Characterization of Unimorph-Membrane Microactuators and Error-Analysis of the Characterization Process

NASA Technical Reports Server (NTRS)

Wright, Matthew W.

2005-01-01

Microactuators are versatile, low-cost, low-mass electrical-mechanical devices that can be used in many applications. Microactuators consist of two electrodes sandwiching a PZT (piezo-electric) film between them. The centers of the microactuators deflect when a voltage is applied across the electrodes. In order to correctly apply this technology for use, it is important to fully characterize the actuation behavior. Measuring the deflection profile as a function of the voltage of various microactuators is crucial. This measurement process has errors associated with it, so it is being studied to determine the accuracy of the data. In certain applications, microactuators may undergo many cycles of deflection; testing various microactuators through many cycles of deflection simulates these circumstances. However, due to an unknown issue, many of the microactuators exhibit defects that cause them to fail when voltage is applied to their electrodes. These defects do not allow for the acquisition of significant deflection profiles. Vibrations are the largest cause of error in deflection measurements, and the microactuators withstand continuous cycles of deflection, yet the cause of damage is still to be determined. Future projects will be needed to characterize the deflection profiles of various microactuators and to overcome the defects in the microactuators that are currently present.

Photodeformable polymer materials: towards light-driven spoke-type micromotor application

NASA Astrophysics Data System (ADS)

Zhu, Yutian; Zheng, Lihui; Liu, Zhao; Liu, Heng; Yu, Yanlei

2014-06-01

Using a photodeformable polymer material, liquid-crystalline polymer incorporated with azobenzene moieties, a spoke-type micromotor is designed, which could convert light energy directly into mechanical work. It consists of four driving belts, whose mechanical model is established and the driving moment of the micromotor upon irradiation with UV light and without photoirradiation is calculated, respectively. According to the calculated driving moment, the UV light and the visible light are arranged to irradiate from parallel and opposite direction of the micromotor simultaneously, which convert the bending deflection of the photodeformable polymer material belts to continuous rotation of the micromotor. As light is a green energy source that can be controlled remotely, instantly and without the aid of electric wires, the photodeformable polymer material has great potential to be utilized in micro-actuator and other relative applications.

Functional Response of NiTi Elements for Smart Micro-actuation Applications

NASA Astrophysics Data System (ADS)

Biffi, C. A.; Nespoli, A.; Previtali, B.; Villa, E.; Tuissi, A.

2014-07-01

Shape memory alloys (SMAs) can be considered a good candidate for actuation applications in the current micro-technology field. In the micro-scale, the temporal response of the SMA actuators can be improved, because of faster cooling during the austenite-martensite transformation. One of the most investigated geometries for this purpose has been the snake-like arrangement, which allows high strokes with considerable forces to be obtained. In this work, SMA elements for micro-actuators were patterned by laser machining in a snake-like shape. Subsequent surface chemical etching was adopted to improve the functional properties of the micro-elements. Calorimetric analysis and thermo-mechanical response of 90 μm thick SMA elements were reported for the evaluation of their functional performances. Moreover, the effect of post-thermal treatment and grain orientation were also evaluated on the final performances.

Microstructure and Shape Memory Behavior of Ti-Nb Shape Memory Alloy Thin Film

NASA Astrophysics Data System (ADS)

Meng, X. L.; Sun, B.; Sun, J. Y.; Gao, Z. Y.; Cai, W.; Zhao, L. C.

2017-09-01

Ti-Nb shape memory alloy (SMA) thin film is a promising candidate applied as microactuator in biomedical field. In this study, the microstructure and shape memory behavior of Ti-Nb SMA thin films in different heat treatment conditions have been investigated. Fine ω phases embedded in the β phase matrix suppress the martensitic transformation of the films. As a result, the as-deposited and most of the annealed films consist of the β and α″ dual phases. The annealed Ti-Nb thin film shows excellent superelasticity effect when deformed above the reverse martensitic transformation temperature, that is 3.5% total recovery strain can be obtained when 4% pre-strain is loaded.

Evolution from MEMS-based Linear Drives to Bio-based Nano Drives

NASA Astrophysics Data System (ADS)

Fujita, Hiroyuki

The successful extension of semiconductor technology to fabricate mechanical parts of the sizes from 10 to 100 micrometers opened wide ranges of possibilities for micromechanical devices and systems. The fabrication technique is called micromachining. Micromachining processes are based on silicon integrated circuits (IC) technology and used to build three-dimensional structures and movable parts by the combination of lithography, etching, film deposition, and wafer bonding. Microactuators are the key devices allowing MEMS to perform physical functions. Some of them are driven by electric, magnetic, and fluidic forces. Some others utilize actuator materials including piezoelectric (PZT, ZnO, quartz) and magnetostrictive materials (TbFe), shape memory alloy (TiNi) and bio molecular motors. This paper deals with the development of MEMS based microactuators, especially linear drives, following my own research experience. They include an electrostatic actuator, a superconductive levitated actuator, arrayed actuators, and a bio-motor-driven actuator.

Effect of Substrate Roughness on Adhesion and Structural Properties of Ti-Ni Shape Memory Alloy Thin Film.

PubMed

Kim, Donghwan; Lee, Hyunsuk; Bae, Joohyeon; Jeong, Hyomin; Choi, Byeongkeun; Nam, Taehyun; Noh, Jungpil

2018-09-01

Ti-Ni shape memory alloy (SMA) thin films are very attractive material for industrial and medical applications such as micro-actuator, micro-sensors, and stents for blood vessels. An important property besides shape memory effect in the application of SMA thin films is the adhesion between the film and the substrate. When using thin films as micro-actuators or micro-sensors in MEMS, the film must be strongly adhered to the substrate. On the other hand, when using SMA thin films in medical devices such as stents, the deposited alloy thin film must be easily separable from the substrate for efficient processing. In this study, we investigated the effect of substrate roughness on the adhesion of Ti-Ni SMA thin films, as well as the structural properties and phase-transformation behavior of the fabricated films. Ti-Ni SMA thin films were deposited onto etched glass substrates with magnetron sputtering. Radio frequency plasma was used for etching the substrate. The adhesion properties were investigated through progressive scratch test. Structural properties of the films were determined via Feld emission scanning electron microscopy, X-ray diffraction measurements (XRD) and Energy-dispersive X-ray spectroscopy analysis. Phase transformation behaviors were observed with differential scanning calorimetry and low temperature-XRD. Ti-Ni SMA thin film deposited onto rough substrate provides higher adhesive strength than smooth substrate. However the roughness of the substrate has no influence on the growth and crystallization of the Ti-Ni SMA thin films.

Laser and Surface Processes of NiTi Shape Memory Elements for Micro-actuation

NASA Astrophysics Data System (ADS)

Nespoli, Adelaide; Biffi, Carlo Alberto; Previtali, Barbara; Villa, Elena; Tuissi, Ausonio

2014-04-01

In the current microtechnology for actuation field, shape memory alloys (SMA) are considered one of the best candidates for the production of mini/micro devices thanks to their high power-to-weight ratio as function of the actuator weight and hence for their capability of generating high mechanical performance in very limited spaces. In the microscale the most suitable conformation of a SMA actuator is given by a planar wavy formed arrangement, i.e., the snake-like shape, which allows high strokes, considerable forces, and devices with very low sizes. This uncommon and complex geometry becomes more difficult to be realized when the actuator dimensions are scaled down to micrometric values. In this work, micro-snake-like actuators are laser machined using a nanosecond pulsed fiber laser, starting from a 120- μm-thick NiTi sheet. Chemical and electrochemical surface polishes are also investigated for the removal of the thermal damages of the laser process. Calorimetric and thermo-mechanical tests are accomplished to assess the NiTi microdevice performance after each step of the working process. It is shown that laser machining has to be followed by some post-processes in order to obtain a micro-actuator with good thermo-mechanical properties.

Scaling Laws of Microactuators and Potential Applications of Electroactive Polymers in MEMS

NASA Technical Reports Server (NTRS)

Liu, Chang; Bar-Cohen, Y.

1999-01-01

Besides the scale factor that distinguishes the various species, fundamentally biological muscles changes little between species, indicating a highly optimized system. Electroactive polymer actuators offer the closest resemblance to biological muscles, however besides the large actuation displacement these materials are falling short with regards to the actuation force. As improved materials are emerging it is becoming necessary to address key issues such as the need for effective electromechanical modeling and guiding parameters in scaling the actuators. In this paper, we will review the scaling laws for three major actuation mechanisms that are of relevance to micro electromechanical systems: electrostatic actuation, magnetic actuation, thermal bimetallic actuation, and piezoelectric actuation.

Investigations on colour dependent photo induced microactuation effect of FSMA and proposing suitable mechanisms to control the effect

NASA Astrophysics Data System (ADS)

Bagchi, A.; Sarkar, S.; Mukhopadhyay, P. K.

2018-02-01

Three different coloured focused laser beams were used to study the photo induced microactuation effect found in some ferromagnetic shape memory alloys. Besides trying to uncover the basic causes of this unique and as yet unexplained effect, these studies are to help find other conditions to further characterize the effect for practical use. In this study some mechanisms have been proposed to control the amplitude of actuation of the sample. Control of the actuation of the FSMA sample both linearly with the help of a continuously variable neutral density filter as well periodically with the help of a linear polarizer was achieved. Statistical analysis of the experimental data was also done by applying ANOVA studies on the data to conclusively provide evidence in support of the relationship between the actuation of the sample and the various controlling factors. This study is expected to pave the way to implement this property of the sample in fabricating and operating useful micro-mechanical systems in the near future.

Investigations on colour dependent photo induced microactuation effect of FSMA and proposing suitable mechanisms to control the effect

NASA Astrophysics Data System (ADS)

Bagchi, A.; Sarkar, S.; Mukhopadhyay, P. K.

2018-07-01

Three different coloured focused laser beams were used to study the photo induced microactuation effect found in some ferromagnetic shape memory alloys. Besides trying to uncover the basic causes of this unique and as yet unexplained effect, these studies are to help find other conditions to further characterize the effect for practical use. In this study some mechanisms have been proposed to control the amplitude of actuation of the sample. Control of the actuation of the FSMA sample both linearly with the help of a continuously variable neutral density filter as well periodically with the help of a linear polarizer was achieved. Statistical analysis of the experimental data was also done by applying ANOVA studies on the data to conclusively provide evidence in support of the relationship between the actuation of the sample and the various controlling factors. This study is expected to pave the way to implement this property of the sample in fabricating and operating useful micro-mechanical systems in the near future.

Fabrication of piezoelectric ceramic micro-actuator and its reliability for hard disk drives.

PubMed

Jing, Yang; Luo, Jianbin; Yang, Wenyan; Ju, Guoxian

2004-11-01

A new U-type micro-actuator for precisely positioning a magnetic head in high-density hard disk drives was proposed and developed. The micro-actuator is composed of a U-type stainless steel substrate and two piezoelectric ceramic elements. Using a high-d31 piezoelectric coefficient PMN-PZT ceramic plate and adopting reactive ion etching process fabricate the piezoelectric elements. Reliability against temperature was investigated to ensure the practical application to the drive products. The U-type substrate attached to each side via piezoelectric elements also was simulated by the finite-element method and practically measured by a laser Doppler vibrometer in order to testify the driving mechanics of it. The micro-actuator coupled with two piezoelectric elements featured large displacement of 0.875 microm and high-resonance frequency over 22 kHz. The novel piezoelectric micro-actuators then possess a useful compromise performance to displacement, resonance frequency, and generative force. The results reveal that the new design concept provides a valuable alternative for multilayer piezoelectric micro-actuators.

Arrays of EAP micro-actuators for single-cell stretching applications

NASA Astrophysics Data System (ADS)

Akbari, S.; Niklaus, M.; Shea, H.

2010-04-01

Mechanical stimuli are critical for the development and maintenance of most tissues such as muscles, cartilage, bones and blood vessels. The commercially available cell culture systems replicating the in vivo environment are typically based on simple membrane cell-stretching equipment, which can only measure the average response of large colonies of cells over areas of greater than one cm2. We present here the conceptual design and the complete fabrication process of an array of 128 Electro-Active Polymer (EAP) micro-actuators which are uni-axially stretched and hence used to impose unidirectional strain on single cells, make it feasible to do experiments on the cytomechanics of individual cells. The Finite Element Method is employed to study the effect of different design parameters on achievable strain, leading to the optimized design. Compliant gold electrodes are deposited by low-energy ion implantation on both sides of a PDMS membrane, as this technique allows making electrodes that support large strain with minimal stiffening of the elastomer. The membrane is bonded to a rigid support, leading to an array of 100×100 μm2 EAP actuators.

Design of a Shape Memory Alloy deployment hinge for reflector facets

NASA Technical Reports Server (NTRS)

Anders, W. S.; Rogers, C. A.

1991-01-01

A design concept for a Shape Memory Alloy (SMA) actuated hinge mechanism for deploying segmented facet-type reflector surfaces on antenna truss structures is presented. The mechanism uses nitinol, a nickel-titanium shape memory alloy, as a displacement-force micro-actuator. An electrical current is used to resistively heat a 'plastically' elongated SMA actuator wire, causing it to contract in response to a thermally-induced phase transformation. The resulting tension creates a moment, imparting rotary motion between two adjacent panels. Mechanical stops are designed into the device to limit its range of motion and to establish positioning accuracy at the termination of deployment. The concept and its operation are discussed in detail, and an analytical dynamic simulation model is presented. The model has been used to perform nondimensionalized parametric design studies.

Nature-inspired polymer actuators for micro-fluidic mixing.

NASA Astrophysics Data System (ADS)

den Toonder, Jaap M. J.; Bos, Femke; de Goede, Judith; Anderson, Patrick

2007-11-01

One particular micro-fluidics manipulation mechanism ``designed'' by nature is that due to a covering of beating cilia over the external surface of micro-organisms (e.g. Paramecium). A cilium can be viewed as a small hair or flexible rod (in protozoa: typical length 10 microns and diameter 0.1 microns) which is attached to the surface. We have developed polymer micro-actuators, made with standard micro-technology processing, which respond to an applied electrical or magnetic field by changing their shape. The shape and size of the polymer actuators mimics that of cilia occurring in nature. Flow visualization experiments show that the cilia can generate substantial fluid velocities, in the order of 1 mm/s. In addition, using specially designed geometrical configurations of the cilia, very efficient mixing is obtained. Since the artificial cilia can be actively controlled using electrical signals, they have exciting applications in micro-fluidic devices.

Environmentally responsive optical microstructured hybrid actuator assemblies and applications thereof

DOEpatents

Aizenberg, Joanna; Aizenberg, Michael; Kim, Philseok

2016-01-05

Microstructured hybrid actuator assemblies in which microactuators carrying designed surface properties to be revealed upon actuation are embedded in a layer of responsive materials. The microactuators in a microactuator array reversibly change their configuration in response to a change in the environment without requiring an external power source to switch their optical properties.

Cantilever-type Thermal Microactuators Fabricated by SOI-MUMPs with U-type and I-type Configurations

NASA Astrophysics Data System (ADS)

Osada, Takahiro; Ochiai, Kuniyuki; Osada, Kazuki; Muro, Hideo

Recently, the micro fluid systems have been extensively studied, where microactuators such as micro valves fabricated by MEMS technology are essential for realizing these systems. In this paper thermal microactuators with U-type and I-type shapes fabricated by SOI-MUMPs technology have been investigated for optimizing their configurations.

SMA Foils for MEMS: From Material Properties to the Engineering of Microdevices

NASA Astrophysics Data System (ADS)

Kohl, Manfred; Ossmer, Hinnerk; Gueltig, Marcel; Megnin, Christof

2018-03-01

In the early nineties, microelectromechanical systems (MEMS) technology has been still in its infancy. As silicon (Si) is not a transducer material, it was clear at the very beginning that mechanically active materials had to be introduced to MEMS in order to enable functional microdevices with actuation capability beyond electrostatics. At that time, shape memory alloys (SMAs) have been available in bulk form, mainly as SMA wires and SMA plates. On the macro scale, these materials show highest work densities compared to other actuation principles in the order of 107 J/m3, which stimulated research on the integration of SMA to MEMS. Subsequently, two approaches for producing planar materials have been initiated (1) magnetron sputtering of SMA thin films and (2) the integration of rolled SMA foils, which both turned out to be very successful creating a paradigm change in microactuation technology. The following review covers important milestones of the research and development of SMA foil-based microactuators including materials characterization, design engineering, technology, and demonstrator development as well as first commercial products.

SMA Foils for MEMS: From Material Properties to the Engineering of Microdevices

NASA Astrophysics Data System (ADS)

Kohl, Manfred; Ossmer, Hinnerk; Gueltig, Marcel; Megnin, Christof

2017-12-01

In the early nineties, microelectromechanical systems (MEMS) technology has been still in its infancy. As silicon (Si) is not a transducer material, it was clear at the very beginning that mechanically active materials had to be introduced to MEMS in order to enable functional microdevices with actuation capability beyond electrostatics. At that time, shape memory alloys (SMAs) have been available in bulk form, mainly as SMA wires and SMA plates. On the macro scale, these materials show highest work densities compared to other actuation principles in the order of 107 J/m3, which stimulated research on the integration of SMA to MEMS. Subsequently, two approaches for producing planar materials have been initiated (1) magnetron sputtering of SMA thin films and (2) the integration of rolled SMA foils, which both turned out to be very successful creating a paradigm change in microactuation technology. The following review covers important milestones of the research and development of SMA foil-based microactuators including materials characterization, design engineering, technology, and demonstrator development as well as first commercial products.

[Development of photothermal microactuator based on spectral analysis of photothermal expansion material].

PubMed

Liu, Chao; Zhang, Dong-Xian; Zhang, Hai-Jun

2009-11-01

The spectral characteristic of materials is the key factor of the photothermal microactuator's performance. The present article introduces the operating principle, and analyzes the relationship between the material spectral characteristic and its expansion. As the photothermal microactuator is an innovative microactuator based on photothermal expansion that absorbs the laser energy and converts it into internal energy to realize the microdrive, the optimal photothermal expansion material with proper absorption spectrum characteristic matching the spectrum of light driving source needs to be found. The reflection and absorption spectra of four types of polymeric material, including PVC, HDPE, LDPE and PET, were obtained by using the single integrating sphere method. The results indicate that the reflection spectrum of the dyed high-density polyethylene (HDPE) is of double-peak structure in visible band, and there is strong absorption within the range of 600-690 nm, which means it would match the light driving source quite well in the broad spectral range. Therefore, HDPE was chosen as the photothermal expansion material. In order to check out the feasibility and performance of the photothermal microactuactor based on HDPE, a prototyping microactuator 1 500 mm in length and 30 mm in thickness was manufactured by using an excimer laser micromachining system. With a laser diode (10 mW/650 nm) as the external power source to activate the microactuator, performance measurement experiments were carried out by using a self-produced video movement measurement system with a CCD-coupled microscope. The experiment results demonstrate that the deflection of the microactuator reaches 18.7 mm at 10 mW of laser power, showing that the characteristics of spectral absorption and light-heat transition are quite well at 650 nm. This novel photothermal microactuator has simple structure, adjustable displacement output, and more mobility, and can be controlled remotely, so it will be quite useful for applications in the fields of micro-optical-electro-mechanical systems (MOEMS).

My Experience with Ti-Ni-Based and Ti-Based Shape Memory Alloys

NASA Astrophysics Data System (ADS)

Miyazaki, Shuichi

2017-12-01

The present author has been studying shape memory alloys including Cu-Al-Ni, Ti-Ni-based, and Ni-free Ti-based alloys since 1979. This paper reviews the present author's research results for the latter two materials since 1981. The topics on the Ti-Ni-based alloys include the achievement of superelasticity in Ti-Ni alloys through understanding of the role of microstructures consisting of dislocations and precipitates, followed by the contribution to the development of application market of shape memory effect and superelasticity, characterization of the R-phase and monoclinic martensitic transformations, clarification of the basic characteristics of fatigue properties, development of sputter-deposited shape memory thin films and fabrication of prototypes of microactuators utilizing thin films, development of high temperature shape memory alloys, and so on. The topics of Ni-free Ti-based shape memory alloys include the characterization of the orthorhombic phase martensitic transformation and related shape memory effect and superelasticity, the effects of texture, omega phase and adding elements on the martensitic transformation and shape memory properties, clarification of the unique effects of oxygen addition to induce non-linear large elasticity, Invar effect and heating-induced martensitic transformation, and so on.

Unitaxial constant velocity microactuator

DOEpatents

McIntyre, Timothy J.

1994-01-01

A uniaxial drive system or microactuator capable of operating in an ultra-high vacuum environment. The mechanism includes a flexible coupling having a bore therethrough, and two clamp/pusher assemblies mounted in axial ends of the coupling. The clamp/pusher assemblies are energized by voltage-operated piezoelectrics therewithin to operatively engage the shaft and coupling causing the shaft to move along its rotational axis through the bore. The microactuator is capable of repeatably positioning to sub-manometer accuracy while affording a scan range in excess of 5 centimeters. Moreover, the microactuator generates smooth, constant velocity motion profiles while producing a drive thrust of greater than 10 pounds. The system is remotely controlled and piezoelectrically driven, hence minimal thermal loading, vibrational excitation, or outgassing is introduced to the operating environment.

Nature-inspired micro-fluidic manipulation using artificial cilia

NASA Astrophysics Data System (ADS)

den Toonder, Jaap; de Goede, Judith; Khatavkar, Vinayak; Anderson, Patrick

2006-11-01

One particular micro-fluidics manipulation mechanism ``designed'' by nature is that due to a covering of beating cilia over the external surface of micro-organisms (e.g. Paramecium). A cilium can be viewed as a small hair or flexible rod (in protozoa: typical length 10 μm and diameter 0.1 μm) which is attached to the surface. We have developed polymer micro-actuators, made with standard micro-technology processing, which respond to an applied electrical or magnetic field by changing their shape. The shape and size of the polymer actuators mimics that of cilia occurring in nature. We have shown experimentally that, indeed, our artificial cilia can induce significant flow velocities of at least 75 μm/s in a fluid with a viscosity of 10 mPas. In this paper we will give an overview of our activities in developing the polymer actuators and the corresponding technology, show experimental and numerical fluid flow results, and finally assess the feasibility of applying this new and attractive micro-fluidic actuation method in functional biosensors.

