Characterizing the effects of regolith surface roughness on photoemission from surfaces in space

NASA Astrophysics Data System (ADS)

Dove, A.; Horanyi, M.; Wang, X.

2017-12-01

Surfaces of airless bodies and spacecraft in space are exposed to a variety of charging environments. A balance of currents due to plasma bombardment, photoemission, electron and ion emission and collection, and secondary electron emission determines the surface's charge. Photoelectron emission is the dominant charging process on sunlit surfaces in the inner solar system due to the intense solar UV radiation. This can result in a net positive surface potential, with a cloud of photoelectrons immediately above the surface, called the photoelectron sheath. Conversely, the unlit side of the body will charge negatively due the collection of the fast-moving solar wind electrons. The interaction of charged dust grains with these positively and negatively charged surfaces, and within the photoelectron and plasma sheaths may explain the occurrence of dust lofting, levitation and transport above the lunar surface. The surface potential of exposed objects is also dependent on the material properties of their surfaces. Composition and particle size primarily affect the quantum efficiency of photoelectron generation; however, surface roughness can also control the charging process. In order to characterize these effects, we have conducted laboratory experiments to examine the role of surface roughness in generating photoelectrons in dedicated laboratory experiments using solid and dusty surfaces of the same composition (CeO2), and initial comparisons with JSC-1 lunar simulant. Using Langmuir probe measurements, we explore the measured potentials above insulating surfaces exposed to UV and an electric field, and we show that the photoemission current from a dusty surface is largely reduced due to its higher surface roughness, which causes a significant fraction of the emitted photoelectrons to be re-absorbed within the surface. We will discuss these results in context of similar situations on planetary surfaces.

Suppression of surface charge accumulation on Al{sub 2}O{sub 3}-filled epoxy resin insulator under dc voltage by direct fluorination

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

Zhang, Boya; Zhang, Guixin, E-mail: guixin@mail.tsinghua.edu.cn; Li, Chuanyang

2015-12-15

Surface charge accumulation on insulators under high dc voltage is a major factor that may lead to the reduction of insulation levels in gas insulated devices. In this paper, disc insulators made of Al{sub 2}O{sub 3}-filled epoxy resin were surface fluorinated using a F{sub 2}/N{sub 2} mixture (12.5% F{sub 2}) at 50 °C and 0.1 MPa for different durations of 15 min, 30 min and 60 min. A dc voltage was applied to the insulator for 30 min and the charge density on its surface was measured by an electrostatic probe. The results revealed significant lower surface charge densities on themore » fluorinated insulators in comparison with the original one. Surface conductivity measurements indicated a higher surface conductivity by over three orders of magnitude after fluorination, which would allow the charges to transfer along the surface and thus may suppress their accumulation. Further, attenuated total reflection infrared analysis and surface morphology observations of the samples revealed that the introduction of fluoride groups altered the surface physicochemical properties. These structure changes, especially the physical defects reduced the depth of charge traps in the surface layer, which was verified by the measurement of energy distributions of the electron and hole traps based on the isothermal current theory. The results in this paper demonstrate that fluorination can be a promising and effective method to suppress surface charge accumulation on epoxy insulators in gas insulated devices.« less

Correlation between charge input and cycle life of MgNi electrode for Ni-MH batteries

NASA Astrophysics Data System (ADS)

Ruggeri, Stéphane; Roué, Lionel

Amorphous MgNi material has been prepared by mechanically alloying magnesium and nickel powders for 10 h. Its cycle life as a negative electrode for nickel-metal hydride (Ni-MH) batteries has been studied with charge inputs varying from 0 to 600 mAh/g. For charge inputs lower than 400 mAh/g, the first cycle discharge capacity is superior to the charge input capacity. This surplus discharge capacity can be associated with the alloy oxidation to Mg(OH) 2 and Ni(OH) 2. For charge inputs higher than 400 mAh/g, the initial discharge capacity becomes inferior to the charge input capacity due to the progressive decrease of the charge efficiency related to the hydrogen evolution side reaction. From the second charge/discharge cycle, no additional discharge capacity appears and no discharge capacity degradation occurs for charge inputs inferior or equal to 233 mAh/g. In contrast, for higher charge input values, an important decay in the discharge capacity appears, which is accentuated with increasing charge input. The thresholds charge input of 233 mAh/g corresponds to an amount of hydrogen absorbed into the alloy of 0.8 wt.% (MgNiH 0.7). For higher absorbed hydrogen amounts, it is assumed that extended electrode pulverization occurs, which breaks the passive surface layer of Mg(OH) 2 formed during the first charge/discharge cycle. This creates unprotected fresh MgNi surfaces and consequently, leads to electrode capacity degradation. The stability of the MgNi electrode for absorbed hydrogen content lower than 0.8 wt.% may be related to its amorphous character, which favors a gradual volume expansion upon hydrogen absorption in contrast to crystalline compounds characterized by an abrupt α-to-β lattice expansion.

Effects of Ni particle morphology on cell performance of Na/NiCl2 battery

NASA Astrophysics Data System (ADS)

Kim, Mangi; Ahn, Cheol-Woo; Hahn, Byung-Dong; Jung, Keeyoung; Park, Yoon-Cheol; Cho, Nam-ung; Lee, Heesoo; Choi, Joon-Hwan

2017-11-01

Electrochemical reaction of Ni particle, one of active cathode materials in the Na/NiCl2 battery, occurs on the particle surface. The NiCl2 layer formed on the Ni particle surface during charging can disconnect the electron conduction path through Ni particles because the NiCl2 layer has very low conductivity. The morphology and size of Ni particles, therefore, need to be controlled to obtain high charge capacity and excellent cyclic retention. Effects of the Ni particle size on the cell performance were investigated using spherical Ni particles with diameters of 0.5 μm, 6 μm, and 50 μm. The charge capacities of the cells with spherical Ni particles increased when the Ni particle size becomes smaller because of their higher surface area but their charge capacities were significantly decreased with increasing cyclic tests owing to the disconnection of electron conduction path. The inferior cyclic retention of charge capacity was improved using reticular Ni particles which maintained the reliable connection for the electron conduction in the Na/NiCl2 battery. The charge capacity of the cell with the reticular Ni particles was higher than the cell with the small-sized spherical Ni particles approximately by 26% at 30th cycle.

Anomalous pH-Dependent Nanofluidic Salinity Gradient Power.

PubMed

Yeh, Li-Hsien; Chen, Fu; Chiou, Yu-Ting; Su, Yen-Shao

2017-12-01

Previous studies on nanofluidic salinity gradient power (NSGP), where energy associated with the salinity gradient can be harvested with ion-selective nanopores, all suggest that nanofluidic devices having higher surface charge density should have higher performance, including osmotic power and conversion efficiency. In this manuscript, this viewpoint is challenged and anomalous counterintuitive pH-dependent NSGP behaviors are reported. For example, with equal pH deviation from its isoelectric point (IEP), the nanopore at pH < IEP is shown to have smaller surface charge density but remarkably higher NSGP performance than that at pH > IEP. Moreover, for sufficiently low pH, the NSGP performance decreases with lowering pH (increasing nanopore charge density). As a result, a maximum osmotic power density as high as 5.85 kW m -2 can be generated along with a conversion efficiency of 26.3% achieved for a single alumina nanopore at pH 3.5 under a 1000-fold concentration ratio. Using the rigorous model with considering the surface equilibrium reactions on the pore wall, it is proved that these counterintuitive surface-charge-dependent NSGP behaviors result from the pH-dependent ion concentration polarization effect, which yields the degradation in effective concentration ratio across the nanopore. These findings provide significant insight for the design of next-generation, high-performance NSGP devices. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Highly charged ion based time of flight emission microscope

DOEpatents

Barnes, Alan V.; Schenkel, Thomas; Hamza, Alex V.; Schneider, Dieter H.; Doyle, Barney

2001-01-01

A highly charged ion based time-of-flight emission microscope has been designed, which improves the surface sensitivity of static SIMS measurements because of the higher ionization probability of highly charged ions. Slow, highly charged ions are produced in an electron beam ion trap and are directed to the sample surface. The sputtered secondary ions and electrons pass through a specially designed objective lens to a microchannel plate detector. This new instrument permits high surface sensitivity (10.sup.10 atoms/cm.sup.2), high spatial resolution (100 nm), and chemical structural information due to the high molecular ion yields. The high secondary ion yield permits coincidence counting, which can be used to enhance determination of chemical and topological structure and to correlate specific molecular species.

Effect of Atomic Oxygen Exposure on Surface Resistivity Change of Spacecraft Insulator Material

NASA Astrophysics Data System (ADS)

Mundari, Noor Danish Ahrar; Khan, Arifur Rahman; Chiga, Masaru; Okumura, Teppei; Masui, Hirokazu; Iwata, Minoru; Toyoda, Kazuhiro; Cho, Mengu

Spacecraft surface charging can lead to arcing and a loss of electricity generation capability in solar panels or even loss of a satellite. The charging problem may be further aggravated by atomic oxygen (AO) exposure in Low Earth orbits, which modifies the surface of materials like polyimide, Teflon, anti-reflective coatings, cover glass etc, used on satellite surfaces, affecting materials properties, such as resistivity, secondary electron emissivity and photo emission, which govern the charging behavior. These properties are crucial input parameters for spacecraft charging analysis. To study the AO exposure effect on charging governing properties, an atomic oxygen exposure facility based on laser detonation of oxygen was built. The facility produces AO with a peak velocity value around 10-12km/s and a higher flux than that existing in orbit. After exposing the polyimide test material to the equivalent of 10 years of AO fluence at an altitude of 700-800 km, surface charging properties like surface resistivity and volume resistivity were measured. The measurement was performed in a vacuum using the charge storage decay method at room temperature, which is considered the most appropriate for measuring resistivity for space applications. The results show that the surface resistivity increases and the volume resistivity remains almost the same for the AO exposure fluence of 5.4×1018 atoms cm-2.

Electroviscous effect and electrokinetic energy conversion in time periodic pressure-driven flow through a parallel-plate nanochannel with surface charge-dependent slip

NASA Astrophysics Data System (ADS)

Buren, Mandula; Jian, Yongjun; Zhao, Yingchun; Chang, Long

2018-05-01

In this paper we analytically investigate the electroviscous effect and electrokinetic energy conversion in the time periodic pressure-driven flow of an incompressible viscous Newtonian liquid through a parallel-plate nanochannel with surface charge-dependent slip. Analytical and semi-analytical solutions for electric potential, velocity and streaming electric field are obtained and are utilized to compute electrokinetic energy conversion efficiency. The results show that velocity amplitude and energy conversion efficiency are reduced when the effect of surface charge on slip length is considered. The surface charge effect increases with zeta potential and ionic concentration. In addition, the energy conversion efficiency is large when the ratio of channel half-height to the electric double layer thickness is small. The boundary slip results in a large increase in energy conversion. Higher values of the frequency of pressure pulsation lead to higher values of the energy conversion efficiency. We also obtain the energy conversion efficiency in constant pressure-driven flow and find that the energy conversion efficiency in periodical pressure-driven flow becomes larger than that in constant pressure-driven flow when the frequency is large enough.

Charged Vaidya solution satisfies weak energy condition

NASA Astrophysics Data System (ADS)

Chatterjee, Soumyabrata; Ganguli, Suman; Virmani, Amitabh

2016-07-01

The external matter stress-tensor supporting charged Vaidya solution appears to violate weak energy condition in certain region of the spacetime. Motivated by this, a new interpretation of charged Vaidya solution was proposed by Ori (Class Quant Grav 8:1559, 1991) in which the energy condition continues to be satisfied. In this construction, one glues an outgoing Vaidya solution to the original ingoing Vaidya solution provided the surface where the external stress-tensor vanishes is spacelike. We revisit this study and extend it to higher-dimensions, to AdS settings, and to higher-derivative f( R) theories. In asymptotically flat space context, we explore in detail the case when the mass function m( v) is proportional to the charge function q( v). When the proportionality constant ν = q(v)/m(v) lies in between zero and one, we show that the surface where the external stress-tensor vanishes is spacelike and lies in between the inner and outer apparent horizons.

Design guidelines for assessing and controlling spacecraft charging effects

NASA Technical Reports Server (NTRS)

Purvis, C. K.; Garrett, H. B.; Whittlesey, A. C.; Stevens, N. J.

1984-01-01

The need for uniform criteria, or guidelines, to be used in all phases of spacecraft design is discussed. Guidelines were developed for the control of absolute and differential charging of spacecraft surfaces by the lower energy space charged particle environment. Interior charging due to higher energy particles is not considered. A guide to good design practices for assessing and controlling charging effects is presented. Uniform design practices for all space vehicles are outlined.

Design guidelines for assessing and controlling spacecraft charging effects

NASA Technical Reports Server (NTRS)

Purvis, C. K.; Garrett, H. B.; Whittlesey, A.; Stevens, N. J.

1985-01-01

The need for uniform criteria, or guidelines, to be used in all phases of spacecraft design is discussed. Guidelines were developed for the control of absolute and differential charging of spacecraft surfaces by the lower energy space charged particle environment. Interior charging due to higher energy particles is not considered. A guide to good design practices for assessing and controlling charging effects is presented. Uniform design practices for all space vehicles are outlined.

Atomistic Molecular Dynamics Simulations of Charged Latex Particle Surfaces in Aqueous Solution.

PubMed

Li, Zifeng; Van Dyk, Antony K; Fitzwater, Susan J; Fichthorn, Kristen A; Milner, Scott T

2016-01-19

Charged particles in aqueous suspension form an electrical double layer at their surfaces, which plays a key role in suspension properties. For example, binder particles in latex paint remain suspended in the can because of repulsive forces between overlapping double layers. Existing models of the double layer assume sharp interfaces bearing fixed uniform charge, and so cannot describe aqueous binder particle surfaces, which are soft and diffuse, and bear mobile charge from ionic surfactants as well as grafted multivalent oligomers. To treat this industrially important system, we use atomistic molecular dynamics simulations to investigate a structurally realistic model of commercial binder particle surfaces, informed by extensive characterization of particle synthesis and surface properties. We determine the interfacial profiles of polymer, water, bound and free ions, from which the charge density and electrostatic potential can be calculated. We extend the traditional definitions of the inner and outer Helmholtz planes to our diffuse interfaces. Beyond the Stern layer, the simulated electrostatic potential is well described by the Poisson-Boltzmann equation. The potential at the outer Helmholtz plane compares well to the experimental zeta potential. We compare particle surfaces bearing two types of charge groups, ionic surfactant and multivalent oligomers, with and without added salt. Although the bare charge density of a surface bearing multivalent oligomers is much higher than that of a surfactant-bearing surface at realistic coverage, greater counterion condensation leads to similar zeta potentials for the two systems.

FOB-SH: Fragment orbital-based surface hopping for charge carrier transport in organic and biological molecules and materials

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

Spencer, J.; Gajdos, F.; Blumberger, J., E-mail: j.blumberger@ucl.ac.uk

2016-08-14

We introduce a fragment orbital-based fewest switches surface hopping method, FOB-SH, designed to efficiently simulate charge carrier transport in strongly fluctuating condensed phase systems such as organic semiconductors and biomolecules. The charge carrier wavefunction is expanded and the electronic Hamiltonian constructed in a set of singly occupied molecular orbitals of the molecular sites that mediate the charge transfer. Diagonal elements of the electronic Hamiltonian (site energies) are obtained from a force field, whereas the off-diagonal or electronic coupling matrix elements are obtained using our recently developed analytic overlap method. We derive a general expression for the exact forces on themore » adiabatic ground and excited electronic state surfaces from the nuclear gradients of the charge localized electronic states. Applications to electron hole transfer in a model ethylene dimer and through a chain of ten model ethylenes validate our implementation and demonstrate its computational efficiency. On the larger system, we calculate the qualitative behaviour of charge mobility with change in temperature T for different regimes of the intermolecular electronic coupling. For small couplings, FOB-SH predicts a crossover from a thermally activated regime at low temperatures to a band-like transport regime at higher temperatures. For higher electronic couplings, the thermally activated regime disappears and the mobility decreases according to a power law. This is interpreted by a gradual loss in probability for resonance between the sites as the temperature increases. The polaron hopping model solved for the same system gives a qualitatively different result and underestimates the mobility decay at higher temperatures. Taken together, the FOB-SH methodology introduced here shows promise for a realistic investigation of charge carrier transport in complex organic, aqueous, and biological systems.« less

FOB-SH: Fragment orbital-based surface hopping for charge carrier transport in organic and biological molecules and materials

NASA Astrophysics Data System (ADS)

Spencer, J.; Gajdos, F.; Blumberger, J.

2016-08-01

We introduce a fragment orbital-based fewest switches surface hopping method, FOB-SH, designed to efficiently simulate charge carrier transport in strongly fluctuating condensed phase systems such as organic semiconductors and biomolecules. The charge carrier wavefunction is expanded and the electronic Hamiltonian constructed in a set of singly occupied molecular orbitals of the molecular sites that mediate the charge transfer. Diagonal elements of the electronic Hamiltonian (site energies) are obtained from a force field, whereas the off-diagonal or electronic coupling matrix elements are obtained using our recently developed analytic overlap method. We derive a general expression for the exact forces on the adiabatic ground and excited electronic state surfaces from the nuclear gradients of the charge localized electronic states. Applications to electron hole transfer in a model ethylene dimer and through a chain of ten model ethylenes validate our implementation and demonstrate its computational efficiency. On the larger system, we calculate the qualitative behaviour of charge mobility with change in temperature T for different regimes of the intermolecular electronic coupling. For small couplings, FOB-SH predicts a crossover from a thermally activated regime at low temperatures to a band-like transport regime at higher temperatures. For higher electronic couplings, the thermally activated regime disappears and the mobility decreases according to a power law. This is interpreted by a gradual loss in probability for resonance between the sites as the temperature increases. The polaron hopping model solved for the same system gives a qualitatively different result and underestimates the mobility decay at higher temperatures. Taken together, the FOB-SH methodology introduced here shows promise for a realistic investigation of charge carrier transport in complex organic, aqueous, and biological systems.

High-surface-area architectures for improved charge transfer kinetics at the dark electrode in dye-sensitized solar cells.

PubMed

Hoffeditz, William L; Katz, Michael J; Deria, Pravas; Martinson, Alex B F; Pellin, Michael J; Farha, Omar K; Hupp, Joseph T

2014-06-11

Dye-sensitized solar cell (DSC) redox shuttles other than triiodide/iodide have exhibited significantly higher charge transfer resistances at the dark electrode. This often results in poor fill factor, a severe detriment to device performance. Rather than moving to dark electrodes of untested materials that may have higher catalytic activity for specific shuttles, the surface area of platinum dark electrodes could be increased, improving the catalytic activity by simply presenting more catalyst to the shuttle solution. A new copper-based redox shuttle that experiences extremely high charge-transfer resistance at conventional Pt dark electrodes yields cells having fill-factors of less than 0.3. By replacing the standard Pt dark electrode with an inverse opal Pt electrode fabricated via atomic layer deposition, the dark electrode surface area is boosted by ca. 50-fold. The resulting increase in interfacial electron transfer rate (decrease in charge-transfer resistance) nearly doubles the fill factor and therefore the overall energy conversion efficiency, illustrating the utility of this high-area electrode for DSCs.

Surface charge method for molecular surfaces with curved areal elements I. Spherical triangles

NASA Astrophysics Data System (ADS)

Yu, Yi-Kuo

2018-03-01

Parametrizing a curved surface with flat triangles in electrostatics problems creates a diverging electric field. One way to avoid this is to have curved areal elements. However, charge density integration over curved patches appears difficult. This paper, dealing with spherical triangles, is the first in a series aiming to solve this problem. Here, we lay the ground work for employing curved patches for applying the surface charge method to electrostatics. We show analytically how one may control the accuracy by expanding in powers of the the arc length (multiplied by the curvature). To accommodate not extremely small curved areal elements, we have provided enough details to include higher order corrections that are needed for better accuracy when slightly larger surface elements are used.

On charging of snow particles in blizzard

NASA Technical Reports Server (NTRS)

Shio, Hisashi

1991-01-01

The causes of the charge polarity on the blizzard, which consisted of fractured snow crystals and ice particles, were investigated. As a result, the charging phenomena showed that the characteristics of the blizzard are as follows: (1) In the case of the blizzard with snowfall, the fractured snow particles drifting near the surface of snow field (lower area: height 0.3 m) had positive charge, while those drifting at higher area (height 2 m) from the surface of snow field had negative charge. However, during the series of blizzards two kinds of particles positively and negatively charged were collected in equal amounts in a Faraday Cage. It may be considered that snow crystals with electrically neutral properties were separated into two kinds of snow flakes (charged positively and negatively) by destruction of the snow crystals. (2) In the case of the blizzard which consisted of irregularly formed ice drops (generated by peeling off the hardened snow field), the charge polarity of these ice drops salting over the snow field was particularly controlled by the crystallographic characteristics of the surface of the snow field hardened by the powerful wind pressure.

Effect of charge on the current-voltage characteristics of silicon pin structures with and without getter annealing under beta irradiation of Ni-63.

PubMed

Nagornov, Yuri S

2018-05-01

The charge model for efficiency of betavoltaics effect is proposed. It allows calculating the charge value for pin structures under irradiation of Ni-63. We approximated the current-voltage characteristics of the structures using an equivalent diode circuit with a charge on the barrier capacitance. We calculated the charge function from current-voltage characteristics for two types of silicon pin structures - with and without getter annealing. The charging on the surface of pin structure decreases the efficiency of betavoltaics effect. Value of charge for our structures is changed in the range from -50 to +15mC/cm 2 and depends on the applied potential. The getter annealing allows getting the structures with a higher efficiency of betavoltaic effect, but it does not exclude the surface charging under beta irradiation from Ni-63. Copyright © 2018 Elsevier Ltd. All rights reserved.

Design of asymmetric particles containing a charged interior and a neutral surface charge: comparative study on in vivo circulation of polyelectrolyte microgels.

PubMed

Chen, Kai; Xu, Jing; Luft, J Christopher; Tian, Shaomin; Raval, Jay S; DeSimone, Joseph M

2014-07-16

Lowering the modulus of hydrogel particles could enable them to bypass in vivo physical barriers that would otherwise filter particles with similar size but higher modulus. Incorporation of electrolyte moieties into the polymer network of hydrogel particles to increase the swelling ratio is a straightforward and quite efficient way to decrease the modulus. In addition, charged groups in hydrogel particles can also help secure cargoes. However, the distribution of charged groups on the surface of a particle can accelerate the clearance of particles. Herein, we developed a method to synthesize highly swollen microgels of precise size with near-neutral surface charge while retaining interior charged groups. A strategy was employed to enable a particle to be highly cross-linked with very small mesh size, and subsequently PEGylated to quench the exterior amines only without affecting the internal amines. Acidic degradation of the cross-linker allows for swelling of the particles to microgels with a desired size and deformability. The microgels fabricated demonstrated extended circulation in vivo compared to their counterparts with a charged surface, and could potentially be utilized in in vivo applications including as oxygen carriers or nucleic acid scavengers.

Secondary Structures of Ubiquitin Ions Soft-Landed onto Self-Assembled Monolayer Surfaces

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

Hu, Qichi; Laskin, Julia

2016-06-09

The secondary structures of multiply charged ubiquitin ions soft-landed onto self-assembled monolayer (SAM) surfaces were studied using in situ infrared reflection-absorption spectroscopy (IRRAS). Two charge states of ubiquitin, 5+ and 13+, were mass selected separately from a mixture of different charge states produced by electrospray ionization (ESI). The low 5+ charge state represents a native-like folded state of ubiquitin, while the high 13+ charge state assumes an extended, almost linear conformation. Each of the two charge states was soft-landed onto a CH 3- and COOH-terminated SAM of alkylthiols on gold (HSAM and COOH-SAM). HSAM is a hydrophobic surface known tomore » stabilize helical conformations of soft-landed protonated peptides, whereas COOH-SAM is a hydrophilic surface that preferentially stabilizes β-sheet conformations. IRRAS spectra of the soft-landed ubiquitin ions were acquired as a function of time during and after ion soft-landing. Similar to smaller peptide ions, helical conformations of ubiquitin are found to be more abundant on HSAM, while the relative abundance of β-sheet conformations increases on COOH-SAM. The initial charge state of ubiquitin also has a pronounced effect on its conformation on the surface. Specifically, on both surfaces, a higher relative abundance of helical conformations and lower relative abundance of β-sheet conformations is observed for the 13+ charge state compared to the 5+ charge state. Time-resolved experiments indicate that the α-helical band in the spectrum of the 13+ charge state slowly increases with time on the HSAM surface and decreases in the spectrum of the 13+ charge state on COOH-SAM. These results further support the preference of the hydrophobic HSAM surface toward helical conformations and demonstrate that soft-landed protein ions may undergo slow conformational changes during and after deposition.« less

Cellulose nanocrystals with tunable surface charge for nanomedicine

NASA Astrophysics Data System (ADS)

Hosseinidoust, Zeinab; Alam, Md Nur; Sim, Goeun; Tufenkji, Nathalie; van de Ven, Theo G. M.

2015-10-01

Crystalline nanoparticles of cellulose exhibit attractive properties as nanoscale carriers for bioactive molecules in nanobiotechnology and nanomedicine. For applications in imaging and drug delivery, surface charge is one of the most important factors affecting the performance of nanocarriers. However, current methods of preparation offer little flexibility for controlling the surface charge of cellulose nanocrystals, leading to compromised colloidal stability under physiological conditions. We report a synthesis method that results in nanocrystals with remarkably high carboxyl content (6.6 mmol g-1) and offers continuous control over surface charge without any adjustment to the reaction conditions. Six fractions of nanocrystals with various surface carboxyl contents were synthesized from a single sample of softwood pulp with carboxyl contents varying from 6.6 to 1.7 mmol g-1 and were fully characterized. The proposed method resulted in highly stable colloidal nanocrystals that did not aggregate when exposed to high salt concentrations or serum-containing media. Interactions of these fractions with four different tissue cell lines were investigated over a wide range of concentrations (50-300 μg mL-1). Darkfield hyperspectral imaging and confocal microscopy confirmed the uptake of nanocrystals by selected cell lines without any evidence of membrane damage or change in cell density; however a charge-dependent decrease in mitochondrial activity was observed for charge contents higher than 3.9 mmol g-1. A high surface carboxyl content allowed for facile conjugation of fluorophores to the nanocrystals without compromising colloidal stability. The cellular uptake of fluoresceinamine-conjugated nanocrystals exhibited a time-dose dependent relationship and increased significantly with doubling of the surface charge.Crystalline nanoparticles of cellulose exhibit attractive properties as nanoscale carriers for bioactive molecules in nanobiotechnology and nanomedicine. For applications in imaging and drug delivery, surface charge is one of the most important factors affecting the performance of nanocarriers. However, current methods of preparation offer little flexibility for controlling the surface charge of cellulose nanocrystals, leading to compromised colloidal stability under physiological conditions. We report a synthesis method that results in nanocrystals with remarkably high carboxyl content (6.6 mmol g-1) and offers continuous control over surface charge without any adjustment to the reaction conditions. Six fractions of nanocrystals with various surface carboxyl contents were synthesized from a single sample of softwood pulp with carboxyl contents varying from 6.6 to 1.7 mmol g-1 and were fully characterized. The proposed method resulted in highly stable colloidal nanocrystals that did not aggregate when exposed to high salt concentrations or serum-containing media. Interactions of these fractions with four different tissue cell lines were investigated over a wide range of concentrations (50-300 μg mL-1). Darkfield hyperspectral imaging and confocal microscopy confirmed the uptake of nanocrystals by selected cell lines without any evidence of membrane damage or change in cell density; however a charge-dependent decrease in mitochondrial activity was observed for charge contents higher than 3.9 mmol g-1. A high surface carboxyl content allowed for facile conjugation of fluorophores to the nanocrystals without compromising colloidal stability. The cellular uptake of fluoresceinamine-conjugated nanocrystals exhibited a time-dose dependent relationship and increased significantly with doubling of the surface charge. Electronic supplementary information (ESI) available: Additional results are presented in the ESI in Fig. S1 through S4. See DOI: 10.1039/c5nr02506k

Detailed modeling of electron emission for transpiration cooling of hypersonic vehicles

NASA Astrophysics Data System (ADS)

Hanquist, Kyle M.; Hara, Kentaro; Boyd, Iain D.

2017-02-01

Electron transpiration cooling (ETC) is a recently proposed approach to manage the high heating loads experienced at the sharp leading edges of hypersonic vehicles. Computational fluid dynamics (CFD) can be used to investigate the feasibility of ETC in a hypersonic environment. A modeling approach is presented for ETC, which includes developing the boundary conditions for electron emission from the surface, accounting for the space-charge limit effects of the near-wall plasma sheath. The space-charge limit models are assessed using 1D direct-kinetic plasma sheath simulations, taking into account the thermionically emitted electrons from the surface. The simulations agree well with the space-charge limit theory proposed by Takamura et al. for emitted electrons with a finite temperature, especially at low values of wall bias, which validates the use of the theoretical model for the hypersonic CFD code. The CFD code with the analytical sheath models is then used for a test case typical of a leading edge radius in a hypersonic flight environment. The CFD results show that ETC can lower the surface temperature of sharp leading edges of hypersonic vehicles, especially at higher velocities, due to the increase in ionized species enabling higher electron heat extraction from the surface. The CFD results also show that space-charge limit effects can limit the ETC reduction of surface temperatures, in comparison to thermionic emission assuming no effects of the electric field within the sheath.

The influence of space charge shielding on dielectric multipactor

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

Chang, C.; Liu, G. Z.; Tang, C. X.

2009-05-15

A model of space charge influenced by multipactor electrons and plasma has been established. The positive space charge potential/field for vacuum dielectric multipactor is analytically studied. After considering the plasma, the positive space charge field is further shielded, and multipactor saturates at higher surface accumulated field, compared with that for only considering multipactor electrons. The negative space charge potential/field for dielectric breakdown at high pressure is analyzed. It is found that the negative potential can be nonmonotonously varied, forming a minimum potential well.

Dust Grain Charge in the Lunar Environment

NASA Astrophysics Data System (ADS)

Vaverka, Jakub; Richterova, Ivana; Vysinka, Marek; Pavlu, Jiri; Safrankova, Jana; Nemecek, Zdenek

2014-05-01

Interaction of a lunar surface with solar wind and magnetosphere plasmas leads to it charging by several processes as photoemission, a collection of primary particles and secondary electron emission. Nevertheless, charging of the lunar surface is complicated by a presence of crustal magnetic anomalies with can generate a "mini-magnetosphere" capable for more or less complete shielding the surface. On the other hand, shielding of solar light and plasma particles by rocks and craters can also locally influence the surface potential as well as a presence of a plasma wake strongly changes this potential at the night side of the Moon. A typical surface potential varies from slightly positive (dayside) to negative values of the order of several hundred of volts (night side). At the night side, negative potentials can reach -4 kV during solar energetic particle (SEP) events. Recent measurements of the surface potential by Lunar Prospector and Artemis spacecraft have shown surprisingly high negative dayside surface potentials (-500 V) during the magnetotail crossings as well as the positive surface potential higher than 100 V. One possible explanation is its non-monotonic profile above a surface where the potential minimum is formed by the space charge. Dust grains presented in this complicated environment are also charged by similar processes as the lunar surface. A strong dependence of the secondary electron yield on the grain size can significantly influence dust charging mainly in the Earth's plasma sheet where an equilibrium grain potential can by different than the surface potential and can reach even the opposite sign. This process can lead to levitation of dust above a surface observed by the Surveyor spacecraft.

Measurement of surface charges on the dielectric film based on field mills under the HVDC corona wire

NASA Astrophysics Data System (ADS)

Donglai, WANG; Tiebing, LU; Yuan, WANG; Bo, CHEN; Xuebao, LI

2018-05-01

The ion flow field on the ground is one of the significant parameters used to evaluate the electromagnetic environment of high voltage direct current (HVDC) power lines. HVDC lines may cross the greenhouses due to the restricted transmission corridors. Under the condition of ion flow field, the dielectric films on the greenhouses will be charged, and the electric fields in the greenhouses may exceed the limit value. Field mills are widely used to measure the ground-level direct current electric fields under the HVDC power lines. In this paper, the charge inversion method is applied to calculate the surface charges on the dielectric film according to the measured ground-level electric fields. The advantages of hiding the field mill probes in the ground are studied. The charge inversion algorithm is optimized in order to decrease the impact of measurement errors. Based on the experimental results, the surface charge distribution on a piece of quadrate dielectric film under a HVDC corona wire is studied. The enhanced effect of dielectric film on ground-level electric field is obviously weakened with the increase of film height. Compared with the total electric field strengths, the normal components of film-free electric fields at the corresponding film-placed positions have a higher effect on surface charge accumulation.

Effect of laundry surfactants on surface charge and colloidal stability of silver nanoparticles.

PubMed

Skoglund, Sara; Lowe, Troy A; Hedberg, Jonas; Blomberg, Eva; Wallinder, Inger Odnevall; Wold, Susanna; Lundin, Maria

2013-07-16

The stability of silver nanoparticles (Ag NPs) potentially released from clothing during a laundry cycle and their interactions with laundry-relevant surfactants [anionic (LAS), cationic (DTAC), and nonionic (Berol)] have been investigated. Surface interactions between Ag NPs and surfactants influence their speciation and stability. In the absence of surfactants as well as in the presence of LAS, the negatively charged Ag NPs were stable in solution for more than 1 day. At low DTAC concentrations (≤1 mM), DTAC-Ag NP interactions resulted in charge neutralization and formation of agglomerates. The surface charge of the particles became positive at higher concentrations due to a bilayer type formation of DTAC that prevents from agglomeration due to repulsive electrostatic forces between the positively charged colloids. The adsorption of Berol was enhanced when above its critical micelle concentration (cmc). This resulted in a surface charge close to zero and subsequent agglomeration. Extended DLVO theory calculations were in compliance with observed findings. The stability of the Ag NPs was shown to depend on the charge and concentration of the adsorbed surfactants. Such knowledge is important as it may influence the subsequent transport of Ag NPs through different chemical transients and thus their potential bioavailability and toxicity.

Direct simulation of electroosmosis around a spherical particle with inhomogeneously acquired surface charge.

PubMed

Alizadeh, Amer; Wang, Moran

2017-03-01

Uncovering electroosmosis around an inhomogeneously acquired charge spherical particle in a confined space could provide detailed insights into its broad applications from biology to geology. In the present study, we developed a direct simulation method with the effects of inhomogeneously acquired charges on the particle surface considered, which has been validated by the available analytical and experimental data. Modeling results reveal that the surface charge and zeta potential, which are acquired through chemical interactions, strongly depend on the local solution properties and the particle size. The surface charge and zeta potential of the particle would significantly vary with the tangential positions on the particle surface by increasing the particle radius. Moreover, regarding the streaming potential for a particle-fluid tube system, our results uncover that the streaming potential has a reverse relation with the particle size in a micro or nanotube. To explain this phenomenon, we present a simple relation that bridges the streaming potential with the particle size and tube radius, zeta potential, bulk and surface conductivity. This relation could predict good results specifically for higher ion concentrations and provide deeper understanding of the particle size effects on the streaming potential measurements of the particle fluid tube system. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Measurements and theoretical interpretation of points of zero charge/potential of BSA protein.

PubMed

Salis, Andrea; Boström, Mathias; Medda, Luca; Cugia, Francesca; Barse, Brajesh; Parsons, Drew F; Ninham, Barry W; Monduzzi, Maura

2011-09-20

The points of zero charge/potential of proteins depend not only on pH but also on how they are measured. They depend also on background salt solution type and concentration. The protein isoelectric point (IEP) is determined by electrokinetical measurements, whereas the isoionic point (IIP) is determined by potentiometric titrations. Here we use potentiometric titration and zeta potential (ζ) measurements at different NaCl concentrations to study systematically the effect of ionic strength on the IEP and IIP of bovine serum albumin (BSA) aqueous solutions. It is found that high ionic strengths produce a shift of both points toward lower (IEP) and higher (IIP) pH values. This result was already reported more than 60 years ago. At that time, the only available theory was the purely electrostatic Debye-Hückel theory. It was not able to predict the opposite trends of IIP and IEP with ionic strength increase. Here, we extend that theory to admit both electrostatic and nonelectrostatic (NES) dispersion interactions. The use of a modified Poisson-Boltzmann equation for a simple model system (a charge regulated spherical colloidal particle in NaCl salt solutions), that includes these ion specific interactions, allows us to explain the opposite trends observed for isoelectric point (zero zeta potential) and isoionic point (zero protein charge) of BSA. At higher concentrations, an excess of the anion (with stronger NES interactions than the cation) is adsorbed at the surface due to an attractive ionic NES potential. This makes the potential relatively more negative. Consequently, the IEP is pushed toward lower pH. But the charge regulation condition means that the surface charge becomes relatively more positive as the surface potential becomes more negative. Consequently, the IIP (measuring charge) shifts toward higher pH as concentration increases, in the opposite direction from the IEP (measuring potential). © 2011 American Chemical Society

Protein interactions with layers of TiO2 nanotube and nanopore arrays: Morphology and surface charge influence.

PubMed

Kulkarni, Mukta; Mazare, Anca; Park, Jung; Gongadze, Ekaterina; Killian, Manuela Sonja; Kralj, Slavko; von der Mark, Klaus; Iglič, Aleš; Schmuki, Patrik

2016-11-01

In the present work we investigate the key factors involved in the interaction of small-sized charged proteins with TiO 2 nanostructures, i.e. albumin (negatively charged), histone (positively charged). We examine anodic nanotubes with specific morphology (simultaneous control over diameter and length, e.g. diameter - 15, 50 or 100nm, length - 250nm up to 10μm) and nanopores. The nanostructures surface area has a direct influence on the amount of bound protein, nonetheless the protein physical properties as electric charge and size (in relation to nanotopography and biomaterial's electric charge) are crucial too. The highest quantity of adsorbed protein is registered for histone, for 100nm diameter nanotubes (10μm length) while higher values are registered for 15nm diameter nanotubes when normalizing protein adsorption to nanostructures' surface unit area (evaluated from dye desorption measurements) - consistent with theoretical considerations. The proteins presence on the nanostructures is evaluated by XPS and ToF-SIMS; additionally, we qualitatively assess their presence along the nanostructures length by ToF-SIMS depth profiles, with decreasing concentration towards the bottom. Surface nanostructuring of titanium biomedical devices with TiO 2 nanotubes was shown to significantly influence the adhesion, proliferation and differentiation of mesenchymal stem cells (and other cells too). A high level of control over the nanoscale topography and over the surface area of such 1D nanostructures enables a direct influence on protein adhesion. Herein, we investigate and show how the nanostructure morphology (nanotube diameter and length) influences the interactions with small-sized charged proteins, using as model proteins bovine serum albumin (negatively charged) and histone (positively charged). We show that the protein charge strongly influences their adhesion to the TiO 2 nanostructures. Protein adhesion is quantified by ELISA measurements and determination of the nanostructures' total surface area. We use a quantitative surface charge model to describe charge interactions and obtain an increased magnitude of the surface charge density at the top edges of the nanotubes. In addition, we track the proteins presence on and inside the nanostructures. We believe that these aspects are crucial for applications where the incorporation of active molecules such as proteins, drugs, growth factors, etc., into nanotubes is desired. Copyright © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Complex interaction of subsequent surface streamers via deposited charge: a high-resolution experimental study

NASA Astrophysics Data System (ADS)

Hoder, T.; Synek, P.; Chorvát, D.; Ráhel', J.; Brandenburg, R.; Černák, M.

2017-07-01

The coplanar barrier discharge in synthetic air at 30 kPa pressure was studied by time-correlated single photon counting enhanced optical emission spectroscopy, far-field microscopy enhanced intensified CCD camera and sensitive current measurements. The discharge operated in a regime where two subsequent microdischarges appeared within the same voltage half-period. The electrical analysis of the barrier discharge setup enabled us to quantify charge transfer and the effective electric field development. During the second microdischarge the positive surface streamers follow the interface (triple-line) between the area of deposited charge from the previous one and the area of uncharged dielectric surface. It is shown that additional branching and flashes of surface streamers are responsible for the increased spatial complexity of the deposited surface charges at high overvoltage. A suppressed streamer propagating over the area of deposited surface charge was tracked and the evidence of surface streamer reconnection is presented. A spatiotemporal distribution (resolution of 120 ps and 100 μm) of the reduced electric field strength was obtained for both microdischarges from the recorded luminosities of the molecular nitrogen. The reduced electric field of positive streamers in the first microdischarge reached 1200 Td. For the second one, the electric field values for the streamer at the triple-line are slightly lower than that, while for the suppressed streamers are even higher.

Environment-Modulated Crystallization of Cu2O and CuO Nanowires by Electrospinning and Their Charge Storage Properties.

PubMed

Harilal, Midhun; G Krishnan, Syam; Pal, Bhupender; Reddy, M Venkatashamy; Ab Rahim, Mohd Hasbi; Yusoff, Mashitah Mohd; Jose, Rajan

2018-02-06

This article reports the synthesis of cuprous oxide (Cu 2 O) and cupric oxide (CuO) nanowires by controlling the calcination environment of electrospun polymeric nanowires and their charge storage properties. The Cu 2 O nanowires showed higher surface area (86 m 2 g -1 ) and pore size than the CuO nanowires (36 m 2 g -1 ). Electrochemical analysis was carried out in 6 M KOH, and both the electrodes showed battery-type charge storage mechanism. The electrospun Cu 2 O electrodes delivered high discharge capacity (126 mA h g -1 ) than CuO (72 mA h g -1 ) at a current density of 2.4 mA cm -2 . Electrochemical impedance spectroscopy measurements show almost similar charge-transfer resistance in Cu 2 O (1.2 Ω) and CuO (1.6 Ω); however, Cu 2 O showed an order of magnitude higher ion diffusion. The difference in charge storage between these electrodes is attributed to the difference in surface properties and charge kinetics at the electrode. The electrode also shows superior cyclic stability (98%) and Coulombic efficiency (98%) after 5000 cycles. Therefore, these materials could be acceptable choices as a battery-type or pseudocapacitive electrode in asymmetric supercapacitors.

Where are lengths of stay longer and total charges higher for pediatric burn patients?

PubMed

Myers, John; Lehna, Carlee

2014-01-01

Treatment of pediatric burn patients is costly and may require long length of stay in the hospital (LOS). Establishing where these LOS and charges are highest is warranted. The current study investigated whether pediatric burn patients had higher total charges and longer LOS when seen at teaching hospitals, when compared with nonteaching hospitals. The study reviewed inpatient admissions for pediatric burn patients in 2003, 2006, and 2009 by using the Kids' Inpatient Database, which is part of the Healthcare Cost and Utilization Project. International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes 940-947 were used to define burn injury, LOS, total charges, and type of hospital. The authors tested for differences between the LOS and total charges between children seen at three types of hospitals (pediatric, nonpediatric/teaching, nonpediatric/nonteaching) while adjusting for traditional risk factors (eg age, total burn surface area) by using generalized linear mixed-effects modeling. A total of N=28,777 children had burn injuries (n=16,115, 56.0% seen at pediatric hospitals; n=9353, 32.5% seen at nonpediatric/teaching hospitals; and n=3309, 11.5% seen at nonpediatric/nonteaching hospitals). Pediatric burn patients seen at pediatric hospitals, unadjusted, have significantly longer LOS (5.54 days vs 4.25 days and 4.00 days, P<.001) and more total charges in 2009 dollars ($31,319 vs $24,413 and $21,499, P<.001). In addition, patients seen at pediatric hospitals had significantly more total burn surface area (P<.001), more comorbidities (P=.021), and were younger (P<.001). After adjusting for total burn surface area, number of comorbidities, and age, no differences existed between teaching and nonteaching hospitals for LOS (P=.481) or total charges (P=.758). Although pediatric burn patients may have increased LOS and total charges when seen at teaching hospitals, when taking an unadjusted perspective, this may be an artifact that teaching hospitals see pediatric burn patients who are younger, have more comorbidities, and have more total burn surface area. As such, after adjustment, type of hospital may have no influence on LOS and total charges.

Migration of Carbon Adatoms on the Surface of Charged SWCNT

NASA Astrophysics Data System (ADS)

Han, Longtao; Krstic, Predrag; Kaganovich, Igor

2016-10-01

In volume plasma, the growth of SWCNT from a transition metal catalyst could be enhanced by incoming carbon flux on SWCNT surface, which is generated by the adsorption and migration of carbon adatoms on SWCNT surface. In addition, the nanotube can be charged by the irradiation of plasma particles. How this charging effect will influence the adsorption and migration behavior of carbon atom has not been revealed. Using Density Functional Theory, Nudged Elastic Band and Kinetic Monte Carlo method, we found equilibrium sites, vibrational frequency, adsorption energy, most probable pathways for migration of adatoms, and the barrier sizes along these pathways. The metallic (5,5) SWCNT can support a fast migration of the carbon adatom along a straight path with low barriers, which is further enhanced by the presence of negative charge on SWCNT. The enhancement is contributed by the higher adsorption energy and thence longer lifetime of adatom on the charged SWCNT surface. The lifetime and migration distance of adatom increase by three and two orders of magnitude, respectively, as shown by Kinetic Monte Carlo simulation. These results support the surface migration mechanism of SWCNT growth in plasma environment. This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Material Sciences and Engineering Division.

Charge Storage, Conductivity and Charge Profiles of Insulators as Related to Spacecraft Charging

NASA Technical Reports Server (NTRS)

Dennison, J. R.; Swaminathan, Prasanna; Frederickson, A. R.

2004-01-01

Dissipation of charges built up near the surface of insulators due to space environment interaction is central to understanding spacecraft charging. Conductivity of insulating materials is key to determine how accumulated charge will distribute across the spacecraft and how rapidly charge imbalance will dissipate. To understand these processes requires knowledge of how charge is deposited within the insulator, the mechanisms for charge trapping and charge transport within the insulator, and how the profile of trapped charge affects the transport and emission of charges from insulators. One must consider generation of mobile electrons and holes, their trapping, thermal de-trapping, mobility and recombination. Conductivity is more appropriately measured for spacecraft charging applications as the "decay" of charge deposited on the surface of an insulator, rather than by flow of current across two electrodes around the sample. We have found that conductivity determined from charge storage decay methods is 102 to 104 smaller than values obtained from classical ASTM and IEC methods for a variety of thin film insulating samples. For typical spacecraft charging conditions, classical conductivity predicts decay times on the order of minutes to hours (less than typical orbit periods); however, the higher charge storage conductivities predict decay times on the order of weeks to months leading to accumulation of charge with subsequent orbits. We found experimental evidence that penetration profiles of radiation and light are exceedingly important, and that internal electric fields due to charge profiles and high-field conduction by trapped electrons must be considered for space applications. We have also studied whether the decay constants depend on incident voltage and flux or on internal charge distributions and electric fields; light-activated discharge of surface charge to distinguish among differing charge trapping centers; and radiation-induced conductivity. Our experiments also show that "Malter" electron emission occurs for hours after turning off the electron beam. This Malter emission similar to emission due to negative electron affinity in semiconductors is a result of the prior radiation or optical excitations of valence electrons and their slow drift among traps towards the surface where they are subsequently emitted. This work is supported through funding from the NASA Space Environments and Effects Program.

Influence of solvent species on the charge-discharge characteristics of a natural graphite electrode

NASA Astrophysics Data System (ADS)

Fujimoto, Masahisa; Shoji, Yoshihiro; Kida, Yoshinori; Ohshita, Ryuji; Nohma, Toshiyuki; Nishio, Koji

The charge-discharge characteristics of a natural graphite electrode are examined in a mixed solvent composed of ethylene carbonate (EC) and propylene carbonate (PC). The characteristics are influenced largely by the solvent species. Natural graphite electrode displays good charge-discharge characteristics in an electrolyte containing EC with a high volume fraction. In an electrolyte containing PC, however, the electrode cannot be charged and the solvent is decomposed. X-ray photoelectron spectroscopy is used to obtain information about the surface of natural graphite. A thin LiF layer, the decomposition product of lithium hexafluorophosphate (LiPF 6), is formed on the surface of the natural graphite charged to 0.5 V (vs. Li/Li +) in an electrolyte containing a high volume fraction of EC. On the other hand, LiF and a carbonate compound are formed in the bulk and on the surface of natural graphite when the volume fraction of PC is high. These results suggest that the thin LiF layer, which is produced at a potential higher than 0.5 V (vs. Li/Li +) on the surface of natural graphite, enables the lithium ions to intercalate into the natural graphite without further decomposition of the electrolyte.

Alternative Computational Protocols for Supercharging Protein Surfaces for Reversible Unfolding and Retention of Stability

PubMed Central

Der, Bryan S.; Kluwe, Christien; Miklos, Aleksandr E.; Jacak, Ron; Lyskov, Sergey; Gray, Jeffrey J.; Georgiou, George; Ellington, Andrew D.; Kuhlman, Brian

2013-01-01

Reengineering protein surfaces to exhibit high net charge, referred to as “supercharging”, can improve reversibility of unfolding by preventing aggregation of partially unfolded states. Incorporation of charged side chains should be optimized while considering structural and energetic consequences, as numerous mutations and accumulation of like-charges can also destabilize the native state. A previously demonstrated approach deterministically mutates flexible polar residues (amino acids DERKNQ) with the fewest average neighboring atoms per side chain atom (AvNAPSA). Our approach uses Rosetta-based energy calculations to choose the surface mutations. Both protocols are available for use through the ROSIE web server. The automated Rosetta and AvNAPSA approaches for supercharging choose dissimilar mutations, raising an interesting division in surface charging strategy. Rosetta-supercharged variants of GFP (RscG) ranging from −11 to −61 and +7 to +58 were experimentally tested, and for comparison, we re-tested the previously developed AvNAPSA-supercharged variants of GFP (AscG) with +36 and −30 net charge. Mid-charge variants demonstrated ∼3-fold improvement in refolding with retention of stability. However, as we pushed to higher net charges, expression and soluble yield decreased, indicating that net charge or mutational load may be limiting factors. Interestingly, the two different approaches resulted in GFP variants with similar refolding properties. Our results show that there are multiple sets of residues that can be mutated to successfully supercharge a protein, and combining alternative supercharge protocols with experimental testing can be an effective approach for charge-based improvement to refolding. PMID:23741319

Electrostatic field and charge distribution in small charged dielectric droplets

NASA Astrophysics Data System (ADS)

Storozhev, V. B.

2004-08-01

The charge distribution in small dielectric droplets is calculated on the basis of continuum medium approximation. There are considered charged liquid spherical droplets of methanol in the range of nanometer sizes. The problem is solved by the following way. We find the free energy of some ion in dielectric droplet, which is a function of distribution of other ions in the droplet. The probability of location of the ion in some element of volume in the droplet is a function of its free energy in this element of volume. The same approach can be applied to other ions in the droplet. The obtained charge distribution differs considerably from the surface distribution. The curve of the charge distribution in the droplet as a function of radius has maximum near the surface. Relative concentration of charges in the vicinity of the center of the droplet does not equal to zero, and it is the higher, the less is the total charge of the droplet. According to the estimates the model is applicable if the droplet radius is larger than 10 nm.

On the origin of the halo stabilization.

PubMed

Trulsson, Martin; Jönsson, Bo; Labbez, Christophe

2013-01-14

Monte Carlo simulations show that charge-regulation alone can cause highly charged zirconium nanoparticles to adsorb to a similarly charged or neutral silica particle and thereby stabilizing the latter. This mechanism, referred to as halo stabilization, is quite general and applicable in a range of systems provided that pH, van der Waals forces, and dissociation constants of the charge-regulating particles are properly chosen. In our modeling we see an overall attraction at low volume fractions of nanoparticles, while at higher a repulsive barrier is created, stabilizing the microparticles and protecting them from aggregation. The charge-regulation mechanism also turns the silica surface from positively charged, without nanoparticles, to negatively charged in the presence of nanoparticles.

Facile Synthesis of Ultrafine Hematite Nanowire Arrays in Mixed Water-Ethanol-Acetic Acid Solution for Enhanced Charge Transport and Separation.

PubMed

Wang, Jian; Wang, Menglong; Zhang, Tao; Wang, Zhiqiang; Guo, Penghui; Su, Jinzhan; Guo, Liejin

2018-04-18

Nanostructure engineering is of great significance for semiconductor electrode to achieve high photoelectrochemical performance. Herein, we report a novel strategy to fabricate ultrafine hematite (α-Fe 2 O 3 ) nanowire arrays in a mixed water-ethanol-acetic acid (WEA) solvent. To the best of our knowledge, this is the first report on direct growth of ultrafine (∼10 nm) α-Fe 2 O 3 nanowire arrays on fluorine-doped tin oxide substrates through solution-based fabrication process. The effect of WEA ratio on the morphology of nanowires has been systematically studied to understand the formation mechanism. Photoelectrochemical measurements were conducted on both Ti-treated α-Fe 2 O 3 nanowire and nanorod photoelectrodes. It reveals that α-Fe 2 O 3 nanowire electrode has higher photocurrent and charge separation efficiencies than nanorod electrode if the carrier concentration and space-charge carrier width are in the same order of magnitude. Normalized by electrochemically active surface area, the Ti-treated α-Fe 2 O 3 nanowire electrode obtains 6.4 times higher specific photocurrent density than nanorod electrode. This superiority of nanowires arises from the higher bulk and surface charge separation efficiencies, which could be partly attributed to reduced distance that holes must transfer to reach the semiconductor-liquid junction.

Three-dimensional charge coupled device

DOEpatents

Conder, Alan D.; Young, Bruce K. F.

1999-01-01

A monolithic three dimensional charged coupled device (3D-CCD) which utilizes the entire bulk of the semiconductor for charge generation, storage, and transfer. The 3D-CCD provides a vast improvement of current CCD architectures that use only the surface of the semiconductor substrate. The 3D-CCD is capable of developing a strong E-field throughout the depth of the semiconductor by using deep (buried) parallel (bulk) electrodes in the substrate material. Using backside illumination, the 3D-CCD architecture enables a single device to image photon energies from the visible, to the ultra-violet and soft x-ray, and out to higher energy x-rays of 30 keV and beyond. The buried or bulk electrodes are electrically connected to the surface electrodes, and an E-field parallel to the surface is established with the pixel in which the bulk electrodes are located. This E-field attracts charge to the bulk electrodes independent of depth and confines it within the pixel in which it is generated. Charge diffusion is greatly reduced because the E-field is strong due to the proximity of the bulk electrodes.

Process for fabricating a charge coupled device

DOEpatents

Conder, Alan D.; Young, Bruce K. F.

2002-01-01

A monolithic three dimensional charged coupled device (3D-CCD) which utilizes the entire bulk of the semiconductor for charge generation, storage, and transfer. The 3D-CCD provides a vast improvement of current CCD architectures that use only the surface of the semiconductor substrate. The 3D-CCD is capable of developing a strong E-field throughout the depth of the semiconductor by using deep (buried) parallel (bulk) electrodes in the substrate material. Using backside illumination, the 3D-CCD architecture enables a single device to image photon energies from the visible, to the ultra-violet and soft x-ray, and out to higher energy x-rays of 30 keV and beyond. The buried or bulk electrodes are electrically connected to the surface electrodes, and an E-field parallel to the surface is established with the pixel in which the bulk electrodes are located. This E-field attracts charge to the bulk electrodes independent of depth and confines it within the pixel in which it is generated. Charge diffusion is greatly reduced because the E-field is strong due to the proximity of the bulk electrodes.

Polar surface energies of iono-covalent materials: implications of a charge-transfer model tested on Li2FeSiO4 surfaces.

PubMed

Hörmann, Nicolas G; Groß, Axel

2014-07-21

The ionic compounds that are used as electrode materials in Li-based rechargeable batteries can exhibit polar surfaces that in general have high surface energies. We derive an analytical estimate for the surface energy of such polar surfaces assuming charge redistribution as a polarity compensating mechanism. The polar contribution to the converged surface energy is found to be proportional to the bandgap multiplied by the surface charge necessary to compensate for the depolarization field, and some higher order correction terms that depend on the specific surface. Other features, such as convergence behavior, coincide with published results. General conclusions are drawn on how to perform polar surface energy calculations in a slab configuration and upper boundaries of "purely" polar surface energies are estimated. Furthermore, we compare these findings with results obtained in a density functional theory study of Li(2)FeSiO(4) surfaces. We show that typical polar features are observed and provide a decomposition of surface energies into polar and local bond-cutting contributions for 29 different surfaces. We show that the model is able to explain subtle differences of GGA and GGA+U surface energy calculations. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effect of softening precipitate composition and surface characteristics on natural organic matter adsorption.

PubMed

Russell, Caroline G; Lawler, Desmond F; Speitel, Gerald E; Katz, Lynn E

2009-10-15

Natural organic matter (NOM) removal during water softening is thought to occur through adsorption onto or coprecipitation with calcium and magnesium solids. However, details of precipitate composition and surface chemistry and subsequent interactions with NOM are relatively unknown. In this study, zeta potentiometry analyses of precipitates formed from inorganic solutions under varying conditions (e.g., Ca-only, Mg-only, Ca + Mg, increasing lime or NaOH dose) indicated that both CaCO3 and Mg(OH)2 were positively charged at higher lime (Ca(OH)2) and NaOH doses (associated with pH values above 11.5), potentially yielding a greater affinity for adsorbing negatively charged organic molecules. Environmental scanning electron microscopy (ESEM) images of CaCO3 solids illustrated the rhombohedral shape characteristic of calcite. In the presence of increasing concentrations of magnesium, the CaCO3 rhombs shifted to more elongated crystals. The CaCO3 solids also exhibited increasingly positive surface charge from Mg incorporation into the crystal lattice, potentially creating more favorable conditions for adsorption of organic matter. NOM adsorption experiments using humic substances extracted from Lake Austin and Missouri River water elucidated the role of surface charge and surface area on adsorption.

Tribo-electric charging of dielectric solids of identical composition

NASA Astrophysics Data System (ADS)

Angus, John C.; Greber, Isaac

2018-05-01

Despite its long history and importance in many areas of science and technology, there is no agreement on the mechanisms responsible for tribo-electric charging, including especially the tribo-charging of chemically identical dielectric solids. Modeling of the excitation, diffusional transport, and de-excitation of electrons from hot spots shows that a difference in local surface roughness of otherwise identical solid dielectric objects leads to different transient excited electron concentrations during tribo-processes. The model predicts that excited electron concentrations are lower and concentration gradients higher in solids with rougher rather than smoother surfaces. Consequently, during contact, the flux of charge carriers (electrons or holes) from hot spots will be greater into the rougher solid than into the smoother solid. These predictions are in agreement with current and historical observations of tribo-electric charge transfer between solids of the same composition. This effect can take place in parallel with other processes and may also play a role in the charging of solids of different composition.

The role of electrostatic interactions in protease surface diffusion and the consequence for interfacial biocatalysis.

PubMed

Feller, Bob E; Kellis, James T; Cascão-Pereira, Luis G; Robertson, Channing R; Frank, Curtis W

2010-12-21

This study examines the influence of electrostatic interactions on enzyme surface diffusion and the contribution of diffusion to interfacial biocatalysis. Surface diffusion, adsorption, and reaction were investigated on an immobilized bovine serum albumin (BSA) multilayer substrate over a range of solution ionic strength values. Interfacial charge of the enzyme and substrate surface was maintained by performing the measurements at a fixed pH; therefore, electrostatic interactions were manipulated by changing the ionic strength. The interfacial processes were investigated using a combination of techniques: fluorescence recovery after photobleaching, surface plasmon resonance, and surface plasmon fluorescence spectroscopy. We used an enzyme charge ladder with a net charge ranging from -2 to +4 with respect to the parent to systematically probe the contribution of electrostatics in interfacial enzyme biocatalysis on a charged substrate. The correlation between reaction rate and adsorption was determined for each charge variant within the ladder, each of which displayed a maximum rate at an intermediate surface concentration. Both the maximum reaction rate and adsorption value at which this maximum rate occurs increased in magnitude for the more positive variants. In addition, the specific enzyme activity increased as the level of adsorption decreased, and for the lowest adsorption values, the specific enzyme activity was enhanced compared to the trend at higher surface concentrations. At a fixed level of adsorption, the specific enzyme activity increased with positive enzyme charge; however, this effect offers diminishing returns as the enzyme becomes more highly charged. We examined the effect of electrostatic interactions on surface diffusion. As the binding affinity was reduced by increasing the solution ionic strength, thus weakening electrostatic interaction, the rate of surface diffusion increased considerably. The enhancement in specific activity achieved at the lowest adsorption values is explained by the substantial rise in surface diffusion at high ionic strength due to decreased interactions with the surface. Overall, knowledge of the electrostatic interactions can be used to control surface parameters such as surface concentration and surface diffusion, which intimately correlate with surface biocatalysis. We propose that the maximum reaction rate results from a balance between adsorption and surface diffusion. The above finding suggests enzyme engineering and process design strategies for improving interfacial biocatalysis in industrial, pharmaceutical, and food applications.

Stripe-like Clay Nanotubes Patterns in Glass Capillary Tubes for Capture of Tumor Cells.

PubMed

Liu, Mingxian; He, Rui; Yang, Jing; Zhao, Wei; Zhou, Changren

2016-03-01

Here, we used capillary tubes to evaporate an aqueous dispersion of halloysite nanotubes (HNTs) in a controlled manner to prepare a patterned surface with ordered alignment of the nanotubes . Sodium polystyrenesulfonate (PSS) was added to improve the surface charges of the tubes. An increased negative charge of HNTs is realized by PSS coating (from -26.1 mV to -52.2 mV). When the HNTs aqueous dispersion concentration is higher than 10%, liquid crystal phenomenon of the dispersion is found. A typical shear flow behavior and decreased viscosity upon shear is found when HNTs dispersions with concentrations higher than 10%. Upon drying the HNTs aqueous dispersion in capillary tubes, a regular pattern is formed in the wall of the tube. The width and spacing of the bands increase with HNTs dispersion concentration and decrease with the drying temperature for a given initial concentration. Morphology results show that an ordered alignment of HNTs is found especially for the sample of 10%. The patterned surface can be used as a model for preparing PDMS molding with regular micro-/nanostructure. Also, the HNTs rough surfaces can provide much higher tumor cell capture efficiency compared to blank glass surfaces. The HNTs ordered surfaces provide promising application for biomedical areas such as biosensors.

Adsorption of benzene, toluene, and xylene by two tetramethylammonium-smectites having different charge densities

USGS Publications Warehouse

Lee, Jiunn-Fwu; Mortland, Max M.; Chiou, Cary T.; Kite, Daniel E.; Boyd, Stephen A.

1990-01-01

A high-charge smectite from Arizona [cation-exchange capacity (CEC) = 120 meq/100 g] and a low-charge smectite from Wyoming (CEC = 90 meq/100 g) were used to prepare homoionic tetramethylammonium (TMA)-clay complexes. The adsorption of benzene, toluene, and o-xylene as vapors by the dry TMA-clays and as solutes from water by the wet TMA-clays was studied. The adsorption of the organic vapors by the dry TMA-smectite samples was strong and apparently consisted of interactions with both the aluminosilicate mineral surfaces and the TMA exchange ions in the interlayers. In the adsorption of organic vapors, the closer packing of TMA ions in the dry high-charge TMA-smectite, compared with the dry low-charge TMA-smectite, resulted in a somewhat higher degree of shape-selective adsorption of benzene, toluene, and xylene. In the presence of water, the adsorption capacities of both samples for the aromatic compounds were significantly reduced, although the uptake of benzene from water by the low-charge TMA-smectite was still substantial. This lower sorption capacity was accompanied by increased shape-selectivity for the aromatic compounds. The reduction in uptake and increased selectivity was much more pronounced for the water-saturated, high-charge TMA-smectite than for the low-charge TMA-smectite. Hydration of the TMA exchange ions and/or the mineral surfaces apparently reduced the accessibility of the aromatic molecules to interlamellar regions. The resulting water-induced sieving effect was greater for the high-charge TMA-smectite due to the higher density of exchanged TMA-ions. The low-charge Wyoming TMA-smectite was a highly effective adsorbent for removing benzene from water and may be useful for purifying benzene-contaminated water.

Nano-Ni induced surface modification relevant to the hydrogenation performances in La-Mg based alloys

NASA Astrophysics Data System (ADS)

Zhang, Huaiwei; Fu, Li; Xuan, Weidong; Li, Xingguo

2018-05-01

Nano-Ni drived modification in LaMg3/Ni composite is investigated. The new phases of LaMg2 and MgNi2 can be formed on the sample surface during the milling process. There is almost no electric charge transfer process between Ni and La element through XPS analyses. The amorphization structure can be found on the alloy surface with the increasing of reaction duration, and the capacity and cycle stability are also greatly promoted. On the other hand, the milled alloys show the lower charge transfer resistance, better anti-corrosion ability and higher oxidation current density.

Charging and exciton-mediated decharging of metal nanoparticles in organic semiconductor matrices

NASA Astrophysics Data System (ADS)

Ligorio, Giovanni; Vittorio Nardi, Marco; Christodoulou, Christos; Florea, Ileana; Monteiro, Nicolas-Crespo; Ersen, Ovidiu; Brinkmann, Martin; Koch, Norbert

2014-04-01

Gold nanoparticles (Au-NPs) were deposited on the surface of n- and p-type organic semiconductors to form defined model systems for charge storage based electrically addressable memory elements. We used ultraviolet photoelectron spectroscopy to study the electronic properties and found that the Au-NPs become positively charged because of photoelectron emission, evidenced by spectral shifts to higher binding energy. Upon illumination with light that can be absorbed by the organic semiconductors, dynamic charge neutrality of the Au-NPs could be re-established through electron transfer from excitons. The light-controlled charge state of the Au-NPs could add optical addressability to memory elements.

First-Principles Study of MoO3/Graphene Composite as Cathode Material for High-Performance Lithium-Ion Batteries

NASA Astrophysics Data System (ADS)

Cui, Yanhua; Zhao, Yu; Chen, Hong; Wei, Kaiyuan; Ni, Shuang; Cui, Yixiu; Shi, Siqi

2018-03-01

Using first-principles calculations, we have systematically investigated the adsorption and diffusion behavior of Li in MoO3 bulk, on MoO3 (010) surface and in MoO3/graphene composite. Our results indicate that, in case of MoO3 bulk, Li diffusion barriers in the interlayer and intralayer spaces are 0.55 eV and 0.58 eV respectively, which are too high to warrant fast Lithium-ion charge/discharge processes. While on MoO3 (010) surface, Li exhibits a diffusion barrier as low as 0.07 eV which guarantees an extremely fast Li diffusion rate during charge/discharge cycling. However, in MoO3/graphene monolayer, Li diffusion barrier is at the same level as that on MoO3 (010) surface, which also ensures a very rapid Li charge/discharge rate. The rapid Li charge/discharge rate in this system originates from the removal of the upper dangling O1 atoms which hinder the Li diffusion on the lower MoO3 layer. Besides this, due to the interaction between Li and graphene, the Li average binding energy increases to 0.14 eV compared to its value on MoO3 (010) surface which contributes to a higher voltage. Additionally, the increased ratio of surface area provides more space for Li storage and the capacity of MoO3/graphene composite increases up to 279.2 mAhg-1. The last but not the least, due to the high conductivity of graphene, the conductivity of MoO3/graphene composite enhances greatly which is beneficial for electrode materials. In the light of present results, MoO3/graphene composite exhibits higher voltage, good conductivity, large Li capacity and very rapid Li charge/discharge rate, which prove it as a promising cathode material for high-performance lithium-ion batteries (LIBs).

2D Thermoluminescence imaging of dielectric surface long term charge memory of plasma surface interaction in DBD discharges

NASA Astrophysics Data System (ADS)

Ambrico, Paolo F.; Ambrico, Marianna; Schiavulli, Luigi; De Benedictis, Santolo

2014-07-01

The charge trapping effect due to the exposure of alumina surfaces to plasma has been studied in a volume dielectric barrier discharge (DBD) in Ar and He noble gases. The long lasting charge trapping of alumina dielectric plates, used as barriers in DBDs, is evidenced by an ex situ thermoluminescence (TL) experiment performed with a standard and a custom two-dimensional (2D)-TL apparatus. The spatial density of trapped surface charges is found to be strongly correlated to the plasma morphology, and the surface spatial memory lasted for several minutes to hours after plasma exposure. In the case of Ar, the plasma channel impact signature on the surface shows a higher equivalent radiation dose with respect to the surface plasma wave and the post-discharge species signature. As a consequence, for the development of discharges, inside the dielectric surface the availability of lower energy trapped electrons is larger in the first region of plasma impact. The reported spatial memory increases the likelihood of the occurrence of plasma filaments in the same position in different runs. In He plasmas, the dielectric barrier shows an almost uniform distribution of trapped charges, meaning that there is no preferred region for the development of the discharge. In all cases a slight asymmetry was shown in the direction of the gas flow. This can be interpreted as being due to the long-living species moving in the direction of the gas flow, corresponding with the TL side experiment on the sample exposed to the plasma afterglow. The maximum values and the integral of the 2D-TL images showed a linear relation with the total charge per ac cycle, corresponding with findings for the TL glow curve. In conclusion, 2D-TL images allow the retrieval of information regarding the plasma surface interaction such as the plasma morphology, trap sites and their activation temperature.

Lunar dust charging by photoelectric emissions

NASA Astrophysics Data System (ADS)

Abbas, M. M.; Tankosic, D.; Craven, P. D.; Spann, J. F.; LeClair, A.; West, E. A.

2007-05-01

The lunar surface is covered with a thick layer of sub-micron/micron size dust grains formed by meteoritic impact over billions of years. The fine dust grains are levitated and transported on the lunar surface, as indicated by the transient dust clouds observed over the lunar horizon during the Apollo 17 mission. Theoretical models suggest that the dust grains on the lunar surface are charged by the solar ultraviolet (UV) radiation as well as the solar wind. Even without any physical activity, the dust grains are levitated by electrostatic fields and transported away from the surface in the near vacuum environment of the Moon. The current dust charging and levitation models, however, do not fully explain the observed phenomena. Since the abundance of dust on the Moon's surface with its observed adhesive characteristics has the potential of severe impact on human habitat and operations and lifetime of a variety of equipment, it is necessary to investigate the charging properties and the lunar dust phenomena in order to develop appropriate mitigating strategies. Photoelectric emission induced by the solar UV radiation with photon energies higher than the work function (WF) of the grain materials is recognized to be the dominant process for charging of the lunar dust, and requires measurements of the photoelectric yields to determine the charging and equilibrium potentials of individual dust grains. In this paper, we present the first laboratory measurements of the photoelectric efficiencies and yields of individual sub-micron/micron size dust grains selected from sample returns of Apollo 17 and Luna-24 missions as well as similar size dust grains from the JSC-1 simulants. The measurements were made on a laboratory facility based on an electrodynamic balance that permits a variety of experiments to be conducted on individual sub-micron/micron size dust grains in simulated space environments. The photoelectric emission measurements indicate grain size dependence with the yield increasing by an order of magnitude for grains of sub-micron to several micron size radii, at which it reaches asymptotic values. The yield for large size grains is found to be more than an order of magnitude higher than the bulk measurements on lunar fines reported in the literature.

Lunar Dust Charging by Photoelectric Emissions

NASA Technical Reports Server (NTRS)

Abbas, M. M.; Tankosic, D.; Craven, P. D.; Spann, J. F.; LeClair, A.; West, E. A.

2007-01-01

The lunar surface is covered with a thick layer of sub-micron/micron size dust grains formed by meteoritic impact over billions of years. The fine dust grains are levitated and transported on the lunar surface, as indicated by the transient dust clouds observed over the lunar horizon during the Apollo 17 mission. Theoretical models suggest that the dust grains on the lunar surface are charged by the solar ultraviolet (UV) radiation as well as the solar wind. Even without any physical activity, the dust grains are levitated by electrostatic fields and transported away from the surface in the near vacuum environment of the Moon. The current dust charging and levitation models, however, do not fully explain the observed phenomena. Since the abundance of dust on the Moon's surface with its observed adhesive characteristics has the potential of severe impact on human habitat and operations and lifetime of a variety of equipment, it is necessary to investigate the charging properties and the lunar dust phenomena in order to develop appropriate mitigating strategies. Photoelectric emission induced by the solar UV radiation with photon energies higher than the work function (WF) of the grain materials is recognized to be the dominant process for charging of the lunar dust, and requires measurements of the photoelectric yields to determine the charging and equilibrium potentials of individual dust grains. In this paper, we present the first laboratory measurements of the photoelectric efficiencies and yields of individual sub-micron/micron size dust grains selected from sample returns of Apollo 17 and Luna-24 missions as well as similar size dust grains from the JSC-1 simulants. The measurements were made on a laboratory facility based on an electrodynamic balance that permits a variety of experiments to be conducted on individual sub-micron/micron size dust grains in simulated space environments. The photoelectric emission measurements indicate grain size dependence with the yield increasing by an order of magnitude for grains of sub-micron to several micron size radii, at which it reaches asymptotic values. The yield for large size grains is found to be more than an order of magnitude higher than the bulk measurements on lunar fines reported in the literature.

Lunar Dust Charging by Photoelectric Emissions

NASA Technical Reports Server (NTRS)

Abbas, M. M.; Tankosic, D.; Craven, P. D.; Spann, J. F.; LeClair, A.; West, E. A.

2007-01-01

The lunar surface is covered with a thick layer of sub-micron/micron size dust grains formed by meteoritic impact over billions of years. The fine dust grains are levitated and transported on the lunar surface, as indicated by the transient dust clouds observed over the lunar horizon during the Apollo 17 mission. Theoretical models suggest that the dust grains on the lunar surface are charged by the solar UV radiation as well as the solar wind. Even without any physical activity, the dust grains are levitated by electrostatic fields and transported away from the surface in the near vacuum environment of the Moon. The current dust charging and levitation models, however, do not fully explain the observed phenomena. Since the abundance of dust on the Moon s surface with its observed adhesive characteristics has the potential of severe impact on human habitat and operations and lifetime of a variety of equipment, it is necessary to investigate the charging properties and the lunar dust phenomena in order to develop appropriate mitigating strategies. Photoelectric emission induced by the solar UV radiation with photon energies higher than the work function of the grain materials is recognized to be the dominant process for charging of the lunar dust, and requires measurements of the photoelectric yields to determine the charging and equilibrium potentials of individual dust grains. In this paper, we present the first laboratory measurements of the photoelectric efficiencies and yields of individual sub-micron/micron size dust grains selected from sample returns of Apollo 17, and Luna 24 missions, as well as similar size dust grains from the JSC-1 simulants. The measurements were made on a laboratory facility based on an electrodynamic balance that permits a variety of experiments to be conducted on individual sub-micron/micron size dust grains in simulated space environments. The photoelectric emission measurements indicate grain size dependence with the yield increasing by an order of magnitude for grains of sub-micron to several micron size radii, at which it reaches asymptotic values. The yield for large size grains is found to be more than an order of magnitude higher than the bulk measurements on lunar fines reported in the literature.

Electrolyte effects in a model of proton discharge on charged electrodes

NASA Astrophysics Data System (ADS)

Wiebe, Johannes; Kravchenko, Kateryna; Spohr, Eckhard

2015-01-01

We report results on the influence of NaCl electrolyte dissolved in water on proton discharge reactions from aqueous solution to charged platinum electrodes. We have extended a recently developed combined proton transfer/proton discharge model on the basis of empirical valence bond theory to include NaCl solutions with several different concentrations of cations and anions, both stoichiometric (1:1) compositions and non-stoichiometric ones with an excess of cations. The latter solutions partially screen the electrostatic potential from the surface charge of the negatively charged electrode. 500-1000 trajectories of a discharging proton were integrated by molecular dynamics simulations until discharge occurred, or for at most 1.5 ns. The results show a strong dependence on ionic strength, but only a weak dependence on the screening behavior, when comparing stoichiometric and non-stoichiometric solutions. Overall, the Na+ cations exert a more dominant effect on the discharge reaction, which we argue is likely due to the very rigid arrangements of the cations on the negatively polarized electrode surface. Thus, our model predicts, for the given and very high negative surface charge densities, the fastest discharge reaction for pure water, but obviously cannot take into account the fact that such high charge densities are even more out of reach experimentally than for higher electrolyte concentrations.

Osteoinduction on Acid and Heat Treated Porous Ti Metal Samples in Canine Muscle

PubMed Central

Kawai, Toshiyuki; Takemoto, Mitsuru; Fujibayashi, Shunsuke; Akiyama, Haruhiko; Tanaka, Masashi; Yamaguchi, Seiji; Pattanayak, Deepak K.; Doi, Kenji; Matsushita, Tomiharu; Nakamura, Takashi; Kokubo, Tadashi; Matsuda, Shuichi

2014-01-01

Samples of porous Ti metal were subjected to different acid and heat treatments. Ectopic bone formation on specimens embedded in dog muscle was compared with the surface characteristics of the specimen. Treatment of the specimens by H2SO4/HCl and heating at 600°C produced micrometer-scale roughness with surface layers composed of rutile phase of titanium dioxide. The acid- and heat-treated specimens induced ectopic bone formation within 6 months of implantation. A specimen treated using NaOH followed by HCl acid and then heat treatment produced nanometer-scale surface roughness with a surface layer composed of both rutile and anatase phases of titanium dioxide. These specimens also induced bone formation after 6 months of implantation. Both these specimens featured positive surface charge and good apatite-forming abilities in a simulated body fluid. The amount of the bone induced in the porous structure increased with apatite-forming ability and higher positive surface charge. Untreated porous Ti metal samples showed no bone formation even after 12 months. Specimens that were only heat treated featured a smooth surface composed of rutile. A mixed acid treatment produced specimens with micrometer-scale rough surfaces composed of titanium hydride. Both of them also showed no bone formation after 12 months. The specimens that showed no bone formation also featured almost zero surface charge and no apatite-forming ability. These results indicate that osteoinduction of these porous Ti metal samples is directly related to positive surface charge that facilitates formation of apatite on the metal surfaces in vitro. PMID:24520375

Numerical simulation of electroosmotic flow in rough microchannels using the lattice Poisson-Nernst-Planck methods

NASA Astrophysics Data System (ADS)

Kamali, Reza; Soloklou, Mohsen Nasiri; Hadidi, Hooman

2018-05-01

In this study, coupled Lattice Boltzmann method is applied to solve the dynamic model for an electroosmotic flow and investigate the effects of roughness in a 2-D flat microchannel. In the present model, the Poisson equation is solved for the electrical potential, the Nernst- Planck equation is solved for the ion concentration. In the analysis of electroosmotic flows, when the electric double layers fully overlap or the convective effects are not negligible, the Nernst-Planck equation must be used to find the ionic distribution throughout the microchannel. The effects of surface roughness height, roughness interval spacing and roughness surface potential on flow conditions are investigated for two different configurations of the roughness, when the EDL layers fully overlap through the microchannel. The results show that in both arrangements of roughness in homogeneously charged rough channels, the flow rate decreases by increasing the roughness height. A discrepancy in the mass flow rate is observed when the roughness height is about 0.15 of the channel width, which its average is higher for the asymmetric configuration and this difference grows by increasing the roughness height. In the symmetric roughness arrangement, the mass flow rate increases until the roughness interval space is almost 1.5 times the roughness width and it decreases for higher values of the roughness interval space. For the heterogeneously charged rough channel, when the roughness surface potential ψr is less than channel surface potential ψs , the net charge density increases by getting far from the roughness surface, while in the opposite situation, when ψs is more than ψr , the net charge density decreases from roughness surface to the microchannel middle center. Increasing the roughness surface potential induces stronger electric driving force on the fluid which results in larger velocities in the flow.

