, Yanbing; Cao, Anyuan; Tang, Zikang

2015-06-11

Carbon nanotube (CNT) and graphene-based sponges and aerogels have an isotropic porous structure and their mechanical strength and stability are relatively lower. Here, we present a junction-welding approach to fabricate porous CNT solids in which all CNTs are coated and welded in situ by an amorphous carbon layer, forming an integral three-dimensional scaffold with fixed joints. The resulting CNT solids are robust, yet still highly porous and compressible, with compressive strengths up to 72 MPa, flexural strengths up to 33 MPa, and fatigue resistance (recovery after 100,000 large-strain compression cycles at high frequency). Significant enhancement of mechanical properties is attributed to the welding-induced interconnection and reinforcement of structural units, and synergistic effects stemming from the core-shell microstructures consisting of a flexible CNT framework and a rigid amorphous carbon shell. Our results provide a simple and effective method to manufacture high-strength porous materials by nanoscale welding.

In-Situ Welding Carbon Nanotubes into a Porous Solid with Super-High Compressive Strength and Fatigue Resistance

NASA Astrophysics Data System (ADS)

Lin, Zhiqiang; Gui, Xuchun; Gan, Qiming; Chen, Wenjun; Cheng, Xiaoping; Liu, Ming; Zhu, Yuan; Yang, Yanbing; Cao, Anyuan; Tang, Zikang

2015-06-01

Carbon nanotube (CNT) and graphene-based sponges and aerogels have an isotropic porous structure and their mechanical strength and stability are relatively lower. Here, we present a junction-welding approach to fabricate porous CNT solids in which all CNTs are coated and welded in situ by an amorphous carbon layer, forming an integral three-dimensional scaffold with fixed joints. The resulting CNT solids are robust, yet still highly porous and compressible, with compressive strengths up to 72 MPa, flexural strengths up to 33 MPa, and fatigue resistance (recovery after 100,000 large-strain compression cycles at high frequency). Significant enhancement of mechanical properties is attributed to the welding-induced interconnection and reinforcement of structural units, and synergistic effects stemming from the core-shell microstructures consisting of a flexible CNT framework and a rigid amorphous carbon shell. Our results provide a simple and effective method to manufacture high-strength porous materials by nanoscale welding.

Effect of Spark-Plasma-Sintering Conditions on Tensile Properties of Aluminum Matrix Composites Reinforced with Multiwalled Carbon Nanotubes (MWCNTs)

NASA Astrophysics Data System (ADS)

Chen, B.; Imai, H.; Umeda, J.; Takahashi, M.; Kondoh, K.

2017-04-01

In this study, aluminum (Al) matrix composites containing 2 wt.% multiwalled carbon nanotubes (CNTs) were fabricated by powder metallurgy using high-energy ball milling (HEBM), spark plasma sintering (SPS), and subsequent hot extrusion. The effect of SPS conditions on the tensile properties of CNT/Al composites was investigated. The results showed that composites with well-dispersed CNTs and nearly full-density CNT/Al can be obtained. During HEBM, CNTs were shortened, inserted into welded Al powder particles, bonded to Al, and still stable without CNT-Al reaction. After consolidation, Al4C3 phases formed in composites under different sintering conditions. With the increase of sintering temperature and holding time, the strength decreased. Conversely, the ductility and toughness noticeably increased. As a result, a good balance between strength (367 MPa in ultimate tensile strength) and ductility (13% in elongation) was achieved in the as-extruded CNT/Al composite sintered at 630°C with a holding time of 300 min.

Substituted cysteine accessibility method (SCAM) analysis of the transport domain of human concentrative nucleoside transporter 3 (hCNT3) and other family members reveals features of structural and functional importance

PubMed Central

Mulinta, Ras; Yao, Sylvia Y. M.; Ng, Amy M. L.; Cass, Carol E.; Young, James D.

2017-01-01

The human SLC28 family of concentrative nucleoside transporter (CNT) proteins has three members: hCNT1, hCNT2, and hCNT3. Na+-coupled hCNT1 and hCNT2 transport pyrimidine and purine nucleosides, respectively, whereas hCNT3 transports both pyrimidine and purine nucleosides utilizing Na+ and/or H+ electrochemical gradients. Escherichia coli CNT family member NupC resembles hCNT1 in permeant selectivity but is H+-coupled. Using heterologous expression in Xenopus oocytes and the engineered cysteine-less hCNT3 protein hCNT3(C−), substituted cysteine accessibility method analysis with the membrane-impermeant thiol reactive reagent p-chloromercuribenzene sulfonate was performed on the transport domain (interfacial helix 2, hairpin 1, putative transmembrane domain (TM) 7, and TM8), as well as TM9 of the scaffold domain of the protein. This systematic scan of the entire C-terminal half of hCNT3(C−) together with parallel studies of the transport domain of wild-type hCNT1 and the corresponding TMs of cysteine-less NupC(C−) yielded results that validate the newly developed structural homology model of CNT membrane architecture for human CNTs, revealed extended conformationally mobile regions within transport-domain TMs, identified pore-lining residues of functional importance, and provided evidence of an emerging novel elevator-type mechanism of transporter function. PMID:28385889

The optimization of CNT-PVA nanocomposite for mild steel coating: Effect of CNTs concentration on the corrosion rate of mild steel

NASA Astrophysics Data System (ADS)

Maryam, M.; Ibrahim, N. M. A. A.; Eswar, K. A.; Guliling, M.; Suhaimi, M. H. F.; Khusaimi, Z.; Abdullah, S.; Rusop, M.

2018-05-01

Carbon Nanotubes (CNTs) are molecular-scale tubes of graphitic carbon which have outstanding mechanical and magnetic properties with extraordinary strength. It can be said that CNTs can be used in coating application to prevent corrosion and lower the rate of corrosion on steel. However, CNT alone cannot be used for coating purposes. Therefore, by combining it with polymer to produce a nanocomposite thin film, it can be used for nanocoating on mild steel substrate. Polyvinyl alcohol (PVA) was chosen due to its high strength and high modulus polymer fibers and has the possibilities of improving the physicochemical properties of carbon nanotubes. Carbon nanotubes and polyvinyl alcohol (CNT-PVA) nanocomposite were prepared by using sol-gel method and coated as thin film on mild steel substrate by using spin coating. Sol-gel is a convenient technique used for the production of nanocomposite aqueous solution. Five samples were prepared at the different concentration of CNTs-PVA to verify the corrosion rate application. The samples were then characterized by Field Emission Scanning Electron Microscopy (FESEM) and Atomic Force Microscopy (AFM) obtaining the structural properties, surface morphology and topography of samples. Raman spectroscopy was used to determine the microraman spectra of CNTs which showed the quality and purity of samples. Finally, corrosion test was done to measure the corrosion rate of samples at the different concentration of CNTs/PVA nanocomposite.

Multi-Scale Microstructure and Mechanical Properties of High Carbon Eutectic Tantalum Carbide Reinforced with Carbon Nanotubes

DTIC Science & Technology

2012-07-02

more effective grain growth inhibitors. Transverse Rupture Strength of TaC reinforced with shorter CNTs displayed highest strength/density ratio with...microstructural features. 6. Strength to density ratio of CNT reinforced TaC increased from 17 to 28, which is an increase of ~ 65%. 7. Oxidation behavior of... reinforced with carbon fibers for space applications [15,16]. In recent years, Spark Plasma Sintering (SPS) also known as Electric Field Assisted Sintering

Prelithiation of silicon-carbon nanotube anodes for lithium ion batteries by stabilized lithium metal powder (SLMP).

PubMed

Forney, Michael W; Ganter, Matthew J; Staub, Jason W; Ridgley, Richard D; Landi, Brian J

2013-09-11

Stabilized lithium metal powder (SLMP) has been applied during battery assembly to effectively prelithiate high capacity (1500-2500 mAh/g) silicon-carbon nanotube (Si-CNT) anodes, eliminating the 20-40% first cycle irreversible capacity loss. Pressure-activation of SLMP is shown to enhance prelithiation and enable capacity matching between Si-CNT anodes and lithium nickel cobalt aluminum oxide (NCA) cathodes in full batteries with minimal added mass. The prelithiation approach enables high energy density NCA/Si-CNT batteries achieving >1000 cycles at 20% depth-of-discharge.

Modeling of Branched (L, T and Y) Carbon Nanotubes

NASA Technical Reports Server (NTRS)

Han, Jie; Jaffe, Richard; Saini, Subhash (Technical Monitor)

1998-01-01

Models for connecting two or three carbon nanotubes (CNT) using topological defects (i.e., pentagons and heptagons) are presented for the characterization of experimentally observed L, T and Y CNT junctions. The effects of the separation and orientation of the topological defects on the structures and energetics of these junctions are investigated using the nonlocal density function theory (DFT) and semi-empirical molecular orbital (AM1) calculations, and the Brenner empirical potential molecular mechanics simulations. The potential applications of L, Y and T CNT junctions in nanoelectronic devices are also discussed.

DFT study of cyanide oxidation on surface of Ge-embedded carbon nanotube

NASA Astrophysics Data System (ADS)

Gao, Wei; Milad Abrishamifar, Seyyed; Ebrahimzadeh Rajaei, Gholamreza; Razavi, Razieh; Najafi, Meysam

2018-03-01

In recent years, the discovery of suitable catalyst to oxidation of the cyanide (CN) has high importance in the industry. In present study, in the first step, the carbon nanotube (CNT) with the Ge atom embedded and the surface of Ge-CNT via the O2 molecule activated. In second step, the oxidation of CN on surface of the Ge-CNT via the Langmuir Hinshelwood (LH) and the Eley Rideal (ER) mechanisms was investigated. Results show that O2-Ge-CNT oxidized the CN molecule via the Ge-CNT-O-O∗ + CN → Ge-CNT-O-O∗-CN → Ge-CNT-O∗ + OCN and the Ge-CNT-O∗ + CN → Ge-CNT + OCN reactions. Results show that oxidation of CN on surface of Ge-CNT via the LH mechanism has lower energy barrier than ER mechanism. Finally, calculated parameters reveal that Ge-CNT is acceptable catalyst with high performance for CN oxidation, form theoretical point of view.

Fabrication Processes and Mechanical Behavior of CNT/Metal Nanocomposites

DTIC Science & Technology

2013-12-01

process, were investigated and applied for fabrication of CNT/Cu and CNT/Ni nanocomposite powders. The spark plasma sintering process was applied... spark plasma sintering process to fabricate CNT/NiTi and CNT/Al-Cu nanocomposites. It is confirmed that the CNTs were homogeneously dispersed in NiTi...can be seen in Figure 1-1. The CNT/NiTi composite powders were consolidated by spark plasma sintering (SPS, Dr. Sinter Lab., Sumitomo). The CNT/NiTi

3D Printed Polycaprolactone Carbon Nanotube Composite Scaffolds for Cardiac Tissue Engineering.

PubMed

Ho, Chee Meng Benjamin; Mishra, Abhinay; Lin, Pearlyn Teo Pei; Ng, Sum Huan; Yeong, Wai Yee; Kim, Young-Jin; Yoon, Yong-Jin

2017-04-01

Fabrication of tissue engineering scaffolds with the use of novel 3D printing has gained lot of attention, however systematic investigation of biomaterials for 3D printing have not been widely explored. In this report, well-defined structures of polycaprolactone (PCL) and PCL- carbon nanotube (PCL-CNT) composite scaffolds have been designed and fabricated using a 3D printer. Conditions for 3D printing has been optimized while the effects of varying CNT percentages with PCL matrix on the thermal, mechanical and biological properties of the printed scaffolds are studied. Raman spectroscopy is used to characterise the functionalized CNTs and its interactions with PCL matrix. Mechanical properties of the composites are characterised using nanoindentation. Maximum peak load, elastic modulus and hardness increases with increasing CNT content. Differential scanning calorimetry (DSC) studies reveal the thermal and crystalline behaviour of PCL and its CNT composites. Biodegradation studies are performed in Pseudomonas Lipase enzymatic media, showing its specificity and effect on degradation rate. Cell imaging and viability studies of H9c2 cells from rat origin on the scaffolds are performed using fluorescence imaging and MTT assay, respectively. PCL and its CNT composites are able to show cell proliferation and have the potential to be used in cardiac tissue engineering. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Molecular dynamics simulation of a nanofluidic energy absorption system: effects of the chiral vector of carbon nanotubes.