Photomobile polymer materials with crosslinked liquid-crystalline structures: molecular design, fabrication, and functions.

PubMed

Ube, Toru; Ikeda, Tomiki

2014-09-22

Crosslinked liquid-crystalline polymer materials that macroscopically deform when irradiated with light have been extensively studied in the past decade because of their potential in various applications, such as microactuators and microfluidic devices. The basic motions of these materials are contraction-expansion and bending-unbending, which are observed mainly in polysiloxanes and polyacrylates that contain photochromic moieties. Other sophisticated motions such as twisting, oscillation, rotation, and translational motion have also been achieved. In recent years, efforts have been made to improve the photoresponsive and mechanical properties of this novel class of materials through the modification of molecular structures, development of new fabrication methods, and construction of composite structures. Herein, we review structures, functions, and working mechanisms of photomobile materials and recent advances in this field. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electrostatic Microactuators for Precise Positioning of Neural Microelectrodes

PubMed Central

Muthuswamy, Jit; Okandan, Murat; Jain, Tilak; Gilletti, Aaron

2006-01-01

Microelectrode arrays used for monitoring single and multineuronal action potentials often fail to record from the same population of neurons over a period of time likely due to micromotion of neurons away from the microelectrode, gliosis around the recording site and also brain movement due to behavior. We report here novel electrostatic microactuated microelectrodes that will enable precise repositioning of the microelectrodes within the brain tissue. Electrostatic comb-drive microactuators and associated microelectrodes are fabricated using the SUMMiT V™ (Sandia's Ultraplanar Multilevel MEMS Technology) process, a five-layer polysilicon micromachining technology of the Sandia National labs, NM. The microfabricated microactuators enable precise bidirectional positioning of the microelectrodes in the brain with accuracy in the order of 1 μm. The microactuators allow for a linear translation of the microelectrodes of up to 5 mm in either direction making it suitable for positioning microelectrodes in deep structures of a rodent brain. The overall translation was reduced to approximately 2 mm after insulation of the microelectrodes with epoxy for monitoring multiunit activity. The microactuators are capable of driving the microelectrodes in the brain tissue with forces in the order of several micro-Newtons. Single unit recordings were obtained from the somatosensory cortex of adult rats in acute experiments demonstrating the feasibility of this technology. Further optimization of the insulation, packaging and interconnect issues will be necessary before this technology can be validated in long-term experiments. PMID:16235660

Velocity field measurements on high-frequency, supersonic microactuators

NASA Astrophysics Data System (ADS)

Kreth, Phillip A.; Ali, Mohd Y.; Fernandez, Erik J.; Alvi, Farrukh S.

2016-05-01

The resonance-enhanced microjet actuator which was developed at the Advanced Aero-Propulsion Laboratory at Florida State University is a fluidic-based device that produces pulsed, supersonic microjets by utilizing a number of microscale, flow-acoustic resonance phenomena. The microactuator used in this study consists of an underexpanded source jet that flows into a cylindrical cavity with a single, 1-mm-diameter exhaust orifice through which an unsteady, supersonic jet issues at a resonant frequency of 7 kHz. The flowfields of a 1-mm underexpanded free jet and the microactuator are studied in detail using high-magnification, phase-locked flow visualizations (microschlieren) and two-component particle image velocimetry. These are the first direct measurements of the velocity fields produced by such actuators. Comparisons are made between the flow visualizations and the velocity field measurements. The results clearly show that the microactuator produces pulsed, supersonic jets with velocities exceeding 400 m/s for roughly 60 % of their cycles. With high unsteady momentum output, this type of microactuator has potential in a range of ow control applications.

Thermal microactuator dimension analysis

NASA Astrophysics Data System (ADS)

Azman, N. D.; Ong, N. R.; Aziz, M. H. A.; Alcain, J. B.; Haimi, W. M. W. N.; Sauli, Z.

2017-09-01

The focus of this study was to analyse the stress and thermal flow of thermal microactuator with different type of materials and parameter using COMSOL Multiphysics software. Simulations were conducted on the existing thermal actuator and integrated it to be more efficient, low cost and low power consumption. In this simulation, the U-shaped actuator was designed and five different materials of the microactuator were studied. The result showed that Si Polycrystalline was the most suitable material used to produce thermal actuator for commercialization.

Mechanical Evaluation of Unobstructing Magnetic Microactuators for Implantable Ventricular Catheters

PubMed Central

Lee, Hyowon; Kolahi, Kameran; Bergsneider, Marvin; Judy, Jack W.

2017-01-01

Here, we report on the development and evaluation of novel unobstructing magnetic microactuators for maintaining the patency of implantable ventricular catheters used in hydrocephalus application. The treatment of hydrocephalus requires chronic implantation of a shunt system to divert excess cerebrospinal fluid from the brain. These shunt systems suffer from a high failure rate (>40%) within the first year of implantation, often due to biological accumulation. Previously, we have shown that magnetic microactuators can be used to remove biological blockage. The new cantilever-based magnetic microactuator presented in this paper improves upon the previous torsional design using a bimorph to induce a postrelease out-of-plane deflection that will prevent the device from occluding the pore at rest. The mechanical evaluations (i.e., postrelease deflection, static and dynamic responses) of fabricated devices are reported and compared with theoretical values. PMID:29151776

Dynamic properties of symmetric optothermal microactuator

NASA Astrophysics Data System (ADS)

You, Q. Y.; Zhang, H. J.; Wang, Y. D.; Chen, J. J.

2017-10-01

This paper proposes a method of a symmetric optothermal microactuator (S-OTMA) directly driven by laser pulse. Based on the principle of thermal flux, a dynamic model is established describing the laser-induced optothermal temperature rise and optothermal expansion of the S-OTMA’s expansion arm. The dynamic optothermal expansion and the relationship between the expansion amplitude and laser pulse frequency are simulated, indicating that the expansion arm expands and reverts periodically with the same frequency of the laser pulse, and that the expansion amplitude decreases with the increase of laser pulse frequency. Experiments have been further conducted on a micro-fabricated S-OTMA under a laser pulse of 3.3 mW power and 2-18 Hz frequency. It is shown that the S-OTMA can periodically deflect in accordance with the same frequency of the laser pulse, with a maximum response frequency of at least 18 Hz. The maximum deflection (vibration) amplitude is measured to be 13.7 µm (at 2 Hz), and the amplitude decreases as the frequency increases. Both the theoretical model and experiments prove that the S-OTMA is capable of implementing direct laser-controlled microactuation in which only ~3 mW laser power is demanded. Furthermore, bi-directional actuation of the optothermal microactuator (such as S-OTMA) can be easily achieved by alternately irradiating either arm of the microactuator. This work may broaden the applications of the S-OTMA, as well as optothermal microactuators in MEMS/MOEMS and micro/nano-technology.

Theoretical model of an optothermal microactuator directly driven by laser beams

NASA Astrophysics Data System (ADS)

Han, Xu; Zhang, Haijun; Xu, Rui; Wang, Shuying; Qin, Chun

2015-07-01

This paper proposes a novel method of optothermal microactuation based on single and dual laser beams (spots). The theoretical model of the optothermal temperature distribution of an expansion arm is established and simulated, indicating that the maximum temperature of the arm irradiated by dual laser spots, at the same laser power level, is much lower than that irradiated by one single spot, and thus the risk of burning out and damaging the optothermal microactuator (OTMA) can be effectively avoided. To verify the presented method, a 750 μm long OTMA with a 100 μm wide expansion arm is designed and microfabricated, and single/dual laser beams with a wavelength of 650 nm are adopted to carry out experiments. The experimental results showed that the optothermal deflection of the OTMA under the irradiation of dual laser spots is larger than that under the irradiation of a single spot with the same power, which is in accordance with theoretical prediction. This method of optothermal microactuation may expand the practical applications of microactuators, which serve as critical units in micromechanical devices and micro-opto-electro-mechanical systems (MOEMS).

Rate dependent direct inverse hysteresis compensation of piezoelectric micro-actuator used in dual-stage hard disk drive head positioning system.

PubMed

Rahman, Md Arifur; Al Mamun, Abdullah; Yao, Kui

2015-08-01

The head positioning servo system in hard disk drive is implemented nowadays using a dual-stage actuator—the primary stage consisting of a voice coil motor actuator providing long range motion and the secondary stage controlling the position of the read/write head with fine resolution. Piezoelectric micro-actuator made of lead zirconate titanate (PZT) has been a popular choice for the secondary stage. However, PZT micro-actuator exhibits hysteresis—an inherent nonlinear characteristic of piezoelectric material. The advantage expected from using the secondary micro-actuator is somewhat lost by the hysteresis of the micro-actuator that contributes to tracking error. Hysteresis nonlinearity adversely affects the performance and, if not compensated, may cause inaccuracy and oscillation in the response. Compensation of hysteresis is therefore an important aspect for designing head-positioning servo system. This paper presents a new rate dependent model of hysteresis along with rigorous analysis and identification of the model. Parameters of the model are found using particle swarm optimization. Direct inverse of the proposed rate-dependent generalized Prandtl-Ishlinskii model is used as the hysteresis compensator. Effectiveness of the overall solution is underscored through experimental results.

New Magnetic Microactuator Design Based on PDMS Elastomer and MEMS Technologies for Tactile Display.

PubMed

Streque, Jeremy; Talbi, Abdelkrim; Pernod, Philippe; Preobrazhensky, Vladimir

2010-01-01

Highly efficient tactile display devices must fulfill technical requirements for tactile stimulation, all the while preserving the lightness and compactness needed for handheld operation. This paper focuses on the elaboration of highly integrated magnetic microactuators for tactile display devices. FEM simulation, conception, fabrication, and characterization of these microactuators are presented in this paper. The current demonstrator offers a 4 × 4 flexible microactuator array with a resolution of 2 mm. Each actuator is composed of a Poly (Dimethyl-Siloxane) (PDMS) elastomeric membrane, magnetically actuated by coil-magnet interaction. It represents a proof of concept for fully integrated MEMS tactile devices, with fair actuation forces provided for a power consumption up to 100 mW per microactuator. The prototypes are destined to provide both static and dynamic tactile sensations, with an optimized membrane geometry for actuation frequencies between DC and 350 Hz. On the basis of preliminary experiments, this display device can offer skin stimulations for various tactile stimuli for applications in the fields of Virtual Reality or Human-Computer Interaction (HCI). Moreover, the elastomeric material used in this device and its global compactness offer great advantages in matter of comfort of use and capabilities of integration in haptic devices.

Shape memory polymers

DOEpatents

Wilson, Thomas S.; Bearinger, Jane P.

2017-08-29

New shape memory polymer compositions, methods for synthesizing new shape memory polymers, and apparatus comprising an actuator and a shape memory polymer wherein the shape memory polymer comprises at least a portion of the actuator. A shape memory polymer comprising a polymer composition which physically forms a network structure wherein the polymer composition has shape-memory behavior and can be formed into a permanent primary shape, re-formed into a stable secondary shape, and controllably actuated to recover the permanent primary shape. Polymers have optimal aliphatic network structures due to minimization of dangling chains by using monomers that are symmetrical and that have matching amine and hydroxl groups providing polymers and polymer foams with clarity, tight (narrow temperature range) single transitions, and high shape recovery and recovery force that are especially useful for implanting in the human body.

Shape memory polymers

DOEpatents

Wilson, Thomas S.; Bearinger, Jane P.

2015-06-09

New shape memory polymer compositions, methods for synthesizing new shape memory polymers, and apparatus comprising an actuator and a shape memory polymer wherein the shape memory polymer comprises at least a portion of the actuator. A shape memory polymer comprising a polymer composition which physically forms a network structure wherein the polymer composition has shape-memory behavior and can be formed into a permanent primary shape, re-formed into a stable secondary shape, and controllably actuated to recover the permanent primary shape. Polymers have optimal aliphatic network structures due to minimization of dangling chains by using monomers that are symmetrical and that have matching amine and hydroxyl groups providing polymers and polymer foams with clarity, tight (narrow temperature range) single transitions, and high shape recovery and recovery force that are especially useful for implanting in the human body.

Fabrication of a self-sensing electroactive polymer bimorph actuator based on polyvinylidene fluoride and its electrostrictive terpolymer

NASA Astrophysics Data System (ADS)

Engel, Leeya; Van Volkinburg, Kyle R.; Ben-David, Moti; Washington, Gregory N.; Krylov, Slava; Shacham-Diamand, Yosi

2016-04-01

In this paper, we report on the fabrication of a self-sensing electroactive polymer cantilevered bimorph beam actuator and its frequency response. Tip deflections of the beam, induced by applying an AC signal across ferroelectric relaxor polyvinylidene fluoride-trifluoroethylene chlorotrifluoroethylene (P(VDF-TrFE-CTFE)), reached a magnitude of 350μm under a field of ~55MV/m and were recorded externally using a laser Doppler vibrometer (LDV). Deflections were determined simultaneously by applying a sensing model to the voltage measured across the bimorph's integrated layer of piezoelectric polymer polyvinylidene fluoride (PVDF). The sensing model treats the structure as a simple Euler- Bernoulli cantilevered beam with two distributed active elements represented through the use of generalized functions and offers a method through which real time tip deflection can be measured without the need for external visualization. When not being used as a sensing element, the PVDF layer can provide an additional means for actuation of the beam via the converse piezoelectric effect, resulting in bidirectional control of the beam's deflections. Integration of flexible sensing elements together with modeling of the electroactive polymer beam can benefit the developing field of polymer microactuators which have applications in soft robotics as "smart" prosthetics/implants, haptic displays, tools for less invasive surgery, and sensing.

Laminated chemical and physical micro-jet actuators based on conductive media

NASA Astrophysics Data System (ADS)

Gadiraju, Priya D.

2008-04-01

This dissertation presents the development of electrically-powered, lamination-based microactuators for the realization of large arrays of high impulse and short duration micro-jets with potential applications in the field of micro-electro-mechanical systems (MEMS). Microactuators offer unique control opportunities by converting the input electrical or chemical energy stored in a propellant into useful mechanical energy. This small and precise control obtained can potentially be applied towards aerodynamic control and transdermal drug delivery applications. This thesis work discusses the feasibility of using microactuators for two such applications: Control of the motion of a spinning projectile by utilizing the chemically-driven microjets ejected from the actuators, and enhancement of the permeability properties of skin by selectively ablating the stratum corneum layer of skin using the physical microjets ejected from the actuators. This enhanced permeability of skin can later be used for the delivery of high molecular weight drugs for transdermal drug delivery. The development of electrically powered microactuators starts by fabricating an array of radially firing microactuators using lamination-based microfabrication techniques that potentially enable batch fabrication at low cost. The microactuators of this thesis consist of three main parts: a micro chamber in which the propellant is stored; two electrode structures through which electrical energy is supplied to the propellant; and a micro nozzle through which the propellant or released gases from the propellant are expanded as a jet. Once the actuators are fabricated, they are integrated with MEMS-process-compatible propellants and optimized so as to produce instantaneous ignition of the propellant. This instantaneous ignition is achieved either by making the propellant itself conductive, thus, passing an electric current directly through the propellant; or by discharging an arc across the propellant by placing it between two closely spaced electrodes. The first concept is demonstrated for the application of projectile maneuvering where energetic solid propellant is used in generating a high velocity gaseous jet and the second concept is demonstrated for transdermal drug delivery application where a rapid physical jet of a non-energetic propellant is generated. In the case of chemical-based microactuators, the feasibility of using conductive solid propellant based actuators for maneuvering a 25 mm bluff body projectile spinning at 600 Hz is presented. Several conductive solid propellants are developed and characterized for their electrical conductivity and required ignition energy. Finally, the propellant integrated microactuators are characterized for performance in terms of impulse delivered, thrust generated and duration of the jet. These experimental results are then compared to predicted results from simulations. In the case of physical based microactuators, the feasibility of using released physical jets from the microactuator array for transdermal drug delivery application is presented. Several bio-compatible and FDA-approved liquids are used as propellants and are characterized in terms of thrusts delivered and duration of the released jets. These thermo-mechanical jets are then used to expose skin locally so as to create micro conduits in the stratum corneum layer of skin. Both thermal effects and thermo-mechanical effects of the jet on exposed skin are studied. For both cases, histology of exposed skin is presented and its permeability to drug analog molecules is studied.

Development of blood extraction system for health monitoring system

NASA Astrophysics Data System (ADS)

Tsuchiya, Kazuyoshi; Nakanishi, Naoyuki; Nakamachi, Eiji

2004-03-01

The purpose of this research is to develop the compact human blood sampling device applied for a health monitoring system(HMS), which is called "Mobile Hospital". The HMS consists of (1) a micro electrical pumping system for blood extraction, (2) a bio-sensor to detect and evaluate an amount of Glucose, Cholesterol and Urea in extracted blood, by using enzyme such as Glucoseoxidase (GOD), Cholesteroloxidase and Urease. The mechanical design elements of the device are bio-compatible microneedle, indentation unit using a shape memory alloy(SMA) actuator and pumping unit using a piezoelectric microactuator. The design concept is the biomimetic micromachine of female mosquito"s blood sampling mechanism. The performances of the main mechanical elements such as indentation force of the microneedle, actual stroke of the indentation unit using a SMA actuator and liquid sampling ability of the pumping unit using PZT piezoelectric microactuator were measured. The 3 mm stroke of the indentation load generated by SMA actuator was 0.8mN. The amount of imitation blood extracted by using bimorph PZT actuators was about 0.5 microliters for 10 sec. A 60-micrometer outer diameter and 25-micrometer inner diameter Titanium microneedle, which size is same as female mosquito"s labium, was produced by sputter deposition.

Shape memory polymer medical device

DOEpatents

Maitland, Duncan [Pleasant Hill, CA; Benett, William J [Livermore, CA; Bearinger, Jane P [Livermore, CA; Wilson, Thomas S [San Leandro, CA; Small, IV, Ward; Schumann, Daniel L [Concord, CA; Jensen, Wayne A [Livermore, CA; Ortega, Jason M [Pacifica, CA; Marion, III, John E.; Loge, Jeffrey M [Stockton, CA

2010-06-29

A system for removing matter from a conduit. The system includes the steps of passing a transport vehicle and a shape memory polymer material through the conduit, transmitting energy to the shape memory polymer material for moving the shape memory polymer material from a first shape to a second and different shape, and withdrawing the transport vehicle and the shape memory polymer material through the conduit carrying the matter.

Optical switch using Risley prisms

DOEpatents

Sweatt, William C.; Christenson, Todd R.

2003-04-15

An optical switch using Risley prisms and rotary microactuators to independently rotate the wedge prisms of each Risley prism pair is disclosed. The optical switch comprises an array of input Risley prism pairs that selectively redirect light beams from a plurality of input ports to an array of output Risley prism pairs that similarly direct the light beams to a plurality of output ports. Each wedge prism of each Risley prism pair can be independently rotated by a variable-reluctance stepping rotary microactuator that is fabricated by a multi-layer LIGA process. Each wedge prism can be formed integral to the annular rotor of the rotary microactuator by a DXRL process.

Optical Switch Using Risley Prisms

DOEpatents

Sweatt, William C.; Christenson, Todd R.

2005-02-22

An optical switch using Risley prisms and rotary microactuators to independently rotate the wedge prisms of each Risley prism pair is disclosed. The optical switch comprises an array of input Risley prism pairs that selectively redirect light beams from a plurality of input ports to an array of output Risley prism pairs that similarly direct the light beams to a plurality of output ports. Each wedge prism of each Risley prism pair can be independently rotated by a variable-reluctance stepping rotary microactuator that is fabricated by a multi-layer LIGA process. Each wedge prism can be formed integral to the annular rotor of the rotary microactuator by a DXRL process.

Processing and properties of Pb(Mg(1/3)Nb(2/3))O3--PbTiO3 thin films by pulsed laser deposition

NASA Astrophysics Data System (ADS)

Tantigate, C.; Lee, J.; Safari, A.

1995-03-01

The objectives of this study were to prepare in situ Pb(Mg(1/3)Nb(2/3))O3 (PMN) and PMN-PT thin films by pulsed laser deposition and to investigate the electrical features of thin films for possible dynamic random access memory (DRAM) and microactuator applications. The impact of processing parameters such compositions, substrate temperature, and oxygen pressure on perovskite phase formation and dielectric characteristics were reported. It was found that the highest dielectric constant, measured at room temperature and 10 kHz, was attained from the PMN with 99% perovskite.

New Insights into Shape Memory Alloy Bimorph Actuators Formed by Electron Beam Evaporation

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

Sun, Hao; Nykypanchuk, Dmytro

In order to create shape memory alloy (SMA) bimorph microactuators with high-precision features, a novel fabrication process combined with electron beam (E-beam) evaporation, lift-off resist and isotropic XeF2 dry etching method was developed. To examine the effect of E-beam deposition and annealing process on nitinol (NiTi) characteristics, the NiTi thin film samples with different deposition rate and overflow conditions during annealing process were investigated. With the characterizations using scanning electron microscope and x-ray diffraction, the results indicated that low E-beam deposition rate and argon employed annealing process could benefit the formation of NiTi crystalline structure. In addition, SMA bimorph microactuatorsmore » with high-precision features as small as 5 microns were successfully fabricated. Furthermore, the thermomechanical performance was experimentally verified and compared with finite element analysis simulation results.« less

Polymer micromold and fabrication process

DOEpatents

Lee, A.P.; Northrup, M.A.; Ahre, P.E.; Dupuy, P.C.