Polarization of gold in nanopores leads to ion current rectification

DOE PAGES

Yang, Crystal; Hinkle, Preston; Menestrina, Justin; ...

2016-10-03

Biomimetic nanopores with rectifying properties are relevant components of ionic switches, ionic circuits, and biological sensors. Rectification indicates that currents for voltages of one polarity are higher than currents for voltages of the opposite polarity. Ion current rectification requires the presence of surface charges on the pore walls, achieved either by the attachment of charged groups or in multielectrode systems by applying voltage to integrated gate electrodes. Here we present a simpler concept for introducing surface charges via polarization of a thin layer of Au present at one entrance of a silicon nitride nanopore. In an electric field applied bymore » two electrodes placed in bulk solution on both sides of the membrane, the Au layer polarizes such that excess positive charge locally concentrates at one end and negative charge concentrates at the other end. Consequently, a junction is formed between zones with enhanced anion and cation concentrations in the solution adjacent to the Au layer. This bipolar double layer together with enhanced cation concentration in a negatively charged silicon nitride nanopore leads to voltage-controlled surface-charge patterns and ion current rectification. The experimental findings are supported by numerical modeling that confirm modulation of ionic concentrations by the Au layer and ion current rectification even in low-aspect ratio nanopores. Lastly, our findings enable a new strategy for creating ionic circuits with diodes and transistors.« less

Protein Corona Composition of Superparamagnetic Iron Oxide Nanoparticles with Various Physico-Chemical Properties and Coatings

NASA Astrophysics Data System (ADS)

Sakulkhu, Usawadee; Mahmoudi, Morteza; Maurizi, Lionel; Salaklang, Jatuporn; Hofmann, Heinrich

2014-05-01

Because of their biocompatibility and unique magnetic properties, superparamagnetic iron oxide nanoparticles NPs (SPIONs) are recognized as some of the most prominent agents for theranostic applications. Thus, understanding the interaction of SPIONs with biological systems is important for their safe design and efficient applications. In this study, SPIONs were coated with 2 different polymers: polyvinyl alcohol polymer (PVA) and dextran. The obtained NPs with different surface charges (positive, neutral, and negative) were used as a model study of the effect of surface charges and surface polymer materials on protein adsorption using a magnetic separator. We found that the PVA-coated SPIONs with negative and neutral surface charge adsorbed more serum proteins than the dextran-coated SPIONs, which resulted in higher blood circulation time for PVA-coated NPs than the dextran-coated ones. Highly abundant proteins such as serum albumin, serotransferrin, prothrombin, alpha-fetoprotein, and kininogen-1 were commonly found on both PVA- and dextran-coated SPIONs. By increasing the ionic strength, soft- and hard-corona proteins were observed on 3 types of PVA-SPIONs. However, the tightly bound proteins were observed only on negatively charged PVA-coated SPIONs after the strong protein elution.

Molecular layers of ZnPc and FePc on Au(111) surface: Charge transfer and chemical interaction

NASA Astrophysics Data System (ADS)

Ahmadi, Sareh; Shariati, M. Nina; Yu, Shun; Göthelid, Mats

2012-08-01

We have studied zinc phthalocyanine (ZnPc) and iron phthalocyanine (FePc) thick films and monolayers on Au(111) using photoelectron spectroscopy and x-ray absorption spectroscopy. Both molecules are adsorbed flat on the surface at monolayer. ZnPc keeps this orientation in all investigated coverages, whereas FePc molecules stand up in the thick film. The stronger inter-molecular interaction of FePc molecules leads to change of orientation, as well as higher conductivity in FePc layer in comparison with ZnPc, which is reflected in thickness-dependent differences in core-level shifts. Work function changes indicate that both molecules donate charge to Au; through the π-system. However, the Fe3d derived lowest unoccupied molecular orbital receives charge from the substrate when forming an interface state at the Fermi level. Thus, the central atom plays an important role in mediating the charge, but the charge transfer as a whole is a balance between the two different charge transfer channels; π-system and the central atom.

Penetration and release studies of positively and negatively charged nanoemulsions--is there a benefit of the positive charge?

PubMed

Baspinar, Yücel; Borchert, Hans-Hubert

2012-07-01

The surface of all tissues, including the stratum corneum, carries a negative charge. Following that fact it is assumed that a positively charged topical formulation could lead to an enhanced penetration because of an increased interaction with the negative charge of the membrane. The intention of this study is to prove an enhanced penetration of a positively charged nanoemulsion compared to a negatively charged nanoemulsion, both containing prednicarbate. The release and penetration of these nanoemulsions, produced with the high pressure homogenization method, were investigated. Regarding these results reveals that the release of the negatively charged formulation is higher compared to the positively charged nanoemulsion, while the penetration of the positively charged nanoemulsion is enhanced compared to the negatively charged formulation. The results of the investigated positively charged nanoemulsion containing prednicarbate show that its topical use could be advantageous for the therapy of atopic dermatitis, especially regarding phytosphingosine, which was responsible for the positive charge. Copyright © 2012 Elsevier B.V. All rights reserved.

The impacts of surface polarity on the solubility of nanoparticle

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

Zhu, Jianzhuo; Su, Jiguo, E-mail: jiguosu@ysu.edu.cn; Ou, Xinwen

In order to study the dependence of water solubility and hydration behavior of nanoparticles on their surface polarity, we designed polar nanoparticles with varying surface polarity by assigning atomic partial charge to the surface of C60. The water solubility of the nanoparticle is enhanced by several orders of magnitude after the introduction of surface polarity. Nevertheless, when the atomic partial charge grows beyond a certain value (q{sub M}), the solubility continuously decreases to the level of nonpolar nanoparticle. It should be noted that such q{sub M} is comparable with atomic partial charge of a variety of functional groups. The hydrationmore » behaviors of nanoparticles were then studied to investigate the non-monotonic dependence of solubility on the surface polarity. The interaction between the polar nanoparticle and the hydration water is stronger than the nonpolar counterpart, which should facilitate the dissolution of the nanoparticles. On the other hand, the surface polarity also reduces the interaction of hydration water with the other water molecules and enhances the interaction between the nanoparticles which may hinder their dispersion. Besides, the introduction of surface polarity disturbs and even rearranges the hydration structure of nonpolar nanoparticle. Interestingly, the polar nanoparticle with less ordered hydration structure tends to have higher water solubility.« less

Secondary Electron Emission From Solar Cell Coverslides And Its Effect On Absolute Vehicle Charging

NASA Astrophysics Data System (ADS)

Ferguson, Dale C.

2011-10-01

It has often been stated that earthed conductive solar cell coverslides are the best way to prevent electrostatic discharges on space solar arrays in GEO. While it is true that such coverslides will prevent differential charging on the solar arrays, it will be shown through NASCAP- 2k simulations that the secondary electron emission of such coverslides is very important for absolute vehicle charging. In particular, carbon nanotube coatings, due to the extremely low secondary electron emission from carbon, may exacerbate absolute vehicle charging. However, if they are earthed, because of their conductivity they may minimize differential charging and the possibility of arcing elsewhere on the spacecraft. Such results may also be true for insulative coverslides if spacecraft thermal blankets are made of materials with high secondary electron emission. Finally, photoemission from coverslides is investigated, with regard to anti-reflection coatings. Surfaces which reflect UV can have low photoemission, while those that absorb may have higher photoemission rates. Thus, anti-reflection coatings may lead to higher absolute spacecraft charging rates. NASCAP-2k simulations will be used to investigate these dependences for realistic spacecraft.

Probing protein orientation near charged nanosurfaces for simulation-assisted biosensor design.

PubMed

Cooper, Christopher D; Clementi, Natalia C; Barba, Lorena A

2015-09-28

Protein-surface interactions are ubiquitous in biological processes and bioengineering, yet are not fully understood. In biosensors, a key factor determining the sensitivity and thus the performance of the device is the orientation of the ligand molecules on the bioactive device surface. Adsorption studies thus seek to determine how orientation can be influenced by surface preparation, varying surface charge, and ambient salt concentration. In this work, protein orientation near charged nanosurfaces is obtained under electrostatic effects using the Poisson-Boltzmann equation, in an implicit-solvent model. Sampling the free energy for protein G B1 D4' at a range of tilt and rotation angles with respect to the charged surface, we calculated the probability of the protein orientations and observed a dipolar behavior. This result is consistent with published experimental studies and combined Monte Carlo and molecular dynamics simulations using this small protein, validating our method. More relevant to biosensor technology, antibodies such as immunoglobulin G are still a formidable challenge to molecular simulation, due to their large size. With the Poisson-Boltzmann model, we obtained the probability distribution of orientations for the iso-type IgG2a at varying surface charge and salt concentration. This iso-type was not found to have a preferred orientation in previous studies, unlike the iso-type IgG1 whose larger dipole moment was assumed to make it easier to control. Our results show that the preferred orientation of IgG2a can be favorable for biosensing with positive charge on the surface of 0.05 C/m(2) or higher and 37 mM salt concentration. The results also show that local interactions dominate over dipole moment for this protein. Improving immunoassay sensitivity may thus be assisted by numerical studies using our method (and open-source code), guiding changes to fabrication protocols or protein engineering of ligand molecules to obtain more favorable orientations.

Probing protein orientation near charged nanosurfaces for simulation-assisted biosensor design

NASA Astrophysics Data System (ADS)

Cooper, Christopher D.; Clementi, Natalia C.; Barba, Lorena A.

2015-09-01

Protein-surface interactions are ubiquitous in biological processes and bioengineering, yet are not fully understood. In biosensors, a key factor determining the sensitivity and thus the performance of the device is the orientation of the ligand molecules on the bioactive device surface. Adsorption studies thus seek to determine how orientation can be influenced by surface preparation, varying surface charge, and ambient salt concentration. In this work, protein orientation near charged nanosurfaces is obtained under electrostatic effects using the Poisson-Boltzmann equation, in an implicit-solvent model. Sampling the free energy for protein G B1 D4' at a range of tilt and rotation angles with respect to the charged surface, we calculated the probability of the protein orientations and observed a dipolar behavior. This result is consistent with published experimental studies and combined Monte Carlo and molecular dynamics simulations using this small protein, validating our method. More relevant to biosensor technology, antibodies such as immunoglobulin G are still a formidable challenge to molecular simulation, due to their large size. With the Poisson-Boltzmann model, we obtained the probability distribution of orientations for the iso-type IgG2a at varying surface charge and salt concentration. This iso-type was not found to have a preferred orientation in previous studies, unlike the iso-type IgG1 whose larger dipole moment was assumed to make it easier to control. Our results show that the preferred orientation of IgG2a can be favorable for biosensing with positive charge on the surface of 0.05 C/m2 or higher and 37 mM salt concentration. The results also show that local interactions dominate over dipole moment for this protein. Improving immunoassay sensitivity may thus be assisted by numerical studies using our method (and open-source code), guiding changes to fabrication protocols or protein engineering of ligand molecules to obtain more favorable orientations.

Methodology and Data Sources for Assessing Extreme Charging Events within the Earth's Magnetosphere

NASA Astrophysics Data System (ADS)

Parker, L. N.; Minow, J. I.; Talaat, E. R.

2016-12-01

Spacecraft surface and internal charging is a potential threat to space technologies because electrostatic discharges on, or within, charged spacecraft materials can result in a number of adverse impacts to spacecraft systems. The Space Weather Action Plan (SWAP) ionizing radiation benchmark team recognized that spacecraft charging will need to be considered to complete the ionizing radiation benchmarks in order to evaluate the threat of charging to critical space infrastructure operating within the near-Earth ionizing radiation environments. However, the team chose to defer work on the lower energy charging environments and focus the initial benchmark efforts on the higher energy galactic cosmic ray, solar energetic particle, and trapped radiation belt particle environments of concern for radiation dose and single event effects in humans and hardware. Therefore, an initial set of 1 in 100 year spacecraft charging environment benchmarks remains to be defined to meet the SWAP goals. This presentation will discuss the available data sources and a methodology to assess the 1 in 100 year extreme space weather events that drive surface and internal charging threats to spacecraft. Environments to be considered are the hot plasmas in the outer magnetosphere during geomagnetic storms, relativistic electrons in the outer radiation belt, and energetic auroral electrons in low Earth orbit at high latitudes.

Polysaccharide/Surfactant complexes at the air-water interface - effect of the charge density on interfacial and foaming behaviors.

PubMed

Ropers, M H; Novales, B; Boué, F; Axelos, M A V

2008-11-18

The binding of a cationic surfactant (hexadecyltrimethylammonium bromide, CTAB) to a negatively charged natural polysaccharide (pectin) at air-solution interfaces was investigated on single interfaces and in foams, versus the linear charge densities of the polysaccharide. Besides classical methods to investigate polymer/surfactant systems, we applied, for the first time concerning these systems, the analogy between the small angle neutron scattering by foams and the neutron reflectivity of films to measure in situ film thicknesses of foams. CTAB/pectin foam films are much thicker than the pure surfactant foam film but similar for high- and low-charged pectin/CTAB systems despite the difference in structure of complexes at interfaces. The improvement of the foam properties of CTAB bound to pectin is shown to be directly related to the formation of pectin-CTAB complexes at the air-water interface. However, in opposition to surface activity, there is no specific behavior for the highly charged pectin: foam properties depend mainly upon the bulk charge concentration, while the interfacial behavior is mainly governed by the charge density of pectin. For the highly charged pectin, specific cooperative effects between neighboring charged sites along the chain are thought to be involved in the higher surface activity of pectin/CTAB complexes. A more general behavior can be obtained at lower charge density either by using a low-charged pectin or by neutralizing the highly charged pectin in decreasing pH.

Adsorption of surfactants and polymers at interfaces

NASA Astrophysics Data System (ADS)

Rojas, Orlando Jose

Surface tension and high-resolution laser light scattering experiments were used to investigate the adsorption of isomeric sugar-based surfactants at the air/liquid interface in terms of surfactant surface packing and rheology. Soluble monolayers of submicellar surfactant solutions exhibited a relatively viscous behavior. It was also proved that light scattering of high-frequency thermally-induced capillary waves can be utilized to study surfactant exchange between the surface and the bulk solution. Such analysis revealed the existence of a diffusional relaxation mechanism. A procedure based on XPS was developed for quantification, on an absolute basis, of polymer adsorption on mica and Langmuir-Blodgett cellulose films. The adsorption of cationic polyelectrolytes on negatively-charged solid surfaces was highly dependent on the polymer ionicity. It was found that the adsorption process is driven by electrostatic mechanisms. Charge overcompensation (or charge reversal) of mica occurred after adsorption of polyelectrolytes of ca. 50% charge density, or higher. It was demonstrated that low-charge-density polyelectrolytes adsorb on solid surfaces with an extended configuration dominated by loops and tails. In this case the extent of adsorption is limited by steric constraints. The conformation of the polyelectrolyte in the adsorbed layer is dramatically affected by the presence of salts or surfactants in aqueous solution. The phenomena which occur upon increasing the ionic strength are consistent with the screening of the electrostatic attraction between polyelectrolyte segments and solid surface. This situation leads to polyelectrolyte desorption accompanied by both an increase in the layer thickness and the range of the steric force. Adsorbed polyelectrolytes and oppositely charged surfactants readily associate at the solid/liquid interface. Such association induces polyelectrolyte desorption at a surfactant concentration which depends on the polyelectrolyte charge density. In practical systems the adsorption phenomena were found to be far more complex. Electrostatic and hydrogen bonding interactions play a major role in the adsorption of cationic polyelectrolytes on cellulosic substrates. Cationic and underivatized guar gum macromolecules form complexes with fines and dissolved and colloidal carbohydrates which are then retained on the cellulose fibers. The extent of the adsorption and association depends on the charge and nature of all the components present in pulp suspensions.

Quantitative structure-property relationships for octanol-water partition coefficients of polybrominated diphenyl ethers.

PubMed

Li, Linnan; Xie, Shaodong; Cai, Hao; Bai, Xuetao; Xue, Zhao

2008-08-01

Theoretical molecular descriptors were tested against logK(OW) values for polybrominated diphenyl ethers (PBDEs) using the Partial Least-Squares Regression method which can be used to analyze data with many variables and few observations. A quantitative structure-property relationship (QSPR) model was successfully developed with a high cross-validated value (Q(cum)(2)) of 0.961, indicating a good predictive ability and stability of the model. The predictive power of the QSPR model was further cross-validated. The values of logK(OW) for PBDEs are mainly governed by molecular surface area, energy of the lowest unoccupied molecular orbital and the net atomic charges on the oxygen atom. All these descriptors have been discussed to interpret the partitioning mechanism of PBDE chemicals. The bulk property of the molecules represented by molecular surface area is the leading factor, and K(OW) values increase with the increase of molecular surface area. Higher energy of the lowest unoccupied molecular orbital and higher net atomic charge on the oxygen atom of PBDEs result in smaller K(OW). The energy of the lowest unoccupied molecular orbital and the net atomic charge on PBDEs oxygen also play important roles in affecting the partition of PBDEs between octanol and water by influencing the interactions between PBDEs and solvent molecules.

Evaluation of the constant potential method in simulating electric double-layer capacitors

NASA Astrophysics Data System (ADS)

Wang, Zhenxing; Yang, Yang; Olmsted, David L.; Asta, Mark; Laird, Brian B.

2014-11-01

A major challenge in the molecular simulation of electric double layer capacitors (EDLCs) is the choice of an appropriate model for the electrode. Typically, in such simulations the electrode surface is modeled using a uniform fixed charge on each of the electrode atoms, which ignores the electrode response to local charge fluctuations in the electrolyte solution. In this work, we evaluate and compare this Fixed Charge Method (FCM) with the more realistic Constant Potential Method (CPM), [S. K. Reed et al., J. Chem. Phys. 126, 084704 (2007)], in which the electrode charges fluctuate in order to maintain constant electric potential in each electrode. For this comparison, we utilize a simplified LiClO4-acetonitrile/graphite EDLC. At low potential difference (ΔΨ ⩽ 2 V), the two methods yield essentially identical results for ion and solvent density profiles; however, significant differences appear at higher ΔΨ. At ΔΨ ⩾ 4 V, the CPM ion density profiles show significant enhancement (over FCM) of "inner-sphere adsorbed" Li+ ions very close to the electrode surface. The ability of the CPM electrode to respond to local charge fluctuations in the electrolyte is seen to significantly lower the energy (and barrier) for the approach of Li+ ions to the electrode surface.

Effects of different crystal faces on the surface charge of colloidal goethite (α-FeOOH) particles: an experimental and modeling study

NASA Astrophysics Data System (ADS)

Gaboriaud, Fabien; Ehrhardt, Jean-Jacques

2003-03-01

The surface charge of colloidal particles is usually determined by potentiometric titration. These acid-base titrations make it possible to measure the pH of point-of-zero charge (pzc) for oxide minerals. This macroscopic property is the most important parameter used in surface complexation modeling to reproduce experimental data. The pzc values of goethite reported in the literature vary between 7.0 and 9.5. Carbonate adsorption and/or surface morphology are thought to account for this wide range. We demonstrate a procedure for the removal of the carbonate ions that initially adsorb on goethite and strongly affect the titration curves and pzc determination. We also investigated the crystal-face-specific reactivity of two morphologically different goethites. The z-profiles obtained from atomic force microscopy (AFM) images showed that the goethite with the smallest specific surface area ( S = 49 m 2/g, denoted G49) exhibits 70% of the (001) face, whereas this value is only 30% for the goethite with largest specific surface area ( S = 95 m 2/g, denoted G95). This morphologic difference results in slightly different pzc values: 9.0 for G49 goethite and 9.1 for G95 geothite. These experimental pzc values have been correlated with multisite complexation calculations using both the full-site and the 1-pK approaches. We used the full-site approach to consider all of the configurations of hydrogen bond interactions with surface site. The resulting mean charges gave estimated pzc values of 8.9 and 9.2 for the (001) and (101) faces, respectively. Considering these theoretical pzc values for individual faces and the face distributions obtained from AFM analysis, the calculated pzc values are in full agreement with the experimental pzc values. However, this morphologic difference is more expressed in surface charge values than in the pzc values. Indeed, the surface charge of G49 goethite is much higher than that of G95 goethite, and the 1-pK calculations make it possible to fit the titration data satisfactorily.

Preparation of etched tantalum semimicro capacitor stimulation electrodes.

PubMed

Robblee, L S; Kelliher, E M; Langmuir, M E; Vartanian, H; McHardy, J

1983-03-01

The ideal electrode for stimulation of the nervous system is one that will inject charge by purely capacitive processes. One approach is to exploit the type of metal-oxide combination used in electrolytic capacitors, e.g., Ta/Ta2O5. For this purpose, fine tantalum wire (0.25 mm diam) was etched electrolytically at constant current in a methanol solution of NH4Br containing 1.5 wt % H2O. Electrolytic etching produced a conical tip with a length of ca. 0.5 mm and shaft diameters ranging from 0.10 to 0.16 mm. The etched electrodes were anodized to 10 V (vs. SCE) in 0.1 vol % H3PO4. The capacitance values normalized to geometric area of etched electrodes ranged from 0.13 to 0.33 micro F mm-2. Comparison of these values to the capacitance of "smooth" tantalum anodized to 10 V (0.011 micro F mm-2) indicated that the degree of surface enhancement, or etch ratio, was 12-30. The surface roughness was confirmed by scanning electron microscopy studies which revealed an intricate array of irregularly shaped surface projections about 1-2 micrometers wide. The etched electrodes were capable of delivering 0.06-0.1 micro C of charge with 0.1 ms pulses at a pulse repetition rate of 400 Hz when operated at 50% of the anodization voltage. This quantity of charge corresponded to volumetric charge densities of 20-30 micro C mm-3 and area charge densities of 0.55-0.88 micro C mm-2. Charge storage was proportionately higher at higher fractional values of the formation voltage. Leakage currents at 5 V were ca. 2 nA. Neither long-term passive storage (1500 h) nor extended pulsing time (18 h) had a deleterious effect on electrode performance. The trend in electrical stimulation work is toward smaller electrodes. The procedures developed in this study should be particularly well-suited to the fabrication of even smaller electrodes because of the favorable electrical and geometric characteristics of the etched surface.

Surface charge-specific interactions between polymer nanoparticles and ABC transporters in Caco-2 cells

NASA Astrophysics Data System (ADS)

Bhattacharjee, Sourav; van Opstal, Edward J.; Alink, Gerrit M.; Marcelis, Antonius T. M.; Zuilhof, Han; Rietjens, Ivonne M. C. M.

2013-06-01

The surface charge-dependent transport of polymeric nanoparticles (PNPs) across Caco-2 monolayers grown on transwell culture systems as an in vitro model for intestinal transport was tested. The transport of well-characterized, monodisperse, and fluorescent tri-block copolymer nanoparticles (TCNPs/size 45 nm) and polystyrene nanoparticles (PSNPs/size 50 nm), with different surface charges (positive and negative), was quantified. The positive PNPs showed a higher intracellular uptake and flux across the Caco-2 monolayers than the negative PNPs. Multidrug resistance/P-glycoprotein (MDR1/P-gp), a specific ATP-binding cassette (ABC) transporter, was found to play a major role in the cellular efflux of positive PNPs, whereas the multidrug resistance protein 1 took part in the efflux of negative PNPs from Caco-2 cells. The positive PNPs also caused an increased cellular uptake and apical to basolateral transport of the carcinogen PhIP across the Caco-2 monolayer. The flavonoid quercetin, which is known to interact with ABC transporters, promoted the intracellular uptake of different PNPs and interfered with the normal distribution patterns of PNPs in the transwell system. These results indicate that PNPs display surface charge-specific interactions with ABC transporters and can even affect the bioavailability of toxic food-borne compounds (like pro-carcinogens).

Surface charge accumulation of solid insulator under nanosecond pulse in vacuum: 3D distribution features and mechanism

NASA Astrophysics Data System (ADS)

Qi, Bo; Gao, Chunjia; Sun, Zelai; Li, Chengrong

2017-11-01

Surface charge accumulation can incur changes in electric field distribution, involved in the electron propagation process, and result in a significant decrease in the surface flashover voltage. The existing 2D surface charge measurement fails to meet the actual needs in real engineering applications that usually adopt the 45° conical frustum insulators. The present research developed a novel 3D measurement platform to capture surface charge distribution on solid insulation under nanosecond pulse in a vacuum. The results indicate that all surface charges are positive under a positive pulse and negative under a negative pulse. Surface charges tend to accumulate more near the upper electrode. Surface charge density increases significantly with the increase in pulse counts and amplitudes. Accumulation of surface charge results in a certain decrease of flashover voltage. Taking consideration of the secondary electron emission for the surface charge accumulation, four materials were obtained to demonstrate the effects on surface charge. Combining the effect incurred by secondary electron emission and the weighty action taken by surface charge accumulation on the flashover phenomena, the discharge mechanism along the insulator surface under nanosecond pulse voltage was proposed.

Immobilization of E. coli with autodisplayed Z-domains to a surface-modified microplate for immunoassay.

PubMed

Yoo, Gu; Park, Min; Lee, Eun-Hang; Jose, Joachim; Pyun, Jae-Chul

2011-11-30

Escherichia coli with autodisplayed Z-domains was reported to improve the sensitivity of immunoassays by the orientation control of antibodies. In this work, a sensitive microplate-based immunoassay is presented by immobilizing E. coli cells to a surface-modified microplate. The microplate was prepared by coating parylene-H film with formyl groups, and then covalently coupling poly-L-lysine to the parylene-H film. The E. coli cells were bound to the microplate by charge interactions between the negatively charged E. coli outer membrane and the positively charged microplate surface. In this work, the preparation of the microplate coated with poly-L-lysine is presented. The immobilization efficiency of E. coli to the modified surface was estimated to be far higher than non-specific interaction by fluorescence microscope and the optical transmittance of the modified microplate was measured to be feasible for immunoassay. The microplate-based immunoassay is demonstrated to be feasible for medical diagnosis of inflammatory diseases by using C-reactive protein as a target analyte for the medical diagnosis of inflammatory diseases. Copyright © 2011 Elsevier B.V. All rights reserved.

Laboratory Measurements of Optical and Physical Properties of Individual Lunar Dust Grains

NASA Technical Reports Server (NTRS)

Abbas, M. M.; Tankosic, D.; Craven, P. D.; Hoover, R. B.

2006-01-01

The lunar surface is covered with a thick layer of sub-micron/micron size dust grains formed by meteoritic impact over billions of years. The fine dust grains are levitated and transported on the lunar surface, and transient dust clouds over the lunar horizon were observed by experiments during the Apollo 17 mission. Theoretical models suggest that the dust grains on the lunar surface are charged by the solar UV radiation as well as the solar wind. Even without any physical activity, the dust grains are levitated by electrostatic fields and transported away from the surface in the near vacuum environment of the Moon. The current dust charging and levitation models, however, do not fully explain the observed phenomena. Since the abundance of dust on the Moon's surface with its observed adhesive characteristics has the potential of severe impact on human habitat and operations and lifetime of a variety of equipment, it is necessary to investigate the charging properties and the lunar dust phenomena in order to develop appropriate mitigating strategies. Photoelectric emission induced by the solar UV radiation with photon energies higher than the work function of the grain materials is recognized to be the dominant process for charging of the lunar dust, and requires measurements of the photoelectric yields to determine the charging and equilibrium potentials of individual dust grains. In this paper, we present the first laboratory measurements of the photoelectric yields of individual sub-micron/micron size dust grains selected from sample returns of Apollo 17, and Luna 24 missions, as well as similar size dust grains from the JSC-1 simulants. The experimental results were obtained on a laboratory facility based on an electrodynamic balance that permits a variety of experiments to be conducted on individual sub-micron/micron size dust grains in simulated space environments. The photoelectric emission measurements indicate grain size dependence with the yield increasing by an order of magnitude for grains of radii sub-micron size to several micron radii, at which it reaches asymptotic values. The yield for large size grains is found to be more than an order of magnitude higher than the bulk measurements on lunar fines reported in the literature.

Charge reversible gold nanoparticles for high efficient absorption and desorption of DNA

NASA Astrophysics Data System (ADS)

Wang, Can; Zhuang, Jiaqi; Jiang, Shan; Li, Jun; Yang, Wensheng

2012-10-01

Mercaptoundecylamine and mercaptoundecanoic acid co-modified Au nanoparticles were prepared by two-step ligand exchange of 6-mercaptohexanoic acid modified gold nanoparticles. Such particles terminated by appropriate ratios of the amine and carboxyl groups ( R N/C) were identified to show reversible charge on their surface, which were switchable by pH of the solution. The isoelectric point (IEP) of the particles is tunable by changing the ratios of the amine and carboxyl groups on the particle surfaces. The particles can absorb DNA effectively at pH lower than the IEP driven by the direct electrostatic interactions between DNA and the particle surface. When pH of the solutions was elevated to be higher than the IEP, the absorbed DNA can be released almost completely due to the electrostatic repulsion between the particle surface and DNA. With appropriate R N/C ratios of 0.8, the absorption and desorption efficiencies of DNA were 97 and 98 %, respectively, corresponding an extraction efficiency of 95 %. Such particles with reversible surface charges allow the high efficient extraction of DNA by simply changing pH instead of by changing salt concentration in the conventional salt bridge method.

Electrostatic Interactions Influence Protein Adsorption (but Not Desorption) at the Silica-Aqueous Interface.

PubMed

McUmber, Aaron C; Randolph, Theodore W; Schwartz, Daniel K

2015-07-02

High-throughput single-molecule total internal reflection fluorescence microscopy was used to investigate the effects of pH and ionic strength on bovine serum albumin (BSA) adsorption, desorption, and interfacial diffusion at the aqueous-fused silica interface. At high pH and low ionic strength, negatively charged BSA adsorbed slowly to the negatively charged fused silica surface. At low pH and low ionic strength, where BSA was positively charged, or in solutions at higher ionic strength, adsorption was approximately 1000 times faster. Interestingly, neither surface residence times nor the interfacial diffusion coefficients of BSA were influenced by pH or ionic strength. These findings suggested that adsorption kinetics were dominated by energy barriers associated with electrostatic interactions, but once adsorbed, protein-surface interactions were dominated by short-range nonelectrostatic interactions. These results highlight the ability of single-molecule techniques to isolate elementary processes (e.g., adsorption and desorption) under steady-state conditions, which would be impossible to measure using ensemble-averaging methods.

Photonic crystals possessing multiple Weyl points and the experimental observation of robust surface states

PubMed Central

Chen, Wen-Jie; Xiao, Meng; Chan, C. T.

2016-01-01

Weyl points, as monopoles of Berry curvature in momentum space, have captured much attention recently in various branches of physics. Realizing topological materials that exhibit such nodal points is challenging and indeed, Weyl points have been found experimentally in transition metal arsenide and phosphide and gyroid photonic crystal whose structure is complex. If realizing even the simplest type of single Weyl nodes with a topological charge of 1 is difficult, then making a real crystal carrying higher topological charges may seem more challenging. Here we design, and fabricate using planar fabrication technology, a photonic crystal possessing single Weyl points (including type-II nodes) and multiple Weyl points with topological charges of 2 and 3. We characterize this photonic crystal and find nontrivial 2D bulk band gaps for a fixed kz and the associated surface modes. The robustness of these surface states against kz-preserving scattering is experimentally observed for the first time. PMID:27703140

Polyamide desalination membrane characterization and surface modification to enhance fouling resistance.

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

Sharma, Mukul M.; Freeman, Benny D.; Van Wagner, Elizabeth M.

2010-08-01

The market for polyamide desalination membranes is expected to continue to grow during the coming decades. Purification of alternative water sources will also be necessary to meet growing water demands. Purification of produced water, a byproduct of oil and gas production, is of interest due to its dual potential to provide water for beneficial use as well as to reduce wastewater disposal costs. However, current polyamide membranes are prone to fouling, which decreases water flux and shortens membrane lifetime. This research explored surface modification using poly(ethylene glycol) diglycidyl ether (PEGDE) to improve the fouling resistance of commercial polyamide membranes. Characterizationmore » of commercial polyamide membrane performance was a necessary first step before undertaking surface modification studies. Membrane performance was found to be sensitive to crossflow testing conditions. Concentration polarization and feed pH strongly influenced NaCl rejection, and the use of continuous feed filtration led to higher water flux and lower NaCl rejection than was observed for similar tests performed using unfiltered feed. Two commercial polyamide membranes, including one reverse osmosis and one nanofiltration membrane, were modified by grafting PEGDE to their surfaces. Two different PEG molecular weights (200 and 1000) and treatment concentrations (1% (w/w) and 15% (w/w)) were studied. Water flux decreased and NaCl rejection increased with PEGDE graft density ({micro}g/cm{sup 2}), although the largest changes were observed for low PEGDE graft densities. Surface properties including hydrophilicity, roughness and charge were minimally affected by surface modification. The fouling resistance of modified and unmodified membranes was compared in crossflow filtration studies using model foulant solutions consisting of either a charged surfactant or an oil in water emulsion containing n-decane and a charged surfactant. Several PEGDE-modified membranes demonstrated improved fouling resistance compared to unmodified membranes of similar initial water flux, possibly due to steric hindrance imparted by the PEG chains. Fouling resistance was higher for membranes modified with higher molecular weight PEG. Fouling was more extensive for feeds containing the cationic surfactant, potentially due to electrostatic attraction with the negatively charged membranes. However, fouling was also observed in the presence of the anionic surfactant, indicating hydrodynamic forces are also responsible for fouling.« less

Spacecraft Charging and the Microwave Anisotropy Probe Spacecraft

NASA Technical Reports Server (NTRS)

Timothy, VanSant J.; Neergaard, Linda F.

1998-01-01

The Microwave Anisotropy Probe (MAP), a MIDEX mission built in partnership between Princeton University and the NASA Goddard Space Flight Center (GSFC), will study the cosmic microwave background. It will be inserted into a highly elliptical earth orbit for several weeks and then use a lunar gravity assist to orbit around the second Lagrangian point (L2), 1.5 million kilometers, anti-sunward from the earth. The charging environment for the phasing loops and at L2 was evaluated. There is a limited set of data for L2; the GEOTAIL spacecraft measured relatively low spacecraft potentials (approx. 50 V maximum) near L2. The main area of concern for charging on the MAP spacecraft is the well-established threat posed by the "geosynchronous region" between 6-10 Re. The launch in the autumn of 2000 will coincide with the falling of the solar maximum, a period when the likelihood of a substorm is higher than usual. The likelihood of a substorm at that time has been roughly estimated to be on the order of 20% for a typical MAP mission profile. Because of the possibility of spacecraft charging, a requirement for conductive spacecraft surfaces was established early in the program. Subsequent NASCAP/GEO analyses for the MAP spacecraft demonstrated that a significant portion of the sunlit surface (solar cell cover glass and sunshade) could have nonconductive surfaces without significantly raising differential charging. The need for conductive materials on surfaces continually in eclipse has also been reinforced by NASCAP analyses.

Peptide structure: Its effect on penetration into human hair.

PubMed

Silva, Carla J S M; Vasconcelos, Andreia; Cavaco-Paulo, Artur

2007-01-01

The influence of the peptide structure on its penetration inside hair was studied, together with the effect of hair bleaching (oxidation). For that reason, the outcome of positioning a charged sequence (KAKAK) either at the N or C terminal on hair penetration has been studied for peptides with 17 residues each. It was observed that the penetration of these peptides into hair was driven by electrostatic interactions, where the position of the charged group at the peptide structure was of major importance. The penetration was only achieved for damaged hair due to its higher negative charge at the membrane surface. It was also observed that the peptides were able to restore the original tensile strength of bleached hair. Consequently, the knowledge of hair surface properties is of extreme importance when designing peptides directed for hair treatment.

Quantification of surface charge density and its effect on boundary slip.

PubMed

Jing, Dalei; Bhushan, Bharat

2013-06-11

Reduction of fluid drag is important in the micro-/nanofluidic systems. Surface charge and boundary slip can affect the fluid drag, and surface charge is also believed to affect boundary slip. The quantification of surface charge and boundary slip at a solid-liquid interface has been widely studied, but there is a lack of understanding of the effect of surface charge on boundary slip. In this paper, the surface charge density of borosilicate glass and octadecyltrichlorosilane (OTS) surfaces immersed in saline solutions with two ionic concentrations and deionized (DI) water with different pH values and electric field values is quantified by fitting experimental atomic force microscopy (AFM) electrostatic force data using a theoretical model relating the surface charge density and electrostatic force. Results show that pH and electric field can affect the surface charge density of glass and OTS surfaces immersed in saline solutions and DI water. The mechanisms of the effect of pH and electric field on the surface charge density are discussed. The slip length of the OTS surface immersed in saline solutions with two ionic concentrations and DI water with different pH values and electric field values is measured, and their effects on the slip length are analyzed from the point of surface charge. Results show that a larger absolute value of surface charge density leads to a smaller slip length for the OTS surface.

The effect of surface-bulk potential difference on the kinetics of intercalation in core-shell active cathode particles

NASA Astrophysics Data System (ADS)

Kazemiabnavi, Saeed; Malik, Rahul; Orvananos, Bernardo; Abdellahi, Aziz; Ceder, Gerbrand; Thornton, Katsuyo

2018-04-01

Surface modification of active cathode particles is commonly observed in battery research as either a surface phase evolving during the cycling process, or intentionally engineered to improve capacity retention, rate capability, and/or thermal stability of the cathode material. Here, a continuum-scale model is developed to simulate the galvanostatic charge/discharge of a cathode particle with core-shell heterostructure. The particle is assumed to be comprised of a core material encapsulated by a thin layer of a second phase that has a different open-circuit voltage. The effect of the potential difference between the surface and bulk phases (Ω) on the kinetics of lithium intercalation and the galvanostatic charge/discharge profiles is studied at different values of Ω, C-rates, and exchange current densities. The difference between the Li chemical potential in the surface and bulk phases of the cathode particle results in a concentration difference between these two phases. This leads to a charge/discharge asymmetry in the galvanostatic voltage profiles, causing a decrease in the accessible capacity of the particle. These effects are more significant at higher magnitudes of surface-bulk potential difference. The proposed model provides detailed insight into the kinetics and voltage behavior of the intercalation/de-intercalation processes in core-shell heterostructure cathode particles.

An equivalent body surface charge model representing three-dimensional bioelectrical activity

NASA Technical Reports Server (NTRS)

He, B.; Chernyak, Y. B.; Cohen, R. J.

1995-01-01

A new surface-source model has been developed to account for the bioelectrical potential on the body surface. A single-layer surface-charge model on the body surface has been developed to equivalently represent bioelectrical sources inside the body. The boundary conditions on the body surface are discussed in relation to the surface-charge in a half-space conductive medium. The equivalent body surface-charge is shown to be proportional to the normal component of the electric field on the body surface just outside the body. The spatial resolution of the equivalent surface-charge distribution appears intermediate between those of the body surface potential distribution and the body surface Laplacian distribution. An analytic relationship between the equivalent surface-charge and the surface Laplacian of the potential was found for a half-space conductive medium. The effects of finite spatial sampling and noise on the reconstruction of the equivalent surface-charge were evaluated by computer simulations. It was found through computer simulations that the reconstruction of the equivalent body surface-charge from the body surface Laplacian distribution is very stable against noise and finite spatial sampling. The present results suggest that the equivalent body surface-charge model may provide an additional insight to our understanding of bioelectric phenomena.

Adsorption characteristics of Bisphenol-A on tailored activated carbon in aqueous solutions.

PubMed

Yan, Liang; Lv, Di; Huang, Xinwen; Shi, Huixiang; Zhang, Geshan

2016-10-01

The adsorption behavior of pharmaceuticals and personal care product, Bisphenol-A (BPA), according to four coal-based and four wood-based granular activated carbons modified using outgassing treatment, acidic treatment or alkaline treatment was studied. The adsorption isotherm results indicated that carbon surface acidity played a very important role in the adsorption of BPA. It was found that increasing surface acidity would increase the hydrogen bonding effects and increase adsorption of BPA on activated carbon. The acidic modified sample (F600-A and OLC-A) represented the best adsorption capacity, and the equilibrium adsorption amounts reached 346.42 and 338.55 mg/g, respectively. Further, effects of surface charge and surface basicity were examined. It was found that the adsorbed amount of BPA decreased with the increase of surface charge. Finally, there appeared to be a significant oligomerization phenomenon with BPA molecules onto the surface of activated carbon. OLC and OLC-OG, which have higher micropore percentages, are very effective in hampering the oligomerization of BPA under oxic conditions.

Biocontrol of Listeria monocytogenes and Escherichia coli O157:H7 in Meat by Using Phages Immobilized on Modified Cellulose Membranes ▿

PubMed Central

Anany, H.; Chen, W.; Pelton, R.; Griffiths, M. W.

2011-01-01

The ability of phages to specifically interact with and lyse their host bacteria makes them ideal antibacterial agents. The range of applications of bacteriophage can be extended by their immobilization on inert surfaces. A novel method for the oriented immobilization of bacteriophage has been developed. The method was based on charge differences between the bacteriophage head, which exhibits an overall net negative charge, and the tail fibers, which possess an overall net positive charge. Hence, the head would be more likely to attach to positively charged surfaces, leaving the tails free to capture and lyse bacteria. Cellulose membranes modified so that they had a positive surface charge were used as the support for phage immobilization. It was established that the number of infective phages immobilized on the positively charged cellulose membranes was significantly higher than that on unmodified membranes. Cocktails of phages active against Listeria or Escherichia coli immobilized on these membranes were shown to effectively control the growth of L. monocytogenes and E. coli O157:H7 in ready-to-eat and raw meat, respectively, under different storage temperatures and packaging conditions. The phage storage stability was investigated to further extend their industrial applications. It was shown that lyophilization can be used as a phage-drying method to maintain their infectivity on the newly developed bioactive materials. In conclusion, utilizing the charge difference between phage heads and tails provided a simple technique for oriented immobilization applicable to a wide range of phages and allowed the retention of infectivity. PMID:21803890

Mixed-charge nanoparticles for long circulation, low reticuloendothelial system clearance, and high tumor accumulation.

PubMed

Liu, Xiangsheng; Li, Huan; Chen, Yangjun; Jin, Qiao; Ren, Kefeng; Ji, Jian

2014-09-01

Mixed-charge zwitterionic surface modification shows great potential as a simple strategy to fabricate nanoparticle (NP) surfaces that are nonfouling. Here, the in vivo fate of 16 nm mixed-charge gold nanoparticles (AuNPs) is investigated, coated with mixed quaternary ammonium and sulfonic groups. The results show that mixed-charge AuNPs have a much longer blood half-life (≈30.6 h) than do poly(ethylene glycol) (PEG, M¯w = 2000) -coated AuNPs (≈6.65 h) and they accumulate in the liver and spleen far less than do the PEGylated AuNPs. Using transmission electron microscopy, it is further confirmed that the mixed-charge AuNPs have much lower uptake and different existing states in liver Kupffer cells and spleen macrophages one month after injection compared with the PEGylated AuNPs. Moreover, these mixed-charge AuNPs do not cause appreciable toxicity at this tested dose to mice in a period of 1 month as evidenced by histological examinations. Importantly, the mixed-charge AuNPs have higher accumulation and slower clearance in tumors than do PEGylated AuNPs for times of 24-72 h. Results from this work show promise for effectively designing tumor-targeting NPs that can minimize reticuloendothelial system clearance and circulate for long periods by using a simple mixed-charge strategy. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Development of surface functionalized ZnO-doped LiFePO4/C composites as alternative cathode material for lithium ion batteries

NASA Astrophysics Data System (ADS)

Saroha, Rakesh; Panwar, Amrish K.; Sharma, Yogesh; Tyagi, Pawan K.; Ghosh, Sudipto

2017-02-01

Surface modified olivine-type LiFePO4/C-ZnO doped samples were synthesized using sol-gel assisted ball-milling route. In this work, the influence of ZnO-doping on the physiochemical, electrochemical and surface properties such as charge separation at solid-liquid interphase, surface force gradient, surface/ionic conductivity of pristine LiFePO4/C (LFP) has been investigated thoroughly. Synthesized samples were characterized using X-ray diffraction, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. All the synthesized samples were indexed to the orthorhombic phase with Pnma space group. Pristine LiFePO4 retain its structure for higher ZnO concentrations (i.e. 2.5 and 5.0 wt.% of LFP). Surface topography and surface force gradient measurements by EFM revealed that the kinetics of charge carriers, e-/Li+ is more in ZnO-doped LFP samples, which may be attributed to diffusion or conduction process of the charges present at the surface. Among all the synthesized samples LFP/C with 2.5 wt.% of ZnO (LFPZ2.5) displays the highest discharge capacity at all C-rates and exhibit excellent rate performance. LFPZ2.5 delivers a specific discharge capacity of 164 (±3) mAh g-1 at 0.1C rate. LFPZ2.5 shows best cycling performance as it provides a discharge capacity of 135 (±3) mAh g-1 at 1C rate and shows almost 95% capacity retention after 50 charge/discharge cycles. Energy density plot shows that LFPZ2.5 offers high energy and power density measured at high discharge rates (5C), proving its usability for hybrid vehicles application.

Interactions of microbicide nanoparticles with a simulated vaginal fluid.

PubMed

das Neves, José; Rocha, Cristina M R; Gonçalves, Maria Pilar; Carrier, Rebecca L; Amiji, Mansoor; Bahia, Maria Fernanda; Sarmento, Bruno

2012-11-05

The interaction with cervicovaginal mucus presents the potential to impact the performance of drug nanocarriers. These systems must migrate through this biological fluid in order to deliver their drug payload to the underlying mucosal surface. We studied the ability of dapivirine-loaded polycaprolactone (PCL)-based nanoparticles (NPs) to interact with a simulated vaginal fluid (SVF) incorporating mucin. Different surface modifiers were used to produce NPs with either negative (poloxamer 338 NF and sodium lauryl sulfate) or positive (cetyltrimethylammonium bromide) surface charge. Studies were performed using the mucin particle method, rheological measurements, and real-time multiple particle tracking. Results showed that SVF presented rheological properties similar to those of human cervicovaginal mucus. Analysis of NP transport indicated mild interactions with mucin and low adhesive potential. In general, negatively charged NPs underwent subdiffusive transport in SVF, i.e., hindered as compared to their diffusion in water, but faster than for positively charged NPs. These differences were increased when the pH of SVF was changed from 4.2 to 7.0. Diffusivity was 50- and 172-fold lower in SVF at pH 4.2 than in water for negatively charged and positively charged NPs, respectively. At pH 7.0, this decrease was around 20- and 385-fold, respectively. The estimated times required to cross a layer of SVF were equal to or lower than 1.7 h for negatively charged NPs, while for positively charged NPs these values were equal to or higher than 7 h. Overall, our results suggest that negatively charged PCL NPs may be suitable to be used as carriers in order to deliver dapivirine and potentially other antiretroviral drugs to the cervicovaginal mucosal lining. Also, they further reinforce the importance in characterizing the interactions of nanosystems with mucus fluids or surrogates when considering mucosal drug delivery.

Charge retention of soft-landed phosphotungstate Keggin anions on self-assembled monolayers

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

Gunaratne, K. Don D.; Prabhakaran, Venkateshkumar; Andersen, Amity

Soft landing of mass-selected ions onto surfaces often results in partial loss of charge that may affect the structure and reactivity of deposited species. In this study, Keggin phosphotungstate anions in two selected charge states, PW12O403- (WPOM3-) and PW12O402- (WPOM2-), were soft-landed onto different self-assembled monolayer (SAM) surfaces and examined using in situ infrared reflection absorption spectroscopy (IRRAS) and density functional theory (DFT) calculations. Partial retention of the 3- charge was observed when WPOM3- was soft-landed onto the fluorinated SAM (FSAM), while the charge state distribution was dominated by the 2- charge after both WPOM3- and WPOM2- were deposited ontomore » a hydrophilic alkylthiol SAM terminated with cationic NH3+ functional groups (NH3+SAM). We found that during the course of the soft landing of WPOM3-, the relative abundance of WPOM3- on FSAM decreased while that of WPOM2- increased. We propose that the higher stability of immobilized WPOM2- in comparison with WPOM3- makes it the preferred charge state of WPOM on both the FSAM and NH3+SAM. We also observe weaker binding of WPOM anions to SAMs in comparison with phosphomolybdate ions (MoPOM) reported previously (J. Phys. Chem. C 2014, 118, 27611–27622). The weaker binding of WPOM to SAMs is attributed to the lower reactivity of WPOM reported in the literature. This study demonstrates that both the charge retention and the reactivity of deposited anionic POM clusters on surfaces are determined by the type of addenda metal atoms in the cluster.« less

Effects of Systematic Variation in Size and Surface Coating of Silver Nanoparticles on Their In Vitro Toxicity to Macrophage RAW 264.7 Cells.

PubMed

Makama, Sunday; Kloet, Samantha K; Piella, Jordi; van den Berg, Hans; de Ruijter, Norbert C A; Puntes, Victor F; Rietjens, Ivonne M C M; van den Brink, Nico W

2018-03-01

In literature, varying and sometimes conflicting effects of physicochemical properties of nanoparticles (NPs) are reported on their uptake and effects in organisms. To address this, small- and medium-sized (20 and 50 nm) silver nanoparticles (AgNPs) with specified different surface coating/charges were synthesized and used to systematically assess effects of NP-properties on their uptake and effects in vitro. Silver nanoparticles were fully characterized for charge and size distribution in both water and test media. Macrophage cells (RAW 264.7) were exposed to these AgNPs at different concentrations (0-200 µg/ml). Uptake dynamics, cell viability, induction of tumor necrosis factor (TNF)-α, ATP production, and reactive oxygen species (ROS) generation were assessed. Microscopic imaging of living exposed cells showed rapid uptake and subcellular cytoplasmic accumulation of AgNPs. Exposure to the tested AgNPs resulted in reduced overall viability. Influence of both size and surface coating (charge) was demonstrated, with the 20-nm-sized AgNPs and bovine serum albumin (BSA)-coated (negatively charged) AgNPs being slightly more toxic. On specific mechanisms of toxicity (TNF-α and ROS production) however, the AgNPs differed to a larger extent. The highest induction of TNF-α was found in cells exposed to the negatively charged AgNP_BSA, both sizes (80× higher than control). Reactive oxygen species induction was only significant with the 20 nm positively charged AgNP_Chit.

Upregulation of BMSCs Osteogenesis by Positively-Charged Tertiary Amines on Polymeric Implants via Charge/iNOS Signaling Pathway

PubMed Central

Zhang, Wei; Liu, Na; Shi, Haigang; Liu, Jun; Shi, Lianxin; Zhang, Bo; Wang, Huaiyu; Ji, Junhui; Chu, Paul K.

2015-01-01

Positively-charged surfaces on implants have a similar potential to upregulate osteogenesis of bone marrow-derived mesenchymal stem cells (BMSCs) as electromagnetic therapy approved for bone regeneration. Generally, their osteogenesis functions are generally considered to stem from the charge-induced adhesion of extracellular matrix (ECM) proteins without exploring the underlying surface charge/cell signaling molecule pathways. Herein, a positively-charged surface with controllable tertiary amines is produced on a polymer implant by plasma surface modification. In addition to inhibiting the TNF-α expression, the positively-charged surface with tertiary amines exhibits excellent cytocompatibility as well as remarkably upregulated osteogenesis-related gene/protein expressions and calcification of the contacted BMSCs. Stimulated by the charged surface, these BMSCs display high iNOS expressions among the three NOS isoforms. Meanwhile, downregulation of the iNOS by L-Can or siRNA inhibit osteogenic differentiation in the BMSCs. These findings suggest that a positively-charged surface with tertiary amines induces osteogenesis of BMSCs via the surface charge/iNOS signaling pathway in addition to elevated ECM protein adhesion. Therefore, creating a positively-charged surface with tertiary amines is a promising approach to promote osseointegration with bone tissues. PMID:25791957

Performance of colloidal silica and ceria based slurries on CMP of Si-face 6H-SiC substrates

NASA Astrophysics Data System (ADS)

Chen, Guomei; Ni, Zifeng; Xu, Laijun; Li, Qingzhong; Zhao, Yongwu

2015-12-01

Colloidal silica and ceria based slurries, both using KMnO4 as an oxidizer, for chemical mechanical polishing (CMP) of Si-face (0 0 0 1) 6H-SiC substrate, were investigated to obtain higher material removal rate (MRR) and ultra-smooth surface. The results indicate that there was a significant difference in the CMP performance of 6H-SiC between silica and ceria based slurries. For the ceria based slurries, a higher MRR was obtained, especially in strong acid KMnO4 environment, and the maximum MRR (1089 nm/h) and a smoother surface with an average roughness Ra of 0.11 nm was achieved using slurries containing 2 wt% colloidal ceria, 0.05 M KMnO4 at pH 2. In contrast, due to the attraction between negative charged silica particles and positive charged SiC surface below pH 5, the maximum MRR of silica based slurry was only 185 nm/h with surface roughness Ra of 0.254 nm using slurries containing 6 wt% colloidal silica, 0.05 M KMnO4 at pH 6. The polishing mechanism was discussed based on the zeta potential measurements of the abrasives and the X-ray photoelectron spectroscopy (XPS) analysis of the polished SiC surfaces.

Improved Solar-Driven Photocatalytic Performance of Highly Crystalline Hydrogenated TiO2 Nanofibers with Core-Shell Structure

NASA Astrophysics Data System (ADS)

Wu, Ming-Chung; Chen, Ching-Hsiang; Huang, Wei-Kang; Hsiao, Kai-Chi; Lin, Ting-Han; Chan, Shun-Hsiang; Wu, Po-Yeh; Lu, Chun-Fu; Chang, Yin-Hsuan; Lin, Tz-Feng; Hsu, Kai-Hsiang; Hsu, Jen-Fu; Lee, Kun-Mu; Shyue, Jing-Jong; Kordás, Krisztián; Su, Wei-Fang

2017-01-01

Hydrogenated titanium dioxide has attracted intensive research interests in pollutant removal applications due to its high photocatalytic activity. Herein, we demonstrate hydrogenated TiO2 nanofibers (H:TiO2 NFs) with a core-shell structure prepared by the hydrothermal synthesis and subsequent heat treatment in hydrogen flow. H:TiO2 NFs has excellent solar light absorption and photogenerated charge formation behavior as confirmed by optical absorbance, photo-Kelvin force probe microscopy and photoinduced charge carrier dynamics analyses. Photodegradation of various organic dyes such as methyl orange, rhodamine 6G and brilliant green is shown to take place with significantly higher rates on our novel catalyst than on pristine TiO2 nanofibers and commercial nanoparticle based photocatalytic materials, which is attributed to surface defects (oxygen vacancy and Ti3+ interstitial defect) on the hydrogen treated surface. We propose three properties/mechanisms responsible for the enhanced photocatalytic activity, which are: (1) improved absorbance allowing for increased exciton generation, (2) highly crystalline anatase TiO2 that promotes fast charge transport rate, and (3) decreased charge recombination caused by the nanoscopic Schottky junctions at the interface of pristine core and hydrogenated shell thus promoting long-life surface charges. The developed H:TiO2 NFs can be helpful for future high performance photocatalysts in environmental applications.

Improved Solar-Driven Photocatalytic Performance of Highly Crystalline Hydrogenated TiO2 Nanofibers with Core-Shell Structure

PubMed Central

Wu, Ming-Chung; Chen, Ching-Hsiang; Huang, Wei-Kang; Hsiao, Kai-Chi; Lin, Ting-Han; Chan, Shun-Hsiang; Wu, Po-Yeh; Lu, Chun-Fu; Chang, Yin-Hsuan; Lin, Tz-Feng; Hsu, Kai-Hsiang; Hsu, Jen-Fu; Lee, Kun-Mu; Shyue, Jing-Jong; Kordás, Krisztián; Su, Wei-Fang

2017-01-01

Hydrogenated titanium dioxide has attracted intensive research interests in pollutant removal applications due to its high photocatalytic activity. Herein, we demonstrate hydrogenated TiO2 nanofibers (H:TiO2 NFs) with a core-shell structure prepared by the hydrothermal synthesis and subsequent heat treatment in hydrogen flow. H:TiO2 NFs has excellent solar light absorption and photogenerated charge formation behavior as confirmed by optical absorbance, photo-Kelvin force probe microscopy and photoinduced charge carrier dynamics analyses. Photodegradation of various organic dyes such as methyl orange, rhodamine 6G and brilliant green is shown to take place with significantly higher rates on our novel catalyst than on pristine TiO2 nanofibers and commercial nanoparticle based photocatalytic materials, which is attributed to surface defects (oxygen vacancy and Ti3+ interstitial defect) on the hydrogen treated surface. We propose three properties/mechanisms responsible for the enhanced photocatalytic activity, which are: (1) improved absorbance allowing for increased exciton generation, (2) highly crystalline anatase TiO2 that promotes fast charge transport rate, and (3) decreased charge recombination caused by the nanoscopic Schottky junctions at the interface of pristine core and hydrogenated shell thus promoting long-life surface charges. The developed H:TiO2 NFs can be helpful for future high performance photocatalysts in environmental applications. PMID:28102314

Modulation of protein stability and aggregation properties by surface charge engineering.

PubMed

Raghunathan, Govindan; Sokalingam, Sriram; Soundrarajan, Nagasundarapandian; Madan, Bharat; Munussami, Ganapathiraman; Lee, Sun-Gu

2013-09-01

An attempt to alter protein surface charges through traditional protein engineering approaches often affects the native protein structure significantly and induces misfolding. This limitation is a major hindrance in modulating protein properties through surface charge variations. In this study, as a strategy to overcome such a limitation, we attempted to co-introduce stabilizing mutations that can neutralize the destabilizing effect of protein surface charge variation. Two sets of rational mutations were designed; one to increase the number of surface charged amino acids and the other to decrease the number of surface charged amino acids by mutating surface polar uncharged amino acids and charged amino acids, respectively. These two sets of mutations were introduced into Green Fluorescent Protein (GFP) together with or without stabilizing mutations. The co-introduction of stabilizing mutations along with mutations for surface charge modification allowed us to obtain functionally active protein variants (s-GFP(+15-17) and s-GFP(+5-6)). When the protein properties such as fluorescent activity, folding rate and kinetic stability were assessed, we found the possibility that the protein stability can be modulated independently of activity and folding by engineering protein surface charges. The aggregation properties of GFP could also be altered through the surface charge engineering.

On gel electrophoresis of dielectric charged particles with hydrophobic surface: A combined theoretical and numerical study.

PubMed

Majee, Partha Sarathi; Bhattacharyya, Somnath; Gopmandal, Partha Pratim; Ohshima, Hiroyuki

2018-03-01

A theoretical study on the gel electrophoresis of a charged particle incorporating the effects of dielectric polarization and surface hydrophobicity at the particle-liquid interface is made. A simplified model based on the weak applied field and low charge density assumption is also presented and compared with the full numerical model for a nonpolarizable particle to elucidate the nonlinear effects such as double layer polarization and relaxation as well as surface conduction. The main motivation of this study is to analyze the electrophoresis of the surface functionalized nanoparticle with tunable hydrophobicity or charged fluid drop in gel medium by considering the electrokinetic effects and hydrodynamic interactions between the particle and the gel medium. An effective medium approach, in which the transport in the electrolyte-saturated hydrogel medium is governed by the Brinkman equation, is adopted in the present analysis. The governing electrokinetic equations based on the conservation principles are solved numerically. The Navier-slip boundary condition along with the continuity condition of dielectric displacement are imposed on the surface of the hydrophobic polarizable particle. The impact of the slip length on the electrophoresis is profound for a thinner Debye layer, however, surface conduction effect also becomes significant for a hydrophobic particle. Impact of hydrophobicity and relaxation effects are higher for a larger particle. Dielectric polarization creates a reduction in its electrophoretic propulsion and has negligible impact at the thinner Debye length as well as lower gel screening length. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Geometry effect on electrokinetic flow and ionic conductance in pH-regulated nanochannels

NASA Astrophysics Data System (ADS)

Sadeghi, Morteza; Saidi, Mohammad Hassan; Moosavi, Ali; Sadeghi, Arman

2017-12-01

Semi-analytical solutions are obtained for the electrical potential, electroosmotic velocity, ionic conductance, and surface physicochemical properties associated with long pH-regulated nanochannels of arbitrary but constant cross-sectional area. The effects of electric double layer overlap, multiple ionic species, and surface association/dissociation reactions are all taken into account, assuming low surface potentials. The method of analysis includes series solutions which the pertinent coefficients are obtained by applying the wall boundary conditions using either of the least-squares or point matching techniques. Although the procedure is general enough to be applied to almost any arbitrary cross section, nine nanogeometries including polygonal, trapezoidal, double-trapezoidal, rectangular, elliptical, semi-elliptical, isosceles triangular, rhombic, and isotropically etched profiles are selected for presentation. For the special case of an elliptic cross section, full analytical solutions are also obtained utilizing the Mathieu functions. We show that the geometrical configuration plays a key role in determination of the ionic conductance, surface charge density, electrical potential and velocity fields, and proton enhancement. In this respect, the net electric charge and convective ionic conductance are higher for channels of larger perimeter to area ratio, whereas the opposite is true for the average surface charge density and mean velocity; the geometry impact on the two latest ones, however, vanishes if the background salt concentration is high enough. Moreover, we demonstrate that considering a constant surface potential equal to the average charge-regulated potential provides sufficiently accurate results for smooth geometries such as an ellipse at medium-high aspect ratios but leads to significant errors for geometries having narrow corners such as a triangle.

Influence of nanophase titania topography on bacterial attachment and metabolism

PubMed Central

Park, Margaret R; Banks, Michelle K; Applegate, Bruce; Webster, Thomas J

2008-01-01

Surfaces with nanophase compared to conventional (or nanometer smooth) topographies are known to have different properties of area, charge, and reactivity. Previously published research indicates that the attachment of certain bacteria (such as Pseudomonas fluorescens 5RL) is higher on surfaces with nanophase compared to conventional topographies, however, their effect on bacterial metabolism is unclear. Results presented here show that the adhesion of Pseudomonas fluorescens 5RL and Pseudomonas putida TVA8 was higher on nanophase than conventional titania. Importantly, in terms of metabolism, bacteria attached to the nanophase surfaces had higher bioluminescence rates than on the conventional surfaces under all nutrient conditions. Thus, the results from this study show greater select bacterial metabolism on nanometer than conventional topographies, critical results with strong consequences for the design of improved biosensors for bacteria detection. PMID:19337418

Molecular simulation study of feruloyl esterase adsorption on charged surfaces: effects of surface charge density and ionic strength.

PubMed

Liu, Jie; Peng, Chunwang; Yu, Gaobo; Zhou, Jian

2015-10-06

The surrounding conditions, such as surface charge density and ionic strength, play an important role in enzyme adsorption. The adsorption of a nonmodular type-A feruloyl esterase from Aspergillus niger (AnFaeA) on charged surfaces was investigated by parallel tempering Monte Carlo (PTMC) and all-atom molecular dynamics (AAMD) simulations at different surface charge densities (±0.05 and ±0.16 C·m(-2)) and ionic strengths (0.007 and 0.154 M). The adsorption energy, orientation, and conformational changes were analyzed. Simulation results show that whether AnFaeA can adsorb onto a charged surface is mainly controlled by electrostatic interactions between AnFaeA and the charged surface. The electrostatic interactions between AnFaeA and charged surfaces are weakened when the ionic strength increases. The positively charged surface at low surface charge density and high ionic strength conditions can maximize the utilization of the immobilized AnFaeA. The counterion layer plays a key role in the adsorption of AnFaeA on the negatively charged COOH-SAM. The native conformation of AnFaeA is well preserved under all of these conditions. The results of this work can be used for the controlled immobilization of AnFaeA.

High flux and antifouling properties of negatively charged membrane for dyeing wastewater treatment by membrane distillation.

PubMed

An, Alicia Kyoungjin; Guo, Jiaxin; Jeong, Sanghyun; Lee, Eui-Jong; Tabatabai, S Assiyeh Alizadeh; Leiknes, TorOve

2016-10-15

This study investigated the applicability of membrane distillation (MD) to treat dyeing wastewater discharged by the textile industry. Four different dyes containing methylene blue (MB), crystal violet (CV), acid red 18 (AR18), and acid yellow 36 (AY36) were tested. Two types of hydrophobic membranes made of polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) were used. The membranes were characterized by testing against each dye (foulant-foulant) and the membrane-dye (membrane-foulant) interfacial interactions and their mechanisms were identified. The MD membranes possessed negative charges, which facilitated the treatment of acid and azo dyes of the same charge and showed higher fluxes. In addition, PTFE membrane reduced the wettability with higher hydrophobicity of the membrane surface. The PTFE membrane evidenced especially its resistant to dye absorption, as its strong negative charge and chemical structure caused a flake-like (loose) dye-dye structure to form on the membrane surface rather than in the membrane pores. This also enabled the recovery of flux and membrane properties by water flushing (WF), thereby direct-contact MD with PTFE membrane treating 100 mg/L of dye mixtures showed stable flux and superior color removal during five days operation. Thus, MD shows a potential for stable long-term operation in conjunction with a simple membrane cleaning process, and its suitability in dyeing wastewater treatment. Copyright © 2016 Elsevier Ltd. All rights reserved.

Effect of Surface Hydration on Antifouling Properties of Mixed Charged Polymers.

PubMed

Leng, Chuan; Huang, Hao; Zhang, Kexin; Hung, Hsiang-Chieh; Xu, Yao; Li, Yaoxin; Jiang, Shaoyi; Chen, Zhan

2018-05-07

Interfacial water structure on a polymer surface in water (or surface hydration) is related to the antifouling activity of the polymer. Zwitterionic polymer materials exhibit excellent antifouling activity due to their strong surface hydration. It was proposed to replace zwitterionic polymers using mixed charged polymers because it is much easier to prepare mixed charged polymer samples with much lower costs. In this study, using sum frequency generation (SFG) vibrational spectroscopy, we investigated interfacial water structures on mixed charged polymer surfaces in water, and how such structures change while exposing to salt solutions and protein solutions. The 1:1 mixed charged polymer exhibits excellent antifouling property while other mixed charged polymers with different ratios of the positive/negative charges do not. It was found that on the 1:1 mixed charged polymer surface, SFG water signal is dominated by the contribution of the strongly hydrogen bonded water molecules, indicating strong hydration of the polymer surface. The responses of the 1:1 mixed charged polymer surface to salt solutions are similar to those of zwitterionic polymers. Interestingly, exposure to high concentrations of salt solutions leads to stronger hydration of the 1:1 mixed charged polymer surface after replacing the salt solution with water. Protein molecules do not substantially perturb the interfacial water structure on the 1:1 mixed charged polymer surface and do not adsorb to the surface, showing that this mixed charged polymer is an excellent antifouling material.

Effects of Discrete Charge Clustering in Simulations of Charged Interfaces.

PubMed

Grime, John M A; Khan, Malek O

2010-10-12

A system of counterions between charged surfaces is investigated, with the surfaces represented by uniform charged planes and three different arrangements of discrete surface charges - an equispaced grid and two different clustered arrangements. The behaviors of a series of systems with identical net surface charge density are examined, with particular emphasis placed on the long ranged corrections via the method of "charged slabs" and the effects of the simulation cell size. Marked differences are observed in counterion distributions and the osmotic pressure dependent on the particular representation of the charged surfaces; the uniformly charged surfaces and equispaced grids of discrete charge behave in a broadly similar manner, but the clustered systems display a pronounced decrease in osmotic pressure as the simulation size is increased. The influence of the long ranged correction is shown to be minimal for all but the very smallest of system sizes.

Asymptotic symmetries in p-form theories

NASA Astrophysics Data System (ADS)

Afshar, Hamid; Esmaeili, Erfan; Sheikh-Jabbari, M. M.

2018-05-01

We consider ( p + 1)-form gauge fields in flat (2 p + 4)-dimensions for which radiation and Coulomb solutions have the same asymptotic fall-off behavior. Imposing appropriate fall-off behavior on fields and adopting a Maxwell-type action, we construct the boundary term which renders the action principle well-defined in the Lorenz gauge. We then compute conserved surface charges and the corresponding asymptotic charge algebra associated with nontrivial gauge transformations. We show that for p ≥ 1, there are three sets of conserved asymptotic charges associated with exact, coexact and zero-mode parts of the corresponding p-form gauge transformations on the asymptotic S 2 p+2. The coexact and zero-mode charges are higher form extensions of the four dimensional electrodynamics ( p = 0), and are commuting. Charges associated with exact gauge transformations have no counterparts in four dimensions and form infinite copies of Heisenberg algebras. We briefly discuss physical implications of these charges and their algebra.

High voltage space plasma interactions. [charging the solar power satellites

NASA Technical Reports Server (NTRS)

Mccoy, J. E.

1980-01-01

Two primary problems resulted from plasma interactions; one of concern to operations in geosynchronous orbit (GEO), the other in low orbits (LEO). The two problems are not the same. Spacecraft charging has become widely recognized as a problem, particularly for communications satellites operating in GEO. The very thin thermal plasmas at GEO are insufficient to bleed off voltage buildups due to higher energy charged particle radiation collected on outer surfaces. Resulting differential charging/discharging causes electrical transients, spurious command signals and possible direct overload damage. An extensive NASA/Air Force program has been underway for several years to address this problem. At lower altitudes, the denser plasmas of the plasmasphere/ionosphere provide sufficient thermal current to limit such charging to a few volts or less. Unfortunately, these thermal plasma currents which solve the GEO spacecraft charging problem can become large enough to cause just the opposite problem in LEO.

Analytical Debye-Huckel model for electrostatic potentials around dissolved DNA.

PubMed

Wagner, K; Keyes, E; Kephart, T W; Edwards, G

1997-07-01

We present an analytical, Green-function-based model for the electric potential of DNA in solution, treating the surrounding solvent with the Debye-Huckel approximation. The partial charge of each atom is accounted for by modeling DNA as linear distributions of atoms on concentric cylindrical surfaces. The condensed ions of the solvent are treated with the Debye-Huckel approximation. The resultant leading term of the potential is that of a continuous shielded line charge, and the higher order terms account for the helical structure. Within several angstroms of the surface there is sufficient information in the electric potential to distinguish features and symmetries of DNA. Plots of the potential and equipotential surfaces, dominated by the phosphate charges, reflect the structural differences between the A, B, and Z conformations and, to a smaller extent, the difference between base sequences. As the distances from the helices increase, the magnitudes of the potentials decrease. However, the bases and sugars account for a larger fraction of the double helix potential with increasing distance. We have found that when the solvent is treated with the Debye-Huckel approximation, the potential decays more rapidly in every direction from the surface than it did in the concentric dielectric cylinder approximation.

Adsorption of intrinsically disordered barnacle adhesive proteins on silica surface

NASA Astrophysics Data System (ADS)

Wang, Xiaoqiang; Wang, Chao; Xu, Baomei; Wei, Junting; Xiao, Yang; Huang, Fang

2018-01-01

The adsorption of recombinant barnacle proteins Bacp19k and Mrcp19k on hydrophilic silica surface was characterized by spectroscopic ellipsometry in artificial seawater (pH = 8.2). They are homologous adhesive proteins destined for underwater adhesion but bear opposite net charges in seawater. As assessed with their primary and secondary structures, both proteins are intrinsically disordered and thus distinct from globular proteins that have dominated research in the field. Different from Mrcp19k, higher initial rate and adsorbed amount were obtained via curve fitting for Bacp19k in kinetic studies, due to favorable charge interactions with silica surface. The good fitting with the same dynamic model also indicates the formation of monolayer coverage in both cases. The two adsorption isotherms of Bacp19k and Mrcp19k are different in the initial change and maximum adsorption level, indicating different protein-surface affinities and charge interactions. Each isotherm fits the Langmuir model well, which is commonly used to describe monolayer adsorption, thus consistent with the predication from kinetic fitting. To further examine the effect of electrostatic interaction on the adsorption, the isotherm of the 1:1 mixture of Bacp19k and Mrcp19k was also constructed, which showed a higher correlation fit for Jovanovic than for Langmuir model. The presence of electrostatic attraction between Bacp19k and Mrcp19k deviated from one of the required conditions for Langmuir behavior, which may also result in the highest coadsorption level but slowest initial change among the three isotherms. The surface state of the adhesive proteins and the change with adsorption time were also examined by atomic force microscopy. The results thus obtained are in good agreement with the corresponding ellipsometric measurement.

An Investigation of Low Biofouling Copper-charged Membranes

NASA Astrophysics Data System (ADS)

Asapu, Sunitha

Water is essential for the survival of life on Earth, but pollutants in water can cause dangerous diseases and fatalities. The need for purified water has been increasing with increasing world population; however, natural sources of water such as rivers, lakes and streams, are progressively falling shorter and shorter of meeting water needs. The provision of clean, drinkable water to people is a key factor for the development of novel and alternative water purification technologies, such as membrane separations. Nanofiltration (NF) is a membrane separations technology that purifies water from lower quality sources, such as brackish water, seawater and wastewater. During the filtration of such sources, materials that are rejected by the membrane may accumulate on the surface of the membrane to foul it. Such materials include organic and inorganic matter, colloids, salts and microorganisms. The former four can often be controlled via pretreatment; however, the accumulation of microorganisms is more problematic to membranes. Biofouling is the accumulation and growth of microorganisms on the surface of membranes and on feed spacers. After attachment, microorganisms excrete extracellular polymeric substances (EPS), which form a matrix around the organism's outer surface as biofilm. These biofilms are detrimental and result in irreversible membrane fouling. Copper and silver ions inactivate the bacterial cells and prevent the DNA replication in microbial cells. Previous studies using copper-charged feed spacers have shown the ability of copper to control biofouling without a significant amount of copper leaching from copper-charged polypropylene (PP) feed spacers during crossflow filtration. Also, filtration using unmodified speed facers experienced almost 70% flux decline, while filtration using copper-charged feed spacers displayed only 25% flux decline. These intriguing results led to the hypothesis that the polymer chemistry could be extrapolated to produce membranes with increased biofouling resistance. The goal of this project was to develop low-biofouling nanofiltration cellulose acetate (CA) membranes through functionalization with metal chelating ligands charged with biocidal metal ions, i.e. copper ions. To this end, glycidyl methacrylate (GMA), an epoxy, was used to attach a chelating agent, iminodiacetic acid (IDA) to facilitate the charging of copper to the membrane surface. Both CA and CA-GMA membranes were cast using the phase-inversion method. The CA-GMA membranes were then charged with copper ions to make them low biofouling. Pore size distribution analysis of CA and copper charged membranes were conducted using various molecular weights of polyethylene glycol (PEG). CA and copper-charged membranes were characterized using Fourier Transform Infrared (FTIR), contact angle to measure hydrophilicity changes, and using scanning electron microscope (SEM) coupled with X-ray energy dispersive spectroscopy EDS to monitor copper leaching. Permeation experiments were conducted with distilled (DI) water, protein solutions, and synthetic brackish water containing microorganisms. The DI water permeation of the copper-charged membranes was initially lower than the CA membranes. The membranes were then subjected to bovine serum albumin (BSA) and lipase filtration. The copper-charged membranes showed higher pure water flux values for both proteins as compared to CA membranes. The rejection of BSA and lipase was the same for both the copper charged and CA membranes. The filtration with the synthetic brackish water showed that copper-charged membranes had higher flux values as compared to CA membranes, and biofouling analysis showed more bacteria on the CA membranes as compared to copper-charged membranes. Therefore, the copper-charged membranes made here have shown a potential to be used as low-biofouling membranes in the future.

The effect of residual cationic polymers in swine wastewater on the fouling of reverse osmosis membranes.

PubMed

Pedersen, C O; Masse, L; Hjorth, M

2014-01-01

Solid-liquid separation with flocculation can be used as pre-treatment for reverse osmosis (RO) filtration as it produces a liquid fraction (LF) low in suspended solids (SS). However, residual polymers in the LF may foul the membrane. Membrane fouling during RO filtration of swine wastewater containing polymers was investigated with respect to polymer charge density (CD), effluent SS concentration and membrane surface charge. Effluents with 765 mg/L SS and without SS were spiked with low and medium CD polymers (0-40 mg/L effluent) then processed with RO membranes having low and high negative surface charges. Fouling intensity was evaluated by comparing permeate flux and water flux recovery of fouled and cleaned membranes. For effluents containing SS, the presence of polymer reduced permeate flux by 4-16% and water flux recovery of the fouled membrane by 0-18%, relative to effluents without polymer. The extent of the fouling was higher with the low than the medium CD polymer. The fouling was mostly reversible as cleaning allowed for over 95% flux recovery, but the membrane with high negative surface charge was more susceptible to irreversible fouling. Adding the low CD polymer to feed without SS had no effect on permeate flux or flux recovery. Membrane fouling thus appeared to be caused by the polymer changing SS-membrane interaction. If flocculation is applied to pre-treat manure, a medium CD polymer should be used to optimize SS removal and a membrane with low surface charge should be selected to minimize fouling.

The Ostrogradsky Prescription for BFV Formalism

NASA Astrophysics Data System (ADS)

Nirov, Khazret S.

Gauge-invariant systems of a general form with higher order time derivatives of gauge parameters are investigated within the framework of the BFV formalism. Higher order terms of the BRST charge and BRST-invariant Hamiltonian are obtained. It is shown that the identification rules for Lagrangian and Hamiltonian BRST ghost variables depend on the choice of the extension of constraints from the primary constraint surface.

Adsorption of different amphiphilic molecules onto polystyrene latices.

PubMed

Jódar-Reyes, A B; Ortega-Vinuesa, J L; Martín-Rodríguez, A

2005-02-15

In order to know the influence of the surface characteristics and the chain properties on the adsorption of amphiphilic molecules onto polystyrene latex, a set of experiments to study the adsorption of ionic surfactants, nonionic surfactants and an amphiphilic synthetic peptide on different latex dispersions was performed. The adsorbed amount versus the equilibrium surfactant concentration was determined. The main adsorption mechanism was the hydrophobic attraction between the nonpolar tail of the molecule and the hydrophobic regions of the latex surface. This attraction overcame the electrostatic repulsion between chains and latex surface with identical charge sign. However, the electrostatic interactions chain-surface and chain-chain also played a role. General patterns for the adsorption of ionic chains on charged latex surfaces could be established. Regarding the shape, the isotherms presented different plateaus corresponding to electrostatic effects and conformational changes. The surfactant size also affects the adsorption results: the higher the hydrophilic moiety in the surfactant molecule the lower the adsorbed amount.

Modeling of charged particles trajectories in order to optimize the design of a new, higher resolution, Time of flight- Positron Annihilation Induced Auger Electron Spectroscopy (TOF PAES) System

NASA Astrophysics Data System (ADS)

Joglekar, Prasad; Lim, L.; Satyal, Suman; Kalaskar, Sushant; Shastry, K.; Weiss, Alex

2011-03-01

Time of Flight Positron Annihilation Induced~Auger Electron Spectroscopy~(TOF PAES) is a surface analytical technique with high surface selectivity. TOF PAES is used to study elemental composition, surface defects, and various energy loss mechanisms. Positrons incident on the sample surface at low energies can be trapped in an image-potential well just above the surface Prior to annihilation. Consequently it is possible to use positron annihilation related signals to selectively probe the top-most atomic layer. This poster presents the results of modeling of the charge particle beam transport system performed in connection with the optimization of the the design of the new TOF-PAES system currently under construction at U T Arlington. The system will incorporate a 2 m long drift tube in order to achieve better energy resolution than our previous TOF-PAES system design which used a 1 m long drift tube NSF DMR 0907679, Welch Foundation Y 1100.

Competition between surface adsorption and folding of fibril-forming polypeptides

NASA Astrophysics Data System (ADS)

Ni, Ran; Kleijn, J. Mieke; Abeln, Sanne; Cohen Stuart, Martien A.; Bolhuis, Peter G.