PubMed

Ganjiani, Sayed Hossein; Hossein Nezhad, Alireza

2018-02-14

A Nanofluidic Energy Absorption System (NEAS) is a novel nanofluidic system with a small volume and weight. In this system, the input mechanical energy is converted to surface tension energy during liquid infiltration in the nanotube. The NEAS is made of a mixture of nanoporous material particles in a functional liquid. In this work, the effects of the chiral vector of a carbon nanotube (CNT) on the performance characteristics of the NEAS are investigated by using molecular dynamics simulation. For this purpose, six CNTs with different diameters for each type of armchair, zigzag and chiral, and several chiral CNTs with different chiral vectors (different values of indices (m,n)) are selected and studied. The results show that in the chiral CNTs, the contact angle shows the hydrophobicity of the CNT, and infiltration pressure is reduced by increasing the values of m and n (increasing the CNT diameter). Contact angle and infiltration pressure are decreased by almost 1.4% and 9% at all diameters, as the type of CNT is changed from chiral to zigzag and then to armchair. Absorbed energy density and efficiency are also decreased by increasing m and n and by changing the type of CNT from chiral to zigzag and then to armchair.

Electronic structure of cyclodextrin–carbon nanotube composite films

DOE PAGES

Jeong, Hae Kyung; Echeverria, Elena; Chakraborti, Priyanka; ...

2017-02-10

The electronic structures of two kinds of cyclodextrin–carbon nanotube (αCD–CNT and γCD–CNT) composite films are investigated by using (angular dependent) photoelectron spectroscopy to gain insight as to why the αCD–CNT and γCD–CNT composite films show different performances in biosensor applications. The γCD–CNT composite film is likely to have the CD localized on the surface rather than in the bulk of the film, while αCD–CNT has CD relatively more concentrated within the bulk of selvedge region of the film, rather than the surface. The results indicate that the CD, of the γCD–CNT composite, may be more bioactive, and possibly a bettermore » sensor of biomolecules due to the favorable surface position compared with that of αCD–CNT. The valence band of αCD–CNT and γCD–CNT show little difference from the CNT film except for a density of states, originating from CD, evident at a binding energy near 27 eV below Fermi level, meaning that there are few or no redox interactions between the CD and the CNT. The absence of a redox interaction between the CD and the CNT permits a clear electrochemical response to occur when guest biomolecules are captured on the composites, providing a route to biosensor applications.« less

Bioelectronic Device Mimicking Human Sensory System based on Nanovesicle-Carbon Nanotube Hybrid Structure

NASA Astrophysics Data System (ADS)

Kim, Daesan; Jin, Hye; Lee, San; Kim, Tae; Park, Juhun; Song, Hyun; Park, Tai; Hong, Seunghun

2013-03-01

We have developed a nanovesicle-based bioelectronic nose (NBN) that could mimic the receptor-mediated signal transmission of human olfactory systems and recognize a specific odorant. The NBN was comprised of a single-walled carbon nanotube (CNT)-based field effect transistor and cell-derived nanovesicles containing human olfactory receptors and calcium ion signal pathways. Importantly, the NBN took advantages of cell signal pathways for sensing signal amplification. It enabled ~100 times higher sensitivity than that of previous bioelectronic noses based on only olfactory receptor protein and CNT transistors. The NBN sensors exhibited a high sensitivity of 1 fM detection limit and a human-like selectivity with single-carbon-atomic resolution. Furthermore, these sensors could mimic a receptor-mediated cellular signal transmission in live cells. This versatile sensor platform should be useful for the study of molecular recognition and biological processes on cell membranes and also for various practical applications such as food conditioning and medical diagnostics.

Characterization of Hybrid CNT Polymer Matrix Composites

NASA Technical Reports Server (NTRS)

Grimsley, Brian W.; Cano, Roberto J.; Kinney, Megan C.; Pressley, James; Sauti, Godfrey; Czabaj, Michael W.; Kim, Jae-Woo; Siochi, Emilie J.

2015-01-01

Carbon nanotubes (CNTs) have been studied extensively since their discovery and demonstrated at the nanoscale superior mechanical, electrical and thermal properties in comparison to micro and macro scale properties of conventional engineering materials. This combination of properties suggests their potential to enhance multi-functionality of composites in regions of primary structures on aerospace vehicles where lightweight materials with improved thermal and electrical conductivity are desirable. In this study, hybrid multifunctional polymer matrix composites were fabricated by interleaving layers of CNT sheets into Hexcel® IM7/8552 prepreg, a well-characterized toughened epoxy carbon fiber reinforced polymer (CFRP) composite. The resin content of these interleaved CNT sheets, as well as ply stacking location were varied to determine the effects on the electrical, thermal, and mechanical performance of the composites. The direct-current electrical conductivity of the hybrid CNT composites was characterized by in-line and Montgomery four-probe methods. For [0](sub 20) laminates containing a single layer of CNT sheet between each ply of IM7/8552, in-plane electrical conductivity of the hybrid laminate increased significantly, while in-plane thermal conductivity increased only slightly in comparison to the control IM7/8552 laminates. Photo-microscopy and short beam shear (SBS) strength tests were used to characterize the consolidation quality of the fabricated laminates. Hybrid panels fabricated without any pretreatment of the CNT sheets resulted in a SBS strength reduction of 70 percent. Aligning the tubes and pre-infusing the CNT sheets with resin significantly improved the SBS strength of the hybrid composite To determine the cause of this performance reduction, Mode I and Mode II fracture toughness of the CNT sheet to CFRP interface was characterized by double cantilever beam (DCB) and end notch flexure (ENF) testing, respectively. Results are compared to the control IM7/8552 laminate.

A Single Aspiration of Rod-like Carbon Nanotubes Induces Asbestos-like Pulmonary Inflammation Mediated in Part by the IL-1 Receptor.

PubMed

Rydman, Elina M; Ilves, Marit; Vanhala, Esa; Vippola, Minnamari; Lehto, Maili; Kinaret, Pia A S; Pylkkänen, Lea; Happo, Mikko; Hirvonen, Maija-Riitta; Greco, Dario; Savolainen, Kai; Wolff, Henrik; Alenius, Harri

2015-09-01

Carbon nanotubes (CNT) have been eagerly studied because of their multiple applications in product development and potential risks on health. We investigated the difference of two different CNT and asbestos in inducing proinflammatory reactions in C57BL/6 mice after single pharyngeal aspiration exposure. We used long tangled and long rod-like CNT, as well as crocidolite asbestos at a dose of 10 or 40 µg/mouse. The mice were sacrificed 4 and 16 h or 7, 14, and 28 days after the exposure. To find out the importance of a major inflammatory marker IL-1β in CNT-induced pulmonary inflammation, we used etanercept and anakinra as antagonists as well as Interleukin 1 (IL-1) receptor (IL-1R-/-) mice. The results showed that rod-like CNT, and asbestos in lesser extent, induced strong pulmonary neutrophilia accompanied by the proinflammatory cytokines and chemokines 16 h after the exposure. Seven days after the exposure, neutrophilia had essentially disappeared but strong pulmonary eosinophilia peaked in rod-like CNT and asbestos-exposed groups. After 28 days, pulmonary granulomas, goblet cell hyperplasia, and Charcot-Leyden-like crystals containing acidophilic macrophages were observed especially in rod-like CNT-exposed mice. IL-1R-/- mice and antagonists-treated mice exhibited a significant decrease in neutrophilia and messenger ribonucleic acid (mRNA) levels of proinflammatory cytokines at 16 h. However, rod-like CNT-induced Th2-type inflammation evidenced by the expression of IL-13 and mucus production was unaffected in IL-1R-/- mice at 28 days. This study provides knowledge about the pulmonary effects induced by a single exposure to the CNT and contributes to hazard assessment of carbon nanomaterials on airway exposure. © The Author 2015. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

Ultrasensitive and selective 4-aminophenol chemical sensor development based on nickel oxide nanoparticles decorated carbon nanotube nanocomposites for green environment.

PubMed

Hussain, Mohammad Musarraf; Rahman, Mohammed M; Asiri, Abdullah M

2017-03-01

Nickel oxide nanoparticles decorated carbon nanotube nanocomposites (NiO·CNT NCs) were prepared in a basic medium by using facile wet-chemical routes. The optical, morphological, and structural properties of NiO·CNT NCs were characterized using Fourier transformed infra-red (FT-IR), Ultra-violet visible (UV/Vis) spectroscopy, field-emission scanning electron microscopy (FESEM), X-ray energy dispersed spectroscopy (XEDS), X-ray photoelectron spectroscopy (XPS), and powder X-ray diffraction (XRD) methods. Selective 4-aminophenol (4-AP) chemical sensor was developed by a flat glassy carbon electrode (GCE, surface area: 0.0316cm 2 ) fabricated with a thin-layer of NCs. Electrochemical responses including higher sensitivity, large dynamic range (LDR), limit of detection (LOD), and long-term stability towards 4-AP were obtained using the fabricated chemical sensors. The calibration curve was found linear (R 2 =0.914) over a wide range of 4-AP concentration (0.1nmol/L-0.1mol/L). In perspective of slope (2×10 -5 μA/μM), LOD and sensitivity were calculated as 15.0±0.1pM and ~6.33×10 -4 μA/(μM·cm) respectively. The synthesized NiO·CNT NCs using a wet-chemical method is a significant route for the development of ultrasensitive and selective phenolic sensor based on nano-materials for environmental toxic substances. It is suggested that a pioneer and selective development of 4-AP sensitive sensor using NiO·CNT NCs by a facile and reliable current vs voltage (I-V) method for the major application of toxic agents in biological, green environmental, and health-care fields in near future. Copyright © 2016. Published by Elsevier B.V.

Carbon nanotube charge collectors for nanoimprinted hybrid perovskite photovoltaics (Conference Presentation)

NASA Astrophysics Data System (ADS)

Zakhidov, Anvar A.; Haroldson, Ross; Saranin, Danila; Martinez, Patricia; Ishteev, Artur

2017-06-01

The hybrid (organo-inorganic) lead-halide perovskites revolutionized the field of solar cell research due to the impressive power conversion efficiencies of up to 21% recently reported in perovskite based solar cells. This talk will present first the general concepts of excitonic photovoltaics, as compared to conventional Si-type solar cells, asking a question: is hybrid perovskite PV an excitonic solar cell or not? Do we need excitons dissociation at D-A interfaces or CNT charge collectors? Then I will show our recent experimental results on the fast spectroscopy of excitons, magnetic field effect on generation of correlated (e-h) pairs. Also will discuss our Hall effect results, that allows to evaluate intrinsic charge carrier transport and direct measurements of mobility in these materials performed for the first time in steady-state dc transport regime. From these measurements, we have obtained the electron-hole recombination coefficient, the carrier diffusion length and lifetime. Our main results include the intrinsic Hall carrier mobility reaching up to 60 cm2V-1s-1 in perovskite single crystals, carrier lifetimes of up to 3 ms (surprisingly too long!), and carrier diffusion lengths as long as 650 μm (huge if compared to organic and even best inorganic materials). Our results also demonstrate that photocarrier recombination in these disordered solution-processed perovskites is as weak as in the best (high-purity single crystals) of conventional direct-band inorganic semiconductors. Moreover, as we show in our experiment, carrier trapping in perovskites is also strongly suppressed, which accounts for such long carrier lifetimes and diffusion lengths, significantly longer than similar parameters in the best inorganic semiconductors, such e.g. as GaAs. All these remarkable transport properties of hybrid perovskites need to be understood from fundamental physics point of view. Looks like we need some new concepts to explain the mysterious properties of "protected" hybrid perovskites. We suggest that some of this unusual properties can be attributed to a special type of "dipole rotational polaron" formed in their lattice due to interactions of charge with methyl-ammonium organic dipoles, each of 2.3 Debye. Examples of perovskite solar cell with transparent CNT charge collectors will demonstrated the 3 D charge collection in the monolithic tandems of perovskite PV with other dissimilar materials PVs, such as OPV and inorganic PV. We describe the pioneering methods to create highly transparent CNT sheets by dry lamination from vertically alligned CVD forests of MWCNTs. Transparency can be further increased by converting CNT aerogels into locally collapsed meshs with micron scale oppenings by spraying Ag nanowires, which lowers sheet resistance to values of Rsh< 40 ohm/sq. such AgNW@CNT transparent sheets are ideal interlayers in three terminal tandems of perovskite PV with polymeric OPV and/or inorganic solar cells. We show that nanoimprinting can further improve the performance of perovskite photodetectors and optoelectronic devices