1997-08-19

A mold assembly is disclosed with micro-sized features in which the hollow portion thereof is fabricated from a sacrificial mandrel which is surface treated and then coated to form an outer shell. The sacrificial mandrel is then selectively etched away leaving the outer shell as the final product. The sacrificial mandrel is fabricated by a precision lathe, for example, so that when removed by etching the inner or hollow area has diameters as small as 10`s of micros ({micro}m). Varying the inside diameter contours of the mold can be accomplished with specified ramping slopes formed on the outer surface of the sacrificial mandrel, with the inside or hollow section being, for example, 275 {micro}m in length up to 150 {micro}m in diameter within a 6 mm outside diameter (o.d.) mold assembly. The mold assembly itself can serve as a micronozzle or microneedle, and plastic parts, such as microballoons for angioplasty, polymer microparts, and microactuators, etc., may be formed within the mold assembly. 6 figs.

Polymer micromold and fabrication process

DOEpatents

Lee, Abraham P.; Northrup, M. Allen; Ahre, Paul E.; Dupuy, Peter C.

1997-01-01

A mold assembly with micro-sized features in which the hollow portion thereof is fabricated from a sacrificial mandrel which is surface treated and then coated to form an outer shell. The sacrificial mandrel is then selectively etched away leaving the outer shell as the final product. The sacrificial mandrel is fabricated by a precision lathe, for example, so that when removed by etching the inner or hollow area has diameters as small as 10's of micros (.mu.m). Varying the inside diameter contours of the mold can be accomplished with specified ramping slopes formed on the outer surface of the sacrificial mandrel, with the inside or hollow section being, for example, 275 .mu.m in length up to 150 .mu.m in diameter within a 6 mm outside diameter (o.d.) mold assembly. The mold assembly itself can serve as a micronozzle or microneedle, and plastic parts, such as microballoons for angioplasty, polymer microparts, and microactuators, etc., may be formed within the mold assembly.

Chemomechanical synchronization in heterogeneous self-oscillating gels

NASA Astrophysics Data System (ADS)

Yashin, Victor V.; Balazs, Anna C.

2008-04-01

Using computational modeling, we introduce patches of self-oscillating gels undergoing the Belousov-Zhabotinsky (BZ) reaction into a nonreactive polymer network and thereby demonstrate how these BZ gels can be harnessed to impart remarkable functionality to the entire system. By first focusing on two adjacent patches of BZ gels, we show that the patches’ oscillations can become synchronized in phase or out of phase, with the oscillation frequency depending on the synchronization mode and the spatial separation between these domains. We then apply these results to an array of five adjacent BZ patches and by varying the distance between these pieces, we dramatically alter the dynamical behavior of the patterned gel. For example, the sample can be made to exhibit a unidirectional traveling wave or display a concerted expansion and contraction, properties that are valuable for creating gel-based devices, such as micropumps and microactuators. The findings point to a “modular” design approach, which can impart different functionality simply by arranging identical pieces of BZ gels into distinct spatial arrangements within a polymer matrix.

Guide wire extension for shape memory polymer occlusion removal devices

DOEpatents

Maitland, Duncan J [Pleasant Hill, CA; Small, IV, Ward; Hartman, Jonathan [Sacramento, CA

2009-11-03

A flexible extension for a shape memory polymer occlusion removal device. A shape memory polymer instrument is transported through a vessel via a catheter. A flexible elongated unit is operatively connected to the distal end of the shape memory polymer instrument to enhance maneuverability through tortuous paths en route to the occlusion.

An optical microswitch chip integrated with silicon waveguides and touch-down electrostatic micromirrors

NASA Astrophysics Data System (ADS)

Jin, Young-Hyun; Seo, Kyoung-Sun; Cho, Young-Ho; Lee, Sang-Shin; Song, Ki-Chang; Bu, Jong-Uk

2004-12-01

We present an silicon-on-insulator (SOI) optical microswitch, composed of silicon waveguides and electrostatically actuated gold-coated silicon micromirrors integrated with laser diode (LD) receivers and photo diode (PD) transmitters. For a low switching voltage, we modify the conventional curved electrode microactuator into a new microactuator with touch-down beams. We fabricate the waveguides and the actuated micromirror using the inductively coupled plasma (ICP) etching process of SOI wafers. The fabricated microswitch operates at the switching voltage of 31.7 ± 4 V with the resonant frequency of 6.89 kHz. Compared to the conventional microactuator, the touch-down beam microactuator achieves 77.4% reduction of the switching voltage. We observe the single mode wave propagation through the silicon waveguide with the measured micromirror loss of 4.18 ± 0.25 dB. We discuss a feasible method to achieve the switching voltage lower than 10 V by reducing the residual stress in the insulation layers of touch-down beams to the level of 30 MPa. We also analyze the major source of micromirror loss, thereby presenting design guidelines for low-loss micromirror switches.

Development and Implementation of High Bandwidth Pulsed Microactuators for Sub and Supersonic Applications

DTIC Science & Technology

2012-06-15

Microactuators of High –Speed Flow Control”, AIAA- 2938 , 2011. 12. Kreth, P., Solomon, J.T., Alvi, F.S., “Resonance-Enhanced High Frequency Micro...paper 2938 , 2011. 34. Ali, M.Y., Solomon, J.T., Gustavsson, J., Kumar, R., Alvi, F.S., “Control of Supersonic Cavity Flows Using High Bandwidth Micro

Reversible Shape Memory Polymers and Composites: Synthesis, Modeling and Design

DTIC Science & Technology

2013-03-01

Polymer; and (iii) Development of a Shape Memory Assisted Self - Healing Polymer. Page 3 of 19 Mather/FA9550-09-1-0195 IV(i) Modeling and Model...0195 IV(iii) Development of a Shape Memory Assisted Self - Healing Polymer Erika D. Rodriguez, X. Luo, and P.T. Mather, “Linear and Crosslinked...Poly (ε- Caprolactone) Polymers for Shape Memory Assisted Self - Healing (SMASH),” ACS Applied Materials and Interfaces 3 152-161 (2011). Self

Reconfigurable photonic crystals enabled by pressure-responsive shape-memory polymers

PubMed Central

Fang, Yin; Ni, Yongliang; Leo, Sin-Yen; Taylor, Curtis; Basile, Vito; Jiang, Peng

2015-01-01

Smart shape-memory polymers can memorize and recover their permanent shape in response to an external stimulus (for example, heat). They have been extensively exploited for a wide spectrum of applications ranging from biomedical devices to aerospace morphing structures. However, most of the existing shape-memory polymers are thermoresponsive and their performance is hindered by heat-demanding programming and recovery steps. Although pressure is an easily adjustable process variable such as temperature, pressure-responsive shape-memory polymers are largely unexplored. Here we report a series of shape-memory polymers that enable unusual ‘cold' programming and instantaneous shape recovery triggered by applying a contact pressure at ambient conditions. Moreover, the interdisciplinary integration of scientific principles drawn from two disparate fields—the fast-growing photonic crystal and shape-memory polymer technologies—enables fabrication of reconfigurable photonic crystals and simultaneously provides a simple and sensitive optical technique for investigating the intriguing shape-memory effects at nanoscale. PMID:26074349

Thin Film Li Ion Microbatteries for NASA Applications

NASA Technical Reports Server (NTRS)

West, W. C.; Ratnakumar, B. V.; Brandon, E.; Blosiu, J. O.; Surampudi, S.

1999-01-01

Rechargeable thin film microbatteries have recently become the topic of widespread research for use in low power applications such as battery-backed CMOS memory, miniaturized implantable medical devices and smart cards. In particular, the Center for Integrated Space Microsystems (CISM) at NASA's Jet Propulsion Laboratory has interest in applying this technology for secondary power systems in miniaturized satellites, microsensors, microactuators and other remote MEMS applications. The general requirements of the microbatteries for these applications are high specific energy, wide range of temperature stability. low self-discharge rate, and flexibility of cell design. The thin film Li ion materials system using LiCoO2(LiPO(x)N(1-x))SnO is expected to fulfill these requirements.

Experimental characterization and computational modeling of unimorph shape memory polymer actuators incorporating transverse curvature in the substrate

NASA Astrophysics Data System (ADS)

Cantrell, Jason T.

This document outlines in detail the research performed by applying shape memory polymers in a generic unimorph actuator configuration. A set of experiments designed to investigate the influence of transverse curvature, the relative widths of shape memory polymer and composite substrates, and shape memory polymer thickness on actuator recoverability after multiple thermo-mechanical cycles is presented in detail. A theoretical model of the moment required to maintain shape fixity with minimal shape retention loss was developed and experimentally validated for unimorph composite actuators of varying cross-sectional areas. Theoretical models were also developed and evaluated to determine the relationship between the materials neutral axes and thermal stability during a thermo-mechanical cycle. Research was conducted on the incorporation of shape memory polymers on micro air vehicle wings to maximize shape fixity and shape recoverability while minimizing the volume of shape memory polymer on the wing surface. Applications based research also included experimentally evaluating the feasibility of shape memory polymers on deployable satellite antenna ribs both with and without resistance heaters which could be utilized to assist in antenna deployment.

Post polymerization cure shape memory polymers

DOEpatents

Wilson, Thomas S.; Hearon, II, Michael Keith; Bearinger, Jane P.

2017-01-10

This invention relates to chemical polymer compositions, methods of synthesis, and fabrication methods for devices regarding polymers capable of displaying shape memory behavior (SMPs) and which can first be polymerized to a linear or branched polymeric structure, having thermoplastic properties, subsequently processed into a device through processes typical of polymer melts, solutions, and dispersions and then crossed linked to a shape memory thermoset polymer retaining the processed shape.

Post polymerization cure shape memory polymers

DOEpatents

Wilson, Thomas S; Hearon, Michael Keith; Bearinger, Jane P

2014-11-11

This invention relates to chemical polymer compositions, methods of synthesis, and fabrication methods for devices regarding polymers capable of displaying shape memory behavior (SMPs) and which can first be polymerized to a linear or branched polymeric structure, having thermoplastic properties, subsequently processed into a device through processes typical of polymer melts, solutions, and dispersions and then crossed linked to a shape memory thermoset polymer retaining the processed shape.

Biodegradable Shape Memory Polymers in Medicine.

PubMed

Peterson, Gregory I; Dobrynin, Andrey V; Becker, Matthew L

2017-11-01

Shape memory materials have emerged as an important class of materials in medicine due to their ability to change shape in response to a specific stimulus, enabling the simplification of medical procedures, use of minimally invasive techniques, and access to new treatment modalities. Shape memory polymers, in particular, are well suited for such applications given their excellent shape memory performance, tunable materials properties, minimal toxicity, and potential for biodegradation and resorption. This review provides an overview of biodegradable shape memory polymers that have been used in medical applications. The majority of biodegradable shape memory polymers are based on thermally responsive polyesters or polymers that contain hydrolyzable ester linkages. These materials have been targeted for use in applications pertaining to embolization, drug delivery, stents, tissue engineering, and wound closure. The development of biodegradable shape memory polymers with unique properties or responsiveness to novel stimuli has the potential to facilitate the optimization and development of new medical applications. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Resistive switching characteristics of polymer non-volatile memory devices in a scalable via-hole structure.

PubMed

Kim, Tae-Wook; Choi, Hyejung; Oh, Seung-Hwan; Jo, Minseok; Wang, Gunuk; Cho, Byungjin; Kim, Dong-Yu; Hwang, Hyunsang; Lee, Takhee

2009-01-14

The resistive switching characteristics of polyfluorene-derivative polymer material in a sub-micron scale via-hole device structure were investigated. The scalable via-hole sub-microstructure was fabricated using an e-beam lithographic technique. The polymer non-volatile memory devices varied in size from 40 x 40 microm(2) to 200 x 200 nm(2). From the scaling of junction size, the memory mechanism can be attributed to the space-charge-limited current with filamentary conduction. Sub-micron scale polymer memory devices showed excellent resistive switching behaviours such as a large ON/OFF ratio (I(ON)/I(OFF) approximately 10(4)), excellent device-to-device switching uniformity, good sweep endurance, and good retention times (more than 10,000 s). The successful operation of sub-micron scale memory devices of our polyfluorene-derivative polymer shows promise to fabricate high-density polymer memory devices.

Nanofiber-structured hydrogel yarns with pH-response capacity and cardiomyocyte-drivability for bio-microactuator application.

PubMed

Wu, Shaohua; Duan, Bin; Qin, Xiaohong; Butcher, Jonathan T

2017-09-15

Polymeric hydrogels have great potential in soft biological micro-actuator applications. However, inappropriate micro-architecture, non-anisotropy, weak biomechanics, and inferior response behaviors limit their development. In this study, we designed and manufactured novel polyacrylonitrile (PAN)-based hydrogel yarns composed with uniaxially aligned nanofibers. The nanofibrous hydrogel yarns possessed anisotropic architecture and robust mechanical properties with flexibility, and could be assembled into defined scaffold structures by subsequent processes. The as-prepared hydrogel yarns showed excellent pH response behaviors, with around 100% maximum length and 900% maximum diameter changes, and the pH response was completed within several seconds. Moreover, the hydrogel yarns displayed unique cell-responsive abilities to promote the cell adhesion, proliferation, and smooth muscle differentiation of human adipose derived mesenchymal stem cells (HADMSC). Chicken cardiomyocytes were further seeded onto our nanofibrous hydrogel yarns to engineer living cell-based microactuators. Our results demonstrated that the uniaxially aligned nanofibrous networks within the hydrogel yarns were the key characteristics leading to the anisotropic organization of cardiac cells, and improved sarcomere organization, mimicking the cardiomyocyte bundles in the native myocardium. The construct is capable of sustaining spontaneous cardiomyocyte pumping behaviors for 7days. Our PAN-based nanofibrous hydrogel yarns are attractive for creating linear microactuators with pH-response capacity and biological microactuators with cardiomyocyte-drivability. A mechanically robust polyacrylonitrile-based nanofibrous hydrogel yarn is fabricated by using a modified electrospinning setup in combination with chemical modification processes. The as-prepared hydrogel yarn possesses a uniaxially aligned nanofiber microarchitecture and supports a rapid, pH-dependent expansion/contraction response within a few seconds. Embryonic cardiomyocytes-seeded hydrogel yarn improves the sarcomere organization and mimics the cardiomyocyte bundles in the native myocardium, which sustains spontaneous cardiomyocyte pumping behaviors. The nanofibrous hydrogel yarn has several advantages over traditional bulk hydrogel scaffolds in terms of robust biomechanics, anisotropic aligned architecture, and superior pH response behaviors. Our nanofibrous hydrogel yarn holds the potential to be developed into novel linear and biological microactuators for various biomedical applications. Copyright © 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Preservation of auditory brainstem response thresholds after cochleostomy and titanium microactuator implantation in the lateral wall of cat scala tympani.

PubMed

Lesinski, S George; Prewitt, Jessica; Bray, Victor; Aravamudhan, Radhika; Bermeo Blanco, Oscar A; Farmer-Fedor, Brenda L; Ward, Jonette A

2014-04-01

The safety of implanting a titanium microactuator into the lateral wall of cat scala tympani was assessed by comparing preoperative and postoperative auditory brainstem response (ABR) thresholds for 1 to 3 months. The safety of directly stimulating cochlear perilymph with an implantable hearing system requires maintaining preoperative hearing levels. This cat study is an essential step in the development of the next generation of fully implantable hearing devices for humans. Following GLP surgical standards, a 1-mm cochleostomy was drilled into the lateral wall of the scala tympani, and a nonfunctioning titanium anchor/microactuator assembly was inserted in 8 cats. The scala media was damaged in the 1 cat. ABR thresholds with click and 4- and 8-kHz stimuli were measured preoperatively and compared with postoperative thresholds at 1, 2, and 3 months. Nonimplanted ear thresholds were also measured to establish statistical significance for threshold shifts (>28.4 dB). Two audiologists independently interpreted thresholds. Postoperatively, 7 cats implanted in the scala tympani demonstrated no significant ABR threshold shift for click stimulus; one shifted ABR thresholds to 4- and 8-kHz stimuli. The eighth cat, with surgical damage to the scala media, maintained stable click threshold but had a significant shift to 4- and 8-kHz stimuli. This cat study provides no evidence of worsening hearing thresholds after fenestration of the scala tympani and insertion of a titanium anchor/microactuator, provided there is no surgical trauma to the scala media and the implanted device is securely anchored in the cochleostomy. These 2 issues have been resolved in the development of a fully implantable hearing system for humans. The long-term hearing stability (combined with histologic studies) reaffirm that the microactuator is well tolerated by the cat cochlea.

Modeling and simulation of a 2-DOF bidirectional electrothermal microactuator

NASA Astrophysics Data System (ADS)

Topaloglu, N.; Elbuken, C.; Nieva, P. M.; Yavuz, M.; Huissoon, J. P.

2008-03-01

In this paper we present the modeling and simulation of a 2 degree-of-freedom (DOF) bidirectional electrothermal actuator. The four arm microactuator was designed to move in both the horizontal and vertical axes. By tailoring the geometrical parameters of the design, the in-plane and out-of-plane motions were decoupled, resulting in enhanced mobility in both directions. The motion of the actuator was modeled analytically using an electro-thermo-mechanical analysis. To validate the analytical model, finite element simulations were performed using ANSYS. The microactuators were fabricated using PolyMUMPS process and experimental results show good agreement with both the analytical model and the simulations. We demonstrated that the 2-DOF bidirectional electrothermal actuator can achieve 3.7 μm in-plane and 13.3 μm out-of-plane deflections with an input voltage of 10 V.

High-dielectric-constant polymers as high-energy-density (HED) field effect actuator and capacitor materials

NASA Astrophysics Data System (ADS)

Huang, Cheng; Zhang, Qiming

2004-07-01

The development of high dielectric constant polymers as active materials in high-performance devices is one of the challenges in polymeric electronics and opto-electronics such as flexible thin-film capacitors, memory devices and microactuators for deformable micromirror technology. A group of poly(vinylidene fluoridetrifluoroethylene) P(VDF-TrFE) based high-dielectric-constant fluoroterpolymers have been developed, which have high room-temperature dielectric constant (K>60) and very high strain level and high energy density. The longitudinal and transverse strain of these materials can reach about -7% and 4.5%, respectively, and the elastic energy density is around 1.1 J/cm^3 under a high electric field of 150 MV/m. The influence on the electromechanical properties of copolymerizing poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) with a third monomer, chlorofluoroethylene (CFE), was investigated. It was found that increasing the CFE content from 0 to 8.5% slowly converts the ferroelectric structure of the copolymer to a relaxor ferroelectric system. This allows for a greatly decreased polarization and dielectric hysteresis and a much higher strain. Above 8.5%, increased CFE content substantially degrades the bulk crystallinity and the Young's modulus. These terpolymers have the potential to achieve above 10 J/cm^3 whole capacity energy density, which makes them good candidates for applications in pulse power capacitors. An all-polymer percolative composite by the combination of conductive polyaniline particles (K>10^5) within a fluoroterpolymer matrix, is introduced which exhibits very high dielectric constant (>7,000). The experimental results show that the dielectric behavior of this new class of percolative composites follows the prediction of the percolation theory and the analysis of the conductive percolation phenomena. The very high dielectric constant of the all-polymer composites which are also very flexible and possess elastic modulus not very much different from that of the insulation polymer matrix makes it possible to induce a high electromechanical response under a much reduced electric field (a strain of 2.65% with an elastic energy density of 0.18 J/cm^3 can be achieved under a low field of 16 MV/m). Data analysis also suggests that in these composites, the non-uniform local field distribution as well as interface effects can significantly enhance the strain responses. Furthermore, the experimental data as well as the data analysis indicate that the conduction loss in these composites will not affect the strain hysteresis. Flexible high dielectric constant electroactive polymers provide potential applications in high-energy-density (HED) energy storage and conversion systems such as lightweight field effect actuators and capacitors.

Improving of Mechanical and Shape-Memory Properties in Hyperbranched Epoxy Shape-Memory Polymers

NASA Astrophysics Data System (ADS)

Santiago, David; Fabregat-Sanjuan, Albert; Ferrando, Francesc; De la Flor, Silvia

2016-09-01

A series of shape-memory epoxy polymers were synthesized using an aliphatic amine and two different commercial hyperbranched poly(ethyleneimine)s with different molecular weights as crosslinking agents. Thermal, mechanical, and shape-memory properties in materials modified with different hyperbranched polymers were analyzed and compared in order to establish the effect of the structure and the molecular weight of the hyperbranched polymers used. The presence of hyperbranched polymers led to more heterogeneous networks, and the crosslinking densities of which increase as the hyperbranched polymer content increases. The transition temperatures can be tailored from 56 to 117 °C depending on the molecular weight and content of the hyperbranched polymer. The mechanical properties showed excellent values in all formulations at room temperature and, specially, at T_{{g}}^{{E^' with stress at break as high as 15 MPa and strain at break as high as 60 %. The shape-memory performances revealed recovery ratios around 95 %, fixity ratios around 97 %, and shape-recovery velocities as high as 22 %/min. The results obtained in this study reveal that hyperbranched polymers with different molecular weights can be used to enhance the thermal and mechanical properties of epoxy-based SMPs while keeping excellent shape-memory properties.

Design of ultra-thin high frequency trilayer conducting polymer micro-actuators for tactile feedback interfaces

NASA Astrophysics Data System (ADS)

Ebrahimi Takalloo, Saeedeh; Seifi, Hasti; Madden, John D. W.