2015-02-01

Self-assembly of polypeptides into fibrillar structures can be initiated by planar surfaces that interact favorably with certain residues. Using a coarse-grained model, we systematically studied the folding and adsorption behavior of a β -roll forming polypeptide. We find that there are two different folding pathways depending on the temperature: (i) at low temperature, the polypeptide folds in solution into a β -roll before adsorbing onto the attractive surface; (ii) at higher temperature, the polypeptide first adsorbs in a disordered state and folds while on the surface. The folding temperature increases with increasing attraction as the folded β -roll is stabilized by the surface. Surprisingly, further increasing the attraction lowers the folding temperature again, as strong attraction also stabilizes the adsorbed disordered state, which competes with folding of the polypeptide. Our results suggest that to enhance the folding, one should use a weakly attractive surface. They also explain the recent experimental observation of the nonmonotonic effect of charge on the fibril formation on an oppositely charged surface [C. Charbonneau et al., ACS Nano 8, 2328 (2014), 10.1021/nn405799t].

Impact of GaN cap on charges in Al₂O₃/(GaN/)AlGaN/GaN metal-oxide-semiconductor heterostructures analyzed by means of capacitance measurements and simulations

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

Ťapajna, M., E-mail: milan.tapajna@savba.sk; Jurkovič, M.; Válik, L.

2014-09-14

Oxide/semiconductor interface trap density (D{sub it}) and net charge of Al₂O₃/(GaN)/AlGaN/GaN metal-oxide-semiconductor high-electron mobility transistor (MOS-HEMT) structures with and without GaN cap were comparatively analyzed using comprehensive capacitance measurements and simulations. D{sub it} distribution was determined in full band gap of the barrier using combination of three complementary capacitance techniques. A remarkably higher D{sub it} (∼5–8 × 10¹²eV⁻¹ cm⁻²) was found at trap energies ranging from E C-0.5 to 1 eV for structure with GaN cap compared to that (D{sub it} ∼ 2–3 × 10¹²eV⁻¹ cm⁻²) where the GaN cap was selectively etched away. D{sub it} distributions were then used for simulation of capacitance-voltage characteristics. A good agreement betweenmore » experimental and simulated capacitance-voltage characteristics affected by interface traps suggests (i) that very high D{sub it} (>10¹³eV⁻¹ cm⁻²) close to the barrier conduction band edge hampers accumulation of free electron in the barrier layer and (ii) the higher D{sub it} centered about E C-0.6 eV can solely account for the increased C-V hysteresis observed for MOS-HEMT structure with GaN cap. Analysis of the threshold voltage dependence on Al₂O₃ thickness for both MOS-HEMT structures suggests that (i) positive charge, which compensates the surface polarization, is not necessarily formed during the growth of III-N heterostructure, and (ii) its density is similar to the total surface polarization charge of the GaN/AlGaN barrier, rather than surface polarization of the top GaN layer only. Some constraints for the positive surface compensating charge are discussed.« less

pH-dependence of pesticide adsorption by wheat-residue-derived black carbon.

PubMed

Yang, Yaning; Chun, Yuan; Sheng, Guangyao; Huang, Minsheng

2004-08-03

The potential of black carbon as an adsorbent for pesticides in soils may be strongly influenced by the properties of the adsorbent and pesticides and by the environmental conditions. This study evaluated the effect of pH on the adsorption of diuron, bromoxynil, and ametryne by a wheat (Triticum aestivum L.) residue derived black carbon (WC) as compared to a commercial activated carbon (AC). The pH drift method indicated that WC had a point of zero charge of 4.2, much lower than that of 7.8 for AC. The density of oxygen-containing surface functional groups, measured by the Boehm titration, on WC was 5.4 times higher than that on AC, resulting in a pesticide adsorption by WC being 30-50% of that by AC, due to the blockage of WC surface by the waters associated with the functional groups. A small decrease (5.5%/unit pH) in diuron adsorption by WC with increase in pH resulted from increased deprotonation of surface functional groups at higher pH values. A much larger decrease (14-21%/unit pH) in bromoxynil adsorption by WC with increase in pH resulted from the deprotonation of both the adsorbate and surface functional groups of the adsorbent. The deprotonation reduced the adsorptive interaction between bromoxynil and the neutral carbon surface and increased the electrical repulsion between the negatively charged WC surface and bromoxynil anions. Deprotonation of ametryne with increase in pH over the low pH range increased its fraction of molecular form and thus adsorption on WC by 15%/unit pH. Further increase in pH resulted in a 20%/unit pH decrease in ametryne adsorption by WC due primarily to the development of a negative charge on the surface of WC. The pH-dependent adsorption of pesticides by black carbon may significantly influence their environmental fate in soils.

Studies of Surface Charging of Polymers by Indirect Triboelectrification

NASA Astrophysics Data System (ADS)

Mantovani, James; Calle, Carlos; Groop, Ellen; Buehler, Martin

2001-03-01

Charge is known to develop on the surface of an insulating polymer by frictional charging through direct physical contact with another material. We will present results of recent triboelectrification studies of polymer surfaces that utilized an indirect method of frictional charging. This method first involves placing a grounded thin metal foil in stationary contact over the polymer surface. The exposed metal foil is then rubbed with the surface of the material that generates the triboelectric charge. Data is presented for five types of polymers: fiberglass/epoxy, polycarbonate (Lexan), polytetraflouroethylene (Teflon), Rulon J, and polymethylmethacrylate (PMMA, Lucite). The amount of charge that develops on an insulator's surface is measured using the MECA Electrometer, which was developed jointly by NASA Kennedy Space Center and the Jet Propulsion Laboratory to study the electrostatic properties of soil on the surface of Mars. Even though the insulator's surface is electrically shielded from the rubbing material by the grounded metal foil, charge measurements obtained by the MECA Electrometer after the metal foil is separated from the insulator's surface reveal that the insulator's surface does accumulate charge by indirect frictional charging. A possible explanation of the observations will be presented based on a simple contact barrier model.

Current-voltage characteristics influenced by the nanochannel diameter and surface charge density in a fluidic field-effect-transistor.

PubMed

Singh, Kunwar Pal; Guo, Chunlei

2017-06-21

The nanochannel diameter and surface charge density have a significant impact on current-voltage characteristics in a nanofluidic transistor. We have simulated the effect of the channel diameter and surface charge density on current-voltage characteristics of a fluidic nanochannel with positive surface charge on its walls and a gate electrode on its surface. Anion depletion/enrichment leads to a decrease/increase in ion current with gate potential. The ion current tends to increase linearly with gate potential for narrow channels at high surface charge densities and narrow channels are more effective to control the ion current at high surface charge densities. The current-voltage characteristics are highly nonlinear for wide channels at low surface charge densities and they show different regions of current change with gate potential. The ion current decreases with gate potential after attaining a peak value for wide channels at low values of surface charge densities. At low surface charge densities, the ion current can be controlled by a narrow range of gate potentials for wide channels. The current change with source drain voltage shows ohmic, limiting and overlimiting regions.

Glutamate Induced Thermal Equilibrium Intermediate and Counteracting Effect on Chemical Denaturation of Proteins.

PubMed

Anumalla, Bramhini; Prabhu, N Prakash

2018-01-25

When organisms are subjected to stress conditions, one of their adaptive responses is accumulation of small organic molecules called osmolytes. These osmolytes affect the structure and stability of the biological macromolecules including proteins. The present study examines the effect of a negatively charged amino acid osmolyte, glutamate (Glu), on two model proteins, ribonuclease A (RNase A) and α-lactalbumin (α-LA), which have positive and negative surface charges at pH 7, respectively. These proteins follow two-state unfolding transitions during both heat and chemical induced denaturation processes. The addition of Glu stabilizes the proteins against temperature and induces an early equilibrium intermediate during unfolding. The stability is found to be enthalpy-driven, and the free energy of stabilization is more for α-LA compared to RNase A. The decrease in the partial molar volume and compressibility of both of the proteins in the presence of Glu suggests that the proteins attain a more compact state through surface hydration which could provide a more stable conformation. This is also supported by molecule dynamic simulation studies which demonstrate that the water density around the proteins is increased upon the addition of Glu. Further, the intermediates could be completely destabilized by lower concentrations (∼0.5 M) of guanidinium chloride and salt. However, urea subverts the Glu-induced intermediate formed by α-LA, whereas it only slightly destabilizes in the case of RNase A which has a positive surface charge and could possess charge-charge interactions with Glu. This suggests that, apart from hydration, columbic interactions might also contribute to the stability of the intermediate. Gdm-induced denaturation of RNase A and α-LA in the absence and the presence of Glu at different temperatures was carried out. These results also show the Glu-induced stabilization of both of the proteins; however, all of the unfolding transitions followed two-state transitions during chemical denaturation. The extent of stability exerted by Glu is higher for RNase A at higher temperature, whereas it provides more stability for α-LA at lower temperature. Thus, the experiments indicate that Glu induces a thermal equilibrium intermediate and increases the thermodynamic stability of proteins irrespective of their surface charges. The extent of stability varies between the proteins in a temperature-dependent manner.

Persistent photoconductivity due to trapping of induced charges in Sn/ZnO thin film based UV photodetector

NASA Astrophysics Data System (ADS)

Yadav, Harish Kumar; Sreenivas, K.; Gupta, Vinay

2010-05-01

Photoconductivity relaxation in rf magnetron sputtered ZnO thin films integrated with ultrathin tin metal overlayer is investigated. Charge carriers induced at the ZnO-metal interface by the tin metal overlayer compensates the surface lying trap centers and leads to the enhanced photoresponse. On termination of ultraviolet radiation, recombination of the photoexcited electrons with the valence band holes leaves the excess carriers deeply trapped at the recombination center and holds the dark conductivity level at a higher value. Equilibrium between the recombination centers and valence band, due to trapped charges, eventually stimulates the persistent photoconductivity in the Sn/ZnO photodetectors.

Investigating local degradation and thermal stability of charged nickel-based cathode materials through real-time electron microscopy.

PubMed

Hwang, Sooyeon; Kim, Seung Min; Bak, Seong-Min; Cho, Byung-Won; Chung, Kyung Yoon; Lee, Jeong Yong; Chang, Wonyoung; Stach, Eric A

2014-09-10

In this work, we take advantage of in situ transmission electron microscopy (TEM) to investigate thermally induced decomposition of the surface of Li(x)Ni(0.8)Co(0.15)Al(0.05)O2 (NCA) cathode materials that have been subjected to different states of charge (SOC). While uncharged NCA is stable up to 400 °C, significant changes occur in charged NCA with increasing temperature. These include the development of surface porosity and changes in the oxygen K-edge electron energy loss spectra, with pre-edge peaks shifting to higher energy losses. These changes are closely related to O2 gas released from the structure, as well as to phase changes of NCA from the layered structure to the disordered spinel structure, and finally to the rock-salt structure. Although the temperatures where these changes initiate depend strongly on the state of charge, there also exist significant variations among particles with the same state of charge. Notably, when NCA is charged to x = 0.33 (the charge state that is the practical upper limit voltage in most applications), the surfaces of some particles undergo morphological and oxygen K-edge changes even at temperatures below 100 °C, a temperature that electronic devices containing lithium ion batteries (LIB) can possibly see during normal operation. Those particles that experience these changes are likely to be extremely unstable and may trigger thermal runaway at much lower temperatures than would be usually expected. These results demonstrate that in situ heating experiments are a unique tool not only to study the general thermal behavior of cathode materials but also to explore particle-to-particle variations, which are sometimes of critical importance in understanding the performance of the overall system.

Rectification of nanopores at surfaces

PubMed Central

Sa, Niya

2011-01-01

At the nanoscale, methods to measure surface charge can prove challenging. Herein we describe a general method to report surface charge through the measurement of ion current rectification of a nanopipette brought in close proximity to a charged substrate. This method is able to discriminate between charged cationic and anionic substrates when the nanopipette is brought within distances from ten to hundreds of nanometers from the surface. Further studies of the pH dependence on the observed rectification support a surface-induced mechanism and demonstrate the ability to further discriminate between cationic and nominally uncharged surfaces. This method could find application in measurement and mapping of heterogeneous surface charges and is particularly attractive for future biological measurements, where noninvasive, noncontact probing of surface charge will prove valuable. PMID:21675734

Two superconducting transitions in single-crystal La 2 - x Ba x CuO 4

DOE PAGES

Tee, X. Y.; Ito, T.; Ushiyama, T.; ...

2017-02-27

Here, we use spatially-resolved transport techniques to investigate the superconducting properties of single crystals La 2-xBa xCuO 4. We also found a superconducting transition temperature T cs associated with the ab-plane surface region which is considerably higher than the bulk T c. This effect is pronounced in the region of charge carrier doping x with strong spin-charge stripe correlations, reaching T cs = 36 K or 1.64T c.

Protein-Nanoparticle Interactions: Improving Immobilized Lytic Enzyme Activity and Surface Energy Effects

NASA Astrophysics Data System (ADS)

Downs, Emily Elizabeth

Protein-nanostructure conjugates, particularly particles, are a subject of significant interest due to changes in their fundamental behavior compared to bulk surfaces. As the size scale of nano-structured materials and proteins are on the same order of magnitude, nanomaterial properties can heavily influence how proteins adsorb and conform to the surface. Previous work has demonstrated the ability of nanoscale surfaces to modulate protein activity, conformation, and retention by modifying the particle surface curvature, morphology, and surface charge. This work has improved our understanding of the protein material interactions, but a complete understanding is still lacking. The goal of this thesis is to investigate two missing areas of understanding using two distinct systems. The first system utilizes a particle with controlled surface energy to observe the impact of surface energy on protein-particle interactions, while the second system uses a modified Listeria-specific protein to determine how protein structure and flexibility affects protein adsorption and activity on particles. Spherical, amorphous, and uniformly doped Zn-silica particles with tailored surface energies were synthesized to understand the impact of surface energy on protein adsorption behavior. Particle surface energy increased with a decrease in particle size and greater dopant concentrations. Protein adsorption and structural loss increased with both particle size and particle surface energy. Higher surface energies promoted protein-particle association and increased protein unfolding. Particle curvature and protein steric hindrance effects limited adsorption and structural loss on smaller particles. Protein surface charge heterogeneity was also found to be linked to both protein adsorption and unfolding behavior on larger particles. Greater surface charge heterogeneity led to higher adsorption concentrations and multilayer formation. These multilayers transitioned from protein-particle interactions to protein-protein interactions and were thicker with greater surface energy, which resulted in the recovery of secondary structure in the outermost layer. To help understand the impact of protein structure on nano-bio conjugate interactions, a listeria specific protein was used. This system was chosen as it has applications in the food industry in preventing bacterial contamination. The insertion of an amino acid linker between the enzymatic and binding domain of the protein improved the flexibility between domains, leading to increased adsorption, and improved activity in both cell-wall and plating assays. Additionally, linker modified protein incorporated into the silica-polymer nanocomposite showed significant activity in a real-world example of contaminated lettuce. This thesis study has isolated the impact of surface energy and protein flexibility on protein adsorption and structure. Particle surface energy affects adsorbed protein concentration and conformation. Coupled with protein surface charge, surface energy was also found to dictate multilayer thickness. The conformational flexibility of the protein was shown to help in controlling not only protein adsorption concentration but also in retaining protein activity after immobilization. Also, a controllable synthesis method for particles with adjustable surface energy, an ideal platform for studying protein-particle interactions, has been established.

Interactive effects of biochar ageing in soils related to feedstock, pyrolysis temperature, and historic charcoal production.

NASA Astrophysics Data System (ADS)

Heitkötter, Julian; Marschner, Bernd

2015-04-01

Biochar is suggested for soil amelioration and carbon sequestration, based on its assumed role as the key factor for the long-term fertility of Terra preta soils. Several studies have shown that certain biochar properties can undergo changes through ageing processes, especially regarding charge characteristics. However, only a few studies determined the changes of different biochars under the same incubation conditions and in different soils. The objective of this study was to characterize the changes of pine chip (PC)- and corn digestate (CD)-derived biochars pyrolyzed at 400 or 600 °C during 100 days of laboratory incubation in a historical kiln soil and an adjacent control soil. Separation between soil and biochar was ensured by using mesh bags. Especially, changes in charge characteristics depended on initial biochar properties affected by feedstock and pyrolysis temperature and on soil properties affected by historic charcoal production. While the cation exchange capacity (CEC) markedly increased for both CD biochars during incubation, PC biochars showed no or only slight increases in CEC. Corresponding to the changes in CEC, ageing of biochars also increased the amount of acid functional groups with increases being in average about 2-fold higher in CD biochars than in PC biochars. Further and in contrast to other studies, the surface areas of biochars increased during ageing, likely due to ash leaching and degradation of tar residues. Changes in CEC and surface acidity of CD biochars were more pronounced after incubation in the control soil, while surface area increase was higher in the kiln soil. Since the two acidic forest soils used in this this study did not greatly differ in physical or chemical properties, the main process for inducing these differences in the buried biochar most likely is related to the differences in dissolved organic carbon (DOC). Although the kiln soil contained about 50% more soil organic carbon due to the presence of charcoal particles, extractable DOC was lower and less aromatic than in the adjacent control soil, likely due to strong sorption of dissolved organic matter (DOM) onto charcoal particles. We suggest that higher sorption of DOM onto the surface of biochar in the control soil provided additional acid functional groups and thus increased the surface charge to a greater extent than in the DOC poorer kiln soil. Hence, biochars incubated in the kiln soil showed less changes in CEC and surface acidity. Higher availability of DOM in the control soil could also stimulate microbial activity to a larger extent, resulting in higher oxidation rates of biochars incubated in the control soil.

The electrokinetic behavior of calcium oxalate monohydrate in macromolecular solutions

NASA Technical Reports Server (NTRS)

Curreri, P. A.; Onoda, G. Y., Jr.; Finlayson, B.

1988-01-01

Electrophoretic mobilities were measured for calcium oxalate monohydrate (COM) in solutions containing macromolecules. Two mucopolysaccharides (sodium heparin and chrondroitin sulfate) and two proteins (positively charged lysozyme and negatively charged bovine serum albumin) were studied as adsorbates. The effects of pH, calcium oxalate surface charge (varied by calcium or oxalate ion activity), and citrate concentration were investigated. All four macromolecules showed evidence for chemical adsorption. The macromolecule concentrations needed for reversing the surface charge indicated that the mucopopolysacchrides have greater affinity for the COM surface than the proteins. The amount of proteins that can chemically adsorb appears to be limited to approximately one monomolecular layer. When the surface charge is high, an insufficient number of proteins can chemically adsorb to neutralize or reverse the surface charge. The remaining surface charge is balanced by proteins held near the surface by longer range electrostatic forces only. Citrate ions at high concentrations appear to compete effectively with the negative protein for surface sites but show no evidence for competing with the positively charged protein.

Swelling properties of montmorillonite and beidellite clay minerals from molecular simulation: Comparison of temperature interlayer cation, and charge location effects

DOE PAGES

Teich-McGoldrick, Stephanie L.; Greathouse, Jeffery A.; Jove-Colon, Carlos F.; ...

2015-08-27

In this study, the swelling properties of smectite clay minerals are relevant to many engineering applications including environmental remediation, repository design for nuclear waste disposal, borehole stability in drilling operations, and additives for numerous industrial processes and commercial products. We used molecular dynamics and grand canonical Monte Carlo simulations to study the effects of layer charge location, interlayer cation, and temperature on intracrystalline swelling of montmorillonite and beidellite clay minerals. For a beidellite model with layer charge exclusively in the tetrahedral sheet, strong ion–surface interactions shift the onset of the two-layer hydrate to higher water contents. In contrast, for amore » montmorillonite model with layer charge exclusively in the octahedral sheet, weaker ion–surface interactions result in the formation of fully hydrated ions (two-layer hydrate) at much lower water contents. Clay hydration enthalpies and interlayer atomic density profiles are consistent with the swelling results. Water adsorption isotherms from grand canonical Monte Carlo simulations are used to relate interlayer hydration states to relative humidity, in good agreement with experimental findings.« less

Protein adsorption at charged surfaces: the role of electrostatic interactions and interfacial charge regulation.

PubMed

Hartvig, Rune A; van de Weert, Marco; Østergaard, Jesper; Jorgensen, Lene; Jensen, Henrik

2011-03-15

The understanding of protein adsorption at charged surfaces is important for a wide range of scientific disciplines including surface engineering, separation sciences and pharmaceutical sciences. Compared to chemical entities having a permanent charge, the adsorption of small ampholytes and proteins is more complicated as the pH near a charged surface can be significantly different from the value in bulk solution. In this work, we have developed a phenomenological adsorption model which takes into account the combined role of interfacial ion distribution, interfacial charge regulation of amino acids in the proximity of the surface, electroneutrality, and mass balance. The model is straightforward to apply to a given set of experimental conditions as most model parameters are obtained from bulk properties and therefore easy to estimate or are directly measurable. The model provides a detailed understanding of the importance of surface charge on adsorption and in particular of how changes in surface charge, concentration, and surface area may affect adsorption behavior. The model is successfully used to explain the experimental adsorption behavior of the two model proteins lysozyme and α-lactalbumin. It is demonstrated that it is possible to predict the pH and surface charge dependent adsorption behavior from experimental or theoretical estimates of a preferred orientation of a protein at a solid charged interface.

The Charging Events in Contact-Separation Electrification.

PubMed

Musa, Umar G; Cezan, S Doruk; Baytekin, Bilge; Baytekin, H Tarik

2018-02-06

Contact electrification (CE)-charging of surfaces that are contacted and separated, is a common phenomenon, however it is not completely understood yet. Recent studies using surface imaging techniques and chemical analysis revealed a 'spatial' bipolar distribution of charges at the nano dimension, which made a paradigm shift in the field. However, such analyses can only provide information about the charges that remained on the surface after the separation, providing limited information about the actual course of the CE event. Tapping common polymers and metal surfaces to each other and detecting the electrical potential produced on these surfaces 'in-situ' in individual events of contact and separation, we show that, charges are generated and transferred between the surfaces in both events; the measured potential is bipolar in contact and unipolar in separation. We show, the 'contact-charges' on the surfaces are indeed the net charges that results after the separation process, and a large contribution to tribocharge harvesting comes, in fact, from the electrostatic induction resulting from the generated CE charges. Our results refine the mechanism of CE providing information for rethinking the conventional ranking of materials' charging abilities, charge harvesting, and charge prevention.

Charged particle detectors with active detector surface for partial energy deposition of the charged particles and related methods

DOEpatents

Gerts, David W; Bean, Robert S; Metcalf, Richard R

2013-02-19

A radiation detector is disclosed. The radiation detector comprises an active detector surface configured to generate charge carriers in response to charged particles associated with incident radiation. The active detector surface is further configured with a sufficient thickness for a partial energy deposition of the charged particles to occur and permit the charged particles to pass through the active detector surface. The radiation detector further comprises a plurality of voltage leads coupled to the active detector surface. The plurality of voltage leads is configured to couple to a voltage source to generate a voltage drop across the active detector surface and to separate the charge carriers into a plurality of electrons and holes for detection. The active detector surface may comprise one or more graphene layers. Timing data between active detector surfaces may be used to determine energy of the incident radiation. Other apparatuses and methods are disclosed herein.

Influence of pH, layer charge location and crystal thickness distribution on U(VI) sorption onto heterogeneous dioctahedral smectite.

PubMed

Guimarães, Vanessa; Rodríguez-Castellón, Enrique; Algarra, Manuel; Rocha, Fernando; Bobos, Iuliu

2016-11-05

The UO2(2+) adsorption on smectite (samples BA1, PS2 and PS3) with a heterogeneous structure was investigated at pH 4 (I=0.02M) and pH 6 (I=0.2M) in batch experiments, with the aim to evaluate the influence of pH, layer charge location and crystal thickness distribution. Mean crystal thickness distribution of smectite crystallite used in sorption experiments range from 4.8nm (sample PS2), to 5.1nm (sample PS3) and, to 7.4nm (sample BA1). Smaller crystallites have higher total surface area and sorption capacity. Octahedral charge location favor higher sorption capacity. The sorption isotherms of Freundlich, Langmuir and SIPS were used to model the sorption experiments. The surface complexation and cation exchange reactions were modeled using PHREEQC-code to describe the UO2(2+) sorption on smectite. The amount of UO2(2+) adsorbed on smectite samples decreased significantly at pH 6 and higher ionic strength, where the sorption mechanism was restricted to the edge sites of smectite. Two binding energy components at 380.8±0.3 and 382.2±0.3eV, assigned to hydrated UO2(2+) adsorbed by cation exchange and by inner-sphere complexation on the external sites at pH 4, were identified after the U4f7/2 peak deconvolution by X-photoelectron spectroscopy. Also, two new binding energy components at 380.3±0.3 and 381.8±0.3eV assigned to AlOUO2(+) and SiOUO2(+) surface species were observed at pH 6. Copyright © 2016 Elsevier B.V. All rights reserved.

Endogenous minerals have influences on surface electrochemistry and ion exchange properties of biochar.

PubMed

Zhao, Ling; Cao, Xinde; Zheng, Wei; Wang, Qun; Yang, Fan

2015-10-01

The feedstocks for biochar production are diverse and many of them contain various minerals in addition to being rich in carbon. Twelve types of biomass classified into 2 categories: plant-based and municipal waste, were employed to produce biochars under 350 °C and 500 °C. Their pH, point of zero net charge (PZNC), zeta potential, cation and anion exchange capacity (CEC and AEC) were analyzed. The municipal waste-based biochars (MW-BC) had higher mineral levels than the plant-based biochars (PB-BC). However, the water soluble mineral levels were lower in the MW-BCs due to the dominant presence of less soluble minerals, such as CaCO3 and (Ca,Mg)3(PO4)2. The higher total minerals in MW-BCs accounted for the higher PZNC (5.47-9.95) than in PB-BCs (1.91-8.18), though the PZNCs of the PB-BCs increased more than that of the MW-BCs as the production temperature rose. The minerals had influence on the zeta potentials via affecting the negative charges of biochars and the ionic strength of solution. The organic functional groups in PB-BCs such as -COOH and -OH had a greater effect on the CEC and AEC, while the minerals had a greater effect on that of MW-BCs. The measured CEC and AEC values had a strong positive correlation with the total amount of soluble cations and anions, respectively. Results indicated that biochar surface charges depend not only on the organic functional groups, but also on the minerals present and to some extent, minerals have more influences on the surface electrochemistry and ion exchange properties of biochar. Copyright © 2015 Elsevier Ltd. All rights reserved.

NASA charging analyzer program: A computer tool that can evaluate electrostatic contamination

NASA Technical Reports Server (NTRS)

Stevens, N. J.; Roche, J. C.; Mandell, M. J.

1978-01-01

A computer code, the NASA Charging Analyzer Program (NASCAP), was developed to study the surface charging of bodies subjected to geomagnetic substorm conditions. This program will treat the material properties of a surface in a self-consistent manner and calculate the electric fields in space due to the surface charge. Trajectories of charged particles in this electric field can be computed to determine if these particles enhance surface contamination. A preliminary model of the Spacecraft Charging At The High Altitudes (SCATHA) satellite was developed in the NASCAP code and subjected to a geomagnetic substorm environment to investigate the possibility of electrostatic contamination. The results indicate that differential voltages will exist between the spacecraft ground surfaces and the insulator surfaces. The electric fields from this differential charging can enhance the contamination of spacecraft surfaces.

An insight into the mechanism of charge-transfer of hybrid polymer:ternary/quaternary chalcopyrite colloidal nanocrystals.

PubMed

Chawla, Parul; Singh, Son; Sharma, Shailesh Narain

2014-01-01

In this work, we have demonstrated the structural and optoelectronic properties of the surface of ternary/quaternary (CISe/CIGSe/CZTSe) chalcopyrite nanocrystallites passivated by tri-n-octylphosphine-oxide (TOPO) and tri-n-octylphosphine (TOP) and compared their charge transfer characteristics in the respective polymer: chalcopyrite nanocomposites by dispersing them in poly(3-hexylthiophene) polymer. It has been found that CZTSe nanocrystallites due to their high crystallinity and well-ordered 3-dimensional network in its pristine form exhibit a higher steric- and photo-stability, resistance against coagulation and homogeneity compared to the CISe and CIGSe counterparts. Moreover, CZTSe nanocrystallites display efficient photoluminescence quenching as evident from the high value of the Stern-Volmer quenching constant (K SV) and eventually higher charge transfer efficiency in their respective polymer P3HT:CZTSe composites. We modelled the dependency of the charge transfer from the donor and the charge separation mechanism across the donor-acceptor interface from the extent of crystallinity of the chalcopyrite semiconductors (CISe/CIGSe/CZTSe). Quaternary CZTSe chalcopyrites with their high crystallinity and controlled morphology in conjunction with regioregular P3HT polymer is an attractive candidate for hybrid solar cells applications.

Adhesion of osteoblasts to a nanorough titanium implant surface

PubMed Central

Gongadze, Ekaterina; Kabaso, Doron; Bauer, Sebastian; Slivnik, Tomaž; Schmuki, Patrik; van Rienen, Ursula; Iglič, Aleš

2011-01-01

This work considers the adhesion of cells to a nanorough titanium implant surface with sharp edges. The basic assumption was that the attraction between the negatively charged titanium surface and a negatively charged osteoblast is mediated by charged proteins with a distinctive quadrupolar internal charge distribution. Similarly, cation-mediated attraction between fibronectin molecules and the titanium surface is expected to be more efficient for a high surface charge density, resulting in facilitated integrin mediated osteoblast adhesion. We suggest that osteoblasts are most strongly bound along the sharp convex edges or spikes of nanorough titanium surfaces where the magnitude of the negative surface charge density is the highest. It is therefore plausible that nanorough regions of titanium surfaces with sharp edges and spikes promote the adhesion of osteoblasts. PMID:21931478

Improved electrochemical properties of morphology-controlled titania/titanate nanostructures prepared by in-situ hydrothermal surface modification of self-source Ti substrate for high-performance supercapacitors.

PubMed

Banerjee, Arghya Narayan; Anitha, V C; Joo, Sang W

2017-10-16

Ti substrate surface is modified into two-dimensional (2D) TiO 2 nanoplatelet or one-dimensional (1D) nanorod/nanofiber (or a mixture of both) structure in a controlled manner via a simple KOH-based hydrothermal technique. Depending on the KOH concentration, different types of TiO 2 nanostructures (2D platelets, 1D nanorods/nanofibers and a 2D+1D mixed sample) are fabricated directly onto the Ti substrate surface. The novelty of this technique is the in-situ modification of the self-source Ti surface into titania nanostructures, and its direct use as the electrochemical microelectrode without any modifications. This leads to considerable improvement in the interfacial properties between metallic Ti and semiconducting TiO 2 . Since interfacial states/defects have profound effect on charge transport properties of electronic/electrochemical devices, therefore this near-defect-free interfacial property of Ti-TiO 2 microelectrode has shown high supercapacitive performances for superior charge-storage devices. Additionally, by hydrothermally tuning the morphology of titania nanostructures, the electrochemical properties of the electrodes are also tuned. A Ti-TiO 2 electrode comprising of a mixture of 2D-platelet+1D-nanorod structure reveals very high specific capacitance values (~7.4 mF.cm -2 ) due to the unique mixed morphology which manifests higher active sites (hence, higher utilization of the active materials) in terms of greater roughness at the 2D-platelet structures and higher surface-to-volume-ratio in the 1D-nanorod structures.

Effects of image charges, interfacial charge discreteness, and surface roughness on the zeta potential of spherical electric double layers.

PubMed

Gan, Zecheng; Xing, Xiangjun; Xu, Zhenli

2012-07-21

We investigate the effects of image charges, interfacial charge discreteness, and surface roughness on spherical electric double layer structures in electrolyte solutions with divalent counterions in the setting of the primitive model. By using Monte Carlo simulations and the image charge method, the zeta potential profile and the integrated charge distribution function are computed for varying surface charge strengths and salt concentrations. Systematic comparisons were carried out between three distinct models for interfacial charges: (1) SURF1 with uniform surface charges, (2) SURF2 with discrete point charges on the interface, and (3) SURF3 with discrete interfacial charges and finite excluded volume. By comparing the integrated charge distribution function and the zeta potential profile, we argue that the potential at the distance of one ion diameter from the macroion surface is a suitable location to define the zeta potential. In SURF2 model, we find that image charge effects strongly enhance charge inversion for monovalent interfacial charges, and strongly suppress charge inversion for multivalent interfacial charges. For SURF3, the image charge effect becomes much smaller. Finally, with image charges in action, we find that excluded volumes (in SURF3) suppress charge inversion for monovalent interfacial charges and enhance charge inversion for multivalent interfacial charges. Overall, our results demonstrate that all these aspects, i.e., image charges, interfacial charge discreteness, their excluding volumes, have significant impacts on zeta potentials of electric double layers.

On the physics of both surface overcharging and charge reversal at heterophase interfaces.

PubMed

Wang, Zhi-Yong; Zhang, Pengli; Ma, Zengwei

2018-02-07

The conventional paradigm for characterizing surface overcharging and charge reversal is based on the so-called Stern layer, in which surface dissociation reaction and specific chemical adsorption are assumed to take place. In this article, a series of Monte Carlo simulations have been applied to obtain useful insights into the underlying physics responsible for these two kinds of anomalous phenomena at the interface of two dielectrics, with special emphasis on the case of divalent counterions that are more relevant in natural and biological environments. At a weakly charged surface, it is found that independent of the type of surface charge distribution and the dielectric response of the solution, the overcharging event is universally driven by the ion size-asymmetric effect. Exceptionally, the overcharging still persists when the surface is highly charged but is only restricted to the case of discrete surface charge in a relatively low dielectric medium. As compared to the adsorption onto the homogeneously smeared charge surface that has the same average affinity for counterions, on the other hand, charge reversal under the action of a dielectric response can be substantially enhanced in the discrete surface charge representation due to strong association of counterions with interfacial groups, and the degree of enhancement depends in a nontrivial way on the reduction of the medium dielectric constant and the steric effects of finite ion size. Rather interestingly, the charge reversal is of high relevance to the overcharging of interfaces because the overwhelming interfacial association forces the coions closer to the surface due to their smaller size than the counterions. Upon the addition of a monovalent salt to the solution, the interfacial association with divalent counterions makes surface overcharging and charge reversal widely unaffected, in contrast to the prevailing notion that screening of surface charge of a homogeneous nature is determined by the competitive effects between size-exclusion effects and energetic contributions. Overall, the present work highlights that the complex interplay between the electrostatic and steric interactions should be coupled to the realistic character of surface charge to establish a faithful description of the overcharging and charge reversal at heterophase interfaces.

Surface-potential decay of biased-probe contact-charged amorphous polymer films

NASA Astrophysics Data System (ADS)

Knorr, Nikolaus; Rosselli, Silvia; Nelles, Gabriele

2010-03-01

We have investigated the decay of scanning Kelvin probe force microscopy (KPFM) and electric force microscopy (EFM) signals from biased-probe contact-charged films of three different amorphous polymers representing wide-ranging water absorption capabilities. The surface-potential decay (SPD) has been measured by repeatedly scanning the charge pattern as a function of dissipation time t while varying the relative humidity (RH), the film thickness d, the temperature, the charging voltage, and the load on the scanning probe. Whereas increases in KPFM and EFM peak widths are appreciable only in the long run, the decay in the peak heights is rapid at the beginning and then strongly slowing down with time. Peak heights can be approximated for t <1 hour by power laws of negative exponents (-β), with 0<β<0.5 in dry conditions. β increases for thinner films and when scanning with higher probe loads. Raising the humidity or heating to temperatures well below the glass transition temperature of the polymer considerably increases β, with much stronger impacts for polymers with a higher water uptake capability. From the findings, we conclude that ionic charge carriers are trapped by the charge injection process in the volume of the polymers at low depths. A main contribution to SPD is by drift of the ions in their own space-charge field, mutually repelling each other and being attracted by their mirror charge in the grounded back electrode. Lateral drifts for small t are not resolved, increases in peak widths for t ≫1 h are predominantly due to increased probe—charge carrier distances. We interpret the power law approximation in terms of dispersive transport theory. We approximate trap-controlled apparent mobilities μ from isothermal KPFM peak height data, taken within a few minutes after charging, by a linear and a hyperbolic SPD model. Both models yield μ ≈10-14 cm2/(V s) for thin films (d ≈50 nm) in dry conditions. For mobilities derived similarly from isohumid measurements series, we find an exponential increase as a function of RH%. We furthermore suggest that two more mechanisms contributing to SPD are: first, by potential shielding of charge carriers by water dipoles, and second, in an indirect manner, by diffusion of injected water.

Nanopipette delivery: influence of surface charge.

PubMed

Shi, Wenqing; Sa, Niya; Thakar, Rahul; Baker, Lane A

2015-07-21

In this report, transport through a nanopipette is studied and the interplay between current rectification and ion delivery for small pipettes is examined. First, surface charge dependence of concentration polarization effects in a quartz nanopipette was investigated. Electrical characterization was performed through current-potential (I-V) measurements. In addition, fluorescein (an anionic fluorescent probe) was utilized to optically map ion enrichment and ion depletion in the nanopipette tip. Bare nanopipettes and polyethylenimine (PEI)-modified nanopipettes were examined. Results confirm that concentration polarization is a surface charge dependent phenomenon and delivery can be controlled through modification of surface charge. The relationship between concentration polarization effects and voltage-driven delivery of charged electroactive species was investigated with a carbon ring/nanopore electrode fabricated from pyrolyzed parylene C (PPC). Factors such as surface charge polarity of the nanopipette, electrolyte pH, and electrolyte concentration were investigated. Results indicate that with modification of surface charge, additional control over delivery of charged species can be achieved.

Organic-inorganic hybrid perovskite quantum dots with high PLQY and enhanced carrier mobility through crystallinity control by solvent engineering and solid-state ligand exchange.

PubMed

Woo Choi, Jin; Woo, Hee Chul; Huang, Xiaoguang; Jung, Wan-Gil; Kim, Bong-Joong; Jeon, Sie-Wook; Yim, Sang-Youp; Lee, Jae-Suk; Lee, Chang-Lyoul

2018-05-22

The photoluminescence quantum yield (PLQY) and charge carrier mobility of organic-inorganic perovskite QDs were enhanced by the optimization of crystallinity and surface passivation as well as solid-state ligand exchange. The crystallinity of perovskite QDs was determined by the Effective solvent field (Esol) of various solvents for precipitation. The solvent with high Esol could more quickly countervail the localized field generated by the polar solvent, and it causes fast crystallization of the dissolved precursor, which results in poor crystallinity. The post-ligand adding process (PLAP) and post-ligand exchange process (PLEP) increase the PLQY of perovskite QDs by reducing non-radiative recombination and the density of surface defect states through surface passivation. Particularly, the post ligand exchange process (PLEP) in the solid-state improved the charge carrier mobility of perovskite QDs in addition to the PLQY enhancement. The ligand exchange with short alkyl chain length ligands could improve the packing density of perovskite QDs in films by reducing the inter-particle distance between perovskite QDs. The maximum hole mobility of 6.2 × 10-3 cm2 V-1 s-1, one order higher than that of pristine QDs without the PLEP, is obtained at perovskite QDs with hexyl ligands. By using PLEP treatment, compared to the pristine device, a 2.5 times higher current efficiency in perovskite QD-LEDs was achieved due to the improved charge carrier mobility and PLQY.

Improvement of calcium mineral separation contrast using anionic reagents: electrokinetics properties and flotation

NASA Astrophysics Data System (ADS)

Lafhaj, Z.; Filippov, L. O.; Filippova, I. V.

2017-07-01

The flotation separation of salt type calcium minerals is problematic, due to the similarities in their same active Ca2+ related site for interaction with anionic collectors and similar physicochemical characteristics such as solubility, zero-point charge, surface speciation and Ca-site density. The work was performed to achieve effective and selective separation of the calcium-minerals using pure minerals samples: orange calcite with Mg impurities, optic calcite with impurities level and an apatite. The pure samples surface was examined using techniques sensitive near-surface like infrared spectroscopy (FTIR) and chemical composition was obtained by ICPMS. The isoelectric point (IEP) and point of zero charge (PZC) in electrolyte were recorded using electrophoresis method at different ionic strengths of the solution. Mechanisms of charge development at the mineral-water interface are discussed. The time of contact as important parameter for the charge equilibrium was deduced from kinetics study and fixed to 30 minutes. The difference in the values obtained between IEP and PZSE can be explained by the presence of a specific adsorption of cations and anions on the surface. The effect of pure anionic collectors such as oleic and linoleic acid were studied. At low pH, both collectors lead to a good recovery for the calcites. The flotation recovery of optic calcite at pH 9 with sodium oleate is higher than with sodium linoleate. At alkaline pH, apatite showed a better recovery with sodium linoleate.

Positive selection in octopus haemocyanin indicates functional links to temperature adaptation.

PubMed

Oellermann, Michael; Strugnell, Jan M; Lieb, Bernhard; Mark, Felix C

2015-07-05

Octopods have successfully colonised the world's oceans from the tropics to the poles. Yet, successful persistence in these habitats has required adaptations of their advanced physiological apparatus to compensate impaired oxygen supply. Their oxygen transporter haemocyanin plays a major role in cold tolerance and accordingly has undergone functional modifications to sustain oxygen release at sub-zero temperatures. However, it remains unknown how molecular properties evolved to explain the observed functional adaptations. We thus aimed to assess whether natural selection affected molecular and structural properties of haemocyanin that explains temperature adaptation in octopods. Analysis of 239 partial sequences of the haemocyanin functional units (FU) f and g of 28 octopod species of polar, temperate, subtropical and tropical origin revealed natural selection was acting primarily on charge properties of surface residues. Polar octopods contained haemocyanins with higher net surface charge due to decreased glutamic acid content and higher numbers of basic amino acids. Within the analysed partial sequences, positive selection was present at site 2545, positioned between the active copper binding centre and the FU g surface. At this site, methionine was the dominant amino acid in polar octopods and leucine was dominant in tropical octopods. Sites directly involved in oxygen binding or quaternary interactions were highly conserved within the analysed sequence. This study has provided the first insight into molecular and structural mechanisms that have enabled octopods to sustain oxygen supply from polar to tropical conditions. Our findings imply modulation of oxygen binding via charge-charge interaction at the protein surface, which stabilize quaternary interactions among functional units to reduce detrimental effects of high pH on venous oxygen release. Of the observed partial haemocyanin sequence, residue 2545 formed a close link between the FU g surface and the active centre, suggesting a role as allosteric binding site. The prevalence of methionine at this site in polar octopods, implies regulation of oxygen affinity via increased sensitivity to allosteric metal binding. High sequence conservation of sites directly involved in oxygen binding indicates that functional modifications of octopod haemocyanin rather occur via more subtle mechanisms, as observed in this study.

Polarization-induced surface charges in hydroxyapatite ceramics

NASA Astrophysics Data System (ADS)

Horiuchi, N.; Nakaguki, S.; Wada, N.; Nozaki, K.; Nakamura, M.; Nagai, A.; Katayama, K.; Yamashita, K.

2014-07-01

Calcium hydroxyapatite (HAp; Ca10(PO4)6(OH)2) is a well-known biomaterial that is the main inorganic component of bones and teeth. Control over the surface charge on HAp would be a key advance in the development of the material for tissue engineering. We demonstrate here that surface charge can be induced by an electrical poling process using the Kelvin method. Positive and negative charges were induced on the HAp surface in response to the applied electric field in the poling process. The surface charging is attributed to dipole polarization that is homogeneously distributed in HAp. Additionally, the surface charging is considered to originate from the organization of OH- ions into a polar phase in the structure.

Genetically tunable M13 phage films utilizing evaporating droplets.

PubMed

Alberts, Erik; Warner, Chris; Barnes, Eftihia; Pilkiewicz, Kevin; Perkins, Edward; Poda, Aimee

2018-01-01

This effort utilizes a genetically tunable system of bacteriophage to evaluate the effect of charge, temperature and particle concentration on biomaterial synthesis utilizing the coffee ring (CR) effect. There was a 1.6-3 fold suppression of the CR at higher temperatures while maintaining self-assembled structures of thin films. This suppression was observed in phage with charged and uncharged surface chemistry, which formed ordered and disordered assemblies respectively, indicating CR suppression is not dependent on short-range ordering or surface chemistry. Analysis of the drying process suggests weakened capillary flow at elevated temperatures caused CR suppression and could be further enhanced for controlled assembly for advanced biomaterials. Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.

Simulation of external and internal electrostatic discharges at the spacecraft system test level

NASA Technical Reports Server (NTRS)

Whittlesey, A.; Leung, P.

1984-01-01

Environmental test activities concerned with space plasma-caused charging and discharing phenomena are discussed. It is pointed out that the origin of such an electrostatic discharge (ESD) is charging of spacecraft dielectrics by an energetic plasma in geosynchronous orbit, Jupiter's magnetosphere, or other similar space environments. In dealing with environmental testing problems, it is necessary to define the location and magnitude of any ESD's in preparation for a subsequent simulation of the given conditions. Questions of external and internal charging are discussed separately. The environmental hazard from an external discharge can be assessed by viewing the dielectric surface as one side of a parallel plate capacitor. In the case of internal charging, the level of environmental concern depends on the higher energy spectrum of the ambient electrons.

Structural Insight into and Mutational Analysis of Family 11 Xylanases: Implications for Mechanisms of Higher pH Catalytic Adaptation.

PubMed

Bai, Wenqin; Zhou, Cheng; Zhao, Yueju; Wang, Qinhong; Ma, Yanhe

2015-01-01

To understand the molecular basis of higher pH catalytic adaptation of family 11 xylanases, we compared the structures of alkaline, neutral, and acidic active xylanases and analyzed mutants of xylanase Xyn11A-LC from alkalophilic Bacillus sp. SN5. It was revealed that alkaline active xylanases have increased charged residue content, an increased ratio of negatively to positively charged residues, and decreased Ser, Thr, and Tyr residue content relative to non-alkaline active counterparts. Between strands β6 and β7, alkaline xylanases substitute an α-helix for a coil or turn found in their non-alkaline counterparts. Compared with non-alkaline xylanases, alkaline active enzymes have an inserted stretch of seven amino acids rich in charged residues, which may be beneficial for xylanase function in alkaline conditions. Positively charged residues on the molecular surface and ionic bonds may play important roles in higher pH catalytic adaptation of family 11 xylanases. By structure comparison, sequence alignment and mutational analysis, six amino acids (Glu16, Trp18, Asn44, Leu46, Arg48, and Ser187, numbering based on Xyn11A-LC) adjacent to the acid/base catalyst were found to be responsible for xylanase function in higher pH conditions. Our results will contribute to understanding the molecular mechanisms of higher pH catalytic adaptation in family 11 xylanases and engineering xylanases to suit industrial applications.

Structural Insight into and Mutational Analysis of Family 11 Xylanases: Implications for Mechanisms of Higher pH Catalytic Adaptation

PubMed Central

Bai, Wenqin; Zhou, Cheng; Zhao, Yueju; Wang, Qinhong; Ma, Yanhe

2015-01-01

To understand the molecular basis of higher pH catalytic adaptation of family 11 xylanases, we compared the structures of alkaline, neutral, and acidic active xylanases and analyzed mutants of xylanase Xyn11A-LC from alkalophilic Bacillus sp. SN5. It was revealed that alkaline active xylanases have increased charged residue content, an increased ratio of negatively to positively charged residues, and decreased Ser, Thr, and Tyr residue content relative to non-alkaline active counterparts. Between strands β6 and β7, alkaline xylanases substitute an α-helix for a coil or turn found in their non-alkaline counterparts. Compared with non-alkaline xylanases, alkaline active enzymes have an inserted stretch of seven amino acids rich in charged residues, which may be beneficial for xylanase function in alkaline conditions. Positively charged residues on the molecular surface and ionic bonds may play important roles in higher pH catalytic adaptation of family 11 xylanases. By structure comparison, sequence alignment and mutational analysis, six amino acids (Glu16, Trp18, Asn44, Leu46, Arg48, and Ser187, numbering based on Xyn11A-LC) adjacent to the acid/base catalyst were found to be responsible for xylanase function in higher pH conditions. Our results will contribute to understanding the molecular mechanisms of higher pH catalytic adaptation in family 11 xylanases and engineering xylanases to suit industrial applications. PMID:26161643

Poisson-Boltzmann theory of the charge-induced adsorption of semi-flexible polyelectrolytes.

PubMed

Ubbink, Job; Khokhlov, Alexei R

2004-03-15

A model is suggested for the structure of an adsorbed layer of a highly charged semi-flexible polyelectrolyte on a weakly charged surface of opposite charge sign. The adsorbed phase is thin, owing to the effective reversal of the charge sign of the surface upon adsorption, and ordered, owing to the high surface density of polyelectrolyte strands caused by the generally strong binding between polyelectrolyte and surface. The Poisson-Boltzmann equation for the electrostatic interaction between the array of adsorbed polyelectrolytes and the charged surface is solved for a cylindrical geometry, both numerically, using a finite element method, and analytically within the weak curvature limit under the assumption of excess monovalent salt. For small separations, repulsive surface polarization and counterion osmotic pressure effects dominate over the electrostatic attraction and the resulting electrostatic interaction curve shows a minimum at nonzero separations on the Angstrom scale. The equilibrium density of the adsorbed phase is obtained by minimizing the total free energy under the condition of equality of chemical potential and osmotic pressure of the polyelectrolyte in solution and in the adsorbed phase. For a wide range of ionic conditions and charge densities of the charged surface, the interstrand separation as predicted by the Poisson-Boltzmann model and the analytical theory closely agree. For low to moderate charge densities of the adsorbing surface, the interstrand spacing decreases as a function of the charge density of the charged surface. Above about 0.1 M excess monovalent salt, it is only weakly dependent on the ionic strength. At high charge densities of the adsorbing surface, the interstrand spacing increases with increasing ionic strength, in line with the experiments by Fang and Yang [J. Phys. Chem. B 101, 441 (1997)]. (c) 2004 American Institute of Physics.

Modeling of polymer brush grafted nanoparticles for algal harvesting

NASA Astrophysics Data System (ADS)

Goins, Jason

Microalgae derived biofuel shows great potential as a replacement to petroleum based fuels. However, industrial scale and economical production of fuel from microalgae suffer from an expensive dewatering step brought on by the organism's specific cell properties. A retrievable, paramagnetic nanoparticle polyelectrolyte brush (NPPB) has been designed as a flocculation agent to provide a low cost method in collecting algal biomass in biofuel production. In conjunction with experiment, subsequent theoretical investigations have been conducted in order to understand experimental observations and inform future design. A strategy has been implemented to provide informative descriptions for the relationship between flocculation agent parameters and dewatering efficiency. We studied the effect altering the degree of polymerization and monomer charge fraction had on the harvesting efficiency by considering flocculation as the criteria for harvesting. As the number of charges on the polymer backbone of the NPPB is increased, less NPPB concentrations are required to achieve equal harvesting efficiencies. This is a result of needing less NPPB to completely screen the effective charge on the algae surface. However, the Debye length limits the amount of charge on the algae surface one NPPB can screen. Using the free energy calculations for the complete set of pair interactions between the NPPB and the algae, we determined how many adsorbed NPPB were required in order for the force between coated algae to become attractive at some algae surface separation. This corresponded to the NPPB bridging two algae surfaces. NPPB with higher monomer charge fractions and degree of polymerizations led to a stronger bridging bond and larger bridging gap that could outweigh the algae pair repulsion. Optimized structures maximize these effects.

Adsorptive Removal of Nitrate from Aqueous Solution Using Nitrogen Doped Activated Carbon.

PubMed

Machida, Motoi; Goto, Tatsuru; Amano, Yoshimasa; Iida, Tatsuya

2016-01-01

Activated carbon (AC) has been widely applied for adsorptive removal of organic contaminants from aqueous phase, but not for ionic pollutants. In this study, nitrogen doped AC was prepared to increase the adsorption capacity of nitrate from water. AC was oxidized with (NH 4 ) 2 S 2 O 8 solution to maximize oxygen content for the first step, and then NH 3 gas treatment was carried out at 950°C to aim at forming quaternary nitrogen (N-Q) species on AC surface (Ox-9.5AG). Influence of solution pH was examined so as to elucidate the relationship between surface charge and adsorption amounts of nitrate. The results showed that Ox-9.5AG exhibited about twice higher adsorption capacity than non-treatment AC at any initial nitrate concentration and any equilibrium solution pH (pH e ) investigated. The more decrease in pH e value, the more adsorption amount of negatively charged nitrate ion, because the surface charge of AC and Ox-9.5AG could become more positive in acidic solution. The oxidation and consecutive ammonia treatments lead to increase in nitrogen content from 0.35 to 6.4% and decrease in the pH of the point of zero charge (pH pzc ) from 7.1 to 4.0 implying that positively charged N-Q of a Lewis acid was created on the surface of Ox-9.5AG. Based on a Langmuir data analysis, maximum adsorption capacity attained 0.5-0.6 mmol/g of nitrate and adsorption affinity was 3.5-4.0 L/mmol at pH e 2.5 for Ox-9.5AG.

A smoothed particle hydrodynamics model for electrostatic transport of charged lunar dust on the moon surface

NASA Astrophysics Data System (ADS)

Mao, Zirui; Liu, G. R.

2018-02-01

The behavior of lunar dust on the Moon surface is quite complicated compared to that on the Earth surface due to the small lunar gravity and the significant influence of the complicated electrostatic filed in the Universe. Understanding such behavior is critical for the exploration of the Moon. This work develops a smoothed particle hydrodynamics (SPH) model with the elastic-perfectly plastic constitutive equation and Drucker-Prager yield criterion to simulate the electrostatic transporting of multiple charged lunar dust particles. The initial electric field is generated based on the particle-in-cell method and then is superposed with the additional electric field from the charged dust particles to obtain the resultant electric field in the following process. Simulations of cohesive soil's natural failure and electrostatic transport of charged soil under the given electric force and gravity were carried out using the SPH model. Results obtained in this paper show that the negatively charged dust particles levitate and transport to the shadow area with a higher potential from the light area with a lower potential. The motion of soil particles finally comes to a stable state. The numerical result for final distribution of soil particles and potential profile above planar surface by the SPH method matches well with the experimental result, and the SPH solution looks sound in the maximum levitation height prediction of lunar dust under an uniform electric field compared to theoretical solution, which prove that SPH is a reliable method in describing the behavior of soil particles under a complicated electric field and small gravity field with the consideration of interactions among soil particles.

Surface characteristics of Bacillus cereus and its adhesion to stainless steel.

PubMed

Peng, J S; Tsai, W C; Chou, C C

2001-04-11

The ability of a Bacillus cereus strain, isolated from spoiled milk, to adhere to the surface of stainless steel chips was evaluated during its growth in diluted tryptic soy broth (DTSB). The number of cells that adhered to the surface increased markedly as the culture reached the end of the log phase and entered stationary phase, and continued to increase with further incubation. The surface properties of cells from the log, stationary, and late stationary phases were measured by hydrophobic interaction chromatography (HIC) and electrostatic interaction chromatography (ESIC). It was found that surface hydrophobicity of B. cereus vegetative cells from the late stationary phase was the highest followed by those from the stationary phase and the log phase cultures. While the vegetative cells prepared from stationary phase and log phase cultures, respectively, had the highest and the lowest surface charges. Adhesion of B. cereus vegetative cells to stainless steel was positively correlated with the cell surface hydrophobicity (R = 0.979). Surface hydrophobicity and surface positive charge noted on the spores harvested from diluted tryptic soy agar (DTSA) and Mn2+-tryptone glucose extract agar were higher than those harvested from the sucrose or lactose-added DTSA. A wide variation in the surface charge values was noted on the surface of various spores prepared from cultures grown on the four different media tested, while their ability to adhere to stainless steel chips in phosphate buffered saline (PBS) showed no significant difference (p > 0.05). Similarly, the number of spores or vegetative cells adhering to stainless steel suspended in PBS, milk or diluted milk (1000 x) did not differ significantly (p > 0.05).

Coarse-graining, Electrostatics and pH effects in phospholipid systems

NASA Astrophysics Data System (ADS)

Travesset, Alex; Vangaveti, Sweta

2010-03-01

We introduce a minimal free energy describing the interaction of charged groups and counterions including both classical electrostatic and specific interactions. The predictions of the model are compared against the standard model for describing ions next to charged interfaces, consisting of Poisson-Boltzmann theory with additional constants describing ion binding, which are specific to the counterion and the interfacial charge (``chemical binding''). It is shown that the ``chemical'' model can be appropriately described by an underlying ``physical'' model over several decades in concentration, but the extracted binding constants are not uniquely defined, as they differ depending on the particular observable quantity being studied. It is also shown that electrostatic correlations for divalent (or higher valence) ions enhance the surface charge by increasing deprotonation, an effect not properly accounted within chemical models. The model is applied to the charged phospholipids phosphatidylserine, Phosphatidc acid and Phosphoinositides and implications for different biological processes are discussed.

Lunar Surface Charging during Solar Energetic Particle Events

NASA Astrophysics Data System (ADS)

Halekas, Jasper S.; Delory, G. T.; Mewaldt, R. A.; Lin, R. P.; Fillingim, M. O.; Brain, D. A.; Lee, C. O.; Stubbs, T. J.; Farrell, W. M.; Hudson, M. K.

2006-09-01

The surface of the Moon, not protected by any substantial atmosphere, is directly exposed to the impact of both solar UV and solar wind plasma and energetic particles. This creates a complex lunar electrostatic environment, with the surface typically charging slightly positive in sunlight, and negative in shadow. Observations from the Apollo era and theoretical considerations strongly suggest that surface charging leads to dust electrification and transport, posing a potentially significant hazard for exploration. The most significant charging effects should occur when the Moon is exposed to high-temperature plasmas like those encountered in the terrestrial plasmasheet or in solar storms. We now present evidence for kilovolt-scale negative charging of the shadowed lunar surface during solar energetic particle (SEP) events, utilizing data from the Lunar Prospector Electron Reflectometer (LP ER). We find that SEP events are associated with the most extreme lunar surface charging observed during the LP mission - rivaled only by previously reported charging during traversals of the terrestrial plasmasheet. The largest charging event observed by LP is a 4 kV negative surface potential (as compared to typical values of V) during a SEP event in May 1998. We characterize lunar surface charging during several SEP events, and compare to energetic particle measurements from ACE, Wind, and SOHO in order to determine the relationship between SEP events and extreme lunar surface charging. Space weather events are already considered by NASA to be a significant hazard to lunar exploration, due to high-energy ionizing radiation. Our observations demonstrate that plasma interactions with the lunar surface during SEP events, causing extreme surface charging and potentially significant dust electrification and transport, represent an additional hazard associated with space weather.

Charge-Spot Model for Electrostatic Forces in Simulation of Fine Particulates

NASA Technical Reports Server (NTRS)

Walton, Otis R.; Johnson, Scott M.

2010-01-01

The charge-spot technique for modeling the static electric forces acting between charged fine particles entails treating electric charges on individual particles as small sets of discrete point charges, located near their surfaces. This is in contrast to existing models, which assume a single charge per particle. The charge-spot technique more accurately describes the forces, torques, and moments that act on triboelectrically charged particles, especially image-charge forces acting near conducting surfaces. The discrete element method (DEM) simulation uses a truncation range to limit the number of near-neighbor charge spots via a shifted and truncated potential Coulomb interaction. The model can be readily adapted to account for induced dipoles in uncharged particles (and thus dielectrophoretic forces) by allowing two charge spots of opposite signs to be created in response to an external electric field. To account for virtual overlap during contacts, the model can be set to automatically scale down the effective charge in proportion to the amount of virtual overlap of the charge spots. This can be accomplished by mimicking the behavior of two real overlapping spherical charge clouds, or with other approximate forms. The charge-spot method much more closely resembles real non-uniform surface charge distributions that result from tribocharging than simpler approaches, which just assign a single total charge to a particle. With the charge-spot model, a single particle may have a zero net charge, but still have both positive and negative charge spots, which could produce substantial forces on the particle when it is close to other charges, when it is in an external electric field, or when near a conducting surface. Since the charge-spot model can contain any number of charges per particle, can be used with only one or two charge spots per particle for simulating charging from solar wind bombardment, or with several charge spots for simulating triboelectric charging. Adhesive image-charge forces acting on charged particles touching conducting surfaces can be up to 50 times stronger if the charge is located in discrete spots on the particle surface instead of being distributed uniformly over the surface of the particle, as is assumed by most other models. Besides being useful in modeling particulates in space and distant objects, this modeling technique is useful for electrophotography (used in copiers) and in simulating the effects of static charge in the pulmonary delivery of fine dry powders.

Mesoporous gold sponges: electric charge-assisted seed mediated synthesis and application as surface-enhanced Raman scattering substrates

NASA Astrophysics Data System (ADS)

Yi, Zao; Luo, Jiangshan; Tan, Xiulan; Yi, Yong; Yao, Weitang; Kang, Xiaoli; Ye, Xin; Zhu, Wenkun; Duan, Tao; Yi, Yougen; Tang, Yongjian

2015-11-01

Mesoporous gold sponges were prepared using 4-dimethylaminopyridine (DMAP)-stabilized Au seeds. This is a general process, which involves a simple template-free method, room temperature reduction of HAuCl4·4H2O with hydroxylamine. The formation process of mesoporous gold sponges could be accounted for the electrostatic interaction (the small Au nanoparticles (~3 nm) and the positively charged DMAP-stabilized Au seeds) and Ostwald ripening process. The mesoporous gold sponges had appeared to undergo electrostatic adsorption initially, sequentially linear aggregation, welding and Ostwald ripening, then, they randomly cross link into self-supporting, three-dimensional networks with time. The mesoporous gold sponges exhibit higher surface area than the literature. In addition, application of the spongelike networks as an active material for surface-enhanced Raman scattering has been investigated by employing 4-aminothiophenol (4-ATP) molecules as a probe.

Mesoporous gold sponges: electric charge-assisted seed mediated synthesis and application as surface-enhanced Raman scattering substrates

PubMed Central

Yi, Zao; Luo, Jiangshan; Tan, Xiulan; Yi, Yong; Yao, Weitang; Kang, Xiaoli; Ye, Xin; Zhu, Wenkun; Duan, Tao; Yi, Yougen; Tang, Yongjian

2015-01-01

Mesoporous gold sponges were prepared using 4-dimethylaminopyridine (DMAP)-stabilized Au seeds. This is a general process, which involves a simple template-free method, room temperature reduction of HAuCl4·4H2O with hydroxylamine. The formation process of mesoporous gold sponges could be accounted for the electrostatic interaction (the small Au nanoparticles (~3 nm) and the positively charged DMAP-stabilized Au seeds) and Ostwald ripening process. The mesoporous gold sponges had appeared to undergo electrostatic adsorption initially, sequentially linear aggregation, welding and Ostwald ripening, then, they randomly cross link into self-supporting, three-dimensional networks with time. The mesoporous gold sponges exhibit higher surface area than the literature. In addition, application of the spongelike networks as an active material for surface-enhanced Raman scattering has been investigated by employing 4-aminothiophenol (4-ATP) molecules as a probe. PMID:26538365

Atomistic and molecular effects in electric double layers at high surface charges

DOE PAGES

Templeton, Jeremy Alan; Lee, Jonathan; Mani, Ali

2015-06-16

Here, the Poisson–Boltzmann theory for electrolytes near a charged surface is known to be invalid due to unaccounted physics associated with high ion concentration regimes. In order to investigate this regime, fluids density functional theory (f-DFT) and molecular dynamics (MD) simulations were used to determine electric surface potential as a function of surface charge. Based on these detailed computations, for electrolytes with nonpolar solvent, the surface potential is shown to depend quadratically on the surface charge in the high charge limit. We demonstrate that modified Poisson–Boltzmann theories can model this limit if they are augmented with atomic packing densities providedmore » by MD. However, when the solvent is a highly polar molecule water an intermediate regime is identified in which a constant capacitance is realized. Simulation results demonstrate the mechanism underlying this regime, and for the salt water system studied here, it persists throughout the range of physically realistic surface charge densities so the potential’s quadratic surface charge dependence is not obtained.« less

Spectroscopic study of surface enhanced Raman scattering of caffeine on borohydride-reduced silver colloids

NASA Astrophysics Data System (ADS)

Chen, Xiaomin; Gu, Huaimin; Shen, Gaoshan; Dong, Xiao; Kang, Jian

2010-06-01

The surface enhanced Raman scattering (SERS) of caffeine on borohydride-reduced silver colloids system under different aqueous solution environment has been studied in this paper. The relative intensity of SERS of caffeine significantly varies with different concentrations of sodium chloride and silver particles. However, at too high or too low concentration of sodium chloride and silver particle, the enhancement of SERS spectra is not evident. The SERS spectra of caffeine suggest that the contribution of the charge transfer mechanism to SERS may be dominant. The chloride ions can significantly enhance the efficiency of SERS, while the enhancement is selective, as the efficiency in charge transfer enhancement is higher than in electromagnetic enhancement. Therefore, it can be concluded that the active site of chloride ion locates on the bond between the caffeine and the silver surface. In addition, the SERS spectra of caffeine on borohydride-reduced and citrate-reduced silver colloids are different, which may be due to different states caffeine adsorbed on silver surface under different silver colloids.

Direct k-space mapping of the electronic structure in an oxide-oxide interface.

PubMed

Berner, G; Sing, M; Fujiwara, H; Yasui, A; Saitoh, Y; Yamasaki, A; Nishitani, Y; Sekiyama, A; Pavlenko, N; Kopp, T; Richter, C; Mannhart, J; Suga, S; Claessen, R

2013-06-14

The interface between LaAlO(3) and SrTiO(3) hosts a two-dimensional electron system of itinerant carriers, although both oxides are band insulators. Interface ferromagnetism coexisting with superconductivity has been found and attributed to local moments. Experimentally, it has been established that Ti 3d electrons are confined to the interface. Using soft x-ray angle-resolved resonant photoelectron spectroscopy we have directly mapped the interface states in k space. Our data demonstrate a charge dichotomy. A mobile fraction contributes to Fermi surface sheets, whereas a localized portion at higher binding energies is tentatively attributed to electrons trapped by O vacancies in the SrTiO(3). While photovoltage effects in the polar LaAlO(3) layers cannot be excluded, the apparent absence of surface-related Fermi surface sheets could also be fully reconciled in a recently proposed electronic reconstruction picture where the built-in potential in the LaAlO(3) is compensated by surface O vacancies serving also as a charge reservoir.

Surface charge mapping with a nanopipette.

PubMed

McKelvey, Kim; Kinnear, Sophie L; Perry, David; Momotenko, Dmitry; Unwin, Patrick R

2014-10-01

Nanopipettes are emerging as simple but powerful tools for probing chemistry at the nanoscale. In this contribution the use of nanopipettes for simultaneous surface charge mapping and topographical imaging is demonstrated, using a scanning ion conductance microscopy (SICM) format. When a nanopipette is positioned close to a surface in electrolyte solution, the direct ion current (DC), driven by an applied bias between a quasi-reference counter electrode (QRCE) in the nanopipette and a second QRCE in the bulk solution, is sensitive to surface charge. The charge sensitivity arises because the diffuse double layers at the nanopipette and the surface interact, creating a perm-selective region which becomes increasingly significant at low ionic strengths (10 mM 1:1 aqueous electrolyte herein). This leads to a polarity-dependent ion current and surface-induced rectification as the bias is varied. Using distance-modulated SICM, which induces an alternating ion current component (AC) by periodically modulating the distance between the nanopipette and the surface, the effect of surface charge on the DC and AC is explored and rationalized. The impact of surface charge on the AC phase (with respect to the driving sinusoidal signal) is highlighted in particular; this quantity shows a shift that is highly sensitive to interfacial charge and provides the basis for visualizing charge simultaneously with topography. The studies herein highlight the use of nanopipettes for functional imaging with applications from cell biology to materials characterization where understanding surface charge is of key importance. They also provide a framework for the design of SICM experiments, which may be convoluted by topographical and surface charge effects, especially for small nanopipettes.

Photocatalytic Applications of Electrospun TiO2 Nanofibres Embedded with Bimodal Sized and Prismatic Gold Nanoparticles.

PubMed

Gopika, G; Asha, A M; Sivakumar, N; Balakrishnan, A; Nair, S V; Subramanian, K R V

2015-09-01

In this paper, we have synthesized electrospun TiO2 nanofibers embedded with bimodal sized and prismatic gold nanoparticles. The surface plasmons generated in the gold nanoparticles were used to enhance the performance of photocatalysis. The photocatalytic conversion efficiencies of these bimodal sized/prismatic gold nanoparticles when embedded in electrospun TiO2 fibres showed an enhancement of upto 60% over bare fiber systems and also show higher efficiencies than electrospun fibrous systems embedded with unimodal sized gold nanoparticles. Anisotropic bimodal gold nanoparticles show the highest degree of photocatalytic activity. This may be attributed to greater density/concentration of nanoparticles with higher effective surface area and formation of a junction between the smaller and larger nanoparticles. Such a bimodally distributed range of nanoparticles could also lead to greater trapping of charge carriers at the TiO2 conduction band edge and promoting catalytic reactions on account of these trapped charges. This enhanced photocatalytic activity is explained by invoking different operating mechanisms such as improved surface area, greater trapping, coarse plasmon resonance and band effects. Thus, a useful applicability of the gold nanoparticles is shown in the area of photocatalysis.

High resolution printing of charge

DOEpatents

Rogers, John; Park, Jang-Ung

2015-06-16

Provided are methods of printing a pattern of charge on a substrate surface, such as by electrohydrodynamic (e-jet) printing. The methods relate to providing a nozzle containing a printable fluid, providing a substrate having a substrate surface and generating from the nozzle an ejected printable fluid containing net charge. The ejected printable fluid containing net charge is directed to the substrate surface, wherein the net charge does not substantially degrade and the net charge retained on the substrate surface. Also provided are functional devices made by any of the disclosed methods.

Aggregation and charge behavior of metallic and nonmetallic nanoparticles in the presence of competing similarly-charged inorganic ions.

PubMed

Mukherjee, Biplab; Weaver, James W

2010-05-01

The influence of competing, similarly charged, inorganic ions on the size and charge behavior of suspended titanium-dioxide (nTiO(2)), silver (nAg) and fullerene (nC(60)) nanoparticles (NPs) was investigated. Under pH and ionic conditions similar to natural water bodies, Ca(2+) induced aggregation of nTiO(2) and nAg NPs more strongly than K(+) and Na(+). Although K(+) and Na(+) had a similar effect on aggregation, K(+) provided better screening of the particle surface charge presumably because of its small hydrated radius. These effects were decidedly more prominent for TiO(2) than Ag. Anions (co-ions), SO(4)(2-) and Cl(-), affected the surface charge behavior of nTiO(2) but not of nAg NPs. The zeta potential (ZP) of nTiO(2) NPs was more negative at higher SO(4)(2-)/Cl(-) ratios than lower. When Mg(2+) was the counterion, charge inversion and rapid aggregation of nC(60) NPs occurred under alkaline conditions, with a more pronounced effect for Cl(-) than SO(4)(2-). Response dissimilarities suggest fundamental differences in the interfacial-interaction characteristics of these NPs in the aquatic environment with corresponding differences in transport of these particles. Our study also shows the important role played by the iso-electric point pH (pH(iep)) of the NPs in determining their aggregation kinetics in the environment.

Analytical Debye-Huckel model for electrostatic potentials around dissolved DNA.

PubMed Central

Wagner, K; Keyes, E; Kephart, T W; Edwards, G

1997-01-01

We present an analytical, Green-function-based model for the electric potential of DNA in solution, treating the surrounding solvent with the Debye-Huckel approximation. The partial charge of each atom is accounted for by modeling DNA as linear distributions of atoms on concentric cylindrical surfaces. The condensed ions of the solvent are treated with the Debye-Huckel approximation. The resultant leading term of the potential is that of a continuous shielded line charge, and the higher order terms account for the helical structure. Within several angstroms of the surface there is sufficient information in the electric potential to distinguish features and symmetries of DNA. Plots of the potential and equipotential surfaces, dominated by the phosphate charges, reflect the structural differences between the A, B, and Z conformations and, to a smaller extent, the difference between base sequences. As the distances from the helices increase, the magnitudes of the potentials decrease. However, the bases and sugars account for a larger fraction of the double helix potential with increasing distance. We have found that when the solvent is treated with the Debye-Huckel approximation, the potential decays more rapidly in every direction from the surface than it did in the concentric dielectric cylinder approximation. Images FIGURE 1 FIGURE 2 FIGURE 3 FIGURE 4 FIGURE 5 FIGURE 7 PMID:9199767

Surface modification of poly(L-lactic acid) to improve its cytocompatibility via assembly of polyelectrolytes and gelatin.

PubMed

Lin, Yuan; Wang, Luling; Zhang, Peibiao; Wang, Xin; Chen, Xuesi; Jing, Xiabin; Su, Zhaohui

2006-03-01

Poly(L-lactide) (PLLA) surface was modified via aminolysis by poly(allylamine hydrochloride) (PAH) at high pH and subsequent electrostatic self-assembly of poly(sodium styrenesulfonate) (PSS) and PAH, and the process was monitored by X-ray photoelectron spectroscopy (XPS) and contact angle measurement. These modified PLLAs were then used as charged substrates for further incorporation of gelatin to improve their cytocompatibility. The amphoteric nature of the gelatin was exploited and the gelatin was adsorbed to the negatively charged PLLA/PSS and positively charged PLLA/PAH at pH=3.4 and 7.4, respectively. XPS and water contact angle data indicated that the gelatin adsorption at pH=3.4 resulted in much higher surface coverage by gelatin than at pH=7.4. All the modified PLLA surfaces became more hydrophilic than the virgin PLLA. Chondrocyte culture was used to test the cell attachment, cell morphology and cell viability on the modified PLLA substrates. The results showed that the PAH and PSS modified PLLA exhibited better cytocompatibility than virgin PLLA, and the incorporation of the gelatin on these modified PLLA substrates further improved their cytocompatibility, with the PLLA/PSS substrate treated with the gelatin at pH=3.4 being the best, exceeding the chondrocyte compatibility of the tissue culture polystyrene.

Peptide:lipid ratio and membrane surface charge determine the mechanism of action of the antimicrobial peptide BP100. Conformational and functional studies.

PubMed

Manzini, Mariana C; Perez, Katia R; Riske, Karin A; Bozelli, José C; Santos, Talita L; da Silva, Marcia A; Saraiva, Greice K V; Politi, Mario J; Valente, Ana P; Almeida, Fábio C L; Chaimovich, Hernan; Rodrigues, Magali A; Bemquerer, Marcelo P; Schreier, Shirley; Cuccovia, Iolanda M

2014-07-01

The cecropin-melittin hybrid antimicrobial peptide BP100 (H-KKLFKKILKYL-NH2) is selective for Gram-negative bacteria, negatively charged membranes, and weakly hemolytic. We studied BP100 conformational and functional properties upon interaction with large unilamellar vesicles, LUVs, and giant unilamellar vesicles, GUVs, containing variable proportions of phosphatidylcholine (PC) and negatively charged phosphatidylglycerol (PG). CD and NMR spectra showed that upon binding to PG-containing LUVs BP100 acquires α-helical conformation, the helix spanning residues 3-11. Theoretical analyses indicated that the helix is amphipathic and surface-seeking. CD and dynamic light scattering data evinced peptide and/or vesicle aggregation, modulated by peptide:lipid ratio and PG content. BP100 decreased the absolute value of the zeta potential (ζ) of LUVs with low PG contents; for higher PG, binding was analyzed as an ion-exchange process. At high salt, BP100-induced LUVS leakage requires higher peptide concentration, indicating that both electrostatic and hydrophobic interactions contribute to peptide binding. While a gradual release took place at low peptide:lipid ratios, instantaneous loss occurred at high ratios, suggesting vesicle disruption. Optical microscopy of GUVs confirmed BP100-promoted disruption of negatively charged membranes. The mechanism of action of BP100 is determined by both peptide:lipid ratio and negatively charged lipid content. While gradual release results from membrane perturbation by a small number of peptide molecules giving rise to changes in acyl chain packing, lipid clustering (leading to membrane defects), and/or membrane thinning, membrane disruption results from a sequence of events - large-scale peptide and lipid clustering, giving rise to peptide-lipid patches that eventually would leave the membrane in a carpet-like mechanism. Copyright © 2014 Elsevier B.V. All rights reserved.

Photoelectric charging of partially sunlit dielectric surfaces in space

NASA Technical Reports Server (NTRS)

De, B. R.; Criswell, D. R.

1977-01-01

Sunlight-shadow effects may substantially alter the charging situation for a dielectric surface. The sunlight-shadow boundary tends to be the site of intense multipole electric fields. Charges on a sunlit dielectric surface have a finite effective mobility. The charge distribution tends to resemble that on a conducting surface. A boundary between a conducting and a dielectric surface may not represent a conductivity discontinuity when this boundary is sunlit; charges may migrate at a nontrivial rate across the boundary. A contracting or expanding sunlit area may experience a supercharging.

Effect of the surface charge discretization on electric double layers: a Monte Carlo simulation study.

PubMed

Madurga, Sergio; Martín-Molina, Alberto; Vilaseca, Eudald; Mas, Francesc; Quesada-Pérez, Manuel

2007-06-21

The structure of the electric double layer in contact with discrete and continuously charged planar surfaces is studied within the framework of the primitive model through Monte Carlo simulations. Three different discretization models are considered together with the case of uniform distribution. The effect of discreteness is analyzed in terms of charge density profiles. For point surface groups, a complete equivalence with the situation of uniformly distributed charge is found if profiles are exclusively analyzed as a function of the distance to the charged surface. However, some differences are observed moving parallel to the surface. Significant discrepancies with approaches that do not account for discreteness are reported if charge sites of finite size placed on the surface are considered.

Luminescent systems based on the isolation of conjugated PI systems and edge charge compensation with polar molecules on a charged nanostructured surface

DOEpatents

Ivanov, Ilia N.; Puretzky, Alexander A.; Zhao, Bin; Geohegan, David B.; Styers-Barnett, David J.; Hu, Hui

2014-07-15

A photoluminescent or electroluminescent system and method of making a non-luminescent nanostructured material into such a luminescent system is presented. The method of preparing the luminescent system, generally, comprises the steps of modifying the surface of a nanostructured material to create isolated regions to act as luminescent centers and to create a charge imbalance on the surface; applying more than one polar molecule to the charged surface of the nanostructured material; and orienting the polar molecules to compensate for the charge imbalance on the surface of the nanostructured material. The compensation of the surface charge imbalance by the polar molecules allows the isolated regions to exhibit luminescence.

Characterization of the surface charge distribution on kaolinite particles using high resolution atomic force microscopy

NASA Astrophysics Data System (ADS)

Kumar, Naveen; Zhao, Cunlu; Klaassen, Aram; van den Ende, Dirk; Mugele, Frieder; Siretanu, Igor

2016-02-01

Most solid surfaces, in particular clay minerals and rock surfaces, acquire a surface charge upon exposure to an aqueous environment due to adsorption and/or desorption of ionic species. Macroscopic techniques such as titration and electrokinetic measurements are commonly used to determine the surface charge and ζ -potential of these surfaces. However, because of the macroscopic averaging character these techniques cannot do justice to the role of local heterogeneities on the surfaces. In this work, we use dynamic atomic force microscopy (AFM) to determine the distribution of surface charge on the two (gibbsite-like and silica-like) basal planes of kaolinite nanoparticles immersed in aqueous electrolyte with a lateral resolution of approximately 30 nm. The surface charge density is extracted from force-distance curves using DLVO theory in combination with surface complexation modeling. While the gibbsite-like and the silica-like facet display on average positive and negative surface charge values as expected, our measurements reveal lateral variations of more than a factor of two on seemingly atomically smooth terraces, even if high resolution AFM images clearly reveal the atomic lattice on the surface. These results suggest that simple surface complexation models of clays that attribute a unique surface chemistry and hence homogeneous surface charge densities to basal planes may miss important aspects of real clay surfaces.