Transparent conducting oxide-free nitrogen-doped graphene/reduced hydroxylated carbon nanotube composite paper as flexible counter electrodes for dye-sensitized solar cells

NASA Astrophysics Data System (ADS)

Zhang, Jindan; Yu, Mei; Li, Songmei; Meng, Yanbing; Wu, Xueke; Liu, Jianhua

2016-12-01

Three-dimensional nitrogen-doped graphene/reduced hydroxylated carbon nanotube composite aerogel (NG/CNT-OH) with unique hierarchical porosity and mechanical stability is developed through a two-step hydrothermal reaction. With plenty of exposed active sites and efficient multidimensional transport pathways of electrons and ions, NG/CNT-OH exhibits great electrocatalytic performances for I-/I3- redox couple. The subsequent compressed NG/CNT-OH papers possess high electrical conductivity and good flexibility, thus generating high-performance flexible counter electrodes (CEs) with transparent conducting oxide free (TCO-free) for dye-sensitized solar cells (DSSCs). The flexible NG/CNT-OH electrodes show good stability and the DSSCs with the optimized NG/CNT-OH CE had higher short-circuit current density (13.62 mA cm-2) and cell efficiency (6.36%) than DSSCs using Pt CE, whereas those of the DSSCs using Pt CE were only 12.81 mA cm-2 and 5.74%, respectively. Increasing the ratio of hydroxylated carbon nanotubes (CNT-OH) to the graphene oxide (GO) in the reactant would lead to less content of doped N, but better diffusion of electrolyte in the CEs because of more complete GO etching reaction. The design strategy presents a facile and cost effective way to synthesis three-dimensional graphene/CNT composite aerogel with excellent performance, and it can be potentially used as flexible TCO-free CE in other power conversion or energy storage devices.

In situ electrodeposition of CoP nanoparticles on carbon nanomaterial doped polyphenylene sulfide flexible electrode for electrochemical hydrogen evolution

NASA Astrophysics Data System (ADS)

Wang, Tingxia; Jiang, Yimin; Zhou, Yaxin; Du, Yongling; Wang, Chunming

2018-06-01

Active and durable electrocatalyst for hydrogen evolution reaction (HER) is pivotal to generate molecular hydrogen more energy-efficient, but directly grafting electrocatalyst on electrode material by a single-step method without compromising the catalytic activity and stability remains a challenge. Herein, an intriguing electrode, reduced graphene oxide modified carbon nanotube/reduced graphene oxide/polyphenylene sulfide (RGO-CNT/RGO/PPS) film, is used to replace conventional electrodes. In situ electrodeposition is proposed to fabricate CoP on the RGO-CNT/RGO/PPS (CoP-RGO-CNT/RGO/PPS) electrode and achieves a favorably electrical contact between CoP nanoparticles and RGO-CNT/RGO/PPS electrode due to without any polymer binder. Additionally, the coupling of different electrodeposition stages with scanning electron microscope (SEM) can investigate the nanostructure evolution of CoP nanoparticles, which gives valuable insights into the optimized electrodeposition cycles. The rational integration of RGO onto CNT/RGO/PPS film is an effective approach for enhancing its intrinsic electrical conductivity and favoring the formation of a high density of dispersive CoP nanoparticles. The CoP-RGO-CNT/RGO/PPS film has shown outstanding HER electrocatalytic behaviors performed a current density of 10 mA cm-2 at a relatively low overpotential of 160 mV with a Tafel slope of 60 mV dec-1 in acidic medium, which can be mainly attributed to the synergistic effect between optimized morphology and accelerated kinetics. Additionally, this film electrocatalyst exhibits a good HER activity and stability under both neutral and basic conditions.

Multifunctional Hybrid Carbon Nanotube/Carbon Fiber Polymer Composites

NASA Technical Reports Server (NTRS)

Kang, Jin Ho; Cano, Roberto J.; Ratcliffe, James G.; Luong, Hoa; Grimsley, Brian W.; Siochi, Emilie J.

2016-01-01

For aircraft primary structures, carbon fiber reinforced polymer (CFRP) composites possess many advantages over conventional aluminum alloys due to their light weight, higher strengthand stiffness-to-weight ratio, and low life-cycle maintenance costs. However, the relatively low electrical and thermal conductivities of CFRP composites fail to provide structural safety in certain operational conditions such as lightning strikes. Despite several attempts to solve these issues with the addition of carbon nanotubes (CNT) into polymer matrices, and/or by interleaving CNT sheets between conventional carbon fiber (CF) composite layers, there are still interfacial problems that exist between CNTs (or CF) and the resin. In this study, hybrid CNT/CF polymer composites were fabricated by interleaving layers of CNT sheets with Hexcel® IM7/8852 prepreg. Resin concentrations from 1 wt% to 50 wt% were used to infuse the CNT sheets prior to composite fabrication. The interlaminar properties of the resulting hybrid composites were characterized by mode I and II fracture toughness testing (double cantilever beam and end-notched flexure test). Fractographical analysis was performed to study the effect of resin concentration. In addition, multi-directional physical properties like thermal conductivity of the orthotropic hybrid polymer composite were evaluated. Interleaving CNT sheets significantly improved the in-plane (axial and perpendicular direction of CF alignment) thermal conductivity of the hybrid composite laminates by 50 - 400%.

Sintering characteristic and microwave dielectric properties of 0.45Ca0.6Nd0.267TiO3-0.55Li0.5Nd0.5TiO3 ceramics with La2O3-B2O3-ZnO additive

NASA Astrophysics Data System (ADS)

Chen, Yawei; Zhang, Shuren; Li, Enzhu; Niu, Na; Yang, Hongcheng

2018-02-01

The La2O3-B2O3-ZnO (LBZ) glass was proved to be an effective sintering aid of the 0.45Ca0.6Nd0.26TiO3-0.55Li0.5Nd0.5TiO3 (CNT-LNT) ceramics. The influence of LBZ glass on the phase composition, low temperature sintering process, microstructure, activation energy, and dielectric properties of CNT-LNT ceramics was investigated in detail. The LBZ glass induced an obvious decrease of the CNT-LNT ceramics sintering temperature from 1350 to 1000 °C due to the liquid phase formation, which reduced the activation energy ( E a) of the CNT-LNT ceramics. In addition, the near zero temperature coefficient of resonant frequency (τƒ) value was obtained by adding moderate quantity of LBZ glass. CNT-LNT + 5 wt% LBZ (CNT-LNT + 5L) ceramics sintered at 1000°C/4 h displayed good microwave dielectric properties of: ɛ r = 101.7, Q × f = 1560 GHz ( f = 3.25 GHz) and τ ƒ = 2.3 ppm °C-1.

Effect of solvent/polymer infiltration and irradiation on microstructure and tensile properties of carbon nanotube yarns

DOE PAGES

Hiremath, Nitilaksha; Lu, Xinyi; Evora, Maria Cecilia; ...

2016-07-29

Recently carbon nanotube (CNT) yarns have been gaining importance as an approach to harvest the excellent properties of the CNTs. However, the properties of CNT yarns at this stage are well below the expected value. Investigation of the structure of CNT yarns and possible approaches to enhance the strength and modulus are reported. Scanning electron microscopy and focused ion beam imaging reveal the inherently porous structure and poor orientation, emphasizing the need to enhance packing of CNT bundles in the yarns for increased strength and modulus. Densification of CNT yarn by toluene or polystyrene increases the strength by 140 ormore » 172 % and modulus by 79 or 218 %, respectively, as compared to that of the pristine yarn. E-beam irradiation was investigated as a means to introduce crosslinking and enhanced internanotubes bonding to increase strength and modulus. However, the irradiation resulted in generation of defects and damages to the yarn contributing to reduction in strength and modulus. Raman spectroscopy studies on the irradiated samples reveal the change in bonding characteristics resulting in poor mechanical properties. As a result, denser packing of nanotubes and increased interaction without any damage is the key to improve the properties of CNT yarns.« less

Effect of solvent/polymer infiltration and irradiation on microstructure and tensile properties of carbon nanotube yarns

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hiremath, Nitilaksha; Lu, Xinyi; Evora, Maria Cecilia

Recently carbon nanotube (CNT) yarns have been gaining importance as an approach to harvest the excellent properties of the CNTs. However, the properties of CNT yarns at this stage are well below the expected value. Investigation of the structure of CNT yarns and possible approaches to enhance the strength and modulus are reported. Scanning electron microscopy and focused ion beam imaging reveal the inherently porous structure and poor orientation, emphasizing the need to enhance packing of CNT bundles in the yarns for increased strength and modulus. Densification of CNT yarn by toluene or polystyrene increases the strength by 140 ormore » 172 % and modulus by 79 or 218 %, respectively, as compared to that of the pristine yarn. E-beam irradiation was investigated as a means to introduce crosslinking and enhanced internanotubes bonding to increase strength and modulus. However, the irradiation resulted in generation of defects and damages to the yarn contributing to reduction in strength and modulus. Raman spectroscopy studies on the irradiated samples reveal the change in bonding characteristics resulting in poor mechanical properties. As a result, denser packing of nanotubes and increased interaction without any damage is the key to improve the properties of CNT yarns.« less

Calculation of the Raman intensity in graphene and carbon nanotubes

NASA Astrophysics Data System (ADS)

Moutinho, Marcus; Venezuela, Pedro

2014-03-01

Raman spectroscopy is one of the most important experimental techniques for characterization of carbon materials because it can give a lot of information about electronic and phonon structure in a non destructive way. We use a third-order quantum field model to obtain the theoretical Raman intensity for graphene and carbon nanotubes (CNT). The most important Raman peaks in graphitic materials comes from to the iLo and iTo phonon branches near to Γ and K points and, in this work, we focus our attention on some of these peaks, like the G, D and 2D bands, as a function of laser energy. The electronic and phonon dispersion used in our calculations reproduces the graphene ab initio results with GW corrections and the zone folding method is used to obtain the CNT ones. Our results show that the experimental G band Raman excitation profile for CNT can be reproduced if we use the proper electronic and phonon dispersions. We also show that the phonon dispersion may influence the shape of the graphene D band and the dispersive behavior of the 2D band for graphene and CNT. This work was supported by the Brazilian Nanocarbon Institute of Science and Technology (INCT/Nanocarbono), the Brazilian Network on Carbon Nanotube Research and the Brazilian agency CAPES

Carbon nanotube-based bioceramic grafts for electrotherapy of bone.

PubMed

Mata, D; Horovistiz, A L; Branco, I; Ferro, M; Ferreira, N M; Belmonte, M; Lopes, M A; Silva, R F; Oliveira, F J

2014-01-01

Bone complexity demands the engineering of new scaffolding solutions for its reconstructive surgery. Emerging bone grafts should offer not only mechanical support but also functional properties to explore innovative bone therapies. Following this, ceramic bone grafts of Glass/hydroxyapatite (HA) reinforced with conductive carbon nanotubes (CNTs) - CNT/Glass/HA - were prepared for bone electrotherapy purposes. Computer-aided 3D microstructural reconstructions and TEM analysis of CNT/Glass/HA composites provided details on the CNT 3D network and further correlation to their functional properties. CNTs are arranged as sub-micrometric sized ropes bridging homogenously distributed ellipsoid-shaped agglomerates. This arrangement yielded composites with a percolation threshold of pc=1.5vol.%. At 4.4vol.% of CNTs, thermal and electrical conductivities of 1.5W·m(-1)·K(-1) and 55S·m(-1), respectively, were obtained, matching relevant requisites in electrical stimulation protocols. While the former avoids bone damaging from Joule's heat generation, the latter might allow the confinement of external electrical fields through the conductive material if used for in vivo electrical stimulation. Moreover, the electrically conductive bone grafts have better mechanical properties than those of the natural cortical bone. Overall, these highly conductive materials with controlled size CNT agglomerates might accelerate bone bonding and maximize the delivery of electrical stimulation during electrotherapy practices. © 2013.