2017-04-01

Fast actuation of conducting polymer trilayers has been achieved by reducing the thickness of the device to as little as 6 μm. Reducing size also reduces force and displacement. Here the tradeoffs between speed of response, force and deformation angle are explored, and related to an example application - a tactile feedback interface that aims to make use of the very high sensitivity of our fingertip skin to vibrations of about 150 Hz. In general, the actuation rate in these devices is limited by the speed of charging, and by inertia. Here we use an established transmission line model to simulate charging speed. By making use of the empirical relationship between strain and charge, and using beam bending theory, the extent of charging enables estimation of the degree of actuator deformation and the forces that can be generated. In seeking to achieve non-resonant actuation at frequencies of 150 Hz or more, while also generating the forces and displacements needed for tactile stimulation, it is found that electronic and ionic conductivities of the conducting polymer electrodes needs to be on the order of 24,000 S/m and 0.04 S/m, respectively. These values along with the required dimensions appear to be feasible.

Constitutive modeling of glassy shape memory polymers

NASA Astrophysics Data System (ADS)

Khanolkar, Mahesh

The aim of this research is to develop constitutive models for non-linear materials. Here, issues related for developing constitutive model for glassy shape memory polymers are addressed in detail. Shape memory polymers are novel material that can be easily formed into complex shapes, retaining memory of their original shape even after undergoing large deformations. The temporary shape is stable and return to the original shape is triggered by a suitable mechanism such heating the polymer above a transition temperature. Glassy shape memory polymers are called glassy because the temporary shape is fixed by the formation of a glassy solid, while return to the original shape is due to the melting of this glassy phase. The constitutive model has been developed to capture the thermo-mechanical behavior of glassy shape memory polymers using elements of nonlinear mechanics and polymer physics. The key feature of this framework is that a body can exist stress free in numerous natural configurations, the underlying natural configuration of the body changing during the process, with the response of the body being elastic from these evolving natural configurations. The aim of this research is to formulate a constitutive model for glassy shape memory polymers (GSMP) which takes in to account the fact that the stress-strain response depends on thermal expansion of polymers. The model developed is for the original amorphous phase, the temporary glassy phase and transition between these phases. The glass transition process has been modeled using a framework that was developed recently for studying crystallization in polymers and is based on the theory of multiple natural configurations. Using the same frame work, the melting of the glassy phase to capture the return of the polymer to its original shape is also modeled. The effect of nanoreinforcement on the response of shape memory polymers (GSMP) is studied and a model is developed. In addition to modeling and solving boundary value problems for GSMP's, problems of importance for CSMP, specifically a shape memory cycle (Torsion of a Cylinder) is solved using the developed crystallizable shape memory polymer model. To solve complex boundary value problems in realistic geometries a user material subroutine (UMAT) for GSMP model has been developed for use in conjunction with the commercial finite element software ABAQUS. The accuracy of the UMAT has been verified by testing it against problems for which the results are known.

Toward milli-Newton electro- and magneto-static microactuators

NASA Technical Reports Server (NTRS)

Fan, Long-Sheng

1993-01-01

Microtechnologies can potentially push integrated electro- and magnetostatic actuators toward the regime where constant forces in the order of milli-Newton (or torques in the order of micro-Newton meter) can be generated with constant inputs within a volume of 1.0 x 1.0 x 0.02 mm with 'conventional' technology. 'Micro' actuators are, by definition, actuators with dimensions confined within a millimeter cube. Integrated microactuators based on electrostatics typically have force/torque in the order of sub-micro-Newton (sub-nano-Newton meter). These devices are capable of moving small objects at MHz frequencies. On the other hand, suppose we want to move a one cubic millimeter object around with 100 G acceleration; a few milli-Newton force will be required. Thus, milli-Newton microactuators are very desirable for some immediate applications, and it challenges micromechanical researchers to develop new process technologies, designs, and materials toward this goal.

Lab on chip microdevices for cellular mechanotransduction in urothelial cells

NASA Astrophysics Data System (ADS)

Maziz, A.; Guan, N.; Svennersten, K.; Hallén-Grufman, K.; Jager, Edwin W. H.

2016-04-01

Cellular mechanotransduction is crucial for physiological function in the lower urinary tract. The bladder is highly dependent on the ability to sense and process mechanical inputs, illustrated by the regulated filling and voiding of the bladder. However, the mechanisms by which the bladder integrates mechanical inputs, such as intravesicular pressure, and controls the smooth muscles, remain unknown. To date no tools exist that satisfactorily mimic in vitro the dynamic micromechanical events initiated e.g. by an emerging inflammatory process or a growing tumour mass in the urinary tract. More specifically, there is a need for tools to study these events on a single cell level or in a small population of cells. We have developed a micromechanical stimulation chip that can apply physiologically relevant mechanical stimuli to single cells to study mechanosensitive cells in the urinary tract. The chips comprise arrays of microactuators based on the electroactive polymer polypyrrole (PPy). PPy offers unique possibilities and is a good candidate to provide such physiological mechanical stimulation, since it is driven at low voltages, is biocompatible, and can be microfabricated. The PPy microactuators can provide mechanical stimulation at different strains and/or strain rates to single cells or clusters of cells, including controls, all integrated on one single chip, without the need to preprepare the cells. This paper reports initial results on the mechano-response of urothelial cells using the micromechanical stimulation chips. We show that urothelial cells are viable on our microdevices and do respond with intracellular Ca2+ increase when subjected to a micro-mechanical stimulation.

Thin film fabrication and system integration test run for a microactuator for a tuneable lens

NASA Astrophysics Data System (ADS)

Hoheisel, Dominik; Rissing, Lutz

2014-03-01

An electromagnetic microactuator, for controlling of a tuneable lens, with an integrated electrostatic element is fabricated by thin film technology. The actuator consists of two parts: the first part with microcoil and flux guide and the second part with a ring shaped back iron on a polyimide membrane. The back iron is additionally useable as electrode for electrostatic measurement of the air gap and for electrostatic actuation. By attracting the back iron an optical liquid is displaced and forms a liquid lens inside the back iron ring covered by the membrane. For testing the thin film fabrication sequence, up-scaled systems are generated in a test run. To fabricate the flux guide in an easy and quick way, a Ni-Fe foil with a thickness of 50 μm is laminated on the Si-wafer. This foil is also utilized in the following fabrication sequence as seed layer for electroplating. Compared to Ni-Fe structures deposited by electroplating, the foil is featuring better soft magnetic properties. The foil is structured by wet chemical etching and the backside of the wafer is structured by deep reactive ion etching (DRIE). For post fabrication thinning, the polyimide membrane is treated by oxygen plasma etching. To align the back iron to the microcoil and the flux guide, a flip-chip-bonder is used during test run of system integration. To adjust a constant air gap, a water solvable polymer is tested. A two component epoxy and a polyimide based glue are compared for their bonding properties of the actuator parts.

Fabrication and characterization of shape memory polymers at small-scales

NASA Astrophysics Data System (ADS)

Wornyo, Edem

The objective of this research is to thoroughly investigate the shape memory effect in polymers, characterize, and optimize these polymers for applications in information storage systems. Previous research effort in this field concentrated on shape memory metals for biomedical applications such as stents. Minimal work has been done on shape memory polymers; and the available work on shape memory polymers has not characterized the behaviors of this category of polymers fully. Copolymer shape memory materials based on diethylene glycol dimethacrylate (DEGDMA) crosslinker, and tert butyl acrylate (tBA) monomer are designed. The design encompasses a careful control of the backbone chemistry of the materials. Characterization methods such as dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC); and novel nanoscale techniques such as atomic force microscopy (AFM), and nanoindentation are applied to this system of materials. Designed experiments are conducted on the materials to optimize spin coating conditions for thin films. Furthermore, the recovery, a key for the use of these polymeric materials for information storage, is examined in detail with respect to temperature. In sum, the overarching objectives of the proposed research are to: (i) Design shape memory polymers based on polyethylene glycol dimethacrylate (PEGDMA) and diethylene glycol dimethacrylate (DEGDMA) crosslinkers, 2-hydroxyethyl methacrylate (HEMA) and tert-butyl acrylate monomer (tBA). (ii) Utilize dynamic mechanical analysis (DMA) to comprehend the thermomechanical properties of shape memory polymers based on DEGDMA and tBA. (iii) Utilize nanoindentation and atomic force microscopy (AFM) to understand the nanoscale behavior of these SMPs, and explore the strain storage and recovery of the polymers from a deformed state. (iv) Study spin coating conditions on thin film quality with designed experiments. (iv) Apply neural networks and genetic algorithms to optimize these systems.

A Facile and General Approach to Recoverable High-Strain Multishape Shape Memory Polymers.

PubMed

Li, Xingjian; Pan, Yi; Zheng, Zhaohui; Ding, Xiaobin

2018-03-01

Fabricating a single polymer network with no need to design complex structures to achieve an ideal combination of tunable high-strain multiple-shape memory effects and highly recoverable shape memory property is a great challenge for the real applications of advanced shape memory devices. Here, a facile and general approach to recoverable high-strain multishape shape memory polymers is presented via a random copolymerization of acrylate monomers and a chain-extended multiblock copolymer crosslinker. As-prepared shape memory networks show a large width at the half-peak height of the glass transition, far wider than current classical multishape shape memory polymers. A combination of tunable high-strain multishape memory effect and as high as 1000% recoverable strain in a single chemical-crosslinking network can be obtained. To the best of our knowledge, this is the first thermosetting material with a combination of highly recoverable strain and tunable high-strain multiple-shape memory effects. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Resistively heated shape memory polymer device

DOEpatents

Marion, III, John E.; Bearinger, Jane P.; Wilson, Thomas S.; Maitland, Duncan J.

2017-09-05

A resistively heated shape memory polymer device is made by providing a rod, sheet or substrate that includes a resistive medium. The rod, sheet or substrate is coated with a first shape memory polymer providing a coated intermediate unit. The coated intermediate unit is in turn coated with a conductive material providing a second intermediate unit. The second coated intermediate unit is in turn coated with an outer shape memory polymer. The rod, sheet or substrate is exposed and an electrical lead is attached to the rod, sheet or substrate. The conductive material is exposed and an electrical lead is attached to the conductive material.

Resistively heated shape memory polymer device

DOEpatents

Marion, III, John E.; Bearinger, Jane P.; Wilson, Thomas S.; Maitland, Duncan J.

2016-10-25

A resistively heated shape memory polymer device is made by providing a rod, sheet or substrate that includes a resistive medium. The rod, sheet or substrate is coated with a first shape memory polymer providing a coated intermediate unit. The coated intermediate unit is in turn coated with a conductive material providing a second intermediate unit. The second coated intermediate unit is in turn coated with an outer shape memory polymer. The rod, sheet or substrate is exposed and an electrical lead is attached to the rod, sheet or substrate. The conductive material is exposed and an electrical lead is attached to the conductive material.

Shape memory polymer actuator and catheter

DOEpatents

Maitland, Duncan J.; Lee, Abraham P.; Schumann, Daniel L.; Matthews, Dennis L.; Decker, Derek E.; Jungreis, Charles A.

2004-05-25

An actuator system is provided for acting upon a material in a vessel. The system includes an optical fiber and a shape memory polymer material operatively connected to the optical fiber. The shape memory polymer material is adapted to move from a first shape for moving through said vessel to a second shape where it can act upon said material.

Shape memory polymer actuator and catheter

DOEpatents

Maitland, Duncan J.; Lee, Abraham P.; Schumann, Daniel L.; Matthews, Dennis L.; Decker, Derek E.; Jungreis, Charles A.

2007-11-06

An actuator system is provided for acting upon a material in a vessel. The system includes an optical fiber and a shape memory polymer material operatively connected to the optical fiber. The shape memory polymer material is adapted to move from a first shape for moving through said vessel to a second shape where it can act upon said material.

Deformation rate-, hold time-, and cycle-dependent shape-memory performance of Veriflex-E resin

NASA Astrophysics Data System (ADS)

McClung, Amber J. W.; Tandon, Gyaneshwar P.; Baur, Jeffery W.

2013-02-01

Shape-memory polymers have attracted great interest in recent years for application in reconfigurable structures (for instance morphing aircraft, micro air vehicles, and deployable space structures). However, before such applications can be attempted, the mechanical behavior of the shape-memory polymers must be thoroughly understood. The present study represents an assessment of viscous effects during multiple shape-memory cycles of Veriflex-E, an epoxy-based, thermally triggered shape-memory polymer resin. The experimental program is designed to explore the influence of multiple thermomechanical cycles on the shape-memory performance of Veriflex-E. The effects of the deformation rate and hold times at elevated temperature on the shape-memory behavior are also investigated.

Shape-memory alloy micro-actuator

NASA Technical Reports Server (NTRS)

Busch, John D. (Inventor); Johnson, Alfred D. (Inventor)

1991-01-01

A method of producing an integral piece of thermo-sensitive material, which is responsive to a shift in temperature from below to above a phase transformation temperature range to alter the material's condition to a shape-memory condition and move from one position to another. The method is characterized by depositing a thin film of shape-memory material, such as Nickel titanium (Ni-Ti) onto a substrate by vacuum deposition process such that the alloy exhibits an amorphous non-crystalline structure. The coated substrate is then annealed in a vacuum or in the presence of an inert atmosphere at a selected temperature, time and cool down rate to produce an ordered, partially disordered or fully disordered BCC structure such that the alloy undergoes thermoelastic, martinsetic phase transformation in response to alteration in temperature to pass from a martinsetic phase when at a temperature below a phase transformation range and capable of a high level of recoverable strain to a parent austenitic phase in a memory shape when at a temperature above the phase transformation range. Also disclosed are actuator devices employing shape-memory material actuators that deform from a set shape toward an original shape when subjected to a critical temperature level after having been initially deformed from the original shape into the set shape while at a lower temperature. The actuators are mechanically coupled to one or more movable elements such that the temperature-induce deformation of the actuators exerts a force or generates a motion of the mechanical element(s).

Methods of Making and Using Shape Memory Polymer Composite Patches

NASA Technical Reports Server (NTRS)

Hood, Patrick J.

2011-01-01

A method of repairing a composite component having a damaged area including: laying a composite patch over the damaged area: activating the shape memory polymer resin to easily and quickly mold said patch to said damaged area; deactivating said shape memory polymer so that said composite patch retains the molded shape; and bonding said composite patch to said damaged part.

Mechanical performance of PPy helix tube microactuator

NASA Astrophysics Data System (ADS)

Bahrami Samani, Mehrdad; Spinks, Geoffrey M.; Cook, Christopher

2004-02-01

Conducting polymer actuators with favourable properties such as linearity, high power density and compliance are of increasing demand in micro applications. These materials generate forces over two times larger than produced by mammalian skeletal muscles. They operate to convert electro chemical energy to mechanical stress and strain. On the other hand, the application of conducting polymers is limited by the lack of a full description of the relation between four essential parameters: stress, strain, voltage and current. In this paper, polypyrrole helix tube micro actuator mechanical characteristics are investigated. The electrolyte is propylene carbonate and the dopant is TBA. PF6. The experiments are both in isotonic and isometric conditions and the input parameters are both electrical and mechanical. A dual mode force and length control and potentiostat / galvanostat are utilized for this purpose. Ultimately, the viscoelastic behaviour of the actuator is presented in this paper by a standard stress relaxation test. The effect of electrical stimulus on mechanical parameters is also explored by cyclic voltametry at different scan rates to obtain the best understanding of the actuation mechanism. The results demonstrate that the linear viscoelastic model, which performed well on conducting polymer film actuators, has to be modified to explain the mechanical behaviour of PPy helix tube fibre micro actuators. Secondly, the changes in mechanical properties of PPy need to be considered when modelling electromechanical behaviour.

A-site- and/or B-site-modified PbZrTiO3 materials and (Pb, Sr, Ca, Ba, Mg) (Zr, Ti, Nb, Ta)O3 films having utility in ferroelectric random access memories and high performance thin film microactuators

NASA Technical Reports Server (NTRS)

Bilodeau, Steven (Inventor); Baum, Thomas H. (Inventor); Roeder, Jeffrey F. (Inventor); Chen, Ing-Shin (Inventor)

2001-01-01

A modified PbZrTiO.sub.3 perovskite crystal material thin film, wherein the PbZrTiO.sub.3 perovskite crystal material includes crystal lattice A-sites and B-sites at least one of which is modified by the presence of a substituent selected from the group consisting of (i) A-site substituents consisting of Sr, Ca, Ba and Mg, and (ii) B-site substituents selected from the group consisting of Nb and Ta. The perovskite crystal thin film material may be formed by liquid delivery MOCVD from metalorganic precursors of the metal components of the thin film, to form PZT and PSZT, and other piezoelectric and ferroelectric thin film materials. The thin films of the invention have utility in non-volatile ferroelectric memory devices (NV-FeRAMs), and in microelectromechanical systems (MEMS) as sensor and/or actuator elements, e.g., high speed digital system actuators requiring low input power levels.

A-SITE-AND/OR B-SITE-MODIFIED PBZRTIO3 MATERIALS AND (PB, SR, CA, BA, MG) (ZR, TI,NB, TA)O3 FILMS HAVING UTILITY IN FERROELECTRIC RANDOM ACCESS MEMORIES AND HIGH PERFORMANCE THIN FILM MICROACTUATORS

NASA Technical Reports Server (NTRS)

Bilodeau, Steven (Inventor); Baum, Thomas H. (Inventor); Roeder, Jeffrey F. (Inventor); Chen, Ing-Shin (Inventor)

2004-01-01

A modified PbZrTiO.sub.3 perovskite crystal material thin film, wherein the PbZrTiO.sub.3 perovskite crystal material includes crystal lattice A-sites and B-sites at least one of which is modified by the presence of a substituent selected from the group consisting of (i) A-site substituents consisting of Sr, Ca, Ba and Mg, and (ii) B-site substituents selected from the group consisting of Nb and Ta. The perovskite crystal thin film material may be formed by liquid delivery MOCVD from metalorganic precursors of the metal components of the thin film, to form PZT and PSZT, and other piezoelectric and ferroelectric thin film materials. The thin films of the invention have utility in non-volatile ferroelectric memory devices (NV-FeRAMs), and in microelectromechanical systems (MEMS) as sensor and/or actuator elements, e.g., high speed digital system actuators requiring low input power levels.

All-organic electrostrictive polymer composites with low driving electrical voltages for micro-fluidic pump applications

PubMed Central

Le, Minh Quyen; Capsal, Jean-Fabien; Galineau, Jérémy; Ganet, Florent; Yin, Xunqian; Yang, Mingchia (Dawn); Chateaux, Jean-François; Renaud, Louis; Malhaire, Christophe; Cottinet, Pierre-Jean; Liang, Richard

2015-01-01

This paper focuses on the improvement of a relaxor ferroelectric terpolymer, i.e., poly (vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) [P(VDF-TrFE-CFE)], filled with a bis(2-ethylhexyl) phthalate (DEHP). The developed material gave rise to a significantly increased longitudinal electrostrictive strain, as well as an increased mechanical energy density under a relatively low electric field. These features were attributed to the considerably enhanced dielectric permittivity and a decreased Young modulus as a result of the introduction of only small DEHP plasticizer molecules. In addition, the plasticizer-filled terpolymer only exhibited a slight decrease of the dielectric breakdown strength, which was a great advantage with respect to the traditional polymer-based electrostrictive composites. More importantly, the approach proposed herein is promising for the future development and scale-up of new high-performance electrostrictive dielectrics under low applied electrical fields through modification simply by blending with a low-cost plasticizer. An experimental demonstration based on a flexible micro-fluidic application is described at the end of this paper, confirming the attractive characteristics of the proposed materials as well as the feasibility of integrating them as micro-actuators in small-scale devices. PMID:26139015

Electrochromic conductive polymer fuses for hybrid organic/inorganic semiconductor memories

NASA Astrophysics Data System (ADS)

Möller, Sven; Forrest, Stephen R.; Perlov, Craig; Jackson, Warren; Taussig, Carl

2003-12-01

We demonstrate a nonvolatile, write-once-read-many-times (WORM) memory device employing a hybrid organic/inorganic semiconductor architecture consisting of thin film p-i-n silicon diode on a stainless steel substrate integrated in series with a conductive polymer fuse. The nonlinearity of the silicon diodes enables a passive matrix memory architecture, while the conductive polyethylenedioxythiophene:polystyrene sulfonic acid polymer serves as a reliable switch with fuse-like behavior for data storage. The polymer can be switched at ˜2 μs, resulting in a permanent decrease of conductivity of the memory pixel by up to a factor of 103. The switching mechanism is primarily due to a current and thermally dependent redox reaction in the polymer, limited by the double injection of both holes and electrons. The switched device performance does not degrade after many thousand read cycles in ambient at room temperature. Our results suggest that low cost, organic/inorganic WORM memories are feasible for light weight, high density, robust, and fast archival storage applications.

Modeling the Coupled Chemo-Thermo-Mechanical Behavior of Amorphous Polymer Networks.

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

Zimmerman, Jonathan A.; Nguyen, Thao D.; Xiao, Rui

2015-02-01

Amorphous polymers exhibit a rich landscape of time-dependent behavior including viscoelasticity, structural relaxation, and viscoplasticity. These time-dependent mechanisms can be exploited to achieve shape-memory behavior, which allows the material to store a programmed deformed shape indefinitely and to recover entirely the undeformed shape in response to specific environmental stimulus. The shape-memory performance of amorphous polymers depends on the coordination of multiple physical mechanisms, and considerable opportunities exist to tailor the polymer structure and shape-memory programming procedure to achieve the desired performance. The goal of this project was to use a combination of theoretical, numerical and experimental methods to investigate themore » effect of shape memory programming, thermo-mechanical properties, and physical and environmental aging on the shape memory performance. Physical and environmental aging occurs during storage and through exposure to solvents, such as water, and can significantly alter the viscoelastic behavior and shape memory behavior of amorphous polymers. This project – executed primarily by Professor Thao Nguyen and Graduate Student Rui Xiao at Johns Hopkins University in support of a DOE/NNSA Presidential Early Career Award in Science and Engineering (PECASE) – developed a theoretical framework for chemothermo- mechanical behavior of amorphous polymers to model the effects of physical aging and solvent-induced environmental factors on their thermoviscoelastic behavior.« less

Medical applications of shape memory polymers

NASA Technical Reports Server (NTRS)

Sokolowski, Witold M.