Graphite anode surface modification with controlled reduction of specific aryl diazonium salts for improved microbial fuel cells power output.

PubMed

Picot, Matthieu; Lapinsonnière, Laure; Rothballer, Michael; Barrière, Frédéric

2011-10-15

Graphite electrodes were modified with reduction of aryl diazonium salts and implemented as anodes in microbial fuel cells. First, reduction of 4-aminophenyl diazonium is considered using increased coulombic charge density from 16.5 to 200 mC/cm(2). This procedure introduced aryl amine functionalities at the surface which are neutral at neutral pH. These electrodes were implemented as anodes in "H" type microbial fuel cells inoculated with waste water, acetate as the substrate and using ferricyanide reduction at the cathode and a 1000 Ω external resistance. When the microbial anode had developed, the performances of the microbial fuel cells were measured under acetate saturation conditions and compared with those of control microbial fuel cells having an unmodified graphite anode. We found that the maximum power density of microbial fuel cell first increased as a function of the extent of modification, reaching an optimum after which it decreased for higher degree of surface modification, becoming even less performing than the control microbial fuel cell. Then, the effect of the introduction of charged groups at the surface was investigated at a low degree of surface modification. It was found that negatively charged groups at the surface (carboxylate) decreased microbial fuel cell power output while the introduction of positively charged groups doubled the power output. Scanning electron microscopy revealed that the microbial anode modified with positively charged groups was covered by a dense and homogeneous biofilm. Fluorescence in situ hybridization analyses showed that this biofilm consisted to a large extent of bacteria from the known electroactive Geobacter genus. In summary, the extent of modification of the anode was found to be critical for the microbial fuel cell performance. The nature of the chemical group introduced at the electrode surface was also found to significantly affect the performance of the microbial fuel cells. The method used for modification is easy to control and can be optimized and implemented for many carbon materials currently used in microbial fuel cells and other bioelectrochemical systems. Copyright © 2011 Elsevier B.V. All rights reserved.

Label-free detection of DNA using a light-addressable potentiometric sensor modified with a positively charged polyelectrolyte layer

NASA Astrophysics Data System (ADS)

Wu, Chunsheng; Bronder, Thomas; Poghossian, Arshak; Werner, Carl Frederik; Schöning, Michael J.

2015-03-01

A multi-spot (16 spots) light-addressable potentiometric sensor (MLAPS) consisting of an Al-p-Si-SiO2 structure modified with a weak polyelectrolyte layer of PAH (poly(allylamine hydrochloride)) was applied for the label-free electrical detection of DNA (deoxyribonucleic acid) immobilization and hybridization by the intrinsic molecular charge for the first time. To achieve a preferentially flat orientation of DNA strands and thus, to reduce the distance between the DNA charge and MLAPS surface, the negatively charged probe single-stranded DNAs (ssDNA) were electrostatically adsorbed onto the positively charged PAH layer using a simple layer-by-layer (LbL) technique. In this way, more DNA charge can be positioned within the Debye length, yielding a higher sensor signal. The surface potential changes in each spot induced due to the surface modification steps (PAH adsorption, probe ssDNA immobilization, hybridization with complementary target DNA (cDNA), non-specific adsorption of mismatched ssDNA) were determined from the shifts of photocurrent-voltage curves along the voltage axis. A high sensor signal of 83 mV was registered after immobilization of probe ssDNA onto the PAH layer. The hybridization signal increases from 5 mV to 32 mV with increasing the concentration of cDNA from 0.1 nM to 5 μM. In contrast, a small signal of 5 mV was recorded in the case of non-specific adsorption of fully mismatched ssDNA (5 μM). The obtained results demonstrate the potential of the MLAPS in combination with the simple and rapid LbL immobilization technique as a promising platform for the future development of multi-spot light-addressable label-free DNA chips with direct electrical readout.A multi-spot (16 spots) light-addressable potentiometric sensor (MLAPS) consisting of an Al-p-Si-SiO2 structure modified with a weak polyelectrolyte layer of PAH (poly(allylamine hydrochloride)) was applied for the label-free electrical detection of DNA (deoxyribonucleic acid) immobilization and hybridization by the intrinsic molecular charge for the first time. To achieve a preferentially flat orientation of DNA strands and thus, to reduce the distance between the DNA charge and MLAPS surface, the negatively charged probe single-stranded DNAs (ssDNA) were electrostatically adsorbed onto the positively charged PAH layer using a simple layer-by-layer (LbL) technique. In this way, more DNA charge can be positioned within the Debye length, yielding a higher sensor signal. The surface potential changes in each spot induced due to the surface modification steps (PAH adsorption, probe ssDNA immobilization, hybridization with complementary target DNA (cDNA), non-specific adsorption of mismatched ssDNA) were determined from the shifts of photocurrent-voltage curves along the voltage axis. A high sensor signal of 83 mV was registered after immobilization of probe ssDNA onto the PAH layer. The hybridization signal increases from 5 mV to 32 mV with increasing the concentration of cDNA from 0.1 nM to 5 μM. In contrast, a small signal of 5 mV was recorded in the case of non-specific adsorption of fully mismatched ssDNA (5 μM). The obtained results demonstrate the potential of the MLAPS in combination with the simple and rapid LbL immobilization technique as a promising platform for the future development of multi-spot light-addressable label-free DNA chips with direct electrical readout. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr07225a

Proximity charge sensing for semiconductor detectors

DOEpatents

Luke, Paul N; Tindall, Craig S; Amman, Mark

2013-10-08

A non-contact charge sensor includes a semiconductor detector having a first surface and an opposing second surface. The detector includes a high resistivity electrode layer on the first surface and a low resistivity electrode on the high resistivity electrode layer. A portion of the low resistivity first surface electrode is deleted to expose the high resistivity electrode layer in a portion of the area. A low resistivity electrode layer is disposed on the second surface of the semiconductor detector. A voltage applied between the first surface low resistivity electrode and the second surface low resistivity electrode causes a free charge to drift toward the first or second surface according to a polarity of the free charge and the voltage. A charge sensitive preamplifier coupled to a non-contact electrode disposed at a distance from the exposed high resistivity electrode layer outputs a signal in response to movement of free charge within the detector.

Infrared thermography based studies on mobile phone induced heating

NASA Astrophysics Data System (ADS)

Lahiri, B. B.; Bagavathiappan, S.; Soumya, C.; Jayakumar, T.; Philip, John

2015-07-01

Here, we report the skin temperature rise due to the absorption of radio frequency (RF) energy from three handheld mobile phones using infrared thermography technique. Experiments are performed under two different conditions, viz. when the mobile phones are placed in soft touch with the skin surface and away from the skin surface. Additionally, the temperature rise of mobile phones during charging, operation and simultaneous charging and talking are monitored under different exposure conditions. It is observed that the temperature of the cheek and ear regions monotonically increased with time during the usage of mobile phones and the magnitude of the temperature rise is higher for the mobile phone with higher specific absorption rate. The increase in skin temperature is higher when the mobile phones are in contact with the skin surface due to the combined effect of absorption of RF electromagnetic power and conductive heat transfer. The increase in the skin temperature in non-contact mode is found to be within the safety limit of 1 °C. The measured temperature rise is in good agreement with theoretical predictions. The empirical equation obtained from the temperature rise on the cheek region of the subjects correlates well with the specific absorption rate of the mobile phones. Our study suggests that the use of mobile phones in non-contact mode can significantly lower the skin temperature rise during its use and hence, is safer compared to the contact mode.

Characterizing the surface charge of synthetic nanomembranes by the streaming potential method

PubMed Central

Datta, Subhra; Conlisk, A. T.; Kanani, Dharmesh M.; Zydney, Andrew L.; Fissell, William H.; Roy, Shuvo

2010-01-01

The inference of the surface charge of polyethylene glycol (PEG)-coated and uncoated silicon membranes with nanoscale pore sizes from streaming potential measurements in the presence of finite electric double layer (EDL) effects is studied theoretically and experimentally. The developed theoretical model for inferring the pore wall surface charge density from streaming potential measurements is applicable to arbitrary pore cross-sectional shapes and accounts for the effect of finite salt concentration on the ionic mobilities and the thickness of the deposited layer of PEG. Theoretical interpretation of the streaming potential data collected from silicon membranes having nanoscale pore sizes, with/without pore wall surface modification with PEG, indicates that finite electric double layer (EDL) effects in the pore-confined electrolyte significantly affect the interpretation of the membrane charge and that surface modification with PEG leads to a reduction in the pore wall surface charge density. The theoretical model is also used to study the relative significance of the following uniquely nanoscale factors affecting the interpretation of streaming potential in moderate to strongly charged pores: altered net charge convection by applied pressure differentials, surface-charge effects on ionic conduction, and electroosmotic convection of charges. PMID:20462592

Electronically shielded solid state charged particle detector

DOEpatents

Balmer, D.K.; Haverty, T.W.; Nordin, C.W.; Tyree, W.H.

1996-08-20

An electronically shielded solid state charged particle detector system having enhanced radio frequency interference immunity includes a detector housing with a detector entrance opening for receiving the charged particles. A charged particle detector having an active surface is disposed within the housing. The active surface faces toward the detector entrance opening for providing electrical signals representative of the received charged particles when the received charged particles are applied to the active surface. A conductive layer is disposed upon the active surface. In a preferred embodiment, a nonconductive layer is disposed between the conductive layer and the active surface. The conductive layer is electrically coupled to the detector housing to provide a substantially continuous conductive electrical shield surrounding the active surface. The inner surface of the detector housing is supplemented with a radio frequency absorbing material such as ferrite. 1 fig.

Electronically shielded solid state charged particle detector

DOEpatents

Balmer, David K.; Haverty, Thomas W.; Nordin, Carl W.; Tyree, William H.

1996-08-20

An electronically shielded solid state charged particle detector system having enhanced radio frequency interference immunity includes a detector housing with a detector entrance opening for receiving the charged particles. A charged particle detector having an active surface is disposed within the housing. The active surface faces toward the detector entrance opening for providing electrical signals representative of the received charged particles when the received charged particles are applied to the active surface. A conductive layer is disposed upon the active surface. In a preferred embodiment, a nonconductive layer is disposed between the conductive layer and the active surface. The conductive layer is electrically coupled to the detector housing to provide a substantially continuous conductive electrical shield surrounding the active surface. The inner surface of the detector housing is supplemented with a radio frequency absorbing material such as ferrite.

Electro-osmosis of nematic liquid crystals under weak anchoring and second-order surface effects

NASA Astrophysics Data System (ADS)

Poddar, Antarip; Dhar, Jayabrata; Chakraborty, Suman

2017-07-01

Advent of nematic liquid crystal flows has attracted renewed attention in view of microfluidic transport phenomena. Among various transport processes, electro-osmosis stands as one of the efficient flow actuation mechanisms through narrow confinements. In the present study, we explore the electrically actuated flow of an ordered nematic fluid with ionic inclusions, taking into account the influences from surface-induced elasticity and electrical double layer (EDL) phenomena. Toward this, we devise the coupled flow governing equations from fundamental free-energy analysis, considering the contributions from first- and second-order elastic, dielectric, flexoelectric, charged surface polarization, ionic and entropic energies. The present study focuses on the influence of surface charge and elasticity effects in the resulting linear electro-osmosis through a slit-type microchannel whose surfaces are chemically treated to display a homeotropic-type weak anchoring state. An optical periodic stripe configuration of the nematic director has been observed, especially for higher electric fields, wherein the Ericksen number for the dynamic study is restricted to the order of unity. Contrary to the isotropic electrolytes, the EDL potential in this case was found to be dependent on the external field strength. Through a systematic investigation, we brought out the fact that the wavelength of the oscillating patterns is dictated mainly by the external field, while the amplitude depends on most of the physical variables ranging from the anchoring strength and the flexoelectric coefficients to the surface charge density and electrical double layer thickness.

Adsorption and redox reactions of heavy metals on synthesized Mn oxide minerals.

PubMed

Feng, Xiong Han; Zhai, Li Mei; Tan, Wen Feng; Liu, Fan; He, Ji Zheng

2007-05-01

Several Mn oxide minerals commonly occurring in soils were synthesized by modified or optimized methods. The morphologies, structures, compositions and surface properties of the synthesized Mn oxide minerals were characterized. Adsorption and redox reactions of heavy metals on these minerals in relation to the mineral structures and surface properties were also investigated. The synthesized birnessite, todorokite, cryptomelane, and hausmannite were single-phased minerals and had the typical morphologies from analyses of XRD and TEM/ED. The PZCs of the synthesized birnessite, todorokite and cryptomelane were 1.75, 3.50 and 2.10, respectively. The magnitude order of their surface variable negative charge was: birnessite> or =cryptomelane>todorokite. The hausmannite had a much higher PZC than others with the least surface variable negative charge. Birnessite exhibited the largest adsorption capacity on heavy metals Pb(2+), Cu(2+), Co(2+), Cd(2+) and Zn(2+), while hausmannite the smallest one. Birnessite, cryptomelane and todorokite showed the greatest adsorption capacity on Pb(2+) among the tested heavy metals. Hydration tendency (pK(1)) of the heavy metals and the surface variable charge of the Mn minerals had significant impacts on the adsorption. The ability in Cr(III) oxidation and concomitant release of Mn(2+) varied greatly depending on the structure, composition, surface properties and crystallinity of the minerals. The maximum amounts of Cr(III) oxidized by the Mn oxide minerals in order were (mmol/kg): birnessite (1330.0)>cryptomelane (422.6)>todorokite (59.7)>hausmannite (36.6).

Strong coupling electrostatics for randomly charged surfaces: antifragility and effective interactions.

PubMed

Ghodrat, Malihe; Naji, Ali; Komaie-Moghaddam, Haniyeh; Podgornik, Rudolf

2015-05-07

We study the effective interaction mediated by strongly coupled Coulomb fluids between dielectric surfaces carrying quenched, random monopolar charges with equal mean and variance, both when the Coulomb fluid consists only of mobile multivalent counterions and when it consists of an asymmetric ionic mixture containing multivalent and monovalent (salt) ions in equilibrium with an aqueous bulk reservoir. We analyze the consequences that follow from the interplay between surface charge disorder, dielectric and salt image effects, and the strong electrostatic coupling that results from multivalent counterions on the distribution of these ions and the effective interaction pressure they mediate between the surfaces. In a dielectrically homogeneous system, we show that the multivalent counterions are attracted towards the surfaces with a singular, disorder-induced potential that diverges logarithmically on approach to the surfaces, creating a singular but integrable counterion density profile that exhibits an algebraic divergence at the surfaces with an exponent that depends on the surface charge (disorder) variance. This effect drives the system towards a state of lower thermal 'disorder', one that can be described by a renormalized temperature, exhibiting thus a remarkable antifragility. In the presence of an interfacial dielectric discontinuity, the singular behavior of counterion density at the surfaces is removed but multivalent counterions are still accumulated much more strongly close to randomly charged surfaces as compared with uniformly charged ones. The interaction pressure acting on the surfaces displays in general a highly non-monotonic behavior as a function of the inter-surface separation with a prominent regime of attraction at small to intermediate separations. This attraction is caused directly by the combined effects from charge disorder and strong coupling electrostatics of multivalent counterions, which dominate the surface-surface repulsion due to the (equal) mean charges on the two surfaces and the osmotic pressure of monovalent ions residing between them. These effects can be quite significant even with a small degree of surface charge disorder relative to the mean surface charge. The strong coupling, disorder-induced attraction is typically much stronger than the van der Waals interaction between the surfaces, especially within a range of several nanometers for the inter-surface separation, where such effects are predicted to be most pronounced.

Effect of surface material on electrostatic charging of houseflies (Musca domestica L).

PubMed

McGonigle, Daniel F; Jackson, Chris W

2002-04-01

Houseflies (Musca domestica L) accumulated electrostatic charges when walking over clean, uncharged dielectric surfaces. The charges elicited on a walking housefly by a range of materials were quantified, allowing a triboelectric series to be determined relative to M domestica. This ranged from surfaces that charged individuals positively, e.g. Correx (corrugated polypropylene) [.1 (+/- 4.2)pC], to those that applied a negative charge, e.g. clear cast acrylic [-14.9 (+/- 2.9)pC]. Maximum positive and negative charges accumulated by individual M domestica were +73 and -27 pC. Replicate measurements on the same fly and surface showed little variation. Variation between individuals was not related to sex and was not consistent between surfaces. Different materials charged M domestica significantly differently and individual flies had significantly different charging properties. Variation in temperature between 21.3 degrees C and 24.7 degrees C and humidity between 24% and 41% RH significantly affected charge accumulated by M domestica on some surfaces, although further experimentation is needed to confirm this. The implications of this work are discussed in relation to insect trap design and pollination biology.

Analysis of a Lunar Base Electrostatic Radiation Shield Concept

NASA Technical Reports Server (NTRS)

Buhler, Charles R.

2004-01-01

Space weather can be defined as the total ensemble of radiation in space, as well as on the surface of moons and asteroids. It consists of electromagnetic, charged-particle, and neutral particle radiation. The fundamental goal behind this NIAC Phase I research is to investigate methods of generating a static electric-field potential phi(x, y, z) in the volume above and around a "safe" or protected area on the lunar surface so that trajectories of harmful charged particle radiation are modified (deflected or reflected), thus creating a shadow over that region. Since the charged particles are not neutralized but merely redirected, there will be areas outside of the shadowed protected region that will have a higher flux concentration of radiation. One of the fundamental limitations of the static electric (electrostatic)-field approach to radiation shielding is that complete shadowing is accomplished only by complete reflection, which can only occur for shield voltages greater than or equal to the kinetic energy (in electron volts) of the incoming charged particles. Just as habitats on Earth are protected from severe weather events and conditions, such as extreme temperatures, high winds, and UV radiation, using multiple methods of shielding protection from severe space weather will undoubtedly require multiple strategies. The electrostatic shield concept may be one of many methods employed to protect astronaut habitats on the lunar surface from some of the harmful effects of space weather.

Graphene-based supercapacitors in the parallel-plate electrode configuration: ionic liquids versus organic electrolytes.

PubMed

Shim, Youngseon; Kim, Hyung J; Jung, Younjoon

2012-01-01

Supercapacitors with two single-sheet graphene electrodes in the parallel plate geometry are studied via molecular dynamics (MD) computer simulations. Pure 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI+BF4-) and a 1.1 M solution of EMI+BF4- in acetonitrile are considered as prototypes of room-temperature ionic liquids (RTILs) and organic electrolytes. Electrolyte structure, charge density and associated electric potential are investigated by varying the charges and separation of the two electrodes. Multiple charge layers formed in the electrolytes in the vicinity of the electrodes are found to screen the electrode surface charge almost completely. As a result, the supercapacitors show nearly an ideal electric double layer behavior, i.e., the electric potential exhibits essentially a plateau behavior in the entire electrolyte region except for sharp changes in screening zones very close to the electrodes. Due to its small size and large charge separation, BF4- is considerably more efficient in shielding electrode charges than EMI+. In the case of the acetonitrile solution, acetonitrile also plays an important role by aligning its dipoles near the electrodes; however, the overall screening mainly arises from ions. Because of the disparity of shielding efficiency between cations and anions, the capacitance of the positively-charged anode is significantly larger than that of the negatively-charged cathode. Therefore, the total cell capacitance in the parallel plate configuration is primarily governed by the cathode. Ion conductivity obtained via the Green-Kubo (GK) method is found to be largely independent of the electrode surface charge. Interestingly, EMI+BF4- shows higher GK ion conductivity than the 1.1 M acetonitrile solution between two parallel plate electrodes.

Critical Dipole Length for the Wetting Transition Due to Collective Water-dipoles Interactions

PubMed Central

Wang, Chunlei; Zhou, Bo; Tu, Yusong; Duan, Manyi; Xiu, Peng; Li, Jingye; Fang, Haiping

2012-01-01

The wetting behavior of water on the solid surfaces is fundamental to various physical, chemical and biological processes. Conventionally, the surface with charges or charge dipoles is hydrophilic, whereas the non-polar surface is hydrophobic though some exceptions were recently reported. Using molecular dynamics simulations, we show that there is a critical length of the charge dipoles on the solid surface. The solid surface still exhibited hydrophobic behavior when the dipole length was less than the critical value, indicating that the water molecules on the solid surface seemed not “feel” attractive interactions from the charge dipoles on the solid surface. Those unexpected observations result from the collective interactions between the water molecules and charge dipoles on the solid surface, where the steric exclusion effect between water molecules greatly reduces the water-dipole interactions. Remarkably, the steric exclusion effect is also important for surfaces with charge dipole lengths greater than this critical length. PMID:22496954

Freight railroads : industry health has improved, but concerns about competition and capacity should be addressed : report to Congressional requesters

DOT National Transportation Integrated Search

2006-10-01

The Staggers Rail Act deregulated the freight rail industry, relying on competition to set rates, and allowed for differential pricing (charging higher rates to those more dependent on rail). The act gave the Surface Transportation Board (STB) author...

Electric field makes Leidenfrost droplets take a leap.

PubMed

Wildeman, Sander; Sun, Chao

2016-12-06

Leidenfrost droplets, i.e. droplets whose mobility is ensured by a thin vapor film between the droplet and a hot plate, are exposed to an external electric field. We find that in a strong vertical electric field the droplet can start to bounce progressively higher, defying gravitational attraction. From the droplet's trajectory we infer the temporal evolution of the amount of charge on the droplet. This reveals that the charge starts high and then decreases in steps as the droplet slowly evaporates. After each discharge event the charge is in a fixed proportion to the droplet's surface area. We show that this behavior can be accurately modeled by treating the droplet as a conducting sphere that occasionally makes electrical contact with the hot plate, at intervals dictated by an electro-capillary instability in the vapor film. An analysis of the kinetic and potential energies of the bouncing droplet reveals that, while the overall motion is damped, the droplet occasionally experiences a sudden boost, keeping its energy close to the value for which the free fall trajectory and droplet oscillation are in sync. This helps the droplet to escape from the hot surface when finally the electrical surface forces overtake gravity.

Polyelectrolyte adsorption onto like-charged surfaces mediated by trivalent counterions: A Monte Carlo simulation study

NASA Astrophysics Data System (ADS)

Luque-Caballero, Germán; Martín-Molina, Alberto; Quesada-Pérez, Manuel

2014-05-01

Both experiments and theory have evidenced that multivalent cations can mediate the interaction between negatively charged polyelectrolytes and like-charged objects, such as anionic lipoplexes (DNA-cation-anionic liposome complexes). In this paper, we use Monte Carlo simulations to study the electrostatic interaction responsible for the trivalent-counterion-mediated adsorption of polyelectrolytes onto a like-charged planar surface. The evaluation of the Helmholtz free energy allows us to characterize both the magnitude and the range of the interaction as a function of the polyelectrolyte charge, surface charge density, [3:1] electrolyte concentration, and cation size. Both polyelectrolyte and surface charge favor the adsorption. It should be stressed, however, that the adsorption will be negligible if the surface charge density does not exceed a threshold value. The effect of the [3:1] electrolyte concentration has also been analyzed. In certain range of concentrations, the counterion-mediated attraction seems to be independent of this parameter, whereas very high concentrations of salt weaken the adsorption. If the trivalent cation diameter is doubled the adsorption moderates due to the excluded volume effects. The analysis of the integrated charge density and ionic distributions suggests that a delicate balance between charge inversion and screening effects governs the polyelectrolyte adsorption onto like-charged surfaces mediated by trivalent cations.

Charge renormalization and inversion of a highly charged lipid bilayer: effects of dielectric discontinuities and charge correlations.

PubMed

Taheri-Araghi, Sattar; Ha, Bae-Yeun

2005-08-01

We reexamine the problem of charge renormalization and inversion of a highly charged surface of a low dielectric constant immersed in ionic solutions. To be specific, we consider an asymmetrically charged lipid bilayer, in which only one layer is negatively charged. In particular, we study how dielectric discontinuities and charge correlations (among lipid charges and condensed counterions) influence the effective charge of the surface. When counterions are monovalent (e.g., Na+), our mean-field approach implies that dielectric discontinuities can enhance counterion condensation. A simple scaling picture shows how the effects of dielectric discontinuities and surface-charge distributions are intertwined: Dielectric discontinuities diminish condensation if the backbone charge is uniformly smeared out while counterions are localized in space; they can, however, enhance condensation when the backbone charge is discrete. In the presence of asymmetric salts such as CaCl2 , we find that the correlation effect, treated at the Gaussian level, is more pronounced when the surface has a lower dielectric constant, inverting the sign of the charge at a smaller value of Ca2+ concentration.

Ion association at discretely-charged dielectric interfaces: Giant charge inversion [Dielectric response controlled ion association at physically heterogeneous surfaces: Giant charge reversal

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

Wang, Zhi -Yong; Wu, Jianzhong

2017-07-11

Giant charge reversal has been identified for the first time by Monte Carlo simulation for a discretely charged surface in contact with a trivalent electrolyte solution. It takes place regardless of the surface charge density under study and the monovalent salt. In stark contrast to earlier predictions based on the 2-dimensional Wigner crystal model to describe strong correlation of counterions at the macroion surface, we find that giant charge reversal reflects an intricate interplay of ionic volume effects, electrostatic correlations, surface charge heterogeneity, and the dielectric response of the confined fluids. While the novel phenomenon is yet to be confirmedmore » with experiment, the simulation results appear in excellent agreement with a wide range of existing observations in the subregime of charge inversion. Lastly, our findings may have far-reaching implications to understanding complex electrochemical phenomena entailing ionic fluids under dielectric confinements.« less

Triboelectric, Corona, and Induction Charging of Insulators as a Function of Pressure

NASA Technical Reports Server (NTRS)

Hogue, Michael D.; Mucciolo, Eduardo R.; Calle, Carlos I.

2006-01-01

Theoretical and experimental research has been performed that shows that the surface charge on an insulator after triboelectric charging with another insulator is rapidly dissipated with lowered atmospheric pressure. This pressure discharge is consistent with surface ions being evaporated off the surface once their vapor pressure is attained. In this paper we will report on the results of three different charging techniques (triboelectric, corona, and induction) performed on selected polymers with varying atmospheric pressure. This data will show that ion exchange between the polymer samples is the mechanism responsible for most of the surface charge on the polymer surfaces.

Experimental Investigation of Charging Properties of Interstellar Type Silica Dust Grains by Secondary Electron Emissions

NASA Technical Reports Server (NTRS)

Tankosic, D.; Abbas, M. M.

2013-01-01

The dust charging by electron impact is an important dust charging processes in astrophysical and planetary environments. Incident low energy electrons are reflected or stick to the grains charging the dust grains negatively. At sufficiently high energies electrons penetrate the grains, leading to excitation and emission of electrons referred to as secondary electron emission (SEE). Available classical theoretical models for calculations of SEE yields are generally applicable for neutral, planar, or bulk surfaces. These models, however, are not valid for calculations of the electron impact charging properties of electrostatically charged micron/submicron-size dust grains in astrophysical environments. Rigorous quantum mechanical models are not yet available, and the SEE yields have to be determined experimentally for development of more accurate models for charging of individual dust grains. At the present time, very limited experimental data are available for charging of individual micron-size dust grains, particularly for low energy electron impact. The experimental results on individual, positively charged, micron-size lunar dust grains levitated carried out by us in a unique facility at NASA-MSFC, based on an electrodynamic balance, indicate that the SEE by electron impact is a complex process. The electron impact may lead to charging or discharging of dust grains depending upon the grain size, surface potential, electron energy, electron flux, grain composition, and configuration (Abbas et al, 2010, 2012). In this paper, we discuss SEE charging properties of individual micron-size silica microspheres that are believed to be analogs of a class of interstellar dust grains. The measurements indicate charging of the 0.2m silica particles when exposed to 25 eV electron beams and discharging when exposed to higher energy electron beams. Relatively large size silica particles (5.2-6.82m) generally discharge to lower equilibrium potentials at both electron energies. These measurements conducted on silica microspheres are qualitatively similar in nature to our previous SEE measurements on lunar Apollo missions dust samples.

Modulating the fixed charge density in silicon nitride films while monitoring the surface recombination velocity by photoluminescence imaging

NASA Astrophysics Data System (ADS)

Bazilchuk, Molly; Haug, Halvard; Marstein, Erik Stensrud

2015-04-01

Several important semiconductor devices such as solar cells and photodetectors may be fabricated based on surface inversion layer junctions induced by fixed charge in a dielectric layer. Inversion layer junctions can easily be fabricated by depositing layers with a high density of fixed charge on a semiconducting substrate. Increasing the fixed charge improves such devices; for instance, the efficiency of a solar cell can be substantially increased by reducing the surface recombination velocity, which is a function of the fixed charge density. Methods for increasing the charge density are therefore of interest. In this work, the fixed charge density in silicon nitride layers deposited by plasma enhanced chemical vapor deposition is increased to very high values above 1 × 1013 cm-2 after the application of an external voltage to a gate electrode. The effect of the fixed charge density on the surface recombination velocity was experimentally observed using the combination of capacitance-voltage characterization and photoluminescence imaging, showing a significant reduction in the surface recombination velocity for increasing charge density. The surface recombination velocity vs. charge density data was analyzed using a numerical device model, which indicated the presence of a sub-surface damage region formed during deposition of the layers. Finally, we have demonstrated that the aluminum electrodes used for charge injection may be chemically removed in phosphoric acid without loss of the underlying charge. The injected charge was shown to be stable for a prolonged time period, leading us to propose charge injection in silicon nitride films by application of soaking voltage as a viable method for fabricating inversion layer devices.

Assessment of capacitor electrodes for intracortical neural stimulation.

PubMed

Rose, T L; Kelliher, E M; Robblee, L S

1985-01-01

Capacitor electrodes offer the potential for the safest method of stimulation of neural tissue because they operate without any faradaic process occurring at the electrode-electrolyte interface. Their use eliminates problems associated with metal dissolution or water electrolysis which may occur with electrodes of noble metals. This paper reviews recent work aimed at increasing the charge storage density of capacitor electrodes to allow their application with the small areas of 10(-4) mm2 required for intracortical stimulation of single neurons. Increased charge storage with electrodes using anodic films such as TiO2 and Ta2O5 has been obtained by increasing the real surface area of microelectrodes. Experiments have also been done with BaTiO3 films which have a much higher dielectric constant than the anodic film dielectrics. State-of-the-art electrodes made with these materials, however, have a charge storage density which at best is comparable to that obtained with Pt and is considerably lower than electrochemically safe charge densities that have been reported for activated Ir. It is concluded that for very small intracortical electrodes, capacitor electrodes will not be competitive with electrodes which operate using surface localized faradaic reactions.

Rethinking of the regolith transport on airless bodies in the Solar system

NASA Astrophysics Data System (ADS)

Hsu, S.; Wang, X.; Seiss, M.; Schwan, J.; Sternovsky, Z.; Horanyi, M.

2016-12-01

Recent laboratory experiments provided important constraints on the characteristics of electrostatic dust transport on airless bodies. The proposed "patched charging model" illustrates how regolith particles acquire grain charges much higher than expected to drive the surface dust movements, including rotation and hopping of individual regolith particle as well as the overall smoothing of the regolith surface observed in the experiments. Here we apply the experimental results to re-examine the regolith transport on the airless bodies in the Solar systems, including both observation (e.g., dust ponds on Eros) and theoretical aspects (e.g., electrostatic dust levitation). We will also discuss the observational criteria and implications to be expected from current and future missions, such as Asteroid Redirect Mission, Cassini, Hayabusa 2, and OSIRIS-Rex.

Noise Threshold and Resource Cost of Fault-Tolerant Quantum Computing with Majorana Fermions in Hybrid Systems.

PubMed

Li, Ying

2016-09-16

Fault-tolerant quantum computing in systems composed of both Majorana fermions and topologically unprotected quantum systems, e.g., superconducting circuits or quantum dots, is studied in this Letter. Errors caused by topologically unprotected quantum systems need to be corrected with error-correction schemes, for instance, the surface code. We find that the error-correction performance of such a hybrid topological quantum computer is not superior to a normal quantum computer unless the topological charge of Majorana fermions is insusceptible to noise. If errors changing the topological charge are rare, the fault-tolerance threshold is much higher than the threshold of a normal quantum computer and a surface-code logical qubit could be encoded in only tens of topological qubits instead of about 1,000 normal qubits.

Electric Double-Layer Interaction between Dissimilar Charge-Conserved Conducting Plates.

PubMed

Chan, Derek Y C

2015-09-15

Small metallic particles used in forming nanostructured to impart novel optical, catalytic, or tribo-rheological can be modeled as conducting particles with equipotential surfaces that carry a net surface charge. The value of the surface potential will vary with the separation between interacting particles, and in the absence of charge-transfer or electrochemical reactions across the particle surface, the total charge of each particle must also remain constant. These two physical conditions require the electrostatic boundary condition for metallic nanoparticles to satisfy an equipotential whole-of-particle charge conservation constraint that has not been studied previously. This constraint gives rise to a global charge conserved constant potential boundary condition that results in multibody effects in the electric double-layer interaction that are either absent or are very small in the familiar constant potential or constant charge or surface electrochemical equilibrium condition.

Bacterial attachment to RO membranes surface-modified by concentration-polarization-enhanced graft polymerization.

PubMed

Bernstein, Roy; Belfer, Sofia; Freger, Viatcheslav

2011-07-15

Concentration polarization-enhanced radical graft polymerization, a facile surface modification technique, was examined as an approach to reduce bacterial deposition onto RO membranes and thus contribute to mitigation of biofouling. For this purpose an RO membrane ESPA-1 was surface-grafted with a zwitterionic and negatively and positively charged monomers. The low monomer concentrations and low degrees of grafting employed in modifications moderately reduced flux (by 20-40%) and did not affect salt rejection, yet produced substantial changes in surface chemistry, charge and hydrophilicity. The propensity to bacterial attachment of original and modified membranes was assessed using bacterial deposition tests carried out in a parallel plate flow setup using a fluorescent strain of Pseudomonas fluorescens. Compared to unmodified ESPA-1 the deposition (mass transfer) coefficient was significantly increased for modification with the positively charged monomer. On the other hand, a substantial reduction in bacterial deposition rates was observed for membranes modified with zwitterionic monomer and, still more, with very hydrophilic negatively charged monomers. This trend is well explained by the effects of surface charge (as measured by ζ-potential) and hydrophilicity (contact angle). It also well correlated with force distance measurements by AFM using surrogate spherical probes with a negative surface charge mimicking the bacterial surface. The positively charged surface showed a strong hysteresis with a large adhesion force, which was weaker for unmodified ESPA-1 and still weaker for zwitterionic surface, while negatively charged surface showed a long-range repulsion and negligible hysteresis. These results demonstrate the potential of using the proposed surface- modification approach for varying surface characteristics, charge and hydrophilicity, and thus minimizing bacterial deposition and potentially reducing propensity biofouling.

Space charge dynamics Of CF4 fluorinated LDPE samples from different fluorination conditions and their DC conductivities

NASA Astrophysics Data System (ADS)

Liu, Ning; Li, Ziyun; Chen, George; Chen, Qiang; Li, Shengtao

2017-07-01

Taking advantage of plasma technology using mixing gas CF4/H2, a fluorination process was performed on LDPE samples in the present paper. Different exposure times and discharge voltage levels were applied to produce four different types of samples. It has been found that after fluorination, space charge injection is obviously suppressed. And with longer fluorination times and higher discharge voltage, injected homocharges are reduced. By employing x-ray photoelectron spectroscopy, new chemical groups of C-F bindings are confirmed to be introduced by fluorination process of the plasma treatment. The charge suppression effect can be explained as: surface traps introduced by fluorination will reduce the interface field at both electrodes. Moreover, for fluorinated samples, heterocharge emerges obviously under 30 kV \\text{m}{{\\text{m}}-1} , which are considered as charges ionized from degradation products of etching and/or lower weight molecular specifies. Through the conductivity measurements also performed at 30 kV \\text{m}{{\\text{m}}-1} , it is found that, for the fluorinated samples with the better charge blocking effect, the conductivity is lowered. However, the conductivity of the fluorinated sample with the lightest degree of fluorination is found to be higher than that of normal samples.

Charging of moving surfaces by corona discharges sustained in air

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

Wang, Jun-Chieh, E-mail: junchwan@umich.edu; Kushner, Mark J., E-mail: mjkush@umich.edu; Zhang, Daihua, E-mail: dhzhang@tju.edu.cn

Atmospheric pressure corona discharges are used in electrophotographic (EP) printing technologies for charging imaging surfaces such as photoconductors. A typical corona discharge consists of a wire (or wire array) biased with a few hundred volts of dc plus a few kV of ac voltage. An electric discharge is produced around the corona wire from which electrons drift towards and charge the underlying dielectric surface. The surface charging reduces the voltage drop across the gap between the corona wire and the dielectric surface, which then terminates the discharge, as in a dielectric barrier discharge. In printing applications, this underlying surface ismore » continuously moving throughout the charging process. For example, previously charged surfaces, which had reduced the local electric field and terminated the local discharge, are translated out of the field of view and are replaced with uncharged surface. The uncharged surface produces a rebound in the electric field in the vicinity of the corona wire which in turn results in re-ignition of the discharge. The discharge, so reignited, is then asymmetric. We found that in the idealized corona charging system we investigated, a negatively dc biased corona blade with a dielectric covered ground electrode, the discharge is initially sustained by electron impact ionization from the bulk plasma and then dominated by ionization from sheath accelerated secondary electrons. Depending on the speed of the underlying surface, the periodic re-ignition of the discharge can produce an oscillatory charging pattern on the moving surface.« less

Effects of charge design features on parameters of acoustic and seismic waves and cratering, for SMR chemical surface explosions

NASA Astrophysics Data System (ADS)

Gitterman, Y.

2012-04-01

A series of experimental on-surface shots was designed and conducted by the Geophysical Institute of Israel at Sayarim Military Range (SMR) in Negev desert, including two large calibration explosions: about 82 tons of strong IMI explosives in August 2009, and about 100 tons of ANFO explosives in January 2011. It was a collaborative effort between Israel, CTBTO, USA and several European countries, with the main goal to provide fully controlled ground truth (GT0) infrasound sources in different weather/wind conditions, for calibration of IMS infrasound stations in Europe, Middle East and Asia. Strong boosters and the upward charge detonation scheme were applied to provide a reduced energy release to the ground and an enlarged energy radiation to the atmosphere, producing enhanced infrasound signals, for better observation at far-regional stations. The following observations and results indicate on the required explosives energy partition for this charge design: 1) crater size and local seismic (duration) magnitudes were found smaller than expected for these large surface explosions; 2) small test shots of the same charge (1 ton) conducted at SMR with different detonation directions showed clearly lower seismic amplitudes/energy and smaller crater size for the upward detonation; 3) many infrasound stations at local and regional distances showed higher than expected peak amplitudes, even after application of a wind-correction procedure. For the large-scale explosions, high-pressure gauges were deployed at 100-600 m to record air-blast properties, evaluate the efficiency of the charge design and energy generation, and provide a reliable estimation of the charge yield. Empirical relations for air-blast parameters - peak pressure, impulse and the Secondary Shock (SS) time delay - depending on distance, were developed and analyzed. The parameters, scaled by the cubic root of estimated TNT equivalent charges, were found consistent for all analyzed explosions, except of SS time delays clearly separated for the shot of IMI explosives (characterized by much higher detonation velocity than ANFO). Additionally acoustic records at close distances from WSMR explosions Distant Image (2440 tons of ANFO) and Minor Uncle (2725 tons of ANFO) were used to extend the charge and distance range for the SS delay scaled relationship, that showed consistency with SMR ANFO shots. The developed specific charge design contributed to the success of this unique dual Sayarim explosion experiment, providing the strongest GT0 sources since the establishment of the IMS network, that demonstrated clearly the most favorable westward/ eastward infrasound propagation up to 3400/6250 km according to appropriate summer/winter weather pattern and stratospheric wind directions, respectively, and thus verified empirically common models of infrasound propagation in the atmosphere. The research was supported by the CTBTO, Vienna, and the Israel Ministry of Immigrant Absorption.

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 surface charge density on the affinity of oxide nanoparticles for the vapor-water interface.

PubMed

Brown, Matthew A; Duyckaerts, Nicolas; Redondo, Amaia Beloqui; Jordan, Inga; Nolting, Frithjof; Kleibert, Armin; Ammann, Markus; Wörner, Hans Jakob; van Bokhoven, Jeroen A; Abbas, Zareen

2013-04-23

Using in-situ X-ray photoelectron spectroscopy at the vapor-water interface, the affinity of nanometer-sized silica colloids to adsorb at the interface is shown to depend on colloid surface charge density. In aqueous suspensions at pH 10 corrected Debye-Hückel theory for surface complexation calculations predict that smaller silica colloids have increased negative surface charge density that originates from enhanced screening of deprotonated silanol groups (≡Si-O(-)) by counterions in the condensed ion layer. The increased negative surface charge density results in an electrostatic repulsion from the vapor-water interface that is seen to a lesser extent for larger particles that have a reduced charge density in the XPS measurements. We compare the results and interpretation of the in-situ XPS and corrected Debye-Hückel theory for surface complexation calculations with traditional surface tension measurements. Our results show that controlling the surface charge density of colloid particles can regulate their adsorption to the interface between two dielectrics.

Integrating high electrical conductivity and photocatalytic activity in cotton fabric by cationizing for enriched coating of negatively charged graphene oxide.

PubMed

Sahito, Iftikhar Ali; Sun, Kyung Chul; Arbab, Alvira Ayoub; Qadir, Muhammad Bilal; Jeong, Sung Hoon

2015-10-05

Electroconductive textiles have attended tremendous focus recently and researchers are making efforts to increase conductivity of e-textiles, in order to increase the use of such flexible and low cost textile materials. In this study, surface conductivity and photo catalytic activity of standard cotton fabric (SCF) was enhanced by modifying its surface charge, from negative to positive, using Bovine Serum Albumin (BSA) as a cationic agent, to convert it into cationised cotton fabric (CCF). Then, both types of fabrics were dip coated with a simple dip and dry technique for the adsorption of negatively charged graphene oxide (GO) sheets onto its surface. This resulted in 67.74% higher loading amount of GO on the CCF making self-assembly. Finally, this coating was chemically converted by vapor reduction using hydrazine hydrate to reduced graphene oxide (rGO) for restoration of a high electrical conductivity at the fabric surface. Our results revealed that with such high loading of GO, the surface resistance of CCF was only 40Ω/sq as compared to 510Ω/sq of the SCF and a 66% higher photo catalytic activity was also achieved through cationization for improved GO coating. Graphene coated SCF and CCF were characterized using FE-SEM, FTIR, Raman, UV-vis, WAXD, EDX and XPS spectroscopy to ascertain successful reduction of GO to rGO. The effect of BSA treatment on adsorption of cotton fabric was studied using drop shape analyzer to measure contact angle and for thermal and mechanical resistance, the fabric was tested for TGA and tensile strength, respectively. rGO coated fabric also showed slightly improved thermal stability yet a minor loss of strength was observed. The high flexibility, photocatalytic activity and excellent conductivity of this fabric suggests that it can be used as an electrode material for various applications. Copyright © 2015 Elsevier Ltd. All rights reserved.

Hollow nanostructures of metal oxides as next generation electrode materials for supercapacitors.

PubMed

Sharma, Vikas; Singh, Inderjeet; Chandra, Amreesh

2018-01-22

Hollow nanostructures of copper oxides help to stabilize appreciably higher electrochemical characteristics than their solid counter parts of various morphologies. The specific capacitance values, calculated using cyclic voltammetry (CV) and charge-discharge (CD) studies, are found to be much higher than the values reported in literature for copper oxide particles showing  intriguing morphologies or even composites with trendy systems like CNTs, rGO, graphene, etc. The proposed cost-effective synthesis route makes these materials industrially viable for application in alternative energy storage devices. The improved electrochemical response can be attributed to effective access to the higher number of redox sites that become available on the surface, as well as in the cavity of the hollow particles. The ion transport channels also facilitate efficient de-intercalation, which results in the enhancement of cyclability and Coulombic efficiency. The charge storage mechanism in copper oxide structures is also proposed in the paper.

Photosensitized electron transfer processes in SiO2 colloids and sodium lauryl sulfate micellar systems: Correlation of quantum yields with interfacial surface potentials

PubMed Central

Laane, Colja; Willner, Itamar; Otvos, John W.; Calvin, Melvin

1981-01-01

The effectiveness of negatively charged colloidal SiO2 particles in controlling photosensitized electron transfer reactions has been studied and compared with that of the negatively charged sodium lauryl sulfate (NaLauSO4) micellar system. In particular, the photosensitized reduction of the zwitterionic electron acceptor propylviologen sulfonate (PVS0) with tris(2,2′-bipyridinium)ruthenium(II) [Ru(bipy)32+] as the sensitizer and triethanolamine as the electron donor is found to have a quantum yield of 0.033 for formation of the radical anion (PVS[unk]) in the SiO2 colloid compared with 0.005 in the homogeneous system and 0.0086 in a NaLauSO4 micellar solution. The higher quantum yields obtained with the SiO2 colloidal system are attributed to substantial stabilization against back reaction of the intermediate photoproducts—i.e., Ru(bipy)33+ and PVS[unk]—by electrostatic repulsion of the reduced electron acceptor from the negatively charged particle surface. The binding properties of the SiO2 particles and NaLauSO4 micelles were investigated by flow dialysis. The results show that the sensitizer binds to both interfaces and that the SiO2 interface is characterized by a much higher surface potential than the micellar interface (≈-170 mV vs. -85 mV). The effect of ionic strength on the surface potential was estimated from the Gouy-Chapman theory, and the measured quantum yields of photosensitized electron transfer were correlated with surface potential at different ionic strengths. This correlation shows that the quantum yield is not affected by surface potentials smaller than ≈-40 mV. At larger potentials, the quantum yield increases rapidly. The quantum yield obtained in the micellar system at different strengths fits nicely on the correlation curve for the colloid SiO2 system. These results indicate that the surface potential is the dominant factor in the quantum yield improvement for PVS0 reduction. PMID:16593095

Three-Dimensional Porous Particles Composed of Curved, Two-Dimensional, Nano-Sized Layers for Li-Ion Batteries

NASA Technical Reports Server (NTRS)

Yushin, Gleb; Evanoff, Kara; Magasinski, Alexander

2012-01-01

Thin Si films coated on porous 3D particles composed of curved 2D graphene sheets have been synthesized utilizing techniques that allow for tunable properties. Since graphene exhibits specific surface area up to 100 times higher than carbon black or graphite, the deposition of the same mass of Si on graphene is much faster in comparison -- a factor which is important for practical applications. In addition, the distance between graphene layers is tunable and variation in the thickness of the deposited Si film is feasible. Both of these characteristics allow for optimization of the energy and power characteristics. Thicker films will allow higher capacity, but slower rate capabilities. Thinner films will allow more rapid charging, or higher power performance. In this innovation, uniform deposition of Si and C layers on high-surface area graphene produced granules with specific surface area (SSA) of 5 sq. m/g.

The effect of surface charge, negative and bipolar ionization on the deposition of airborne bacteria.

PubMed

Meschke, S; Smith, B D; Yost, M; Miksch, R R; Gefter, P; Gehlke, S; Halpin, H A

2009-04-01

A series of experiments were conducted to evaluate the effect of surface charge and air ionization on the deposition of airborne bacteria. The interaction between surface electrostatic potential and the deposition of airborne bacteria in an indoor environment was investigated using settle plates charged with electric potentials of 0, +/-2.5kV and +/-5kV. Results showed that bacterial deposition on the plates increased proportionally with increased potential to over twice the gravitational sedimentation rate at +5kV. Experiments were repeated under similar conditions in the presence of either negative or bipolar air ionization. Bipolar air ionization resulted in reduction of bacterial deposition onto the charged surfaces to levels nearly equal to gravitational sedimentation. In contrast, diffusion charging appears to have occurred during negative air ionization, resulting in an even greater deposition onto the oppositely charged surface than observed without ionization. Static charges on fomitic surfaces may attract bacteria resulting in deposition in excess of that expected by gravitational sedimentation or simple diffusion. Implementation of bipolar ionization may result in reduction of bacterial deposition. Fomitic surfaces are important vehicles for the transmission of infectious organisms. This study has demonstrated a simple strategy for minimizing charge related deposition of bacteria on surfaces.

Selection of pecan shell-based activated carbons for removal of organic and inorganic impurities from water.

PubMed

Niandou, Mohamed A S; Novak, Jeffrey M; Bansode, Rishipal R; Yu, Jianmei; Rehrah, Djaafar; Ahmedna, Mohamed

2013-01-01

Activated carbons are a byproduct from pyrolysis and have value as a purifying agent. The effectiveness of activated carbons is dependent on feedstock selection and pyrolysis conditions that modify their surface properties. Therefore, pecan shell-based activated carbons (PSACs) were prepared by soaking shells in 50% (v/v) HPO or 25 to 50% of KOH-NaHCO followed by pyrolysis at 400 to 700°C under a N atmosphere. Physically activated PSACs were produced by pyrolysis at 700°C under N followed by activation with steam or CO at 700 to 900°C. Physicochemical, surface, and adsorption properties of the PSACs were compared with two commercially available activated carbons. The average mass yield of PSACs with respect to the initial mass of the biomass was about 20 and 34% for physically activated and chemically activated carbons, respectively. Acid-activated carbons exhibited higher surface area, higher bulk density, and lower ash content compared with steam- or CO-activated carbons and the two commercial products. Base activation led to the development of biochar with moderate to high surface area with surface charges suitable for adsorption of anionic species. Regardless of the activation method, PSACs had high total surface area ranging from 400 to 1000 m g, better pore size distribution, and more surface charges than commercial samples. Our results also showed that PSACs were effective in removing inorganic contaminants such as Cu and NO as well as organic contaminants such as atrazine and metolachlor. This study showed that pyrolysis conditions and activation had a large influence on the PSAC's surface characteristics, which can limit its effectiveness as a custom sorbent for targeted water contaminants. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.

The role of electrostatic charge in the adhesion of spherical particles onto planar surfaces in atmospheric systems

DOE PAGES

Kweon, Hyojin; Yiacoumi, Sotira Z.; Tsouris, Costas

2015-06-19

In this study, the influence of electrostatic charge on the adhesive force between spherical particles and planar surfaces in atmospheric systems was studied using atomic force microscopy. Electrical bias was applied to modify the surface charge, and it was found that application of a stronger positive bias to a particle induces a stronger total adhesive force. The sensitivity of the system to changes in the bias depended on the surface charge density. For larger-size particles, the contribution of the electrostatic force decreased, and the capillary force became the major contributor to the total adhesive force. The influence of water adsorptionmore » on the total adhesive force and, specifically, on the contribution of the electrostatic force depended on the hydrophobicity of interacting surfaces. For a hydrophilic surface, water adsorption either attenuated the surface charge or screened the effect of surface potential. An excessive amount of adsorbed water provided a path to surface charge leakage, which might cancel out the electrostatic force, leading to a reduction in the adhesive force. Theoretically calculated forces were comparable with measured adhesive forces except for mica which has a highly localized surface potential. The results of this study provide information on the behavior of charged colloidal particles in atmospheric systems.« less

Altering surface charge nonuniformity on individual colloidal particles.

PubMed

Feick, Jason D; Chukwumah, Nkiru; Noel, Alexandra E; Velegol, Darrell

2004-04-13

Charge nonuniformity (sigmazeta) was altered on individual polystyrene latex particles and measured using the novel experimental technique of rotational electrophoresis. It has recently been shown that unaltered sulfated latices often have significant charge nonuniformity (sigmazeta = 100 mV) on individual particles. Here it is shown that anionic polyelectrolytes and surfactants reduce the native charge nonuniformity on negatively charged particles by 80% (sigmazeta = 20 mV), even while leaving the average surface charge density almost unchanged. Reduction of charge uniformity occurs as large domains of nonuniformity are minimized, giving a more random distribution of charge on individual particle surfaces. Targeted reduction of charge nonuniformity opens new opportunities for the dispersion of nanoparticles and the oriented assembly of particles.

Mechanism of the free charge carrier generation in the dielectric breakdown

NASA Astrophysics Data System (ADS)

Rahim, N. A. A.; Ranom, R.; Zainuddin, H.

2017-12-01

Many studies have been conducted to investigate the effect of environmental, mechanical and electrical stresses on insulator. However, studies on physical process of discharge phenomenon, leading to the breakdown of the insulator surface are lacking and difficult to comprehend. Therefore, this paper analysed charge carrier generation mechanism that can cause free charge carrier generation, leading toward surface discharge development. Besides, this paper developed a model of surface discharge based on the charge generation mechanism on the outdoor insulator. Nernst’s Planck theory was used in order to model the behaviour of the charge carriers while Poisson’s equation was used to determine the distribution of electric field on insulator surface. In the modelling of surface discharge on the outdoor insulator, electric field dependent molecular ionization was used as the charge generation mechanism. A mathematical model of the surface discharge was solved using method of line technique (MOL). The result from the mathematical model showed that the behaviour of net space charge density was correlated with the electric field distribution.

Collisional charging of individual submillimeter particles: Using ultrasonic levitation to initiate and track charge transfer

NASA Astrophysics Data System (ADS)

Lee, Victor; James, Nicole M.; Waitukaitis, Scott R.; Jaeger, Heinrich M.

2018-03-01

Electrostatic charging of insulating fine particles can be responsible for numerous phenomena ranging from lightning in volcanic plumes to dust explosions. However, even basic aspects of how fine particles become charged are still unclear. Studying particle charging is challenging because it usually involves the complexities associated with many-particle collisions. To address these issues, we introduce a method based on acoustic levitation, which makes it possible to initiate sequences of repeated collisions of a single submillimeter particle with a flat plate, and to precisely measure the particle charge in situ after each collision. We show that collisional charge transfer between insulators is dependent on the hydrophobicity of the contacting surfaces. We use glass, which we modify by attaching nonpolar molecules to the particle, the plate, or both. We find that hydrophilic surfaces develop significant positive charges after contacting hydrophobic surfaces. Moreover, we demonstrate that charging between a hydrophilic and a hydrophobic surface is suppressed in an acidic environment and enhanced in a basic one. Application of an electric field during each collision is found to modify the charge transfer, again depending on surface hydrophobicity. We discuss these results within the context of contact charging due to ion transfer, and we show that they lend strong support to O H- ions as the charge carriers.

Effect of silicon, tantalum, and tungsten doping and polarization on bioactivity of hydroxyapatite

NASA Astrophysics Data System (ADS)

Dhal, Jharana

Hydroxyapatite (HAp) ceramics has important applications as bone graft because of the structural and compositional similarities with bone tissue. However, inferior osteogenic capacity to bone and poor mechanical properties have been identified to be major disadvantages of synthetic HAp compared to the living bone tissue. The objective of the current study is to evaluate the effect of doping with higher valent cations (Tungsten, tantalum, and silicon) and polarization or combination of both on change in property of doped HAp and subsequent impact its bioactivity. In vitro study with human osteoblast cells was used to investigate the influences of doping and polarization on bone cell-materials interactions. The bioactivity of doped HAp was compared with pure HAp. Effect of doping and polarization on the change in HAp was investigated by monitoring change in mineral phases, stored charge, and activation energy of HAp. Activation energy of depolarization was used to explain the possible mechanism of polarization in doped samples. Bioactivity of HAp increased when doped with tantalum and tungsten. Polarization further increased the bioactivity of tungsten- and tantalum-doped samples. Increase in bioactivity on polarized and doped samples was attributed to increase in surface energy and increase in surface wettability. Whereas, an increase in bioactivity on doped unpolarized surface was attributed to change in microstructure. Polarized charge calculated from TSDC indicates that polarized charge decreases on tantalum- and tungsten-doped HAp. The decrease in polarized charge was attributed to the presence of significant amount of different phases that may hinder the ionic motion in doped samples. However, for silicon-doped HAp, TSDC study showed no difference in the mechanism of polarization between doped and undoped samples. Increase in silicon doping decreased the grain size though mechanism is not affected by grain size. Total stored charge decreased with increase in dopant concentration at a particular sintering temperature. Results of this study provide further evidence for use of higher valence cations to improve biological performance of HAp ceramics and to advance our understanding on mechanism of polarization in doped samples.

A Combined Model of Charging of the Surface and Bulk of a Dielectric Target by Electrons with the Energies 10-30 keV

NASA Astrophysics Data System (ADS)

Zykov, V. M.; Neiman, D. A.

2018-04-01

A physico-mathematical model of the processes of radiation-induced charging of dielectric materials with open surfaces, irradiated with monoenergetic electrons in the energy range 10-30 keV, is described. The model takes into account the relationship between the processes of surface and bulk charging for the given conditions of the experimental design, which accounts for the effect of anomalously long charging of dielectrics after the incident energy of primary electrons during charging is reduced to below the second critical energy for the secondary electronic emission coefficient. The initial fast phase of charging a high-resistivity dielectric material (Al2O3) is investigated. It is shown that as the incident electron energy is approaching the second critical energy during charging, the secondary electronic emission is partially suppressed due to negative charging of the open surface of the dielectric and formation of a near-surface inversion electrical field retarding the electronic emission yield.

Ion association at discretely-charged dielectric interfaces: Giant charge inversion

NASA Astrophysics Data System (ADS)

Wang, Zhi-Yong; Wu, Jianzhong

2017-07-01

Giant charge reversal has been identified for the first time by Monte Carlo simulation for a discretely charged surface in contact with a trivalent electrolyte solution. It takes place regardless of the surface charge density under study and the monovalent salt. In stark contrast to earlier predictions based on the 2-dimensional Wigner crystal model to describe strong correlation of counterions at the macroion surface, we find that giant charge reversal reflects an intricate interplay of ionic volume effects, electrostatic correlations, surface charge heterogeneity, and the dielectric response of the confined fluids. While the novel phenomenon is yet to be confirmed with experiment, the simulation results appear in excellent agreement with a wide range of existing observations in the subregime of charge inversion. Our findings may have far-reaching implications to understanding complex electrochemical phenomena entailing ionic fluids under dielectric confinements.

Fullerene ion chemistry: a journey of discovery and achievement

PubMed Central

Böhme, Diethard K.

2016-01-01

An account is provided of the extraordinary features of buckminster fullerene cations and their chemistry that we discovered in our Ion Chemistry Laboratory at York University (Canada) during a ‘golden’ period of research in the early 1990s, just after C60 powder became available. We identified new chemical ways of C60 ionization and tracked novel chemistry of C60n+ as a function of charge state (n=1–3) with some 50 different reagent molecules. We found that multiple charges enhance reaction rates and diversify reaction products and mechanisms. Strong electrostatic interactions with reagent molecules were seen to reduce barriers to carbon surface bonding and charge-separation reactions, while intramolecular Coulomb repulsion appeared to localize charge on the surface or the substituent and so influence higher order chemistry, including ‘spindle’, ‘star’, ‘fuzzy ball’, ‘ball-and-chain’ and dimer ion formation. We introduced the notion of ‘apparent’ gas-phase acidity with measurements of proton-transfer reactions of multiply charged fullerene cations. We also explored the attachment of atomic metal cations to C60 and their subsequent reactions. All these findings were applied to the possible chemistry of fullerene cations in the interstellar medium with a focus on multiply charged fullerene ion formation and the intervention of fullerene cations in fullerene derivatization and molecular synthesis, with a view to their possible future detection. This article is part of the themed issue ‘Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene’. PMID:27501972

VARIABLE CHARGE SOILS: MINERALOGY AND CHEMISTRY

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

Van Ranst, Eric; Qafoku, Nikolla; Noble, Andrew

2016-09-19

Soils rich in particles with amphoteric surface properties in the Oxisols, Ultisols, Alfisols, Spodosols and Andisols orders (1) are considered to be variable charge soils (2) (Table 1). The term “variable charge” is used to describe organic and inorganic soil constituents with reactive surface groups whose charge varies with pH and ionic concentration and composition of the soil solution. Such groups are the surface carboxyl, phenolic and amino functional groups of organic materials in soils, and surface hydroxyl groups of Fe and Al oxides, allophane and imogolite. The hydroxyl surface groups are also present on edges of some phyllosilicate mineralsmore » such as kaolinite, mica, and hydroxyl-interlayered vermiculite. The variable charge is developed on the surface groups as a result of adsorption or desorption of ions that are constituents of the solid phase, i.e., H+, and the adsorption or desorption of solid-unlike ions that are not constituents of the solid phase. Highly weathered soils and subsoils (e.g., Oxisols and some Ultisols, Alfisols and Andisols) may undergo isoelectric weathering and reach a “zero net charge” stage during their development. They usually have a slightly acidic to acidic soil solution pH, which is close to either the point of zero net charge (PZNC) (3) or the point of zero salt effect (PZSE) (3). They are characterized by high abundances of minerals with a point of zero net proton charge (PZNPC) (3) at neutral and slightly basic pHs; the most important being Fe and Al oxides and allophane. Under acidic conditions, the surfaces of these minerals are net positively charged. In contrast, the surfaces of permanent charge phyllosilicates are negatively charged regardless of ambient conditions. Variable charge soils therefore, are heterogeneous charge systems.« less

Water organization between oppositely charged surfaces: Implications for protein sliding along DNA a)

NASA Astrophysics Data System (ADS)

Marcovitz, Amir; Naftaly, Aviv; Levy, Yaakov

2015-02-01

Water molecules are abundant in protein-DNA interfaces, especially in their nonspecific complexes. In this study, we investigated the organization and energetics of the interfacial water by simplifying the geometries of the proteins and the DNA to represent them as two equally and oppositely charged planar surfaces immersed in water. We found that the potential of mean force for bringing the two parallel surfaces into close proximity comprises energetic barriers whose properties strongly depend on the charge density of the surfaces. We demonstrated how the organization of the water molecules into discretized layers and the corresponding energetic barriers to dehydration can be modulated by the charge density on the surfaces, salt, and the structure of the surfaces. The 1-2 layers of ordered water are tightly bound to the charged surfaces representing the nonspecific protein-DNA complex. This suggests that water might mediate one-dimensional diffusion of proteins along DNA (sliding) by screening attractive electrostatic interactions between the positively charged molecular surface on the protein and the negatively charged DNA backbone and, in doing so, reduce intermolecular friction in a manner that smoothens the energetic landscape for sliding, and facilitates the 1D diffusion of the protein.

Laboratory Studies of Charging Properties of Dust Grains in Astrophysical/Planetary Environments

NASA Technical Reports Server (NTRS)

Tankosic, D.; Abbas, M. M.

2012-01-01

Dust grains in various astrophysical environments are generally charged electrostatically by photoelectric emissions with UV/X-ray radiation, as well as by electron/ion impact. Knowledge of physical and optical properties of individual dust grains is required for understanding of the physical and dynamical processes in space environments and the role of dust in formation of stellar and planetary systems. In this paper we focus on charging of individual micron/submicron dust grains by processes that include: (a) UV photoelectric emissions involving incident photon energies higher than the work function of the material and b) electron impact, where low energy electrons are scattered or stick to the dust grains, thereby charging the dust grains negatively, and at sufficiently high energies the incident electrons penetrate the grain leading to excitation and emission of electrons referred to as secondary electron emission (SEE). It is well accepted that the charging properties of individual micron/submicron size dust grains are expected to be substantially different from the bulk materials. However, no viable models for calculation of the charging properties of individual micron size dust grains are available at the present time. Therefore, the photoelectric yields, and secondary electron emission yields of micron-size dust grains have to be obtained by experimental methods. Currently, very limited experimental data are available for charging of individual micron-size dust grains. Our experimental results, obtained on individual, micron-size dust grains levitated in an electrodynamic balance facility (at NASA-MSFC), show that: (1) The measured photoelectric yields are substantially higher than the bulk values given in the literature and indicate a particle size dependence with larger particles having order-of-magnitude higher values than for submicron-size grains; (2) dust charging by low energy electron impact is a complex process. Also, our measurements indicate that the electron impact may lead to charging or discharging of dust grains depending upon the grain size, surface potential, electron energy, electron flux, grain composition, and configuration (e.g. Abbas et al, 2010). Laboratory measurements on charging of analogs of the interstellar dust as well as Apollo 11 dust grains conducted at the NASA-MSFC Dusty Plasma Lab. are presented here

Space and surface charge behavior analysis of charge-eliminated polymer films

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

Oda, Tetsuji; Takashima, Kazunori; Ichiyama, Shinichiro

1995-12-31

Charge behavior of corona-charged or charge eliminated polymer films being dipped in the city water were studied. They were polytetrafluoroethylene (PTFE teflon{trademark}), polypropylene (PP), low density or high density polyethylene (LDPE or HDPE) thin films which are as grown (native) or plasma-processed. The plasma processing at low pressure was tested as antistatic processing. Charge elimination was done by being dipped in alcohol or city water. TSDC analysis and surface charge profile measurement were done for both charged and charge eliminated polymer films. Surface charge density of plasma processed polymer films just after corona charging is roughly the same as thatmore » of an original film. There is little difference between surface charge density profile of a native film and that of a plasma processed film. A large hetero current peak of TSDC was observed at room temperature for a processed film. It was found that the hetero peak disappears after charge elimination process. A pressure pulse wave method by using a pulse-driven piezoelectric PVDF polymer film as a piezoelectric actuator was newly developed to observe real space charge distribution. A little difference of internal space charge distribution between the plasma processed film and the native one after corona charging is found.« less

Ordered adsorption of coagulation factor XII on negatively charged polymer surfaces probed by sum frequency generation vibrational spectroscopy.

PubMed

Chen, Xiaoyun; Wang, Jie; Paszti, Zoltan; Wang, Fulin; Schrauben, Joel N; Tarabara, Volodymyr V; Schmaier, Alvin H; Chen, Zhan

2007-05-01

Electrostatic interactions between negatively charged polymer surfaces and factor XII (FXII), a blood coagulation factor, were investigated by sum frequency generation (SFG) vibrational spectroscopy, supplemented by several analytical techniques including attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), quartz crystal microbalance (QCM), zeta-potential measurement, and chromogenic assay. A series of sulfonated polystyrenes (sPS) with different sulfonation levels were synthesized as model surfaces with different surface charge densities. SFG spectra collected from FXII adsorbed onto PS and sPS surfaces with different surface charge densities showed remarkable differences in spectral features and especially in spectral intensity. Chromogenic assay experiments showed that highly charged sPS surfaces induced FXII autoactivation. ATR-FTIR and QCM results indicated that adsorption amounts on the PS and sPS surfaces were similar even though the surface charge densities were different. No significant conformational change was observed from FXII adsorbed onto surfaces studied. Using theoretical calculations, the possible contribution from the third-order nonlinear optical effect induced by the surface electric field was evaluated, and it was found to be unable to yield the SFG signal enhancement observed. Therefore it was concluded that the adsorbed FXII orientation and ordering were the main reasons for the remarkable SFG amide I signal increase on sPS surfaces. These investigations indicate that negatively charged surfaces facilitate or induce FXII autoactivation on the molecular level by imposing specific orientation and ordering on the adsorbed protein molecules.

Electric field measurements during the blowing snow in a cryogenic wind tunnel by a non-contact voltmeter

NASA Astrophysics Data System (ADS)

Sato, A.; Omiya, S.

2011-12-01

It is known that the average atmospheric electric field is +100V/m in fair weather (positive electric field vector points downward). An increase of atmospheric electric field is reported when the blowing snow occurred. This phenomenon is mainly explained by the fact that the blowing snow particles have negative charge in average. It is suggested that an electrostatic force, given by the product of the electric field and the charge of the particle, may influence the particle trajectory and change those movements, saltation and suspension. The purpose of this experiment is to clarify the characteristics of the electric field during blowing snow event. Experiments were carried out in the cryogenic wind tunnel of Snow and Ice Research Center, NIED. A non-contact voltmeter was used to measure the electric field. An artificial blowing snow was generated by a snow particle supply machine. The rolling brushes of the machine scratch the snow surface and supply snow particles into the airflow. This machine made it possible to supply the snow particles at an arbitrary rate. This experiment was conducted in the following experimental conditions; wind speed of 5 to 7 m/s (3 patterns), supply snow quantity of 8.7 to 34.9 g/m/s (4 patterns), air temperature of -10 degree Celsius, fetch of 10 m and hard snow surface. Measured electric field was all negative, which is opposite direction to the previous measurements. This means that the blowing snow particles had positive charges. The negative electric field tended to increase with increase of the wind speed and the mass flux. These results can be explained from the previous experiment by Omiya and Sato (2010). The snow particles gain positive charges by the friction with the rolling brush which is made from polypropylene, however the particles accumulate negative charges gradually with increase of the collisions to the snow surface. Probably, the positive charges might have remained on the snow particles that had passed over the measurement point. Moreover, it is thought that because the saltation length is longer when the wind speed is higher, fewer collision frequencies left the particles more positive charges. REFERENCE:Omiya and Sato(2010): Measurement of electrostatic charge of blowing snow particles in a wind tunnel focusing on collision frequency to the snow surface. Hokkaido University Collection of Scholarly and Academic Papers

Experimental and Theoretical Investigations of Glass Surface Charging Phenomena

NASA Astrophysics Data System (ADS)

Agnello, Gabriel

Charging behavior of multi-component display-type (i.e. low alkali) glass surfaces has been studied using a combination of experimental and theoretical methods. Data obtained by way of a Rolling Sphere Test (RST), streaming/zeta potential and surface energy measurements from commercially available display glass surfaces (Corning EAGLE XGRTM and Lotus(TM) XT) suggest that charge accumulation is highly dependent on surface treatment (chemical and/or physical modification) and measurement environment, presumably through reactionary mechanisms at the surface with atmospheric moisture. It has been hypothesized that water dissociation, along with the corresponding hydroxylation of the glass surface, are important processes related to charging in glass-metal contact systems. Classical Molecular Dynamics (MD) simulations, in conjunction with various laboratory based measurements (RST, a newly developed ElectroStatic Gauge (ESG) and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS)) on simpler Calcium AluminoSilicate (CAS) glass surfaces were used to further explore these phenomena. Analysis of simulated high-silica content (≥50%) (CAS) glass structures suggest that controlled variation of bulk chemistry can directly affect surface defect concentrations, such as non-bridging oxygen (NBO), which can be suitable high-energy sites for hydrolysis-type reactions to occur. Calculated NBO surface concentrations correlate well with charge based measurements on laboratory fabricated CAS surfaces. The data suggest that a directional/polar shift in contact-charge transfer occurs at low silica content (≤50%) where the highest concentrations of NBOs are observed. Surface charging sensitivity with respect to NBO concentration decreases as the relative humidity of the measurement environment increases; which should be expected as the highly reactive sites are progressively covered by liquid water layers. DRIFTS analysis of CAS powders expand on this analysis showing a gradual increase in molecular water absorption at the surface in samples containing ≥60% silica, and an abrupt decrease in those with ≤60% silica. This behavior is very likely related to the aforementioned charge polarity shift (negative (-) to positive (+)) in low silica containing glasses, leading to the conclusion that structural defect mediated charge accumulation and/or transfer are likely to be important mechanisms related to the contact charging of glass surfaces.

Gravity dependency of the gramicidin A channel conductivity. A model for gravity perception on the cellular level.

PubMed

Schatz, A; Linke-Hommes, A; Neubert, J

1996-01-01

Theoretical investigations involving the membrane-solution interface have revealed that the density of the solution varies appreciably within interfacial layers adjacent to charged membrane surfaces. The hypothesis that gravity interacts with this configuration and modifies transport rates across horizontal and vertical membranes differently was supported by initial experiments with gramicidin A channels in phosphatidylserine (PS) membranes in 0.1 M KCl. Channel conductivity was found to be about 1.6 times higher in horizontal membranes than in vertical membranes. Here we present the results of further experiments with gramicidin A channels (incorporated into charged PS- and uncharged phosphatidylcholine (PC) membranes in KCl- and CsCl-solutions) to demonstrate that the hypothesis is more generally applicable. Again, channel conductivity was found to be higher in horizontal PS membranes by a factor of between 1.20 and 1.75 in 0.1 M CsCl. No difference in channel conductivity was found for uncharged PC membranes in 0.1 M KCl and in 0.1 M CsCl. However, for PC membranes in 0.05 M KCl the channel conductivity was significantly higher in horizontal membranes by a factor of between 1.07 and 1.14. These results are consistent with the results of our model calculations of layer density and extension, which showed that the layer formation is enhanced by increasing membrane surface charge and decreasing electrolyte ion concentration. The mechanism of gravity interaction with membrane transport processes via interface reactions might be utilized by biological systems for orientational behaviour in the gravity field, which has been observed even for cellular systems.

Direct measurement of sub-Debye-length attraction between oppositely charged surfaces.

PubMed

Kampf, Nir; Ben-Yaakov, Dan; Andelman, David; Safran, S A; Klein, Jacob

2009-09-11

Using a surface force balance with fast video analysis, we have measured directly the attractive forces between oppositely charged solid surfaces (charge densities sigma(+), sigma(-)) across water over the entire range of interaction, in particular, at surface separations D below the Debye screening length lambda(S). At very low salt concentration we find a long-ranged attraction between the surfaces (onset ca. 100 nm), whose variation at D

Ultrafast high-power microwave window breakdown: nonlinear and postpulse effects.

PubMed

Chang, C; Verboncoeur, J; Guo, M N; Zhu, M; Song, W; Li, S; Chen, C H; Bai, X C; Xie, J L

2014-12-01

The time- and space-dependent optical emissions of nanosecond high-power microwave discharges near a dielectric-air interface have been observed by nanosecond-response four-framing intensified-charged-coupled device cameras. The experimental observations indicate that plasma developed more intensely at the dielectric-air interface than at the free-space region with a higher electric-field amplitude. A thin layer of intense light emission above the dielectric was observed after the microwave pulse. The mechanisms of the breakdown phenomena are analyzed by a three-dimensional electromagnetic-field modeling and a two-dimensional electromagnetic particle-in-cell simulation, revealing the formation of a space-charge microwave sheath near the dielectric surface, accelerated by the normal components of the microwave field, significantly enhancing the local-field amplitude and hence ionization near the dielectric surface. The nonlinear positive feedback of ionization, higher electron mobility, and ultraviolet-driven photoemission due to the elevated electron temperature are crucial for achieving the ultrafast discharge. Following the high-power microwave pulse, the sheath sustains a glow discharge until the sheath collapses.

Mapping surface charge density of lipid bilayers by quantitative surface conductivity microscopy

PubMed Central

Klausen, Lasse Hyldgaard; Fuhs, Thomas; Dong, Mingdong

2016-01-01

Local surface charge density of lipid membranes influences membrane–protein interactions leading to distinct functions in all living cells, and it is a vital parameter in understanding membrane-binding mechanisms, liposome design and drug delivery. Despite the significance, no method has so far been capable of mapping surface charge densities under physiologically relevant conditions. Here, we use a scanning nanopipette setup (scanning ion-conductance microscope) combined with a novel algorithm to investigate the surface conductivity near supported lipid bilayers, and we present a new approach, quantitative surface conductivity microscopy (QSCM), capable of mapping surface charge density with high-quantitative precision and nanoscale resolution. The method is validated through an extensive theoretical analysis of the ionic current at the nanopipette tip, and we demonstrate the capacity of QSCM by mapping the surface charge density of model cationic, anionic and zwitterionic lipids with results accurately matching theoretical values. PMID:27561322

Mapping surface charge density of lipid bilayers by quantitative surface conductivity microscopy

NASA Astrophysics Data System (ADS)

Klausen, Lasse Hyldgaard; Fuhs, Thomas; Dong, Mingdong

2016-08-01

Local surface charge density of lipid membranes influences membrane-protein interactions leading to distinct functions in all living cells, and it is a vital parameter in understanding membrane-binding mechanisms, liposome design and drug delivery. Despite the significance, no method has so far been capable of mapping surface charge densities under physiologically relevant conditions. Here, we use a scanning nanopipette setup (scanning ion-conductance microscope) combined with a novel algorithm to investigate the surface conductivity near supported lipid bilayers, and we present a new approach, quantitative surface conductivity microscopy (QSCM), capable of mapping surface charge density with high-quantitative precision and nanoscale resolution. The method is validated through an extensive theoretical analysis of the ionic current at the nanopipette tip, and we demonstrate the capacity of QSCM by mapping the surface charge density of model cationic, anionic and zwitterionic lipids with results accurately matching theoretical values.

Mapping surface charge density of lipid bilayers by quantitative surface conductivity microscopy.

PubMed

Klausen, Lasse Hyldgaard; Fuhs, Thomas; Dong, Mingdong

2016-08-26

Local surface charge density of lipid membranes influences membrane-protein interactions leading to distinct functions in all living cells, and it is a vital parameter in understanding membrane-binding mechanisms, liposome design and drug delivery. Despite the significance, no method has so far been capable of mapping surface charge densities under physiologically relevant conditions. Here, we use a scanning nanopipette setup (scanning ion-conductance microscope) combined with a novel algorithm to investigate the surface conductivity near supported lipid bilayers, and we present a new approach, quantitative surface conductivity microscopy (QSCM), capable of mapping surface charge density with high-quantitative precision and nanoscale resolution. The method is validated through an extensive theoretical analysis of the ionic current at the nanopipette tip, and we demonstrate the capacity of QSCM by mapping the surface charge density of model cationic, anionic and zwitterionic lipids with results accurately matching theoretical values.

Surface charges for gravity and electromagnetism in the first order formalism

NASA Astrophysics Data System (ADS)

Frodden, Ernesto; Hidalgo, Diego

2018-02-01

A new derivation of surface charges for 3  +  1 gravity coupled to electromagnetism is obtained. Gravity theory is written in the tetrad-connection variables. The general derivation starts from the Lagrangian, and uses the covariant symplectic formalism in the language of forms. For gauge theories, surface charges disentangle physical from gauge symmetries through the use of Noether identities and the exactness symmetry condition. The surface charges are quasilocal, explicitly coordinate independent, gauge invariant and background independent. For a black hole family solution, the surface charge conservation implies the first law of black hole mechanics. As a check, we show the first law for an electrically charged, rotating black hole with an asymptotically constant curvature (the Kerr–Newman (anti-)de Sitter family). The charges, including the would-be mass term appearing in the first law, are quasilocal. No reference to the asymptotic structure of the spacetime nor the boundary conditions is required and therefore topological terms do not play a rôle. Finally, surface charge formulae for Lovelock gravity coupled to electromagnetism are exhibited, generalizing the one derived in a recent work by Barnich et al Proc. Workshop ‘ About Various Kinds of Interactions’ in honour of Philippe Spindel (4–5 June 2015, Mons, Belgium) C15-06-04 (2016 (arXiv:1611.01777 [gr-qc])). The two different symplectic methods to define surface charges are compared and shown equivalent.

Exact analysis of surface field reduction due to field-emitted vacuum space charge, in parallel-plane geometry, using simple dimensionless equations

NASA Astrophysics Data System (ADS)

Forbes, Richard G.

2008-10-01

This paper reports (a) a simple dimensionless equation relating to field-emitted vacuum space charge (FEVSC) in parallel-plane geometry, namely 9ζ2θ2-3θ-4ζ+3=0, where ζ is the FEVSC "strength" and θ is the reduction in emitter surface field (θ =field-with/field-without FEVSC), and (b) the formula j =9θ2ζ/4, where j is the ratio of emitted current density JP to that predicted by Child's law. These equations apply to any charged particle, positive or negative, emitted with near-zero kinetic energy. They yield existing and additional basic formulas in planar FEVSC theory. The first equation also yields the well-known cubic equation describing the relationship between JP and applied voltage; a method of analytical solution is described. Illustrative FEVSC effects in a liquid metal ion source and in field electron emission are discussed. For Fowler-Nordheim plots, a "turn-over" effect is predicted in the high FEVSC limit. The higher the voltage-to-local-field conversion factor for the emitter concerned, then the higher is the field at which turn over occurs. Past experiments have not found complete turn over; possible reasons are noted. For real field emitters, planar theory is a worst-case limit; however, adjusting ζ on the basis of Monte Carlo calculations might yield formulae adequate for real situations.