Advanced gecko-foot-mimetic dry adhesives based on carbon nanotubes.

PubMed

Hu, Shihao; Xia, Zhenhai; Dai, Liming

2013-01-21

Geckos can run freely on vertical walls and even ceilings. Recent studies have discovered that gecko's extraordinary climbing ability comes from a remarkable design of nature with nanoscale beta-keratin elastic hairs on their feet and toes, which collectively generate sufficiently strong van der Waals force to hold the animal onto an opposing surface while at the same time disengaging at will. Vertically aligned carbon nanotube (VA-CNT) arrays, resembling gecko's adhesive foot hairs with additional superior mechanical, chemical and electrical properties, have been demonstrated to be a promising candidate for advanced fibrillar dry adhesives. The VA-CNT arrays with tailor-made hierarchical structures can be patterned and/or transferred onto various flexible substrates, including responsive polymers. This, together with recent advances in nanofabrication techniques, could offer 'smart' dry adhesives for various potential applications, even where traditional adhesives cannot be used. A detailed understanding of the underlying mechanisms governing the material properties and adhesion performances is critical to the design and fabrication of gecko inspired CNT dry adhesives of practical significance. In this feature article, we present an overview of recent progress in both fundamental and applied frontiers for the development of CNT-based adhesives by summarizing important studies in this exciting field, including our own work.

Advanced gecko-foot-mimetic dry adhesives based on carbon nanotubes

NASA Astrophysics Data System (ADS)

Hu, Shihao; Xia, Zhenhai; Dai, Liming

2012-12-01

Geckos can run freely on vertical walls and even ceilings. Recent studies have discovered that gecko's extraordinary climbing ability comes from a remarkable design of nature with nanoscale beta-keratin elastic hairs on their feet and toes, which collectively generate sufficiently strong van der Waals force to hold the animal onto an opposing surface while at the same time disengaging at will. Vertically aligned carbon nanotube (VA-CNT) arrays, resembling gecko's adhesive foot hairs with additional superior mechanical, chemical and electrical properties, have been demonstrated to be a promising candidate for advanced fibrillar dry adhesives. The VA-CNT arrays with tailor-made hierarchical structures can be patterned and/or transferred onto various flexible substrates, including responsive polymers. This, together with recent advances in nanofabrication techniques, could offer `smart' dry adhesives for various potential applications, even where traditional adhesives cannot be used. A detailed understanding of the underlying mechanisms governing the material properties and adhesion performances is critical to the design and fabrication of gecko inspired CNT dry adhesives of practical significance. In this feature article, we present an overview of recent progress in both fundamental and applied frontiers for the development of CNT-based adhesives by summarizing important studies in this exciting field, including our own work.

As(III) Removal from Drinking Water by Carbon Nanotube Membranes with Magnetron-Sputtered Copper: Performance and Mechanisms.

PubMed

Luan, Hongyan; Zhang, Quan; Cheng, Guo-An; Huang, Haiou

2018-06-20

Current approaches for functionalizing carbon nanotubes (CNTs) often utilize harsh chemical conditions, and the resulting harmful wastes can cause various environmental and health concerns. In this study, magnetron sputtering technique is facilely employed to functionalize CNT membranes by depositing Cu onto premade CNT membranes without using any chemical treatment. A comparative evaluation of the substrate polymeric membrane (mixed cellulose ester (MCE)), MCE sputtered with copper (Cu/MCE), the pristine CNT membrane (CNT), and CNT membrane sputtered with Cu (Cu/CNT) shows that Cu/CNT possesses mechanically stable structures and similar membrane permeability as MCE. More importantly, Cu/CNT outperforms other membranes with high As(III) removal efficiency of above 90%, as compared to less than 10% by MCE and CNT, and 75% by Cu/MCE from water. The performance of Cu/CNT membranes for As(III) removal is also investigated as a function of ionic strength, sputtering time, co-existing ions, solution pH, and the reusability. Further characterizations of As speciation in the filtrate and on Cu/CNT reveal that arsenite removal by Cu/CNT possibly began with Cu-catalyzed oxidation of arsenite to arsenate, followed by adsorptive filtration of arsenate by the membrane. Overall, this study demonstrates that magnetron sputtering is a promising greener technology for the productions of metal-CNT composite membranes for environmental applications.

Evaluating the Environmental Impacts of a Nano-Enhanced Field Emission Display Using Life Cycle Assessment: A Screening-Level Study

EPA Science Inventory

Carbon nanotube (CNT) field emission displays (FEDs) are currently in the product development stage and are expected to be commercialized in the near future because they offer image quality and viewing angles comparable to a cathode ray tube (CRT) while using a thinner structure,...

A carbon nanotube based ammonia sensor on cotton textile

NASA Astrophysics Data System (ADS)

Han, Jin-Woo; Kim, Beomseok; Li, Jing; Meyyappan, M.

2013-05-01

A single-wall carbon nanotube (CNT) based ammonia (NH3) sensor was implemented on a cotton yarn. Two types of sensors were fabricated: Au/sensing CNT/Au and conducting/sensing/conducting all CNT structures. Two perpendicular Au wires were designed to contact CNT-cotton yarn for metal-CNT sensor, whereas nanotubes were used for the electrode as well as sensing material for the all CNT sensor. The resistance shift of the CNT network upon NH3 was monitored in a chemiresistor approach. The CNT-cotton yarn sensors exhibited uniformity and repeatability. Furthermore, the sensors displayed good mechanical robustness against bending. The present approach can be utilized for low-cost smart textile applications.

A randomized trial evaluating a parent based intervention to reduce college drinking.

PubMed

Doumas, Diana M; Turrisi, Rob; Ray, Anne E; Esp, Susan M; Curtis-Schaeffer, Amy K

2013-07-01

This study evaluated the effectiveness of a parent based intervention (PBI) in reducing drinking among first year college students (N=443). Students were assigned to one of three conditions: PBI, PBI plus booster brochures (PBI-B), and an assessment only control group (CNT). At a 4-month post-intervention follow-up, results indicated students in the PBI-B group reported significantly less drinking to intoxication and peak drinking relative to the PBI group and CNT group. No significant differences were found between the PBI group and CNT group. Results provide further support for PBIs to reduce college student drinking and suggest that a booster brochure increases the effectiveness of PBIs. Copyright © 2013 Elsevier Inc. All rights reserved.

Electrochemical activity evaluation of chemically damaged carbon nanotube with palladium nanoparticles for ethanol oxidation

NASA Astrophysics Data System (ADS)

Ahmed, Mohammad Shamsuddin; Jeon, Seungwon

2015-05-01

The carbon nanotube (CNT) has unique electrical and structural properties due to it's sp2 π-conjugative structure that leads to the higher electrocatalysis. The π-conjugative structure, that allows the CNT interact with various compounds and metal nanoparticles (NPs) through π-π electronic interaction. However, the damage of π-conjugative sidewall of CNT that can be hinder the electrocatalytic activity has found. For this study, the CNT, as base material, has been prepared through a conventional acid treatment method up to 15 h; the higher degree of sidewall damage has been observed in last 5 h during treatment period. The short and long term acid treated (denoted as CNT and CNT-COOH, respectively) CNTs have been subsequently fabricated with palladium NPs (denoted as CNT/Pd and CNT-Pd, respectively) and employed as ethanol oxidation reaction (EOR) catalysts. The CNT-Pd displays a poor electrocatalytic performance towards EOR than that of CNT/Pd due to the damage of π-conjugative sidewall. The kinetic parameters including poisoning tolerance have also been hampered by the surface damage. The CNT/Pd (∼3.3 folds) and CNT-Pd (∼1.5 folds) are express higher electrocatalytic activity and poisoning tolerance than that of Pd/C while Pd mass loading remains in the same amount.

Status of characterization techniques for carbon nanotubes and suggestions towards standards suitable for toxicological assessment

NASA Astrophysics Data System (ADS)

Schweinberger, Florian F.; Meyer-Plath, Asmus

2011-07-01

Nanotechnologies promise to contribute significantly to major technological challenges of the upcoming century. Despite profound scientific progress in the last decades, only minor advances have been made in the field of nanomaterial toxicology. The International Team in Nanosafety (TITNT) is an international and multidisciplinary group of scientists, which aims at better understanding the risks of nanomaterials. Carbon nanotubes (CNT) account for one of the most promising nanomaterials and have therefore been chosen as representative material for nanoscaled particles. They are currently investigated by the different platforms of TITNT. As a starting point, the present report summarizes a literature-based study on the physico-chemical properties of CNT, as they are closely linked with toxicological properties. A brief introduction to synthesis, purification and material properties is given. Characterization methods for CNT are discussed with respect to their reliability and the information content on chemical properties. Recommendations for a set of standard characterizations mandatory for toxicological assessment are derived.

Welding of 3D-printed carbon nanotube–polymer composites by locally induced microwave heating

PubMed Central

Sweeney, Charles B.; Lackey, Blake A.; Pospisil, Martin J.; Achee, Thomas C.; Hicks, Victoria K.; Moran, Aaron G.; Teipel, Blake R.; Saed, Mohammad A.; Green, Micah J.

2017-01-01

Additive manufacturing through material extrusion, often termed three-dimensional (3D) printing, is a burgeoning method for manufacturing thermoplastic components. However, a key obstacle facing 3D-printed plastic parts in engineering applications is the weak weld between successive filament traces, which often leads to delamination and mechanical failure. This is the chief obstacle to the use of thermoplastic additive manufacturing. We report a novel concept for welding 3D-printed thermoplastic interfaces using intense localized heating of carbon nanotubes (CNTs) by microwave irradiation. The microwave heating of the CNT-polymer composites is a function of CNT percolation, as shown through in situ infrared imaging and simulation. We apply CNT-loaded coatings to a 3D printer filament; after printing, microwave irradiation is shown to improve the weld fracture strength by 275%. These remarkable results open up entirely new design spaces for additive manufacturing and also yield new insight into the coupling between dielectric properties and radio frequency field response for nanomaterial networks. PMID:28630927

Welding of 3D-printed carbon nanotube-polymer composites by locally induced microwave heating.

PubMed

Sweeney, Charles B; Lackey, Blake A; Pospisil, Martin J; Achee, Thomas C; Hicks, Victoria K; Moran, Aaron G; Teipel, Blake R; Saed, Mohammad A; Green, Micah J

2017-06-01

Additive manufacturing through material extrusion, often termed three-dimensional (3D) printing, is a burgeoning method for manufacturing thermoplastic components. However, a key obstacle facing 3D-printed plastic parts in engineering applications is the weak weld between successive filament traces, which often leads to delamination and mechanical failure. This is the chief obstacle to the use of thermoplastic additive manufacturing. We report a novel concept for welding 3D-printed thermoplastic interfaces using intense localized heating of carbon nanotubes (CNTs) by microwave irradiation. The microwave heating of the CNT-polymer composites is a function of CNT percolation, as shown through in situ infrared imaging and simulation. We apply CNT-loaded coatings to a 3D printer filament; after printing, microwave irradiation is shown to improve the weld fracture strength by 275%. These remarkable results open up entirely new design spaces for additive manufacturing and also yield new insight into the coupling between dielectric properties and radio frequency field response for nanomaterial networks.

Piezoresistivity of Resin-Impregnated Carbon Nanotube Film at High Temperatures.