2005-01-01

Shape memory polymers are described here and major advantages in some applications are identified over other medical materials such as shape memory alloys (SMA). A number of medical applications are anticipated for shape memory polymers. Some simple applications are already utilized in medical world, others are in examination process. Lately, several important applications are being considered for CHEM foams for self-deployable vascular and coronary devices. One of these potential applications, the endovascular treatment of aneurysm was experimentally investigated with encouraging results and is described in this paper as well.

Impact of vane size and separation on radiometric forces for microactuation

NASA Astrophysics Data System (ADS)

Gimelshein, Natalia; Gimelshein, Sergey; Ketsdever, Andrew; Selden, Nathaniel

2011-04-01

A kinetic approach is used to study the feasibility of increasing the efficiency of microactuators that use radiometric force through etching holes in a single radiometer vane. It has been shown that a radiometer that consists of small vanes is capable of producing at least an order of magnitude larger force than a single-vane radiometer that takes up the same area. The optimum gap between the vanes is found to be slightly smaller than the vane size, with the optimum Knudsen number of about 0.05 based on the vane height.

AC Electric Field Activated Shape Memory Polymer Composite

NASA Technical Reports Server (NTRS)

Kang, Jin Ho; Siochi, Emilie J.; Penner, Ronald K.; Turner, Travis L.

2011-01-01

Shape memory materials have drawn interest for applications like intelligent medical devices, deployable space structures and morphing structures. Compared to other shape memory materials like shape memory alloys (SMAs) or shape memory ceramics (SMCs), shape memory polymers (SMPs) have high elastic deformation that is amenable to tailored of mechanical properties, have lower density, and are easily processed. However, SMPs have low recovery stress and long response times. A new shape memory thermosetting polymer nanocomposite (LaRC-SMPC) was synthesized with conductive fillers to enhance its thermo-mechanical characteristics. A new composition of shape memory thermosetting polymer nanocomposite (LaRC-SMPC) was synthesized with conductive functionalized graphene sheets (FGS) to enhance its thermo-mechanical characteristics. The elastic modulus of LaRC-SMPC is approximately 2.7 GPa at room temperature and 4.3 MPa above its glass transition temperature. Conductive FGSs-doped LaRC-SMPC exhibited higher conductivity compared to pristine LaRC SMP. Applying an electric field at between 0.1 Hz and 1 kHz induced faster heating to activate the LaRC-SMPC s shape memory effect relative to applying DC electric field or AC electric field at frequencies exceeding1 kHz.

Residual stresses in injection molded shape memory polymer parts

NASA Astrophysics Data System (ADS)

Katmer, Sukran; Esen, Huseyin; Karatas, Cetin

2016-03-01

Shape memory polymers (SMPs) are materials which have shape memory effect (SME). SME is a property which has the ability to change shape when induced by a stimulator such as temperature, moisture, pH, electric current, magnetic field, light, etc. A process, known as programming, is applied to SMP parts in order to alter them from their permanent shape to their temporary shape. In this study we investigated effects of injection molding and programming processes on residual stresses in molded thermoplastic polyurethane shape memory polymer, experimentally. The residual stresses were measured by layer removal method. The study shows that injection molding and programming process conditions have significantly influence on residual stresses in molded shape memory polyurethane parts.

Multi-photon vertical cross-sectional imaging with a dynamically-balanced thin-film PZT z-axis microactuator.

PubMed

Choi, Jongsoo; Duan, Xiyu; Li, Haijun; Wang, Thomas D; Oldham, Kenn R

2017-10-01

Use of a thin-film piezoelectric microactuator for axial scanning during multi-photon vertical cross-sectional imaging is described. The actuator uses thin-film lead-zirconate-titanate (PZT) to generate upward displacement of a central mirror platform, micro-machined from a silicon-on-insulator (SOI) wafer to dimensions compatible with endoscopic imaging instruments. Device modeling in this paper focuses on existence of frequencies near device resonance producing vertical motion with minimal off-axis tilt even in the presence of multiple vibration modes and non-uniformity in fabrication outcomes. Operation near rear resonance permits large stroke lengths at low voltages relative to other vertical microactuators. Highly uniform vertical motion of the mirror platform is a key requirement for vertical cross-sectional imaging in the remote scan architecture being used for multi-photon instrument prototyping. The stage is installed in a benchtop testbed in combination with an electrostatic mirror that performs in-plane scanning. Vertical sectional images are acquired from 15 μm diameter beads and excised mouse colon tissue.

Unconstrained Recovery Characterization of Shape-Memory Polymer Networks for Cardiovascular Applications

PubMed Central

Yakacki, Christopher M.; Shandas, Robin; Lanning, Craig; Rech, Bryan; Eckstein, Alex; Gall, Ken

2009-01-01

Shape-memory materials have been proposed in biomedical device design due to their ability to facilitate minimally invasive surgery and recover to a predetermined shape in-vivo. Use of the shape-memory effect in polymers is proposed for cardiovascular stent interventions to reduce the catheter size for delivery and offer highly controlled and tailored deployment at body temperature. Shape-memory polymer networks were synthesized via photopolymerization of tert-butyl acrylate and poly (ethylene glycol) dimethacrylate to provide precise control over the thermomechanical response of the system. The free recovery response of the polymer stents at body temperature was studied as a function of glass transition temperature (Tg), crosslink density, geometrical perforation, and deformation temperature, all of which can be independently controlled. Room temperature storage of the stents was shown to be highly dependent on Tg and crosslink density. The pressurized response of the stents is also demonstrated to depend on crosslink density. This polymer system exhibits a wide range of shape-memory and thermomechanical responses to adapt and meet specific needs of minimally invasive cardiovascular devices. PMID:17296222

Experimental study of thermo-mechanical behavior of a thermosetting shape-memory polymer

NASA Astrophysics Data System (ADS)

Liu, Ruoxuan; Li, Yunxin; Liu, Zishun

2018-01-01

The thermo-mechanical behavior of shape-memory polymers (SMPs) serves for the engineering applications of SMPs. Therefore the understanding of thermo-mechanical behavior of SMPs is of great importance. This paper investigates the influence of loading rate and loading level on the thermo-mechanical behavior of a thermosetting shape-memory polymer through experimental study. A series of cyclic tension tests and shape recovery tests at different loading conditions are performed to study the strain level and strain rate effect. The results of tension tests show that the thermosetting shape-memory polymer will behave as rubber material at temperature lower than the glass transition temperature (Tg) and it can obtain a large shape fix ratio at cyclic loading condition. The shape recovery tests exhibit that loading rate and loading level have little effect on the beginning and ending of shape recovery process of the thermosetting shape-memory polymer. Compared with the material which is deformed at temperature higher than Tg, the material deformed at temperature lower than Tg behaves a bigger recovery speed.

Drug-releasing shape-memory polymers - the role of morphology, processing effects, and matrix degradation.

PubMed

Wischke, Christian; Behl, Marc; Lendlein, Andreas

2013-09-01

Shape-memory polymers (SMPs) have gained interest for temporary drug-release systems that should be anchored in the body by self-sufficient active movements of the polymeric matrix. Based on the so far published scientific literature, this review highlights three aspects that require particular attention when combining SMPs with drug molecules: i) the defined polymer morphology as required for the shape-memory function, ii) the strong effects that processing conditions such as drug-loading methodologies can have on the drug-release pattern from SMPs, and iii) the independent control of drug release and degradation by their timely separation. The combination of SMPs with a drug-release functionality leads to multifunctional carriers that are an interesting technology for pharmaceutical sciences and can be further expanded by new materials such as thermoplastic SMPs or temperature-memory polymers. Experimental studies should include relevant molecules as (model) drugs and provide a thermomechanical characterization also in an aqueous environment, report on the potential effect of drug type and loading levels on the shape-memory functionality, and explore the potential correlation of polymer degradation and drug release.

Microactuateur electrothermique bistable: Etude d'implementation avec une technologie standard CMOS

NASA Astrophysics Data System (ADS)

Ressejac, Isabelle

The general objective of this Ph.D. thesis was to study the implementation of a new type of eletrothermal microactuator. This actuator presents the advantages to be bistable and fabricated in a standard CMOS process, allowing the integration of a microelectronics addressing circuit on the same substrate. Experimental research work, presented in this thesis, relate to the different steps carried out in order to implement this CMOS MEMS device: its theoretical conception, its fabrication with a standard CMOS technology, its micromachining as a post-process, its characterization and its electro-thermo-mechanical modeling. The device was designed and fabricated by using Mitel 1,5 mum CMOS technology and the Can-MEMS service which are both available via the Canadian Microelectronics Corporation. Fabricated monolithically within a standard CMOS process, our microactuator is suitable for large-scale integration due to its small dimensions (length ˜1000 mum and width ˜150 mum). It constitutes the basic component of a N by N matrix controlled by a microelectronic addressing system built on the same substrate. Initially, only one micromachining technique (involving TMAH) was used, and long etching times (>9 h) were requires} in order to release the microstructures. However, the passivation layer from the CMOS process could protect the underlying metal from the TMAH for a sufficient time (only ˜1--2 h). Consequently, we had to develop a micromachining strategy with shorter etching times to allow the complete release of the microstructures without damaging them. Post-processing begins with deposition (by sputtering) of a platinum layer intended to protect the abutment from subsequent etching. Our micromachining strategy is mainly based on the use of a hybrid etching process starting with a first anisotropic TMAH etching followed by a XeF2 isotropic etching. After micromachining, the released microactuator has a significant initial deflection with its tip reaching a height up to a hundred times higher than its thickness. This natural deflection results from the relaxation of internal stresses inside the thin films which are part of the microactuator. These internal stresses are intrinsics to the host CMOS process. We have developed a model of the microactuator's initial deflection using mechanical properties of thin films and dimensions of the structure. Actuation experiments were performed in order to characterize the deflection of the microactuator with respect to the heating of the bilayers (separately and together). We have developed a thermal actuation analytical model for an n-layers multimorph structure, which takes into account the initial deflection resulting from the relaxation of stresses as well as the deflection due to the temperature increase during the electrothermal activation of the bilayers. (Abstract shortened by UMI.)

A polymer/semiconductor write-once read-many-times memory

NASA Astrophysics Data System (ADS)

Möller, Sven; Perlov, Craig; Jackson, Warren; Taussig, Carl; Forrest, Stephen R.

2003-11-01

Organic devices promise to revolutionize the extent of, and access to, electronics by providing extremely inexpensive, lightweight and capable ubiquitous components that are printed onto plastic, glass or metal foils. One key component of an electronic circuit that has thus far received surprisingly little attention is an organic electronic memory. Here we report an architecture for a write-once read-many-times (WORM) memory, based on the hybrid integration of an electrochromic polymer with a thin-film silicon diode deposited onto a flexible metal foil substrate. WORM memories are desirable for ultralow-cost permanent storage of digital images, eliminating the need for slow, bulky and expensive mechanical drives used in conventional magnetic and optical memories. Our results indicate that the hybrid organic/inorganic memory device is a reliable means for achieving rapid, large-scale archival data storage. The WORM memory pixel exploits a mechanism of current-controlled, thermally activated un-doping of a two-component electrochromic conducting polymer.

Durability of carbon fiber reinforced shape memory polymer composites in space

NASA Astrophysics Data System (ADS)

Jang, Joon Hyeok; Hong, Seok Bin; Ahn, Yong San; Kim, Jin-Gyun; Nam, Yong-Youn; Lee, Geun Ho; Yu, Woong-Ryeol

2016-04-01

Shape memory polymer (SMP) is one of smart polymers which exhibit shape memory effect upon external stimuli. Recently, shape memory polymer composites (SMPCs) have been considered for space structure instead of shape memory alloys due to their deformability, lightweight and large recovery ratio, requiring characterization of their mechanical properties against harsh space environment and further prediction of the durability of SMPCs in space. As such, the durability of carbon fiber reinforced shape memory polymer composites (CF-SMPCs) was investigated using accelerated testing method based on short-term testing of CF-SMPCs in harsh condition. CF-SMPCs were prepared using woven carbon fabrics and a thermoset SMP via vacuum assisted resin transfer molding process. Bending tests with constant strain rate of CF-SMPCs were conducted using universal tensile machine (UTM) and Storage modulus test were conducted using dynamic mechanical thermal analysis (DMTA). Using the results, a master curve based on time-temperature superposition principle was then constructed, through which the mechanical properties of CF-SMPCs at harsh temperature were predicted. CF-SMPCs would be exposed to simulated space environments under ultra-violet radiations at various temperatures. The mechanical properties including flexural and tensile strength and shape memory properties of SMPCs would be measured using UTM before and after such exposures for comparison. Finally, the durability of SMPCs in space would be assessed by developing a degradation model of SMPC.

Reconfigurable and Reprocessable Thermoset Shape Memory Polymer with Synergetic Triple Dynamic Covalent Bonds.

PubMed

Wang, Yongwei; Pan, Yi; Zheng, Zhaohui; Ding, Xiaobin

2018-04-20

Degradable shape memory polymers (SMPs), especially for polyurethane-based SMPs, have shown great potential for biomedical applications. How to reasonably fabricate SMPs with the ideal combination of degradability, shape reconfigurability, and reprocessability is a critical issue and remains a challenge for medical disposable materials. Herein, a shape memory poly(urethane-urea) with synergetic triple dynamic covalent bonds is reported via embedding polycaprolactone unit into poly(urethane-urea) with the hindered urea dynamic bond. The single polymer network is biodegradable, thermadapt, and reprocessable, without sacrificing the outstanding shape memory performance. Such a shape memory network with plasticity and reprocessability is expected to have significant and positive impact on the medical device industry. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Comparative performance study of smart structure for thermal microactuators

NASA Astrophysics Data System (ADS)

Yahya, Zulkarnain; Johar, Muhammad Akmal

2017-04-01

Thermal microactuator is one of earliest types of microactuators. Typical thermal actuators are in the form of Bimorph and Chevron structures. A bimorph thermal actuator has a complex movement direction, in arc motion and thus it is not feasible in the most MEMS designs. While Chevron actuator has a tendency to produce an off-plane movement which lead to low precision in lateral movement. A new thermal actuator design in the form of serpentine structures shows promising feature to have better performances in terms of more predictive lateral movement with smaller off-plane displacement. In MEMS chip design, areas play a critical role as it will impact with the cost of the final product. In this study, four different structures of thermal actuator were simulated using ANSYS v15. Three different set of area sizes which are 240 µm x 1000 µm, 240 µm x 1500 µm and 240 µm x 2000 µm have been analyzed. All four structures were named as Serpentine01, Serpentine02, Bimorph and Chevron. The data with regards to temperature produced by the structure and z-axis directional deformation were collected and analyzed. This paper reported the investigation result of comparison between these three types of thermal actuator structures design with a given area. From all of the result obtained, it is shown that the area 240 µm x 1500 µm showed a well balance performance in term of huge deformations and low power consumption. The Serpentine01 structure produced 16.7 µm deformation at 4mA of current. The results shows the potential of Serpentine01 structure as a new candidate for thermal microactuator for MEMS applications.

Mathematical modeling and design of a novel 2-DOF micro attraction actuator for a micro optical switch

NASA Astrophysics Data System (ADS)

Kamiya, Daiki; Bagheri, Saeed; Horie, Mikio

2004-08-01

Many studies on optical switches have been performed in an attempt to develop optical information networks to speed information technology. In reality, however, mirror manipulators cannot be applied to multiple input and output systems due to both insufficient output displacements by the mirror parts inside the manipulator, and the difficulty of designing structures and mechanisms suitable for multi-dimensional manipulation. The principal reasons for insufficient displacement are the high rigidity of the elastic parts compared to the available driving forces and the pull-in effect. Therefore, in order to develop optical switches capable of multiple input and output switching, we suggest a novel 2-DOF(degree of freedom) electrostatic microactuator. The actuator is composed of one mirror with four beams laid about it in a corkscrew pattern, with four corkscrew electrodes on the substrate below and one mirror support pyramid situated under the mirror. Using electrostatic force, one or more of the beams are attracted from their outer ends toward the substrate. The mirror is then tilted by an angle proportional to the attracted length along the beam. The inclination and direction of the mirror are determined by the combined attracted length of the four beams. In this work we derive the mathematical model for the corkscrew beam microactuator for optical switches and show that this mathematical model accurately simulates the device by comparison with finite element analysis results. We use this mathematical model for design of the microactuator. Further we show that the designed optical switch microactuator is capable of rotating the mirror from +32 to -32 degrees about two axes with a maximum operating voltage of 163 volts. Finally, stress analysis of the actuator shows that the generated stress in the structure is at most 369 MPa.

Exploiting NiTi shape memory alloy films in design of tunable high frequency microcantilever resonators

NASA Astrophysics Data System (ADS)

Stachiv, I.; Sittner, P.; Olejnicek, J.; Landa, M.; Heller, L.

2017-11-01

Shape memory alloy (SMA) films are very attractive materials for microactuators because of their high energy density. However, all currently developed SMA actuators utilize martensitic transformation activated by periodically generated heating and cooling; therefore, they have a slow actuation speed, just a few Hz, which restricts their use in most of the nanotechnology applications such as high frequency microcantilever based physical and chemical sensors, atomic force microscopes, or RF filters. Here, we design tunable high frequency SMA microcantilevers for nanotechnology applications. They consist of a phase transforming NiTi SMA film sputtered on the common elastic substrate material; in our case, it is a single-crystal silicon. The reversible tuning of microcantilever resonant frequencies is then realized by intentionally changing the Young's modulus and the interlayer stress of the NiTi film by temperature, while the elastic substrate guarantees the high frequency actuation (up to hundreds of kHz) of the microcantilever. The experimental results qualitatively agree with predictions obtained from the dedicated model based on the continuum mechanics theory and a phase characteristic of NiTi. The present design of SMA microcantilevers expands the capability of current micro-/nanomechanical resonators by enabling tunability of several consecutive resonant frequencies.

Air-stable memory array of bistable rectifying diodes based on ferroelectric-semiconductor polymer blends

NASA Astrophysics Data System (ADS)

Kumar, Manasvi; Sharifi Dehsari, Hamed; Anwar, Saleem; Asadi, Kamal

2018-03-01

Organic bistable diodes based on phase-separated blends of ferroelectric and semiconducting polymers have emerged as promising candidates for non-volatile information storage for low-cost solution processable electronics. One of the bottlenecks impeding upscaling is stability and reliable operation of the array in air. Here, we present a memory array fabricated with an air-stable amine-based semiconducting polymer. Memory diode fabrication and full electrical characterizations were carried out in atmospheric conditions (23 °C and 45% relative humidity). The memory diodes showed on/off ratios greater than 100 and further exhibited robust and stable performance upon continuous write-read-erase-read cycles. Moreover, we demonstrate a 4-bit memory array that is free from cross-talk with a shelf-life of several months. Demonstration of the stability and reliable air operation further strengthens the feasibility of the resistance switching in ferroelectric memory diodes for low-cost applications.

Dynamic modelling and experimental study of asymmetric optothermal microactuator

NASA Astrophysics Data System (ADS)

Wang, Shuying; Chun, Qin; You, Qingyang; Wang, Yingda; Zhang, Haijun

2017-01-01

This paper reports the dynamic modelling and experimental study of an asymmetric optothermal microactuator (OTMA). According to the principle of thermal flux, a theoretical model for instantaneous temperature distribution of an expansion arm is established and the expression of expansion increment is derived. Dynamic expansion properties of the arm under laser pulse irradiation are theoretically analyzed indicating that both of the maximum expansion and expansion amplitude decrease with the pulse frequency increasing. Experiments have been further carried out on an OTMA fabricated by using an excimer laser micromachining system. It is shown that the OTMA deflects periodically with the same frequency of laser pulse irradiation. Experimental results also prove that both OTMA's maximum deflection and deflection amplitude (related to maximum expansion and expansion amplitude of the arm) decrease as frequency increases, matching with the theoretical model quite well. Even though the OTMA's deflection decrease at higher frequency, it is still capable of generating 8.2 μm maximum deflection and 4.2 μm deflection amplitude under 17 Hz/2 mW laser pulse irradiation. This work improves the potential applications of optothermal microactuators in micro-opto-electro-mechanical system (MOEMS) and micro/nano-technology fields.

Robust Vacuum-/Air-Dried Graphene Aerogels and Fast Recoverable Shape-Memory Hybrid Foams.

PubMed

Li, Chenwei; Qiu, Ling; Zhang, Baoqing; Li, Dan; Liu, Chen-Yang

2016-02-17

New graphene aerogels can be fabricated by vacuum/air drying, and because of the mechanical robustness of the graphene aerogels, shape-memory polymer/graphene hybrid foams can be fabricated by a simple infiltration-air-drying-crosslinking method. Due to the superelasticity, high strength, and good electrical conductivity of the as-prepared graphene aerogels, the shape-memory hybrid foams exhibit excellent thermotropical and electrical shape-memory properties, outperforming previously reported shape-memory polymer foams. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

3D Printing of Shape Memory Polymers for Flexible Electronic Devices.

PubMed

Zarek, Matt; Layani, Michael; Cooperstein, Ido; Sachyani, Ela; Cohn, Daniel; Magdassi, Shlomo

2016-06-01

The formation of 3D objects composed of shape memory polymers for flexible electronics is described. Layer-by-layer photopolymerization of methacrylated semicrystalline molten macromonomers by a 3D digital light processing printer enables rapid fabrication of complex objects and imparts shape memory functionality for electrical circuits. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Interventional Application of Shape Memory Polymer Foam Final Report CRADA No. TC-02067-03

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

Maitland, D.; Metzger, M. F.

This was a collaborative effort between The Regents of the University of California, Lawrence Livermore National Laboratory (LLNL) and Sierra Interventions, LLC, to develop shape memory polymer foam devices for treating hemorrhagic stroke.