Direct Observation of Charge Transfer at a MgO(111) Surface

NASA Astrophysics Data System (ADS)

Subramanian, A.; Marks, L. D.; Warschkow, O.; Ellis, D. E.

2004-01-01

Transmission electron diffraction (TED) combined with direct methods have been used to study the √(3)×√(3)R30° reconstruction on the polar (111) surface of MgO and refine the valence charge distribution. The surface is nonstoichiometric and is terminated by a single magnesium atom. A charge-compensating electron hole is localized in the next oxygen layer and there is a nominal charge transfer from the oxygen atoms to the top magnesium atom. The partial charges that we obtain for the surface atoms are in reasonable agreement with empirical bond-valence estimations.

Electrochemical capacitors: mechanism, materials, systems, characterization and applications.

PubMed

Wang, Yonggang; Song, Yanfang; Xia, Yongyao

2016-10-24

Electrochemical capacitors (i.e. supercapacitors) include electrochemical double-layer capacitors that depend on the charge storage of ion adsorption and pseudo-capacitors that are based on charge storage involving fast surface redox reactions. The energy storage capacities of supercapacitors are several orders of magnitude higher than those of conventional dielectric capacitors, but are much lower than those of secondary batteries. They typically have high power density, long cyclic stability and high safety, and thus can be considered as an alternative or complement to rechargeable batteries in applications that require high power delivery or fast energy harvesting. This article reviews the latest progress in supercapacitors in charge storage mechanisms, electrode materials, electrolyte materials, systems, characterization methods, and applications. In particular, the newly developed charge storage mechanism for intercalative pseudocapacitive behaviour, which bridges the gap between battery behaviour and conventional pseudocapacitive behaviour, is also clarified for comparison. Finally, the prospects and challenges associated with supercapacitors in practical applications are also discussed.

Carrier transport and collection in fully depleted semiconductors by a combined action of the space charge field and the field due to electrode voltages

DOEpatents

Rehak, P.; Gatti, E.

1984-02-24

A semiconductor charge transport device and method for making same, characterized by providing a thin semiconductor wafer having rectifying functions on its opposing major surfaces and including a small capacitance ohmic contact, in combination with bias voltage means and associated circuit means for applying a predetermined voltage to effectively deplete the wafer in regions thereof between the rectifying junctions and the ohmic contact. A charge transport device of the invention is usable as a drift chamber, a low capacitance detector, or a charge coupled device each constructed according to the methods of the invention for making such devices. Detectors constructed according to the principles of the invention are characterized by having significantly higher particle position indicating resolution than is attainable with prior art detectors, while at the same time requiring substantially fewer readout channels to realize such high resolution.

Carrier transport and collection in fully depleted semiconductors by a combined action of the space charge field and the field due to electrode voltages

DOEpatents

Rehak, Pavel; Gatti, Emilio

1987-01-01

A semiconductor charge transport device and method for making same, characterized by providing a thin semiconductor wafer having rectifying junctions on its opposing major surfaces and including a small capacitance ohmic contact, in combination with bias voltage means and associated circuit means for applying a predetermined voltage to effectively deplete the wafer in regions thereof between the rectifying junctions and the ohmic contact. A charge transport device of the invention is usable as a drift chamber, a low capacitance detector, or a charge coupled device each constructed according to the methods of the invention for making such devices. Detectors constructed according to the principles of the invention are characterized by having significantly higher particle position indicating resolution than is attainable with prior art detectors, while at the same time requiring substantially fewer readout channels to realize such high resolution.

Carrier transport and collection in fully depleted semiconductors by a combined action of the space charge field and the field due to electrode voltages

DOEpatents

Rehak, P.; Gatti, E.

1987-08-18

A semiconductor charge transport device and method for making same are disclosed, characterized by providing a thin semiconductor wafer having rectifying junctions on its opposing major surfaces and including a small capacitance ohmic contact, in combination with bias voltage means and associated circuit means for applying a predetermined voltage to effectively deplete the wafer in regions thereof between the rectifying junctions and the ohmic contact. A charge transport device of the invention is usable as a drift chamber, a low capacitance detector, or a charge coupled device each constructed according to the methods of the invention for making such devices. Detectors constructed according to the principles of the invention are characterized by having significantly higher particle position indicating resolution than is attainable with prior art detectors, while at the same time requiring substantially fewer readout channels to realize such high resolution. 16 figs.

The surface charge of trypanosomatids.

PubMed

Souto-Padrón, Thaïs

2002-12-01

The surface charge of trypanosomatids was evaluated by means of the binding of cationic particles, as visualized by electron microscopy and by direct measurements of the electrophoretic mobility of cells. The results obtained indicate that most of the trypanosomatids exhibit a negatively charged surface whose value is species specific and varies according to the developmental stages. Sialic acids associated with glycoproteins, glycolipids and phosphate groups are the major components responsible for the net negative surface charge of the trypanosomatids.

Mesoporous tungsten oxynitride as electrocatalyst for promoting redox reactions of vanadium redox couple and performance of vanadium redox flow battery

NASA Astrophysics Data System (ADS)

Lee, Wonmi; Jo, Changshin; Youk, Sol; Shin, Hun Yong; Lee, Jinwoo; Chung, Yongjin; Kwon, Yongchai

2018-01-01

For enhancing the performance of vanadium redox flow battery (VRFB), a sluggish reaction rate issue of V2+/V3+ redox couple evaluated as the rate determining reaction should be addressed. For doing that, mesoporous tungsten oxide (m-WO3) and oxyniride (m-WON) structures are proposed as the novel catalysts, while m-WON is gained by NH3 heat treatment of m-WO3. Their specific surface area, crystal structure, surface morphology and component analysis are measured using BET, XRD, TEM and XPS, while their catalytic activity for V2+/V3+ redox reaction is electrochemically examined. As a result, the m-WON shows higher peak current, smaller peak potential difference, higher electron transfer rate constant and lower charge transfer resistance than other catalysts, like the m-WO3, WO3 nanoparticle and mesoporous carbon, proving that it is superior catalyst. Regarding the charge-discharge curve tests, the VRFB single cell employing the m-WON demonstrates high voltage and energy efficiencies, high specific capacity and low capacity loss rate. The excellent results of m-WON are due to the reasons like (i) reduced energy band gap, (ii) reaction familiar surface functional groups and (ii) greater electronegativity.

Miniaturized ultrafine particle sizer and monitor

NASA Technical Reports Server (NTRS)

Qi, Chaolong (Inventor); Chen, Da-Ren (Inventor)

2011-01-01

An apparatus for measuring particle size distribution includes a charging device and a precipitator. The charging device includes a corona that generates charged ions in response to a first applied voltage, and a charger body that generates a low energy electrical field in response to a second applied voltage in order to channel the charged ions out of the charging device. The corona tip and the charger body are arranged relative to each other to direct a flow of particles through the low energy electrical field in a direction parallel to a direction in which the charged ions are channeled out of the charging device. The precipitator receives the plurality of particles from the charging device, and includes a disk having a top surface and an opposite bottom surface, wherein a predetermined voltage is applied to the top surface and the bottom surface to precipitate the plurality of particles.

Hydroxy-Al and cell-surface negativity are responsible for the enhanced sensitivity of Rhodotorula taiwanensis to aluminum by increased medium pH.

PubMed

Zhao, Xue Qiang; Bao, Xue Min; Wang, Chao; Xiao, Zuo Yi; Hu, Zhen Min; Zheng, Chun Li; Shen, Ren Fang

2017-10-01

Aluminum (Al) is ubiquitous and toxic to microbes. High Al 3+ concentration and low pH are two key factors responsible for Al toxicity, but our present results contradict this idea. Here, an Al-tolerant yeast strain Rhodotorula taiwanensis RS1 was incubated in glucose media containing Al with a continuous pH gradient from pH 3.1-4.2. The cells became more sensitive to Al and accumulated more Al when pH increased. Calculations using an electrostatic model Speciation Gouy Chapman Stern indicated that, the increased Al sensitivity of cells was associated with AlOH 2+ and Al(OH) 2 + rather than Al 3+ . The alcian blue (a positively charged dye) adsorption and zeta potential determination of cell surface indicated that, higher pH than 3.1 increased the negative charge and Al adsorption at the cell surface. Taken together, the enhanced sensitivity of R. taiwanensis RS1 to Al from pH 3.1-4.2 was associated with increased hydroxy-Al and cell-surface negativity.

Luminescence evolution from alumina ceramic surface before flashover under direct and alternating current voltage in vacuum

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

Su, Guo-Qiang; Wang, Yi-Bo; Song, Bai-Peng

2016-06-15

The luminescence evolution phenomena from alumina ceramic surface in vacuum under high voltage of direct and alternating current are reported, with the voltage covering a large range from far below to close to the flashover voltage. Its time resolved and spatial distributed behaviors are examined by a photon counting system and an electron-multiplying charge-coupled device (EMCCD) together with a digital camera, respectively. The luminescence before flashover exhibits two stages as voltage increasing, i.e., under a relative low voltage (Stage A), the luminescence is ascribed to radiative recombination of hetero-charges injected into the sample surface layer by Schottky effect; under amore » higher voltage (Stage B), a stable secondary electron emission process, resulting from the Fowler-Nordheim emission at the cathode triple junction (CTJ), is responsible for the luminescence. Spectrum analysis implies that inner secondary electrons within the surface layer of alumina generated during the SSEE process also participate in the luminescence of Stage B. A comprehensive interpretation of the flashover process is formulated, which might promote a better understanding of flashover issue in vacuum.« less

Luminescence evolution from alumina ceramic surface before flashover under direct and alternating current voltage in vacuum

NASA Astrophysics Data System (ADS)

Su, Guo-Qiang; Wang, Yi-Bo; Song, Bai-Peng; Mu, Hai-Bao; Zhang, Guan-Jun; Li, Feng; Wang, Meng

2016-06-01

The luminescence evolution phenomena from alumina ceramic surface in vacuum under high voltage of direct and alternating current are reported, with the voltage covering a large range from far below to close to the flashover voltage. Its time resolved and spatial distributed behaviors are examined by a photon counting system and an electron-multiplying charge-coupled device (EMCCD) together with a digital camera, respectively. The luminescence before flashover exhibits two stages as voltage increasing, i.e., under a relative low voltage (Stage A), the luminescence is ascribed to radiative recombination of hetero-charges injected into the sample surface layer by Schottky effect; under a higher voltage (Stage B), a stable secondary electron emission process, resulting from the Fowler-Nordheim emission at the cathode triple junction (CTJ), is responsible for the luminescence. Spectrum analysis implies that inner secondary electrons within the surface layer of alumina generated during the SSEE process also participate in the luminescence of Stage B. A comprehensive interpretation of the flashover process is formulated, which might promote a better understanding of flashover issue in vacuum.

Method of adhesion between an oxide layer and a metal layer

DOEpatents

Jennison, Dwight R.; Bogicevic, Alexander; Kelber, Jeffry A.; Chambers, Scott A.

2004-09-14

A method of controlling the wetting characteristics and increasing the adhesion between a metal and an oxide layer. By introducing a negatively-charged species to the surface of an oxide layer, layer-by-layer growth of metal deposited onto the oxide surface is promoted, increasing the adhesion strength of the metal-oxide interface. The negatively-charged species can either be deposited onto the oxide surface or a compound can be deposited that dissociates on, or reacts with, the surface to form the negatively-charged species. The deposited metal adatoms can thereby bond laterally to the negatively-charged species as well as vertically to the oxide surface as well as react with the negatively charged species, be oxidized, and incorporated on or into the surface of the oxide.

Soil pH on mobility of imazaquin in oxisols with positive balance of charges.

PubMed

Regitano, Jussara B; da Rocha, Wadson S D; Alleoni, Luís R F

2005-05-18

The influence of soil pH on the leaching potential of the ionizable herbicide imazaquin was assessed on the profile of two highly weathered soils having a net positive charge in the B horizon, in contrast to a soil having a net negative charge in the whole profile, using packed soil column experiments. Imazaquin leached to a large extent and faster at Kd values lower than 1.0 L kg(-1), a much more lenient limit than usually proposed for pesticides in the literature (Kd < 5.0 L kg(-1)). The amount of imazaquin leached increased with soil pH. As the soil pH increased, the percentage of imazaquin in the anionic forms, the negative surface potential of the soils, as well as imazaquin water solubility also increased, thus reducing sorption because of repulsive electrostatic forces (hydrophilic interactions). For all surface samples (0-0.2 m), imazaquin did not leach at soil pH values lower than pKa (3.8) and more than 80% of the applied amount was leached at pH values higher than 5.5. For subsurface samples from the acric soils, imazaquin only began to leach at soil pH values > zero point of salt effects (ZPSE > 5.7). In conclusion, the use of surface K(oc) values to predict the amount of imazaquin leached within soil profiles having a positive balance of charges may greatly overestimate its actual leaching potential.

Electrostatic correlations at the Stern layer: Physics or chemistry?

NASA Astrophysics Data System (ADS)

Travesset, A.; Vangaveti, S.

2009-11-01

We introduce a minimal free energy describing the interaction of charged groups and counterions including both classical electrostatic and specific interactions. The predictions of the model are compared against the standard model for describing ions next to charged interfaces, consisting of Poisson-Boltzmann theory with additional constants describing ion binding, which are specific to the counterion and the interfacial charge ("chemical binding"). It is shown that the "chemical" model can be appropriately described by an underlying "physical" model over several decades in concentration, but the extracted binding constants are not uniquely defined, as they differ depending on the particular observable quantity being studied. It is also shown that electrostatic correlations for divalent (or higher valence) ions enhance the surface charge by increasing deprotonation, an effect not properly accounted within chemical models. The charged phospholipid phosphatidylserine is analyzed as a concrete example with good agreement with experimental results. We conclude with a detailed discussion on the limitations of chemical or physical models for describing the rich phenomenology of charged interfaces in aqueous media and its relevance to different systems with a particular emphasis on phospholipids.

Crystal structure of class III chitinase from pomegranate provides the insight into its metal storage capacity.

PubMed

Masuda, Taro; Zhao, Guanghua; Mikami, Bunzo

2015-01-01

Chitinase hydrolyzes the β-1,4-glycosidic bond in chitin. In higher plants, this enzyme has been regarded as a pathogenesis-related protein. Recently, we identified a class III chitinase, which functions as a calcium storage protein in pomegranate (Punica granatum) seed (PSC, pomegranate seed chitinase). Here, we solved a crystal structure of PSC at 1.6 Å resolution. Although its overall structure, including the structure of catalytic site and non-proline cis-peptides, was closely similar to those of other class III chitinases, PSC had some unique structural characteristics. First, there were some metal-binding sites with coordinated water molecules on the surface of PSC. Second, many unconserved aspartate residues were present in the PSC sequence which rendered the surface of PSC negatively charged. This acidic electrostatic property is in contrast to that of hevamine, well-characterized plant class III chitinase, which has rather a positively charged surface. Thus, the crystal structure provides a clue for metal association property of PSC.

Method and system for treating an interior surface of a workpiece using a charged particle beam

DOEpatents

Swenson, David Richard

2007-05-23

A method and system of treating an interior surface on an internal cavity of a workpiece using a charged particle beam. A beam deflector surface of a beam deflector is placed within the internal cavity of the workpiece and is used to redirect the charged particle beam toward the interior surface to treat the interior surface.

Determination of molecular configuration by debye length modulation.

PubMed

Vacic, Aleksandar; Criscione, Jason M; Rajan, Nitin K; Stern, Eric; Fahmy, Tarek M; Reed, Mark A

2011-09-07

Silicon nanowire field effect transistors (FETs) have emerged as ultrasensitive, label-free biodetectors that operate by sensing bound surface charge. However, the ionic strength of the environment (i.e., the Debye length of the solution) dictates the effective magnitude of the surface charge. Here, we show that control of the Debye length determines the spatial extent of sensed bound surface charge on the sensor. We apply this technique to different methods of antibody immobilization, demonstrating different effective distances of induced charge from the sensor surface.

Mapping the surface charge distribution of amyloid fibril

NASA Astrophysics Data System (ADS)

Lee, Gyudo; Lee, Wonseok; Lee, Hyungbeen; Woo Lee, Sang; Sung Yoon, Dae; Eom, Kilho; Kwon, Taeyun

2012-07-01

It is of high importance to measure and map the surface charge distribution of amyloids, since electrostatic interaction between amyloidogenic proteins and biomolecules plays a vital role in amyloidogenesis. In this work, we have measured and mapped the surface charge distributions of amyloids (i.e., β-lactoglobulin fibril) using Kelvin probe force microscopy. It is shown that the surface charge distribution is highly dependent on the conformation of amyloids (e.g., the helical pitch of amyloid fibrils) as well as the pH of a solvent.

Charging Characteristics of an Insulating Hollow Cylinder in Vacuum

NASA Astrophysics Data System (ADS)

Yamamoto, Osamu; Hayashi, Hirotaka; Wadahama, Toshihiko; Takeda, Daisuke; Hamada, Shoji; Ohsawa, Yasuharu

This paper deals with charging characteristics of the inner surface of an insulating hollow cylinder in vacuum. We conducted measurements of electric field strength near the triple points on cathode by using an electrostatic probe. Also we conducted a computer simulation of charging based on the Secondary Electron Emission Avalanche (SEEA) mechanism. These results are compared with those obtained previously for solid cylinders. As a result, we have clarified that hollow cylinders acquire surface charge which is larger than that of solid cylinders. We have also found that charge controlling effect by roughening the inner surface, which have been proved effective to depress charging on the surface of solid cylinders in our previous studies, is limited for hollow cylinders.

Relating Silica Scaling in Reverse Osmosis to Membrane Surface Properties.

PubMed

Tong, Tiezheng; Zhao, Song; Boo, Chanhee; Hashmi, Sara M; Elimelech, Menachem

2017-04-18

We investigated the relationship between membrane surface properties and silica scaling in reverse osmosis (RO). The effects of membrane hydrophilicity, free energy for heterogeneous nucleation, and surface charge on silica scaling were examined by comparing thin-film composite polyamide membranes grafted with a variety of polymers. Results show that the rate of silica scaling was independent of both membrane hydrophilicity and free energy for heterogeneous nucleation. In contrast, membrane surface charge demonstrated a strong correlation with the extent of silica scaling (R 2 > 0.95, p < 0.001). Positively charged membranes significantly facilitated silica scaling, whereas a more negative membrane surface charge led to reduced scaling. This observation suggests that deposition of negatively charged silica species on the membrane surface plays a critical role in silica scale formation. Our findings provide fundamental insights into the mechanisms governing silica scaling in reverse osmosis and highlight the potential of membrane surface modification as a strategy to reduce silica scaling.

Design and intestinal mucus penetration mechanism of core-shell nanocomplex.

PubMed

Zhang, Xin; Cheng, Hongbo; Dong, Wei; Zhang, Meixia; Liu, Qiaoyu; Wang, Xiuhua; Guan, Jian; Wu, Haiyang; Mao, Shirui

2018-02-28

The objective of this study was to design intestinal mucus-penetrating core-shell nanocomplex by functionally mimicking the surface of virus, which can be used as the carrier for peroral delivery of macromolecules, and further understand the influence of nanocomplex surface properties on the mucosal permeation capacity. Taking insulin as a model drug, the core was formed by the self-assembly among positively charged chitosan, insulin and negatively charged sodium tripolyphosphate, different types of alginates were used as the shell forming material. The nanocomplex was characterized by dynamic light scattering (DLS), atomic force microscopy (AFM) and FTIR. Nanocomplex movement in mucus was recorded using multiple particle tracking (MPT) method. Permeation and uptake of different nanocomplex were studied in rat intestine. It was demonstrated that alginate coating layer was successfully formed on the core and the core-shell nanocomplex showed a good physical stability and improved enzymatic degradation protection. The mucus penetration and MPT study showed that the mucus penetration capacity of the nanocomplex was surface charge and coating polymer structure dependent, nanocomplex with negative alginate coating had 1.6-2.5 times higher mucus penetration ability than that of positively charged chitosan-insulin nanocomplex. Moreover, the mucus penetration ability of the core-shell nanocomplex was alginate structure dependent, whereas alginate with lower G content and lower molecular weight showed the best permeation enhancing ability. The improvement of intestine permeation and intestinal villi uptake of the core-shell nanocomplex were further confirmed in rat intestine and multiple uptake mechanisms were involved in the transport process. In conclusion, core-shell nanocomplex composed of oppositely charged materials could provide a strategy to overcome the mucus barrier and enhance the mucosal permeability. Copyright © 2018 Elsevier B.V. All rights reserved.

Camel and bovine chymosin: the relationship between their structures and cheese-making properties

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

Langholm Jensen, Jesper; Chr. Hansen A/S, Bøge Allé 10-12, DK-2970 Hørsholm; Mølgaard, Anne

Analysis of the crystal structures of the two milk-clotting enzymes bovine and camel chymosin has revealed that the better milk-clotting activity towards bovine milk of camel chymosin compared with bovine chymosin is related to variations in their surface charges and their substrate-binding clefts. Bovine and camel chymosin are aspartic peptidases that are used industrially in cheese production. They cleave the Phe105-Met106 bond of the milk protein κ-casein, releasing its predominantly negatively charged C-terminus, which leads to the separation of the milk into curds and whey. Despite having 85% sequence identity, camel chymosin shows a 70% higher milk-clotting activity than bovinemore » chymosin towards bovine milk. The activities, structures, thermal stabilities and glycosylation patterns of bovine and camel chymosin obtained by fermentation in Aspergillus niger have been examined. Different variants of the enzymes were isolated by hydrophobic interaction chromatography and showed variations in their glycosylation, N-terminal sequences and activities. Glycosylation at Asn291 and the loss of the first three residues of camel chymosin significantly decreased its activity. Thermal differential scanning calorimetry revealed a slightly higher thermal stability of camel chymosin compared with bovine chymosin. The crystal structure of a doubly glycosylated variant of camel chymosin was determined at a resolution of 1.6 Å and the crystal structure of unglycosylated bovine chymosin was redetermined at a slightly higher resolution (1.8 Å) than previously determined structures. Camel and bovine chymosin share the same overall fold, except for the antiparallel central β-sheet that connects the N-terminal and C-terminal domains. In bovine chymosin the N-terminus forms one of the strands which is lacking in camel chymosin. This difference leads to an increase in the flexibility of the relative orientation of the two domains in the camel enzyme. Variations in the amino acids delineating the substrate-binding cleft suggest a greater flexibility in the ability to accommodate the substrate in camel chymosin. Both enzymes possess local positively charged patches on their surface that can play a role in interactions with the overall negatively charged C-terminus of κ-casein. Camel chymosin contains two additional positive patches that favour interaction with the substrate. The improved electrostatic interactions arising from variation in the surface charges and the greater malleability both in domain movements and substrate binding contribute to the better milk-clotting activity of camel chymosin towards bovine milk.« less

Soft Landing of Mass-Selected Gold Clusters: Influence of Ion and Ligand on Charge Retention and Reactivity

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

Johnson, Grant E.; Laskin, Julia

Herein, we employ a combination of reduction synthesis in solution, soft landing of mass-selected precursor and product ions, and in situ time-of-flight secondary ion mass spectrometry (TOF-SIMS) to examine the influence of ion and the length of diphosphine ligands on the charge retention and reactivity of ligated gold clusters deposited onto self-assembled monolayer surfaces (SAMs). Product ions (Au10L42+, (10,4)2+, L = 1,3-bis(diphenyl-phosphino)propane, DPPP) were prepared through in-source collision induced dissociation (CID) and precursor ions [(8,4)2+, L = 1,6-bis(diphenylphosphino)hexane, DPPH] were synthesized in solution for comparison to (11,5)3+ precursor ions ligated with DPPP investigated previously (ACS Nano 2012, 6, 573 andmore » J. Phys. Chem. C. 2012, 116, 24977). Similar to (11,5)3+ precursor ions, the (10,4)2+ product ions are shown to retain charge on 1H,1H,2H,2H-perfluorodecanethiol monolayers (FSAMs). Additional abundant peaks at higher m/z indicative of reactivity are observed in the TOF-SIMS spectrum of (10,4)2+ product ions that are not seen for (11,5)3+ precursor ions. The abundance of (10,4)2+ on 16-mercaptohexadecanoic acid (COOH-SAMs) is demonstrated to be lower than on FSAMs, consistent with partial reduction of charge. The (10,4)2+ product ion on 1-dodecanethiol (HSAMs) exhibits peaks similar to those seen on the COOH-SAM. On the HSAM, higher m/z peaks indicative of reactivity are observed similar to those on the FSAM. The (8,4)2+ DPPH precursor ions are shown to retain charge on FSAMs similar to (11,5)3+ precursor ions prepared with DPPP. An additional peak corresponding to attachment of one gold atom to (8,4)2+ is observed at higher m/z for DPPH-ligated clusters. On the COOH-SAM, (8,4)2+ is less abundant than on the FSAM consistent with partial neutralization. The results indicate that although retention of charge by product ions generated by CID is similar to precursor ions their reactivity during analysis with SIMS is different resulting in the formation of peaks corresponding to reaction products. The length of the ligand exerts only a minor influence on the charge retention and reactivity of gold clusters. Based on the observed reactivity of (10,4)2+ it is anticipated that in-source CID will be increasingly applied for the preparation of a distribution of product ions, including undercoordinated and reactive species, for soft landing onto surfaces.« less

Molecular dynamics investigation of the ionic liquid/enzyme interface: application to engineering enzyme surface charge.

PubMed

Burney, Patrick R; Nordwald, Erik M; Hickman, Katie; Kaar, Joel L; Pfaendtner, Jim

2015-04-01

Molecular simulations of the enzymes Candida rugosa lipase and Bos taurus α-chymotrypsin in aqueous ionic liquids 1-butyl-3-methylimidazolium chloride and 1-ethyl-3-methylimidazolium ethyl sulfate were used to study the change in enzyme-solvent interactions induced by modification of the enzyme surface charge. The enzymes were altered by randomly mutating lysine surface residues to glutamate, effectively decreasing the net surface charge by two for each mutation. These mutations resemble succinylation of the enzyme by chemical modification, which has been shown to enhance the stability of both enzymes in ILs. After establishing that the enzymes were stable on the simulated time scales, we focused the analysis on the organization of the ionic liquid substituents about the enzyme surface. Calculated solvent charge densities show that for both enzymes and in both solvents that changing positively charged residues to negative charge does indeed increase the charge density of the solvent near the enzyme surface. The radial distribution of IL constituents with respect to the enzyme reveals decreased interactions with the anion are prevalent in the modified systems when compared to the wild type, which is largely accompanied by an increase in cation contact. Additionally, the radial dependence of the charge density and ion distribution indicates that the effect of altering enzyme charge is confined to short range (≤1 nm) ordering of the IL. Ultimately, these results, which are consistent with that from prior experiments, provide molecular insight into the effect of enzyme surface charge on enzyme stability in ILs. © 2015 Wiley Periodicals, Inc.

Spatial Charge Inhomogeneity and Defect States in Topological Dirac Semimetal Thin Films

NASA Astrophysics Data System (ADS)

Edmonds, Mark; Collins, James; Hellerstedt, Jack; Yudhistira, Indra; Rodrigues, Joao Nuno Barbosa; Gomes, Lidia Carvalho; Adam, Shaffique; Fuhrer, Michael

Dirac materials are characterized by a charge neutrality point, where the system breaks into electron/hole puddles. In graphene, substrate disorder drives fluctuations in EF, necessitating ultra-clean substrates to observe Dirac point physics. Three-dimensional topological Dirac semimetals (TDS) obviate the substrate, and should show reduced EF fluctuations due to better metallic screening and higher dielectric constants. Yet, the local response of the charge carriers in a TDS to various perturbations has yet to be explored. Here we map the potential fluctuations in TDS 20nm Na3Bi films grown via MBE using scanning tunneling microscopy/spectroscopy. The potential fluctuations are significantly smaller than room temperature (ΔEF 5 meV = 60 K) and comparable to the highest quality graphene on h-BN; far smaller than graphene on SiO2,or the Dirac surface state of a topological insulator. This observation bodes well for exploration of Dirac point physics in TDS materials. Furthermore, surface Na vacancies show a bound resonance state close to the Dirac point with large spatial extent, a possible analogue to resonant impurities in graphene.

Self-assembled micellar aggregates based monomethoxyl poly(ethylene glycol)-b-poly(ε-caprolactone)-b-poly(aminoethyl methacrylate) triblock copolymers as efficient gene delivery vectors.

PubMed

Ma, Ming; Li, Feng; Liu, Xiu-hong; Yuan, Zhe-fan; Chen, Fu-jie; Zhuo, Ren-xi

2010-10-01

Amphiphilic triblock copolymers monomethoxyl poly(ethylene glycol) (mPEG)-b-poly(ε-caprolactone) (PCL)-b-poly(aminoethyl methacrylate)s (PAMAs) (mPECAs) were synthesized as gene delivery vectors. They exhibited lower cytotoxicity and higher transfection efficiency in COS-7 cells in presence of serum compared to 25 kDa bPEI. The influence of mPEG and PCL segments in mPECAs was evaluated by comparing with corresponding diblock copolymers. The studies showed the incorporation of the hydrophobic PCL segment in triblock copolymers affected the binding capability to pDNA and surface charges of complexes due to the formation of micelles increasing the local charges. The presence of mPEG segment in gene vector decreased the surface charges of the complexes and increased the stability of the complexes in serum because of the steric hindrance effect. It was also found that the combination of PEG and PCL segments into one macromolecule might lead to synergistic effect for better transfection efficiency in serum.

The electronic and optical properties of Cs adsorbed GaAs nanowires via first-principles study

NASA Astrophysics Data System (ADS)

Diao, Yu; Liu, Lei; Xia, Sihao; Feng, Shu; Lu, Feifei

2018-07-01

In this study, we investigate the Cs adsorption mechanism on (110) surface of zinc-blende GaAs nanowire. The adsorption energy, work function, dipole moment, geometric structure, Mulliken charge distribution, charge transfer index, band structures, density of state and optical properties of Cs adsorption structures are calculated utilizing first-principles method based on density function theory. Total-energy calculations show that all the adsorption energies are negative, indicating that Cs adsorption process is exothermic and Cs covered GaAs nanowires are stable. The work function of nanowire surface has an obvious decrease after Cs adsorption. Besides, the ionization of nanowire surface is enhanced as well. More importantly, Cs adsorption contributes to a lower side shift of bands near Fermi level, and the corresponding band gap disappears. Additionally, the absorption peak and energy loss function after Cs adsorption are far higher than those before adsorption, implying better light absorption characteristic of nanowire surface after Cs adsorption. These theoretical calculations can directly guide the Cs activation experiment for negative electron affinity GaAs nanowire, and also lay a foundation for the further study of Cs/O co-adsorption on the nanowire surface.

The titration of carboxyl-terminated monolayers revisited: in situ calibrated fourier transform infrared study of well-defined monolayers on silicon.

PubMed

Aureau, D; Ozanam, F; Allongue, P; Chazalviel, J-N

2008-09-02

The acid-base equilibrium at the surface of well-defined mixed carboxyl-terminated/methyl-terminated monolayers grafted on silicon (111) has been investigated using in situ calibrated infrared spectroscopy (attenuated total reflectance (ATR)) in the range of 900-4000 cm (-1). Spectra of surfaces in contact with electrolytes of various pH provide a direct observation of the COOH <--> COO (-) conversion process. Quantitative analysis of the spectra shows that ionization of the carboxyl groups starts around pH 6 and extends over more than 6 pH units: approximately 85% ionization is measured at pH 11 (at higher pH, the layers become damaged). Observations are consistently accounted for by a single acid-base equilibrium and discussed in terms of change in ion solvation at the surface and electrostatic interactions between surface charges. The latter effect, which appears to be the main limitation, is qualitatively accounted for by a simple model taking into account the change in the Helmholtz potential associated with the surface charge. Furthermore, comparison of calculated curves with experimental titration curves of mixed monolayers suggests that acid and alkyl chains are segregated in the monolayer.

Battery Power Management in Heavy-duty HEVs based on the Estimated Critical Surface Charge

DTIC Science & Technology

2011-03-01

health prospects without any penalty on fuel efficiency. Keywords: Lithium - ion battery ; power management; critical surface charge; Lithium-ion...fuel efficiency. 15. SUBJECT TERMS Lithium - ion battery ; power management; critical surface charge; Lithium-ion concentration; estimation; extended...Di Domenico, D., Fiengo, G., and Stefanopoulou, A. (2008) ’ Lithium - ion battery state of charge estimation with a kalman filter based on a

Aggregation and charging of sulfate and amidine latex particles in the presence of oxyanions.

PubMed

Sugimoto, Takuya; Cao, Tianchi; Szilagyi, Istvan; Borkovec, Michal; Trefalt, Gregor

2018-08-15

Electrophoretic mobility and time resolved light scattering are used to measure the effect on charging and aggregation of amidine and sulfate latex particles of different oxyanions namely, phosphate, arsenate, sulfate, and selenate. In the case of negatively charged sulfate latex particles oxyanions represent the coions, while they represent counterions in the case of the positively charged amidine latex. Repulsive interaction between the sulfate latex surface and the coions results in weak ion specific effects on the charging and aggregation. On the other hand the interaction of oxyanions with the amidine latex surface is highly specific. The monovalent dihydrogen phosphate ion strongly adsorbs to the positively charged surface and reverses the charge of the particle. This charge reversal leads also to the restabilization of the amidine latex suspension at the intermediate phosphate concentrations. In the case of dihydrogen arsenate the adsorption to amidine latex surface is weaker and no charge reversal and restabilization occurs. Similar differences are seen between the sulfate and selenate analogues, where selenate adsorbs more strongly to the surface as compared to the sulfate ion and invokes charge reversal. The present results indicate that ion specificity is much more pronounced in the case of counterions. Copyright © 2018 Elsevier Inc. All rights reserved.

Hierarchical FeTiO3-TiO2 hollow spheres for efficient simulated sunlight-driven water oxidation.

PubMed

Han, Taoran; Chen, Yajie; Tian, Guohui; Wang, Jian-Qiang; Ren, Zhiyu; Zhou, Wei; Fu, Honggang

2015-10-14

Oxygen generation is the key step for the photocatalytic overall water splitting and considered to be kinetically more challenging than hydrogen generation. Here, an effective water oxidation catalyst of hierarchical FeTiO3-TiO2 hollow spheres are prepared via a two-step sequential solvothermal processes and followed by thermal treatment. The existence of an effective heterointerface and built-in electric field in the surface space charge region in FeTiO3-TiO2 hollow spheres plays a positive role in promoting the separation of photoinduced electron-hole pairs. Surface photovoltage, transient-state photovoltage, fluorescence and electrochemical characterization are used to investigate the transfer process of photoinduced charge carriers. The photogenerated charge carriers in the hierarchical FeTiO3-TiO2 hollow spheres with a proper molar ratio display much higher separation efficiency and longer lifetime than those in the FeTiO3 alone. Moreover, it is suggested that the hierarchical porous hollow structure can contribute to the enhancement of light utilization, surface active sites and material transportation through the framework walls. This specific synergy significantly contributes to the remarkable improvement of the photocatalytic water oxidation activity of the hierarchical FeTiO3-TiO2 hollow spheres under simulated sunlight (AM1.5).

Conversion of spin current into charge current in a topological insulator: Role of the interface

NASA Astrophysics Data System (ADS)

Dey, Rik; Prasad, Nitin; Register, Leonard F.; Banerjee, Sanjay K.

2018-05-01

Three-dimensional spin current density injected onto the surface of a topological insulator (TI) produces a two-dimensional charge current density on the surface of the TI, which is the so-called inverse Edelstein effect (IEE). The ratio of the surface charge current density on the TI to the spin current density injected across the interface defined as the IEE length was shown to be exactly equal to the mean free path in the TI determined to be independent of the electron transmission rate across the interface [Phys. Rev. B 94, 184423 (2016), 10.1103/PhysRevB.94.184423]. However, we find that the transmission rate across the interface gives a nonzero contribution to the transport relaxation rate in the TI as well as to the effective IEE relaxation rate (over and above any surface hybridization effects), and the IEE length is always less than the original mean free path in the TI without the interface. We show that both the IEE relaxation time and the transport relaxation time in the TI are modified by the interface transmission time. The correction becomes significant when the transmission time across the interface becomes comparable to or less than the original momentum scattering time in the TI. This correction is similar to experimental results in Rashba electron systems in which the IEE relaxation time was found shorter in the case of direct interface with metal in which the interface transmission rate will be much higher, compared to interfaces incorporating insulating oxides. Our results indicate the continued importance of the interface to obtain a better spin-to-charge current conversion and a limitation to the conversion efficiency due to the quality of the interface.

Mapping disease-related missense mutations in the immunoglobulin-like fold domain of lamin A/C reveals novel genotype-phenotype associations for laminopathies.

PubMed

Scharner, Juergen; Lu, Hui-Chun; Fraternali, Franca; Ellis, Juliet A; Zammit, Peter S

2014-06-01

Mutations in A-type nuclear lamins cause laminopathies. However, genotype-phenotype correlations using the 340 missense mutations within the LMNA gene are unclear: partially due to the limited availability of three-dimensional structure. The immunoglobulin (Ig)-like fold domain has been solved, and using bioinformatics tools (including Polyphen-2, Fold X, Parameter OPtimized Surfaces, and PocketPicker) we characterized 56 missense mutations for position, surface exposure, change in charge and effect on Ig-like fold stability. We find that 21 of the 27 mutations associated with a skeletal muscle phenotype are distributed throughout the Ig-like fold, are nonsurface exposed and predicted to disrupt overall stability of the Ig-like fold domain. Intriguingly, the remaining 6 mutations clustered, had higher surface exposure, and did not affect stability. The majority of 9 lipodystrophy or 10 premature aging syndrome mutations also did not disrupt Ig-like fold domain stability and were surface exposed and clustered in distinct regions that overlap predicted binding pockets. Although buried, the 10 cardiac mutations had no other consistent properties. Finally, most lipodystrophy and premature aging mutations resulted in a -1 net charge change, whereas skeletal muscle mutations caused no consistent net charge changes. Since premature aging, lipodystrophy and the subset of 6 skeletal muscle mutations cluster tightly in distinct, charged regions, they likely affect lamin A/C -protein/DNA/RNA interactions: providing a consistent genotype-phenotype relationship for mutations in this domain. Thus, this subgroup of skeletal muscle laminopathies that we term the 'Skeletal muscle cluster', may have a distinct pathological mechanism. These novel associations refine the ability to predict clinical features caused by certain LMNA missense mutations. © 2013 Wiley Periodicals, Inc.

Role of protein surface charge in monellin sweetness.

PubMed

Xue, Wei-Feng; Szczepankiewicz, Olga; Thulin, Eva; Linse, Sara; Carey, Jannette

2009-03-01

A small number of proteins have the unusual property of tasting intensely sweet. Despite many studies aimed at identifying their sweet taste determinants, the molecular basis of protein sweetness is not fully understood. Recent mutational studies of monellin have implicated positively charged residues in sweetness. In the present work, the effect of overall net charge was investigated using the complementary approach of negative charge alterations. Multiple substitutions of Asp/Asn and Glu/Gln residues radically altered the surface charge of single-chain monellin by removing six negative charges or adding four negative charges. Biophysical characterization using circular dichroism, fluorescence, and two-dimensional NMR demonstrates that the native fold of monellin is preserved in the variant proteins under physiological solution conditions although their stability toward chemical denaturation is altered. A human taste test was employed to determine the sweetness detection threshold of the variants. Removal of negative charges preserves monellin sweetness, whereas added negative charge has a large negative impact on sweetness. Meta-analysis of published charge variants of monellin and other sweet proteins reveals a general trend toward increasing sweetness with increasing positive net charge. Structural mapping of monellin variants identifies a hydrophobic surface predicted to face the receptor where introduced positive or negative charge reduces sweetness, and a polar surface where charges modulate long-range electrostatic complementarity.

Fibronectin module FN(III)9 adsorption at contrasting solid model surfaces studied by atomistic molecular dynamics.

PubMed

Kubiak-Ossowska, Karina; Mulheran, Paul A; Nowak, Wieslaw

2014-08-21

The mechanism of human fibronectin adhesion synergy region (known as integrin binding region) in repeat 9 (FN(III)9) domain adsorption at pH 7 onto various and contrasting model surfaces has been studied using atomistic molecular dynamics simulations. We use an ionic model to mimic mica surface charge density but without a long-range electric field above the surface, a silica model with a long-range electric field similar to that found experimentally, and an Au {111} model with no partial charges or electric field. A detailed description of the adsorption processes and the contrasts between the various model surfaces is provided. In the case of our model silica surface with a long-range electrostatic field, the adsorption is rapid and primarily driven by electrostatics. Because it is negatively charged (-1e), FN(III)9 readily adsorbs to a positively charged surface. However, due to its partial charge distribution, FN(III)9 can also adsorb to the negatively charged mica model because of the absence of a long-range repulsive electric field. The protein dipole moment dictates its contrasting orientation at these surfaces, and the anchoring residues have opposite charges to the surface. Adsorption on the model Au {111} surface is possible, but less specific, and various protein regions might be involved in the interactions with the surface. Despite strongly influencing the protein mobility, adsorption at these model surfaces does not require wholesale FN(III)9 conformational changes, which suggests that the biological activity of the adsorbed protein might be preserved.

Charge heterogeneity of surfaces: mapping and effects on surface forces.

PubMed

Drelich, Jaroslaw; Wang, Yu U

2011-07-11

The DLVO theory treats the total interaction force between two surfaces in a liquid medium as an arithmetic sum of two components: Lifshitz-van der Waals and electric double layer forces. Despite the success of the DLVO model developed for homogeneous surfaces, a vast majority of surfaces of particles and materials in technological systems are of a heterogeneous nature with a mosaic structure composed of microscopic and sub-microscopic domains of different surface characteristics. In such systems, the heterogeneity of the surface can be more important than the average surface character. Attractions can be stronger, by orders of magnitude, than would be expected from the classical mean-field DLVO model when area-averaged surface charge or potential is employed. Heterogeneity also introduces anisotropy of interactions into colloidal systems, vastly ignored in the past. To detect surface heterogeneities, analytical tools which provide accurate and spatially resolved information about material surface chemistry and potential - particularly at microscopic and sub-microscopic resolutions - are needed. Atomic force microscopy (AFM) offers the opportunity to locally probe not only changes in material surface characteristic but also charges of heterogeneous surfaces through measurements of force-distance curves in electrolyte solutions. Both diffuse-layer charge densities and potentials can be calculated by fitting the experimental data with a DLVO theoretical model. The surface charge characteristics of the heterogeneous substrate as recorded by AFM allow the charge variation to be mapped. Based on the obtained information, computer modeling and simulation can be performed to study the interactions among an ensemble of heterogeneous particles and their collective motions. In this paper, the diffuse-layer charge mapping by the AFM technique is briefly reviewed, and a new Diffuse Interface Field Approach to colloid modeling and simulation is briefly discussed. Copyright © 2011 Elsevier B.V. All rights reserved.

The impact of nano-coating on surface charge accumulation of epoxy resin insulator: characteristic and mechanism

NASA Astrophysics Data System (ADS)

Qi, Bo; Gao, Chunjia; Lv, Yuzhen; Li, Chengrong; Tu, Youping; Xiong, Jun

2018-06-01

The flashover phenomenon of the insulator is the main cause for insulating failure of GIS/GIL, and one of the most critical impacting factors is the accumulation of surface charge. The common methods to restrain the surface charge accumulation are reviewed in this paper. Through the reasonable comparison and analysis of these methods, nano-coatings for the insulator were selected as a way to restrain the surface charge accumulation. Based on this, six nano-coated epoxy resin samples with different concentrations of P25-TiO2 nanoparticles were produced. A high precision 3D surface charge measurement system was developed in this paper with a spatial resolution of 4.0 mm2 and a charge resolution of 0.01 µC (m2 · mV)‑1. The experimental results for the epoxy resin sample showed that with the concentration of nanoparticles of the coating material increasing, the surface charge density tended to first decrease and then increase. In the sample coated with 0.5% concentration of nanoparticles, the suppression effect is the optimum, leading to a 63.8% reduction of charge density under DC voltage. The application test for actual nano-coated GIS/GIL basin insulator indicated that the maximum suppression degree for the charge density under DC voltage could reach 48.3%, while it could reach 22.2% for switching impulse voltage and 12.5% for AC context. The control mechanism of nano-coatings on charge accumulation was proposed based on the analysis for surface morphology features and traps characteristics; the shallow traps dominate in the migration of charges while the deep traps operate on the charge accumulation. With the concentration of nanoparticles in nano-coating material mounting up, the density of shallow traps continuously increases, while for deep traps, it first decreases and then increases. For the sample with 0.5% concentration of nanoparticles coated, the competition between shallow traps and deep traps comes to the most balanced state, producing the most significant suppression impact on surface charge accumulation.

Role of Adsorbed Water on Charge Carrier Dynamics in Photoexcited TiO2

PubMed Central

2017-01-01

Overall photocatalytic water splitting is one of the most sought after processes for sustainable solar-to-chemical energy conversion. The efficiency of this process strongly depends on charge carrier recombination and interaction with surface adsorbates at different time scales. Here, we investigated how hydration of TiO2 P25 affects dynamics of photogenerated electrons at the millisecond to minute time scale characteristic for chemical reactions. We used rapid scan diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS). The decay of photogenerated electron absorption was substantially slower in the presence of associated water. For hydrated samples, the charge carrier recombination rates followed an Arrhenius-type behavior in the temperature range of 273–423 K; these became temperature-independent when the material was dehydrated at temperatures above 423 K or cooled below 273 K. A DFT+U analysis revealed that hydrogen bonding with adsorbed water stabilizes surface-trapped holes at anatase TiO2(101) facet and lowers the barriers for hole migration. Hence, hole mobility should be higher in the hydrated material than in the dehydrated system. This demonstrates that adsorbed associated water can efficiently stabilize photogenerated charge carriers in nanocrystalline TiO2 and suppress their recombination at the time scale up to minutes. PMID:28413570

Isolated Bacterial Spores at High-velocity Survive Surface Impacts in Vacuum

NASA Astrophysics Data System (ADS)

Austin, Daniel; Barney, Brandon

We present experiments in which bacterial spores were found to survive being accelerated in vacuum to velocities in the range 30-120 m/s and impacted on a dense target. In these experiments, spores of Bacillus subtilis spores were charged using electrospray at atmospheric pressure, dried, and then introduced into high vacuum. Through choice of skimmers and beam tubes, different velocity ranges were achieved. An image-charge detector observed the charged spores, providing total charge and velocity. The spores then impacted a glass target within a collection vessel. After the experiment, the collection vessel contents were extracted and cultured. Several positive and negative controls were used, including the use of antibiotic-resistant spores and antibiotic-containing (rifampicin) agar for culturing. These impact velocities are of particular interest for possible transport of bacterial spores from Mars to Phobos, and may have implications for planetary protection in a Phobos sample return mission. In addition, bacteria may reach similar velocities during a spacecraft crash (e.g., within components, or from spacecraft to surface materials during impact, etc.), raising concerns about forward contamination. The velocities of interest to transport of life between planets (panspermia) are somewhat higher, but these results complement shock-based experiments and contribute to the general discussion of impact survivability of organisms.

The study of surface wetting, nanobubbles and boundary slip with an applied voltage: A review

PubMed Central

Pan, Yunlu; Zhao, Xuezeng

2014-01-01

Summary The drag of fluid flow at the solid–liquid interface in the micro/nanoscale is an important issue in micro/nanofluidic systems. Drag depends on the surface wetting, nanobubbles, surface charge and boundary slip. Some researchers have focused on the relationship between these interface properties. In this review, the influence of an applied voltage on the surface wettability, nanobubbles, surface charge density and slip length are discussed. The contact angle (CA) and contact angle hysteresis (CAH) of a droplet of deionized (DI) water on a hydrophobic polystyrene (PS) surface were measured with applied direct current (DC) and alternating current (AC) voltages. The nanobubbles in DI water and three kinds of saline solution on a PS surface were imaged when a voltage was applied. The influence of the surface charge density on the nanobubbles was analyzed. Then the slip length and the electrostatic force on the probe were measured on an octadecyltrichlorosilane (OTS) surface with applied voltage. The influence of the surface charge on the boundary slip and drag of fluid flow has been discussed. Finally, the influence of the applied voltage on the surface wetting, nanobubbles, surface charge, boundary slip and the drag of liquid flow are summarized. With a smaller surface charge density which could be achieved by applying a voltage on the surface, larger and fewer nanobubbles, a larger slip length and a smaller drag of liquid flow could be found. PMID:25161839

The study of surface wetting, nanobubbles and boundary slip with an applied voltage: A review.

PubMed

Pan, Yunlu; Bhushan, Bharat; Zhao, Xuezeng

2014-01-01

The drag of fluid flow at the solid-liquid interface in the micro/nanoscale is an important issue in micro/nanofluidic systems. Drag depends on the surface wetting, nanobubbles, surface charge and boundary slip. Some researchers have focused on the relationship between these interface properties. In this review, the influence of an applied voltage on the surface wettability, nanobubbles, surface charge density and slip length are discussed. The contact angle (CA) and contact angle hysteresis (CAH) of a droplet of deionized (DI) water on a hydrophobic polystyrene (PS) surface were measured with applied direct current (DC) and alternating current (AC) voltages. The nanobubbles in DI water and three kinds of saline solution on a PS surface were imaged when a voltage was applied. The influence of the surface charge density on the nanobubbles was analyzed. Then the slip length and the electrostatic force on the probe were measured on an octadecyltrichlorosilane (OTS) surface with applied voltage. The influence of the surface charge on the boundary slip and drag of fluid flow has been discussed. Finally, the influence of the applied voltage on the surface wetting, nanobubbles, surface charge, boundary slip and the drag of liquid flow are summarized. With a smaller surface charge density which could be achieved by applying a voltage on the surface, larger and fewer nanobubbles, a larger slip length and a smaller drag of liquid flow could be found.

Profiling charge complementarity and selectivity for binding at the protein surface.

PubMed

Sulea, Traian; Purisima, Enrico O

2003-05-01

A novel analysis and representation of the protein surface in terms of electrostatic binding complementarity and selectivity is presented. The charge optimization methodology is applied in a probe-based approach that simulates the binding process to the target protein. The molecular surface is color coded according to calculated optimal charge or according to charge selectivity, i.e., the binding cost of deviating from the optimal charge. The optimal charge profile depends on both the protein shape and charge distribution whereas the charge selectivity profile depends only on protein shape. High selectivity is concentrated in well-shaped concave pockets, whereas solvent-exposed convex regions are not charge selective. This suggests the synergy of charge and shape selectivity hot spots toward molecular selection and recognition, as well as the asymmetry of charge selectivity at the binding interface of biomolecular systems. The charge complementarity and selectivity profiles map relevant electrostatic properties in a readily interpretable way and encode information that is quite different from that visualized in the standard electrostatic potential map of unbound proteins.

DNA Immobilization and Hybridization Detection by the Intrinsic Molecular Charge Using Capacitive Field-Effect Sensors Modified with a Charged Weak Polyelectrolyte Layer.

PubMed

Bronder, Thomas S; Poghossian, Arshak; Scheja, Sabrina; Wu, Chunsheng; Keusgen, Michael; Mewes, Dieter; Schöning, Michael J

2015-09-16

Miniaturized setup, compatibility with advanced micro- and nanotechnologies, and ability to detect biomolecules by their intrinsic molecular charge favor the semiconductor field-effect platform as one of the most attractive approaches for the development of label-free DNA chips. In this work, a capacitive field-effect EIS (electrolyte-insulator-semiconductor) sensor covered with a layer-by-layer prepared, positively charged weak polyelectrolyte layer of PAH (poly(allylamine hydrochloride)) was used for the label-free electrical detection of DNA (deoxyribonucleic acid) immobilization and hybridization. The negatively charged probe single-stranded DNA (ssDNA) molecules were electrostatically adsorbed onto the positively charged PAH layer, resulting in a preferentially flat orientation of the ssDNA molecules within the Debye length, thus yielding a reduced charge-screening effect and a higher sensor signal. Each sensor-surface modification step (PAH adsorption, probe ssDNA immobilization, hybridization with complementary target DNA (cDNA), reducing an unspecific adsorption by a blocking agent, incubation with noncomplementary DNA (ncDNA) solution) was monitored by means of capacitance-voltage and constant-capacitance measurements. In addition, the surface morphology of the PAH layer was studied by atomic force microscopy and contact-angle measurements. High hybridization signals of 34 and 43 mV were recorded in low-ionic strength solutions of 10 and 1 mM, respectively. In contrast, a small signal of 4 mV was recorded in the case of unspecific adsorption of fully mismatched ncDNA. The density of probe ssDNA and dsDNA molecules as well as the hybridization efficiency was estimated using the experimentally measured DNA immobilization and hybridization signals and a simplified double-layer capacitor model. The results of field-effect experiments were supported by fluorescence measurements, verifying the DNA-immobilization and hybridization event.

A New Kinetic Simulation Model with Self-Consistent Calculation of Regolith Layer Charging for Moon-Plasma Interactions

NASA Astrophysics Data System (ADS)

Han, D.; Wang, J.

2015-12-01

The moon-plasma interactions and the resulting surface charging have been subjects of extensive recent investigations. While many particle-in-cell (PIC) based simulation models have been developed, all existing PIC simulation models treat the surface of the Moon as a boundary condition to the plasma flow. In such models, the surface of the Moon is typically limited to simple geometry configurations, the surface floating potential is calculated from a simplified current balance condition, and the electric field inside the regolith layer cannot be resolved. This paper presents a new full particle PIC model to simulate local scale plasma flow and surface charging. A major feature of this new model is that the surface is treated as an "interface" between two mediums rather than a boundary, and the simulation domain includes not only the plasma but also the regolith layer and the bedrock underneath it. There are no limitations on the surface shape. An immersed-finite-element field solver is applied which calculates the regolith surface floating potential and the electric field inside the regolith layer directly from local charge deposition. The material property of the regolith layer is also explicitly included in simulation. This new model is capable of providing a self-consistent solution to the plasma flow field, lunar surface charging, the electric field inside the regolith layer and the bedrock for realistic surface terrain. This new model is applied to simulate lunar surface-plasma interactions and surface charging under various ambient plasma conditions. The focus is on the lunar terminator region, where the combined effects from the low sun elevation angle and the localized plasma wake generated by plasma flow over a rugged terrain can generate strongly differentially charged surfaces and complex dust dynamics. We discuss the effects of the regolith properties and regolith layer charging on the plasma flow field, dust levitation, and dust transport.

Adsorption of hydrophobin on different self-assembled monolayers: the role of the hydrophobic dipole and the electric dipole.

PubMed

Peng, Chunwang; Liu, Jie; Zhao, Daohui; Zhou, Jian

2014-09-30

In this work, the adsorptions of hydrophobin (HFBI) on four different self-assembled monolayers (SAMs) (i.e., CH3-SAM, OH-SAM, COOH-SAM, and NH2-SAM) were investigated by parallel tempering Monte Carlo and molecular dynamics simulations. Simulation results indicate that the orientation of HFBI adsorbed on neutral surfaces is dominated by a hydrophobic dipole. HFBI adsorbs on the hydrophobic CH3-SAM through its hydrophobic patch and adopts a nearly vertical hydrophobic dipole relative to the surface, while it is nearly horizontal when adsorbed on the hydrophilic OH-SAM. For charged SAM surfaces, HFBI adopts a nearly vertical electric dipole relative to the surface. HFBI has the narrowest orientation distribution on the CH3-SAM, and thus can form an ordered monolayer and reverse the wettability of the surface. For HFBI adsorption on charged SAMs, the adsorption strength weakens as the surface charge density increases. Compared with those on other SAMs, a larger area of the hydrophobic patch is exposed to the solution when HFBI adsorbs on the NH2-SAM. This leads to an increase of the hydrophobicity of the surface, which is consistent with the experimental results. The binding of HFBI to the CH3-SAM is mainly through hydrophobic interactions, while it is mediated through a hydration water layer near the surface for the OH-SAM. For the charged SAM surfaces, the adsorption is mainly induced by electrostatic interactions between the charged surfaces and the oppositely charged residues. The effect of a hydrophobic dipole on protein adsorption onto hydrophobic surfaces is similar to that of an electric dipole for charged surfaces. Therefore, the hydrophobic dipole may be applied to predict the probable orientations of protein adsorbed on hydrophobic surfaces.

Analysis of SiO2 nanoparticles binding proteins in rat blood and brain homogenate.

PubMed

Shim, Kyu Hwan; Hulme, John; Maeng, Eun Ho; Kim, Meyoung-Kon; An, Seong Soo A

2014-01-01

A multitude of nanoparticles, such as titanium oxide (TiO2), zinc oxide, aluminum oxide, gold oxide, silver oxide, iron oxide, and silica oxide, are found in many chemical, cosmetic, pharmaceutical, and electronic products. Recently, SiO2 nanoparticles were shown to have an inert toxicity profile and no association with an irreversible toxicological change in animal models. Hence, exposure to SiO2 nanoparticles is on the increase. SiO2 nanoparticles are routinely used in numerous materials, from strengthening filler for concrete and other construction composites, to nontoxic platforms for biomedical application, such as drug delivery and theragnostics. On the other hand, recent in vitro experiments indicated that SiO2 nanoparticles were cytotoxic. Therefore, we investigated these nanoparticles to identify potentially toxic pathways by analyzing the adsorbed protein corona on the surface of SiO2 nanoparticles in the blood and brain of the rat. Four types of SiO2 nanoparticles were chosen for investigation, and the protein corona of each type was analyzed using liquid chromatography-tandem mass spectrometry technology. In total, 115 and 48 plasma proteins from the rat were identified as being bound to negatively charged 20 nm and 100 nm SiO2 nanoparticles, respectively, and 50 and 36 proteins were found for 20 nm and 100 nm arginine-coated SiO2 nanoparticles, respectively. Higher numbers of proteins were adsorbed onto the 20 nm sized SiO2 nanoparticles than onto the 100 nm sized nanoparticles regardless of charge. When proteins were compared between the two charges, higher numbers of proteins were found for arginine-coated positively charged SiO2 nanoparticles than for the negatively charged nanoparticles. The proteins identified as bound in the corona from SiO2 nanoparticles were further analyzed with ClueGO, a Cytoscape plugin used in protein ontology and for identifying biological interaction pathways. Proteins bound on the surface of nanoparticles may affect functional and conformational properties and distributions in complicated biological processes.

Influence of polymer size, liposomal composition, surface charge, and temperature on the permeability of pH-sensitive liposomes containing lipid-anchored poly(2-ethylacrylic acid).

PubMed

Lu, Tingli; Wang, Zhao; Ma, Yufan; Zhang, Yang; Chen, Tao

2012-01-01

Liposomes containing pH-sensitive polymers are promising candidates for the treatment of tumors and localized infection. This study aimed to identify parameters influencing the extent of contents release from poly(ethylacrylic acid) (PEAA) vesicles, focusing on the effects of polymer size, lipid composition, vesicle surface charge, and temperature. Anchored lipid pH-sensitive PEAA was synthesized using PEAA with a molecular weight of 8.4 kDa. PEAA vesicles were prepared by insertion of the lipid-anchored PEAA into preformed large unilamellar vesicles. The preformed liposomes were manipulated by varying the phosphocholine and cholesterol content, and by adding negative or positive charges to the liposomes. A calcein release assay was used to evaluate the effects of polymer size, liposome composition, surface charge, and temperature on liposomal permeability. The release efficiency of the calcein-entrapped vesicles was found to be dependent on the PEAA polymer size. PEAA vesicles containing a phosphatidylcholine to cholesterol ratio of 60:40 (mol/mol) released more than 80% of their calcein content when the molecular weight of PEAA was larger than 8.4 kDa. Therefore, the same-sized polymer of 8.4 kDa was used for the rest of study. The calcein release potential was found to decrease as the percentage of cholesterol increased and with an increase in the phosphocholine acyl chain length (DMPC DPPC DSPC). Negatively charged and neutral vesicles released similar amounts of calcein, whereas positively charged liposomes released a significant amount of their contents. pH-sensitive release was dependent on temperature. Dramatic content release was observed at higher temperatures. The observed synergistic effect of pH and temperature on release of the contents of PEAA vesicles suggests that this pH-sensitive liposome might be a good candidate for intracellular drug delivery in the treatment of tumors or localized infection.

Influence of polymer size, liposomal composition, surface charge, and temperature on the permeability of pH-sensitive liposomes containing lipid-anchored poly(2-ethylacrylic acid)

PubMed Central

Lu, Tingli; Wang, Zhao; Ma, Yufan; Zhang, Yang; Chen, Tao

2012-01-01

Background Liposomes containing pH-sensitive polymers are promising candidates for the treatment of tumors and localized infection. This study aimed to identify parameters influencing the extent of contents release from poly(ethylacrylic acid) (PEAA) vesicles, focusing on the effects of polymer size, lipid composition, vesicle surface charge, and temperature. Methods Anchored lipid pH-sensitive PEAA was synthesized using PEAA with a molecular weight of 8.4 kDa. PEAA vesicles were prepared by insertion of the lipid-anchored PEAA into preformed large unilamellar vesicles. The preformed liposomes were manipulated by varying the phosphocholine and cholesterol content, and by adding negative or positive charges to the liposomes. A calcein release assay was used to evaluate the effects of polymer size, liposome composition, surface charge, and temperature on liposomal permeability. Results The release efficiency of the calcein-entrapped vesicles was found to be dependent on the PEAA polymer size. PEAA vesicles containing a phosphatidylcholine to cholesterol ratio of 60:40 (mol/mol) released more than 80% of their calcein content when the molecular weight of PEAA was larger than 8.4 kDa. Therefore, the same-sized polymer of 8.4 kDa was used for the rest of study. The calcein release potential was found to decrease as the percentage of cholesterol increased and with an increase in the phosphocholine acyl chain length (DMPC DPPC DSPC). Negatively charged and neutral vesicles released similar amounts of calcein, whereas positively charged liposomes released a significant amount of their contents. pH-sensitive release was dependent on temperature. Dramatic content release was observed at higher temperatures. Conclusion The observed synergistic effect of pH and temperature on release of the contents of PEAA vesicles suggests that this pH-sensitive liposome might be a good candidate for intracellular drug delivery in the treatment of tumors or localized infection. PMID:23028220

Determination of Protein Surface Hydration by Systematic Charge Mutations

NASA Astrophysics Data System (ADS)

Yang, Jin; Jia, Menghui; Qin, Yangzhong; Wang, Dihao; Pan, Haifeng; Wang, Lijuan; Xu, Jianhua; Zhong, Dongping; Dongping Zhong Collaboration; Jianhua Xu Collaboration

Protein surface hydration is critical to its structural stability, flexibility, dynamics and function. Recent observations of surface solvation on picosecond time scales have evoked debate on the origin of such relatively slow motions, from hydration water or protein charged sidechains, especially with molecular dynamics simulations. Here, we used a unique nuclease with a single tryptophan as a local probe and systematically mutated neighboring three charged residues to differentiate the contributions from hydration water and charged sidechains. By mutations of alternative one and two and all three charged residues, we observed slight increases in the total tryptophan Stokes shifts with less neighboring charged residue(s) and found insensitivity of charged sidechains to the relaxation patterns. The dynamics is correlated with hydration water relaxation with the slowest time in a dense charged environment and the fastest time at a hydrophobic site. On such picosecond time scales, the protein surface motion is restricted. The total Stokes shifts are dominantly from hydration water relaxation and the slow dynamics is from water-driven relaxation, coupled with local protein fluctuations.

Effect of hydrogen on cathodic corrosion of titanium aluminide

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

Gao, K.W.; Jin, J.W.; Qiao, L.J.

1996-01-01

Cathodic corrosion of titanium aluminide (TiAl) during hydrogen charging in various acidic aqueous solutions and in molten salt at 160 C was studied. At constant potential, the rate of cathodic corrosion (V) was much higher than during anodic dissolution, and V increased linearly with increasing current. V was 10 times higher in the acid solution than in the salt solution under the same current. Disruption of the surface film by local hydride formation during cathodic polarization was shown to be the key step.

Phosphorus solubility of agricultural soils: a surface charge and phosphorus-31 NMR speciation study

USDA-ARS?s Scientific Manuscript database

We investigated ten soils from six states in United States to determine the relationship between potentiometric titration derived soil surface charge and Phosphorus-31 (P) nuclear magnetic resonance (NMR) speciation with the concentration of water-extractable P (WEP). The surface charge value at the...

Positively Charged Nanostructured Lipid Carriers and Their Effect on the Dissolution of Poorly Soluble Drugs.

PubMed

Choi, Kyeong-Ok; Choe, Jaehyeog; Suh, Seokjin; Ko, Sanghoon

2016-05-20

The objective of this study is to develop suitable formulations to improve the dissolution rate of poorly water soluble drugs. We selected lipid-based formulation as a drug carrier and modified the surface using positively charged chitosan derivative (HTCC) to increase its water solubility and bioavailability. Chitosan and HTCC-coated lipid particles had higher zeta-potential values than uncoated one over the whole pH ranges and improved encapsulation efficiency. In vitro drug release showed that all NLC formulations showed higher in vitro release efficiency than drug particle at pH 7.4. Furthermore, NLC formulation prepared with chitosan or HTCC represented good sustained release property. The results indicate that chitosan and HTCC can be excellent formulating excipients of lipid-based delivery carrier for improving poorly water soluble drug delivery.

Charge gradient microscopy

DOEpatents

Roelofs, Andreas; Hong, Seungbum

2018-02-06

A method for rapid imaging of a material specimen includes positioning a tip to contact the material specimen, and applying a force to a surface of the material specimen via the tip. In addition, the method includes moving the tip across the surface of the material specimen while removing electrical charge therefrom, generating a signal produced by contact between the tip and the surface, and detecting, based on the data, the removed electrical charge induced through the tip during movement of the tip across the surface. The method further includes measuring the detected electrical charge.

Variable Charge Soils: Mineralogy and Chemistry

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

Qafoku, Nik; Van Ranst, Eric; Noble, Andrew

2003-11-01

Soils rich in particles with amphoteric surface properties in the Oxisols, Ultisols, Alfisols, Spodosols and Andisols orders (1) are considered variable charge soils (2). The term “variable charge” is used to describe organic and inorganic soil constituents with reactive surface groups whose charge varies with pH, ionic concentration and composition of the soil solution. Such groups are the surface carboxyl, phenolic and amino functional groups of organic materials in soils, and surface hydroxyl groups of Fe and Al oxides, allophane and imogolite. The hydroxyl surface groups are also present on edges of some phyllosilicate minerals such as kaolinite, mica, andmore » hydroxyl-interlayered vermiculite. The variable charge is developed on the surface groups as a result of adsorption or desorption of ions that are constituents of the solid phase, i.e., H+, and the adsorption or desorption of solid-unlike ions that are not constituents of the solid. Highly weathered soils usually undergo isoeletric weathering and reach a “zero net charge” stage during their development. They have a slightly acidic to acidic soil solution pH, which is close to either point of zero net charge (PZNC) (3) or point of zero salt effect (PZSE) (3). They are characterized by high abundances of minerals with a point of zero net proton charge (PZNPC) (3) at neutral and slightly basic pHs; the most important being Fe and Al oxides and allophane. Under acidic conditions, the surfaces of these minerals are net positively charged. In contrast, the surfaces of permanent charge phyllosilicates are negatively charged regardless of ambient conditions. Variable charge soils therefore, are heterogeneous charge systems. The coexistence and interactions of oppositely charged surfaces or particles confers a different pattern of physical and chemical behavior on the soil, relatively to a homogeneously charged system of temperate regions. In some variable charge soils (Oxisols and some Ultisols developed on ferromagnesian-rich parent materials) the surfaces of phyllosilicates are coated to a lesser or greater extent by amorphous or crystalline, oppositely charged nanoparticles of Fe and Al oxides. These coatings exhibit a high reactive surface area and help cementing larger particles with one another. As a result of these electrostatic interactions, stable microaggregates that are difficult to disperse are formed in variable charge soils. Most of highly weathered soils have reached the “advanced stage” of Jackson-Sherman weathering sequence that is characterized by the removal of Na, K, Ca, Mg, and Fe(II), the presence of Fe and Al polymers, and very dilute soil solutions with an ionic strength (IS) of less than 1 mmol L-1. The inter-penetration or overlapping of the diffuse double layers on oppositely charged surfaces may occur in these dilute systems. These diffuse layer interactions may affect the magnitude of the effective charge, i.e., the counter-ion charge (4). In addition, salt adsorption, which is defined as the simultaneous adsorption in equivalent amounts of the cation and anion of an electrolyte with no net release of other ions into the soil solution, appears to be a common phenomenon in these soils. They act as cation- and anion-exchangers and as salt-sorbers. The magnitude of salt adsorption depends strongly on initial IS in the soil solution and the presence in appreciable amounts of oppositely charged surfaces. Among the authors that have made illustrious contributions towards a better understanding of these fascinating soil systems are S. Matson, R.K. Schofield, van Olphen, M.E. Sumner, G.W. Thomas, G.P. Gillman, G. Uehara, B.K.G. Theng, K. Wada, N.J. Barrow, J.W. Bowden, R.J. Hunter and G. Sposito. This entry is mainly based on publications by these authors.« less

Effect of Surfaces on Amyloid Fibril Formation

PubMed Central

Moores, Bradley; Drolle, Elizabeth; Attwood, Simon J.; Simons, Janet; Leonenko, Zoya

2011-01-01

Using atomic force microscopy (AFM) we investigated the interaction of amyloid beta (Aβ) (1–42) peptide with chemically modified surfaces in order to better understand the mechanism of amyloid toxicity, which involves interaction of amyloid with cell membrane surfaces. We compared the structure and density of Aβ fibrils on positively and negatively charged as well as hydrophobic chemically-modified surfaces at physiologically relevant conditions. We report that due to the complex distribution of charge and hydrophobicity amyloid oligomers bind to all types of surfaces investigated (CH3, COOH, and NH2) although the charge and hydrophobicity of surfaces affected the structure and size of amyloid deposits as well as surface coverage. Hydrophobic surfaces promote formation of spherical amorphous clusters, while charged surfaces promote protofibril formation. We used the nonlinear Poisson-Boltzmann equation (PBE) approach to analyze the electrostatic interactions of amyloid monomers and oligomers with modified surfaces to complement our AFM data. PMID:22016789

Parallel tempering Monte Carlo simulations of lysozyme orientation on charged surfaces

NASA Astrophysics Data System (ADS)

Xie, Yun; Zhou, Jian; Jiang, Shaoyi

2010-02-01

In this work, the parallel tempering Monte Carlo (PTMC) algorithm is applied to accurately and efficiently identify the global-minimum-energy orientation of a protein adsorbed on a surface in a single simulation. When applying the PTMC method to simulate lysozyme orientation on charged surfaces, it is found that lysozyme could easily be adsorbed on negatively charged surfaces with "side-on" and "back-on" orientations. When driven by dominant electrostatic interactions, lysozyme tends to be adsorbed on negatively charged surfaces with the side-on orientation for which the active site of lysozyme faces sideways. The side-on orientation agrees well with the experimental results where the adsorbed orientation of lysozyme is determined by electrostatic interactions. As the contribution from van der Waals interactions gradually dominates, the back-on orientation becomes the preferred one. For this orientation, the active site of lysozyme faces outward, which conforms to the experimental results where the orientation of adsorbed lysozyme is co-determined by electrostatic interactions and van der Waals interactions. It is also found that despite of its net positive charge, lysozyme could be adsorbed on positively charged surfaces with both "end-on" and back-on orientations owing to the nonuniform charge distribution over lysozyme surface and the screening effect from ions in solution. The PTMC simulation method provides a way to determine the preferred orientation of proteins on surfaces for biosensor and biomaterial applications.

Effect of electrical polarization of hydroxyapatite ceramics on new bone formation.

PubMed

Itoh, S; Nakamura, S; Kobayashi, T; Shinomiya, K; Yamashita, K; Itoh, S

2006-03-01

Large surface charges can be induced on hydroxyapatite (HAp) ceramics by proton transport polarization, but this does not affect beta-tricalcium phosphate (TCP) because of its low polarizability. We wished to examine differences in osteogenic cell activity and new bone growth between positively or negatively surface-charged HAp and HAp/TCP plates using a calvarial bone defect model. In the first group of rats, test pieces were placed with their positively charged surfaces face down on the dura mater. In the second group, test pieces were placed with their negatively charged surfaces face down on the dura mater. A third group received noncharged test pieces. Histological examination, including enzymatic staining for osteoblasts and osteoclasts, was carried out. While no bone formation was observed at the pericranium, direct bone formation on the cranial bone debris and new bone growth expanded from the margins of the sites of injury to bridge across both the positively and negatively charged surfaces of HAp and HAp/TCP plates occurred. Electrical polarization of implanted plates, including positive charge, led to enhanced osteoblast activity, though decreased osteoclast activity was seen on the positively charged plate surface. Thus, polarization of HAp ceramics may modulate new bone formation and resorption.

PALS and SPM/EFM investigation of charged nanoporous electret films

NASA Astrophysics Data System (ADS)

Chiang, Dar-Ming; Liu, Wen-Liang; Chen, Jen-Luan; Susuki, Ryoichi

2005-08-01

The electret properties of nanoporous Teflon-FEP films, fabricated by the super-critical fluids method and charged by the corona method at room temperature, are investigated. PALS and SAXS are applied first to examine the charge characteristics of a free volume of electret materials. The topography and surface charges of electret materials are determined by scanning probe microscopy and electric field microscopy, respectively. The experimental results reveal that the interior surface areas of the pores of the electret materials influence the retention and stability of charge. Initial and aged surface charge was increased by factors of two and ten, with and without nanoporous Teflon-FEP films, respectively.

Solar Wind Access to Lunar Polar Craters: Feedback Between Surface Charging and Plasma Expansion

NASA Technical Reports Server (NTRS)

Zimmerman, M. I.; Farrell, W. M.; Stubbs, T. J.; Halekas, J. S.; Jackson, T. L.

2011-01-01

Determining the plasma environment within permanently shadowed lunar craters is critical to understanding local processes such as surface charging, electrostatic dust transport, volatile sequestration, and space weathering. In order to investigate the nature of this plasma environment, the first two-dimensional kinetic simulations of solar wind expansion into a lunar crater with a self-consistent plasma-surface interaction have been undertaken. The present results reveal how the plasma expansion into a crater couples with the electrically-charged lunar surface to produce a quasi-steady wake structure. In particular, there is a negative feedback between surface charging and ambipolar wake potential that allows an equilibrium to be achieved, with secondary electron emission strongly moderating the process. A range of secondary electron yields is explored, and two distinct limits are highlighted in which either surface charging or ambipoiar expansion is responsible for determining the overall wake structure.

Microelectrophoretic study of calcium oxalate monohydrate in macromolecular solutions

NASA Technical Reports Server (NTRS)

Curreri, P. A.; Onoda, G. Y., Jr.; Finlayson, B.

1987-01-01

Electrophoretic mobilities were measured for calcium oxalate monohydrate (COM) in solutions containing macromolecules. Two mucopolysaccharides (sodium heparin and chondroitin sulfate) and two proteins (positively charged lysozyme and negatively charged bovine serum albumin) were studied as adsorbates. The effects of pH, calcium oxalate surface charge (varied by calcium or oxalate ion activity), and citrate concentration were investigated. All four macromolecules showed evidence for adsorption. The macromolecule concentrations needed for reversing the surface charge indicated that the mucopolysaccharides have greater affinity for the COM surface than the proteins. Citrate ions at high concentrations appear to compete effectively with the negative protein for surface sites but show no evidence for competing with the positively charged protein.

Structural charge site influence on the interlayer hydration of expandable three-sheet clay minerals

USGS Publications Warehouse

Kerns, Raymond L.; Mankin, Charles J.

1968-01-01

Previous investigations have demonstrated the influences of interlayer cation composition, relative humidity, temperature, and magnitude of interlayer surface charge on the interlayer hydration of montmorillonites and vermiculites. It has been suggested that the sites of layer charge deficiencies may also have an influence upon the amount of hydration that can take place in the interlayers of expandable clay minerals. If the interlayer cation-to-layer bonds are considered as ideally electrostatic, the magnitude of the forces resisting expansion may be expressed as a form of Coulomb's law. If this effect is significant, expandable structures in which the charge-deficiency sites are predominantly in the tetrahedral sheet should have less pronounced swelling properties than should structures possessing charge deficiencies located primarily in the octahedral sheet.Three samples that differed in location of layer charge sites were selected for study. An important selection criterion was a non-correlation between tetrahedral charge sites and high surface-charge density, and between octahedral charge sites and low surface-charge density.The effects of differences in interlayer cation composition were eliminated by saturating portions of each sample with the same cations. Equilibrium (001) d values at controlled constant humidities were used as a measure of the relative degree of interlayer hydration.Although no correlation could be made between the degree of interlayer hydration and total surface-charge density, the investigation does not eliminate total surface-charge density as being significant to the swelling properties of three-sheet clay-mineral structures. The results do indicate a correlation between more intense expandability and predominance of charge deficiencies in the octahedral sheet. Conversely, less intense swelling behavior is associated with predominantly tetrahedral charge deficiencies.

The role of surface charge on the uptake and biocompatibility of hydroxyapatite nanoparticles with osteoblast cells

PubMed Central

Chen, Liang; Mccrate, Joseph M.; Lee, James C-M.; Li, Hao

2011-01-01

The objective of this study is to evaluate the effect of hydroxyapatite (HAP) nanoparticles with different surface charges on the cellular uptake behavior and in vitro cell viability and proliferation of MC3T3-E1 cell lines (osteoblast). The nanoparticles surface charge was varied by the surface modification with two carboxylic acids: 12-aminododecanoic acid (positive) and dodecanedioic acid (negative). The untreated HAP nanoparticles and dodecanoic acid modified HAP nanoparticles (neutral) were used as the control. X-ray diffraction (XRD) revealed that surface modifications by the three carboxylic acids did not change the crystal structure of HAP nanoparticles; Fourier transform infrared spectroscopy (FTIR) confirmed the adsorption and binding of the carboxylic acids on HAP nanoparticle surface; and zeta potential measurement confirmed that the chemicals successfully modified the surface charge of HAP nanoparticles in water based solution. Transmission electron microscopy (TEM) images showed that positively charged, negatively charged and untreated HAP nanoparticles, with similar size and shape, all penetrated into the cells and cells had more uptake of HAP nanoparticles with positive charge compared to those with negative charge, which might be attributed to the attractive or repulsive interaction between the negatively charged cell membrane and positively/negatively charged HAP nanoparticles. The neutral HAP nanoparticles could not penetrate cell membrane due to the larger size. MTT assay and LDH assay results indicated that as compared with the polystyrene control, greater cell viability and cell proliferation were measured on MC3T3-E1 cells treated with the three kinds of the HAP nanoparticles (neutral, positive, and untreated), among which positively charged HAP nanoparticles shows strongest improvement for cell viability and cell proliferation. In summary, the surface charge of HAP nanoparticles can be modified to influence the cellular uptake of HAP nanoparticles and the different uptake also influence the behavior of cells. These in-vitro results may also provide useful information for investigations of HAP nanoparticles applications in the gene delivery and intracellular drug delivery. PMID:21289408

Charge Retention by Monodisperse Gold Clusters on Surfaces Prepared Using Soft Landing of Mass Selected Ions

NASA Astrophysics Data System (ADS)

Johnson, Grant; Priest, Thomas; Laskin, Julia

2012-02-01

Monodisperse gold clusters have been prepared on surfaces in different charge states through soft landing of mass-selected ions. Gold clusters were synthesized in methanol solution by reduction of a gold precursor with a weak reducing agent in the presence of a diphosphine capping ligand. Electrospray ionization was used to introduce the clusters into the gas-phase and mass-selection was employed to isolate a single ionic cluster species which was delivered to surfaces at well controlled kinetic energies. Using in-situ time of flight secondary ion mass spectrometry (SIMS) it is demonstrated that the cluster retains its 3+ charge state when soft landed onto the surface of a fluorinated self assembled monolayer on gold. In contrast, when deposited onto carboxylic acid terminated and conventional alkyl thiol surfaces on gold the clusters exhibit larger relative abundances of the 2+ and 1+ charge states, respectively. The kinetics of charge reduction on the surface have been investigated using in-situ Fourier Transform Ion Cyclotron Resonance SIMS. It is shown that an extremely slow interfacial charge reduction occurs on the fluorinated monolayer surface while an almost instantaneous neutralization takes place on the surface of the alkyl thiol monolayer. Our results demonstrate that the size and charge state of small gold clusters on surfaces, both of which exert a dramatic influence on their chemical and physical properties, may be tuned through soft landing of mass-selected ions onto selected substrates.