PubMed

Li, Min; Zuo, Tianyi; Wang, Shaokai; Gu, Yizhuo; Gao, Limin; Li, Yanxia; Zhang, Zuoguang

2018-06-13

This paper presents the development of a continuous carbon nanotube (CNT) composite film sensor with a strain detecting range of 0-2% for structural composites. The strain-dependent resistance responses of continuous CNT film and its resin-impregnated composite films were investigated at temperatures as high as 200 °C. The results manifest that impregnation with resin leads to a much larger gauge factor than pristine film. Both the pristine and composite films show an increase in resistivity with increasing temperature. For different composite films, the ordering of gauge factors is consistent with that of the matrix moduli. This indicates that a resin matrix with higher modulus and strong interactions between CNTs/CNT bundles and the resin matrix are beneficial for enhancing the piezoresistive effect. The CNT/PAA composite film has a gauge factor of 4.3 at 150 °C, an order of magnitude higher than the metal foil sensor. Therefore, the CNT composite films have great potential for simultaneous application for reinforcement and as strain sensor to realise a multifunctional composite. © 2018 IOP Publishing Ltd.

Multifunctional Interlayer Based on Molybdenum Diphosphide Catalyst and Carbon Nanotube Film for Lithium-Sulfur Batteries.

PubMed

Luo, Yufeng; Luo, Nannan; Kong, Weibang; Wu, Hengcai; Wang, Ke; Fan, Shoushan; Duan, Wenhui; Wang, Jiaping

2018-02-01

A multifunctional interlayer, composed of molybdenum diphosphide (MoP 2 ) nanoparticles and a carbon nanotube (CNT) film, is introduced into a lithium-sulfur (Li-S) battery system to suppress polysulfide migration. Molybdenum diphosphide acts as the catalyst and can capture polysulfides and improve the polysulfide conversion activity during the discharge/charge processes. The CNT film acts as a conductive skeleton to support the MoP 2 nanoparticles and to ensure their uniform distribution. The CNT film physically hinders polysulfide migration, acts as a current collector, and provides abundant electron pathways. The Li-S battery containing the multifunctional MoP 2 /CNT interlayer exhibits excellent electrochemical performance. It delivers a reversible specific capacity of 905 mA h g -1 over 100 cycles at 0.2 C, with a capacity decay of 0.152% per cycle. These results suggest the introduction of the multifunctional CNT/MoP 2 interlayer as an effective and practical method for producing high-performance Li-S batteries. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Filaments Production and Fused Deposition Modelling of ABS/Carbon Nanotubes Composites

PubMed Central

Fambri, Luca

2018-01-01

Composite acrylonitrile–butadiene–styrene (ABS)/carbon nanotubes (CNT) filaments at 1, 2, 4, 6 and 8 wt %, suitable for fused deposition modelling (FDM) were obtained by using a completely solvent-free process based on direct melt compounding and extrusion. The optimal CNT content in the filaments for FDM was found to be 6 wt %; for this composite, a detailed investigation of the thermal, mechanical and electrical properties was performed. Presence of CNT in ABS filaments and 3D-printed parts resulted in a significant enhancement of the tensile modulus and strength, accompanied by a reduction of the elongation at break. As documented by dynamic mechanical thermal analysis, the stiffening effect of CNTs in ABS is particularly pronounced at high temperatures. Besides, the presence of CNT in 3D-printed parts accounts for better creep and thermal dimensional stabilities of 3D-printed parts, accompanied by a reduction of the coefficient of thermal expansion). 3D-printed nanocomposite samples with 6 wt % of CNT exhibited a good electrical conductivity, even if lower than pristine composite filaments. PMID:29346291

Effect of the addition mode of carbon nanotubes for the production of chitosan hydrogel core-shell beads on adsorption of Congo red from aqueous solution.

PubMed

Chatterjee, Sudipta; Chatterjee, Tania; Lim, Seong-Rin; Woo, Seung H

2011-03-01

The adsorption performance of chitosan (CS) hydrogel beads (CSBs) generated by sodium dodecyl sulfate (SDS) gelation with multi-walled carbon nanotube (CNT) impregnation was investigated for Congo red removal as a model anionic dye. CNT-impregnated CSBs were prepared by four different strategies for dispersing CNTs: (a) in CS solution (CSBN1), (b) in SDS solution (CSBN2), (c) in CS solution containing cetyltrimethylammonium bromide (CTAB) (CSBN3), and (d) in SDS solution for gelation with CTAB-containing CS solution (CSBN4). It was observed from FE-SEM study that depending on nature of CNT dispersion, CNTs were found on the outer surface of CSBN2 and CSBN4 only. The adsorption capacity of the CSBs varied with the strategy used for CNT impregnation, and CSBN4 exhibited the highest maximum adsorption capacity (375.94 mg/g) from the Sips model. The lowest Sips maximum adsorption capacity by CSBN3 (121.07 mg/g) suggested significant blocking of binding sites of CS by CNT impregnation. Copyright © 2011 Elsevier Ltd. All rights reserved.

Filaments Production and Fused Deposition Modelling of ABS/Carbon Nanotubes Composites.

PubMed

Dul, Sithiprumnea; Fambri, Luca; Pegoretti, Alessandro

2018-01-18

Composite acrylonitrile-butadiene-styrene (ABS)/carbon nanotubes (CNT) filaments at 1, 2, 4, 6 and 8 wt %, suitable for fused deposition modelling (FDM) were obtained by using a completely solvent-free process based on direct melt compounding and extrusion. The optimal CNT content in the filaments for FDM was found to be 6 wt %; for this composite, a detailed investigation of the thermal, mechanical and electrical properties was performed. Presence of CNT in ABS filaments and 3D-printed parts resulted in a significant enhancement of the tensile modulus and strength, accompanied by a reduction of the elongation at break. As documented by dynamic mechanical thermal analysis, the stiffening effect of CNTs in ABS is particularly pronounced at high temperatures. Besides, the presence of CNT in 3D-printed parts accounts for better creep and thermal dimensional stabilities of 3D-printed parts, accompanied by a reduction of the coefficient of thermal expansion). 3D-printed nanocomposite samples with 6 wt % of CNT exhibited a good electrical conductivity, even if lower than pristine composite filaments.

Structural CNT Composites. Part I; Developing a Carbon Nanotube Filament Winder

NASA Technical Reports Server (NTRS)

Sauti, Godfrey; Kim, Jae-Woo; Wincheski, Russell A.; Antczak, Andrew; Campero, Jamie C.; Luong, Hoa H.; Shanahan, Michelle H.; Stelter, Christopher J.; Siochi, Emilie J.

2015-01-01

Carbon nanotube (CNT) based materials promise advances in the production of high strength and multifunctional components for aerospace and other applications. Specifically, in tension dominated applications, the latest CNT based filaments are yielding composite properties comparable to or exceeding composites from more established fibers such as Kevlar and carbon fiber. However, for the properties of these materials to be fully realized at the component level, suitable manufacturing processes have to be developed. These materials handle differently from conventional fibers, with different wetting characteristics and behavior under load. The limited availability of bulk forms also requires that the equipment be scaled down accordingly to tailor the process development approach to material availability. Here, the development of hardware and software for filament winding of carbon nanotube based tapes and yarns is described. This hardware features precision guidance of the CNT material and control of the winding tension over a wide range in an open architecture that allows for effective process control and troubleshooting during winding. Use of the filament winder to develop CNT based Composite Overwrapped Pressure Vessels (COPVs) shall also be discussed.

Molecular dynamics study of mechanical properties of carbon nanotube reinforced aluminum composites

NASA Astrophysics Data System (ADS)

Srivastava, Ashish Kumar; Mokhalingam, A.; Singh, Akhileshwar; Kumar, Dinesh

2016-05-01

Atomistic simulations were conducted to estimate the effect of the carbon nanotube (CNT) reinforcement on the mechanical behavior of CNT-reinforced aluminum (Al) nanocomposite. The periodic system of CNT-Al nanocomposite was built and simulated using molecular dynamics (MD) software LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator). The mechanical properties of the nanocomposite were investigated by the application of uniaxial load on one end of the representative volume element (RVE) and fixing the other end. The interactions between the atoms of Al were modeled using embedded atom method (EAM) potentials, whereas Adaptive Intermolecular Reactive Empirical Bond Order (AIREBO) potential was used for the interactions among carbon atoms and these pair potentials are coupled with the Lennard-Jones (LJ) potential. The results show that the incorporation of CNT into the Al matrix can increase the Young's modulus of the nanocomposite substantially. In the present case, i.e. for approximately 9 with % reinforcement of CNT can increase the axial Young's modulus of the Al matrix up to 77 % as compared to pure Al.

Effect of different carrier gases and their flow rates on the growth of carbon nanotubes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tewari, Aarti; Sharma, Suresh C.

2015-04-15

The present paper examines the effect of different carrier gases and their flow rates on the growth of carbon nanotubes (CNTs). A theoretical model is developed incorporating the charging rate of the carbon nanotube, kinetics of all the plasma species, and the growth rate of the CNTs because of diffusion and accretion of ions on the catalyst nanoparticle. The three different carrier gases, i.e., argon (Ar), ammonia, and nitrogen, are considered in the present investigation, and flow rates of all the three carrier gases are varied individually (keeping the flow rates of hydrocarbon and hydrogen gas constant) to investigate themore » variations in the number densities of hydrocarbon and hydrogen ions in the plasma and their consequent effects on the height and radius of CNT. Based on the results obtained, it is concluded that Ar favors the formation of CNTs with larger height and radius whereas ammonia contributes to better height of CNT but decreases the radius of CNT, and nitrogen impedes both the height and radius of CNT. The present work can serve to the better understanding of process parameters during growth of CNTs by a plasma enhanced chemical vapor deposition process.« less

Effect of B, N, Ge, Sn, K doping on electronic-transport properties of (5, 0) zigzag carbon nanotube

NASA Astrophysics Data System (ADS)

Kamalian, Monir; Seyed Jalili, Yousef; Abbasi, Afshin

2018-04-01

In this paper the effect of impurity on the electronic properties and quantum conductance of zigzag (5, 0) carbon nanotube have been studied by using the Density Functional Theory (DFT) combined with Non-Equilibrium Green’s Function (NEGF) formalism with TranSIESTA software. The effect of Boron (B), Nitrogen (N), Germanium (Ge), Tin (Sn) and Potassium (K) impurities on the CNT conduction behavior and physical characteristics, like density of states (DOS), band structure, transmission coefficients and quantum conductance was considered and discussed simultaneously. The current‑voltage (I‑V) curves of all the proposed models were studied for comparative study under low-bias conditions. The distinct changes in conductance reported as the positions, number and type of dopants was varied in central region of the CNT between two electrodes at different bias voltages. This suggested conductance enhancement mechanism for the charge transport in the doped CNT at different positions is important for the design of CNT based nanoelectronic devices. The results show that Germanium, Tin and Potassium dopant atoms has increased the conductance of the model manifold than other doping atoms furthermore 10 Boron and 10 Nitrogen dopant atoms showed the amazing property of Negative Differential Resistance (NDR).

Sonication-Induced Modification of Carbon Nanotubes: Effect on the Rheological and Thermo-Oxidative Behaviour of Polymer-Based Nanocomposites.

PubMed

Arrigo, Rossella; Teresi, Rosalia; Gambarotti, Cristian; Parisi, Filippo; Lazzara, Giuseppe; Dintcheva, Nadka Tzankova

2018-03-05

The aim of this work is the investigation of the effect of ultrasound treatment on the structural characteristics of carbon nanotubes (CNTs) and the consequent influence that the shortening induced by sonication exerts on the morphology, rheological behaviour and thermo-oxidative resistance of ultra-high molecular weight polyethylene (UHMWPE)-based nanocomposites. First, CNTs have been subjected to sonication for different time intervals and the performed spectroscopic and morphological analyses reveal that a dramatic decrease of the CNT's original length occurs with increased sonication time. The reduction of the initial length of CNTs strongly affects the nanocomposite rheological behaviour, which progressively changes from solid-like to liquid-like as the CNT sonication time increases. The study of the thermo-oxidative behaviour of the investigated nanocomposites reveals that the CNT sonication has a detrimental effect on the thermo-oxidative stability of nanocomposites, especially for long exposure times. The worsening of the thermo-oxidative resistance of sonicated CNT-containing nanocomposites could be attributed to the lower thermal conductivity of low-aspect-ratio CNTs, which causes the increase of the local temperature at the polymer/nanofillers interphase, with the consequent acceleration of the degradative phenomena.