Mechanical analysis of carbon fiber reinforced shape memory polymer composite for self-deployable structure in space environment

NASA Astrophysics Data System (ADS)

Hong, Seok Bin; Ahn, Yong San; Jang, Joon Hyeok; Kim, Jin-Gyun; Goo, Nam Seo; Yu, Woong-Ryeol

2016-04-01

Shape memory polymer (SMP) is one of smart polymers which exhibit shape memory effect upon external stimuli. Reinforcements as carbon fiber had been used for making shape memory polymer composite (CF-SMPC). This study investigated a possibility of designing self-deployable structures in harsh space condition using CF-SMPCs and analyzed their shape memory behaviors with constitutive equation model.CF-SMPCs were prepared using woven carbon fabrics and a thermoset epoxy based SMP to obtain their basic mechanical properties including actuation in harsh environment. The mechanical and shape memory properties of SMP and CF-SMPCs were characterized using dynamic mechanical analysis (DMA) and universal tensile machine (UTM) with an environmental chamber. The mechanical properties such as flexural strength and tensile strength of SMP and CF-SMPC were measured with simple tensile/bending test and time dependent shape memory behavior was characterized with designed shape memory bending test. For mechanical analysis of CF-SMPCs, a 3D constitutive equation of SMP, which had been developed using multiplicative decomposition of the deformation gradient and shape memory strains, was used with material parameters determined from CF-SMPCs. Carbon fibers in composites reinforced tensile and flexural strength of SMP and acted as strong elastic springs in rheology based equation models. The actuation behavior of SMP matrix and CF-SMPCs was then simulated as 3D shape memory bending cases. Fiber bundle property was imbued with shell model for more precise analysis and it would be used for prediction of deploying behavior in self-deployable hinge structure.

Synthesis and characterization of shape memory poly (epsilon-caprolactone) polyurethane-ureas

NASA Astrophysics Data System (ADS)

Ren, Hongfeng

Shape memory polymers (SMPs) have attracted significant interest in recent times because of their potential applications in a number of areas, such as medical devices and textiles. However, there are some major drawbacks of SMPs, such as their relatively low moduli resulting in small recovery stresses, and their long response times compared with shape memory alloys (SMAs). A suitable recovery stress which comes from the elastic recovery stress generated in the deformation process is critical in some medical devices. To address some of these shortcomings, the work in this dissertation mainly focuses on the design and synthesis of linear shape memory polymers with higher recovery stress. A series of segmented poly (epsilon-caprolactone) polyurethane-ureas (PCLUUs) were prepared from poly (epsilon-caprolactone) (PCL) diol, different dissociates and chain extenders. NMR and FT-IR were used to identify the structure of the synthesized shape memory polyurethane-ureas. Parameters such as soft segment content (molecular weight and content), chain extender and the rigidity of the main chain were investigated to understand the structure-property relationships of the shape memory polymer systems through DSC, DMA, physical property test, etc. Cyclic thermal mechanic tests were applied to measure the shape memory properties which showed that the recovery stress can be improved above 200% simply by modifying the chain extender. Meanwhile, the synthesis process was optimized to be similar to that of Spandex /LYCRA®. Continuous fibers form shape memory polyurethane-ureas were made from a wet spinning process, which indicated excellent spinnability of the polymer solution. Small angle neutron scattering (SANS) was used to study the morphology of the hard segment at different temperatures and stretch rates and found that the monodisperse rigid cylinder model fit the SANS data quite well. From the cylinder model, the radius of the cylinder increased with increasing hard segment content. The SANS results revealed phase separation of hard and soft segments into nano scale domains. The overall objectives of this dissertation were: ■ To improve the recovery stress of linear shape memory polymers. ■ To study the morphology and structure property relationships of shape memory polymers. Chapter 1 reviews the literature on SMAs and SMPs, especially on linear SMPs. Chapter 2 is devoted to SMPUUs with the aliphatic amine 1, 4-Butanediamine (BDA) as chain extender. Chapter 3 reports the effects of different aliphatic diamines as the chain extenders. Chapter 4 covers the results for shape memory polyurethane-ureas with aromatic diamine 4, 4’-Methylenedianiline (MDA) as the chain extender. The effect of different diisocyanates is covered in Chapter 5. Chapter 6-7 show some synthesized polymer systems with unimproved recovery stress or even no shape memory properties. The overall conclusions of this work are reported in Chapter 8.

Nonvolatile memory characteristics of organic thin film transistors using poly(2-hydroxyethyl methacrylate)-based polymer multilayer dielectric

NASA Astrophysics Data System (ADS)

Chen, Ying-Chih; Su, Yan-Kuin; Yu, Hsin-Chieh; Huang, Chun-Yuan; Huang, Tsung-Syun

2011-10-01

A wide hysteresis width characteristic (memory window) was observed in the organic thin film transistors (OTFTs) using poly(2-hydroxyethyl methacrylate) (PHEMA)-based polymer multilayers. In this study, a strong memory effect was also found in the pentacene-based OTFTs and the electric characteristics were improved by introducing PHEMA/poly(methyl methacrylate) (PMMA)/PHEMA trilayer to replace the conventional PHEMA monolayer or PMMA/PHEMA and PHEMA/PMMA bilayer as the dielectric layers of OTFTs. The memory effect was originated from the electron trapping and slow polarization of the dielectrics. The hydroxyl (-OH) groups inside the polymer dielectric were the main charge storage sites of the electrons. This charge-storage phenomenon could lead to a wide flat-band voltage shift (memory window, △VFB = 22 V) which is essential for the OTFTs' memory-related applications. Moreover, the fabricated transistors also exhibited significant switchable channel current due to the charge-storage and slow charge relaxation.

Operating principles of an electrothermal vibrometer for optical switching applications

NASA Astrophysics Data System (ADS)

Pai, Min-fan; Tien, Norman C.

1999-09-01

A compact polysilicon surface-micromachined microactuator designed for optical switching applications is described. This actuator is fabricated using the foundry MUMPs process provided by Cronos Integrated Microsystems Inc. Actuated electrothermally, the microactuator allows fast switching speeds and can be operated with a low voltage square-wave signal. The design, operation mechanisms for this long-range and high frequency thermal actuation are described. A vertical micromirror integrated with this actuator can be operated with a 10.5 V, 20 kHz 15% duty-cycle pulse signal, achieving a lateral moving speed higher than 15.6 mm/sec. The optical switch has been operated to frequencies as high as 30 kHz.

Epitaxial Growth of Thin Ferroelectric Polymer Films on Graphene Layer for Fully Transparent and Flexible Nonvolatile Memory.

PubMed

Kim, Kang Lib; Lee, Wonho; Hwang, Sun Kak; Joo, Se Hun; Cho, Suk Man; Song, Giyoung; Cho, Sung Hwan; Jeong, Beomjin; Hwang, Ihn; Ahn, Jong-Hyun; Yu, Young-Jun; Shin, Tae Joo; Kwak, Sang Kyu; Kang, Seok Ju; Park, Cheolmin

2016-01-13

Enhancing the device performance of organic memory devices while providing high optical transparency and mechanical flexibility requires an optimized combination of functional materials and smart device architecture design. However, it remains a great challenge to realize fully functional transparent and mechanically durable nonvolatile memory because of the limitations of conventional rigid, opaque metal electrodes. Here, we demonstrate ferroelectric nonvolatile memory devices that use graphene electrodes as the epitaxial growth substrate for crystalline poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) polymer. The strong crystallographic interaction between PVDF-TrFE and graphene results in the orientation of the crystals with distinct symmetry, which is favorable for polarization switching upon the electric field. The epitaxial growth of PVDF-TrFE on a graphene layer thus provides excellent ferroelectric performance with high remnant polarization in metal/ferroelectric polymer/metal devices. Furthermore, a fully transparent and flexible array of ferroelectric field effect transistors was successfully realized by adopting transparent poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] semiconducting polymer.

Resistive Switching Memory Phenomena in PEDOT PSS: Coexistence of Switchable Diode Effect and Write Once Read Many Memory

PubMed Central

Nguyen, Viet Cuong; Lee, Pooi See

2016-01-01

We study resistive switching memory phenomena in conducting polymer PEDOT PSS. In the same film, there are two types of memory behavior coexisting; namely, the switchable diode effect and write once read many memory. This is the first report on switchable diode phenomenon based on conducting organic materials. The effect was explained as charge trapping of PEDOT PSS film and movement of proton. The same PEDOT PSS device also exhibits write once read many memory (WORM) phenomenon which arises due to redox reaction that reduces PEDOT PSS and renders it non-conducting. The revelation of these two types of memory phenomena in PEDOT PSS highlights the remarkable versatility of this conducting conjugated polymer. PMID:26806868

Study of Galfenol direct cytotoxicity and remote microactuation in cells.

PubMed

Vargas-Estevez, Carolina; Blanquer, Andreu; Dulal, Prabesh; Pérez Del Real, Rafael; Duch, Marta; Ibáñez, Elena; Barrios, Leonardo; Murillo, Gonzalo; Torras, Núria; Nogués, Carme; Stadler, Bethanie J H; Plaza, José A; Esteve, Jaume

2017-09-01

Remote microactuators are of great interest in biology and medicine as minimally-invasive tools for cellular stimulation. Remote actuation can be achieved by active magnetostrictive transducers which are capable of changing shape in response to external magnetic fields thereby creating controlled displacements. Among the magnetostrictive materials, Galfenol, the multifaceted iron-based smart material, offers high magnetostriction with robust mechanical properties. In order to explore these capabilities for biomedical applications, it is necessary to study the feasibility of material miniaturization in standard fabrication processes as well as evaluate the biocompatibility. Here we develop a technology to fabricate, release, and suspend Galfenol-based microparticles, without affecting the integrity of the material. The morphology, composition and magnetic properties of the material itself are characterized. The direct cytotoxicity of Galfenol is evaluated in vitro using human macrophages, osteoblast and osteosarcoma cells. In addition, cytotoxicity and actuation of Galfenol microparticles in suspension are evaluated using human macrophages. The biological parameters analyzed indicate that Galfenol is not cytotoxic, even after internalization of some of the particles by macrophages. The microparticles were remotely actuated forming intra- and extracellular chains that did not impact the integrity of the cells. The results propose Galfenol as a suitable material to develop remote microactuators for cell biology studies and intracellular applications. Copyright © 2017 Elsevier Ltd. All rights reserved.

Multifunctional shape-memory polymers.

PubMed

Behl, Marc; Razzaq, Muhammad Yasar; Lendlein, Andreas

2010-08-17

The thermally-induced shape-memory effect (SME) is the capability of a material to change its shape in a predefined way in response to heat. In shape-memory polymers (SMP) this shape change is the entropy-driven recovery of a mechanical deformation, which was obtained before by application of external stress and was temporarily fixed by formation of physical crosslinks. The high technological significance of SMP becomes apparent in many established products (e.g., packaging materials, assembling devices, textiles, and membranes) and the broad SMP development activities in the field of biomedical as well as aerospace applications (e.g., medical devices or morphing structures for aerospace vehicles). Inspired by the complex and diverse requirements of these applications fundamental research is aiming at multifunctional SMP, in which SME is combined with additional functions and is proceeding rapidly. In this review different concepts for the creation of multifunctionality are derived from the various polymer network architectures of thermally-induced SMP. Multimaterial systems, such as nanocomposites, are described as well as one-component polymer systems, in which independent functions are integrated. Future challenges will be to transfer the concept of multifunctionality to other emerging shape-memory technologies like light-sensitive SMP, reversible shape changing effects or triple-shape polymers.

Ferroelectric polarization induces electronic nonlinearity in ion-doped conducting polymers

PubMed Central

Fabiano, Simone; Sani, Negar; Kawahara, Jun; Kergoat, Loïg; Nissa, Josefin; Engquist, Isak; Crispin, Xavier; Berggren, Magnus

2017-01-01

Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is an organic mixed ion-electron conducting polymer. The PEDOT phase transports holes and is redox-active, whereas the PSS phase transports ions. When PEDOT is redox-switched between its semiconducting and conducting state, the electronic and optical properties of its bulk are controlled. Therefore, it is appealing to use this transition in electrochemical devices and to integrate those into large-scale circuits, such as display or memory matrices. Addressability and memory functionality of individual devices, within these matrices, are typically achieved by nonlinear current-voltage characteristics and bistability—functions that can potentially be offered by the semiconductor-conductor transition of redox polymers. However, low conductivity of the semiconducting state and poor bistability, due to self-discharge, make fast operation and memory retention impossible. We report that a ferroelectric polymer layer, coated along the counter electrode, can control the redox state of PEDOT. The polarization switching characteristics of the ferroelectric polymer, which take place as the coercive field is overcome, introduce desired nonlinearity and bistability in devices that maintain PEDOT in its highly conducting and fast-operating regime. Memory functionality and addressability are demonstrated in ferro-electrochromic display pixels and ferro-electrochemical transistors. PMID:28695197

Optical Input/Electrical Output Memory Elements based on a Liquid Crystalline Azobenzene Polymer.

PubMed

Mosciatti, Thomas; Bonacchi, Sara; Gobbi, Marco; Ferlauto, Laura; Liscio, Fabiola; Giorgini, Loris; Orgiu, Emanuele; Samorì, Paolo

2016-03-01

Responsive polymer materials can change their properties when subjected to external stimuli. In this work, thin films of thermotropic poly(metha)acrylate/azobenzene polymers are explored as active layer in light-programmable, electrically readable memories. The memory effect is based on the reversible modifications of the film morphology induced by the photoisomerization of azobenzene mesogenic groups. When the film is in the liquid crystalline phase, the trans → cis isomerization induces a major surface reorganization on the mesoscopic scale that is characterized by a reduction in the effective thickness of the film. The film conductivity is measured in vertical two-terminal devices in which the polymer is sandwiched between a Au contact and a liquid compliant E-GaIn drop. We demonstrate that the trans → cis isomerization is accompanied by a reversible 100-fold change in the film conductance. In this way, the device can be set in a high- or low-resistance state by light irradiation at different wavelengths. This result paves the way toward the potential use of poly(metha)acrylate/azobenzene polymer films as active layer for optical input/electrical output memory elements.

Estimation of aneurysm wall stresses created by treatment with a shape memory polymer foam device

PubMed Central

Hwang, Wonjun; Volk, Brent L.; Akberali, Farida; Singhal, Pooja; Criscione, John C.

2012-01-01

In this study, compliant latex thin-walled aneurysm models are fabricated to investigate the effects of expansion of shape memory polymer foam. A simplified cylindrical model is selected for the in-vitro aneurysm, which is a simplification of a real, saccular aneurysm. The studies are performed by crimping shape memory polymer foams, originally 6 and 8 mm in diameter, and monitoring the resulting deformation when deployed into 4-mm-diameter thin-walled latex tubes. The deformations of the latex tubes are used as inputs to physical, analytical, and computational models to estimate the circumferential stresses. Using the results of the stress analysis in the latex aneurysm model, a computational model of the human aneurysm is developed by changing the geometry and material properties. The model is then used to predict the stresses that would develop in a human aneurysm. The experimental, simulation, and analytical results suggest that shape memory polymer foams have potential of being a safe treatment for intracranial saccular aneurysms. In particular, this work suggests oversized shape memory foams may be used to better fill the entire aneurysm cavity while generating stresses below the aneurysm wall breaking stresses. PMID:21901546

High-frequency, resonance-enhanced microactuators with active structures for high-speed flow control

NASA Astrophysics Data System (ADS)

Kreth, Phillip Andrew

The need for actuators that are adaptable for use in a wide array of applications has been the motivation behind actuator development research over the past few years. Recent developments at the Advanced Aero-Propulsion Laboratory (AAPL) at Florida State University have produced a microactuator that uses the unsteadiness of a small-scale impinging jet to produce pulsed, supersonic microjets -- this is referred to as the Resonance-Enhanced Microjet (REM) actuator. Prior studies on these actuators at AAPL have been somewhat limited in that the actuator response has only been characterized through pressure/acoustic measurements and qualitative flow visualizations. Highly-magnified particle image velocimetry (PIV) measurements were performed to measure the velocity fields of both a 1 mm underexpanded jet and an REM actuator. The results demonstrate that this type of microactuator is capable of producing pulsed, supersonic microjets that have velocities of approximately 400 m/s that are sustained for significant portions of their cycles (> 60 %). These are the first direct velocity measurements of these flowfields, and they allow for a greater understanding of the flow physics associated with this microactuator. The previous studies on the REM actuators have shown that the microactuator volume is among the principal parameters in determining the actuator's maximum-amplitude frequency component. In order to use this actuator in a closed-loop, feedback control system, a modified design that incorporates smart materials is studied. The smart materials (specifically piezoelectric ceramic stack actuators) have been implemented into the microactuator to actively change its geometry, thus permitting controllable changes in the microactuator's resonant frequency. The distinct feature of this design is that the smart materials are not used to produce the primary perturbation or flow from the actuator (which has in the past limited the control authority of other designs) but to change its dynamic properties. Various static and dynamic control inputs to the piezo-stacks illustrate that the actuator's resonant frequency can be modulated by a few hundred Hertz at very fast rates (up to 1 kHz or more). These frequency modulation capabilities allow for off-design frequencies to be present in the actuator's output, thereby increasing its range of potential flow control applications. A series of closed-loop control demonstrations clearly show the ability of this actuator to track and produce outputs at specified frequencies. The robustness of this control technique was also demonstrated. By combining the REM actuator concept with the precision and control authority of smart materials, the new actuator system (known as the SmartREM actuator) is shown to produce supersonic, pulsing microjets whose frequency can be controlled actively in a closed-loop manner. Three different design possibilities are developed and characterized in this study. An optimal configuration was identified for cavity flow control experiments in both sub- and supersonic freestream conditions (M = 0.4 - 0.7 and M = 1.5). The actuator was designed such that its frequency would lie within the range of the predicted cavity oscillations. The actuator's performance was evaluated in its three modes of operations: pulsed (REM mode), active pulsed (SmartREM mode), and steady. It was found that when the actuator operates in its pulsed modes, the amplitude of the dominant peak is reduced by as much as 6 dB. The high-frequency broadband levels and overall sound pressure levels (OASPLs) are reduced with control as well (by about 3 dB). Operating the actuator in its steady mode at very high pressures provides the most effective results. The dominant peaks were completely eliminated (amplitudes reduced by over 25 dB), and the reductions in the OASPLs exceeded 10 dB.

On the Takayanagi principle for the shape memory effect and thermomechanical behaviors in polymers with multi-phases

NASA Astrophysics Data System (ADS)

Lu, Haibao; Yu, Kai; Huang, Wei Min; Leng, Jinsong

2016-12-01

We present an explicit model to study the mechanics and physics of the shape memory effect (SME) in polymers based on the Takayanagi principle. The molecular structural characteristics and elastic behavior of shape memory polymers (SMPs) with multi-phases are investigated in terms of the thermomechanical properties of the individual components, of which the contributions are combined by using Takayanagi’s series-parallel model and parallel-series model, respectively. After that, Boltzmann superposition principle is employed to couple the multi-SME, elastic modulus parameter (E) and temperature parameter (T) in SMPs. Furthermore, the extended Takayanagi model is proposed to separate the plasticizing effect and physical swelling effect on the thermo-/chemo-responsive SME in polymers and then compared with the available experimental data reported in the literature. This study is expected to provide a powerful simulation tool for modeling and experimental substantiation of the mechanics and working mechanism of SME in polymers.

Characterization of origami shape memory metamaterials (SMMM) made of bio-polymer blends

NASA Astrophysics Data System (ADS)

Kshad, Mohamed Ali E.; Naguib, Hani E.

2016-04-01

Shape memory materials (SMMs) are materials that can return to their virgin state and release mechanically induced strains by external stimuli. Shape memory polymers (SMPs) are a class of SMMs that show a high shape recoverability and which have attractive potential for structural applications. In this paper, we experimentally study the shape memory effect of origami based metamaterials. The main focus is on the Muira origami metamaterials. The fabrication technique used to produce origami structure is direct molding where all the geometrical features are molded from thermally virgin polymers without post folding of flat sheets. The study shows experimental investigations of shape memory metamaterials (SMMMs) made of SMPs that can be used in different applications such as medicine, robotics, and lightweight structures. The origami structure made from SMP blends, activated with uniform heating. The effect of blend composition on the shape memory behavior was studied. Also the influence of the thermomechanical and the viscoelastic properties of origami unit cell on the activation process have been discussed, and stress relaxation and shape recovery were investigated. Activation process of the unit cell has been demonstrated.

Shape-memory polymer foam device for treating aneurysms

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

Ortega, Jason M.; Benett, William J.; Small, Ward

A system for treating an aneurysm in a blood vessel or vein, wherein the aneurysm has a dome, an interior, and a neck. The system includes a shape memory polymer foam in the interior of the aneurysm between the dome and the neck. The shape memory polymer foam has pores that include a first multiplicity of pores having a first pore size and a second multiplicity of pores having a second pore size. The second pore size is larger than said first pore size. The first multiplicity of pores are located in the neck of the aneurysm. The second multiplicitymore » of pores are located in the dome of the aneurysm.« less

Thermally Activated Composite with Two-Way and Multi-Shape Memory Effects

PubMed Central

Basit, Abdul; L’Hostis, Gildas; Pac, Marie José; Durand, Bernard

2013-01-01

The use of shape memory polymer composites is growing rapidly in smart structure applications. In this work, an active asymmetric composite called “controlled behavior composite material (CBCM)” is used as shape memory polymer composite. The programming and the corresponding initial fixity of the composite structure is obtained during a bending test, by heating CBCM above thermal glass transition temperature of the used Epoxy polymer. The shape memory properties of these composites are investigated by a bending test. Three types of recoveries are conducted, two classical recovery tests: unconstrained recovery and constrained recovery, and a new test of partial recovery under load. During recovery, high recovery displacement and force are produced that enables the composite to perform strong two-way actuations along with multi-shape memory effect. The recovery force confirms full recovery with two-way actuation even under a high load. This unique property of CBCM is characterized by the recovered mechanical work. PMID:28788316

Self-Healing Composite of Thermoset Polymer and Programmed Super Contraction Fibers

NASA Technical Reports Server (NTRS)

Li, Guoqiang (Inventor); Meng, Harper (Inventor)

2016-01-01

A composition comprising thermoset polymer, shape memory polymer to facilitate macro scale damage closure, and a thermoplastic polymer for molecular scale healing is disclosed; the composition has the ability to resolve structural defects by a bio-mimetic close-then heal process. In use, the shape memory polymer serves to bring surfaces of a structural defect into approximation, whereafter use of the thermoplastic polymer for molecular scale healing allowed for movement of the thermoplastic polymer into the defect and thus obtain molecular scale healing. The thermoplastic can be fibers, particles or spheres which are used by heating to a level at or above the thermoplastic's melting point, then cooling of the composition below the melting temperature of the thermoplastic. Compositions of the invention have the ability to not only close macroscopic defects, but also to do so repeatedly even if another wound/damage occurs in a previously healed/repaired area.