A Spacecraft Charging Capability for SXTF.

DTIC Science & Technology

1979-01-17

surfaces can charge up. ’Iiiis differential charging of satellite surfaces can cause vacutum sparks , and dielectric breakdowns, and wi 11 effect the S...times required to reach steady charge state in the spacecraft internal dielectrics upon electron irradiation. In space , typical times (order of magni...WORDS (Continue on reverse side it necessary end Identify by block nunmber) Spacecraft charging Dielectric breakdown SGEMP Electron accelerators

Precise control of surface electrostatic forces on polymer brush layers with opposite charges for resistance to protein adsorption.

PubMed

Sakata, Sho; Inoue, Yuuki; Ishihara, Kazuhiko

2016-10-01

Various molecular interaction forces are generated during protein adsorption process on material surfaces. Thus, it is necessary to control them to suppress protein adsorption and the subsequent cell and tissue responses. A series of binary copolymer brush layers were prepared via surface-initiated atom transfer radical polymerization, by mixing the cationic monomer unit and anionic monomer unit randomly in various ratios. Surface characterization revealed that the constructed copolymer brush layers exhibited an uniform super-hydrophilic nature and different surface potentials. The strength of the electrostatic interaction forces operating on these mixed-charge copolymer brush surfaces was evaluated quantitatively using force-versus-distance (f-d) curve measurements by atomic force microscopy (AFM) and probes modified by negatively charged carboxyl groups or positively charged amino groups. The electrostatic interaction forces were determined based on the charge ratios of the copolymer brush layers. Notably, the surface containing equivalent cationic/anionic monomer units hardly interacted with both the charged groups. Furthermore, the protein adsorption force and the protein adsorption mass on these surfaces were examined by AFM f-d curve measurement and surface plasmon resonance measurement, respectively. To clarify the influence of the electrostatic interaction on the protein adsorption behavior on the surface, three kinds of proteins having negative, positive, and relatively neutral net charges under physiological conditions were used in this study. We quantitatively demonstrated that the amount of adsorbed proteins on the surfaces would have a strong correlation with the strength of surface-protein interaction forces, and that the strength of surface-protein interaction forces would be determined from the combination between the properties of the electrostatic interaction forces on the surfaces and the charge properties of the proteins. Especially, the copolymer brush surface composed of equivalent cationic/anionic monomer units exhibited no significant interaction forces, and dramatically suppressed the adsorption of proteins regardless of their charge properties. We conclude that the established methodology could elucidate relationship between the protein adsorption behavior and molecular interaction, especially the electrostatic interaction forces, and demonstrated that the suppression of the electrostatic interactions with the ionic functional groups would be important for the development of new polymeric biomaterials with a high repellency of protein adsorption. Copyright © 2016 Elsevier Ltd. All rights reserved.

The role of interfacial water layer in atmospherically relevant charge separation

NASA Astrophysics Data System (ADS)

Bhattacharyya, Indrani

Charge separation at interfaces is important in various atmospheric processes, such as thunderstorms, lightning, and sand storms. It also plays a key role in several industrial processes, including ink-jet printing and electrostatic separation. Surprisingly, little is known about the underlying physics of these charging phenomena. Since thin films of water are ubiquitous, they may play a role in these charge separation processes. This talk will focus on the experimental investigation of the role of a water adlayer in interfacial charging, with relevance to meteorologically important phenomena, such as atmospheric charging due to wave actions on oceans and sand storms. An ocean wave generates thousands of bubbles, which upon bursting produce numerous large jet droplets and small film droplets that are charged. In the 1960s, Blanchard showed that the jet droplets are positively charged. However, the charge on the film droplets was not known. We designed an experiment to exclusively measure the charge on film droplets generated by bubble bursting on pure water and aqueous salt solution surfaces. We measured their charge to be negative and proposed a model where a slight excess of hydroxide ions in the interfacial water layer is responsible for generating these negatively charged droplets. The findings from this research led to a better understanding of the ionic disposition at the air-water interface. Sand particles in a wind-blown sand layer, or 'saltation' layer, become charged due to collisions, so much so, that it can cause lightning. Silica, being hydrophilic, is coated with a water layer even under low-humidity conditions. To investigate the importance of this water adlayer in charging the silica surfaces, we performed experiments to measure the charge on silica surfaces due to contact and collision processes. In case of contact charging, the maximum charge separation occurred at an optimum relative humidity. On the contrary, in collisional charging process, no humidity effect was observed. We proposed an ion transfer mechanism in case of contact charging. However, an electron transfer mechanism explained the collisional charging process. The effects of temperature, surface roughness, and chemical nature of surface were also studied for both contact and collisional charging processes.

Polyelectrolytes tethered to a free surface

NASA Astrophysics Data System (ADS)

Dubreuil, F.; Guenoun, P.

Several attempts have been already carried out in order to tether charged chains by an end at a free fluctuating surface. We review here most of these attempts and focus on how close the physics of charged brushes can be investigated by such an approach. We first describe results about films of charged-neutral diblock copolymers spread at the surface of water. Results can be mostly rationalized in terms of charged brushes although additional structurations and fluctuations of the interface can be observed. The latter deformations are also observed when adsorbed layers of charged-neutral diblock copolymers are considered. At last, we examine how free suspended films of charged-neutral diblock copolymers can be viewed as two opposing charged brushes, both in terms of thickness and pressure.

Programmable ion-sensitive transistor interfaces. III. Design considerations, signal generation, and sensitivity enhancement

NASA Astrophysics Data System (ADS)

Jayant, Krishna; Auluck, Kshitij; Rodriguez, Sergio; Cao, Yingqiu; Kan, Edwin C.

2014-05-01

We report on factors that affect DNA hybridization detection using ion-sensitive field-effect transistors (ISFETs). Signal generation at the interface between the transistor and immobilized biomolecules is widely ascribed to unscreened molecular charges causing a shift in surface potential and hence the transistor output current. Traditionally, the interaction between DNA and the dielectric or metal sensing interface is modeled by treating the molecular layer as a sheet charge and the ionic profile with a Poisson-Boltzmann distribution. The surface potential under this scenario is described by the Graham equation. This approximation, however, often fails to explain large hybridization signals on the order of tens of mV. More realistic descriptions of the DNA-transistor interface which include factors such as ion permeation, exclusion, and packing constraints have been proposed with little or no corroboration against experimental findings. In this study, we examine such physical models by their assumptions, range of validity, and limitations. We compare simulations against experiments performed on electrolyte-oxide-semiconductor capacitors and foundry-ready floating-gate ISFETs. We find that with weakly charged interfaces (i.e., low intrinsic interface charge), pertinent to the surfaces used in this study, the best agreement between theory and experiment exists when ions are completely excluded from the DNA layer. The influence of various factors such as bulk pH, background salinity, chemical reactivity of surface groups, target molecule concentration, and surface coatings on signal generation is studied. Furthermore, in order to overcome Debye screening limited detection, we suggest two signal enhancement strategies. We first describe frequency domain biosensing, highlighting the ability to sort short DNA strands based on molecular length, and then describe DNA biosensing in multielectrolytes comprising trace amounts of higher-valency salt in a background of monovalent saline. Our study provides guidelines for optimized interface design, signal enhancement, and the interpretation of FET-based biosensor signals.

Electric field measurements in nanosecond pulse discharges in air over liquid water surface

NASA Astrophysics Data System (ADS)

Simeni Simeni, Marien; Baratte, Edmond; Zhang, Cheng; Frederickson, Kraig; Adamovich, Igor V.

2018-01-01

Electric field in nanosecond pulse discharges in ambient air is measured by picosecond four-wave mixing, with absolute calibration by a known electrostatic field. The measurements are done in two geometries, (a) the discharge between two parallel cylinder electrodes placed inside quartz tubes, and (b) the discharge between a razor edge electrode and distilled water surface. In the first case, breakdown field exceeds DC breakdown threshold by approximately a factor of four, 140 ± 10 kV cm-1. In the second case, electric field is measured for both positive and negative pulse polarities, with pulse durations of ˜10 ns and ˜100 ns, respectively. In the short duration, positive polarity pulse, breakdown occurs at 85 kV cm-1, after which the electric field decreases over several ns due to charge separation in the plasma, with no field reversal detected when the applied voltage is reduced. In a long duration, negative polarity pulse, breakdown occurs at a lower electric field, 30 kV cm-1, after which the field decays over several tens of ns and reverses direction when the applied voltage is reduced at the end of the pulse. For both pulse polarities, electric field after the pulse decays on a microsecond time scale, due to residual surface charge neutralization by transport of opposite polarity charges from the plasma. Measurements 1 mm away from the discharge center plane, ˜100 μm from the water surface, show that during the voltage rise, horizontal field component (Ex ) lags in time behind the vertical component (Ey ). After breakdown, Ey is reduced to near zero and reverses direction. Further away from the water surface (≈0.9 mm), Ex is much higher compared to Ey during the entire voltage pulse. The results provide insight into air plasma kinetics and charge transport processes near plasma-liquid interface, over a wide range of time scales.

Depletion region surface effects in electron beam induced current measurements.

PubMed

Haney, Paul M; Yoon, Heayoung P; Gaury, Benoit; Zhitenev, Nikolai B

2016-09-07

Electron beam induced current (EBIC) is a powerful characterization technique which offers the high spatial resolution needed to study polycrystalline solar cells. Current models of EBIC assume that excitations in the p - n junction depletion region result in perfect charge collection efficiency. However we find that in CdTe and Si samples prepared by focused ion beam (FIB) milling, there is a reduced and nonuniform EBIC lineshape for excitations in the depletion region. Motivated by this, we present a model of the EBIC response for excitations in the depletion region which includes the effects of surface recombination from both charge-neutral and charged surfaces. For neutral surfaces we present a simple analytical formula which describes the numerical data well, while the charged surface response depends qualitatively on the location of the surface Fermi level relative to the bulk Fermi level. We find the experimental data on FIB-prepared Si solar cells is most consistent with a charged surface, and discuss the implications for EBIC experiments on polycrystalline materials.

Effects of Particle Hydrophobicity, Surface Charge, Media pH Value and Complexation with Human Serum Albumin on Drug Release Behavior of Mitoxantrone-Loaded Pullulan Nanoparticles

PubMed Central

Tao, Xiaojun; Jin, Shu; Wu, Dehong; Ling, Kai; Yuan, Liming; Lin, Pingfa; Xie, Yongchao; Yang, Xiaoping

2015-01-01

We prepared two types of cholesterol hydrophobically modified pullulan nanoparticles (CHP) and carboxyethyl hydrophobically modified pullulan nanoparticles (CHCP) substituted with various degrees of cholesterol, including 3.11, 6.03, 6.91 and 3.46 per polymer, and named CHP−3.11, CHP−6.03, CHP−6.91 and CHCP−3.46. Dynamic laser light scattering (DLS) showed that the pullulan nanoparticles were 80–120 nm depending on the degree of cholesterol substitution. The mean size of CHCP nanoparticles was about 160 nm, with zeta potential −19.9 mV, larger than CHP because of the carboxyethyl group. A greater degree of cholesterol substitution conferred greater nanoparticle hydrophobicity. Drug-loading efficiency depended on nanoparticle hydrophobicity, that is, nanoparticles with the greatest degree of cholesterol substitution (6.91) showed the most drug encapsulation efficiency (90.2%). The amount of drug loading increased and that of drug release decreased with enhanced nanoparticle hydrophobicity. Nanoparticle surface-negative charge disturbed the amount of drug loading and drug release, for an opposite effect relative to nanoparticle hydrophobicity. The drug release in pullulan nanoparticles was higher pH 4.0 than pH 6.8 media. However, the changed drug release amount was not larger for negative-surface nanoparticles than CHP nanoparticles in the acid release media. Drug release of pullulan nanoparticles was further slowed with human serum albumin complexation and was little affected by nanoparticle hydrophobicity and surface negative charge. PMID:28344259

Significance of surface charge and shell material of superparamagnetic iron oxide nanoparticle (SPION) based core/shell nanoparticles on the composition of the protein corona.

PubMed

Sakulkhu, Usawadee; Mahmoudi, Morteza; Maurizi, Lionel; Coullerez, Geraldine; Hofmann-Amtenbrink, Margarethe; Vries, Marcel; Motazacker, Mahdi; Rezaee, Farhad; Hofmann, Heinrich

2015-02-01

As nanoparticles (NPs) are increasingly used in many applications their safety and efficient applications in nanomedicine have become concerns. Protein coronas on nanomaterials' surfaces can influence how the cell "recognizes" nanoparticles, as well as the in vitro and in vivo NPs' behaviors. The SuperParamagnetic Iron Oxide Nanoparticle (SPION) is one of the most prominent agents because of its superparamagnetic properties, which is useful for separation applications. To mimic surface properties of different types of NPs, a core-shell SPION library was prepared by coating with different surfaces: polyvinyl alcohol polymer (PVA) (positive, neutral and negative), SiO2 (positive and negative), titanium dioxide and metal gold. The SPIONs with different surfaces were incubated at a fixed serum : nanoparticle surface ratio, magnetically trapped and washed. The tightly bound proteins were quantified and identified. The surface charge has a great impact on protein adsorption, especially on PVA and silica where proteins preferred binding to the neutral and positively charged surfaces. The importance of surface material on protein adsorption was also revealed by preferential binding on TiO2 and gold coated SPION, even negatively charged. There is no correlation between the protein net charge and the nanoparticle surface charge on protein binding, nor direct correlation between the serum proteins' concentration and the proteins detected in the coronas.

Understanding and removing surface states limiting charge transport in TiO2 nanowire arrays for enhanced optoelectronic device performance.

PubMed

Sheng, Xia; Chen, Liping; Xu, Tao; Zhu, Kai; Feng, Xinjian

2016-03-01

Charge transport within electrode materials plays a key role in determining the optoelectronic device performance. Aligned single-crystal TiO 2 nanowire arrays offer an ideal electron transport path and are expected to have higher electron mobility. Unfortunately, their transport is found not to be superior to that in nanoparticle films. Here we show that the low electron transport in rutile TiO 2 nanowires is mainly caused by surface traps in relatively deep energy levels, which cannot be removed by conventional approaches, such as oxygen annealing treatment. Moreover, we demonstrate an effective wet-chemistry approach to minimize these trap states, leading to over 20-fold enhancement in electron diffusion coefficient and 62% improvement in solar cell performance. On the basis of our results, the potential of TiO 2 NWs can be developed and well-utilized, which is significantly important for their practical applications.

Interrelation of electret properties of polyethylene foam from the method of cross-linking

NASA Astrophysics Data System (ADS)

Gilmanov, I. R.; Galikhanov, M. F.; Gilmanova, A. R.

2017-09-01

The electret properties of chemically cross-linked polyethylene foam and physically cross-linked polyethylene foam have been studied. It has been shown that chemically cross-linked polyethylene foam has higher surface potential, effective surface charge density and electric field strength compared to physically bonded polyethylene foam. This is due to the presence of molecules and fragments of dicumyl peroxide, which can play the role of traps for injection charge carriers, a greater degree of cross-linking and with the oxidation of polyethylene, which occurs during irradiation during physical cross-linking. When the foam is deformed, its electret properties are reduced, and when the volume is relaxed, they are restored. This is due to the partial mutual compensation of homo- and heterocharge during compression and the return of the structure of the gas-filled polymer to its former position when the load is removed.

Design of magnetic polyplexes taken up efficiently by dendritic cell for enhanced DNA vaccine delivery.

PubMed

Nawwab Al-Deen, F M; Selomulya, C; Kong, Y Y; Xiang, S D; Ma, C; Coppel, R L; Plebanski, M

2014-02-01

Dendritic cells (DC) targeting vaccines require high efficiency for uptake, followed by DC activation and maturation. We used magnetic vectors comprising polyethylenimine (PEI)-coated superparamagnetic iron oxide nanoparticles, with hyaluronic acid (HA) of different molecular weights (<10 and 900 kDa) to reduce cytotoxicity and to facilitate endocytosis of particles into DCs via specific surface receptors. DNA encoding Plasmodium yoelii merozoite surface protein 1-19 and a plasmid encoding yellow fluorescent gene were added to the magnetic complexes with various % charge ratios of HA: PEI. The presence of magnetic fields significantly enhanced DC transfection and maturation. Vectors containing a high-molecular-weight HA with 100% charge ratio of HA: PEI yielded a better transfection efficiency than others. This phenomenon was attributed to their longer molecular chains and higher mucoadhesive properties aiding DNA condensation and stability. Insights gained should improve the design of more effective DNA vaccine delivery systems.

42 CFR 405.506 - Charges higher than customary or prevailing charges or lowest charge levels.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 42 Public Health 2 2010-10-01 2010-10-01 false Charges higher than customary or prevailing charges... prevailing charges or lowest charge levels. A charge which exceeds the customary charge of the physician or other person who rendered the medical or other health service, or the prevailing charge in the locality...

Interstitial distribution of charged macromolecules in the dog lung: a kinetic model.

PubMed

Parker, J C; Miniati, M; Pitt, R; Taylor, A E

1987-01-01

A mathematic model was constructed to investigate conflicting physiologic data concerning the charge effect of continuous capillaries to macromolecules in the lung. We simulated the equilibration kinetics of lactate dehydrogenase (MR 4.2 nM) isozymes LDH 1 (pI = 5.0) and LDH 5 (pI = 7.9) between plasma and lymph using previously measured permeability coefficients, lung tissue distribution volumes (VA) and plasma concentrations (CP) in lung tissue. Our hypothesis is that the fixed anionic charges in interstitium, basement membrane, and cell surfaces determine equilibration rather than charged membrane effects at the capillary barrier, so the same capillary permeability coefficients were used for both isozymes. Capillary filtration rates and protein fluxes were calculated using conventional flux equations. Initial conditions at baseline and increased left atrial pressures (PLA) were those measured in animal studies. Simulated equilibration of isozymes over 30 h in the model at baseline capillary pressures accurately predicted the observed differences in lymph/plasma concentration ratios (CL/CP) between isotopes at 4 h and equilibration of these ratios at 24 h. Quantitative prediction of isozyme CL/CP ratios was also obtained at increased PLA. However, an additional cation selective compartment representing the surface glycocalyx was required to accurately simulate the initial higher transcapillary clearances of cationic LDH 5. Thus experimental data supporting the negative barrier, positive barrier, and no charge barrier hypotheses were accurately reproduced by the model using only the observed differences in interstitial partitioning of isozymes without differences in capillary selectivity.

Surface-Charge-Based Micro-Models--A Solid Foundation for Learning about Direct Current Circuits

ERIC Educational Resources Information Center

Hirvonen, P. E.

2007-01-01

This study explores how the use of a surface-charge-based instructional approach affects introductory university level students' understanding of direct current (dc) circuits. The introduced teaching intervention includes electrostatics, surface-charge-based micro-models that explain the existence of an electric field inside the current-carrying…

Modulating interactions between ligand-coated nanoparticles and phase-separated lipid bilayers by varying the ligand density and the surface charge.

PubMed

Chen, Xiaojie; Tieleman, D Peter; Liang, Qing

2018-02-01

The interactions between nanoparticles and lipid bilayers are critical in applications of nanoparticles in nanomedicine, cell imaging, toxicology, and elsewhere. Here, we investigate the interactions between nanoparticles coated with neutral and/or charged ligands and phase-separated lipid bilayers using coarse-grained molecular dynamics simulation. Both penetration and adsorption processes as well as the final distribution of the nanoparticles can be readily modulated by varying the ligand density and the surface charge of the nanoparticles. Completely hydrophobic (neutral) nanoparticles with larger size initially preferentially penetrate into the liquid-disordered region of the lipid bilayer and finally transfer into the liquid-ordered region; partially hydrophilic nanoparticles with low or moderate surface charge tend to either distribute in the liquid-disordered region or be adsorbed on the surface of the lipid bilayer, while strongly hydrophilic nanoparticles with high surface charge always reside on the surface of the lipid bilayer. Interactions of the nanoparticles with the lipid bilayers are affected by the surface charge of nanoparticles, hydrophobic mismatch, bending of the ligands, and the packing state of the lipids. Insight in these factors can be used to improve the efficiency of designing nanoparticles for specific applications.

Modulation of Silica Nanoparticle Uptake into Human Osteoblast Cells by Variation of the Ratio of Amino and Sulfonate Surface Groups: Effects of Serum

PubMed Central

2015-01-01

To study the importance of the surface charge for cellular uptake of silica nanoparticles (NPs), we synthesized five different single- or multifunctionalized fluorescent silica NPs (FFSNPs) by introducing various ratios of amino and sulfonate groups into their surface. The zeta potential values of these FFSNPs were customized from highly positive to highly negative, while other physicochemical properties remained almost constant. Irrespective of the original surface charge, serum proteins adsorbed onto the surface, neutralized the zeta potential values, and prevented the aggregation of the tailor-made FFSNPs. Depending on the surface charge and on the absence or presence of serum, two opposite trends were found concerning the cellular uptake of FFSNPs. In the absence of serum, positively charged NPs were more strongly accumulated by human osteoblast (HOB) cells than negatively charged NPs. In contrast, in serum-containing medium, anionic FFSNPs were internalized by HOB cells more strongly, despite the similar size and surface charge of all types of protein-covered FFSNPs. Thus, at physiological condition, when the presence of proteins is inevitable, sulfonate-functionalized silica NPs are the favorite choice to achieve a desired high rate of NP internalization. PMID:26030456

Non-conservation of global charges in the Brane Universe and baryogenesis

NASA Astrophysics Data System (ADS)

Dvali, Gia; Gabadadze, Gregory

1999-08-01

We argue that global charges, such as baryon or lepton number, are not conserved in theories with the Standard Model fields localized on the brane which propagates in higher-dimensional space-time. The global-charge non-conservation is due to quantum fluctuations of the brane surface. These fluctuations create ``baby branes'' that can capture some global charges and carry them away into the bulk of higher-dimensional space. Such processes are exponentially suppressed at low-energies, but can be significant at high enough temperatures or energies. These effects can lead to a new, intrinsically high-dimensional mechanism of baryogenesis. Baryon asymmetry might be produced due either to ``evaporation'' into the baby branes, or creation of the baryon number excess in collisions of two Brane Universes. As an example we discuss a possible cosmological scenario within the recently proposed ``Brane Inflation'' framework. Inflation is driven by displaced branes which slowly fall on top of each other. When the branes collide inflation stops and the Brane Universe reheats. During this non-equilibrium collision baryon number can be transported from one brane to another one. This results in the baryon number excess in our Universe which exactly equals to the hidden ``baryon number'' deficit in the other Brane Universe. © 1999

Increasing binding density of yeast cells by control of surface charge with allylamine grafting to ion modified polymer surfaces.

PubMed

Tran, Clara T H; Kondyurin, Alexey; Chrzanowski, Wojciech; Bilek, Marcela M M; McKenzie, David R

2014-10-01

Plasma immersion ion implantation (PIII) treatment of polymers creates a biointerface capable of direct covalent immobilization of biomolecules. The immobilization of protein molecules is achieved by covalent bonds formed between embedded radicals on the treated surface and amino acid side chains and cells can be immobilized through cell-wall proteins. The attachment density of negatively charged entities on a PIII treated surface is inhibited by its negative surface charge at neutral pH. To reduce the negative charge of PIII treated surfaces in phosphate buffer (pH 7.4, 11mM), we develop an effective approach of grafting allylamine monomers onto the treated surface. The results reveal reactions between allylamine and radicals on the PIII treated surface. One of these triggers polymerization, increasing the number of amine groups grafted. As a consequence, the PIII treated polystyrene surface after allylamine exposure becomes more hydrophobic and less negatively charged in phosphate buffer. Using yeast cells as an example, we have shown a significant improvement (6-15 times) of cell density immobilized on the PIII treated surface after exposure to allylamine. Copyright © 2014 Elsevier B.V. All rights reserved.

Numerical modelling of needle-grid electrodes for negative surface corona charging system

NASA Astrophysics Data System (ADS)

Zhuang, Y.; Chen, G.; Rotaru, M.

2011-08-01

Surface potential decay measurement is a simple and low cost tool to examine electrical properties of insulation materials. During the corona charging stage, a needle-grid electrodes system is often used to achieve uniform charge distribution on the surface of the sample. In this paper, a model using COMSOL Multiphysics has been developed to simulate the gas discharge. A well-known hydrodynamic drift-diffusion model was used. The model consists of a set of continuity equations accounting for the movement, generation and loss of charge carriers (electrons, positive and negative ions) coupled with Poisson's equation to take into account the effect of space and surface charges on the electric field. Four models with the grid electrode in different positions and several mesh sizes are compared with a model that only has the needle electrode. The results for impulse current and surface charge density on the sample clearly show the effect of the extra grid electrode with various positions.

Surface transport processes in charged porous media

DOE PAGES

Gabitto, Jorge; Tsouris, Costas

2017-03-03

Surface transport processes are important in chemistry, colloidal sciences, engineering, biology, and geophysics. Natural or externally produced charges on surfaces create electrical double layers (EDLs) at the solid-liquid interface. The existence of the EDLs produces several complex processes including bulk and surface transport of ions. In this work, a model is presented to simulate bulk and transport processes in homogeneous porous media comprising big pores. It is based on a theory for capacitive charging by ideally polarizable porous electrodes without Faradaic reactions or specific adsorption of ions. A volume averaging technique is used to derive the averaged transport equations inmore » the limit of thin electrical double layers. Description of the EDL between the electrolyte solution and the charged wall is accomplished using the Gouy-Chapman-Stern (GCS) model. The surface transport terms enter into the average equations due to the use of boundary conditions for diffuse interfaces. Two extra surface transports terms appear in the closed average equations. One is a surface diffusion term equivalent to the transport process in non-charged porous media. The second surface transport term is a migration term unique to charged porous media. The effective bulk and transport parameters for isotropic porous media are calculated solving the corresponding closure problems.« less

Dust Grain Charge above the Lunar terminator

NASA Astrophysics Data System (ADS)

Vaverka, Jakub; Richterova, Ivana; Nemecek, Zdenek; Safrankova, Jana; Pavlu, Jiri; Vysinka, Marek

Interaction of a lunar surface with the solar wind and magnetosphere leads to its charging by several processes as photoemission, a collection of primary particles, and secondary electron emission. Nevertheless, charging of the lunar surface is complicated by a shielding of solar light and solar wind ions by hills, craters, and boulders that can locally influence the surface potential. Moreover, a presence of a plasma wake can strongly affect this potential at the night side of the Moon. A typical surface potential varies from slightly positive (dayside) to negative values of the order of several hundred volts (night side). An electric field above the charged surface can lead to a levitation of dust grains as it has been observed by several spacecraft and by astronauts during Apollo missions. Although charging and transport of dust grains above the lunar surface are in the center of interest for many years, these phenomena are not still completely understood. We present calculation of an equilibrium potential of dust grains above the lunar surface. We focus on a terminator area during the Earth’s plasma sheet crossing. We use the secondary electron emission model for dust grains which takes into account an influence of the grain size, material, and surface roughness and findings from laboratory experiments with charging of lunar dust simulants by an electron beam.

Surface transport processes in charged porous media

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

Gabitto, Jorge; Tsouris, Costas

Surface transport processes are important in chemistry, colloidal sciences, engineering, biology, and geophysics. Natural or externally produced charges on surfaces create electrical double layers (EDLs) at the solid-liquid interface. The existence of the EDLs produces several complex processes including bulk and surface transport of ions. In this work, a model is presented to simulate bulk and transport processes in homogeneous porous media comprising big pores. It is based on a theory for capacitive charging by ideally polarizable porous electrodes without Faradaic reactions or specific adsorption of ions. A volume averaging technique is used to derive the averaged transport equations inmore » the limit of thin electrical double layers. Description of the EDL between the electrolyte solution and the charged wall is accomplished using the Gouy-Chapman-Stern (GCS) model. The surface transport terms enter into the average equations due to the use of boundary conditions for diffuse interfaces. Two extra surface transports terms appear in the closed average equations. One is a surface diffusion term equivalent to the transport process in non-charged porous media. The second surface transport term is a migration term unique to charged porous media. The effective bulk and transport parameters for isotropic porous media are calculated solving the corresponding closure problems.« less

Profiling Charge Complementarity and Selectivity for Binding at the Protein Surface

PubMed Central

Sulea, Traian; Purisima, Enrico O.

2003-01-01

A novel analysis and representation of the protein surface in terms of electrostatic binding complementarity and selectivity is presented. The charge optimization methodology is applied in a probe-based approach that simulates the binding process to the target protein. The molecular surface is color coded according to calculated optimal charge or according to charge selectivity, i.e., the binding cost of deviating from the optimal charge. The optimal charge profile depends on both the protein shape and charge distribution whereas the charge selectivity profile depends only on protein shape. High selectivity is concentrated in well-shaped concave pockets, whereas solvent-exposed convex regions are not charge selective. This suggests the synergy of charge and shape selectivity hot spots toward molecular selection and recognition, as well as the asymmetry of charge selectivity at the binding interface of biomolecular systems. The charge complementarity and selectivity profiles map relevant electrostatic properties in a readily interpretable way and encode information that is quite different from that visualized in the standard electrostatic potential map of unbound proteins. PMID:12719221

Screening of charged impurities as a possible mechanism for conductance change in graphene gas sensing

NASA Astrophysics Data System (ADS)

Liang, Sang-Zi; Chen, Gugang; Harutyunyan, Avetik R.; Sofo, Jorge O.

2014-09-01

In carbon nanotube and graphene gas sensing, the measured conductance change after the sensor is exposed to target molecules has been traditionally attributed to carrier density change due to charge transfer between the sample and the adsorbed molecule. However, this explanation has many problems when it is applied to graphene: The increased amount of Coulomb impurities should lead to decrease in carrier mobility which was not observed in many experiments, carrier density is controlled by the gate voltage in the experimental setup, and there are inconsistencies in the energetics of the charge transfer. In this paper we explore an alternative mechanism. Charged functional groups and dipolar molecules on the surface of graphene may counteract the effect of charged impurities on the substrate. Because scattering of electrons with these charged impurities has been shown to be the limiting factor in graphene conductivity, this leads to significant changes in the transport behavior. A model for the conductivity is established using the random phase approximation dielectric function of graphene and the first-order Born approximation for scattering. The model predicts optimal magnitudes for the charge and dipole moment which maximally screen a given charged impurity. The dipole screening is shown to be generally weaker than the charge screening although the former becomes more effective with higher gate voltage away from the charge neutrality point. The model also predicts that with increasing amount of adsorbates, the charge impurities eventually become saturated and additional adsorption always lead to decreasing conductivity.

Study of thermal aging effects on the conduction and trapping of charges in XLPE cable insulations under electron beam irradiation

NASA Astrophysics Data System (ADS)

Boukezzi, L.; Rondot, S.; Jbara, O.; Boubakeur, A.

2018-08-01

The effect of thermal aging on the charging phenomena in cross-linked polyethylene (XLPE) has been studied under electron beam irradiation in scanning electron microscope (SEM). The dynamic variation of trapped charge represents the trapping process of XLPE under electron beam irradiation. We have found that the trapped charge variation can be approximated by a first order exponential function. The amount of trapped charge presents enhanced values at the beginning of aging at lower temperatures (80 °C and 100 °C). This suggests the diffusion of cross-linking by-products to the surface of sample that acts as traps for injected electrons. The oxidation which is a very important form of XLPE degradation has an effect at the advanced stage of the aging process. For higher temperatures (120 °C and 140 °C), the taken part process in the evolution of the trapped charge is the crystallinity increase at the beginning of aging leading to the trapped charge decreasing, and the polar groups generated by thermo-oxidation process at the end of aging leading to the trapped charge increase. Variations of leakage current according to the aging time have quite similar trends with the dielectric losses factor and consequently some correlations must be made between charging mechanisms and the electrical behaviour of XLPE under thermal aging.

Deionization and desalination using electrostatic ion pumping

DOEpatents

Bourcier, William L.; Aines, Roger D.; Haslam, Jeffery J.; Schaldach, Charlene M.; O& #x27; Brien, Kevin C.; Cussler, Edward

2013-06-11

The present invention provides a new method and apparatus/system for purifying ionic solutions, such as, for example, desalinating water, using engineered charged surfaces to sorb ions from such solutions. Surface charge is applied externally, and is synchronized with oscillatory fluid movements between substantially parallel charged plates. Ions are held in place during fluid movement in one direction (because they are held in the electrical double layer), and released for transport during fluid movement in the opposite direction by removing the applied electric field. In this way the ions, such as salt, are "ratcheted" across the charged surface from the feed side to the concentrate side. The process itself is very simple and involves only pumps, charged surfaces, and manifolds for fluid collection.

Deionization and desalination using electrostatic ion pumping

DOEpatents

Bourcier, William L [Livermore, CA; Aines, Roger D [Livermore, CA; Haslam, Jeffery J [Livermore, CA; Schaldach, Charlene M [Pleasanton, CA; O'Brien, Kevin C [San Ramon, CA; Cussler, Edward [Edina, MN

2011-07-19

The present invention provides a new method and apparatus/system for purifying ionic solutions, such as, for example, desalinating water, using engineered charged surfaces to sorb ions from such solutions. Surface charge is applied externally, and is synchronized with oscillatory fluid movements between substantially parallel charged plates. Ions are held in place during fluid movement in one direction (because they are held in the electrical double layer), and released for transport during fluid movement in the opposite direction by removing the applied electric field. In this way the ions, such as salt, are "ratcheted" across the charged surface from the feed side to the concentrate side. The process itself is very simple and involves only pumps, charged surfaces, and manifolds for fluid collection.

A switchable polymer layer: Chain folding in end-charged polymer brushes

NASA Astrophysics Data System (ADS)

Heine, David; Wu, David T.

2001-03-01

We use a self-consistent field approximation to model the configurations of end-charged homopolymer and block copolymer brushes in response to an external electric field due to charges on the grafting surface. By varying the charge density on the grafting surface, we can cause the chains either to extend outward, greatly increasing the brush height, or to loop back to the grafting surface. We show that such a copolymer brush can present one block at the exposed surface in the extended state and present the other block in the retracted state. This occurs for both a solvated brush and a dry brush. We also compare these results to those of a modified Alexander-de Gennes model for the end-charged homopolymer brush.

Complexation of ferric oxide particles with pectins of different charge density.

PubMed

Milkova, Viktoria; Kamburova, Kamelia; Petkanchin, Ivana; Radeva, Tsetska

2008-09-02

The effect of polyelectrolyte charge density on the electrical properties and stability of suspensions of oppositely charged oxide particles is followed by means of electro-optics and electrophoresis. Variations in the electro-optical effect and the electrophoretic mobility are examined at conditions where fully ionized pectins of different charge density adsorb onto particles with ionizable surfaces. The charge neutralization point coincides with the maximum of particle aggregation in all suspensions. We find that the concentration of polyelectrolyte, needed to neutralize the particle charge, decreases with increasing charge density of the pectin. The most highly charged pectin presents an exception to this order, which is explained with a reduction of the effective charge density of this pectin due to condensation of counterions. The presence of condensed counterions, remaining bound to the pectin during its adsorption on the particle surface, is proved by investigation of the frequency behavior of the electro-optical effect at charge reversal of the particle surface.

Ions, metabolites, and cells: Water as a reporter of surface conditions during bacterial growth.

PubMed

Jarisz, Tasha A; Lane, Sarah; Gozdzialski, Lea; Hore, Dennis K

2018-06-14

Surface-specific nonlinear vibrational spectroscopy, combined with bulk solution measurements and imaging, is used to study the surface conditions during the growth of E. coli. As a result of the silica high surface charge density, the water structure at the silica-aqueous interface is known to be especially sensitive to pH and ionic strength, and surface concentration profiles develop that can be appreciably different from the bulk solution conditions. We illustrate that, in the presence of growing cells, a unique surface micro-environment is established as a result of metabolites accumulating on the silica surface. Even in the subsequent absence of the cells, this surface layer works to reduce the interfacial ionic strength as revealed by the enhanced signal from surface water molecules. In the presence of growing cells, an additional boost in surface water signal is attributed to a local pH that is higher than that of the bulk solution.

Ions, metabolites, and cells: Water as a reporter of surface conditions during bacterial growth

NASA Astrophysics Data System (ADS)

Jarisz, Tasha A.; Lane, Sarah; Gozdzialski, Lea; Hore, Dennis K.

2018-06-01

Surface-specific nonlinear vibrational spectroscopy, combined with bulk solution measurements and imaging, is used to study the surface conditions during the growth of E. coli. As a result of the silica high surface charge density, the water structure at the silica-aqueous interface is known to be especially sensitive to pH and ionic strength, and surface concentration profiles develop that can be appreciably different from the bulk solution conditions. We illustrate that, in the presence of growing cells, a unique surface micro-environment is established as a result of metabolites accumulating on the silica surface. Even in the subsequent absence of the cells, this surface layer works to reduce the interfacial ionic strength as revealed by the enhanced signal from surface water molecules. In the presence of growing cells, an additional boost in surface water signal is attributed to a local pH that is higher than that of the bulk solution.

Effects of rutin on the physicochemical properties of skin fibroblasts membrane disruption following UV radiation.

PubMed

Dobrzyńska, Izabela; Gęgotek, Agnieszka; Gajko, Ewelina; Skrzydlewska, Elżbieta; Figaszewski, Zbigniew A

2018-02-25

Human skin provides the body's first line of defense against physical and environmental assaults. This study sought to determine how rutin affects the membrane electrical properties, sialic acid content, and lipid peroxidation levels of fibroblast membranes after disruption by ultraviolet (UV) radiation. Changes in cell function may affect the basal electrical surface properties of cell membranes, and changes can be detected by electrokinetic measurements. The charge density of the fibroblast membrane surface was measured as a function of pH. A four-component equilibrium model was used to describe the interaction between ions in solution and ions on the membrane surface. Agreement was found between experimental and theoretical charge variation curves of fibroblast cells between pH 2.5 and 8. Sialic acid content was determined by Svennerholm's resorcinol method, and lipid peroxidation was estimated by measuring the malondialdehyde level. Compared to untreated cells, ultraviolet A (UVA)- or ultraviolet B (UVB)-treated skin cell membranes exhibited higher concentrations of acidic functional groups and higher average association constants with hydroxyl ions, but lower average association constants with hydrogen ions. Moreover, our results showed that UVA and UVB radiation is associated with increased levels of sialic acid and lipid peroxidation products in fibroblasts. Rutin protected cells from some deleterious UV-associated membrane changes, including changes in electrical properties, oxidative state, and biological functions. Copyright © 2018 Elsevier B.V. All rights reserved.

Kinetics of optically excited charge carriers at the GaN surface: Influence of catalytic Pt nanostructures

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

Winnerl, Andrea, E-mail: andrea.winnerl@wsi.tum.de; Pereira, Rui N.; Stutzmann, Martin

2015-10-21

In this work, we use GaN with different deposited Pt nanostructures as a controllable model system to investigate the kinetics of photo-generated charge carriers in hybrid photocatalysts. We combine conductance and contact potential difference measurements to investigate the influence of Pt on the processes involved in the capture and decay of photo-generated charge carriers at and close to the GaN surface. We found that in the presence of Pt nanostructures the photo-excitation processes are similar to those found in Pt free GaN. However, in GaN with Pt nanostructures, photo-generated holes are preferentially trapped in surface states of the GaN coveredmore » with Pt and/or in electronic states of the Pt and lead to an accumulation of positive charge there, whereas negative charge is accumulated in localized states in a shallow defect band of the GaN covered with Pt. This preferential accumulation of photo-generated electrons close to the surface is responsible for a dramatic acceleration of the turn-off charge transfer kinetics and a stronger dependence of the surface photovoltage on light intensity when compared to a Pt free GaN surface. Our study shows that in hybrid photocatalysts, the metal nanostructures induce a spatially inhomogeneous surface band bending of the semiconductor that promotes a lateral drift of photogenerated charges towards the catalytic nanostructures.« less

Mediating electrostatic binding of 1-butyl-3-methylimidazolium chloride to enzyme surfaces improves conformational stability.

PubMed

Nordwald, Erik M; Kaar, Joel L

2013-08-01

We have recently developed a general approach to improve the utility of enzymes in ionic liquids (ILs) via tuning of the ratio of enzyme-containing positive to negative surface charges. In this work, the impact of enzyme surface charge ratio on the biophysical interaction of 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]) with chymotrypsin and lipase was investigated to understand this approach at the molecular level. Results of fluorescence quenching assays indicated that the extent of binding of the [BMIM] cation decreased (7- and 3.5-fold for chymotrypsin and lipase, respectively) as a function of increasing ratio of positive to negative surface charges. Conformational stability assays further showed a close correlation between thermodynamic stabilization and enzyme surface charge ratio as well as [BMIM] binding. As evidence of this correlation, succinylation and acetylation resulted in the stabilization of chymotrypsin in 10% (v/v) [BMIM][Cl] by 17.0 and 6.6 kJ/mol, respectively, while cationization destabilized chymotrypsin by 3.6 kJ/mol. Combined, these results indicate that altering the surface charge ratio mediates the organization of IL molecules, namely, [BMIM] and [Cl], around the enzymes. Preferential exclusion of [Cl], in particular, via lowering of the ratio of positive to negative surface charges, correlated with increased enzyme stability. Accordingly, these results more broadly provide insight into the mechanism of stabilization in ILs via charge modification.

Surface charge sensing by altering the phase transition in VO2

NASA Astrophysics Data System (ADS)

Kumar, S.; Esfandyarpour, R.; Davis, R.; Nishi, Y.

2014-08-01

Detection of surface charges has various applications in medicine, electronics, biotechnology, etc. The source of surface charge induction may range from simple charge-polarized molecules like water to complicated proteins. It was recently discovered that surface charge accumulation can alter the temperature at which VO2 undergoes a Mott transition. Here, we deposited polar molecules onto the surface of two-terminal thin-film VO2 lateral devices and monitored the joule-heating-driven Mott transition, or conductance switching. We observed that the power required to induce the conductance switching reduced upon treatment with polar molecules and, using in-situ blackbody-emission direct measurement of local temperature, we show that this reduction in power was accompanied by reduction in the Mott transition temperature. Further evidence suggested that this effect has specificity to the nature of the species used to induce surface charges. Using x-ray absorption spectroscopy, we also show that there is no detectable change in oxidation state of vanadium or structural phase in the bulk of the 40 nm VO2 thin-film even as the phase transition temperature is reduced by up to 20 K by the polar molecules. The ability to alter the phase transition parameters by depositing polar molecules suggests a potential application in sensing surface charges of different origins and this set of results also highlights interesting aspects of the phase transition in VO2.

Competitive Adsorption of Metals onto Magnetic Graphene Oxide: Comparison with Other Carbonaceous Adsorbents

PubMed Central

Hur, Jin; Shin, Jaewon; Yoo, Jeseung; Seo, Young-Soo

2015-01-01

Competitive adsorption isotherms of Cu(II), Pb(II), and Cd(II) were examined on a magnetic graphene oxide (GO), multiwalled carbon nanotubes (MWCNTs), and powered activated carbon (PAC). A series of analyses confirmed the successful synthesis of the magnetic GO based on a simple ultrasonification method. Irrespective of the adsorbents, the adsorption was highly dependent on pH, and the adsorption was well described by the Langmuir isotherm model. The maximum adsorption capacities of the adsorbents were generally higher in the order of Pb(II) > Cu(II) > Cd(II), which is the same as the degree of the electronegativity and the hydrated radius of the metals, suggesting that the metal adsorption may be governed by an ion exchange between positively charged metals and negatively charged surfaces, as well as diffusion of metals into the surface layer. The adsorption of each metal was mostly lower for multi- versus single-metal systems. The antagonistic effects were influenced by solution pH as well as the type of metals, and they were higher in the order of the magnetic GO > MWCNT > PAC. Dissolved HS played a greater role than HS adsorbed onto the adsorbents, competing with the adsorption sites for metal complexation. PMID:25861683

Photoelectric Emission Measurements on the Analogs of Individual Cosmic Dust Grains

NASA Technical Reports Server (NTRS)

Abbas, M. M.; Tankosic, D.; Craven, P. D.; Spann, J. F.; LeClair, A.; West, E. A.; Weingartner, J. C.; Tielens, A. G. G. M.; Nuth, J. a.; Camata, R. P.

2006-01-01

The photoelectric emission process is considered to be the dominant mechanism for charging of cosmic dust grains in many astrophysical environments. The grain charge and equilibrium potentials play an important role in the dynamical and physical processes that include heating of the neutral gas in the interstellar medium, coagulation processes in the dust clouds, and levitation and dynamical processes in the interplanetary medium and planetary surfaces and rings. An accurate evaluation of photoelectric emission processes requires knowledge of the photoelectric yields of individual dust grains of astrophysical composition as opposed to the values obtained from measurements on flat surfaces of bulk materials, as it is generally assumed on theoretical considerations that the yields for the small grains are much different from the bulk values. We present laboratory measurements of the photoelectric yields of individual dust grains of silica, olivine, and graphite of approx. 0.09-5 micrometer radii levitated in an electrodynamic balance and illuminated with ultraviolet radiation at 120-160 nm wavelengths. The measured yields are found to be substantially higher than the bulk values given in the literature and indicate a size dependence with larger particles having order-of-magnitude higher values than for submicron-size grains.

Heavy metals alter the electrokinetic properties of bacteria, yeasts, and clay minerals.

PubMed Central

Collins, Y E; Stotzky, G

1992-01-01

The electrokinetic patterns of four bacterial species (Bacillus subtilis, Bacillus megaterium, Pseudomonas aeruginosa, and Agrobacterium radiobacter), two yeasts (Saccharomyces cerevisiae and Candida albicans), and two clay minerals (montmorillonite and kaolinite) in the presence of the chloride salts of the heavy metals, Cd, Cr, Cu, Hg, Ni, Pb, and Zn, and of Na and Mg were determined by microelectrophoresis. The cells and kaolinite were net negatively charged at pH values above their isoelectric points (pI) in the presence of Na, Mg, Hg, and Pb at an ionic strength (mu) of 3 x 10(-4); montmorillonite has no pI and was net negatively charged at all pH values in the presence of these metals. However, the charge of some bacteria, S. cerevisiae, and kaolinite changed to a net positive charge (charge reversal) in the presence of Cd, Cr, Cu, Ni, and Zn at pH values above 5.0 (the pH at which charge reversal occurred differed with the metal) and then, at higher pH values, again became negative. The charge of the bacteria and S. cerevisiae also reversed in solutions of Cu and Ni with a mu of greater than 3 x 10(-4), whereas there was no reversal in solutions with a mu of less than 3 x 10(-4). The clays became net positively charged when the mu of Cu was greater than 3 x 10(-4) and that of Ni was greater than 1.5 x 10(-4). The charge of the cells and clays also reversed in solutions containing both Mg and Ni or both Cu and Ni (except montmorillonite) but not in solutions containing both Mg and Cu (except kaolinite) (mu = 3 x 10(-4)). The pIs of the cells in the presence of the heavy metals were at either higher or lower pH values than in the presence of Na and Mg. Exposure of the cells to the various metals at pH values from 2 to 9 for the short times (ca. 10 min) required to measure the electrophoretic mobility did not affect their viability. The specific adsorption on the cells and clays of the hydrolyzed species of some of the heavy metals that formed at higher pH values was probably responsible for the charge reversal. These results suggest that the toxicity of some heavy metals to microorganisms varies with pH because the hydrolyzed speciation forms of these metals, which occur at higher pH values, bind on the cell surface and alter the net charge of the cell.(ABSTRACT TRUNCATED AT 400 WORDS) PMID:1622229

Host-guest chemistry of dendrimer-drug complexes. 2. Effects of molecular properties of guests and surface functionalities of dendrimers.

PubMed

Hu, Jingjing; Cheng, Yiyun; Wu, Qinglin; Zhao, Libo; Xu, Tongwen

2009-08-06

The host-guest chemistry of dendrimer-drug complexes is investigated by NMR techniques, including (1)H NMR and 2D-NOESY studies. The effects of molecular properties of drug molecules (protonation ability and spatial steric hindrance of charged groups) and surface functionalities of dendrimers (positively charged amine groups and negatively charged carboxylate groups) on the host-guest interactions are discussed. Different interaction mechanisms between dendrimers and drug molecules are proposed on the basis of NMR results. Primary amine- and secondary amine-containing drugs preferentially bind to negatively charged dendrimers by strong electrostatic interactions, whereas tertiary amine and quaternary ammonium-containing drugs have weak binding ability with dendrimers due to relatively low protonation ability of the tertiary amine group and serious steric hindrance of the quaternary ammonium group. Positively charged drugs locate only on the surface of negatively charged dendrimers, whereas negatively charged drugs locate both on the surface and in the interior cavities of positively charged dendrimers. The host-guest chemistry of dendrimer-drug complexes is promising for the development of new drug delivery systems.

Effect of surface charge alteration on stability of L-asparaginase II from Escherichia sp.

PubMed

Vidya, Jalaja; Ushasree, Mrudula Vasudevan; Pandey, Ashok

2014-03-05

Escherichia coli L-asparaginases have great significance in the treatment of leukemia. Consequently, there is considerable interest in engineering this enzyme for improving its stability. In this work, the effect of surface charge on the stability of the enzyme l-asparaginase II was studied by site-directed mutagenesis of the cloned ansB gene from Escherichia sp. Replacement of two positively charged residues (K139 and K207) on the surface loops with neutral and reverse charges resulted in altered thermo stability in designed variants. Neutral charge substitutions (K139A and K207A) retained greater tolerance and stability followed by negative charge substitutions (K139D and K207D) compared to control mutant K139R and wild enzyme. From the results, it was concluded that the optimization of surface charge contributed much to the thermal properties of proteins without affecting the structure. Copyright © 2013 Elsevier Inc. All rights reserved.

Analysis of microscopic parameters of surface charging in polymer caused by defocused electron beam irradiation.

PubMed

Liu, Jing; Zhang, Hai-Bo

2014-12-01

The relationship between microscopic parameters and polymer charging caused by defocused electron beam irradiation is investigated using a dynamic scattering-transport model. The dynamic charging process of an irradiated polymer using a defocused 30 keV electron beam is conducted. In this study, the space charge distribution with a 30 keV non-penetrating e-beam is negative and supported by some existing experimental data. The internal potential is negative, but relatively high near the surface, and it decreases to a maximum negative value at z=6 μm and finally tend to 0 at the bottom of film. The leakage current and the surface potential behave similarly, and the secondary electron and leakage currents follow the charging equilibrium condition. The surface potential decreases with increasing beam current density, trap concentration, capture cross section, film thickness and electron-hole recombination rate, but with decreasing electron mobility and electron energy. The total charge density increases with increasing beam current density, trap concentration, capture cross section, film thickness and electron-hole recombination rate, but with decreasing electron mobility and electron energy. This study shows a comprehensive analysis of microscopic factors of surface charging characteristics in an electron-based surface microscopy and analysis. Copyright © 2014 Elsevier Ltd. All rights reserved.

The role of surface charge density in cationic liposome-promoted dendritic cell maturation and vaccine-induced immune responses

NASA Astrophysics Data System (ADS)

Ma, Yifan; Zhuang, Yan; Xie, Xiaofang; Wang, Ce; Wang, Fei; Zhou, Dongmei; Zeng, Jianqiang; Cai, Lintao

2011-05-01

Cationic liposomes have emerged as a novel adjuvant and antigen delivery system to enhance vaccine efficacy. However, the role of surface charge density in cationic liposome-regulated immune responses has not yet been elucidated. In the present study, we prepared a series of DOTAP/DOPC cationic liposomes with different surface densities by incorporating varying amounts of DOPC (a neutral lipid) into DOTAP (a cationic lipid). The results showed that DOTAP/DOPC cationic liposome-regulated immune responses relied on the surface charge density, and might occur through ROS signaling. The liposomes with a relatively high charge density, such as DOTAP/DOPC 5 : 0 and 4 : 1 liposomes, potently enhanced dendritic cell maturation, ROS generaion, antigen uptake, as well as the production of OVA-specific IgG2a and IFN-γ. In contrast, low-charge liposomes, such as DOTAP/DOPC 1 : 4 liposome, failed to promote immune responses even at high concentrations, confirming that the immunoregulatory effect of cationic liposomes is mostly attributable to their surface charge density. Moreover, the DOTAP/DOPC 1 : 4 liposome suppressed anti-OVA antibody responses in vivo. Overall, maintaining an appropriate surface charge is crucial for optimizing the adjuvant effect of cationic liposomes and enhancing the efficacy of liposome-based vaccines.

Effect of plasma-induced surface charging on catalytic processes: application to CO2 activation

NASA Astrophysics Data System (ADS)

Bal, Kristof M.; Huygh, Stijn; Bogaerts, Annemie; Neyts, Erik C.

2018-02-01

Understanding the nature and effect of the multitude of plasma-surface interactions in plasma catalysis is a crucial requirement for further process development and improvement. A particularly intriguing and rather unique property of a plasma-catalytic setup is the ability of the plasma to modify the electronic structure, and hence chemical properties, of the catalyst through charging, i.e. the absorption of excess electrons. In this work, we develop a quantum chemical model based on density functional theory to study excess negative surface charges in a heterogeneous catalyst exposed to a plasma. This method is specifically applied to investigate plasma-catalytic CO2 activation on supported M/Al2O3 (M = Ti, Ni, Cu) single atom catalysts. We find that (1) the presence of a negative surface charge dramatically improves the reductive power of the catalyst, strongly promoting the splitting of CO2 to CO and oxygen, and (2) the relative activity of the investigated transition metals is also changed upon charging, suggesting that controlled surface charging is a powerful additional parameter to tune catalyst activity and selectivity. These results strongly point to plasma-induced surface charging of the catalyst as an important factor contributing to the plasma-catalyst synergistic effects frequently reported for plasma catalysis.

Effect of temperature on anodic behavior of 13Cr martensitic steel in CO2 environment

NASA Astrophysics Data System (ADS)

Zhao, G. X.; Zheng, M.; Lv, X. H.; Dong, X. H.; Li, H. L.

2005-04-01

The corrosion behavior of 13Cr martensitic stainless steel in a CO2 environment in a stimulated oilfield was studied with potentiodynamic polarization and the impedance spectra technique. The results showed that the microstructure of the surface scale clearly changed with temperature. This decreased the sensitivity of pitting corrosion and increased the tendency toward general (or uniform) corrosion. The capacitance, the charge transfer resistance, and the polarization resistance of the corrosion product scale decrease with increasing temperature from 90 to 120 °C, and thus the corrosion is a thermal activation controlled process. Charge transfer through the scale is difficult and the corrosion is controlled by a diffusion process at a temperature of 150 °C. Resistance charge transfer through the corrosion product layer is higher than that in the passive film.

Sorption of lead ions on diatomite and manganese oxides modified diatomite.

PubMed

Al-Degs, Y; Khraisheh, M A; Tutunji, M F

2001-10-01

Naturally occurring diatomaceous earth (diatomite) has been tested as a potential sorbent for Pb(II) ions. The intrinsic exchange properties were further improved by modification with manganese oxides. Modified adsorbent (referred to as Mn-diatomite) showed a higher tendency for adsorbing lead ions from solution at pH 4. The high performance exhibited by Mn-diatomite was attributed to increased surface area and higher negative surface charge after modification. Scanning electron microscope pictures revealed a birnessite structure of manganese oxides, which was featured by a plate-like-crystal structure. Diatomite filtration quality was improved after modification by manganese oxides. Good filtration qualities combined with high exchange capacity emphasised the potential use of Mn-diatomite in filtration systems.

Charge reversal at a planar boundary between two dielectrics.

PubMed

Wang, Zhi-Yong

2016-01-01

Despite the ubiquitous character and relevance of the electric double layer in the entire realm of interface and colloid science, very little is known of the effect that surface heterogeneity exerts on the underlying mechanisms of ion adsorption. Herein, computer simulations offer a perspective that, in sharp contrast to the homogeneously charged surface, discrete groups promote multivalent counterion binding, leading to charge reversal but possibly having not a sign change of the electrophoretic mobility. Counterintuitively, the introduction of dielectric images yields a significantly greater accumulation of counterions, which further facilitates the magnitude of charge reversal. The reported results are very sensitive to both the degree of ion hydration and the representation of surface charges. Our findings shed light on the mechanism for charge reversal over a broad range of coupling regimes operating the adsorption of counterions through surface group bridging attraction with their own images and provide opportunities for experimental studies and theoretical development.

Charge reversal at a planar boundary between two dielectrics

NASA Astrophysics Data System (ADS)

Wang, Zhi-Yong

2016-01-01

Despite the ubiquitous character and relevance of the electric double layer in the entire realm of interface and colloid science, very little is known of the effect that surface heterogeneity exerts on the underlying mechanisms of ion adsorption. Herein, computer simulations offer a perspective that, in sharp contrast to the homogeneously charged surface, discrete groups promote multivalent counterion binding, leading to charge reversal but possibly having not a sign change of the electrophoretic mobility. Counterintuitively, the introduction of dielectric images yields a significantly greater accumulation of counterions, which further facilitates the magnitude of charge reversal. The reported results are very sensitive to both the degree of ion hydration and the representation of surface charges. Our findings shed light on the mechanism for charge reversal over a broad range of coupling regimes operating the adsorption of counterions through surface group bridging attraction with their own images and provide opportunities for experimental studies and theoretical development.

Electrostatic thin film chemical and biological sensor

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

Prelas, Mark A.; Ghosh, Tushar K.; Tompson, Jr., Robert V.

A chemical and biological agent sensor includes an electrostatic thin film supported by a substrate. The film includes an electrostatic charged surface to attract predetermined biological and chemical agents of interest. A charge collector associated with said electrostatic thin film collects charge associated with surface defects in the electrostatic film induced by the predetermined biological and chemical agents of interest. A preferred sensing system includes a charge based deep level transient spectroscopy system to read out charges from the film and match responses to data sets regarding the agents of interest. A method for sensing biological and chemical agents includesmore » providing a thin sensing film having a predetermined electrostatic charge. The film is exposed to an environment suspected of containing the biological and chemical agents. Quantum surface effects on the film are measured. Biological and/or chemical agents can be detected, identified and quantified based on the measured quantum surface effects.« less

Ionic transport through sub-10 nm diameter hydrophobic high-aspect ratio nanopores: experiment, theory and simulation

PubMed Central

Balme, Sébastien; Picaud, Fabien; Manghi, Manoel; Palmeri, John; Bechelany, Mikhael; Cabello-Aguilar, Simon; Abou-Chaaya, Adib; Miele, Philippe; Balanzat, Emmanuel; Janot, Jean Marc

2015-01-01

Fundamental understanding of ionic transport at the nanoscale is essential for developing biosensors based on nanopore technology and new generation high-performance nanofiltration membranes for separation and purification applications. We study here ionic transport through single putatively neutral hydrophobic nanopores with high aspect ratio (of length L = 6 μm with diameters ranging from 1 to 10 nm) and with a well controlled cylindrical geometry. We develop a detailed hybrid mesoscopic theoretical approach for the electrolyte conductivity inside nanopores, which considers explicitly ion advection by electro-osmotic flow and possible flow slip at the pore surface. By fitting the experimental conductance data we show that for nanopore diameters greater than 4 nm a constant weak surface charge density of about 10−2 C m−2 needs to be incorporated in the model to account for conductance plateaus of a few pico-siemens at low salt concentrations. For tighter nanopores, our analysis leads to a higher surface charge density, which can be attributed to a modification of ion solvation structure close to the pore surface, as observed in the molecular dynamics simulations we performed. PMID:26036687

Kinetic analysis of the interaction between poly(amidoamine) dendrimers and model lipid membranes.

PubMed

Tiriveedhi, Venkataswarup; Kitchens, Kelly M; Nevels, Kerrick J; Ghandehari, Hamidreza; Butko, Peter

2011-01-01

We used fluorescence spectroscopy and surface tensiometry to study the interaction between low-generation (G1 and G4) poly(amidoamine) (PAMAM) dendrimers, potential vehicles for intracellular drug delivery, and model lipid bilayers. Membrane association of fluorescently labeled dendrimers, measured by fluorescence anisotropy, increased with increasing size of the dendrimer and with increasing negative charge density in the membrane, indicating the electrostatic nature of the interaction. When the membrane was doped with pyrene-labeled phosphatidyl glycerol (pyrene-PG), pyrene excimer fluorescence demonstrated a dendrimer-induced selective aggregation of negatively charged lipids when the membrane was in the liquid crystalline state. A nonlinear Stern-Volmer quenching of dendrimer fluorescence with cobalt bromide suggested a dendrimer-induced aggregation of lipid vesicles, which increased with the dendrimer's generation number. Surface tensiometry measurements showed that dendrimers penetrated into the lipid monolayer only at subphysiologic surface pressures (<30mN/m). We conclude that the low-generation PAMAM dendrimers associate with lipid membranes predominantly electrostatically, without significantly compromising the bilayer integrity. They bind stronger to membranes with higher fluidity and lower surface pressure, which are characteristic of rapidly dividing cells. Copyright © 2010 Elsevier B.V. All rights reserved.

Effective charge measurements reveal selective and preferential accumulation of anions, but not cations, at the protein surface in dilute salt solutions

PubMed Central

Gokarn, Yatin R; Fesinmeyer, R Matthew; Saluja, Atul; Razinkov, Vladimir; Chase, Susan F; Laue, Thomas M; Brems, David N

2011-01-01

Specific-ion effects are ubiquitous in nature; however, their underlying mechanisms remain elusive. Although Hofmeister-ion effects on proteins are observed at higher (>0.3M) salt concentrations, in dilute (<0.1M) salt solutions nonspecific electrostatic screening is considered to be dominant. Here, using effective charge (Q*) measurements of hen-egg white lysozyme (HEWL) as a direct and differential measure of ion-association, we experimentally show that anions selectively and preferentially accumulate at the protein surface even at low (<100 mM) salt concentrations. At a given ion normality (50 mN), the HEWL Q* was dependent on anion, but not cation (Li+, Na+, K+, Rb+, Cs+, GdnH+, and Ca2+), identity. The Q* decreased in the order F− > Cl− > Br− > NO3− ∼ I− > SCN− > ClO4− ≫ SO42−, demonstrating progressively greater binding of the monovalent anions to HEWL and also show that the SO42− anion, despite being strongly hydrated, interacts directly with the HEWL surface. Under our experimental conditions, we observe a remarkable asymmetry between anions and cations in their interactions with the HEWL surface. PMID:21432935

Anisotropy of the Seebeck Coefficient in the Cuprate Superconductor YBa2 Cu3 Oy : Fermi-Surface Reconstruction by Bidirectional Charge Order

NASA Astrophysics Data System (ADS)

Cyr-Choinière, O.; Badoux, S.; Grissonnanche, G.; Michon, B.; Afshar, S. A. A.; Fortier, S.; LeBoeuf, D.; Graf, D.; Day, J.; Bonn, D. A.; Hardy, W. N.; Liang, R.; Doiron-Leyraud, N.; Taillefer, Louis

2017-07-01

The Seebeck coefficient S of the cuprate YBa2 Cu3 Oy is measured in magnetic fields large enough to suppress superconductivity, at hole dopings p =0.11 and p =0.12 , for heat currents along the a and b directions of the orthorhombic crystal structure. For both directions, S /T decreases and becomes negative at low temperature, a signature that the Fermi surface undergoes a reconstruction due to broken translational symmetry. Above a clear threshold field, a strong new feature appears in Sb, for conduction along the b axis only. We attribute this feature to the onset of 3D-coherent unidirectional charge-density-wave modulations seen by x-ray diffraction, also along the b axis only. Because these modulations have a sharp onset temperature well below the temperature where S /T starts to drop towards negative values, we infer that they are not the cause of Fermi-surface reconstruction. Instead, the reconstruction must be caused by the quasi-2D bidirectional modulations that develop at significantly higher temperature. The unidirectional order only confers an additional anisotropy to the already reconstructed Fermi surface, also manifest as an in-plane anisotropy of the resistivity.

Biochemical Study of Anti-Inflammatory Proteins vCCI and vMIP-II

DTIC Science & Technology

2014-07-17

protein ), where we showed that vCCI is able to bind so many different chemokines due to its general negatively charged surface , allowing it to bind...sample of these competition curves. Our conclusion from the data in Table 1 and Figure 1 is that the negatively charged surface of vCCI allows it to...Similar to our mutagenesis results, the overall data indicate that vCCI uses a negatively charged surface to bind positive charges on the chemokine

SPM observation of nano-dots induced by slow highly charged ions

NASA Astrophysics Data System (ADS)

Nakamura, Nobuyuki; Terada, Masashi; Nakai, Yoichi; Kanai, Yasuyuki; Ohtani, Shunsuke; Komaki, Ken-ichiro; Yamazaki, Yasunori

2005-05-01

We have observed nano-dots on a highly oriented pyrolytic graphite (HOPG) surface produced by highly charged ion impacts with a scanning probe microscope. In order to clarify the role of potential and kinetic energies in surface modification, we have measured the kinetic energy and incident ion charge dependences of the dot size. The results showed that the potential energy or the incident ion charge has strong influence on the surface modification rather than the kinetic energy.

Dolomite surface speciation and reactivity in aquatic systems

NASA Astrophysics Data System (ADS)

Pokrovsky, Oleg S.; Schott, Jacques; Thomas, Fabien

1999-10-01

The surface charge of dolomite (CaMg(CO3)2) was measured as a function of pH (6.5-11.5), pCO2 (10-3.5, 0.01, and 0.96 atm) and ionic strength (0.01, 0.1, and 0.5 M NaCl) using potentiometric titrations in a limited residence time reactor. Dolomite zeta potential (ζ) was determined using streaming potential and electrophoresis techniques at pH 2 to 12 in solutions having ionic strengths from 0.001 to 0.1 M NaCl as a function of aqueous Ca2+, Mg2+, and CO32- concentrations. The point of zero charge (PZC) and isoelectric point (IEP) of dolomite are the same (pH ∼8 at pCO2 ∼10-3.5 atm) and very close to those of calcite and magnesite. On the basis of these results, a surface complexation model (SCM) is proposed that postulates the presence of three distinct primary hydration sites: >CO3H°, >CaOH°, and >MgOH°. The intrinsic stability constants of dolomite surface reactions were determined by fitting the pH dependence of the surface charge and taking into account the isoelectric points and ζ-potential values for a wide range of solution compositions. In most natural aquatic environments, dolomite surface speciation can be modeled using the following species: >CO3-, >CO3Me+, >MeOH2+, >MeHCO3o, and >MeCO3-, where Me = Ca, Mg. The speciation model presented in this study allows description of metal and ligand adsorption onto dolomite surface and provides new insights on the mechanisms that control dolomite dissolution/crystallization in aqueous solutions. In particular, it is shown that dolomite dissolution is controlled by the protonation of >CO3H° surface complexes at pH < 6 and by hydrolysis of >MeOH2+ groups at higher pH.

Electrostatic dust transport on the surfaces of airless bodies

NASA Astrophysics Data System (ADS)

Wang, X.; Schwan, J.; Hsu, H. W.; Horanyi, M.

2015-12-01

The surfaces of airless bodies are charged due to the exposure to solar wind plasma and UV radiation. Dust particles on the regolith of these surfaces can become charged, and may move and even get lofted due to electrostatic force. Electrostatic dust transport has been a long-standing problem that may be related to many observed phenomena on the surfaces of airless planetary bodies, including the lunar horizon glow, the dust ponds on asteroid Eros, the spokes in Saturn's rings, and more recently, the collection of dust particles ejected off Comet 67P, observed by Rosetta. In order to resolve these puzzles, a handful of laboratory experiments have been performed in the past and demonstrated that dust indeed moves and lifts from surfaces exposed to plasma. However, the exact mechanisms for the mobilization of dust particles still remain a mystery. Current charging models, including the so-called "shared charge model" and the charge fluctuation theory, will be discussed. It is found that neither of these models can explain the results from either laboratory experiments or in-situ observations. Recently, single dust trajectories were captured with our new dust experiments, enabling novel micro-scale investigations. The particles' initial launch speeds and size distributions are analyzed, and a new so-called "patched charge model" is proposed to explain our findings. We identify the role of plasma micro-cavities that are formed in-between neighboring dust particles. The emitted secondary or photo- electrons are proposed to be absorbed inside the micro-cavities, resulting in significant charge accumulation on the exposed patches of the surfaces of neighboring particles. The resulting enhanced Coulomb force (repulsion) between particles is likely the dominant force to mobilize and lift them off the surface. The role of other properties, including surface morphology, cohesion and photoelectron charging, will also be discussed.

Understanding the crack formation of graphite particles in cycled commercial lithium-ion batteries by focused ion beam - scanning electron microscopy

NASA Astrophysics Data System (ADS)

Lin, Na; Jia, Zhe; Wang, Zhihui; Zhao, Hui; Ai, Guo; Song, Xiangyun; Bai, Ying; Battaglia, Vincent; Sun, Chengdong; Qiao, Juan; Wu, Kai; Liu, Gao

2017-10-01

The structure degradation of commercial Lithium-ion battery (LIB) graphite anodes with different cycling numbers and charge rates was investigated by focused ion beam (FIB) and scanning electron microscopy (SEM). The cross-section image of graphite anode by FIB milling shows that cracks, resulted in the volume expansion of graphite electrode during long-term cycling, were formed in parallel with the current collector. The crack occurs in the bulk of graphite particles near the lithium insertion surface, which might derive from the stress induced during lithiation and de-lithiation cycles. Subsequently, crack takes place along grain boundaries of the polycrystalline graphite, but only in the direction parallel with the current collector. Furthermore, fast charge graphite electrodes are more prone to form cracks since the tensile strength of graphite is more likely to be surpassed at higher charge rates. Therefore, for LIBs long-term or high charge rate applications, the tensile strength of graphite anode should be taken into account.

Influence of charge and flexibility on smectic phase formation in filamentous virus suspensions

NASA Astrophysics Data System (ADS)

Purdy, Kirstin R.; Fraden, Seth

2007-07-01

We present experimental measurements of the cholesteric-smectic phase transition of suspensions of charged semiflexible rods as a function of rod flexibility and surface charge. The rod particles consist of the bacteriophage M13 and closely related mutants, which are structurally identical to M13, but vary either in contour length and therefore ratio of persistence length to contour length, or surface charge. Surface charge is altered in two ways; by changing solution pH and by comparing M13 with fd virus, a virus which differs from M13 only by the substitution of a single charged amino acid for a neutral one per viral coat protein. Phase diagrams are measured as a function of particle length, particle charge, and ionic strength. The experimental results are compared with existing theoretical predictions for the phase behavior of flexible rods and charged rods.

Influence of radioactivity on surface charging and aggregation kinetics of particles in the atmosphere.

PubMed

Kim, Yong-Ha; Yiacoumi, Sotira; Lee, Ida; McFarlane, Joanna; Tsouris, Costas

2014-01-01

Radioactivity can influence surface interactions, but its effects on particle aggregation kinetics have not been included in transport modeling of radioactive particles. In this research, experimental and theoretical studies have been performed to investigate the influence of radioactivity on surface charging and aggregation kinetics of radioactive particles in the atmosphere. Radioactivity-induced charging mechanisms have been investigated at the microscopic level, and heterogeneous surface potential caused by radioactivity is reported. The radioactivity-induced surface charging is highly influenced by several parameters, such as rate and type of radioactive decay. A population balance model, including interparticle forces, has been employed to study the effects of radioactivity on particle aggregation kinetics in air. It has been found that radioactivity can hinder aggregation of particles because of similar surface charging caused by the decay process. Experimental and theoretical studies provide useful insights into the understanding of transport characteristics of radioactive particles emitted from severe nuclear events, such as the recent accident of Fukushima or deliberate explosions of radiological devices.

The role of charged surface residues in the binding ability of small hubs in protein-protein interaction networks

PubMed Central

Patil, Ashwini; Nakamura, Haruki

2007-01-01

Hubs are highly connected proteins in a protein-protein interaction network. Previous work has implicated disordered domains and high surface charge as the properties significant in the ability of hubs to bind multiple proteins. While conformational flexibility of disordered domains plays an important role in the binding ability of large hubs, high surface charge is the dominant property in small hubs. In this study, we further investigate the role of the high surface charge in the binding ability of small hubs in the absence of disordered domains. Using multipole expansion, we find that the charges are highly distributed over the hub surfaces. Residue enrichment studies show that the charged residues in hubs are more prevalent on the exposed surface, with the exception of Arg, which is predominantly found at the interface, as compared to non-hubs. This suggests that the charged residues act primarily from the exposed surface rather than the interface to affect the binding ability of small hubs. They do this through (i) enhanced intra-molecular electrostatic interactions to lower the desolvation penalty, (ii) indirect long – range intermolecular interactions with charged residues on the partner proteins for better complementarity and electrostatic steering, and (iii) increased solubility for enhanced diffusion-controlled rate of binding. Along with Arg, we also find a high prevalence of polar residues Tyr, Gln and His and the hydrophobic residue Met at the interfaces of hubs, all of which have the ability to form multiple types of interactions, indicating that the interfaces of hubs are optimized to participate in multiple interactions. PMID:27857564

The role of charged surface residues in the binding ability of small hubs in protein-protein interaction networks.

PubMed

Patil, Ashwini; Nakamura, Haruki

2007-01-01

Hubs are highly connected proteins in a protein-protein interaction network. Previous work has implicated disordered domains and high surface charge as the properties significant in the ability of hubs to bind multiple proteins. While conformational flexibility of disordered domains plays an important role in the binding ability of large hubs, high surface charge is the dominant property in small hubs. In this study, we further investigate the role of the high surface charge in the binding ability of small hubs in the absence of disordered domains. Using multipole expansion, we find that the charges are highly distributed over the hub surfaces. Residue enrichment studies show that the charged residues in hubs are more prevalent on the exposed surface, with the exception of Arg, which is predominantly found at the interface, as compared to non-hubs. This suggests that the charged residues act primarily from the exposed surface rather than the interface to affect the binding ability of small hubs. They do this through (i) enhanced intra-molecular electrostatic interactions to lower the desolvation penalty, (ii) indirect long - range intermolecular interactions with charged residues on the partner proteins for better complementarity and electrostatic steering, and (iii) increased solubility for enhanced diffusion-controlled rate of binding. Along with Arg, we also find a high prevalence of polar residues Tyr, Gln and His and the hydrophobic residue Met at the interfaces of hubs, all of which have the ability to form multiple types of interactions, indicating that the interfaces of hubs are optimized to participate in multiple interactions.

Effect of pectin charge density on formation of multilayer films with chitosan.

PubMed

Kamburova, Kamelia; Milkova, Viktoria; Petkanchin, Ivana; Radeva, Tsetska

2008-04-01

The effect of pectin charge density on the formation of multilayer films with chitosan (PEC/CHI) is studied by means of electro-optics. Pectins of low (21%) and high (71%) degrees of esterification, which are inversely proportional to the pectin charge density, are used to form films on colloidal beta-FeOOH particles at pH 4.0 when the CHI is fully ionized. We find that, after deposition of the first 3-4 layers, the film thickness increases linearly with the number of adsorbed layers. However, the increase in the film thickness is larger when the film is terminated with CHI. Irregular increase of the film thickness is more marked for the PEC with higher density of charge. Oscillation in the electrical polarizability of the film-coated particles with the number of deposited layers is also registered in the PEC/CHI films. The charge balance of the multilayers, calculated from electrical polarizability of the film-coated particles, is positive, with larger excess of positive charge within the film constructed from CHI and less charged PEC. This is attributed to the ability of CHI to diffuse into the film at each deposition step. Despite the CHI diffusion, the film thickness increases linearly due to the dissolution of unstable PEC/CHI complexes from the film surface.

The effect of charging rate on the graphite electrode of commercial lithium-ion cells: A post-mortem study

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

Somerville, L.; Bareno, J.; Trask, S.

Increased charging rates negatively affect the lifetime of lithium-ion cells by increasing cell resistance and reducing capacity. This work is a post-mortem study of 18650 cells subjected to charge rates of 0.7-, 2-, 4-, and 6-C. For cells charged at 0.7-C to 4-C, this performance degradation is primarily related to surface film thickness with no observable change in surface film chemical composition. However, at charge rates of 6-C, the chemical composition of the surface film changes significantly, suggesting that this change is the reason for the sharper increase in cell resistance compared to the lower charge rates. In addition, wemore » found that surface film formation was not uniform across the electrode. Surface film was thicker and chemically different along the central band of the electrode “jelly roll”. This result is most likely attributable to an increase in temperature that results from non-uniform electrode wetting during manufacture. As a result, this non-uniform change further resulted in active material delamination from the current collector owing to chemical changes to the binder for the cell charged at 6-C.« less

The effect of charging rate on the graphite electrode of commercial lithium-ion cells: A post-mortem study

DOE PAGES

Somerville, L.; Bareno, J.; Trask, S.; ...

2016-10-22

Increased charging rates negatively affect the lifetime of lithium-ion cells by increasing cell resistance and reducing capacity. This work is a post-mortem study of 18650 cells subjected to charge rates of 0.7-, 2-, 4-, and 6-C. For cells charged at 0.7-C to 4-C, this performance degradation is primarily related to surface film thickness with no observable change in surface film chemical composition. However, at charge rates of 6-C, the chemical composition of the surface film changes significantly, suggesting that this change is the reason for the sharper increase in cell resistance compared to the lower charge rates. In addition, wemore » found that surface film formation was not uniform across the electrode. Surface film was thicker and chemically different along the central band of the electrode “jelly roll”. This result is most likely attributable to an increase in temperature that results from non-uniform electrode wetting during manufacture. As a result, this non-uniform change further resulted in active material delamination from the current collector owing to chemical changes to the binder for the cell charged at 6-C.« less

The role of surface ligands in determining the electronic properties of quantum dot solids and their impact on photovoltaic figure of merits.

PubMed

Goswami, Prasenjit N; Mandal, Debranjan; Rath, Arup K

2018-01-18

Surface chemistry plays a crucial role in determining the electronic properties of quantum dot solids and may well be the key to mitigate loss processes involved in quantum dot solar cells. Surface ligands help to maintain the shape and size of the individual dots in solid films, to preserve the clean energy band gap of the individual particles and to control charge carrier conduction across solid films, in turn regulating their performance in photovoltaic applications. In this report, we show that the changes in size, shape and functional groups of small chain organic ligands enable us to modulate mobility, dielectric constant and carrier doping density of lead sulfide quantum dot solids. Furthermore, we correlate these results with performance, stability and recombination processes in the respective photovoltaic devices. Our results highlight the critical role of surface chemistry in the electronic properties of quantum dots. The role of the size, functionality and the surface coverage of the ligands in determining charge transport properties and the stability of quantum dot solids have been discussed. Our findings, when applied in designing new ligands with higher mobility and improved passivation of quantum dot solids, can have important implications for the development of high-performance quantum dot solar cells.