Controlling drug efficiency by encapsulation into carbon nanotubes: A theoretical study of the antitumor Cisplatin and the anti-HIV TIBO molecules

NASA Astrophysics Data System (ADS)

Bessrour, R.; Belmiloud, Y.; Hosni, Z.; Tangour, B.

2012-06-01

From the beginning of last century, Paul Ehrlich, a specialist in the immune system and the Nobel Prize (1908) had raised the possibility of "magic bullets" can directly address, in an organism, drugs in a particular area of the body, sparing all other parts of side effects. Carbon nanotubes (CNTs) have particular property to cross cell membranes easily. In an effort to optimize the use of CNT as drug nanocarriers, we divided our study into two parts. In the first, our concern was to find the minimum diameter of a single wall CNT can encapsulate an anticancer drug that iscisplatin without altering its geometry in order conserve its therapeutic power. Behavior of one and two Cisplatin(Cp) molecules confined in capped and opened single-walled carbon nanotubes (CNTs) is studied by means of ab-initio calculations. Single molecule binding energies clearly exhibit encapsulation dependence on tube diameters that range from 6.26 Å to 12.04 Å. A weak stabilization energy of the Cp@(11,0) equal to -70 kcal.mol-1 has been obtained corresponding to a CNT's diameter of 8.5Å. We noticed that Cisplatin molecule changes shape when encapsulated into CNTs' whose diameters are less than 7.6 Å. In the presence of a second Cisplatin molecule in the (10,0) CNT, preferred position stays parallel to CNT's axis leading to a linear density of roughly 1588 molecules/μm of CNT's length corresponding to a linear density of 7.9 10-19 g/μm. The 195Pt chemical shift tensors are calculated using GIAO method. NMR calculations reveal that Platinum chemical shift is sensitive to CNT's diameter and is linearly correlated to confinement energy. 195Pt chemical shift measurement may be a direct method to access to the diameter of the encapsulating CNT's and to control the amount of drug molecule transported by this CNT. In the second part, the opposite has been sought is to say how the use of nanotubes with different diameters can control the change in a geometry of an anti-HIV drug that is TIBO molecule to bypass the mutation of the virus which wiped out its therapeutic effect. This work deals with the butterfly conformation control of the anti-HIV TIBO molecule confined into carbon nanotubes (CNT). This theoretical study concerns the variation of some pertinent conformation descriptors such as butterfly angle, wingspan, volume, dipole moment, solvation energy and confinement energy versus carbon nanotube diameters. Obtained results show that it is possible to describe the configurations of actual drugs as 8-Cl or 9-Cl TIBO as the parent molecule TIBO encapsulated in an adequate CNT. Our approach indicates that drug confinement inside CNTs may be a promising way to use a same drug in order to fellow HIV virus mutations.

Controlled growth of well-aligned carbon nanotubes with large diameters

NASA Astrophysics Data System (ADS)

Wang, Xianbao; Liu, Yunqi; Zhu, Daoben

2001-06-01

Well-aligned carbon nanotubes (CNTs) with large diameters (25-200 nm) were synthesized by pyrolysis of iron(II) phthalocyanine. The outer diameter up to 218.5 nm and the length of the well-aligned CNTs can be systematically controlled by varying the growth time. A tube-in-tube nano-structure with large and small diameters of 176 and 16.7 nm, respectively, was found. The grain sizes of the iron catalyst play an important role in controlling the CNT diameters. These results are of great importance to design new aligned CNT-based electron field emitters in the potential application of panel displays.

Texture design for microwave dielectric (Ca0.7Nd0.3)0.87TiO3 ceramics through reactive-templated grain growth

PubMed Central

Tani, Toshihiko; Takeuchi, Tsuguto

2015-01-01

Plate-like Ca3Ti2O7 (CT) and Nd2Ti2O7 (NT) particles were synthesized in molten salts and used as reactive templates for the preparation of highly textured (Ca0.7Nd0.3)0.87TiO3 bulk ceramics (CNT) with preferred pseudocubic 〈100〉 and 〈110〉 orientations, respectively. During flux growth CT and NT particles developed facets parallel to the pseudocubic {100} and {110} planes, respectively, in a perovskite unit cell, since those planes correspond to the interlayers of the layered perovskite-type crystal structures. Complementary reactants for the CNT stoichiometry were wet-mixed with the reactive templates and the slurries were tape-cast. Then stacked tapes were heat-treated for dense single-phase CNT ceramics with a distorted and A-site deficient regular perovskite-type structure. The CNT ceramics prepared with CT and NT reactive templates exhibited strong pseudocubic 100- and 110-family x-ray diffraction peaks, respectively, with other peaks drastically suppressed when non-perovskite sources were used as complementary reactants. The textured ceramics possess unique microstructures; as either parallel or obliquely stacked block structures with a pseudocubic {100} plane faceted. The pseudocubic {100}-and {110}-textured CNT ceramics exhibited ∼10 and ∼20% higher products of the dielectric quality factor and frequency, Q · f, respectively, than conventional ceramic sintered at the same temperature. When Q · f is compared based on the same grain size, the {100}-textured CNT exhibited 27% higher values than non-textured while relative permittivity and temperature coefficient of resonant frequency were of similar values. Simple geometrical relationships between electric field and penetrated pseudocubic {hk0}-type grain boundaries must lead to the reduced scattering and dielectric loss. PMID:27877809

Nucleation in food colloids

NASA Astrophysics Data System (ADS)

Povey, Malcolm J. W.

2016-12-01

Nucleation in food colloids has been studied in detail using ultrasound spectroscopy. Our data show that classical nucleation theory (CNT) remains a sound basis from which to understand nucleation in food colloids and analogous model systems using n-alkanes. Various interpretations and modifications of CNT are discussed with regard to their relevance to food colloids. Much of the evidence presented is based on the ultrasound velocity spectrometry measurements which has many advantages for the study of nucleating systems compared to light scattering and NMR due to its sensitivity at low solid contents and its ability to measure true solid contents in the nucleation and early crystal growth stages. Ultrasound attenuation spectroscopy also responds to critical fluctuations in the induction region. We show, however, that a periodic pressure fluctuation such as a quasi-continuous (as opposed to a pulse comprising only a few pressure cycles) ultrasound field can alter the nucleation process, even at very low acoustic intensity. Thus care must be taken when using ultrasound techniques that the measurements do not alter the studied processes. Quasi-continuous ultrasound fields may enhance or suppress nucleation and the criteria to determine such effects are derived. The conclusions of this paper are relevant to colloidal systems in foods, pharmaceuticals, agro-chemicals, cosmetics, and personal products.

Divergent effect of electric fields on the mechanical property of water-filled carbon nanotubes with an application as a nanoscale trigger

NASA Astrophysics Data System (ADS)

Ye, Hongfei; Zheng, Yonggang; Zhou, Lili; Zhao, Junfei; Zhang, Hongwu; Chen, Zhen

2018-01-01

Polar water molecules exhibit extraordinary phenomena under nanoscale confinement. Through the application of an electric field, a water-filled carbon nanotube (CNT) that has been successfully fabricated in the laboratory is expected to have distinct responses to the external electricity. Here, we examine the effect of electric field direction on the mechanical property of water-filled CNTs. It is observed that a longitudinal electric field enhances, but the transverse electric field reduces the elastic modulus and critical buckling stress of water-filled CNTs. The divergent effect of the electric field is attributed to the competition between the axial and circumferential pressures induced by polar water molecules. Furthermore, it is notable that the transverse electric field could result in an internal pressure with elliptical distribution, which is an effective and convenient approach to apply nonuniform pressure on nanochannels. Based on pre-strained water-filled CNTs, we designed a nanoscale trigger with an evident and rapid height change initiated by switching the direction of the electric field. The reported finding provides a foundation for an electricity-controlled property of nanochannels filled with polar molecules and provides an insight into the design of nanoscale functional devices.

Divergent effect of electric fields on the mechanical property of water-filled carbon nanotubes with an application as a nanoscale trigger.

PubMed

Ye, Hongfei; Zheng, Yonggang; Zhou, Lili; Zhao, Junfei; Zhang, Hongwu; Chen, Zhen

2017-12-11

Polar water molecules exhibit extraordinary phenomena under nanoscale confinement. Through the application of an electric field, a water-filled carbon nanotube (CNT) that has been successfully fabricated in the laboratory is expected to have distinct responses to the external electricity. Here, we examine the effect of electric field direction on the mechanical property of water-filled CNTs. It is observed that a longitudinal electric field enhances, but the transverse electric field reduces the elastic modulus and critical buckling stress of water-filled CNTs. The divergent effect of the electric field is attributed to the competition between the axial and circumferential pressures induced by polar water molecules. Furthermore, it is notable that the transverse electric field could result in an internal pressure with elliptical distribution, which is an effective and convenient approach to apply nonuniform pressure on nanochannels. Based on pre-strained water-filled CNTs, we designed a nanoscale trigger with an evident and rapid height change initiated by switching the direction of the electric field. The reported finding provides a foundation for an electricity-controlled property of nanochannels filled with polar molecules and provides an insight into the design of nanoscale functional devices.

Carbon nanotubes functionalized with fibroblast growth factor accelerate proliferation of bone marrow-derived stromal cells and bone formation

NASA Astrophysics Data System (ADS)

Hirata, Eri; Ménard-Moyon, Cécilia; Venturelli, Enrica; Takita, Hiroko; Watari, Fumio; Bianco, Alberto; Yokoyama, Atsuro

2013-11-01

Multi-walled carbon nanotubes (MWCNTs) were functionalized with fibroblast growth factor (FGF) and the advantages of their use as scaffolds for bone augmentation were evaluated in vitro and in vivo. The activity of FGF was assessed by measuring the effect on the proliferation of rat bone marrow stromal cells (RBMSCs). The presence of FGF enhanced the proliferation of RBMSCs and the FGF covalently conjugated to the nanotubes (FGF-CNT) showed the same effect as FGF alone. In addition, FGF-CNT coated sponges were implanted between the parietal bone and the periosteum of rats and the formation of new bone was investigated. At day 14 after implantation, a larger amount of newly formed bone was clearly observed in most pores of FGF-CNT coated sponges. These findings indicated that MWCNTs accelerated new bone formation in response to FGF, as well as the integration of particles into new bone during its formation. Scaffolds coated with FGF-CNT could be considered as promising novel substituting materials for bone regeneration in future tissue engineering applications.

Polysulfide Anchoring Mechanism Revealed by Atomic Layer Deposition of V2O5 and Sulfur-Filled Carbon Nanotubes for Lithium-Sulfur Batteries.

PubMed

Carter, Rachel; Oakes, Landon; Muralidharan, Nitin; Cohn, Adam P; Douglas, Anna; Pint, Cary L

2017-03-01

Despite the promise of surface engineering to address the challenge of polysulfide shuttling in sulfur-carbon composite cathodes, melt infiltration techniques limit mechanistic studies correlating engineered surfaces and polysulfide anchoring. Here, we present a controlled experimental demonstration of polysulfide anchoring using vapor phase isothermal processing to fill the interior of carbon nanotubes (CNTs) after assembly into binder-free electrodes and atomic layer deposition (ALD) coating of polar V 2 O 5 anchoring layers on the CNT surfaces. The ultrathin submonolayer V 2 O 5 coating on the CNT exterior surface balances the adverse effect of polysulfide shuttling with the necessity for high sulfur utilization due to binding sites near the conductive CNT surface. The sulfur loaded into the CNT interior provides a spatially separated control volume enabling high sulfur loading with direct sulfur-CNT electrical contact for efficient sulfur conversion. By controlling ALD coating thickness, high initial discharge capacity of 1209 mAh/g S at 0.1 C and exceptional cycling at 0.2 C with 87% capacity retention after 100 cycles and 73% at 450 cycles is achieved and correlated to an optimal V 2 O 5 anchoring layer thickness. This provides experimental evidence that surface engineering approaches can be effective to overcome polysulfide shuttling by controlled design of molecular-scale building blocks for efficient binder free lithium sulfur battery cathodes.