A reconfigurable tactile display based on polymer MEMS technology

NASA Astrophysics Data System (ADS)

Wu, Xiaosong

A tactile display provides information such as shape, texture, temperature, and hardness to a user. Ultimately, a tactile display could be used to recreate a virtual object that may be stored in a computer. However, such advanced displays are not yet widely available, primarily due to the lack of low cost, large area, compact actuator arrays that can stimulate the large numbers of receptors of the user and that can also meet the high requirements for user safety and comfort. This research focuses on the development of polymer microfabrication technologies for the realization of two major components of a pneumatic tactile display: a microactuator array and a complementary microvalve (control) array. In this work, the concept, fabrication, and characterization of a kinematically-stabilized polymeric microbubble actuator ("endoskeletal microbubble actuator") is presented. A systematic design and modeling procedure was carried out to generate an optimized geometry of the corrugated diaphragm to satisfy membrane deflection, force, and stability requirements set forth by the tactile display goals. A mass-manufacturable actuator has been fabricated using the approaches of lithography and micromolding. A prototype of a single endoskeletal bubble actuator with a diameter of 2.6mm has been fabricated and characterized. In addition, in order to further reduce the size and cost of the tactile display, a microvalve array can be integrated into the tactile display system to control the pneumatic fluid that actuates the microbubble actuator. A piezoelectrically-driven and hydraulically-amplified polymer microvalve has been designed, fabricated, and tested. An incompressible elastomer was used as a solid hydraulic medium to convert the small axial displacement of a piezoelectric actuator into a large valve head stroke while maintaining a large blocking force. The function of the microvalve as an on-off switch for a pneumatic microbubble tactile actuator has been demonstrated. Compared to present technologies, the microvalve developed can achieve large flow rate control due to its amplification mechanism, can avoid complex sealing problem because solid rather than liquid medium is used, and can form a dense valve array due to the small lateral dimension of the actuator used. To further reduce the cost of the microvalve, a laterally-laminated multilayer PZT actuator has been fabricated using diced PZT multilayer, high aspect ratio SU-8 photolithography, and molding of electrically conductive polymer composite electrodes. This fabrication process is simple and straightforward compared to previous lateral lamination approaches. An 8-layer device has shown a displacement of 0.63 micron at 100V driving voltage, which agrees well with simulation results. The lateral lamination fabrication process provides a valuable alternative for making compact, low-voltage, multilayer piezoelectric micro-actuators as microvalve driving element. A refreshable Braille cell as a tactile display prototype has been developed based on a 2x3 endoskeletal microbubble array and an array of commercial valves. The prototype can provide both a static display (which meets the displacement and force requirement of a Braille display) and vibratory tactile sensations. Along with the above capabilities, the device was designed to meet the criteria of lightness and compactness to permit portable operation. The design is scalable with respect to the number of tactile actuators while still being simple to fabricate.

Memory operation mechanism of fullerene-containing polymer memory

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

Nakajima, Anri, E-mail: anakajima@hiroshima-u.ac.jp; Fujii, Daiki

2015-03-09

The memory operation mechanism in fullerene-containing nanocomposite gate insulators was investigated while varying the kind of fullerene in a polymer gate insulator. It was cleared what kind of traps and which positions in the nanocomposite the injected electrons or holes are stored in. The reason for the difference in the easiness of programming was clarified taking the role of the charging energy of an injected electron into account. The dependence of the carrier dynamics on the kind of fullerene molecule was investigated. A nonuniform distribution of injected carriers occurred after application of a large magnitude programming voltage due to themore » width distribution of the polystyrene barrier between adjacent fullerene molecules. Through the investigations, we demonstrated a nanocomposite gate with fullerene molecules having excellent retention characteristics and a programming capability. This will lead to the realization of practical organic memories with fullerene-containing polymer nanocomposites.« less

Thermal response of novel shape memory polymer-shape memory alloy hybrids

NASA Astrophysics Data System (ADS)

Rossiter, Jonathan; Takashima, Kazuto; Mukai, Toshiharu

2014-03-01

Shape memory polymers (SMP) and shape memory alloys (SMA) have both been proven important smart materials in their own fields. Shape memory polymers can be formed into complex three-dimensional structures and can undergo shape programming and large strain recovery. These are especially important for deployable structures including those for space applications and micro-structures such as stents. Shape memory alloys on the other hand are readily exploitable in a range of applications where simple, silent, light-weight and low-cost repeatable actuation is required. These include servos, valves and mobile robotic artificial muscles. Despite their differences, one important commonality between SMPs and SMAs is that they are both typically activated by thermal energy. Given this common characteristic it is important to consider how these two will behave when in close environmental proximity, and hence exposed to the same thermal stimulus, and when they are incorporated into a hybrid SMA-SMP structure. In this paper we propose and examine the operation of SMA-SMP hybrids. The relationship between the two temperatures Tg, the glass transition temperature of the polymer, and Ta, the nominal austenite to martensite transition temperature of the alloy is considered. We examine how the choice of these two temperatures affects the thermal response of the hybrid. Electrical stimulation of the SMA is also considered as a method not only of actuating the SMA but also of inducing heating in the surrounding polymer, with consequent effects on actuator behaviour. Likewise by varying the rate and degree of thermal stimulation of the SMA significantly different actuation and structural stiffness can be achieved. Novel SMP-SMA hybrid actuators and structures have many ready applications in deployable structures, robotics and tuneable engineering systems.

Formation of biodegradated polymers as components of future composite materials on the basis of shape memory alloy of medical appointment

NASA Astrophysics Data System (ADS)

Nasakina, E. O.; Baikin, A. S.; Sergiyenko, K. V.; Kaplan, M. A.; Konushkin, S. V.; Yakubov, A. D.; Izvin, A. V.; Sudarchikova, M. A.; Sevost’yanov, M. A.; Kolmakov, A. G.

2018-04-01

The processes of formation of polymer polylactide or polyglycylidactide films for the subsequent creation of a layered composite with a biodegradable layer on the basis of a nickel-free shape memory alloy TiNbTaZr are studied. The structure of the samples was determined using an SEM. The correspondence of morphology of surfaces of and the substrate itself is noted. High adhesion of the polymer to the future basis of the developed composite material is supposed. The formed films is homogeneous and amorphous throughout the polymer volume. By varying the volume of solutions, it is possible to obtain films of a given thickness for any type of polymer, its molecular weight, and the solution concentration of the polymer in chloroform. Poly (glycolide-lactide) should be more plastic than polylactide.

Thermoreversible Folding as a Route to the Unique Shape-Memory Character in Ductile Polymer Networks.

PubMed

McBride, Matthew K; Podgorski, Maciej; Chatani, Shunsuke; Worrell, Brady T; Bowman, Christopher N

2018-06-21

Ductile, cross-linked films were folded as a means to program temporary shapes without the need for complex heating cycles or specialized equipment. Certain cross-linked polymer networks, formed here with the thiol-isocyanate reaction, possessed the ability to be pseudoplastically deformed below the glass transition, and the original shape was recovered during heating through the glass transition. To circumvent the large forces required to plastically deform a glassy polymer network, we have utilized folding, which localizes the deformation in small creases, and achieved large dimensional changes with simple programming procedures. In addition to dimension changes, three-dimensional objects such as swans and airplanes were developed to demonstrate applying origami principles to shape memory. We explored the fundamental mechanical properties that are required to fold polymer sheets and observed that a yield point that does not correspond to catastrophic failure is required. Unfolding occurred during heating through the glass transition, indicating the vitrification of the network that maintained the temporary, folded shape. Folding was demonstrated as a powerful tool to simply and effectively program ductile shape-memory polymers without the need for thermal cycling.

Shape-memory effect by specific biodegradable polymer blending for biomedical applications.

PubMed

Cha, Kook Jin; Lih, Eugene; Choi, Jiyeon; Joung, Yoon Ki; Ahn, Dong Jun; Han, Dong Keun

2014-05-01

Specific biodegradable polymers having shape-memory properties through "polymer-blend" method are investigated and their shape-switching in body temperature (37 °C) is characterized. Poly(L-lactide-co-caprolactone) (PLCL) and poly(L-lactide-co-glycolide) (PLGA) are dissolved in chloroform and the films of several blending ratios of PLCL/PLGA are prepared by solvent casting. The shape-memory properties of films are also examined using dynamic mechanical analysis (DMA). Among the blending ratios, the PLCL50/PLGA50 film shows good performance of shape-fixity and shape-recovery based on glass transition temperature. It displays that the degree of shape recovery is 100% at 37 °C and the shape recovery proceeds within only 15 s. In vitro biocompatibility studies are shown to have good blood compatibility and cytocompatibility for the PLCL50/PLGA50 films. It is expected that this blended biodegradable polymer can be potentially used as a material for blood-contacting medical devices such as a self-expended vascular polymer stents and vascular closure devices in biomedical applications. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Physical and reliability issues in MEMS microrelays with gold contacts

NASA Astrophysics Data System (ADS)

Lafontan, Xavier; Pressecq, Francis; Perez, Guy; Dufaza, Christian; Karam, Jean Michel

2001-10-01

This paper presents the work we have done on micro-relays with gold micro-contacts in MUMPs. Firstly, the theoretical physical principles of MEMS micro-relay are described. This study is divided in two parts: the micro-contact and the micro-actuator. The micro-contact part deals with resistance of constriction, contact area, adhesion, arcing and wear. Whereas the micro-actuator part describes general principles, contact force, restoring force and actuator reliability. Then, in a second part, an innovative electrostatic relay design in MUMPs is presented. The concept, the implementation and the final realization are discussed. Then, in the third part, characterization results are reported. This part particularly focuses on the micro-contact study. Conduction mode, contact area, mechanical and thermal deformation, and adhesion energies are presented.

Shape memory polymer network with thermally distinct elasticity and plasticity.

PubMed

Zhao, Qian; Zou, Weike; Luo, Yingwu; Xie, Tao

2016-01-01

Stimuli-responsive materials with sophisticated yet controllable shape-changing behaviors are highly desirable for real-world device applications. Among various shape-changing materials, the elastic nature of shape memory polymers allows fixation of temporary shapes that can recover on demand, whereas polymers with exchangeable bonds can undergo permanent shape change via plasticity. We integrate the elasticity and plasticity into a single polymer network. Rational molecular design allows these two opposite behaviors to be realized at different temperature ranges without any overlap. By exploring the cumulative nature of the plasticity, we demonstrate easy manipulation of highly complex shapes that is otherwise extremely challenging. The dynamic shape-changing behavior paves a new way for fabricating geometrically complex multifunctional devices.

Shape Memory Polymers for Body Motion Energy Harvesting and Self-Powered Mechanosensing.

PubMed

Liu, Ruiyuan; Kuang, Xiao; Deng, Jianan; Wang, Yi-Cheng; Wang, Aurelia C; Ding, Wenbo; Lai, Ying-Chih; Chen, Jun; Wang, Peihong; Lin, Zhiqun; Qi, H Jerry; Sun, Baoquan; Wang, Zhong Lin

2018-02-01

Growing demand in portable electronics raises a requirement to electronic devices being stretchable, deformable, and durable, for which functional polymers are ideal choices of materials. Here, the first transformable smart energy harvester and self-powered mechanosensation sensor using shape memory polymers is demonstrated. The device is based on the mechanism of a flexible triboelectric nanogenerator using the thermally triggered shape transformation of organic materials for effectively harvesting mechanical energy. This work paves a new direction for functional polymers, especially in the field of mechanosensation for potential applications in areas such as soft robotics, biomedical devices, and wearable electronics. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Temperature and electrical memory of polymer fibers

NASA Astrophysics Data System (ADS)

Yuan, Jinkai; Zakri, Cécile; Grillard, Fabienne; Neri, Wilfrid; Poulin, Philippe

2014-05-01

We report in this work studies of the shape memory behavior of polymer fibers loaded with carbon nanotubes or graphene flakes. These materials exhibit enhanced shape memory properties with the generation of a giant stress upon shape recovery. In addition, they exhibit a surprising temperature memory with a peak of generated stress at a temperature nearly equal to the temperature of programming. This temperature memory is ascribed to the presence of dynamical heterogeneities and to the intrinsic broadness of the glass transition. We present recent experiments related to observables other than mechanical properties. In particular nanocomposite fibers exhibit variations of electrical conductivity with an accurate memory. Indeed, the rate of conductivity variations during temperature changes reaches a well defined maximum at a temperature equal to the temperature of programming. Such materials are promising for future actuators that couple dimensional changes with sensing electronic functionalities.

Recent advances in degradable lactide-based shape-memory polymers.

PubMed

Balk, Maria; Behl, Marc; Wischke, Christian; Zotzmann, Jörg; Lendlein, Andreas

2016-12-15

Biodegradable polymers are versatile polymeric materials that have a high potential in biomedical applications avoiding subsequent surgeries to remove, for example, an implanted device. In the past decade, significant advances have been achieved with poly(lactide acid) (PLA)-based materials, as they can be equipped with an additional functionality, that is, a shape-memory effect (SME). Shape-memory polymers (SMPs) can switch their shape in a predefined manner upon application of a specific external stimulus. Accordingly, SMPs have a high potential for applications ranging from electronic engineering, textiles, aerospace, and energy to biomedical and drug delivery fields based on the perspectives of new capabilities arising with such materials in biomedicine. This study summarizes the progress in SMPs with a particular focus on PLA, illustrates the design of suitable homo- and copolymer structures as well as the link between the (co)polymer structure and switching functionality, and describes recent advantages in the implementation of novel switching phenomena into SMP technology. Copyright © 2016 Elsevier B.V. All rights reserved.

High performance shape memory polymer networks based on rigid nanoparticle cores

PubMed Central

Song, Jie

2010-01-01

Smart materials that can respond to external stimuli are of widespread interest in biomedical science. Thermal-responsive shape memory polymers, a class of intelligent materials that can be fixed at a temporary shape below their transition temperature (Ttrans) and thermally triggered to resume their original shapes on demand, hold great potential as minimally invasive self-fitting tissue scaffolds or implants. The intrinsic mechanism for shape memory behavior of polymers is the freezing and activation of the long-range motion of polymer chain segments below and above Ttrans, respectively. Both Ttrans and the extent of polymer chain participation in effective elastic deformation and recovery are determined by the network composition and structure, which are also defining factors for their mechanical properties, degradability, and bioactivities. Such complexity has made it extremely challenging to achieve the ideal combination of a Ttrans slightly above physiological temperature, rapid and complete recovery, and suitable mechanical and biological properties for clinical applications. Here we report a shape memory polymer network constructed from a polyhedral oligomeric silsesquioxane nanoparticle core functionalized with eight polyester arms. The cross-linked networks comprising this macromer possessed a gigapascal-storage modulus at body temperature and a Ttrans between 42 and 48 °C. The materials could stably hold their temporary shapes for > 1 year at room temperature and achieve full shape recovery ≤ 51 °C in a matter of seconds. Their versatile structures allowed for tunable biodegradability and biofunctionalizability. These materials have tremendous promise for tissue engineering applications. PMID:20375285

Polymeric Helical Microactuators: Achieving High Speed and High Extension.

NASA Astrophysics Data System (ADS)

Kim, Yongjin; Crosby, Alfred

We proposed novel concepts of actuation mechanism and fabrication method to induce fast and highly extensional motion in polymeric actuators. Exceptionally high extensional strain over 1400% was realized by the geometric transformation from a helix to a stretched ribbon in a responsive and reversible manner. As a model system, sub-micron sized helices were fabricated from a self-assembled, UV-cured, thermo-responsive polymer. By controlling the size and the geometrical asymmetries in the system, a combined effect of surface tension and differential volumetric strain during the transition between swollen-deswollen state induced by phase transition of the material was successfully utilized to generate torsional stresses in the system. For the full understanding of the results, a finite element analysis and measurements on the poroelastic properties of the material were conducted as well as a demonstration on macroscopic system made with PDMS. Finally, remaining questions on the chirality of helices were presented. This material is based upon work supported by, or in part by, the U. S. Army Research Laboratory and the U. S. Army Research Office under contract/Grant Number W911NF-15-1-0358.

Ultra-low power, highly uniform polymer memory by inserted multilayer graphene electrode

NASA Astrophysics Data System (ADS)

Jang, Byung Chul; Seong, Hyejeong; Kim, Jong Yun; Koo, Beom Jun; Kim, Sung Kyu; Yang, Sang Yoon; Gap Im, Sung; Choi, Sung-Yool

2015-12-01

Filament type resistive random access memory (RRAM) based on polymer thin films is a promising device for next generation, flexible nonvolatile memory. However, the resistive switching nonuniformity and the high power consumption found in the general filament type RRAM devices present critical issues for practical memory applications. Here, we introduce a novel approach not only to reduce the power consumption but also to improve the resistive switching uniformity in RRAM devices based on poly(1,3,5-trimethyl-3,4,5-trivinyl cyclotrisiloxane) by inserting multilayer graphene (MLG) at the electrode/polymer interface. The resistive switching uniformity was thereby significantly improved, and the power consumption was markedly reduced by 250 times. Furthermore, the inserted MLG film enabled a transition of the resistive switching operation from unipolar resistive switching to bipolar resistive switching and induced self-compliance behavior. The findings of this study can pave the way toward a new area of application for graphene in electronic devices.

Highly reliable top-gated thin-film transistor memory with semiconducting, tunneling, charge-trapping, and blocking layers all of flexible polymers.

PubMed

Wang, Wei; Hwang, Sun Kak; Kim, Kang Lib; Lee, Ju Han; Cho, Suk Man; Park, Cheolmin

2015-05-27

The core components of a floating-gate organic thin-film transistor nonvolatile memory (OTFT-NVM) include the semiconducting channel layer, tunneling layer, floating-gate layer, and blocking layer, besides three terminal electrodes. In this study, we demonstrated OTFT-NVMs with all four constituent layers made of polymers based on consecutive spin-coating. Ambipolar charges injected and trapped in a polymer electret charge-controlling layer upon gate program and erase field successfully allowed for reliable bistable channel current levels at zero gate voltage. We have observed that the memory performance, in particular the reliability of a device, significantly depends upon the thickness of both blocking and tunneling layers, and with an optimized layer thickness and materials selection, our device exhibits a memory window of 15.4 V, on/off current ratio of 2 × 10(4), read and write endurance cycles over 100, and time-dependent data retention of 10(8) s, even when fabricated on a mechanically flexible plastic substrate.

Technical Operations Support III (TOPS III). Task Order 0018: Nanostructured Graphene-Like Polymers

DTIC Science & Technology

2010-06-01

diverse response by a large class of materials: viscoelastic fluids, inelasticity, crystallization of polymers, twinning, shape memory alloys , single...crystal super alloys , and viscoelastic solids. 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT: SAR 18. NUMBER...twinning (Rajagopal and Srinivasa (1997)), Kannan et al. (2002)), shape memory alloys (Rajagopal and Srinivasa (1999)), single crystal super alloys

Towards Low-Cost Effective and Homogeneous Thermal Activation of Shape Memory Polymers

PubMed Central

Lantada, Andrés Díaz; Rebollo, María Ángeles Santamaría

2013-01-01

A typical limitation of intelligent devices based on the use of shape-memory polymers as actuators is linked to the widespread use of distributed heating resistors, via Joule effect, as activation method, which involves several relevant issues needing attention, such as: (a) Final device size is importantly increased due to the additional space required for the resistances; (b) the use of resistances limits materials’ strength and the obtained devices are normally weaker; (c) the activation process through heating resistances is not homogeneous, thus leading to important temperature differences among the polymeric structure and to undesirable thermal gradients and stresses, also limiting the application fields of shape-memory polymers. In our present work we describe interesting activation alternatives, based on coating shape-memory polymers with different kinds of conductive materials, including textiles, conductive threads and conductive paint, which stand out for their easy, rapid and very cheap implementation. Distributed heating and homogeneous activation can be achieved in several of the alternatives studied and the technical results are comparable to those obtained by using advanced shape-memory nanocomposites, which have to deal with complex synthesis, processing and security aspects. Different combinations of shape memory epoxy resin with several coating electrotextiles, conductive films and paints are prepared, simulated with the help of thermal finite element method based resources and characterized using infrared thermography for validating the simulations and overall design process. A final application linked to an active catheter pincer is detailed and the advantages of using distributed heating instead of conventional resistors are discussed. PMID:28788401

Study of scratch drive actuator force characteristics

NASA Astrophysics Data System (ADS)

Li, Lijie; Brown, J. Gordon; Uttamchandani, Deepak

2002-11-01

Microactuators are one of the key components in MEMS technology, and various designs have been realized through different fabrication processes. One type of microactuator commonly used is the scratch drive actuator (SDA) that is frequently fabricated by surface micromachining processes. An experimental investigation has been conducted on the force characteristics of SDAs fabricated using the JDSU Microsystems MUMPs process. One-, two-, three- and four-plate SDAs connected to box-springs have been designed and fabricated for these experiments using MUMPs run 44. The spring constant for the box-springs has been calculated by FEM using ANSYS software. The product of the spring constant and spring extension is used to measure the forces produced by these SDAs. It is estimated that the forces produced exceed 250 μN from a one-plate SDA and 850 μN from a four-plate SDA.