Intergranular Cracking as a Major Cause of Long-Term Capacity Fading of Layered Cathodes

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

Liu, Hao; Wolf, Mark; Karki, Khim

Capacity fading has limited commercial layered Li-ion battery electrodes to <70% of their theoretical capacity. Higher capacities can be achieved initially by charging to higher voltages, however, these gains are quickly eroded by a faster fade in capacity. In-creasing lifetimes and reversible capacity is contingent on identifying the origin of this capacity fade to inform electrode design and synthesis. We must understand how the battery reactions change following capacity loss after long-term cycling. Using operando X-ray diffraction, we followed the reaction of a LiNi 0.8Co 0.15Al 0.05O 2 (NCA) electrode after months of charge-discharge cycles. Furthermore, the heterogeneous reaction kineticsmore » observed during extended cycles quantitatively explain the capacity loss, which is ultimately attributed to inter-granular fracturing that degrades the connectivity of sub-surface grains within the polycrystalline NCA aggregate.« less

Intergranular Cracking as a Major Cause of Long-Term Capacity Fading of Layered Cathodes

DOE PAGES

Liu, Hao; Wolf, Mark; Karki, Khim; ...

2017-05-26

Capacity fading has limited commercial layered Li-ion battery electrodes to <70% of their theoretical capacity. Higher capacities can be achieved initially by charging to higher voltages, however, these gains are quickly eroded by a faster fade in capacity. In-creasing lifetimes and reversible capacity is contingent on identifying the origin of this capacity fade to inform electrode design and synthesis. We must understand how the battery reactions change following capacity loss after long-term cycling. Using operando X-ray diffraction, we followed the reaction of a LiNi 0.8Co 0.15Al 0.05O 2 (NCA) electrode after months of charge-discharge cycles. Furthermore, the heterogeneous reaction kineticsmore » observed during extended cycles quantitatively explain the capacity loss, which is ultimately attributed to inter-granular fracturing that degrades the connectivity of sub-surface grains within the polycrystalline NCA aggregate.« less

Charge transfer through amino groups-small molecules interface improving the performance of electroluminescent devices

NASA Astrophysics Data System (ADS)

Havare, Ali Kemal; Can, Mustafa; Tozlu, Cem; Kus, Mahmut; Okur, Salih; Demic, Şerafettin; Demirak, Kadir; Kurt, Mustafa; Icli, Sıddık

2016-05-01

A carboxylic group functioned charge transporting was synthesized and self-assembled on an indium tin oxide (ITO) anode. A typical electroluminescent device [modified ITO/TPD (50 nm)/Alq3 (60 nm)/LiF (2 nm)/(120 nm)] was fabricated to investigate the effect of the amino groups-small molecules interface on the characteristics of the device. The increase in the surface work function of ITO is expected to facilitate the hole injection from the ITO anode to the Hole Transport Layer (HTL) in electroluminescence. The modified electroluminescent device could endure a higher current and showed a much higher luminance than the nonmodified one. For the produced electroluminescent devices, the I-V characteristics, optical characterization and quantum yields were performed. The external quantum efficiency of the modified electroluminescent device is improved as the result of the presence of the amino groups-small molecules interface.

Modulating protein adsorption onto hydroxyapatite particles using different amino acid treatments

PubMed Central

Lee, Wing-Hin; Loo, Ching-Yee; Van, Kim Linh; Zavgorodniy, Alexander V.; Rohanizadeh, Ramin

2012-01-01

Hydroxyapatite (HA) is a material of choice for bone grafts owing to its chemical and structural similarities to the mineral phase of hard tissues. The combination of osteogenic proteins with HA materials that carry and deliver the proteins to the bone-defective areas will accelerate bone regeneration. The study investigated the treatment of HA particles with different amino acids such as serine (Ser), asparagine (Asn), aspartic acid (Asp) and arginine (Arg) to enhance the adsorption ability of HA carrier for delivering therapeutic proteins to the body. The crystallinity of HA reduced when amino acids were added during HA preparation. Depending on the types of amino acid, the specific surface area of the amino acid-functionalized HA particles varied from 105 to 149 m2 g–1. Bovine serum albumin (BSA) and lysozyme were used as model proteins for adsorption study. The protein adsorption onto the surface of amino acid-functionalized HA depended on the polarities of HA particles, whereby, compared with lysozyme, BSA demonstrated higher affinity towards positively charged Arg-HA. Alternatively, the binding affinity of lysozyme onto the negatively charged Asp-HA was higher when compared with BSA. The BSA and lysozyme adsorptions onto the amino acid-functionalized HA fitted better into the Freundlich than Langmuir model. The amino acid-functionalized HA particles that had higher protein adsorption demonstrated a lower protein-release rate. PMID:21957116

Two-dimensional porous architecture of protonated GCN and reduced graphene oxide via electrostatic self-assembly strategy for high photocatalytic hydrogen evolution under visible light

NASA Astrophysics Data System (ADS)

Pu, Chenchen; Wan, Jun; Liu, Enzhou; Yin, Yunchao; Li, Juan; Ma, Yongning; Fan, Jun; Hu, Xiaoyun

2017-03-01

Herein, porous protonated graphitic carbon nitride (pGCN) is prepared from bulk g-C3N4 (GCN) directly by acidic cutting and hydrothermal process. The holey structure not only provides a lot of bounds on the accelerated and photo induced charge transfer and thus reduce the aggregation, but also endows the GCN with more exposure to the active site. The pGCN is obtained with an increased band gap of 2.91 eV together with a higher specific surface area of 82.76 m2g-1. Meanwhile, the positively charged GCN resulted from the protonation pretreatment is beneficial for improving the interaction with negatively charged GO sheets. Compared with GCN, pGCN-rGO displays a significant decrease of PL intensities and an apparently enhancement of visible-light absorption, resulting a lower charge recombination rate and a better light absorption. Besides, the enhanced charge separation is demonstrated by photoluminescence emission spectroscopy and the transient photocurrent measurement. The photocatalytic performance studies for the degradation of MB indicate that pGCN-rGO exhibits the highest adsorption ability towards dye molecules. In addition, the pGCN-5 wt% rGO composite shows the optimal photocatalytic activity, the photodegradation rate of MB is 99.4% after 80 min of irradiation and the H2 evolution performance up to 557 μmol g-1h-1 under visible light, which is much higher than the other control samples.

Cell-polymer interactions of fluorescent polystyrene latex particles coated with thermosensitive poly(N-isopropylacrylamide) and poly(N-vinylcaprolactam) or grafted with poly(ethylene oxide)-macromonomer.

PubMed

Vihola, Henna; Marttila, Anna-Kaisa; Pakkanen, Jukka S; Andersson, Mirja; Laukkanen, Antti; Kaukonen, Ann Marie; Tenhu, Heikki; Hirvonen, Jouni

2007-10-01

Cell-polymer interactions of thermosensitive poly(N-isopropylacrylamide) (PNIPAM) or poly(N-vinylcaprolactam) (PVCL) coated particles with RAW264.7 macrophages and intestinal Caco-2 cells were evaluated. Nanosized particles were prepared by modifying the surface of fluorescent polystyrene (FPS) particles with the thermosensitive polymer gels or with poly(ethylene oxide) (PEO)-macromonomer grafts. The particles were characterized by IR-spectroscopy for functional groups, light scattering for size distribution and zeta-potential for surface charge. Effects of temperature and polymer coating/grafting on the cellular interactions were evaluated by cell association/uptake and visualized by confocal scanning microscope. PEO and PNIPAM inhibited the polymer-cell contact by steric repulsion, evidenced by weak attachment of the particles. PVCL-coated FPS was adsorbed on the cells more strongly, especially at 37 degrees C, because of more hydrophobic nature at higher temperatures. The results suggest feasibility of the PNIPAM and PVCL for biotechnological/pharmaceutical applications, as the cell-particle interactions may be modified by size, surface charge, hydrophobicity, steric repulsion and temperature.

Deionization shocks in microstructures

NASA Astrophysics Data System (ADS)

Mani, Ali; Bazant, Martin Z.

2011-12-01

Salt transport in bulk electrolytes is limited by diffusion and advection, but in microstructures with charged surfaces (e.g., microfluidic devices, porous media, soils, or biological tissues) surface conduction and electro-osmotic flow also contribute to ionic fluxes. For small applied voltages, these effects lead to well known linear electrokinetic phenomena. In this paper, we predict some surprising nonlinear dynamics that can result from the competition between bulk and interfacial transport at higher voltages. When counterions are selectively removed by a membrane or electrode, a “deionization shock” can propagate through the microstructure, leaving in its wake an ultrapure solution, nearly devoid of coions and colloidal impurities. We elucidate the basic physics of deionization shocks and develop a mathematical theory of their existence, structure, and stability, allowing for slow variations in surface charge or channel geometry. Via asymptotic approximations and similarity solutions, we show that deionization shocks accelerate and sharpen in narrowing channels, while they decelerate and weaken, and sometimes disappear, in widening channels. These phenomena may find applications in separations (deionization, decontamination, biological assays) and energy storage (batteries, supercapacitors) involving electrolytes in microstructures.

Hydroxynaphthoquinone ultrathin films obtained by diazonium electroreduction: toward design of biosensitive electroactive interfaces.

PubMed

March, Gregory; Reisberg, Steeve; Piro, Benoit; Pham, Minh-Chau; Fave, Claire; Noel, Vincent

2010-05-01

Electroactive 2-(phenylsulfanyl)-8-hydroxy-1,4-naphthoquinone has been electrodeposited via the reduction of the corresponding diazonium salt on Au electrodes. Surface characterizations by X-ray photoelectron spectroscopy (XPS) and infrared reflection-absorption spectroscopy (IRRAS) reveal that the mechanism of film deposition follows an aryl radical formation and its immobilization on the electrode surface. Electrochemical study shows that the surface coverage can be finely tuned (thickness between one and four layers) by adjusting the potential and the deposition time. By managing the potential applied when reducing diazonium in potentiostatic mode, the formed layer could mediate or not charge transfer. This is the first time that the films obtained by diazonium process are demonstrated to act as mediators in the growth process. Hence, with potentials higher than the formal potential of quinone group, very thin and homogeneous layers are obtained, whereas thicker films are formed when more cathodic potentials than that of quinone are applied. The possibility to manage the charge-transfer kinetics, the thickness, and the homogeneity of electroactive deposits is interesting in the scope of designing electrochemical transducers.

High-efficient photo-electron transport channel in SiC constructed by depositing cocatalysts selectively on specific surface sites for visible-light H{sub 2} production

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

Wang, Da; Peng, Yuan; Wang, Qi

2016-04-18

Control cocatalyst location on a metal-free semiconductor to promote surface charge transfer for decreasing the electron-hole recombination is crucial for enhancing solar energy conversion. Based on the findings that some metals have an affinity for bonding with the specific atoms of polar semiconductors at a heterostructure interface, we herein control Pt deposition selectively on the Si sites of a micro-SiC photocatalyst surface via in-situ photo-depositing. The Pt-Si bond forming on the interface constructs an excellent channel, which is responsible for accelerating photo-electron transfer from SiC to Pt and then reducing water under visible-light. The hydrogen production is enhanced by twomore » orders of magnitude higher than that of bare SiC, and 2.5 times higher than that of random-depositing nano-Pt with the same loading amount.« less

[Sorption of microorganisms by fiber materials].

PubMed

Nikovskaia, G N; Gordienko, A S; Globa, L I

1986-01-01

Candida guilliermondii and Escherichia coli cells were adsorbed on glass and basalt fibres with a similar specific surface, but with a different charge. The quantity of adsorbed microorganisms did not depend on the type and charge of a fibre surface. However, cells were adsorbed faster and more firmly on positively charged and uncharged fibres than on negatively charged fibres.

Charge collection kinetics on ferroelectric polymer surface using charge gradient microscopy

DOE PAGES

Choi, Yoon-Young; Tong, Sheng; Ducharme, Stephen P.; ...

2016-05-03

Here, a charge gradient microscopy (CGM) probe was used to collect surface screening charges on poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] thin films. These charges are naturally formed on unscreened ferroelectric domains in ambient condition. The CGM data were used to map the local electric current originating from the collected surface charges on the poled ferroelectric domains in the P(VDF-TrFE) thin films. Both the direction and amount of the collected current were controlled by changing the polarity and area of the poled domains. The endurance of charge collection by rubbing the CGM tip on the polymer film was limited to 20 scan cycles,more » after which the current reduced to almost zero. This degradation was attributed to the increase of the chemical bonding strength between the external screening charges and the polarization charges. Once this degradation mechanism is mitigated, the CGM technique can be applied to efficient energy harvesting devices using polymer ferroelectrics.« less

Surface Assisted Transient Displacement Charge Technique. II. Effect of Gases on Photoinduced Charge Transfer in Self-Assembled Monolayers

PubMed Central

Krasnoslobodtsev, Alexey V.; Smirnov, Sergei N.

2008-01-01

Surface assisted photoinduced transient displacement charge (SPTDC) technique was used to study charge transfer in self-assembled monolayers of 7-diethylaminocoumarin covalently linked to oxide surface in atmosphere of different gases. The dipole signal was found to be opposite to that in solution and dependent on the nature of gas and its pressure. The results were explained by collision-induced relaxation that impedes uninhibited tilting of molecules onto the surface. Collisions with paramagnetic oxygen induce intersystem crossing to long-lived triplet dipolar states of coumarin with the rate close to the half of that for the collision rate. PMID:16956285

Evaluation of molecular dynamics simulation methods for ionic liquid electric double layers.

PubMed

Haskins, Justin B; Lawson, John W

2016-05-14

We investigate how systematically increasing the accuracy of various molecular dynamics modeling techniques influences the structure and capacitance of ionic liquid electric double layers (EDLs). The techniques probed concern long-range electrostatic interactions, electrode charging (constant charge versus constant potential conditions), and electrolyte polarizability. Our simulations are performed on a quasi-two-dimensional, or slab-like, model capacitor, which is composed of a polarizable ionic liquid electrolyte, [EMIM][BF4], interfaced between two graphite electrodes. To ensure an accurate representation of EDL differential capacitance, we derive new fluctuation formulas that resolve the differential capacitance as a function of electrode charge or electrode potential. The magnitude of differential capacitance shows sensitivity to different long-range electrostatic summation techniques, while the shape of differential capacitance is affected by charging technique and the polarizability of the electrolyte. For long-range summation techniques, errors in magnitude can be mitigated by employing two-dimensional or corrected three dimensional electrostatic summations, which led to electric fields that conform to those of a classical electrostatic parallel plate capacitor. With respect to charging, the changes in shape are a result of ions in the Stern layer (i.e., ions at the electrode surface) having a higher electrostatic affinity to constant potential electrodes than to constant charge electrodes. For electrolyte polarizability, shape changes originate from induced dipoles that soften the interaction of Stern layer ions with the electrode. The softening is traced to ion correlations vertical to the electrode surface that induce dipoles that oppose double layer formation. In general, our analysis indicates an accuracy dependent differential capacitance profile that transitions from the characteristic camel shape with coarser representations to a more diffuse profile with finer representations.

Role of Surface Charge Density in Nanoparticle-templated Assembly of Bromovirus Protein Cages

PubMed Central

Daniel, Marie-Christine; Tsvetkova, Irina B.; Quinkert, Zachary T.; Murali, Ayaluru; De, Mrinmoy; Rotello, Vincent M.; Kao, C. Cheng; Dragnea, Bogdan

2010-01-01

Self-assembling icosahedral protein cages have potencially useful physical and chemical characteristics for a variety of nanotechnology applications, ranging from therapeutic or diagnostic vectors to building blocks for hierarchical materials. For application-specific functional control of protein cage assemblies, a deeper understanding of the interaction between the protein cage and its payload is necessary. Protein-cage encapsulated nanoparticles, with their well-defined surface chemistry, allow for systematic control over key parameters of encapsulation such as the surface charge, hydrophobicity, and size. Independent control over these variables allows experimental testing of different assembly mechanism models. Previous studies done with Brome mosaic virus capsids and negatively-charged gold nanoparticles indicated that the result of the self-assembly process depends on the diameter of the particle. However, in these experiments, the surface-ligand density was maintained at saturation levels, while the total charge and the radius of curvature remained coupled variables, making the interpretation of the observed dependence on the core size difficult. The current work furnishes evidence of a critical surface charge density for assembly through an analysis aimed at decoupling the surface charge the core size. PMID:20575505

Charge Generation and Propagation in Igneous Rocks

NASA Technical Reports Server (NTRS)

Freund, Friedemann

2002-01-01

Various electrical phenomena have been reported prior to or concurrent with earthquakes such as resistivity changes, ground potentials, electromagnetic (EM), and luminous signals. Doubts have been raised as to whether some of these phenomena are real and indeed precursory. One of the reasons for uncertainty is that, despite decades of intense work, there is still no physically coherent model. Using low- to medium-velocity impacts to measure electrical signals with microsecond time resolution, it has now been observed that when dry gabbro and diorite cores are impacted at relatively low velocities, approximately 100 m/s, highly mobile charge carriers are generated in a small volume near the impact point. They spread through the rocks, causing electric potentials exceeding +400 mV, EM, and light emission. As the charge cloud spreads, the rock becomes momentarily conductive. When a dry granite block is impacted at higher velocity, approximately 1.5 km/s, the propagation of the P and S waves is registered through the transient piezoelectric response of quartz. After the sound waves have passed, the surface of the granite block becomes positively charged, suggesting the same charge carriers as observed during the low-velocity impact experiments, expanding from within the bulk. During the next 2-3 ms the surface potential oscillates, indicating pulses of electrons injected from ground and contact electrodes. The observations are consistent with positive holes, e.g., defect electrons in the O(2-) sublattice, traveling via the O 2p-dominated valence band of the silicate minerals. Before activation, the positive holes lay dormant in the form of electrically inactive positive hole pairs (PHP), chemically equivalent to peroxy links, O3X/OO\\XO3, with X=Si(4+), Al(3+), etc. PHPs are introduced into the minerals by way of hydroxyl,O3X-OH, which all nominally anhydrous minerals incorporate when crystallizing in H2O-laden environments. The fact that positive holes can be activated by low-energy impacts, and their attendant sound waves, suggests that they can also be activated by microfracturing. Depending on where in the stressed rock volume the charge carriers are activated, they will form rapidly moving or fluctuating charge clouds that may account for earthquake-related electrical signals and EM emission. Wherever such charge clouds intersect the surface, high fields are expected, causing electric discharges and earthquake lights.

Ligand-dependent exciton dynamics and photovoltaic properties of PbS quantum dot heterojunction solar cells.

PubMed

Chang, Jin; Ogomi, Yuhei; Ding, Chao; Zhang, Yao Hong; Toyoda, Taro; Hayase, Shuzi; Katayama, Kenji; Shen, Qing

2017-03-01

The surface chemistry of colloidal quantum dots (QDs) plays an important role in determining the photoelectric properties of QD films and the corresponding quantum dot heterojunction solar cells (QDHSCs). To investigate the effects of the ligand structure on the photovoltaic performance and exciton dynamics of QDHSCs, PbS QDHSCs were fabricated by the solid state ligand exchange method with mercaptoalkanoic acid as the cross-linking ligand. Temperature-dependent photoluminescence and ultrafast transient absorption spectra show that the electronic coupling and charge transfer rate within QD ensembles were monotonically enhanced as the ligand length decreased. However, in practical QDHSCs, the second shortest ligand 3-mercaptopropionic acid (MPA) showed higher power conversion efficiency than the shortest ligand thioglycolic acid (TGA). This could be attributed to the difference in their surface trap states, supported by thermally stimulated current measurements. Moreover, compared with the non-conjugated ligand MPA, the conjugated ligand 4-mercaptobenzoic acid (MBA) introduces less trap states and has a similar charge transfer rate in QD ensembles, but has poor photovoltaic properties. This unexpected result could be contributed by the QD-ligand orbital mixing, leading to the charge transfer from QDs to ligands instead of charge transfer between adjacent QDs. This work highlights the significant effects of ligand structures on the photovoltaic properties and exciton dynamics of QDHSCs, which would shed light on the further development of QD-based photoelectric devices.

Improvement of Ion/Ioff for h-BN encapsulated bilayer graphene by graphite local back gate electrode

NASA Astrophysics Data System (ADS)

Uwanno, Teerayut; Taniguchi, Takashi; Watanabe, Kenji; Nagashio, Kosuke

The critical issue for bilayer graphene (BLG) devices is low Ion/Ioff even at the band gap of 0.3eV. Band gap in BLG can be formed by creating potential difference between the two layers of BLG. This can be done by applying external electric field perpendicularly to BLG to induce different carrier densities in the two layers. Due to such origin, the spatial uniformity of band gap in the channel is quite sensitive to charge inhomogeneity in BLG. In order to apply electric field of 3V/nm to open the maximum band gap of 0.3eV, high- k gate stack has been utilized so far. However, oxide dielectrics usually have large charge inhomogeneity causing in-plane potential fluctuation in BLG channel. Due to surface flatness and small charge inhomogeneity, h-BN has been used as dielectrics to achieve high quality graphene devices, however, Ion/Iofffor BLG/ h-BN heterostuctures has not been reported yet. In this study, we used graphite as local back gate electrode to BLG encapsulated with h-BN. This resulted in much higher Ion/Ioff, indicating the importance of screening of charge inhomogeneity from SiO2 substrate surface by local graphite back gate electrode. This research was partly supported by JSPS Core-to-Core Program, A. Advanced Research Networks.

Adsorption and removal of phthalic acid and diethyl phthalate from water with zeolitic imidazolate and metal-organic frameworks.

PubMed

Khan, Nazmul Abedin; Jung, Beom K; Hasan, Zubair; Jhung, Sung Hwa

2015-01-23

ZIF-8 (zinc-methylimidazolate framework-8), one of the zeolitic imidazolate frameworks (ZIFs), has been used for the removal of phthalic acid (H2-PA) and diethyl phthalate (DEP) from aqueous solutions via adsorption. The adsorption capacity of the ZIF-8 for H2-PA was much higher than that of a commercial activated carbon or other typical metal-organic frameworks (MOFs). Because the surface area and pore volume of the adsorbents showed no favorable effect on the adsorption of H2-PA, the remarkable adsorption with ZIF-8 suggests a specific favorable interaction (electrostatic interaction) between the positively charged surface of ZIF-8 and the negatively charged PA anions. In addition, acid-base interactions also have a favorable contribution in the adsorption of H2-PA, based on the adsorptive performances of pristine and amino-functionalized MOFs and adsorption over ZIF-8 at acidic condition (pH=3.5). The reusability of ZIF-8 was also demonstrated after simple washing with methanol. On the other hand, ZIF-8 was not effective in adsorbing DEP probably because of little charge of DEP in a water solution. Copyright © 2014 Elsevier B.V. All rights reserved.

Role of LiCoO 2 Surface Terminations in Oxygen Reduction and Evolution Kinetics

DOE PAGES

Han, Binghong; Qian, Danna; Risch, Marcel; ...

2015-03-22

Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities of LiCoO 2 nanorods with sizes in the range from 9 to 40 nm were studied in alkaline solution. The sides of these nanorods were terminated with low-index surfaces such as (003) while the tips were terminated largely with high-index surfaces such as (104) as revealed by high-resolution transmission electron microscopy. Electron energy loss spectroscopy demonstrated that low-spin Co 3+ prevailed on the sides, while the tips exhibited predominantly high- or intermediate-spin Co 3+. We correlated the electronic and atomic structure to higher specific ORR and OER activities at themore » tips as compared to the sides, which was accompanied by more facile redox of Co 2+/3+ and higher charge transferred per unit area. These findings highlight the critical role of surface terminations and electronic structures of transition metal oxides on the ORR and OER activity.« less

Bioinspired assembly of surface-roughened nanoplatelets.

PubMed

Lin, Tzung-Hua; Huang, Wei-Han; Jun, In-Kook; Jiang, Peng

2010-04-15

Here we report a novel electrophoretic deposition technology for assembling surface-roughened inorganic nanoplatelets into ordered multilayers that mimic the brick-and-mortar nanostructure found in the nacreous layer of mollusk shells. A thin layer of sol-gel silica is coated on smooth gibbsite nanoplatelets in order to increase the surface roughness to mimic the asperity of aragonite platelets found in nacres. To avoid the severe cracking caused by the shrinkage of sol-gel silica during drying, polyelectrolyte polyethyleneimine is used to reverse the surface charge of silica-coated-gibbsite nanoplatelets and increase the adherence and strength of the electrodeposited films. Polymer nanocomposites can then be made by infiltrating the interstitials of the aligned nanoplatelet multilayers with photocurable monomer followed by photopolymerization. The resulting self-standing films are highly transparent and exhibit nearly three times higher tensile strength and one-order-of-magnitude higher toughness than those of pure polymer. The measured tensile strength agrees with that predicted by a simple shear lag model. Published by Elsevier Inc.

In Vitro Biocompatibility of Si Alloyed Multi-Principal Element Carbide Coatings

PubMed Central

Vladescu, Alina; Titorencu, Irina; Dekhtyar, Yuri; Jinga, Victor; Pruna, Vasile; Balaceanu, Mihai; Dinu, Mihaela; Pana, Iulian; Vendina, Viktorija

2016-01-01

In the current study, we have examined the possibility to improve the biocompatibility of the (TiZrNbTaHf)C through replacement of either Ti or Ta by Si. The coatings were deposited on Si and 316L stainless steel substrates by magnetron sputtering in an Ar+CH4 mixed atmosphere and were examined for elemental composition, chemical bonds, surface topography, surface electrical charge and biocompatible characteristics. The net surface charge was evaluated at nano and macroscopic scale by measuring the electrical potential and work function, respectively. The biocompatible tests comprised determination of cell viability and cell attachment to the coated surface. The deposited coatings had C/(metal+Si) ratios close to unity, while a mixture of metallic carbide, free-carbon and oxidized species formed on the film surface. The coatings’ surfaces were smooth and no influence of surface roughness on electrical charge or biocompatibility was found. The biocompatible characteristics correlated well with the electrical potential/work function, suggesting a significant role of surface charge in improving biocompatibility, particularly cell attachment to coating's surface. Replacement of either Ti or Ta by Si in the (TiZrNbTaHf)C coating led to an enhanced surface electrical charge, as well as to superior biocompatible properties, with best results for the (TiZrNbSiHf)C coating. PMID:27571361

Removing adsorbed heavy metal ions from sand surfaces via applying interfacial properties of rhamnolipid.

PubMed

Haryanto, Bode; Chang, Chien-Hsiang

2015-01-01

In this study, the interfacial properties of biosurfactant rhamnolipid were investigated and were applied to remove adsorbed heavy metal ions from sand surfaces with flushing operations. The surface tension-lowering activity, micelle charge characteristic, and foaming ability of rhamnolipid were identified first. For rhamnolipid in water, the negatively charged characteristic of micelles or aggregates was confirmed and the foaming ability at concentrations higher than 40 mg/L was evaluated. By using the rhamnolipid solutions in a batch washing approach, the potential of applying the interfacial properties of rhamnolipid to remove adsorbed copper ions from sand surfaces was then demonstrated. In rhamnolipid solution flushing operations for sand-packed medium, higher efficiency was found for the removal of adsorbed copper ions with residual type than with inner-sphere interaction type, implying the important role of interaction type between the copper ion and the sand surface in the removal efficiency. In addition, the channeling effect of rhamnolipid solution flow in the sand-packed medium was clearly observed in the solution flushing operations and was responsible for the low removal efficiency with low contact areas between solution and sand. By using rhamnolipid solution with foam to flush the sand-packed medium, one could find that the channeling effect of the solution flow was reduced and became less pronounced with the increase in the rhamnolipid concentration, or with the enhanced foaming ability. With the reduced channeling effect in the flushing operations, the removal efficiency for adsorbed copper ions was significantly improved. The results suggested that the foam-enhanced rhamnolipid solution flushing operation was efficient in terms of surfactant usage and operation time.

Measurements of the Martian Gamma/Neutron Spectra with MSL/RAD

NASA Astrophysics Data System (ADS)

Kohler, J.; Zeitlin, C. J.; Ehresmann, B.; Wimmer-Schweingruber, R. F.; Hassler, D.; Reitz, G.; Brinza, D.; Weigle, E.; Boettcher, S.; Burmeister, S.; Guo, J.; Martin-Garcia, C.; Boehm, E.; Posner, A.; Rafkin, S. C.; Kortmann, O.

2013-12-01

The Radiation Assessment Detector (RAD) onboard Mars Science Laboratory's rover curiosity measures the energetic charged and neutral particle spectra and the radiation dose rate on the Martian surface. An important factor for determining the biological impact of the Martian surface radiation is the specific contribution of neutrons, which possess a high biological effectiveness. In contrast to charged particles, neutrons and gamma rays are generally only measured indirectly. Their measurement is the result of a complex convolution of the incident particle spectrum with the measurement process. We apply an inversion method to calculate the gamma/neutron spectra from the RAD neutral particle measurements. Here we show first measurements of the Martian gamma/neutron spectra and compare them to theoretical predictions. We find that the shape of the gamma spectrum is very similar to the predicted one, but with a ~50% higher intensity. The measured neutron spectrum agrees well with prediction up to ~100 MeV, but shows a considerably increased intensity for higher energies. The measured neutron spectrum translates into a radiation dose rate of 25 μGy/day and a dose equivalent rate of 106 μSv/day. This corresponds to 10% of the total surface dose rate, and 15% of the biological relevant surface dose equivalent rate on Mars. Measuring the Martian neutron spectra is an essential step for determining the mutagenic influences to past or present life at or beneath the Martian surface as well as the radiation hazard for future human exploration, including the shielding design of a potential habitat. The contribution of neutrons to the dose equivalent increases considerably with shielding thickness, so our measurements provide an important figure to mitigate cancer risk.

Enhanced flashover strength in polyethylene nanodielectrics by secondary electron emission modification

NASA Astrophysics Data System (ADS)

Wang, Weiwang; Li, Shengtao; Min, Daomin

2016-04-01

This work studies the correlation between secondary electron emission (SEE) characteristics and impulse surface flashover in polyethylene nanodielectrics both theoretically and experimentally, and illustrates the enhancement of flashover voltage in low-density polyethylene (LDPE) through incorporating Al2O3 nanoparticles. SEE characteristics play key roles in surface charging and gas desorption during surface flashover. This work demonstrates that the presence of Al2O3 nanoparticles decreases the SEE coefficient of LDPE and enhances the impact energy at the equilibrium state of surface charging. These changes can be explained by the increase of surface roughness and of surface ionization energy, and the strong interaction between nanoparticles and the polymer dielectric matrix. The surface charge and flashover voltage are calculated according to the secondary electron emission avalanche (SEEA) model, which reveals that the positive surface charges are reduced near the cathode triple point, while the presence of more nanoparticles in high loading samples enhances the gas desorption. Consequently, the surface flashover performance of LDPE/Al2O3 nanodielectrics is improved.

Effects of O 2 and N 2/H 2 plasma treatments on the neuronal cell growth on single-walled carbon nanotube paper scaffolds

NASA Astrophysics Data System (ADS)

Yoon, Ok Ja; Lee, Hyun Jung; Jang, Yeong Mi; Kim, Hyun Woo; Lee, Won Bok; Kim, Sung Su; Lee, Nae-Eung

2011-08-01

The O 2 and N 2/H 2 plasma treatments of single-walled carbon nanotube (SWCNT) papers as scaffolds for enhanced neuronal cell growth were conducted to functionalize their surfaces with different functional groups and to roughen their surfaces. To evaluate the effects of the surface roughness and functionalization modifications of the SWCNT papers, we investigated the neuronal morphology, mitochondrial membrane potential, and acetylcholine/acetylcholinesterase levels of human neuroblastoma during SH-SY5Y cell growth on the treated SWCNT papers. Our results demonstrated that the plasma-chemical functionalization caused changes in the surface charge states with functional groups with negative and positive charges and then the increased surface roughness enhanced neuronal cell adhesion, mitochondrial membrane potential, and the level of neurotransmitter in vitro. The cell adhesion and mitochondrial membrane potential on the negatively charged SWCNT papers were improved more than on the positively charged SWCNT papers. Also, measurements of the neurotransmitter level showed an enhanced acetylcholine level on the negatively charged SWCNT papers compared to the positively charged SWCNT papers.

Proton transfer to charged platinum electrodes. A molecular dynamics trajectory study.

PubMed

Wilhelm, Florian; Schmickler, Wolfgang; Spohr, Eckhard

2010-05-05

A recently developed empirical valence bond (EVB) model for proton transfer on Pt(111) electrodes (Wilhelm et al 2008 J. Phys. Chem. C 112 10814) has been applied in molecular dynamics (MD) simulations of a water film in contact with a charged Pt surface. A total of seven negative surface charge densities σ between -7.5 and -18.9 µC cm(-2) were investigated. For each value of σ, between 30 and 84 initial conditions of a solvated proton within a water slab were sampled, and the trajectories were integrated until discharge of a proton occurred on the charged surfaces. We have calculated the mean rates for discharge and for adsorption of solvated protons within the adsorbed water layer in contact with the metal electrode as a function of surface charge density. For the less negative values of σ we observe a Tafel-like exponential increase of discharge rate with decreasing σ. At the more negative values this exponential increase levels off and the discharge process is apparently transport limited. Mechanistically, the Tafel regime corresponds to a stepwise proton transfer: first, a proton is transferred from the bulk into the contact water layer, which is followed by transfer of a proton to the charged surface and concomitant discharge. At the more negative surface charge densities the proton transfer into the contact water layer and the transfer of another proton to the surface and its discharge occur almost simultaneously.

Adsorption of DNA to mica mediated by divalent counterions: a theoretical and experimental study.

PubMed

Pastré, David; Piétrement, Olivier; Fusil, Stéphane; Landousy, Fabrice; Jeusset, Josette; David, Marie-Odile; Hamon, Loïc; Le Cam, Eric; Zozime, Alain

2003-10-01

The adsorption of DNA molecules onto a flat mica surface is a necessary step to perform atomic force microscopy studies of DNA conformation and observe DNA-protein interactions in physiological environment. However, the phenomenon that pulls DNA molecules onto the surface is still not understood. This is a crucial issue because the DNA/surface interactions could affect the DNA biological functions. In this paper we develop a model that can explain the mechanism of the DNA adsorption onto mica. This model suggests that DNA attraction is due to the sharing of the DNA and mica counterions. The correlations between divalent counterions on both the negatively charged DNA and the mica surface can generate a net attraction force whereas the correlations between monovalent counterions are ineffective in the DNA attraction. DNA binding is then dependent on the fractional surface densities of the divalent and monovalent cations, which can compete for the mica surface and DNA neutralizations. In addition, the attraction can be enhanced when the mica has been pretreated by transition metal cations (Ni(2+), Zn(2+)). Mica pretreatment simultaneously enhances the DNA attraction and reduces the repulsive contribution due to the electrical double-layer force. We also perform end-to-end distance measurement of DNA chains to study the binding strength. The DNA binding strength appears to be constant for a fixed fractional surface density of the divalent cations at low ionic strength (I < 0.1 M) as predicted by the model. However, at higher ionic strength, the binding is weakened by the screening effect of the ions. Then, some equations were derived to describe the binding of a polyelectrolyte onto a charged surface. The electrostatic attraction due to the sharing of counterions is particularly effective if the polyelectrolyte and the surface have nearly the same surface charge density. This characteristic of the attraction force can explain the success of mica for performing single DNA molecule observation by AFM. In addition, we explain how a reversible binding of the DNA molecules can be obtained with a pretreated mica surface.

Performance evaluation of different diamond-like carbon samples as charge state conversion surfaces for neutral atom imaging detectors in space applications

NASA Astrophysics Data System (ADS)

Brigitte Neuland, Maike; Allenbach, Marc; Föhn, Martina; Wurz, Peter

2017-04-01

The detection of energetic neutral atoms is a substantial requirement on every space mission mapping particle populations of a planetary magnetosphere or plasma of the interstellar medium. For imaging neutrals, these first have to be ionised. Regarding the constraints of weight, volume and power consumption, the technique of surface ionisation complies with all specifications of a space mission. Particularly low energy neutral atoms, which cannot be ionised by passing through a foil, are ionised by scattering on a charge state conversion surface [1]. Since more than 30 years intense research work is done to find and optimise suitable materials for use as charge state conversion surfaces for space application. Crucial parameters are the ionisation efficiency of the surface material and the scattering properties. Regarding these parameters, diamond-like carbon was proven advantageously: While efficiently ionising incoming neutral atoms, diamond stands out by its durability and chemical inertness [2]. In the IBEX-Lo sensor, a diamond-like carbon surface is used for ionisation of neutral atoms. Building on the successes of the IBEX mission [3], the follow up mission IMAP (InterstellarMApping Probe) will take up to further explore the boundaries of the heliosphere. The IMAP mission is planned to map neutral atoms in a larger energy range and with a distinct better angular resolution and sensitivity than IBEX [4]. The aspired performance of the IMAP sensors implies also for charge state conversion surfaces with improved characteristics. We investigated samples of diamond-like carbon, manufactured by the chemical vapour deposition (CVD) method, regarding their ionisation efficiency, scattering and reflexion properties. Experiments were carried out at the ILENA facility at the University of Bern [5] with hydrogen and oxygen atoms, which are the species of main interest in magnetospheric research [1]. We compare the results of earlier investigations of a metallised CVD sample [6] to our latest measurements of a Boron-doped CVD diamond sample. We additionally measured the B-concentration in the sample to prove our predictions of the B-concentration needed to reach sufficient conductibility for the sample not getting electrostatically charged during instrument operation. The results of narrower scattering cones and higher ionisation efficiency show that diamond-like carbon still is the preferred material for charge state conversion surfaces and that new surface technologies offer improved diamond conversion surfaces with different properties and hence the possibility for improvement of the performance of neutral atom imaging instruments. References: [1] P. Wurz, Detection of Energetic Neutral Atoms, in The Outer Heliosphere: Beyond the Planets, Copernicus Gesellschaft e.V., Katlenburg-Lindau, Germany, 2000, p. 251-288. [2] P. Wurz, R. Schletti, M.R. Aellig, Surf. Sci. 373(1997), 56-66. [3] D.J. McComas et al., Geophys. Res. Lett. 38(2011), L18101. [4] N.A. Schwadron et al., J. of Phys.. Conf. Series 767(2016): 012025 [5] P. Wahlström, J.A. Scheer, A. Riedo, P. Wurz and M. Wieser, J. Spacecr. Rockets 50 (2013): 402-410. [6] M.B. Neuland, J.A. Scheer, A. Riedo and P. Wurz, Appl. Surf. Sci. 313(2014):293-303.

A first principles study on the electronic origins of silver segregation at the Ag-Au (111) surface

NASA Astrophysics Data System (ADS)

Hoppe, Sandra; Müller, Stefan

2017-12-01

The special electronic structure of gold gives rise to many interesting phenomena, such as its color. The surface segregation of the silver-gold system has been the subject of numerous experimental and theoretical studies, yielding conflicting results ranging from strong Ag surface enrichment to Au surface segregation. Via a combined approach of density functional theory (DFT) and statistical physics, we have analyzed the segregation at the Ag-Au (111) surface with different Ag bulk concentrations. Interestingly, we observe a moderate Au surface segregation, which is due to a charge transfer from the less electronegative Ag to Au. Canonical Monte Carlo simulations suggest that the calculated concentration profile with a Au-enriched surface layer remains stable up to higher temperatures. However, the presence of adsorbed oxygen reverses the segregation behavior and leads to strong Ag enrichment of the surface layer.

Uncovering the role of Nb modification in improving the structure stability and electrochemical performance of LiNi0.6Co0.2Mn0.2O2 cathode charged at higher voltage of 4.5 V

NASA Astrophysics Data System (ADS)

Liu, Siyang; Chen, Xiang; Zhao, Jiayue; Su, Junming; Zhang, Congcong; Huang, Tao; Wu, Jianhua; Yu, Aishui

2018-01-01

Ni-rich cathode materials attract ongoing interest due to their high specific capacity (∼200 mAh g-1). However, these materials suffer rapid capacity fading when charged to a high voltage and cycled at elevated temperature. In this study, we propose a facile method to reconstruct the surface structure of LiNi0.6Co0.2Mn0.2O2 via Nb modification, which integrates the merits of partial Nb5+ doping in the pristine structure and surface Li3NbO4 coating. The obtained results from Rietveld refinement and high resolution transmission electron microscopy confirm that Nb5+ is partially doped into Li+ sites within the surface lattice. Further ex-situ powder X-ray diffraction and kinetic analysis using electrochemical impedance spectroscopy reveal that Nb modification stabilizes the layered structure and facilitates the charge transfer process. Owing to the robust surface structure, 1 mol% Nb modified LiNi0.6Co0.2Mn0.2O2 delivers a discharge capacity of 160.9 mAh g-1 with 91% capacity retention after 100 cycles at 3.0-4.5 V, whereas the discharge capacity of the pristine sample drops to 139.6 mAh g-1, corresponding to 78% of its initial value. The presence of Nb5+ in the Li layer exhibits positive effects on stability of layered structure, and the surface Li3NbO4 coating layer increases interfacial stability, which results in superior electrochemical performance.

Fast and efficient charge breeding of the Californium rare isotope breeder upgrade electron beam ion source

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

Ostroumov, P. N.; Barcikowski, A.; Dickerson, C. A.

The Electron Beam Ion Source (EBIS), developed to breed CARIBU radioactive beams at ATLAS, is being tested off-line. A unique property of the EBIS is a combination of short breeding times, high repetition rates and a large acceptance. Overall, we have implemented many innovative features during the design and construction of the CARIBU EBIS as compared to the existing EBIS breeders. The offline charge breeding tests are being performed using a surface ionization source that produces singly-charged cesium ions. The main goal of the off-line commissioning is to demonstrate stable operation of the EBIS at a 10 Hz repetition ratemore » and a breeding efficiency into single charge state higher than 15%. These goals have been successfully achieved and exceeded. We have measured (20±0.7)% breeding efficiency into the single charge state of 28+ cesium ions with the breeding time of 28 ms. In general, the current CARIBU EBIS operational parameters can provide charge breeding of any ions in the full mass range of periodic table with high efficiency, short breeding times and sufficiently low charge-to-mass ratio, 1/6.3 for the heaviest masses, for further acceleration in ATLAS. In this paper we discuss the parameters of the EBIS and the charge breeding results in a pulsed injection mode with repetition rates up to 10 Hz.« less

Effect of dipolar fields, surface termination, and surface orientation on photochemical reactions on transition metal oxides

NASA Astrophysics Data System (ADS)

Giocondi, Jennifer Lynn

Experiments have been conducted to determine the effects of dipolar fields, surface termination, and surface orientation on the photochemical reactivity of several transition metal oxides. These compounds include BaTiO3, SrTiO3, BaTi4O9, Sr2Nb2O 7, and Sr2Ta2O7 which were studied as polycrystalline ceramics, single crystals, micron-sized faceted particles, or some combination of these forms. The reduction of Ag+ from an aqueous AgNO3 solution (Ag0 product) and the oxidation of Pb2+ from an aqueous lead acetate solution (PbO 2 product) were selected as probe reactions because they leave insoluble products on the oxide surfaces. The reactivity of ferroelectric BaTiO3 was dominated by the effect of dipolar fields on the transport of photogenerated charge carriers. Silver was reduced on domains with a positive surface charge while lead was oxidized on domains with a negative surface charge. This reactivity implies that the dipolar field in individual domains drives photogenerated charge carriers to oppositely charged surfaces. This reaction mechanism results in a physical separation of the photogenerated charge carriers and the locations of the oxidation and reduction half reactions on the catalyst surface. Experiments performed on polycrystalline ceramics, single crystals, and micron-sized particles all showed this domain specific reactivity. SrTiO3 has the ideal cubic perovskite structure from which the tetragonally distorted ferroelectric BaTiO3 phase is derived. Polished and annealed surfaces of randomly oriented grain surfaces were bound by some combination of the following three planes: {110}, {111}, and a complex facet inclined approximately 24° from {100}. Surfaces with the complex {100} facet were found to be the most active for Ag reduction. Single crystal studies also showed that the nonpolar (100) surface is the most reactive and that the composition of the termination layer does not influence this reaction. However, the polar (111) and (110) surfaces had a non-uniform distribution of reaction products. For these orientations, the location of the reduction and oxidation reactions is determined by the chemical and charge terminations of the different terraces or facets. The reactivity for silver reduction on the faceted particles is ranked as (100) > (111) > (110) while the (100) surface was least reactive for lead oxidation. Overall, these results show that the photochemical reactivity of SrTiO3 is anisotropic and that on polar surfaces, dipolar fields arising from charged surface domains influence the transport of photogenerated charge carriers and promote spatially selective oxidation and reduction reactions. (Abstract shortened by UMI.)

Applying simulation model to uniform field space charge distribution measurements by the PEA method

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

Liu, Y.; Salama, M.M.A.

1996-12-31

Signals measured under uniform fields by the Pulsed Electroacoustic (PEA) method have been processed by the deconvolution procedure to obtain space charge distributions since 1988. To simplify data processing, a direct method has been proposed recently in which the deconvolution is eliminated. However, the surface charge cannot be represented well by the method because the surface charge has a bandwidth being from zero to infinity. The bandwidth of the charge distribution must be much narrower than the bandwidths of the PEA system transfer function in order to apply the direct method properly. When surface charges can not be distinguished frommore » space charge distributions, the accuracy and the resolution of the obtained space charge distributions decrease. To overcome this difficulty a simulation model is therefore proposed. This paper shows their attempts to apply the simulation model to obtain space charge distributions under plane-plane electrode configurations. Due to the page limitation for the paper, the charge distribution originated by the simulation model is compared to that obtained by the direct method with a set of simulated signals.« less

Control of single-electron charging of metallic nanoparticles onto amorphous silicon surface.

PubMed

Weis, Martin; Gmucová, Katarína; Nádazdy, Vojtech; Capek, Ignác; Satka, Alexander; Kopáni, Martin; Cirák, Július; Majková, Eva

2008-11-01

Sequential single-electron charging of iron oxide nanoparticles encapsulated in oleic acid/oleyl amine envelope and deposited by the Langmuir-Blodgett technique onto Pt electrode covered with undoped hydrogenated amorphous silicon film is reported. Single-electron charging (so-called quantized double-layer charging) of nanoparticles is detected by cyclic voltammetry as current peaks and the charging effect can be switched on/off by the electric field in the surface region induced by the excess of negative/positive charged defect states in the amorphous silicon layer. The particular charge states in amorphous silicon are created by the simultaneous application of a suitable bias voltage and illumination before the measurement. The influence of charged states on the electric field in the surface region is evaluated by the finite element method. The single-electron charging is analyzed by the standard quantized double layer model as well as two weak-link junctions model. Both approaches are in accordance with experiment and confirm single-electron charging by tunnelling process at room temperature. This experiment illustrates the possibility of the creation of a voltage-controlled capacitor for nanotechnology.

Electrification of particulate entrained fluid flows-Mechanisms, applications, and numerical methodology

NASA Astrophysics Data System (ADS)

Wei, Wei; Gu, Zhaolin

2015-10-01

Particulates in natural and industrial flows have two basic forms: liquid (droplet) and solid (particle). Droplets would be charged in the presence of the applied electric field (e.g. electrospray). Similar to the droplet charging, particles can also be charged under the external electric field (e.g. electrostatic precipitator), while in the absence of external electric field, tribo-electrostatic charging is almost unavoidable in gas-solid two-phase flows due to the consecutive particle contacts (e.g. electrostatic in fluidized bed or wind-blown sand). The particle charging may be beneficial, or detrimental. Although electrostatics in particulate entrained fluid flow systems have been so widely used and concerned, the mechanisms of particulate charging are still lack of a thorough understanding. The motivation of this review is to explore a clear understanding of particulate charging and movement of charged particulate in two-phase flows, by summarizing the electrification mechanisms, physical models of particulate charging, and methods of charging/charged particulate entrained fluid flow simulations. Two effective methods can make droplets charged in industrial applications: corona charging and induction charging. The droplet charge to mass ratio by corona charging is more than induction discharge. The particle charging through collisions could be attributed to electron transfer, ion transfer, material transfer, and/or aqueous ion shift on particle surfaces. The charges on charged particulate surface can be measured, nevertheless, the charging process in nature or industry is difficult to monitor. The simulation method might build a bridge of investigating from the charging process to finally charged state on particulate surface in particulate entrained fluid flows. The methodology combining the interface tracking under the action of the applied electric with the fluid flow governing equations is applicable to the study of electrohydrodynamics problems. The charge distribution and mechanical behaviors of liquid surface can be predicted by using this method. The methodology combining particle charging model with Computational Fluid Dynamics (CFD) and Discrete element method (DEM) is applicable to study the particle charging/charged processes in gas-solid two phase flows, the influence factors of particle charging, such as gas-particle interaction, contact force, contact area, and various velocities, are described systematically. This review would explore a clear understanding of the particulate charging and provide theoretical references to control and utilize the charging/charged particulate entrained fluid system.

Sorption Mechanisms of Antibiotic Cephapirin onto Quartz and Feldspar by Raman Spectroscopy

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

Peterson, Jonathan; Wang, Wei; Gu, Baohua

2009-01-01

Raman spectroscopy was used to investigate the sorption mechanisms of cephapirin (CHP), a veterinary antibiotic, onto quartz (SiO2) and feldspar (KAlSi3O8) at different pH values. Depending on the charge and surface properties of the mineral, different reaction mechanisms including electrostatic attraction, monodentate and bidentate complexation were found to be responsible for CHP sorption. The zwitterion (CHPo) adsorbs to a quartz(+) surface by electrostatic attraction of the carboxylate anion group ( COO-) at a low pH, but adsorbs to a quartz(-) surface through electrostatic attraction of the pyridinium cation and possibly COO- bridge complexes at relatively higher pH conditions. CHP- bondsmore » to a quartz(-) surface by bidentate complexation between one oxygen of COO- and oxygen from the carbonyl (C=O) of the acetoxymethyl group. On a feldspar surface of mixed charge, CHPo forms monodentate complexes between C=O as well as COO- bridging complexes or electrostatically attached to localized edge (hydr)oxy-Al surfaces. CHP- adsorbs to feldspar(-) through monodentate C=O complexation, and similar mechanisms may operate for the sorption of other cephalosporins. This research demonstrates, for the first time, that Raman spectroscopic techniques can be effective for evaluating the sorption processes and mechanisms of cephalosporin antibiotics even at relatively low sorbed concentrations (97-120 μmol/kg).« less

Fabrication of semi-aromatic polyamide/spherical mesoporous silica nanocomposite reverse osmosis membrane with superior permeability

NASA Astrophysics Data System (ADS)

Li, Qiang; Yu, Hui; Wu, Feiyang; Song, Jie; Pan, Xianhui; Zhang, Meng

2016-02-01

Semi-aromatic polyamide (SAP)/spherical mesoporous silica nanocomposite reverse osmosis (RO) membrane was successfully fabricated using m-phenylene diamine aqueous solution and cyclohexane-1,3,5-tricarbonyl chloride/mesoporous-silica-sphere (MSS) organic solution as main raw materials. The experimental suggests that the microstructures and surface features are significantly different from those of the contrast samples (the full- and semi-aromatic polyamide membranes), including the surface morphology, polymer framework structure, surface charge density, hydrophilicity, and the thickness of barrier layer. It was observed that many MSSs with ca. 1.5 nm of pore size are evenly embedded on the surface of the fabricated SAP/MSS RO membrane. Furthermore, the separation performance testing results indicate that the permeabilities range from 62.53 to 72.73 L/m2 h with the increase of the introduced MSSs from 0.02 to 0.08 w/v % under 1.5 MPa operating pressure and 2000 mg/L NaCl solution, which is obviously better than the contrast samples. Simultaneously, their salt rejections can be still maintained at a comparable level (94.78-91.46%). The excellent separation performance of the nanocomposite RO membrane is closely related to the higher-freedom-degree semi-aromatic framework, the incorporation of MSSs, the improved surface hydrophilicity, the thinner barrier layer, and the enhanced surface negative charge density.

Charge Retention by Organometallic Dications on Self-Assembled Monolayer Surfaces

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

Laskin, Julia; Wang, Peng

2014-05-15

Charge retention by mass-selected ruthenium trisbipyridine dications, or Ru(bpy)32+, soft-landed onto self-assembled monolayer (SAM) surfaces of 1H, 1H, 2H, 2H-perfluorodecane-1-thiol (FSAM), 11-mercaptoundecanoic acid (COOH-SAM), and 11-amino-1-undecanethiol (HSAM) on gold was examined using in situ time-resolved secondary ion mass spectrometry in a Fourier transform ion cyclotron resonance apparatus (FT-ICR SIMS). FT-ICR SIMS analysis was performed during ion soft-landing and for 8–15 hours after the ion beam was switched off. Our results demonstrate efficient retention of the doubly charged precursor ion on the FSAM and COOH-SAM surfaces manifested by the abundant Ru(bpy)32+ ions in the SIMS spectra. In contrast, only the singlymore » charged Ru(bpy)3+ and Ru(bpy)2+ ions were observed on HSAM, indicating rapid loss of at least one charge by the deposited dications. The signal of Ru(bpy)32+ on COOH-SAM remained almost constant for more than 8 hours after the end of ion soft-landing, while a relatively fast decay followed by a plateau region was observed on the FSAM surface. However, we found that SIMS analysis of Ru(bpy)32+ ions soft-landed onto FSAM is complicated by facile ion-molecule reactivity occurring either on the surface or in the SIMS plume, making it difficult to accurately measure the charge reduction kinetics. Efficient retention of the doubly charged Ru(bpy)32+ ions on COOH-SAM is remarkably different from facile neutralization of protonated peptides deposited onto this surface reported in previous studies. Our results indicate different mechanisms of charge reduction of protonated molecules and permanent ions, such as Ru(bpy)32+, on SAM surfaces. Thus, we propose that proton loss is the major charge reduction channel for the protonated species, while electron transfer through the insulating SAM is responsible for the charge loss by permanent ions. Fundamental understanding of charge reduction phenomena is essential for controlled preparation of catalytically active substrates using ion soft-landing.« less

Characterization of triboelectrically charged particles deposited on dielectric surfaces

NASA Astrophysics Data System (ADS)

Nesterov, A.; Löffler, F.; Cheng, Yun-Chien; Torralba, G.; König, K.; Hausmann, M.; Lindenstruth, V.; Stadler, V.; Bischoff, F. R.; Breitling, F.

2010-04-01

A device for the measurement of q/m-values and charge degradation of triboelectrically charged particles deposited on a surface was developed. The setup is based on the integration of currents, which are induced in a Faraday cage by insertion of a solid support covered with charged particles. The conductivity of different particle supports was taken into account. The 'blow-off' method, in which the particles are first deposited, and then blown off using an air stream, can be used for characterization of triboelectric properties of particles relative to different surfaces.

Development of Charge to Mass Ratio Microdetector for Future Mars Mission

NASA Technical Reports Server (NTRS)

Chen, Yuan-Lian Albert

2003-01-01

The Mars environment comprises a dry, cold and low air pressure atmosphere with low gravity (0.38g) and high resistivity soil. The global dust storms that cover a large portion of Mars are observed often from Earth. This environment provides an ideal condition for turboelectric charging. The extremely dry conditions on the Martian surface have raised concerns that electrostatic charge buildup will not be dissipated easily. If turboelectrically generated charge cannot be dissipated or avoided, then dust will accumulate on charged surfaces and electrostatic discharge may cause hazards for future exploration missions. The low surface on Mars helps to prolong the charge decay on the dust particles and soil. To better understanding the physics of Martian charged dust particles is essential to future Mars missions. We research and design two sensors, velocity/charge sensor and PZT momentum sensors, to measure the velocity distribution, charge distribution and mass distribution of Martian wed dust particles. These sensors are fabricated at NASA Kenney Space Center, Electrostatic and Surface Physics Laboratory. The sensors are calibrated. The momentum sensor is capable to measure 45 pan size particles. The designed detector is very simple, robust, without moving parts, and does not require a high voltage power supply. Two sensors are combined to form the Dust Microdetector - CHAL.

Camel and bovine chymosin: the relationship between their structures and cheese-making properties.

PubMed

Langholm Jensen, Jesper; Mølgaard, Anne; Navarro Poulsen, Jens Christian; Harboe, Marianne Kirsten; Simonsen, Jens Bæk; Lorentzen, Andrea Maria; Hjernø, Karin; van den Brink, Johannes M; Qvist, Karsten Bruun; Larsen, Sine

2013-05-01

Bovine and camel chymosin are aspartic peptidases that are used industrially in cheese production. They cleave the Phe105-Met106 bond of the milk protein κ-casein, releasing its predominantly negatively charged C-terminus, which leads to the separation of the milk into curds and whey. Despite having 85% sequence identity, camel chymosin shows a 70% higher milk-clotting activity than bovine chymosin towards bovine milk. The activities, structures, thermal stabilities and glycosylation patterns of bovine and camel chymosin obtained by fermentation in Aspergillus niger have been examined. Different variants of the enzymes were isolated by hydrophobic interaction chromatography and showed variations in their glycosylation, N-terminal sequences and activities. Glycosylation at Asn291 and the loss of the first three residues of camel chymosin significantly decreased its activity. Thermal differential scanning calorimetry revealed a slightly higher thermal stability of camel chymosin compared with bovine chymosin. The crystal structure of a doubly glycosylated variant of camel chymosin was determined at a resolution of 1.6 Å and the crystal structure of unglycosylated bovine chymosin was redetermined at a slightly higher resolution (1.8 Å) than previously determined structures. Camel and bovine chymosin share the same overall fold, except for the antiparallel central β-sheet that connects the N-terminal and C-terminal domains. In bovine chymosin the N-terminus forms one of the strands which is lacking in camel chymosin. This difference leads to an increase in the flexibility of the relative orientation of the two domains in the camel enzyme. Variations in the amino acids delineating the substrate-binding cleft suggest a greater flexibility in the ability to accommodate the substrate in camel chymosin. Both enzymes possess local positively charged patches on their surface that can play a role in interactions with the overall negatively charged C-terminus of κ-casein. Camel chymosin contains two additional positive patches that favour interaction with the substrate. The improved electrostatic interactions arising from variation in the surface charges and the greater malleability both in domain movements and substrate binding contribute to the better milk-clotting activity of camel chymosin towards bovine milk.

A classical density functional theory for the asymmetric restricted primitive model of ionic liquids

NASA Astrophysics Data System (ADS)

Lu, Hongduo; Nordholm, Sture; Woodward, Clifford E.; Forsman, Jan

2018-05-01

A new three-parameter (valency, ion size, and charge asymmetry) model, the asymmetric restricted primitive model (ARPM) of ionic liquids, has recently been proposed. Given that ionic liquids generally are composed of monovalent species, the ARPM effectively reduces to a two-parameter model. Monte Carlo (MC) simulations have demonstrated that the ARPM is able to reproduce key properties of room temperature ionic liquids (RTILs) in bulk and at charged surfaces. The relatively modest complexity of the model raises the possibility, which is explored here, that a classical density functional theory (DFT) could resolve its properties. This is relevant because it might generate great improvements in terms of both numerical efficiency and understanding in the continued research of RTILs and their applications. In this report, a DFT for rod-like molecules is proposed as an approximate theoretical tool for an ARPM fluid. Borrowing data on the ion pair fraction from a single bulk simulation, the ARPM is modelled as a mixture of dissociated ions and connected ion pairs. We have specifically studied an ARPM where the hard-sphere diameter is 5 Å, with the charge located 1 Å from the hard-sphere centre. We focus on fluid structure and electrochemical behaviour of this ARPM fluid, into which a model electrode is immersed. The latter is modelled as a perfect conductor, and surface polarization is handled by the method of image charges. Approximate methods, which were developed in an earlier study, to take image interactions into account, are also incorporated in the DFT. We make direct numerical comparisons between DFT predictions and corresponding simulation data. The DFT theory is implemented both in the normal mean field form with respect to the electrostatic interactions and in a correlated form based on hole formation by both steric repulsions and ion-ion Coulomb interactions. The results clearly show that ion-ion correlations play a very important role in the screening of the charged surfaces by our ARPM ionic liquid. We have studied electrostatic potentials and ion density profiles as well the differential capacitance. The mean-field DFT fails to reproduce these properties, but the inclusion of ion-ion correlation by a simple approximate treatment yields quite reasonable agreement with the corresponding simulation results. An interesting finding is that there appears to be a surface phase transition at relatively low surface charge which is readily explored by DFT, but seen also in the MC simulations at somewhat higher asymmetry.

The Review on the Charge Distribution on the Conductor Surface

ERIC Educational Resources Information Center

Matehkolaee, M. Jafari; Asrami, A. Naderi

2013-01-01

In this paper we have a full review on the surface charge density at disordered conductor surfaces. Basically, reading text books does not resolve ambiguities in this field. As far as is possible, we have tried to the concepts easier to turn. In fact we will answer two questions. One of them is that why do charges tend to go where the curvature is…

Cell uptake, intracellular distribution, fate and reactive oxygen species generation of polymer brush engineered CeO2-x NPs

NASA Astrophysics Data System (ADS)

Qiu, Yuan; Rojas, Elena; Murray, Richard A.; Irigoyen, Joseba; Gregurec, Danijela; Castro-Hartmann, Pablo; Fledderman, Jana; Estrela-Lopis, Irina; Donath, Edwin; Moya, Sergio E.

2015-04-01

Cerium Oxide nanoparticles (CeO2-x NPs) are modified with polymer brushes of negatively charged poly (3-sulfopropylmethacrylate) (PSPM) and positively charged poly (2-(methacryloyloxy)ethyl-trimethylammonium chloride) (PMETAC) by Atom Transfer Radical Polymerisation (ATRP). CeO2-x NPs are fluorescently labelled by covalently attaching Alexa Fluor® 488/Fluorescein isothiocyanate to the NP surface prior to polymerisation. Cell uptake, intracellular distribution and the impact on the generation of intracellular Reactive Oxygen Species (ROS) with respect to CeO2-x NPs are studied by means of Raman Confocal Microscopy (CRM), Transmission Electron Microscopy (TEM) and Inductively Coupled Plasma Mass Spectroscopy (ICP-MS). PSPM and PMETAC coated CeO2-x NPs show slower and less uptake compared to uncoated Brush modified NPs display a higher degree of co-localisation with cell endosomes and lysosomes after 24 h of incubation. They also show higher co-localisation with lipid bodies when compared to unmodified CeO2-x NPs. The brush coating does not prevent CeO2-x NPs from displaying antioxidant properties.Cerium Oxide nanoparticles (CeO2-x NPs) are modified with polymer brushes of negatively charged poly (3-sulfopropylmethacrylate) (PSPM) and positively charged poly (2-(methacryloyloxy)ethyl-trimethylammonium chloride) (PMETAC) by Atom Transfer Radical Polymerisation (ATRP). CeO2-x NPs are fluorescently labelled by covalently attaching Alexa Fluor® 488/Fluorescein isothiocyanate to the NP surface prior to polymerisation. Cell uptake, intracellular distribution and the impact on the generation of intracellular Reactive Oxygen Species (ROS) with respect to CeO2-x NPs are studied by means of Raman Confocal Microscopy (CRM), Transmission Electron Microscopy (TEM) and Inductively Coupled Plasma Mass Spectroscopy (ICP-MS). PSPM and PMETAC coated CeO2-x NPs show slower and less uptake compared to uncoated Brush modified NPs display a higher degree of co-localisation with cell endosomes and lysosomes after 24 h of incubation. They also show higher co-localisation with lipid bodies when compared to unmodified CeO2-x NPs. The brush coating does not prevent CeO2-x NPs from displaying antioxidant properties. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr00884k

On the dependence of charge density on surface curvature of an isolated conductor

NASA Astrophysics Data System (ADS)

Bhattacharya, Kolahal

2016-03-01

A study of the relation between the electrostatic charge density at a point on a conducting surface and the curvature of the surface (at that point) is presented. Two major papers in the scientific literature on this topic are reviewed and the apparent discrepancy between them is resolved. Hence, a step is taken towards obtaining a general analytic formula for relating the charge density with surface curvature of conductors. The merit of this formula and its limitations are discussed.

Charging of particles on a surface

NASA Astrophysics Data System (ADS)

Heijmans, Lucas; Nijdam, Sander

2016-09-01

This contribution focusses on the seemingly easy problem of the charging of micrometer sized particles on a substrate in a plasma. This seems trivial, because much is known about both the charging of surfaces near a plasma and of particles in the plasma bulk. The problem, however, becomes much more complicated when the particle is on the substrate surface. The charging currents to the particle are then highly altered by the substrate plasma sheath. Currently there is no consensus in literature about the resulting particle charge. We shall present both experimental measurements and numerical simulations of the charge on these particles. The experimental results are acquired by measuring the particle acceleration in an external electric field. For the simulations we have used our specially developed model. We shall compare these results to other estimates found in literature.

Enhanced electrohydrodynamic force generation in a two-stroke cycle dielectric-barrier-discharge plasma actuator

NASA Astrophysics Data System (ADS)

Sato, Shintaro; Takahashi, Masayuki; Ohnishi, Naofumi

2017-05-01

An approach for electrohydrodynamic (EHD) force production is proposed with a focus on a charge cycle on a dielectric surface. The cycle, consisting of positive-charging and neutralizing strokes, is completely different from the conventional methodology, which involves a negative-charging stroke, in that the dielectric surface charge is constantly positive. The two-stroke charge cycle is realized by applying a DC voltage combined with repetitive pulses. Simulation results indicate that the negative pulse eliminates the surface charge accumulated during constant voltage phase, resulting in repetitive EHD force generation. The time-averaged EHD force increases almost linearly with increasing repetitive pulse frequency and becomes one order of magnitude larger than that driven by the sinusoidal voltage, which has the same peak-to-peak voltage.

Simulation study of spheroidal dust gains charging: Applicable to dust grain alignment

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

Zahed, H.; Sobhanian, S.; Mahmoodi, J.

2006-09-15

The charging process of nonspherical dust grains in an unmagnetized plasma as well as in the presence of a magnetic field is studied. It is shown that unlike the spherical dust grain, due to nonhomogeneity of charge distribution on the spheroidal dust surface, the resultant electric forces on electrons and ions are different. This process produces some surface charge density gradient on the nonspherical grain surface. Effects of a magnetic field and other plasma parameters on the properties of the dust particulate are studied. It has been shown that the alignment direction could be changed or even reversed with themore » magnetic field and plasma parameters. Finally, the charge distribution on the spheroidal grain surface is studied for different ambient parameters including plasma temperature, neutral collision frequency, and the magnitude of the magnetic field.« less

Adsorption of organic ligands on low surface charge clay minerals: the composition in the aqueous interface region.

PubMed

Jelavić, S; Stipp, S L S; Bovet, N

2018-06-27

An understanding of the mechanisms that control the adsorption of organic molecules on clay minerals is of interest in several branches of science and industry. Oil production using low salinity injection fluids can increase yields by as much as 40% over standard injection with seawater or formation water. The mechanism responsible for the low salinity response is still debated, but one hypothesis is a change in pore surface wettability. Organic contamination in soil and drinking water aquifers is a challenge for municipal water suppliers and for agriculture. A better understanding is needed for how mineral species, solution composition and pH affect the desorption of low molecular weight organic ligands from clay minerals and consequently their wettability. We used X-ray photoelectron spectroscopy under cryogenic conditions to investigate the in situ composition in the mineral-solution interface region in a series of experiments with a range of pH and ion concentrations. We demonstrate that both chlorite and kaolinite release organic molecules under conditions relevant for low salinity water flooding. This release increases with a higher solution pH but is only slightly affected by the character of the organic ligand. This is consistent with the observation that low salinity enhanced oil recovery correlates with the presence of chlorite and kaolinite. Our results indicate that the pore surface charge and salinity of formation water and injection fluids are key parameters in determining the low salinity response. In general, our results imply that clay mineral surface charge influences the composition in the interface through an affinity for organic molecules.

Removal of binary dyes mixtures with opposite and similar charges by adsorption, coagulation/flocculation and catalytic oxidation in the presence of CeO2/H2O2 Fenton-like system.

PubMed

Issa Hamoud, Houeida; Finqueneisel, Gisèle; Azambre, Bruno

2017-06-15

In this study, the removal of binary mixtures of dyes with similar (Orange II/Acid Green 25) or opposite charges (Orange II/Malachite Green) was investigated either by simple adsorption on ceria or by the heterogeneous Fenton reaction in presence of H 2 O 2 . First, the CeO 2 nanocatalyst with high specific surface area (269 m 2 /g) and small crystal size (5 nm) was characterized using XRD, Raman spectroscopy and N 2 physisorption at 77 K. The adsorption of single dyes was studied either from thermodynamic and kinetic viewpoints. It is shown that the adsorption of dyes on ceria surface is highly pH-dependent and followed a pseudo-second order kinetic model. Adsorption isotherms fit well the Langmuir model with a complete monolayer coverage and higher affinity towards Orange II at pH 3, compared to other dyes. For the (Orange II/Acid Green 25) mixture, both the amounts of dyes adsorbed on ceria surface and discoloration rates measured from Fenton experiments were decreased by comparison with single dyes. This is due to the adsorption competition existing onto the same surface Ce x+ sites and the reaction competition with hydroxyl radicals, respectively. The behavior of the (Orange II/Malachite Green) mixture is markedly different. Dyes with opposite charges undergo paired adsorption on ceria as well as homogeneous and heterogeneous coagulation/flocculation processes, but can also be removed by heterogeneous Fenton process. Copyright © 2016 Elsevier Ltd. All rights reserved.

Development of a Desalination Membrane Bioinspired by Mangrove Roots for Spontaneous Filtration of Sodium Ions.

PubMed

Kim, Kiwoong; Kim, Hyejeong; Lim, Jae Hong; Lee, Sang Joon

2016-12-27

The shortage of available fresh water is one of the global issues presently faced by humanity. To determine a solution to this problem, the survival strategies of plants have been examined. In this study, a nature-inspired membrane with a highly charged surface is proposed as an effective membrane for the filtration of saline water. To mimic the desalination characteristics of mangrove roots, a macroporous membrane based on polyethylene terephthalate is treated with polyelectrolytes using a layer-by-layer deposition method. The fabricated membrane surface has a highly negative charged ζ-potential value of -97.5 ± 4.3 mV, similar to that of the first layer of mangrove roots. Desalination of saline water using this membrane shows a high salt retention rate of 96.5%. The highly charged surface of the membrane may induce a relatively thick and stable ion depletion zone in front of the membrane. As a result, most co-ions are repelled from the membrane surface, and counterions are also rejected by virtue of their electroneutrality. The water permeability is found to be 7.60-7.69 L/m 2 ·h, which is 10 times higher than that of the reverse osmosis desalination method. This nature-inspired filtration membrane exhibits steady desalination performance over 72 h of operation, successfully demonstrating the stable filtration of saline water. This nature-inspired membrane is applicable to the design of a small-scale, portable, and energy-free desalination device for use in third-world countries or small villages.

Model simulations of the adsorption of statherin to solid surfaces: Effects of surface charge and hydrophobicity

NASA Astrophysics Data System (ADS)

Skepö, M.

2008-11-01

The structural properties of the salivary protein statherin upon adsorption have been examined using a coarse-grained model and Monte Carlo simulation. A simple model system with focus on electrostatic interactions and short-ranged attractions among the uncharged amino acids has been used. To mimic hydrophobically modified surfaces, an extra short-ranged interaction was implemented between the amino acids and the surface. It has been shown that the adsorption and the thickness of the adsorbed layer are determined by (i) the affinity for the surface, i.e., denser layer with an extrashort-ranged potential, and (ii) the distribution of the charges along the chain. If all the amino acids have a high affinity for the surface, the protein adsorbs in a train conformation, if the surface is negatively charged the protein adsorbs in a tail-train conformation, whereas if the surface is positively charged the protein adsorbs in a loop conformation. The latter gives rise to a more confined adsorbed layer.

Investigations of charged particle motion on the surfaces of dusty, airless solar system bodies (Invited)

NASA Astrophysics Data System (ADS)

Dove, A.; Colwell, J. E.

2013-12-01

Dynamic charging conditions exist on the dusty surfaces of planetary bodies such as the Moon, asteroids, and the moons of Mars. On these so-called 'airless bodies', the motions of dust particles above the surface become complex due to grain-grain and grain-plasma interactions. For example, tribocharging and other charge transfer processes can occur due to relative dust grain movements, and charged dust grains immersed in plasma interact with local electromagnetic forces. This is thought to lead to effects such as the lunar 'horizon glow,' (Rennilson and Criswell, 1974, The Moon, 10) and potential dusty 'fountains' above the lunar surface (Stubbs et al., 2006, Adv. Sp. Res., 37). Regolith grains can be mobilized by impacts or other mechanical disturbances, or simply by the Coulomb force acting on grains. Previous work has increased our theoretical understanding of the behavior of charged particles in these low-gravity environments (i.e. Poppe and Horanyi, 2010, JGR, A115; Colwell et al., 2007, Rev. Geophys., 45 (and references therein)). Experimental work has also analyzed grain surface charging due to plasma or tribocharging (Sickafoose et al., 2001, JGR, 106) and the motion of grains on surfaces in the presence of an electric field (Wang et al., 2009, JGR, 114). Occasionally, there is disagreement between theoretical predictions and observations. We present the results of new laboratory experiments aimed at understanding particle charging and the dynamics of charged particles on the surfaces of airless bodies. In the initial experiments, we analyze the motion of particles in the presence of an electric field in vacuum, either in a bell-jar or in a 0.75-second microgravity drop tower experiment box. Prior to motion, particles may be charged due to triboelectric effects, plasma interactions, or a combination of the two. Motion is induced by shaking or by low-velocity impacts in order to simulate the natural motion of slow-moving objects on regolith surfaces, or induced motion such as that due to a spacecraft. The resulting particle dynamics are tracked using high-speed, high-resolution video. Future exploration on or near the surfaces of airless bodies will certainly experience complications arising from these dusty environments, where particles may contaminate or interfere with the operation of almost any mechanical equipment. By exploring the dynamic behavior of charged particles in these environments, we can work towards solutions that will enable exploration.

Doping dependence of the contact resistivity of end-bonded metal contacts to thin heavily doped semiconductor nanowires

NASA Astrophysics Data System (ADS)

Shukkoor, Anvar A.; Karmalkar, Shreepad

2017-12-01

We study the resistivity, ρcN, of end-bonded contacts to semiconductor NanoWires (NWs) of radius R = 5-10 nm over doping Nd = 1018-1020 cm-3. The study is important for NW device design and characterization. It reports realistic calculations of ρcN and highlights and explains how ρcN differs significantly from the resistivity ρcB of bulk contacts. First, the space-charge width in NW contacts is increased by the surrounding field which depends on R, contact geometry, and ambient dielectric; this width also depends on surface charge and dielectric confinement which reduces dopant ionization. Second, thin NWs have a low effective lifetime, τN, due to surface recombination. Third, NW contacts have a lesser image force barrier lowering due to the higher space-charge width. Due to these factors, apart from tunneling (which decides ρcB), space-charge region generation-recombination current also affects ρcN. As Nd is raised from 1018 to 1020 cm-3, ρcB falls rapidly, but ρcN varies slowly and may even increase up to 3-5 × 1018 and then falls rapidly. Further, ρcN/ρcB can be ≪1 at Nd = 1 × 1018 cm-3, reaches a peak ≫1 around Nd = 1 × 1019 cm-3, and → 1 at Nd = 1 × 1020 cm-3, e.g., for 0.8 V contact barrier on 10 nm thick n-type silicon NWs with τN = 1 ps embedded in SiO2, at T = 300 K, even a 10 nm contact extension yields a peak of 75 at Nd = 8 × 1018 cm-3. We study changes in ρcN/ρcB versus Nd behavior with R, contact geometry, ambient dielectric, surface charge, τN, T, tunneling mass, and barrier height.

Frequency and Distribution of Single-Nucleotide Polymorphisms within mprF in Methicillin-Resistant Staphylococcus aureus Clinical Isolates and Their Role in Cross-Resistance to Daptomycin and Host Defense Antimicrobial Peptides.

PubMed

Bayer, Arnold S; Mishra, Nagendra N; Chen, Liang; Kreiswirth, Barry N; Rubio, Aileen; Yang, Soo-Jin

2015-08-01

MprF is responsible for the lysinylation of phosphatidylglycerol (PG) to synthesize the positively charged phospholipid (PL) species, lysyl-PG (L-PG). It has been proposed that the single-nucleotide polymorphisms (SNPs) within the mprF open reading frame (ORF) are associated with a gain-in-function phenotype in terms of daptomycin resistance in Staphylococcus aureus. (Note that although the official term is daptomycin nonsusceptibility, we use the term daptomycin resistance in this paper for ease of presentation.) Using 22 daptomycin-susceptible (DAP(s))/daptomycin-resistant (DAP(r)) clinical methicillin-resistant S. aureus (MRSA) strain pairs, we assessed (i) the frequencies and distribution of putative mprF gain-in-function SNPs, (ii) the relationships of the SNPs to both daptomycin resistance and cross-resistance to the prototypical endovascular host defense peptide (HDP) thrombin-induced platelet microbicidal protein (tPMP), and (iii) the impact of mprF SNPs on positive surface charge phenotype and modifications of membrane PL profiles. Most of the mprF SNPs identified in our DAP(r) strains were clustered within the two MprF loci, (i) the central bifunctional domain and (ii) the C-terminal synthase domain. Moreover, we were able to correlate the presence and location of mprF SNPs in DAP(r) strains with HDP cross-resistance, positive surface charge, and L-PG profiles. Although DAP(r) strains with mprF SNPs in the bifunctional domain showed higher resistance to tPMPs than DAP(r) strains with SNPs in the synthase domain, this relationship was not observed in positive surface charge assays. These results demonstrated that both charge-mediated and -unrelated mechanisms are involved in DAP resistance and HDP cross-resistance in S. aureus. Copyright © 2015, American Society for Microbiology. All Rights Reserved.

Differential photoelectric charging of nonconducting surfaces in space. [on sunlit strip

NASA Technical Reports Server (NTRS)

Pelizzari, M. A.; Criswell, D. R.

1978-01-01

The photoelectric charging caused by an infinitely long strip of sunlight across a nonconducting plane is studied by use of a model which contains an electrical cutoff radius, and the results of numerical calculations are presented. The model simulates charging of a sunlit area with dimensions equal to the strip's width, exposed to a plasma with a comparatively large Debye length. Uniform potential is quickly established on a uniformly sunlit strip as a result of charge redistribution by low-energy photoelectrons. The results are in accord with a theoretical surface conductivity derived for photoelectron sheaths above highly charged sunlit areas. The surface potential, which drops sharply across the sunlight-shadow boundary, is discussed.

On the theoretical description of weakly charged surfaces.

PubMed

Wang, Rui; Wang, Zhen-Gang

2015-03-14

It is widely accepted that the Poisson-Boltzmann (PB) theory provides a valid description for charged surfaces in the so-called weak coupling limit. Here, we show that the image charge repulsion creates a depletion boundary layer that cannot be captured by a regular perturbation approach. The correct weak-coupling theory must include the self-energy of the ion due to the image charge interaction. The image force qualitatively alters the double layer structure and properties, and gives rise to many non-PB effects, such as nonmonotonic dependence of the surface energy on concentration and charge inversion. In the presence of dielectric discontinuity, there is no limiting condition for which the PB theory is valid.