Effect of surfactants and manufacturing methods on the electrical and thermal conductivity of carbon nanotube/silicone composites.

PubMed

Vilčáková, Jarmila; Moučka, Robert; Svoboda, Petr; Ilčíková, Markéta; Kazantseva, Natalia; Hřibová, Martina; Mičušík, Matej; Omastová, Mária

2012-11-05

The effect of ionic surfactants and manufacturing methods on the separation and distribution of multi-wall carbon nanotubes (CNTs) in a silicone matrix are investigated. The CNTs are dispersed in an aqueous solution of the anionic surfactant dodecylbenzene sulfonic acid (DBSA), the cationic surfactant cetyltrimethylammonium bromide (CTAB), and in a DBSA/CTAB surfactant mixture. Four types of CNT-based composites of various concentrations from 0 to 6 vol.% are prepared by simple mechanical mixing and sonication. The morphology, electrical and thermal conductivity of the CNT-based composites are analyzed. The incorporation of both neat and modified CNTs leads to an increase in electrical and thermal conductivity. The dependence of DC conductivity versus CNT concentration shows percolation behaviour with a percolation threshold of about 2 vol.% in composites with neat CNT. The modification of CNTs by DBSA increases the percolation threshold to 4 vol.% due to the isolation/separation of individual CNTs. This, in turn, results in a significant decrease in the complex permittivity of CNT–DBSA-based composites. In contrast to the percolation behaviour of DC conductivity, the concentration dependence of thermal conductivity exhibits a linear dependence, the thermal conductivity of composites with modified CNTs being lower than that of composites with neat CNTs. All these results provide evidence that the modification of CNTs by DBSA followed by sonication allows one to produce composites with high homogeneity.

Continuous Carbon Nanotube-Ultrathin Graphite Hybrid Foams for Increased Thermal Conductivity and Suppressed Subcooling in Composite Phase Change Materials.

PubMed

Kholmanov, Iskandar; Kim, Jaehyun; Ou, Eric; Ruoff, Rodney S; Shi, Li

2015-12-22

Continuous ultrathin graphite foams (UGFs) have been actively researched recently to obtain composite materials with increased thermal conductivities. However, the large pore size of these graphitic foams has resulted in large thermal resistance values for heat conduction from inside the pore to the high thermal conductivity graphitic struts. Here, we demonstrate that the effective thermal conductivity of these UGF composites can be increased further by growing long CNT networks directly from the graphite struts of UGFs into the pore space. When erythritol, a phase change material for thermal energy storage, is used to fill the pores of UGF-CNT hybrids, the thermal conductivity of the UGF-CNT/erythritol composite was found to increase by as much as a factor of 1.8 compared to that of a UGF/erythritol composite, whereas breaking the UGF-CNT bonding in the hybrid composite resulted in a drop in the effective room-temperature thermal conductivity from about 4.1 ± 0.3 W m(-1) K(-1) to about 2.9 ± 0.2 W m(-1) K(-1) for the same UGF and CNT loadings of about 1.8 and 0.8 wt %, respectively. Moreover, we discovered that the hybrid structure strongly suppresses subcooling of erythritol due to the heterogeneous nucleation of erythritol at interfaces with the graphitic structures.

Influence of imperfect end boundary condition on the nonlocal dynamics of CNTs

NASA Astrophysics Data System (ADS)

Fathi, Reza; Lotfan, Saeed; Sadeghi, Morteza H.

2017-03-01

Imperfections that unavoidably occur during the fabrication process of carbon nanotubes (CNTs) have a significant influence on the vibration behavior of CNTs. Among these imperfections, the boundary condition defect is studied in this investigation based on the nonlocal elasticity theory. To this end, a mathematical model of the non-ideal end condition in a cantilever CNT is developed by a strongly non-linear spring to study its effect on the vibration behavior. The weak form equation of motion is derived via Hamilton's principle and solved based on Rayleigh-Ritz approach. Once the frequency response function (FRF) of the CNT is simulated, it is found that the defect parameter injects noise to the FRF in the range of lower frequencies and as a result the small scale effect on the FRF remains undisturbed in high frequency ranges. Besides, in this work a process is introduced to estimate the nonlocal and defect parameters for establishing the mathematical model of the CNT based on FRF, which can be competitive because of its lower instrumentation and data analysis costs. The estimation process relies on the resonance frequencies and the magnitude of noise in the frequency response function of the CNT. The results show that the constructed dynamic response of the system based on estimated parameters is in good agreement with the original response of the CNT.

Carbon nanotube collimator fabrication and application

DOEpatents

Chow, Lee; Chai, Guangyu; Schenkel, Thomas

2010-07-06

Apparatus, methods, systems and devices for fabricating individual CNT collimators. Micron size fiber coated CNT samples are synthesized with chemical vapor deposition method and then the individual CNT collimators are fabricated with focused ion beam technique. Unfocused electron beams are successfully propagated through the CNT collimators. The CNT nano-collimators are used for applications including single ion implantation and in high-energy physics, and allow rapid, reliable testing of the transmission of CNT arrays for transport of molecules.

Absorptive carbon nanotube electrodes: Consequences of optical interference loss in thin film solar cells

NASA Astrophysics Data System (ADS)

Tait, Jeffrey G.; de Volder, Michaël F. L.; Cheyns, David; Heremans, Paul; Rand, Barry P.

2015-04-01

A current bottleneck in the thin film photovoltaic field is the fabrication of low cost electrodes. We demonstrate ultrasonically spray coated multiwalled carbon nanotube (CNT) layers as opaque and absorptive metal-free electrodes deposited at low temperatures and free of post-deposition treatment. The electrodes show sheet resistance as low as 3.4 Ω □-1, comparable to evaporated metallic contacts deposited in vacuum. Organic photovoltaic devices were optically simulated, showing comparable photocurrent generation between reflective metal and absorptive CNT electrodes for photoactive layer thickness larger than 600 nm when using archetypal poly(3-hexylthiophene) (P3HT) : (6,6)-phenyl C61-butyric acid methyl ester (PCBM) cells. Fabricated devices clearly show that the absorptive CNT electrodes display comparable performance to solution processed and spray coated Ag nanoparticle devices. Additionally, other candidate absorber materials for thin film photovoltaics were simulated with absorptive contacts, elucidating device design in the absence of optical interference and reflection.A current bottleneck in the thin film photovoltaic field is the fabrication of low cost electrodes. We demonstrate ultrasonically spray coated multiwalled carbon nanotube (CNT) layers as opaque and absorptive metal-free electrodes deposited at low temperatures and free of post-deposition treatment. The electrodes show sheet resistance as low as 3.4 Ω □-1, comparable to evaporated metallic contacts deposited in vacuum. Organic photovoltaic devices were optically simulated, showing comparable photocurrent generation between reflective metal and absorptive CNT electrodes for photoactive layer thickness larger than 600 nm when using archetypal poly(3-hexylthiophene) (P3HT) : (6,6)-phenyl C61-butyric acid methyl ester (PCBM) cells. Fabricated devices clearly show that the absorptive CNT electrodes display comparable performance to solution processed and spray coated Ag nanoparticle devices. Additionally, other candidate absorber materials for thin film photovoltaics were simulated with absorptive contacts, elucidating device design in the absence of optical interference and reflection. Electronic supplementary information (ESI) available: An animation of the MWCNT spray coating process, and five figures, including: a photograph of completed devices with MWCNT electrodes, performance metrics for devices with photoactive layer thickness up to 3000 nm, contour plots of simulated devices used to build Fig. 5, simulation data for perovskite devices, and a contour plot of the simplified equation of photoactive layer thickness required to attain a specified photocurrent ratio (x-axis) and absorption coefficient (y-axis). See DOI: 10.1039/c5nr01119a

Detection of airborne carbon nanotubes based on the reactivity of the embedded catalyst.

PubMed

Neubauer, N; Kasper, G

2015-01-01

A previously described method for detecting catalyst particles in workplace air((1,2)) was applied to airborne carbon nanotubes (CNT). It infers the CNT concentration indirectly from the catalytic activity of metallic nanoparticles embedded as part of the CNT production process. Essentially, one samples airborne CNT onto a filter enclosed in a tiny chemical reactor and then initiates a gas-phase catalytic reaction on the sample. The change in concentration of one of the reactants is then determined by an IR sensor as measure of activity. The method requires a one-point calibration with a CNT sample of known mass. The suitability of the method was tested with nickel containing (25 or 38% by weight), well-characterized multi-walled CNT aerosols generated freshly in the lab for each experiment. Two chemical reactions were investigated, of which the oxidation of CO to CO2 at 470°C was found to be more effective, because nearly 100% of the nickel was exposed at that temperature by burning off the carbon, giving a linear relationship between CO conversion and nickel mass. Based on the investigated aerosols, a lower detection limit of 1 μg of sampled nickel was estimated. This translates into sampling times ranging from minutes to about one working day, depending on airborne CNT concentration and catalyst content, as well as sampling flow rate. The time for the subsequent chemical analysis is on the order of minutes, regardless of the time required to accumulate the sample and can be done on site.

Molecular dynamics study of the behavior of nitromethanes enclosed inside carbon nanotube containers.

PubMed

Bae, Se Won; Cho, Soo Gyeong

2016-07-01

We utilized molecular dynamics (MD) to investigate the behavior of nitromethane molecules (NMs) enclosed inside carbon nanotube (CNT) containers sealed with buckybowl caps. Two different sizes of CNT containers, i.e., (10,10) and (20,20), were employed to contain the energetic NMs. After loading the NMs into these containers, MD simulations were carried out at different loading densities. The loading density was changed from 0.4 to 2.0 g/cc. At low loading densities, NMs preferentially resided near the surface of the CNT wall (orienting themselves in the cylindrical direction) and near the buckybowl caps (orienting themselves in the principal-axis direction). This behavior suggests the buckybowl caps and the CNT wall have attractive interactions with the NMs. The distribution of the NMs inside the containers did not change upon increasing the temperature from ambient to 100 °C. However, the positional preference of the NMs found at ambient temperature to 100 °C was not the same as that observed at 1000 °C due to the increased thermal motions of the NMs. The size of the CNT container had a significant effect on the fluidity of the NMs. From 25 to 100 °C, the NMs inside the (10,10) CNT container were only mobile at low loading densities. On the other hand, in the (20,20) CNT container, the NMs showed good mobility up to a loading density of 1.6 g/cc. Graphical Abstract Attractive interactions between the nitromethanes and the buckybowl caps as well as the carbon nanotube wall.

Pull-out simulations of a capped carbon nanotube in carbon nanotube-reinforced nanocomposites

NASA Astrophysics Data System (ADS)

Li, Y.; Liu, S.; Hu, N.; Han, X.; Zhou, L.; Ning, H.; Wu, L.; Alamusi, Yamamoto, G.; Chang, C.; Hashida, T.; Atobe, S.; Fukunaga, H.

2013-04-01

Systematic atomic simulations based on molecular mechanics were conducted to investigate the pull-out behavior of a capped carbon nanotube (CNT) in CNT-reinforced nanocomposites. Two common cases were studied: the pull-out of a complete CNT from a polymer matrix in a CNT/polymer nanocomposite and the pull-out of the broken outer walls of a CNT from the intact inner walls (i.e., the sword-in-sheath mode) in a CNT/alumina nanocomposite. By analyzing the obtained relationship between the energy increment (i.e., the difference in the potential energy between two consecutive pull-out steps) and the pull-out displacement, a set of simple empirical formulas based on the nanotube diameter was developed to predict the corresponding pull-out force. The predictions from these formulas are quite consistent with the experimental results. Moreover, the much higher pull-out force for a capped CNT than that of the corresponding open-ended CNT implies a significant contribution from the CNT cap to the interfacial properties of the CNT-reinforced nanocomposites. This finding provides a valuable insight for designing nanocomposites with desirable mechanical properties.

Electronic Properties of Carbon Nanotubes and Junctions

NASA Technical Reports Server (NTRS)

Anantram, M. P.; Han, Jie; Yang, Liu; Govindan, T. R.; Jaffe, R.; Saini, Subhash (Technical Monitor)

1998-01-01

Metallic and semiconducting Single Wall Carbon Nanotubes (CNT) have recently been characterized using scanning tunneling microscopy (STM) and the manipulation of individual CNT has been demonstrated. These developments make the prospect of using CNT as molecular wires and possibly as electronic devices an even more interesting one. We have been modeling various electronic properties such as the density of states and the transmission coefficient of CNT wires and junctions. These studies involve first calculating the stability of junctions using molecular dynamics simulations and then calculating the electronic properties using a pi-electron tight binding Hamiltonian. We have developed the expertise to calculate the electronic properties of both finite-sized CNT and CNT systems with semi-infinite boundary conditions. In this poster, we will present an overview of some of our results. The electronic application of CNT that is most promising at this time is their use as molecular wires. The conductance can however be greatly reduced because of reflection due to defects and contacts. We have modeled the transmission through CNT in the presence of two types of defects: weak uniform disorder and strong isolated scatterers. We find that the conductance is affected in significantly different manners due to these defects Junctions of CNT have also been imaged using STM. This makes it essential to derive rules for the formation of junctions between tubes of different chirality, study their relative energies and electronic properties. We have generalized the rules for connecting two different CNT and have calculated the transmission and density of states through CNT junctions. Metallic and semiconducting CNT can be joined to form a stable junction and their current versus voltage characteristics are asymmetric. CNT are deformed by the application of external forces including interactions with a substrate or other CNT. In many experiments, these deformation are expected to occur naturally. We will present some preliminary results of our calculations of the modification of CNT electronic properties as a result of deformations.

Vibrational energy transfer between carbon nanotubes and nonaqueous solvents: a molecular dynamics study.

PubMed

Nelson, Tammie R; Chaban, Vitaly V; Prezhdo, Victor V; Prezhdo, Oleg V

2011-05-12

We report molecular dynamics (MD) simulation of energy exchange between single-walled carbon nanotubes (CNTs) and two aprotic solvents, acetonitrile and cyclohexane. Following our earlier study of hydrated CNTs, we find that the time scales and molecular mechanisms of the energy transfer are largely independent of the nature of the surrounding medium, and therefore, should hold for other media including polymer matrices and DNA. The vibrational energy exchange between CNT and solvents exhibits two time-scales. Over half of the energy is transferred in less than one picosecond, indicating that the dominant exchange mechanism is inertial relaxation. It occurs by collisions of solvent molecules with CNT walls, facilitated by the short-range Lennard-Jones interaction. Additional several picoseconds are required for the remainder of the vibrational energy exchange, corresponding to the diffusive relaxation mechanism and involving collective molecular motions. The faster stage of the CNT-solvent energy exchange occurs on the same time-scale, and therefore, competes with the vibrational energy relaxation inside CNTs. The energy exchange time-scales are significantly influenced by the arrangement of solvent molecules inside CNTs. Generally, the effects of confinement on the dynamics can be rationalized by analysis of the solvent structure. For the same CNT diameter, the extent of the confinement effect strongly depends on the size of the solvent molecules. Icelike properties in water seen in small CNTs disappear in CNTs with intermediate diameters. In acetonitrile and cyclohexane, medium size CNTs still show strong confinement effects. Rotational motions of acetonitrile molecules are inhibited, and the cyclohexane density is dramatically decreased. The disbalance between the local temperatures of the inside and outside regions of the solvent equilibrates through a tube-mediated interaction, rather than by a direct coupling between the two solvent subsystems. In all cases, the CNT-solvent energy transfer is mediated by slow motions in the frequency range of CNT radial breathing modes.

Shape matters: Cr(VI) removal using iron nanoparticle impregnated 1-D vs 2-D carbon nanohybrids prepared by ultrasonic spray pyrolysis

NASA Astrophysics Data System (ADS)

Masud, Arvid; Cui, Yanbin; Atkinson, John D.; Aich, Nirupam

2018-03-01

Iron nanoparticles (Fe NPs) are used for treating water contaminated with metals or organic compounds. One-dimensional (1-D) carbon nanotubes (CNTs) and two-dimensional (2-D) graphenes act as useful nanocarbon (NC) supports for Fe NPs by resisting aggregation and enhancing adsorption and redox activity. However, no study showed how shape difference between tubular CNT and planar graphene structures dictates the physicochemical properties and pollutant removal potential of their iron-based nanohybrids. In this work, ultrasonic spray pyrolysis was used to continuously prepare Fe-CNT and Fe-rGO nanohybrids. Both NC shape and Fe/NC ratio influenced Fe NP size, loading, and oxidation states. High Fe content (precursor Fe/NC mass ratio = 2) resulted Fe NPs with diameters of 30.97 ± 7.00 and 24.11 ± 4.42 nm for Fe-CNT and Fe-rGO, respectively; however, low Fe content (Fe/NC = 0.2) provided more uniformly dispersed Fe NPs of 15.65 ± 3.06 and 9.67 ± 1.49 nm, respectively, while unsupported Fe NPs were 285.71 ± 132.42 nm. The USP-derived nanohybrids, for the first time, were used for removal of pollutant, i.e., chromium (Cr(VI)) from aqueous media. Both CNT and rGO provided synergistic effects to significantly enhance Fe NPs' ability to remove Cr(VI); the effect was more pronounced in Fe-rGO than Fe-CNT and also for low Fe content in both cases. Fe-rGO with low Fe/NC ratio and smallest Fe NPs provided the highest Cr(VI) removal capacity (25 mg/g), which was a multifold improvement over bare Fe NPs and other synthesized nanohybrids (range 7-14 mg/g). Overall, 2-D rGO improved contaminant removal capacity of the nanohybrids more than 1-D CNT indicating towards shape effect of NC supports. [Figure not available: see fulltext.

Aspects of the Fracture Toughness of Carbon Nanotube Modified Epoxy Polymer Composites

NASA Astrophysics Data System (ADS)

Mirjalili, Vahid

Epoxy resins used in fibre reinforced composites exhibit a brittle fracture behaviour, because they show no sign of damage prior to a catastrophic failure. Rubbery materials and micro-particles have been added to epoxy resins to improve their fracture toughness, which reduces strength and elastic properties. In this research, carbon nanotubes (CNTs) are investigated as a potential toughening agent for epoxy resins and carbon fibre reinforced composites, which can also enhance strength and elastic properties. More specifically, the toughening mechanisms of CNTs are investigated theoretically and experimentally. The effect of aligned and randomly oriented carbon nanotubes (CNTs) on the fracture toughness of polymers was modelled using Elastic Plastic Fracture Mechanics. Toughening from CNT pull-out and rupture were considered, depending on the CNTs critical length. The model was used to identify the effect of CNTs geometrical and mechanical properties on the fracture toughness of CNT-modified epoxies. The modelling results showed that a uniform dispersion and alignment of a high volume fraction of CNTs normal to the crack growth plane would lead to the maximum fracture toughness enhancement. To achieve a uniform dispersion, the effect of processing on the dispersion of single walled and multi walled CNTs in epoxy resins was investigated. An instrumented optical microscope with a hot stage was used to quantify the evolution of the CNT dispersion during cure. The results showed that the reduction of the resin viscosity at temperatures greater than 100 °C caused an irreversible re-agglomeration of the CNTs in the matrix. The dispersion quality was then directly correlated to the fracture toughness of the modified resin. It was shown that the fine tuning of the ratio of epoxy resin, curing agent and CNT content was paramount to the improvement of the base resin fracture toughness. For the epoxy resin (MY0510 from Hexcel), an improvement of 38% was achieved with 0.3 wt.% of Single Walled CNT (SWNT). Finally, the CNT-modified epoxy resin was used to manufacture carbon fibre laminates by resin film infusion and prepreg technologies. The Mode I and Mode II delamination properties of the CNT-modified composite increased by 140% and 127%, respectively. In contrast, this improvement was not observed for the base CNT-modified polymers, used to manufacture the composite laminates. A qualitative analysis of the fractured surface using a Scanning Electron Microscope revealed a good dispersion in the composites samples, confirming the importance of processing to harness the full potential of carbon nanotubes for toughening polymer composites.

Real-Time Imaging of Self-Organization and Mechanical Competition in Carbon Nanotube Forest Growth.

PubMed

Balakrishnan, Viswanath; Bedewy, Mostafa; Meshot, Eric R; Pattinson, Sebastian W; Polsen, Erik S; Laye, Fabrice; Zakharov, Dmitri N; Stach, Eric A; Hart, A John

2016-12-27

The properties of carbon nanotube (CNT) networks and analogous materials comprising filamentary nanostructures are governed by the intrinsic filament properties and their hierarchical organization and interconnection. As a result, direct knowledge of the collective dynamics of CNT synthesis and self-organization is essential to engineering improved CNT materials for applications such as membranes and thermal interfaces. Here, we use real-time environmental transmission electron microscopy (E-TEM) to observe nucleation and self-organization of CNTs into vertically aligned forests. Upon introduction of the carbon source, we observe a large scatter in the onset of nucleation of individual CNTs and the ensuing growth rates. Experiments performed at different temperatures and catalyst particle densities show the critical role of CNT density on the dynamics of self-organization; low-density CNT nucleation results in the CNTs becoming pinned to the substrate and forming random networks, whereas higher density CNT nucleation results in self-organization of the CNTs into bundles that are oriented perpendicular to the substrate. We also find that mechanical coupling between growing CNTs alters their growth trajectory and shape, causing significant deformations, buckling, and defects in the CNT walls. Therefore, it appears that CNT-CNT coupling not only is critical for self-organization but also directly influences CNT quality and likely the resulting properties of the forest. Our findings show that control of the time-distributed kinetics of CNT nucleation and bundle formation are critical to manufacturing well-organized CNT assemblies and that E-TEM can be a powerful tool to investigate the mesoscale dynamics of CNT networks.

Graphene as an atomically thin interface for growth of vertically aligned carbon nanotubes.

PubMed

Rao, Rahul; Chen, Gugang; Arava, Leela Mohana Reddy; Kalaga, Kaushik; Ishigami, Masahiro; Heinz, Tony F; Ajayan, Pulickel M; Harutyunyan, Avetik R

2013-01-01

Growth of vertically aligned carbon nanotube (CNT) forests is highly sensitive to the nature of the substrate. This constraint narrows the range of available materials to just a few oxide-based dielectrics and presents a major obstacle for applications. Using a suspended monolayer, we show here that graphene is an excellent conductive substrate for CNT forest growth. Furthermore, graphene is shown to intermediate growth on key substrates, such as Cu, Pt, and diamond, which had not previously been compatible with nanotube forest growth. We find that growth depends on the degree of crystallinity of graphene and is best on mono- or few-layer graphene. The synergistic effects of graphene are revealed by its endurance after CNT growth and low contact resistances between the nanotubes and Cu. Our results establish graphene as a unique interface that extends the class of substrate materials for CNT growth and opens up important new prospects for applications.

Graphene as an atomically thin interface for growth of vertically aligned carbon nanotubes

PubMed Central

Rao, Rahul; Chen, Gugang; Arava, Leela Mohana Reddy; Kalaga, Kaushik; Ishigami, Masahiro; Heinz, Tony F.; Ajayan, Pulickel M.; Harutyunyan, Avetik R.

2013-01-01

Growth of vertically aligned carbon nanotube (CNT) forests is highly sensitive to the nature of the substrate. This constraint narrows the range of available materials to just a few oxide-based dielectrics and presents a major obstacle for applications. Using a suspended monolayer, we show here that graphene is an excellent conductive substrate for CNT forest growth. Furthermore, graphene is shown to intermediate growth on key substrates, such as Cu, Pt, and diamond, which had not previously been compatible with nanotube forest growth. We find that growth depends on the degree of crystallinity of graphene and is best on mono- or few-layer graphene. The synergistic effects of graphene are revealed by its endurance after CNT growth and low contact resistances between the nanotubes and Cu. Our results establish graphene as a unique interface that extends the class of substrate materials for CNT growth and opens up important new prospects for applications. PMID:23712556