Dynamics of charges and solitons

NASA Astrophysics Data System (ADS)

Barros, Manuel; Ferrández, Ángel; Garay, Óscar J.

2018-02-01

We first show that trajectories traced by charges moving in rotational magnetic fields are, basically, the non-parallel geodesics of surfaces of revolution with coincident axis. Thus, people living in a surface of revolution are not able to sense the magnetic Hall effect induced by the surrounding magnetic field and perceive charges as influenced, exclusively, by the gravity action on the surface of revolution. Secondly, the extended Hasimoto transformations are introduced and then used to identify trajectories of charges moving through a Killing rotational magnetic field in terms of non-circular elastic curves. As a consequence, we see that in this case charges evolve along trajectories which are obtained as extended Hasimoto transforms of solitons of the filament equation.

Charged plate in asymmetric electrolytes: One-loop renormalization of surface charge density and Debye length due to ionic correlations.

PubMed

Ding, Mingnan; Lu, Bing-Sui; Xing, Xiangjun

2016-10-01

Self-consistent field theory (SCFT) is used to study the mean potential near a charged plate inside a m:-n electrolyte. A perturbation series is developed in terms of g=4πκb, where band1/κ are Bjerrum length and bare Debye length, respectively. To the zeroth order, we obtain the nonlinear Poisson-Boltzmann theory. For asymmetric electrolytes (m≠n), the first order (one-loop) correction to mean potential contains a secular term, which indicates the breakdown of the regular perturbation method. Using a renormalizaton group transformation, we remove the secular term and obtain a globally well-behaved one-loop approximation with a renormalized Debye length and a renormalized surface charge density. Furthermore, we find that if the counterions are multivalent, the surface charge density is renormalized substantially downwards and may undergo a change of sign, if the bare surface charge density is sufficiently large. Our results agrees with large MC simulation even when the density of electrolytes is relatively high.

Coarse-grained modeling of proline rich protein 1 (PRP-1) in bulk solution and adsorbed to a negatively charged surface.

PubMed

Skepö, Marie; Linse, Per; Arnebrant, Thomas

2006-06-22

Structural properties of the acidic proline rich protein PRP-1 of salivary origin in bulk solution and adsorbed onto a negatively charged surface have been studied by Monte Carlo simulations. A simple model system with focus on electrostatic interactions and short-ranged attractions among the uncharged amino acids has been used. In addition to PRP-1, some mutants were considered to assess the role of the interactions in the systems. Contrary to polyelectrolytes, the protein has a compact structure in salt-free bulk solutions, whereas at high salt concentration the protein becomes more extended. The protein adsorbs to a negatively charged surface, although its net charge is negative. The adsorbed protein displays an extended structure, which becomes more compact upon addition of salt. Hence, the conformational response upon salt addition in the adsorbed state is the opposite as compared to that in bulk solution. The conformational behavior of PRP-1 in bulk solution and at charged surfaces as well as its propensity to adsorb to surfaces with the same net charge are rationalized by the block polyampholytic character of the protein. The presence of a triad of positively charged amino acids in the C-terminal was found to be important for the adsorption of the protein.

Surface correlation effects in two-band strongly correlated slabs.

PubMed

Esfahani, D Nasr; Covaci, L; Peeters, F M

2014-02-19

Using an extension of the Gutzwiller approximation for an inhomogeneous system, we study the two-band Hubbard model with unequal band widths for a slab geometry. The aim is to investigate the mutual effect of individual bands on the spatial distribution of quasi-particle weight and charge density, especially near the surface of the slab. The main effect of the difference in band width is the presence of two different length scales corresponding to the quasi-particle profile of each band. This is enhanced in the vicinity of the critical interaction of the narrow band where an orbitally selective Mott transition occurs and a surface dead layer forms for the narrow band. For the doped case, two different regimes of charge transfer between the surface and the bulk of the slab are revealed. The charge transfer from surface/center to center/surface depends on both the doping level and the average relative charge accumulated in each band. Such effects could also be of importance when describing the accumulation of charges at the interface between structures made of multi-band strongly correlated materials.

Studies Of Oxidation And Thermal Reduction Of The Cu(100) Surface Using Positron Annihilation Induced Auger Electron Spectroscopy

NASA Astrophysics Data System (ADS)

Fazleev, N. G.; Nadesalingam, M. P.; Maddox, W.; Weiss, A. H.

2011-06-01

Positron annihilation induced Auger electron spectroscopy (PAES) measurements from the surface of an oxidized Cu(100) single crystal show a large increase in the intensity of the annihilation induced Cu M2,3VV Auger peak as the sample is subjected to a series of isochronal anneals in vacuum up to annealing temperature 300 °C. The PAES intensity then decreases monotonically as the annealing temperature is increased to ˜550 °C. Experimental positron annihilation probabilities with Cu 3p and O 1s core electrons are estimated from the measured intensities of the positron annihilation induced Cu M2,3VV and O KLL Auger transitions. PAES results are analyzed by performing calculations of positron surface states and annihilation probabilities of the surface-trapped positrons with relevant core electrons taking into account the charge redistribution at the surface and various surface structures associated with low and high oxygen coverages. The variations in atomic structure and chemical composition of the topmost layers of the oxidized Cu(100) surface are found to affect localization and spatial extent of the positron surface state wave function. The computed positron binding energy and annihilation characteristics reveal their sensitivity to charge transfer effects, atomic structure and chemical composition of the topmost layers of the oxidized Cu(100) surface. Theoretical positron annihilation probabilities with Cu 3p and O 1s core electrons computed for the oxidized Cu(100) surface are compared with experimental ones. The obtained results provide a demonstration of thermal reduction of the copper oxide surface after annealing at 300 °C followed by re-oxidation of the Cu(100) surface at higher annealing temperatures presumably due to diffusion of subsurface oxygen to the surface.

Studies Of Oxidation And Thermal Reduction Of The Cu(100) Surface Using Positron Annihilation Induced Auger Electron Spectroscopy

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

Fazleev, N. G.; Department of Physics, Kazan State University, Kazan 420008; Nadesalingam, M. P.

2011-06-01

Positron annihilation induced Auger electron spectroscopy (PAES) measurements from the surface of an oxidized Cu(100) single crystal show a large increase in the intensity of the annihilation induced Cu M2,3VV Auger peak as the sample is subjected to a series of isochronal anneals in vacuum up to annealing temperature 300 deg. C. The PAES intensity then decreases monotonically as the annealing temperature is increased to {approx}550 deg. C. Experimental positron annihilation probabilities with Cu 3p and O 1s core electrons are estimated from the measured intensities of the positron annihilation induced Cu M{sub 2,3}VV and O KLL Auger transitions. PAESmore » results are analyzed by performing calculations of positron surface states and annihilation probabilities of the surface-trapped positrons with relevant core electrons taking into account the charge redistribution at the surface and various surface structures associated with low and high oxygen coverages. The variations in atomic structure and chemical composition of the topmost layers of the oxidized Cu(100) surface are found to affect localization and spatial extent of the positron surface state wave function. The computed positron binding energy and annihilation characteristics reveal their sensitivity to charge transfer effects, atomic structure and chemical composition of the topmost layers of the oxidized Cu(100) surface. Theoretical positron annihilation probabilities with Cu 3p and O 1s core electrons computed for the oxidized Cu(100) surface are compared with experimental ones. The obtained results provide a demonstration of thermal reduction of the copper oxide surface after annealing at 300 deg. C followed by re-oxidation of the Cu(100) surface at higher annealing temperatures presumably due to diffusion of subsurface oxygen to the surface.« less

Surface Charge and Hydrophobicity of Endospores of Bacillus anthracis and Related Species in Aqueous Solution

EPA Science Inventory

The surface properties of microorganisms play an important role in attachment and detachment in the environment. The change in surface charge can effect coagulation, disinfection, adhesion to surfaces, uptake of chemicals, and environmental transport. In aqueous solution, cell s...

Convective transport of electric charge within the planetary boundary layer

NASA Astrophysics Data System (ADS)

Nicoll, Keri; Harrison, Giles; Silva, Hugo; Silgado, Rui; Melgao, Marta

2017-04-01

Turbulent and convective processes within the planetary boundary layer are responsible for the transport of moisture, momentum and particulate matter, but are also of major importance in determining the electrical charge structure of the lower atmosphere. This paper presents rare experimental measurements of vertical profiles of charge measured during fair weather conditions by specially instrumented radiosonde balloons over Alqueva, Portugal during the summer of 2014. Space charge was measured directly using a sensitive electrometer, rather than the conventional method of deriving it from electric field measurements. The high frequency of balloon flights enabled the diurnal variation in the vertical profile of charge within the boundary layer to be examined in detail, with much smaller levels of charge (up to 20pC m-3) observed during stable night time periods than during the day. Following sunrise, the evolution of the charge profile was much more complex, showing a dependence on lofting of surface aerosol due to daytime convection. This produced charge up to 92pC m-3 up to 500m above the surface. The diurnal variation in the integrated column of charge above the measurement site was also found to track closely with the diurnal variation in near surface charge as measured by an electric field mill at the same site, confirming the importance of the link between surface charge generation processes and aloft. Co-located lidar backscatter measurements were also made during the measurement campaign and will be discussed here in the context of the effect of aerosol on the vertical charge profile.

Polyelectrolytes and Their Biological Interactions

PubMed Central

Katchalsky, A.

1964-01-01

Polyelectrolytes are water-soluble electrically charged polymers. Their properties are determined by the interplay of the electrical forces, the Brownian motion of the macromolecular chain, and intermolecular Van der Waals forces. Charged polyacids or polybases are stretched by the electrostatic forces, as evidenced by increase in solution viscosity, or by the stretching of polyelectrolyte gels. The electrical field of the polyions is neutralized by a dense atmosphere of counter-ions. The counter-ion attraction to the polyions is expressed by a reduction of the osmotic activity of the polyion—the osmotic pressure being only 15 to 20 per cent of the ideal in highly charged polyelectrolytes neutralized by monovalent counter-ions, and as low as 1 to 3 per cent of the ideal for polyvalent counter-ions. Since the ionic atmosphere is only slightly dependent on added low molecular salt, the osmotic pressure of polyelectrolyte salt mixtures is approximately equal to the sum of the osmotic pressure of polyelectrolyte and salt alone. Acidic and basic polyelectrolytes interact electrostatically with precipitation at the point of polymeric electroneutrality. At higher salt concentrations the interaction is inhibited by the screening of polymeric fixed charges. The importance of these interactions in enzymatic processes is discussed. The electrical double layer is polarizable as may be deduced from dielectric and conductometric studies. The polarizability leads to strong dipole formation in an electrical field. These macromolecular dipoles may play a role in the adsorption of polyelectrolytes on charged surfaces. The final part of the paper is devoted to interactions of polyelectrolytes with cell membranes and the gluing of cells to higher aggregates by charged biocolloids. ImagesFigure 17Figure 18Figure 19Figure 20 PMID:14104085

Studies on ocular and parenteral application potentials of azithromycin- loaded anionic, cationic and neutral-charged emulsions.

PubMed

Tamilvanan, Shunmugaperumal; Khanum, Ramona; Senthilkumar, Sudalimuthu Ramachandran; Muthuraman, Marimuthu; Rajasekharan, Thenrajan

2013-10-01

Ocular and parenteral application potentials of azithromycin-containing, non-phospholipid-based cationic nanosized emulsion in comparison to the phospholipid-based anionic and neutral-charged nanosized emulsions were investigated. Various physical, chemical, nonclinical toxicity and antimicrobial activity studies (mean droplet diameter, surface charge, creaming index, entrapment efficiency, accelerated, long-term and freeze-thaw cycling stabilities, TLC study, modified hen's egg chorioallantoic membrane (HET-CAM) test, in vitro hemolysis test, in vitro and in vivo myotoxicity, and in vitro antimicrobial activity) were conducted for assessing the potentials of these three types of emulsions. Following autoclave sterilization, all of these emulsions exhibited a nanometer range mean particle diameter (200 ± 29 to 434 ± 13 nm). While the anionic and cationic emulsions did show high negative (-34.2 ± 1.23 mV) and positive zeta potential (42.6 ± 1.45 mV) values, the neutral-charged emulsion did not. Even with 5 freeze-thaw cycles, the cationic emulsion remained stable whereas other two emulsions underwent phase-separation. The hen's egg chorioallantoic membrane test revealed an irritation score value that was higher for the anionic emulsion than for cationic or neutral-charged emulsion. A significantly higher % hemolysis value was also noticed for the anionic emulsion when compared to the % hemolysis value of cationic emulsion (ANOVA, P ‹ 0.05). However, all of the emulsions showed a lesser intracellular creatine kinase (CK) release/plasma CK level in comparison to the positive control (phenytoin) indicating their lesser myotoxicity at the injection site . When compared to anionic and neutral-charged emulsions, the possible controlled drug release from cationic emulsion delayed the in vitro antimicrobial action against H.influenzae and S.pneumoniae.

Piezoelectric modulation of surface voltage in GaN and AlGaN/GaN: charge screening effects and 2DEG

NASA Astrophysics Data System (ADS)

Wilson, Marshall; Schrayer, Bret; Savtchouk, Alexandre; Hillard, Bob; Lagowski, Jacek

2017-02-01

Surface voltage response to pulses of piezoelectric polarization is measured with a Kelvin-probe providing a unique means for investigation of the dynamics of polarization induced sheet charge and 2DEG. Combined with biasing of the surface with a corona-deposited charge from accumulation to deep depletion and corresponding non-contact C-V type characterization, the technique identifies surface band bending and interface traps as key factors that affect the magnitude and time decay of piezoelectric polarization. For 2DEG structures, surface potential pinning is observed when the 2DEG is fully populated. Pinning is released by negative corona charging to fully deplete the 2DEG. These results are consistent with the role of surface states. Presently demonstrated polarization modulation and wafer scale measurements shall impact the in-depth characterization and fundamental understanding of AlGaN/GaN 2DEG structures.

Characterization of combustion-generated carbonaceous nanoparticles by size-dependent ultraviolet laser photoionization.

PubMed

Commodo, Mario; Sgro, Lee Anne; Minutolo, Patrizia; D'Anna, Andrea

2013-05-16

Photoelectric charging of particles is a powerful tool for online characterization of submicrometer aerosol particles. Indeed photoionization based techniques have high sensitivity and chemical selectivity. Moreover, they yield information on electronic properties of the material and are sensitive to the state of the surface. In the present study the photoionization charging efficiency, i.e., the ratio between the generated positive ions and the corresponding neutral ones, for different classes of flame-generated carbonaceous nanoparticles was measured. The fifth harmonics of a Nd:YAG laser, 213 nm (5.82 eV), was used as an ionization source for the combustion generated nanoparticles, whereas a differential mobility analyzer (DMA) coupled to a Faraday cup electrometer was used for particle classification and detection. Carbonaceous nanoparticles in the nucleation mode, i.e., sizes ranging from 1 to 10 nm, show a photoionization charging efficiency clearly dependent on the flame conditions. In particular, we observed that the richer the flame is, i.e., the higher the equivalent ratio is, the higher the photon charging efficiency is. We hypothesized that such an increase in the photoionization propensity of the carbonaceous nanoparticles from richer flame condition is associated to the presence within the particles of larger aromatic moieties. The results clearly show that photoionization is a powerful diagnostic tool for the physical-chemical characterization of combustion aerosol, and it may lead to further insights into the soot formation mechanism.

Bounding Extreme Spacecraft Charging in the Lunar Environment

NASA Technical Reports Server (NTRS)

Minow, Joseph I.; Parker, Linda N.

2008-01-01

Robotic and manned spacecraft from the Apollo era demonstrated that the lunar surface in daylight will charge to positive potentials of a few tens of volts because the photoelectron current dominates the charging process. In contrast, potentials of the lunar surface in darkness which were predicted to be on the order of a hundred volts negative in the Apollo era have been shown more recently to reach values of a few hundred volts negative with extremes on the order of a few kilovolts. The recent measurements of night time lunar surface potentials are based on electron beams in the Lunar Prospector Electron Reflectometer data sets interpreted as evidence for secondary electrons generated on the lunar surface accelerated through a plasma sheath from a negatively charged lunar surface. The spacecraft potential was not evaluated in these observations and therefore represents a lower limit to the magnitude of the lunar negative surface potential. This paper will describe a method for obtaining bounds on the magnitude of lunar surface potentials from spacecraft measurements in low lunar orbit based on estimates of the spacecraft potential. We first use Nascap-2k surface charging analyses to evaluate potentials of spacecraft in low lunar orbit and then include the potential drops between the ambient space environment and the spacecraft to the potential drop between the lunar surface and the ambient space environment to estimate the lunar surface potential from the satellite measurements.

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

Laskin, Julia; Johnson, Grant E.; Prabhakaran, Venkateshkumar

Immobilization of complex molecules and clusters on supports plays an important role in a variety of disciplines including materials science, catalysis and biochemistry. In particular, deposition of clusters on surfaces has attracted considerable attention due to their non-scalable, highly size-dependent properties. The ability to precisely control the composition and morphology of clusters and small nanoparticles on surfaces is crucial for the development of next generation materials with rationally tailored properties. Soft- and reactive landing of ions onto solid or liquid surfaces introduces unprecedented selectivity into surface modification by completely eliminating the effect of solvent and sample contamination on the qualitymore » of the film. The ability to select the mass-to-charge ratio of the precursor ion, its kinetic energy and charge state along with precise control of the size, shape and position of the ion beam on the deposition target makes soft-landing an attractive approach for surface modification. High-purity uniform thin films on surfaces generated using mass-selected ion deposition facilitate understanding of critical interfacial phenomena relevant to catalysis, energy generation and storage, and materials science. Our efforts have been directed toward understanding charge retention by soft-landed metal and metal-oxide cluster ions, which may affect both their structure and reactivity. Specifically, we have examined the effect of the surface on charge retention by both positively and negatively charged cluster ions. We found that the electronic properties of the surface play an important role in charge retention by cluster cations. Meanwhile, the electron binding energy is a key factor determining charge retention by cluster anions. These findings provide the scientific foundation for the rational design of interfaces for advanced catalysts and energy storage devices. Further optimization of electrode-electrolyte interfaces for applications in energy storage and electrocatalysis may be achieved by understanding and controlling the properties of soft-landed cluster ions.« less

Investigation of surface charge density on solid-liquid interfaces by modulating the electrical double layer.

PubMed

Moon, Jong Kyun; Song, Myung Won; Pak, Hyuk Kyu

2015-05-20

A solid surface in contact with water or aqueous solution usually carries specific electric charges. These surface charges attract counter ions from the liquid side. Since the geometry of opposite charge distribution parallel to the solid-liquid interface is similar to that of a capacitor, it is called an electrical double layer capacitor (EDLC). Therefore, there is an electrical potential difference across an EDLC in equilibrium. When a liquid bridge is formed between two conducting plates, the system behaves as two serially connected EDLCs. In this work, we propose a new method for investigating the surface charge density on solid-liquid interfaces. By mechanically modulating the electrical double layers and simultaneously applying a dc bias voltage across the plates, an ac electric current can be generated. By measuring the voltage drop across a load resistor as a function of bias voltage, we can study the surface charge density on solid-liquid interfaces. Our experimental results agree very well with the simple equivalent electrical circuit model proposed here. Furthermore, using this method, one can determine the polarity of the adsorbed state on the solid surface depending on the material used. We expect this method to aid in the study of electrical phenomena on solid-liquid interfaces.

Study of space charge layer in silver bromide microcrystals by means of ultraviolet photoelectron spectroscopy

NASA Astrophysics Data System (ADS)

Tani, Tadaaki; Inami, Yoshiyasu

2000-09-01

Ultraviolet photoelectron spectroscopy has been successfully used to measure the heights of the tops of the valence bands of the surfaces of AgBr layers on Ag substrates for the verification of the space charge layer model. According to this model, the positive space charge layer (composed of negative charges with excess negative kink sites on the surface and corresponding positive charges with interstitial silver ions in the interior) is formed in silver halides, causing the difference in the electronic energy levels between their surface and interior. The depression of the positive space charge layer of AgBr caused by such adsorbates as photographic stabilizers and antifoggants was estimated from the decrease in the ionic conductivity of cubic AgBr microcrystals by the adsorbates. It was confirmed by the decrease in the heights of the tops of the valence bands of the surfaces of AgBr layers caused by the adsorbates in the presence of thin gelatin membranes on their surfaces. This result provided the explanation for the fact that the adsorbates increased the number of the microcrystals which formed latent image centers on the surface and decreased the number of the microcrystals, which formed latent image centers in the interior.

Instrumentation and Methodology Development for Mars Mission

NASA Technical Reports Server (NTRS)

Chen, Yuan-Liang Albert

2002-01-01

The Mars environment comprises a dry, cold and low air pressure atmosphere with low gravity (0.38g) and high resistivity soil. The global dust storms that cover a large portion of Mars were observed often from Earth. This environment provides an idea condition for triboelectric charging. The extremely dry conditions on the Martian surface have raised concerns that electrostatic charge buildup will not be dissipated easily. If triboelectrically generated charge cannot be dissipated or avoided, then dust will accumulate on charged surfaces and electrostatic discharge may cause hazards for future exploration missions. The low surface temperature on Mars helps to prolong the charge decay on the dust particles and soil. To better understand the physics of Martian charged dust particles is essential to future Mars missions. We research and design two sensors, velocity/charge sensor and PZT momentum sensors, to detect the velocity distribution, charge distribution and mass distribution of Martian charged dust particles. These sensors are fabricated at NASA Kenney Space Center, Electromagnetic Physics Testbed. The sensors will be tested and calibrated for simulated Mars atmosphere condition with JSC MARS-1 Martian Regolith simulant in this NASA laboratory.

Nonlinear optical probe of biopolymer adsorption on colloidal particle surface: poly-L-lysine on polystyrene sulfate microspheres.

PubMed

Eckenrode, Heather M; Dai, Hai-Lung

2004-10-12

A nonlinear optical technique--second harmonic generation (SHG)--has been applied to characterize the adsorption of poly-L-lysine on micrometer size polystyrene particles, whose surface is covered with negatively charged sulfonate groups, in aqueous solutions. Adsorption behavior of the biopolymer with two chain lengths (14 and 75 amino acid units; PL14 and PL75) has been examined. Centrifugation experiments were also performed to support the adsorption measurements made using SHG. The adsorption free energies of the two polymers PL75 and PL14 are determined as -16.57 and -14.40 kcal/mol, respectively. The small difference in the adsorption free energies of the two chain lengths, however, leads to dramatic difference in the concentration needed for saturated surface coverage: nearly 50 times higher concentration is needed for the smaller polymer. Under acidic colloidal conditions, polylysine is found to adsorb in a relatively flat conformation on the surface. The surface area that each polylysine molecule occupies is nearly 1 order of magnitude larger than the size of the molecule in its extended form. The low adsorption density is likely a result from Coulombic repulsion between the positive charges on the amino acid units of PL. The measurements demonstrate the utility of SHG as an efficient and sensitive experimental approach for measuring adsorption characteristics of bio/macromolecules on colloidal particles and define surface and colloidal conditions for achieving maximum surface coverage of a widely used biopolymer. Copyright 2004 American Chemical Society

Silver nanoparticles as a key feature of a plasma polymer composite layer in mitigation of charge injection into polyethylene under dc stress

NASA Astrophysics Data System (ADS)

Milliere, L.; Maskasheva, K.; Laurent, C.; Despax, B.; Boudou, L.; Teyssedre, G.

2016-01-01

The aim of this work is to limit charge injection from a semi-conducting electrode into low density polyethylene (LDPE) under dc field by tailoring the polymer surface using a silver nanoparticles-containing layer. The layer is composed of a plane of silver nanoparticles embedded in a semi-insulating organosilicon matrix deposited on the polyethylene surface by a plasma process. Size, density and surface coverage of the nanoparticles are controlled through the plasma process. Space charge distribution in 300 μm thick LDPE samples is measured by the pulsed-electroacoustic technique following a short term (step-wise voltage increase up to 50 kV mm-1, 20 min in duration each, followed by a polarity inversion) and a longer term (up to 12 h under 40 kV mm-1) protocols for voltage application. A comparative study of space charge distribution between a reference polyethylene sample and the tailored samples is presented. It is shown that the barrier effect depends on the size distribution and the surface area covered by the nanoparticles: 15 nm (average size) silver nanoparticles with a high surface density but still not percolating form an efficient barrier layer that suppress charge injection. It is worthy to note that charge injection is detected for samples tailored with (i) percolating nanoparticles embedded in organosilicon layer; (ii) with organosilicon layer only, without nanoparticles and (iii) with smaller size silver particles (<10 nm) embedded in organosilicon layer. The amount of injected charges in the tailored samples increases gradually in the samples ranking given above. The mechanism of charge injection mitigation is discussed on the basis of complementary experiments carried out on the nanocomposite layer such as surface potential measurements. The ability of silver clusters to stabilize electrical charges close to the electrode thereby counterbalancing the applied field appears to be a key factor in explaining the charge injection mitigation effect.

The Thomas-Fermi model in the theory of systems of charged particles above the surface of liquid dielectrics

NASA Astrophysics Data System (ADS)

Lytvtnenko, D. M.; Slyusarenko, Yu. V.; Kirdin, A. I.

2012-10-01

A consistent theory of equilibrium states of same sign charges above the surface of liquid dielectric film located on solid substrate in the presence of external attracting constant electric field is proposed. The approach to the development of the theory is based on the Thomas-Fermi model generalized to the systems under consideration and on the variational principle. The using of self-consistent field model allows formulating a theory containing no adjustable constants. In the framework of the variational principle we obtain the self-consistency equations for the parameters describing the system: the distribution function of charges above the liquid dielectric surface, the electrostatic field potentials in all regions of the system and the surface profile of the liquid dielectric. The self-consistency equations are used to describe the phase transition associated with the formation of spatially periodic structures in the system of charges on liquid dielectric surface. Assuming the non-degeneracy of the gas of charges above the surface of liquid dielectric film the solutions of the self-consistency equations near the critical point are obtained. In the case of the symmetric phase we obtain the expressions for the potentials and electric fields in all regions of the studied system. The distribution of the charges above the surface of liquid dielectric film for the symmetric phase is derived. The system parameters of the phase transition to nonsymmetric phase - the states with a spatially periodic ordering are obtained. We derive the expression determining the period of two-dimensional lattice as a function of physical parameters of the problem - the temperature, the external attractive electric field, the number of electrons per unit of the flat surface area of the liquid dielectric, the density of the dielectric, its surface tension and permittivity, and the permittivity of the solid substrate. The possibility of generalizing the developed theory in the case of degenerate gas of like-charged particles above the liquid dielectric surface is discussed.

Surface functionalization of dopamine coated iron oxide nanoparticles for various surface functionalities

NASA Astrophysics Data System (ADS)

Sherwood, Jennifer; Xu, Yaolin; Lovas, Kira; Qin, Ying; Bao, Yuping

2017-04-01

We present effective conjugation of four small molecules (glutathione, cysteine, lysine, and Tris(hydroxymethyl)aminomethane) onto dopamine-coated iron oxide nanoparticles. Conjugation of these molecules could improve the surface functionality of nanoparticles for more neutral surface charge at physiological pH and potentially reduce non-specific adsorption of proteins to nanoparticles surfaces. The success of conjugation was evaluated with dynamic light scattering by measuring the surface charge changes and Fourier transform infrared spectroscopy for surface chemistry analysis. The stability of dopamine-coated nanoparticles and the ability of conjugated nanoparticles to reduce the formation of protein corona were evaluated by measuring the size and charge of the nanoparticles in biological medium. This facile conjugation method opens up possibilities for attaching various surface functionalities onto iron oxide nanoparticle surfaces for biomedical applications.

Enhanced flashover strength in polyethylene nanodielectrics by secondary electron emission modification

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

Wang, Weiwang; Li, Shengtao, E-mail: sli@xjtu.edu.cn; Min, Daomin

2016-04-15

This work studies the correlation between secondary electron emission (SEE) characteristics and impulse surface flashover in polyethylene nanodielectrics both theoretically and experimentally, and illustrates the enhancement of flashover voltage in low-density polyethylene (LDPE) through incorporating Al{sub 2}O{sub 3} nanoparticles. SEE characteristics play key roles in surface charging and gas desorption during surface flashover. This work demonstrates that the presence of Al{sub 2}O{sub 3} nanoparticles decreases the SEE coefficient of LDPE and enhances the impact energy at the equilibrium state of surface charging. These changes can be explained by the increase of surface roughness and of surface ionization energy, and themore » strong interaction between nanoparticles and the polymer dielectric matrix. The surface charge and flashover voltage are calculated according to the secondary electron emission avalanche (SEEA) model, which reveals that the positive surface charges are reduced near the cathode triple point, while the presence of more nanoparticles in high loading samples enhances the gas desorption. Consequently, the surface flashover performance of LDPE/Al{sub 2}O{sub 3} nanodielectrics is improved.« less

In situ measurement of surface potential developed on MgO thin film surface under ion irradiation using ion scattering spectroscopy

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

Nagatomi, T.; Kuwayama, T.; Takai, Y.

2009-11-15

The application of ion scattering spectroscopy (ISS) to the in situ measurement of the surface potential developed on an insulator surface under positive ion irradiation was investigated. The ISS spectra measured for a MgO film of 600 nm thickness on a Si substrate by the irradiation of 950 eV He{sup +} ions revealed that the surface is positively charged by approximately 180 V. For accurate measurement of the surface potential, a correction to take into account the angular deflection of primary ions induced by the high surface potential is required. The dependence of the surface potential on the sample temperaturemore » revealed that no charging is induced above 700 deg. C, indicating that accumulated charges can be removed by heating to 700 deg. C. From the measurement of the ion-induced secondary electron yield using a collector electrode located in front of the sample surface, the surface potential and ion-induced secondary electron yield were found to be strongly affected by the experimental setup. Secondary electrons produced by the impact of slow positive secondary ions, the maximum energy of which corresponds to the surface potential, play an important role when the bias voltage applied to the collector electrode is positively high for the present experimental setup. The surface potential developed on the surface of MgO films of 600 and 200 nm thickness was measured in situ, revealing that the amount of accumulated charges and the time required to attain the steady state of charging are slightly dependent on the beam current of primary ions and strongly dependent on the thickness of the MgO film. The present results confirmed that the application of ISS has high potential for investigating charging phenomena and the secondary electron emission from insulator surfaces under positive ion irradiation.« less

Ferrocene Containing Copolymers with Improved Electrostatic Dissipation Properties for Advanced Applications

NASA Technical Reports Server (NTRS)

Smith, T. M.; Nelson, G. L.

2005-01-01

Electrostatic dissipative polymers are used for a variety of functions. Typical methods utilized to transform electrically insulating polymers into either charge dissipative or conductive materials involve incorporating a conductive filler, conductive polymer, oxidizing the surface using plasma, or incorporating surfactants that act as surface wetting agents. Another approach is to synthesize a block copolymer that is expected to result in better electrical properties with minimal impacts to physical, fire, and thermal properties. One such block that can be added into the main chain of polymers is a diol terminated ferrocene oligomer, which is expected to impart electrostatic dissipative properties into the host polymer while concurrently improving the overall fire properties. Previous work with polyurethanes incorporating a ferrocene oligomer into the main chain resulted in much improved fire retardancy. In dealing with electrostatic dissipative materials the important questions are: how easily does the material charge and how quickly can the charge move to ground. One normally describes the materials conductivity, but conductivity only measures the fastest path for an electron not the slowest path. The slowest path is the one of interest, since it is left on the surface and thus can cause discharges. In order to assess ease of charging and decay times corona charge dissipation measurements can accurately assess these properties by introducing a charge on the surface of the material then measuring the surface voltage and the amount of charge deposited. The charge decay curve then will give an indication of a materials electrostatic dissipation properties. Normally, triboelectric testing can be performed, but results vary. Corona charge dissipation results are more repeatable.

Self-consistent simulation of radio frequency multipactor on micro-grooved dielectric surface

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

Cai, Libing; Wang, Jianguo, E-mail: wanguiuc@mail.xjtu.edu.cn; Northwest Institute of Nuclear Technology, Xi'an, Shaanxi 710024

2015-02-07

The multipactor plays a key role in the surface breakdown on the feed dielectric window irradiated by high power microwave. To study the suppression of multipactor, a 2D electrostatic PIC-MCC simulation code was developed. The space charge field, including surface deposited charge and multipactor electron charge field, is obtained by solving 2D Poisson's equation in time. Therefore, the simulation is self-consistent and does not require presetting a fixed space charge field. By using this code, the self-consistent simulation of the RF multipactor on the periodic micro-grooved dielectric surface is realized. The 2D space distributions of the multipactor electrons and spacemore » charge field are presented. From the simulation results, it can be found that only half slopes have multipactor discharge when the slope angle exceeds a certain value, and the groove presents a pronounced suppression effect on the multipactor.« less

Hydrolysis-controlled protein adsorption and antifouling behaviors of mixed charged self-assembled monolayer: A molecular simulation study.

PubMed

Liu, Jie; Zhou, Jian

2016-08-01

Understanding the mechanism of the antimicrobial and antifouling properties of mixed charged materials is of great significance. The interactions between human gamma fibrinogen (γFg) and mixed carboxylic methyl ether-terminated (COOCH3-) and trimethylamino-terminated (N(CH3)3(+)-) SAMs and the influence of hydrolysis were studied by molecular simulations. After hydrolysis, the mixed SAMs exhibit behaviors from antimicrobial to antifouling, since the COOCH3-thiols were translated into carboxylic acid (COO(-)-) terminated thiols, which carried a net charge of -1 e. Simulation results showed that the main differences between COOCH3-/N(CH3)3(+)-SAM and COO(-)-/N(CH3)3(+)-SAM are the charged property and the hydration layer above the surface. γFg could stably adsorb on the positively-charged COOCH3-/N(CH3)3(+)-SAM. The adsorption behavior is mainly induced by the strong electrostatic attraction. There is a single hydration layer bound to the surface, which is related to the N(CH3)3(+) groups. The van der Waals repulsion between γFg and the single hydration layer are not strong enough to compensate the strong electrostatic attraction. After hydrolysis, the positively-charged SAM was transferred to a neutral mixed charged surface, the electrostatic attraction between γFg and the surface disappears. Meanwhile, the SAM surface is covered by double hydration layers, which is induced by the N(CH3)3(+) and COO(-) groups; water molecules around COO(-) groups are obviously denser than that around N(CH3)3(+) groups. With the combined contribution from double hydration layers and the vanishment of electrostatic attraction, γFg is forced to desorb from the surface. After hydrolysis, the internal structure of mixed SAM appears more ordered due to the electrostatic interactions between charged groups on the top of SAMs. The antimicrobial and antifouling materials are of great importance in many biological applications. The strong hydration property of surfaces and the interactions between proteins and surfaces play a key role in resisting protein adsorption. The mixed SAMs, constructed from a 1:1 combination of COOCH3- and N(CH3)3(+)-terminated thiols, can induce protein adsorption mainly through the electrostatic interaction. When the COOCH3-terminated thiols were hydrolyzed to negatively charged COO(-)-terminated thiols, the mixed-charged SAMs switched from antimicrobial to antifouling. Due to the strong hydration property of the mixed charged SAMs, the adsorbed γFg moved away from the surface. Understanding the interactions between protein and mixed-charged SAMs in the atomistic level is important for the practical design and development of new antimicrobial and antifouling materials. Copyright © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

NASCAP modelling computations on large optics spacecraft in geosynchronous substorm environments

NASA Technical Reports Server (NTRS)

Stevens, N. J.; Purvis, C. K.

1980-01-01

Satellites in geosynchronous orbits have been found to be charged to significant negative voltages during encounters with geomagnetic substorms. When satellite surfaces are charged, there is a probability of enhanced contamination from charged particles attracted back to the satellite by electrostatic forces. This could be particularly disturbing to large satellites using sensitive optical systems. In this study the NASA Charging Analyzer Program (NASCAP) is used to evaluate qualitatively the possibility of such enhanced contamination on a conceptual version of a large satellite. The evaluation is made by computing surface voltages on the satellite due to encounters with substorm environments and then computing charged-particle trajectories in the electric fields around the satellite. Particular attention is paid to the possibility of contaminants reaching a mirror surface inside a dielectric tube because this mirror represents a shielded optical surface in the satellite model used. Deposition of low energy charged particles from other parts of the spacecraft onto the mirror was found to be possible in the assumed moderate substorm environment condition. In the assumed severe substorm environment condition, however, voltage build up on the inside and edges of the dielectric tube in which the mirror is located prevents contaminants from reaching the mirror surface.

Extremely large nonsaturating magnetoresistance and ultrahigh mobility due to topological surface states in the metallic Bi2Te3 topological insulator

NASA Astrophysics Data System (ADS)

Shrestha, K.; Chou, M.; Graf, D.; Yang, H. D.; Lorenz, B.; Chu, C. W.

2017-05-01

Weak antilocalization (WAL) effects in Bi2Te3 single crystals have been investigated at high and low bulk charge-carrier concentrations. At low charge-carrier density the WAL curves scale with the normal component of the magnetic field, demonstrating the dominance of topological surface states in magnetoconductivity. At high charge-carrier density the WAL curves scale with neither the applied field nor its normal component, implying a mixture of bulk and surface conduction. WAL due to topological surface states shows no dependence on the nature (electrons or holes) of the bulk charge carriers. The observations of an extremely large nonsaturating magnetoresistance and ultrahigh mobility in the samples with lower carrier density further support the presence of surface states. The physical parameters characterizing the WAL effects are calculated using the Hikami-Larkin-Nagaoka formula. At high charge-carrier concentrations, there is a greater number of conduction channels and a decrease in the phase coherence length compared to low charge-carrier concentrations. The extremely large magnetoresistance and high mobility of topological insulators have great technological value and can be exploited in magnetoelectric sensors and memory devices.

Dangerous liaisons: anion-induced protonation in phosphate-polyamine interactions and their implications for the charge states of biologically relevant surfaces.

PubMed

Laucirica, Gregorio; Marmisollé, Waldemar A; Azzaroni, Omar

2017-03-22

Although not always considered a preponderant interaction, amine-phosphate interactions are omnipresent in multiple chemical and biological systems. This study aims to answer questions that are still pending about their nature and consequences. We focus on the description of the charge state as surface charges constitute directing agents of the interaction of amine groups with either natural or synthetic counterparts. Our results allow us to quantitatively determine the relative affinities of HPO 4 2- and H 2 PO 4 - from the analysis of the influence of phosphates on the zeta-potential of amino-functionalized surfaces in a broad pH range. We show that phosphate anions enhance the protonation of amino groups and, conversely, charged amines induce further proton dissociation of phosphates, yielding a complex dependence of the surface effective charge on the pH and phosphate concentration. We also demonstrate that phosphate-amine interaction is specific and the modulation of surface charge occurs in the physiological phosphate concentration range, emphasizing its biochemical and biotechnological relevance and the importance of considering this veiled association in both in vivo and in vitro studies.

Nano-carbon coating layer prepared by the thermal evaporation of fullerene C60 for lithium metal anodes in rechargeable lithium batteries.

PubMed

Arie, Arenst Andreas; Lee, Joong Kee

2011-07-01

A nano carbon coating layer was prepared by the thermal evaporation of fullerene C60 on the surface of lithium metal anodes for rechargeable lithium batteries. The morphology and structure of the carbon layer was firstly investigated by Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The effects of the nano-carbon coating layer on the electrochemical performance of the lithium electrode were then examined by charge-discharge tests and impedance spectroscopy. Raman spectra of carbon coating layer showed two main peaks (D and G peaks), indicating the amorphous structure of the film. A honey comb-like structure of carbon film was observed by TEM photographs, providing a transport path for the transport of lithium ions at the electrode/electrolyte interface. The carbon coated lithium electrodes exhibited a higher initial coulombic efficiency (91%) and higher specific capacity retention (88%) after the 30th cycle at 0.2 C-rate between 3.4 and 4.5 V. Impedance measurements showed that the charge transfer resistance was significantly reduced after cycle tests for the carbon coated electrodes, revealing that the more stable solid electrolyte (SEI) layer was established on their surface. Based on the experimental results, it suggested that the presence of the nano-carbon coating layer might suppress the dendritic growth on the surface of lithium metal electrodes, as confirmed by the observation of SEM images after cycle tests.

Mechanical Removal and Rescreening of Local Screening Charges on Ferroelectric Surfaces

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

Tong, Sheng; Park, Woon Ik; Choi, YoonYoung

2015-01-20

We report the kinetics of screening charge removal and rescreening on periodically poled lithium niobate using charge-gradient microscopy and electrostatic force microscopy (EFM). A minimum pressure needs to be applied to initiate mechanical screening charge removal, and increasing the pressure leads to further removal of charge until a threshold is reached when all screening charges are removed. We fit all rescreening EFM contrast curves under various pressures into a universal exponential decay. The findings imply that we can control the screening degree of ferroelectric surfaces by mechanical means without affecting the polarization underneath.

Mechanical Removal and Rescreening of Local Screening Charges at Ferroelectric Surfaces

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

Tong, Sheng; Park, Woon Ik; Choi, Yoon-Young

2015-01-20

In this paper, we report the kinetics of screening charge removal and rescreening on periodically poled lithium niobate using charge-gradient microscopy and electrostatic force microscopy (EFM). A minimum pressure needs to be applied to initiate mechanical screening charge removal, and increasing the pressure leads to further removal of charge until a threshold is reached when all screening charges are removed. We fit all rescreening EFM contrast curves under various pressures into a universal exponential decay. Finally, the findings imply that we can control the screening degree of ferroelectric surfaces by mechanical means without affecting the polarization underneath.

Field observations of the electrostatic charges of blowing snow in Hokkaido, Japan

NASA Astrophysics Data System (ADS)

Omiya, S.; Sato, A.

2011-12-01

An electrostatic charge of blowing snow may be a contributing factor in the formation of a snow drift and a snow cornice, and changing of the trajectory of own motion. However, detailed electrification characteristics of blowing snow are not known as there are few reports of charge measurements. We carried out field observations of the electrostatic charges of blowing snow in Tobetsu, Hokkaido, Japan in the mid winter of 2011. An anemovane and a thermohygrometer were used for the meteorological observation. Charge-to-mass ratios of blowing snow were obtained by a Faraday-cage, an electrometer and an electric balance. In this observation period, the air temperature during the blowing snow event was -6.5 to -0.5 degree Celsius. The measured charges in this observation were consistent with the previous studies in sign, which is negative, but they were smaller than the previous one. In most cases, the measured values increased with the temperature decrease, which corresponds with previous studies. However, some results contradicted the tendency, and the maximum value was obtained on the day of the highest air temperature of -0.5 degree Celsius. This discrepancy may be explained from the difference of the snow surface condition on observation day. The day when the maximum value was obtained, the snow surface was covered with old snow, and hard. On the other hand, in many other cases, the snow surface was covered with the fresh snow, and soft. Blowing snow particles on the hard surface can travel longer distance than on the soft one. Therefore, it can be surmised that the hard surface makes the blowing snow particles accumulate a lot of negative charges due to a large number of collisions to the surface. This can be supported by the results of the wind tunnel experiments by Omiya and Sato (2011). By this field observation, it was newly suggested that the electrostatic charge of blowing snow are influenced greatly by the difference of the snow surface condition. REFERENCE: Omiya and Sato,(2010):An electrostatic charge measurement of blowing snow particles focusing on collision frequency to the snow surface. AGU Abstract Database, 2010 Fall Meeting.

ELECTROSTATIC SURFACE STRUCTURES OF COAL AND MINERAL PARTICLES

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

NONE

It is the purpose of this research to study electrostatic charging mechanisms related to electrostatic beneficiation of coal with the goal of improving models of separation and the design of electrostatic separators. Areas addressed in this technical progress report are (a) electrostatic beneficiation of Pittsburgh #8 coal powders as a function of grind size and processing atmosphere; (b) the use of fluorescent micro-spheres to probe the charge distribution on the surfaces of coal particles; (c) the use of electrostatic beneficiation to recover unburned carbon from flyash; (d) the development of research instruments for investigation of charging properties of coal. Pittsburghmore » #8 powders were beneficiated as a function of grind size and under three atmosphere conditions: fresh ground in air , after 24 hours of air exposure, or under N2 atmosphere. The feed and processed powders were analyzed by a variety of methods including moisture, ash, total sulfur, and pyritic sulfur content. Mass distribution and cumulative charge of the processed powders were also measured. Fresh ground coal performed the best in electrostatic beneficiation. Results are compared with those of similar studies conducted on Pittsburgh #8 powders last year (April 1, 1997 to September 30, 1997). Polystyrene latex spheres were charged and deposited onto coal particles that had been passed through the electrostatic separator and collected onto insulating filters. The observations suggest bipolar charging of individual particles and patches of charge on the particles which may be associated with particular maceral types or with mineral inclusions. A preliminary investigation was performed on eletrostatic separation of unburned carbon particles from flyash. Approximately 25% of the flyash acquired positive charge in the copper tribocharger. This compares with 75% of fresh ground coal. The negatively charged material had a slightly reduced ash content suggesting some enrichment of carbonaceous material. There was also evidence that the carbon is present at a higher ratio in larger particles than in small particles. An ultraviolet photoelectron counter for use in ambient atmosphere is nearing completion. The counter will be used to measure work functions of different maceral and mineral types in the coal matrix. A Particle Image Analyzer for measuring size and charge of airborne particles is also under contruction and its current status is presented. A charged, monodisperse, droplet generator is also being constructed for calibration of the Particle Image Analyzer and other airborne particle analyzers in our labs.« less

Origin of higher affinity to RNA of the N-terminal RNA-binding domain than that of the C-terminal one of a mouse neural protein, musashi1, as revealed by comparison of their structures, modes of interaction, surface electrostatic potentials, and backbone dynamics.

PubMed

Miyanoiri, Youhei; Kobayashi, Hisanori; Imai, Takao; Watanabe, Michinao; Nagata, Takashi; Uesugi, Seiichi; Okano, Hideyuki; Katahira, Masato

2003-10-17

Musashi1 is an RNA-binding protein abundantly expressed in the developing mouse central nervous system. Its restricted expression in neural precursor cells suggests that it is involved in maintenance of the character of progenitor cells. Musashi1 contains two ribonucleoprotein-type RNA-binding domains (RBDs), RBD1 and RBD2, the affinity to RNA of RBD1 being much higher than that of RBD2. We previously reported the structure and mode of interaction with RNA of RBD2. Here, we have determined the structure and mode of interaction with RNA of RBD1. We have also analyzed the surface electrostatic potential and backbone dynamics of both RBDs. The two RBDs exhibit the same ribo-nucleoprotein-type fold and commonly make contact with RNA on the beta-sheet side. On the other hand, there is a remarkable difference in surface electrostatic potential, the beta-sheet of RBD1 being positively charged, which is favorable for binding negatively charged RNA, but that of RBD2 being almost neutral. There is also a difference in backbone dynamics, the central portion of the beta-sheet of RBD1 being flexible, but that of RBD2 not being flexible. The flexibility of RBD1 may be utilized in the recognition process to facilitate an induced fit. Thus, comparative studies have revealed the origin of the higher affinity of RBD1 than that of RBD2 and indicated that the affinity of an RBD to RNA is not governed by its fold alone but is also determined by its surface electrostatic potential and/or backbone dynamics. The biological role of RBD2 with lower affinity is also discussed.

Hybrid supercapacitor-battery materials for fast electrochemical charge storage

PubMed Central

Vlad, A.; Singh, N.; Rolland, J.; Melinte, S.; Ajayan, P. M.; Gohy, J.-F.

2014-01-01

High energy and high power electrochemical energy storage devices rely on different fundamental working principles - bulk vs. surface ion diffusion and electron conduction. Meeting both characteristics within a single or a pair of materials has been under intense investigations yet, severely hindered by intrinsic materials limitations. Here, we provide a solution to this issue and present an approach to design high energy and high power battery electrodes by hybridizing a nitroxide-polymer redox supercapacitor (PTMA) with a Li-ion battery material (LiFePO4). The PTMA constituent dominates the hybrid battery charge process and postpones the LiFePO4 voltage rise by virtue of its ultra-fast electrochemical response and higher working potential. We detail on a unique sequential charging mechanism in the hybrid electrode: PTMA undergoes oxidation to form high-potential redox species, which subsequently relax and charge the LiFePO4 by an internal charge transfer process. A rate capability equivalent to full battery recharge in less than 5 minutes is demonstrated. As a result of hybrid's components synergy, enhanced power and energy density as well as superior cycling stability are obtained, otherwise difficult to achieve from separate constituents. PMID:24603843

Influence of Protamine Functionalization on the Colloidal Stability of 1D and 2D Titanium Oxide Nanostructures.

PubMed

Rouster, Paul; Pavlovic, Marko; Horváth, Endre; Forró, László; Dey, Sandwip K; Szilagyi, Istvan

2017-09-26

The colloidal stability of titanium oxide nanosheets (TNS) and nanowires (TiONW) was studied in the presence of protamine (natural polyelectrolyte) in aqueous dispersions, where the nanostructures possessed negative net charge, and the protamine was positively charged. Regardless of their shape, similar charging and aggregation behaviors were observed for both TNS and TiONW. Electrophoretic experiments performed at different protamine loadings revealed that the adsorption of protamine led to charge neutralization and charge inversion depending on the polyelectrolyte dose applied. Light scattering measurements indicated unstable dispersions once the surface charge was close to zero or slow aggregation below and above the charge neutralization point with negatively or positively charged nanostructures, respectively. These stability regimes were confirmed by the electron microscopy images taken at different polyelectrolyte loadings. The protamine dose and salt-dependent colloidal stability confirmed the presence of DLVO-type interparticle forces, and no experimental evidence was found for additional interactions (e.g., patch-charge, hydrophobic, or steric forces), which are usually present in similar polyelectrolyte-particle systems. These findings indicate that the polyelectrolyte adsorbs on the TNS and TiONW surfaces in a flat and extended conformation giving rise to the absence of surface heterogeneities. Therefore, protamine is an excellent biocompatible candidate to form smooth surfaces, for instance in multilayers composed of polyelectrolytes and particles to be used in biomedical applications.

Recovery curves of the surface electric field after lightning discharges occurring between the positive charge pocket and negative charge centre in a thundercloud

NASA Astrophysics Data System (ADS)

Pawar, S. D.; Kamra, A. K.

2002-12-01

Surface observations of the electric field recovery curves of the lightning discharges occurring between the positive charge pocket and negative main charge centre in an overhead thundercloud are reported. Such recovery curves are observed to have an additional step of very slow field-change observed at an after-discharge value of electric field equal to 5-6 kV m-1. The behavior of recovery curves is explained in terms of the coronae charge and the relative efficiencies of the charge generating processes responsible for growth of positive charge pocket and main negative charge centre in the thundercloud. The charging currents responsible for the growth of charge in positive charge pockets is computed to be 2-4 times larger than that for the growth of the main negative charge. However, the charge destroyed in such a discharge is found to be comparable to that in a discharge between the main charge centres of the thundercloud.

A Closer Look at Solar Wind Sputtering of Lunar Surface Materials

NASA Technical Reports Server (NTRS)

Barghouty, A. F.; Adams, J. H., Jr.; Meyer, F.; Mansur, L.; Reinhold, C.

2008-01-01

Solar-wind induced potential sputtering of the lunar surface may be a more efficient erosive mechanism than the "standard" kinetic (or physical) sputtering. This is partly based on new but limited laboratory measurements which show marked enhancements in the sputter yields of slow-moving, highly-charged ions impacting oxides. The enhancements seen in the laboratory can be orders of magnitude for some surfaces and highly charged incident ions, but seem to depend very sensitively on the properties of the impacted surface in addition to the fluence, energy and charge of the impacting ion. For oxides, potential sputtering yields are markedly enhanced and sputtered species, especially hydrogen and light ions, show marked dependence on both charge and dose.

Time and voltage dependences of nanoscale dielectric constant modulation on indium tin oxide films

NASA Astrophysics Data System (ADS)

Li, Liang; Hao, Haoyue; Zhao, Hua

2017-01-01

The modulation of indium tin oxide (ITO) films through surface charge accumulation plays an important role in many different applications. In order to elaborately study the modulation, we measured the dielectric constant of the modulated layer through examining the excitation of surface plasmon polaritons. Charges were pumped on the surfaces of ITO films through applying high voltage in appropriate directions. Experiments unveiled that the dielectric constant of the modulated layer had large variation along with the nanoscale charge accumulation. Corresponding numerical results were worked out through combining Drude model and Mayadas-Shatzkes model. Based on the above results, we deduced the time and voltage dependences of accumulated charge density, which revealed a long-time charge accumulation process.

Electrostatic stabilization of multi-walled carbon nanotubes dispersed in nonaqueous media.

PubMed

Damasceno, João Paulo V; Zarbin, Aldo J G

2018-06-04

Dispersing carbon nanotubes is an easy and low-cost way to manipulate these solids and allows the preparation of more complex materials or devices, so it is fundamental for further uses that these dispersions have controlled properties and high colloidal stability. In this work we report the spontaneous electrical charge build-up in pristine multi-walled carbon nanotubes dispersed in common organic solvents such as chloroform and tetrahydrofuran and the achievement of dispersions stable for long periods without adding passivant agents or functional groups on nanotubes surface. Results from electrokinetics, homo- and heterocoagulation provided macroscopic evidences that carbon nanotubes acquire electric charges after dispersion in some organic liquids and we confirmed this process by measuring in situ Raman spectra of the nanotubes dispersions with higher surface electric potentials. We also show that the signal of electric potential of the dispersions can be predicted by the acid-base behaviour of the dispersing medium, corroborating previously reports for other dispersions of carbon nanomaterials. Copyright © 2018 Elsevier Inc. All rights reserved.

Simulation of Graphene Field-Effect Transistor Biosensors for Bacterial Detection.

PubMed

Wu, Guangfu; Meyyappan, Meyya; Lai, King Wai Chiu

2018-05-25

Foodborne illness is correlated with the existence of infectious pathogens such as bacteria in food and drinking water. Probe-modified graphene field effect transistors (G-FETs) have been shown to be suitable for Escherichia coli ( E. coli ) detection. Here, the G-FETs for bacterial detection are modeled and simulated with COMSOL Multiphysics to understand the operation of the biosensors. The motion of E. coli cells in electrolyte and the surface charge of graphene induced by E. coli are systematically investigated. The comparison between the simulation and experimental data proves the sensing probe size to be a key parameter affecting the surface charge of graphene induced by bacteria. Finally, the relationship among the change in source-drain current (∆ I ds ), graphene-bacteria distance and bacterial concentration is established. The shorter graphene-bacteria distance and higher bacterial concentration give rise to better sensing performance (larger ∆ I ds ) of the G-FETs biosensors. The simulation here could serve as a guideline for the design and optimization of G-FET biosensors for various applications.

Photocurrent generation in SnO2 thin film by surface charged chemisorption O ions

NASA Astrophysics Data System (ADS)

Lee, Po-Ming; Liao, Ching-Han; Lin, Chia-Hua; Liu, Cheng-Yi

2018-06-01

We report a photocurrent generation mechanism in the SnO2 thin film surface layer by the charged chemisorption O ions on the SnO2 thin film surface induced by O2-annealing. A critical build-in electric field in the SnO2 surface layer resulted from the charged O ions on SnO2 surface prolongs the lifetime and reduces the recombination probability of the photo-excited electron-hole pairs by UV-laser irradiation (266 nm) in the SnO2 surface layer, which is the key for the photocurrent generation in the SnO2 thin film surface layer. The critical lifetime of prolonged photo-excited electron-hole pair is calculated to be 8.3 ms.

Nonlinear Analytical Modeling of Interfacial Phenomenon and Nano-Size Microstructural Features to Better Correlate Nde Electronic Property Measurements to Material State

NASA Astrophysics Data System (ADS)

Roubidoux, J. A.; Jackson, J. E.; Lasseigne, A. N.; Mishra, B.; Olson, D. L.

2010-02-01

This paper correlates nonlinear material properties to nondestructive electronic measurements by using wave analysis techniques (e.g. Perturbation Methods) and incorporating higher-order phenomena. The correlations suggest that nondestructive electronic property measurements and practices can be used to assess thin films, surface layers, and other advanced materials that exhibit modified behaviors based on their space-charged interfacial behavior.

Hydration of excess electrons trapped in charge pockets on molecular surfaces

NASA Astrophysics Data System (ADS)

Jalbout, Abraham F.; Del Castillo, R.; Adamowicz, Ludwik

2007-01-01

In this work we strive to design a novel electron trap located on a molecular surface. The process of electron trapping involves hydration of the trapped electron. Previous calculations on surface electron trapping revealed that clusters of OH groups can form stable hydrogen-bonded networks on one side of a hydrocarbon surface (i.e. cyclohexane sheets), while the hydrogen atoms on the opposite side of the surface form pockets of positive charge that can attract extra negative charge. The excess electron density on such surfaces can be further stabilized by interactions with water molecules. Our calculations show that these anionic systems are stable with respect to vertical electron detachment (VDE).

Room-temperature in situ fabrication of Bi2O3/g-C3N4 direct Z-scheme photocatalyst with enhanced photocatalytic activity

NASA Astrophysics Data System (ADS)

He, Rongan; Zhou, Jiaqian; Fu, Huiqing; Zhang, Shiying; Jiang, Chuanjia

2018-02-01

Constructing direct Z-scheme heterojunction is an effective approach to separating photogenerated charge carriers and improving the activity of semiconductor photocatalysts. Herein, a composite of bismuth(III) oxide (Bi2O3) and graphitic carbon nitride (g-C3N4) was in situ fabricated at room temperature by photoreductive deposition of Bi3+ and subsequent air-oxidation of the resultant metallic Bi. Quantum-sized ω-Bi2O3 nanoparticles approximately 6 nm in diameter were uniformly distributed on the surface of mesoporous g-C3N4. The as-prepared Bi2O3/g-C3N4 composite exhibited higher photocatalytic activity than pure Bi2O3 and g-C3N4 for photocatalytic degradation of phenol under visible light. Reactive species trapping experiments revealed that superoxide radicals and photogenerated holes played important roles in the photocatalytic degradation of phenol. The enhanced photocatalytic activity, identification of reactive species and higher rate of charge carrier recombination (as indicated by stronger photoluminescence intensity) collectively suggest that the charge migration within the Bi2O3/g-C3N4 composite followed a Z-scheme mechanism. Photogenerated electrons on the conduction band of Bi2O3 migrate to the valence band of g-C3N4 and combine with photogenerated holes therein. At the cost of these less reactive charge carriers, the Z-scheme heterojunction enables efficient charge separation, while preserving the photogenerated electrons and holes with stronger redox abilities, which is beneficial for enhanced photocatalytic activity.

Work Function of Oxide Ultrathin Films on the Ag(100) Surface.

PubMed

Sementa, Luca; Barcaro, Giovanni; Negreiros, Fabio R; Thomas, Iorwerth O; Netzer, Falko P; Ferrari, Anna Maria; Fortunelli, Alessandro

2012-02-14

Theoretical calculations of the work function of monolayer (ML) and bilayer (BL) oxide films on the Ag(100) surface are reported and analyzed as a function of the nature of the oxide for first-row transition metals. The contributions due to charge compression, charge transfer and rumpling are singled out. It is found that the presence of empty d-orbitals in the oxide metal can entail a charge flow from the Ag(100) surface to the oxide film which counteracts the decrease in the work function due to charge compression. This flow can also depend on the thickness of the film and be reduced in passing from ML to BL systems. A regular trend is observed along first-row transition metals, exhibiting a maximum for CuO, in which the charge flow to the oxide is so strong as to reverse the direction of rumpling. A simple protocol to estimate separately the contribution due to charge compression is discussed, and the difference between the work function of the bare metal surface and a Pauling-like electronegativity of the free oxide slabs is used as a descriptor quantity to predict the direction of charge transfer.

Molecular adsorption at electrolyte/α-Al2O3 interface of aluminum electrolytic capacitor revealed by sum frequency vibrational spectroscopy.

PubMed

Jia, Ming; Hu, Xiaoyu; Liu, Jin; Liu, Yexiang; Ai, Liang

2017-05-21

The operating voltage of an aluminum electrolytic capacitor is determined by the breakdown voltage (U b ) of the Al 2 O 3 anode. U b is related to the molecular adsorption at the Al 2 O 3 /electrolyte interface. Therefore, we have employed sum-frequency vibrational spectroscopy (SFVS) to study the adsorption states of a simple electrolyte, ethylene glycol (EG) solution with ammonium adipate, on an α-Al 2 O 3 surface. In an acidic electrolyte (pH < 6), the Al 2 O 3 surface is positively charged. The observed SFVS spectra show that long chain molecules poly ethylene glycol and ethylene glycol adipate adopt a "lying" orientation at the interface. In an alkaline electrolyte (pH > 8), the Al 2 O 3 surface is negatively charged and the short chain EG molecules adopt a "tilting" orientation. The U b results exhibit a much higher value at pH < 6 compared with that at pH > 8. Since the "lying" long chain molecules cover and protect the Al 2 O 3 surface, U b increases with a decrease of pH. These findings provide new insights to study the breakdown mechanisms and to develop new electrolytes for high operating voltage capacitors.

Tunable supercapacitance of electrospun Mn3O4 beaded chains via charge- discharge cycling and control parameters

NASA Astrophysics Data System (ADS)

Radhamani, A. V.; Ramachandra Rao, M. S.

2017-05-01

Here we report on the tunable supercapacitance of the Mn3O4 beaded chains synthesized by a simple and low cost electro-spinning process. Tuning is achieved by controlled phase transformation of surface spinel Mn3O4 beaded chains to layered-birnessite MnO2 nanoflakes through galvanostatic charge-discharge cycling. Phase transformation rate is optimized to get maximum capacitance by controlling the parameters such as applied specific current value, number of galvanostatic charge-discharge cycles, micro-structure of working electrode material and the selection of potential range. A maximum specific capacitance of ∼445 F g-1 and areal capacitance of ∼495 mF cm-2 are obtained at current densities of 0.5 A g-1 and 0.125 mA cm-2 respectively. The superior performance in case of layered-spinel composites among similar nanostructures is due to high surface to volume ratio of the MnO2 nanoflakes formed from the Mn3O4 beaded chains which in turn give rise to large number of surface active sites for the redox reaction to take place. About 100% of capacity retention and coulombic efficiency are observed for ∼1000 cycles even at a higher current density of 7 A g-1. Morphological dependence of the phase transformation rate is investigated by preparing two different morphologies of Mn3O4viz., octahedrons and spherical nanoparticles.

TiO2 nanocrystals decorated Z-schemed core-shell CdS-CdO nanorod arrays as high efficiency anodes for photoelectrochemical hydrogen generation.

PubMed

Li, Chia-Hsun; Hsu, Chan-Wei; Lu, Shih-Yuan

2018-07-01

TiO 2 nanocrystals decorated core-shell CdS-CdO nanorod arrays, TiO 2 @CdO/CdS NR, were fabricated as high efficiency anodes for photoelctrochemical hydrogen generation. The novel sandwich heterostructure was constructed from first growth of CdS nanorod arrays on a fluorine doped tin oxide (FTO) substrate with a hydrothermal process, followed by in situ generation of CdO thin films of single digit nanometers from the CdS nanorod surfaces through thermal oxidation, and final decoration of TiO 2 nanocrystals of 10-20 nm via a successive ionic layer absorption and reaction process. The core-shell CdS-CdO heterostructure possesses a Z-scheme band structure to enhance interfacial charge transfer, facilitating effective charge separation to suppress electron-hole recombination within CdS for much improved current density generation. The final decoration of TiO 2 nanocrystals passivates surface defects and trap states of CdO, further suppressing surface charge recombination for even higher photovoltaic conversion efficiencies. The photoelectrochemical performances of the plain CdS nanorod array were significantly improved with the formation of the sandwich heterostructure, achieving a photo current density of 3.2 mA/cm 2 at 1.23 V (vs. RHE), a 141% improvement over the plain CdS nanorod array and a 32% improvement over the CdO/CdS nanorod array. Copyright © 2018 Elsevier Inc. All rights reserved.

Effect of Ca2+ ion concentration on adsorption of poly(carboxylate ether)-based (PCE) superplasticizer on mica.

PubMed

Wu, Bo; Chun, Byong-Wa; Gu, Le; Kuhl, Tonya L

2018-05-09

Poly(carboxylate ether)-based (PCE) superplasticizers consist of a carboxylic acid backbone and grafted poly(ethylene glycol) (PEG) side chains. Ca 2+ ion bridging mechanism is commonly purported to control PCE's adsorption on negatively charged cement particle surfaces in cement suspension, thus PCE was expected to adsorb on negatively charged surfaces in synthetic pore solutions via Ca 2+ /COO - interactions. Adsorption behaviors of a commercial PCE on negatively charged mica were studied in aqueous electrolyte solutions by a surface forces apparatus. Direct force measurements indicated that the PCE adsorbed onto mica from 0.1 M K 2 SO 4 due to K + ion chelation by the ether oxygen units CH 2 CH 2 O on the PEG chains, but surprisingly did not adsorb from either 0.1 M K 2 SO 4 with saturated Ca(OH) 2 or 0.1 M Ca(NO 3 ) 2 . The adsorption in K 2 SO 4 was weak, enabling the adsorbed PCE layers to be squeezed out under modest compression. Upon separating the surfaces, the PCE immediately achieved an identical re-adsorption. In high-calcium conditions, the PCE was highly positively charged due to Ca 2+ ion chelation by PEG chains and backbone carboxylic groups COO - , and mica also underwent charge reversal due to electrostatic adsorption/binding of Ca 2+ ions. Consequently, the interaction between mica and PCE was electrostatically repulsive and no PCE adsorption occurred. These findings can be explained by the complex interplay of ion chelation by PEG chains, electrostatic binding and screening interactions with charged surfaces in the presence of monovalent and divalent counterions, and ultimately charge reversal of both the charged surfaces and polyelectrolyte in high divalent ion conditions. Copyright © 2018 Elsevier Inc. All rights reserved.

Study of Perfluorophosphonic Acid Surface Modifications on Zinc Oxide Nanoparticles.

PubMed

Quiñones, Rosalynn; Shoup, Deben; Behnke, Grayce; Peck, Cynthia; Agarwal, Sushant; Gupta, Rakesh K; Fagan, Jonathan W; Mueller, Karl T; Iuliucci, Robbie J; Wang, Qiang

2017-11-28

In this study, perfluorinated phosphonic acid modifications were utilized to modify zinc oxide (ZnO) nanoparticles because they create a more stable surface due to the electronegativity of the perfluoro head group. Specifically, 12-pentafluorophenoxydodecylphosphonic acid, 2,3,4,5,6-pentafluorobenzylphosphonic acid, and (1H,1H,2H,2H-perfluorododecyl)phosphonic acid have been used to form thin films on the nanoparticle surfaces. The modified nanoparticles were then characterized using infrared spectroscopy, X-ray photoelectron spectroscopy, and solid-state nuclear magnetic resonance spectroscopy. Dynamic light scattering and scanning electron microscopy-energy dispersive X-ray spectroscopy were utilized to determine the particle size of the nanoparticles before and after modification, and to analyze the film coverage on the ZnO surfaces, respectively. Zeta potential measurements were obtained to determine the stability of the ZnO nanoparticles. It was shown that the surface charge increased as the alkyl chain length increases. This study shows that modifying the ZnO nanoparticles with perfluorinated groups increases the stability of the phosphonic acids adsorbed on the surfaces. Thermogravimetric analysis was used to distinguish between chemically and physically bound films on the modified nanoparticles. The higher weight loss for 12-pentafluorophenoxydodecylphosphonic acid and (1H,1H,2H,2H-perfluorododecyl)phosphonic acid modifications corresponds to a higher surface concentration of the modifications, and, ideally, higher surface coverage. While previous studies have shown how phosphonic acids interact with the surfaces of ZnO, the aim of this study was to understand how the perfluorinated groups can tune the surface properties of the nanoparticles.

Capacitance, charge dynamics, and electrolyte-surface interactions in functionalized carbide-derived carbon electrodes

DOE PAGES

Dyatkin, Boris; Mamontov, Eugene; Cook, Kevin M.; ...

2015-12-24

Our study analyzed the dynamics of ionic liquid electrolyte inside of defunctionalized, hydrogenated, and aminated pores of carbide-derived carbon supercapacitor electrodes. The approach tailors surface functionalities and tunes nanoporous structures to decouple the influence of pore wall composition on capacitance, ionic resistance, and long-term cyclability. Moreover, quasi-elastic neutron scattering probes the self-diffusion properties and electrode-ion interactions of electrolyte molecules confined in functionalized pores. Room-temperature ionic liquid interactions in confined pores are strongest when the hydrogen-containing groups are present on the surface. This property translates into higher capacitance and greater ion transport through pores during electrochemical cycling. Aminated pores, unlike hydrogenatedmore » pores, do not favorably interact with ionic liquid ions and, subsequently, are outperformed by defunctionalized surfaces.« less

Nanoscale charge transfer and diffusion at the MoS2/SiO2 interface by atomic force microscopy: contact injection versus triboelectrification.

PubMed

Xu, Rui; Ye, Shili; Xu, Kunqi; Lei, Le; Hussain, Sabir; Zheng, Zhiyue; Pang, Fei; Xing, Shuya; Liu, Xinmeng; Ji, Wei; Cheng, Zhihai

2018-08-31

Understanding the process of charge generation, transfer, and diffusion between two-dimensional (2D) materials and their supporting substrates is very important for potential applications of 2D materials. Compared with the systematic studies of triboelectric charging in a bulk sample, a fundamental understanding of the triboelectrification of the 2D material/insulator system is rather limited. Here, the charge transfer and diffusion of both the SiO 2 surface and MoS 2 /SiO 2 interface through contact electrification and frictional electrification are investigated systematically in situ by scanning Kelvin probe microscopy and dual-harmonic electrostatic force microscopy. Different from the simple static charge transfer between SiO 2 and the PtSi alloy atomic force microscope (AFM) tip, the charge transfer between the tip and the MoS 2 /SiO 2 system is complicated. Triboelectric charges, generated by contact or frictional electrification with the AFM tip, are trapped at the MoS 2 /SiO 2 interface and act as floating gates. The local charge discharge processes can be obtained by monitoring the surface potential. The charge decay time (τ) of the MoS 2 /SiO 2 interface is one (or two) orders of magnitude larger than the decay time τ of the SiO 2 surface. This work facilitates an understanding of the triboelectric and de-electrification of the interface between 2D materials and substrates. In addition to the charge transfer and diffusion, we demonstrate the nanopatterns of surface and interfacial charges, which have great potential for the application of self-assembly of charged nanostructures.

Entropic effects in the electric double layer of model colloids with size-asymmetric monovalent ions

NASA Astrophysics Data System (ADS)

Guerrero-García, Guillermo Iván; González-Tovar, Enrique; Olvera de la Cruz, Mónica

2011-08-01

The structure of the electric double layer of charged nanoparticles and colloids in monovalent salts is crucial to determine their thermodynamics, solubility, and polyion adsorption. In this work, we explore the double layer structure and the possibility of charge reversal in relation to the size of both counterions and coions. We examine systems with various size-ratios between counterions and coions (ion size asymmetries) as well as different total ion volume fractions. Using Monte Carlo simulations and integral equations of a primitive-model electric double layer, we determine the highest charge neutralization and electrostatic screening near the electrified surface. Specifically, for two binary monovalent electrolytes with the same counterion properties but differing only in the coion's size surrounding a charged nanoparticle, the one with largest coion size is found to have the largest charge neutralization and screening. That is, in size-asymmetric double layers with a given counterion's size the excluded volume of the coions dictates the adsorption of the ionic charge close to the colloidal surface for monovalent salts. Furthermore, we demonstrate that charge reversal can occur at low surface charge densities, given a large enough total ion concentration, for systems of monovalent salts in a wide range of ion size asymmetries. In addition, we find a non-monotonic behavior for the corresponding maximum charge reversal, as a function of the colloidal bare charge. We also find that the reversal effect disappears for binary salts with large-size counterions and small-size coions at high surface charge densities. Lastly, we observe a good agreement between results from both Monte Carlo simulations and the integral equation theory across different colloidal charge densities and 1:1-elec-trolytes with different ion sizes.

Probing surface charge potentials of clay basal planes and edges by direct force measurements.

PubMed

Zhao, Hongying; Bhattacharjee, Subir; Chow, Ross; Wallace, Dean; Masliyah, Jacob H; Xu, Zhenghe

2008-11-18

The dispersion and gelation of clay suspensions have major impact on a number of industries, such as ceramic and composite materials processing, paper making, cement production, and consumer product formulation. To fundamentally understand controlling mechanisms of clay dispersion and gelation, it is necessary to study anisotropic surface charge properties and colloidal interactions of clay particles. In this study, a colloidal probe technique was employed to study the interaction forces between a silica probe and clay basal plane/edge surfaces. A muscovite mica was used as a representative of 2:1 phyllosilicate clay minerals. The muscovite basal plane was prepared by cleavage, while the edge surface was obtained by a microtome cutting technique. Direct force measurements demonstrated the anisotropic surface charge properties of the basal plane and edge surface. For the basal plane, the long-range forces were monotonically repulsive within pH 6-10 and the measured forces were pH-independent, thereby confirming that clay basal planes have permanent surface charge from isomorphic substitution of lattice elements. The measured interaction forces were fitted well with the classical DLVO theory. The surface potentials of muscovite basal plane derived from the measured force profiles were in good agreement with those reported in the literature. In the case of edge surfaces, the measured forces were monotonically repulsive at pH 10, decreasing with pH, and changed to be attractive at pH 5.6, strongly suggesting that the charge on the clay edge surfaces is pH-dependent. The measured force profiles could not be reasonably fitted with the classical DLVO theory, even with very small surface potential values, unless the surface roughness was considered. The surface element integration (SEI) method was used to calculate the DLVO forces to account for the surface roughness. The surface potentials of the muscovite edges were derived by fitting the measured force profiles with the surface element integrated DLVO model. The point of zero charge of the muscovite edge surface was estimated to be pH 7-8.

Potential of coconut shell activated carbon (CSAC) in removing contaminants for water quality improvement: A critical review

NASA Astrophysics Data System (ADS)

Akhir, Muhammad Fitri Mohd; Saad, Noor Aida; Zakaria, Nor Azazi

2017-10-01

Commonly, water contaminations occur due to human-induced conditions such as industrial discharge and urban activities. The widely identified contaminants are heavy metal. The toxicity of those heavy metal elements is high and very poisonous to humans' health and environment even at lower dose or concentration of exposure. Chronic poisoning can cause fatal or defect to one's body or environment. Organic contaminants such as oil and microbial are also found due to decomposition of organic matter. The excellent quality adsorption of contaminants is highly related to surface area, pore size, pore volume, and amount plus type of functional group on surface of CSAC. The higher the surface area and pore volume, the higher adsorption that CSAC have towards contaminants. In comparison to meso-pore and macro-pore, micro-pore is better for trapping and adsorbing water contaminants. The purpose of this article is to critically review the potential of CSAC in increasing adsorption to remove contaminants for water quality improvement. A critical review is implemented using search engine like Science Direct. Alkali-modification is shown to have good adsorption in anion elements and organic matter due to improvement of hydrophobic organic compound (HOC) while acid-modification is good in cation elements adsorption. Strong alkali impregnated solution makes CSAC more hydrophobic and positively charge especially after increasing the impregnation dosage. Strong acid of adsorbate affects the quality of adsorption by reducing the surface area, pore volume and it also breaks the Van der Waals forces between adsorbent and adsorbate. However, the formation of oxygen helps the activated carbon surface to become more hydrophilic and negative charge is produced. It helps the effectiveness of metal adsorption. Therefore, by controlling dosage and types of functional groups on surface of CSAC and the pH of adsorbate, it can contribute to high adsorption of organic and inorganic contaminants in the water.

The Influence of Particle Charge on Heterogeneous Reaction Rate Coefficients

NASA Technical Reports Server (NTRS)

Aikin, A. C.; Pesnell, W. D.

2000-01-01

The effects of particle charge on heterogeneous reaction rates are presented. Many atmospheric particles, whether liquid or solid are charged. This surface charge causes a redistribution of charge within a liquid particle and as a consequence a perturbation in the gaseous uptake coefficient. The amount of perturbation is proportional to the external potential and the square of the ratio of debye length in the liquid to the particle radius. Previous modeling has shown how surface charge affects the uptake coefficient of charged aerosols. This effect is now included in the heterogeneous reaction rate of an aerosol ensemble. Extension of this analysis to ice particles will be discussed and examples presented.

Group IV nanocrystals with ion-exchangeable surface ligands and methods of making the same

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

Wheeler, Lance M.; Nichols, Asa W.; Chernomordik, Boris D.

Methods are described that include reacting a starting nanocrystal that includes a starting nanocrystal core and a covalently bound surface species to create an ion-exchangeable (IE) nanocrystal that includes a surface charge and a first ion-exchangeable (IE) surface ligand ionically bound to the surface charge, where the starting nanocrystal core includes a group IV element.

Single ion induced surface nanostructures: a comparison between slow highly charged and swift heavy ions.

PubMed

Aumayr, Friedrich; Facsko, Stefan; El-Said, Ayman S; Trautmann, Christina; Schleberger, Marika

2011-10-05

This topical review focuses on recent advances in the understanding of the formation of surface nanostructures, an intriguing phenomenon in ion-surface interaction due to the impact of individual ions. In many solid targets, swift heavy ions produce narrow cylindrical tracks accompanied by the formation of a surface nanostructure. More recently, a similar nanometric surface effect has been revealed for the impact of individual, very slow but highly charged ions. While swift ions transfer their large kinetic energy to the target via ionization and electronic excitation processes (electronic stopping), slow highly charged ions produce surface structures due to potential energy deposited at the top surface layers. Despite the differences in primary excitation, the similarity between the nanostructures is striking and strongly points to a common mechanism related to the energy transfer from the electronic to the lattice system of the target. A comparison of surface structures induced by swift heavy ions and slow highly charged ions provides a valuable insight to better understand the formation mechanisms. © 2011 IOP Publishing Ltd

The influence of size and charge of chitosan/polyglutamic acid hollow spheres on cellular internalization, viability and blood compatibility.

PubMed

Dash, Biraja C; Réthoré, Gildas; Monaghan, Michael; Fitzgerald, Kathleen; Gallagher, William; Pandit, Abhay

2010-11-01

Polymeric hollow spheres can be tailored as efficient carriers of various therapeutic molecules due to their tunable properties. However, the entry of these synthetic vehicles into cells, their cell viability and blood compatibility depend on their physical and chemical properties e.g. size, surface charge. Herein, we report the effect of size and surface charge on cell viability and cellular internalization behaviour and their effect on various blood components using chitosan/polyglutamic acid hollow spheres as a model system. Negatively charged chitosan/polyglutamic acid hollow spheres of various sizes 100, 300, 500 and 1000 nm were fabricated using a template based method and covalently surface modified using linear polyethylene glycol and methoxyethanol amine to create a gradient of surface charge from negative to neutrally charged spheres respectively. The results here suggest that both size and surface charge have a significant influence on the sphere's behaviour, most prominently on haemolysis, platelet activation, plasma recalcification time, cell viability and internalization over time. Additionally, cellular internalization behaviour and viability was found to vary with different cell types. These results are in agreement with those of inorganic spheres and liposomes, and can serve as guidelines for tailoring polymeric solid spheres for specific desired applications in biological and pharmaceutical fields, including the design of nanometer to submicron-sized delivery vehicles. Copyright (c) 2010 Elsevier Ltd. All rights reserved.