Low-Actuation Voltage MEMS Digital-to-Analog Converter with Parylene Spring Structures.

PubMed

Ma, Cheng-Wen; Lee, Fu-Wei; Liao, Hsin-Hung; Kuo, Wen-Cheng; Yang, Yao-Joe

2015-08-28

We propose an electrostatically-actuated microelectromechanical digital-to-analog converter (M-DAC) device with low actuation voltage. The spring structures of the silicon-based M-DAC device were monolithically fabricated using parylene-C. Because the Young's modulus of parylene-C is considerably lower than that of silicon, the electrostatic microactuators in the proposed device require much lower actuation voltages. The actuation voltage of the proposed M-DAC device is approximately 6 V, which is less than one half of the actuation voltages of a previously reported M-DAC equipped with electrostatic microactuators. The measured total displacement of the proposed three-bit M-DAC is nearly 504 nm, and the motion step is approximately 72 nm. Furthermore, we demonstrated that the M-DAC can be employed as a mirror platform with discrete displacement output for a noncontact surface profiling system.

pH-Responsive Shape Memory Poly(ethylene glycol)-Poly(ε-caprolactone)-based Polyurethane/Cellulose Nanocrystals Nanocomposite.

PubMed

Li, Ying; Chen, Hongmei; Liu, Dian; Wang, Wenxi; Liu, Ye; Zhou, Shaobing

2015-06-17

In this study, we developed a pH-responsive shape-memory polymer nanocomposite by blending poly(ethylene glycol)-poly(ε-caprolactone)-based polyurethane (PECU) with functionalized cellulose nanocrystals (CNCs). CNCs were functionalized with pyridine moieties (CNC-C6H4NO2) through hydroxyl substitution of CNCs with pyridine-4-carbonyl chloride and with carboxyl groups (CNC-CO2H) via 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) mediated surface oxidation, respectively. At a high pH value, the CNC-C6H4NO2 had attractive interactions from the hydrogen bonding between pyridine groups and hydroxyl moieties; at a low pH value, the interactions reduced or disappeared due to the protonation of pyridine groups, which are a Lewis base. The CNC-CO2H responded to pH variation in an opposite manner. The hydrogen bonding interactions of both CNC-C6H4NO2 and CNC-CO2H can be readily disassociated by altering pH values, endowing the pH-responsiveness of CNCs. When these functionalized CNCs were added in PECU polymer matrix to form nanocomposite network which was confirmed with rheological measurements, the mechanical properties of PECU were not only obviously improved but also the pH-responsiveness of CNCs could be transferred to the nanocomposite network. The pH-sensitive CNC percolation network in polymer matrix served as the switch units of shape-memory polymers (SMPs). Furthermore, the modified CNC percolation network and polymer molecular chains also had strong hydrogen bonding interactions among hydroxyl, carboxyl, pyridine moieties, and isocyanate groups, which could be formed or destroyed through changing pH value. The shape memory function of the nanocomposite network was only dependent on the pH variation of the environment. Therefore, this pH-responsive shape-memory nancomposite could be potentially developed into a new smart polymer material.

Stretchable electronics for wearable and high-current applications

NASA Astrophysics Data System (ADS)

Hilbich, Daniel; Shannon, Lesley; Gray, Bonnie L.

2016-04-01

Advances in the development of novel materials and fabrication processes are resulting in an increased number of flexible and stretchable electronics applications. This evolving technology enables new devices that are not readily fabricated using traditional silicon processes, and has the potential to transform many industries, including personalized healthcare, consumer electronics, and communication. Fabrication of stretchable devices is typically achieved through the use of stretchable polymer-based conductors, or more rigid conductors, such as metals, with patterned geometries that can accommodate stretching. Although the application space for stretchable electronics is extensive, the practicality of these devices can be severely limited by power consumption and cost. Moreover, strict process flows can impede innovation that would otherwise enable new applications. In an effort to overcome these impediments, we present two modified approaches and applications based on a newly developed process for stretchable and flexible electronics fabrication. This includes the development of a metallization pattern stamping process allowing for 1) stretchable interconnects to be directly integrated with stretchable/wearable fabrics, and 2) a process variation enabling aligned multi-layer devices with integrated ferromagnetic nanocomposite polymer components enabling a fully-flexible electromagnetic microactuator for large-magnitude magnetic field generation. The wearable interconnects are measured, showing high conductivity, and can accommodate over 20% strain before experiencing conductive failure. The electromagnetic actuators have been fabricated and initial measurements show well-aligned, highly conductive, isolated metal layers. These two applications demonstrate the versatility of the newly developed process and suggest potential for its furthered use in stretchable electronics and MEMS applications.

Redox driven conductance changes for resistive memory

NASA Astrophysics Data System (ADS)

Shoute, Lian C. T.; Pekas, Nikola; Wu, Yiliang; McCreery, Richard L.

2011-03-01

The relationship between bias-induced redox reactions and resistance switching is considered for memory devices containing TiO2 or a conducting polymer in "molecular heterojunctions" consisting of thin (2-25 nm) films of covalently bonded molecules, polymers, and oxides. Raman spectroscopy was used to monitor changes in the oxidation state of polythiophene in Au/P3HT/SiO2/Au devices, and it was possible to directly determine the formation and stability of the conducting polaron state of P3HT by applied bias pulses [P3HT = poly(3-hexyl thiophene)]. Polaron formation was strongly dependent on junction composition, particularly on the interfaces between the polymer, oxide, and electrodes. In all cases, trace water was required for polaron formation, leading to the proposal that water reduction acts as a redox counter-reaction to polymer oxidation. Polaron stability was longest for the case of a direct contact between Au and SiO2, implying that catalytic water reduction at the Au surface generated hydroxide ions which stabilized the cationic polaron. The spectroscopic information about the dependence of polaron stability on device composition will be useful for designing and monitoring resistive switching memory based on conducting polymers, with or without TiO2 present.

Electric Field Activated Shape Memory Polymer Composite

NASA Technical Reports Server (NTRS)

Kang, Jin Ho (Inventor); Turner, Travis L. (Inventor); Siochi, Emilie J. (Inventor); Penner, Ronald K. (Inventor)

2017-01-01

Provided is an electrically activated shape memory polymer composite capable of thermal shape reformation using electric power to heat the composite through its matrix glass transition temperature. The composite includes an adaptable polymer matrix component using a diglycidyl ether resin, at least one substantially well-dispersed conductive or magnetic nano-filler component, and at least one elastic, laminated layer. Also provided are methods of preparing the composite and methods of activating the composite. A shape reformation of the composite is triggered by applying an electric field at DC and/or at a frequency above about 1.mu.Hz for a sufficient time.

Poly(Capro-Lactone) Networks as Actively Moving Polymers

NASA Astrophysics Data System (ADS)

Meng, Yuan

Shape-memory polymers (SMPs), as a subset of actively moving polymers, form an exciting class of materials that can store and recover elastic deformation energy upon application of an external stimulus. Although engineering of SMPs nowadays has lead to robust materials that can memorize multiple temporary shapes, and can be triggered by various stimuli such as heat, light, moisture, or applied magnetic fields, further commercialization of SMPs is still constrained by the material's incapability to store large elastic energy, as well as its inherent one-way shape-change nature. This thesis develops a series of model semi-crystalline shape-memory networks that exhibit ultra-high energy storage capacity, with accurately tunable triggering temperature; by introducing a second competing network, or reconfiguring the existing network under strained state, configurational chain bias can be effectively locked-in, and give rise to two-way shape-actuators that, in the absence of an external load, elongates upon cooling and reversibly contracts upon heating. We found that well-defined network architecture plays essential role on strain-induced crystallization and on the performance of cold-drawn shape-memory polymers. Model networks with uniform molecular weight between crosslinks, and specified functionality of each net-point, results in tougher, more elastic materials with a high degree of crystallinity and outstanding shape-memory properties. The thermal behavior of the model networks can be finely modified by introducing non-crystalline small molecule linkers that effectively frustrates the crystallization of the network strands. This resulted in shape-memory networks that are ultra-sensitive to heat, as deformed materials can be efficiently triggered to revert to its permanent state upon only exposure to body temperature. We also coupled the same reaction adopted to create the model network with conventional free-radical polymerization to prepare a dual-cure "double network" that behaves as a real thermal "actuator". This approach places sub-chains under different degrees of configurational bias within the network to utilize the material's propensity to undergo stress-induced crystallization. Reconfiguration of model shape-memory networks containing photo-sensitive linkages can also be employed to program two-way actuator. Chain reshuffling of a partially reconfigurable network is initiated upon exposure to light under specific strains. Interesting photo-induced creep and stress relaxation behaviors were demonstrated and understood based on a novel transient network model we derived. In summary, delicate manipulation of shape-memory network architectures addressed critical issues constraining the application of this type of functional polymer material. Strategies developed in this thesis may provide new opportunity to the field of shape-memory polymers.

Shape memory polymer network with thermally distinct elasticity and plasticity

PubMed Central

Zhao, Qian; Zou, Weike; Luo, Yingwu; Xie, Tao

2016-01-01

Stimuli-responsive materials with sophisticated yet controllable shape-changing behaviors are highly desirable for real-world device applications. Among various shape-changing materials, the elastic nature of shape memory polymers allows fixation of temporary shapes that can recover on demand, whereas polymers with exchangeable bonds can undergo permanent shape change via plasticity. We integrate the elasticity and plasticity into a single polymer network. Rational molecular design allows these two opposite behaviors to be realized at different temperature ranges without any overlap. By exploring the cumulative nature of the plasticity, we demonstrate easy manipulation of highly complex shapes that is otherwise extremely challenging. The dynamic shape-changing behavior paves a new way for fabricating geometrically complex multifunctional devices. PMID:26824077

Biomedical Applications of Thermally Activated Shape Memory Polymers

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

Small IV, W; Singhal, P; Wilson, T S

2009-04-10

Shape memory polymers (SMPs) are smart materials that can remember a primary shape and can return to this primary shape from a deformed secondary shape when given an appropriate stimulus. This property allows them to be delivered in a compact form via minimally invasive surgeries in humans, and deployed to achieve complex final shapes. Here we review the various biomedical applications of SMPs and the challenges they face with respect to actuation and biocompatibility. While shape memory behavior has been demonstrated with heat, light and chemical environment, here we focus our discussion on thermally stimulated SMPs.

Shape-memory surfaces for cell mechanobiology

PubMed Central

Ebara, Mitsuhiro

2015-01-01

Shape-memory polymers (SMPs) are a new class of smart materials, which have the capability to change from a temporary shape ‘A’ to a memorized permanent shape ‘B’ upon application of an external stimulus. In recent years, SMPs have attracted much attention from basic and fundamental research to industrial and practical applications due to the cheap and efficient alternative to well-known metallic shape-memory alloys. Since the shape-memory effect in SMPs is not related to a specific material property of single polymers, the control of nanoarchitecture of polymer networks is particularly important for the smart functions of SMPs. Such nanoarchitectonic approaches have enabled us to further create shape-memory surfaces (SMSs) with tunable surface topography at nano scale. The present review aims to bring together the exciting design of SMSs and the ever-expanding range of their uses as tools to control cell functions. The goal for these endeavors is to mimic the surrounding mechanical cues of extracellular environments which have been considered as critical parameters in cell fate determination. The untapped potential of SMSs makes them one of the most exciting interfaces of materials science and cell mechanobiology. PMID:27877747

Capacitance-voltage measurement in memory devices using ferroelectric polymer

NASA Astrophysics Data System (ADS)

Nguyen, Chien A.; Lee, Pooi See

2006-01-01

Application of thin polymer film as storing mean for non-volatile memory devices is investigated. Capacitance-voltage (C-V) measurement of metal-ferroelectric-metal device using ferroelectric copolymer P(VDF-TrFE) as dielectric layer shows stable 'butter-fly' curve. The two peaks in C-V measurement corresponding to the largest capacitance are coincidental at the coercive voltages that give rise to zero polarization in the polarization hysteresis measurement. By comparing data of C-V and P-E measurement, a correlation between two types of hysteresis is established in which it reveals simultaneous electrical processes occurring inside the device. These processes are caused by the response of irreversible and reversible polarization to the applied electric field that can be used to present a memory window. The memory effect of ferroelectric copolymer is further demonstrated for fabricating polymeric non-volatile memory devices using metal-ferroelectric-insulator-semiconductor structure (MFIS). By applying different sweeping voltages at the gate, bidirectional flat-band voltage shift is observed in the ferroelectric capacitor. The asymmetrical shift after negative sweeping is resulted from charge accumulation at the surface of Si substrate caused by the dipole direction in the polymer layer. The effect is reversed for positive voltage sweeping.

Supplement request for Support of MRS Symposium (PECASE: Active Microstructured Polymer Systems)

DTIC Science & Technology

2015-07-06

materials (e.g., gels, polymers, liquids , liquid crystals and photosensitive materials) that can change shape in a controlled response to stimuli. These...Rogers1. 1, , University of Illinois, Urbana, Illinois, USA. Show Abstract 8:45 AM - *XX1.02 New Wonders of Nafion : Shape Memory, Temperature Memory... Liquid Crystal Institute, Kent State University, Kent, Ohio, USA; 5, Department of Electrical and Computer Engineering, University of Idaho, Moscow

Bulk heterojunction polymer memory devices with reduced graphene oxide as electrodes.

PubMed

Liu, Juqing; Yin, Zongyou; Cao, Xiehong; Zhao, Fei; Lin, Anping; Xie, Linghai; Fan, Quli; Boey, Freddy; Zhang, Hua; Huang, Wei

2010-07-27

A unique device structure with a configuration of reduced graphene oxide (rGO) /P3HT:PCBM/Al has been designed for the polymer nonvolatile memory device. The current-voltage (I-V) characteristics of the fabricated device showed the electrical bistability with a write-once-read-many-times (WORM) memory effect. The memory device exhibits a high ON/OFF ratio (10(4)-10(5)) and low switching threshold voltage (0.5-1.2 V), which are dependent on the sheet resistance of rGO electrode. Our experimental results confirm that the carrier transport mechanisms in the OFF and ON states are dominated by the thermionic emission current and ohmic current, respectively. The polarization of PCBM domains and the localized internal electrical field formed among the adjacent domains are proposed to explain the electrical transition of the memory device.

The quintuple-shape memory effect in electrospun nanofiber membranes

NASA Astrophysics Data System (ADS)

Zhang, Fenghua; Zhang, Zhichun; Liu, Yanju; Lu, Haibao; Leng, Jinsong

2013-08-01

Shape memory fibrous membranes (SMFMs) are an emerging class of active polymers, which are capable of switching from a temporary shape to their permanent shape upon appropriate stimulation. Quintuple-shape memory membranes based on the thermoplastic polymer Nafion, with a stable fibrous structure, are achieved via electrospinning technology, and possess a broad transition temperature. The recovery of multiple temporary shapes of electrospun membranes can be triggered by heat in a single triple-, quadruple-, quintuple-shape memory cycle, respectively. The fiber morphology and nanometer size provide unprecedented design flexibility for the adjustable morphing effect. SMFMs enable complex deformations at need, having a wide potential application field including smart textiles, artificial intelligence robots, bio-medical engineering, aerospace technologies, etc in the future.

Modeling the behaviour of shape memory materials under large deformations

NASA Astrophysics Data System (ADS)

Rogovoy, A. A.; Stolbova, O. S.

2017-06-01

In this study, the models describing the behavior of shape memory alloys, ferromagnetic materials and polymers have been constructed, using a formalized approach to develop the constitutive equations for complex media under large deformations. The kinematic and constitutive equations, satisfying the principles of thermodynamics and objectivity, have been derived. The application of the Galerkin procedure to the systems of equations of solid mechanics allowed us to obtain the Lagrange variational equation and variational formulation of the magnetostatics problems. These relations have been tested in the context of the problems of finite deformation in shape memory alloys and ferromagnetic materials during forward and reverse martensitic transformations and in shape memory polymers during forward and reverse relaxation transitions from a highly elastic to a glassy state.

Surface engineering of ferroelectric polymer for the enhanced electrical performance of organic transistor memory

NASA Astrophysics Data System (ADS)

Kim, Do-Kyung; Lee, Gyu-Jeong; Lee, Jae-Hyun; Kim, Min-Hoi; Bae, Jin-Hyuk

2018-05-01

We suggest a viable surface control method to improve the electrical properties of organic nonvolatile memory transistors. For viable surface control, the surface of the ferroelectric insulator in the memory field-effect transistors was modified using a smooth-contact-curing process. For the modification of the ferroelectric polymer, during the curing of the ferroelectric insulators, the smooth surface of a soft elastomer contacts intimately with the ferroelectric surface. This smooth-contact-curing process reduced the surface roughness of the ferroelectric insulator without degrading its ferroelectric properties. The reduced roughness of the ferroelectric insulator increases the mobility of the organic field-effect transistor by approximately eight times, which results in a high memory on–off ratio and a low-voltage reading operation.

Thermally responsive polymer systems for self-healing, reversible adhesion and shape memory applications

NASA Astrophysics Data System (ADS)

Luo, Xiaofan

Responsive polymers are "smart" materials that are capable of performing prescribed, dynamic functions under an applied stimulus. In this dissertation, we explore several novel design strategies to develop thermally responsive polymers and polymer composites for self-healing, reversible adhesion and shape memory applications. In the first case described in Chapters 2 and 3, a thermally triggered self-healing material was prepared by blending a high-temperature epoxy resin with a thermoplastic polymer, poly(epsilon-caprolactone) (PCL). The initially miscible system undergoes polymerization induced phase separation (PIPS) during the curing of epoxy and yields a variety of compositionally dependent morphologies. At a particular PCL loading, the cured blend displays a "bricks-and-mortar" morphology in which epoxy exists as interconnected spheres ("bricks") within a continuous PCL matrix ("mortar"). A heat induced "bleeding" phenomenon was observed in the form of spontaneous wetting of all free surfaces by the molten PCL, and is attributed to the volumetric thermal expansion of PCL above its melting point in excess of epoxy brick expansion, which we term differential expansive bleeding (DEB). This DEB is capable of healing damage such as cracks. In controlled self-healing experiments, heating of a cracked specimen led to PCL bleeding from the bulk that yields a liquid layer bridging the crack gap. Upon cooling, a "scar" composed of PCL crystals was formed at the site of the crack, restoring a significant portion of mechanical strength. We further utilized DEB to enable strong and thermally-reversible adhesion of the material to itself and to metallic substrates, without any requirement for macroscopic softening or flow. After that, Chapters 4--6 present a novel composite strategy for the design and fabrication of shape memory polymer composites. The basic approach involves physically combining two or more functional components into an interpenetrating fiber/matrix structure, allowing them to function in a synergistic fashion yet remain physically separated. This latter aspect is critical since it enables the control of overall composite properties and functions by separately tuning each component. Utilizing the intrinsic versatility of this approach, composites with novel properties and functions (in addition to "regular" shape memory) have been developed, including (1) shape memory elastomeric composites (SMECs; Chapter 4), (2) triple-shape polymeric composites (TSPCs; Chapter 5), and (3) electrically conductive nanocomposites (Chapter 6). Then in Chapter 7, by combining the success in both thermoplastic based self-healing and shape memory polymer composites, we demonstrate a thermally triggered self-healing coating. This coating features a unique "shape memory assisted self-healing" mechanism in which crack closure (via shape memory) and crack re-bonding (via melting and diffusion of the thermoplastic healing agent) are achieved simultaneously upon a single heating step, leading to both structural and functional (corrosion resistance) recovery. Finally, Chapter 8 presents for the first time the preparation of functionally graded shape memory polymers (SMPs) that, unlike conventional SMPs, have a range of glass transition temperatures that are spatially graded. This was achieved using a temperature gradient curing method that imposes different vitrification limits at different positions along the gradient. The resulting material is capable of responding to a wide range of thermal triggers and a good candidate for low-cost, material based temperature sensors. All the aforementioned materials and methods show great potential for practical applications due to their high performance, low cost and broad applicability. Some recommendations for future research and development are given in Chapter 9.

Design and Verification of a Shape Memory Polymer Peripheral Occlusion Device

PubMed Central

Landsman, Todd L.; Bush, Ruth L.; Glowczwski, Alan; Horn, John; Jessen, Staci L.; Ungchusri, Ethan; Diguette, Katelin; Smith, Harrison R.; Hasan, Sayyeda M.; Nash, Daniel; Clubb, Fred J.; Maitland, Duncan J.

2017-01-01

Shape memory polymer foams have been previously investigated for their safety and efficacy in treating a porcine aneurysm model. Their biocompatibility, rapid thrombus formation, and ability for endovascular catheter-based delivery to a variety of vascular beds makes these foams ideal candidates for use in numerous embolic applications, particularly within the peripheral vasculature. This study sought to investigate the material properties, safety, and efficacy of a shape memory polymer peripheral embolization device in vitro. The material characteristics of the device were analyzed to show tunability of the glass transition temperature (Tg) and the expansion rate of the polymer to ensure adequate time to deliver the device through a catheter prior to excessive foam expansion. Mechanical analysis and flow migration studies were performed to ensure minimal risk of vessel perforation and undesired thromboembolism upon device deployment. The efficacy of the device was verified by performing blood flow studies that established affinity for thrombus formation and blood penetration throughout the foam and by delivery of the device in an ultrasound phantom that demonstrated flow stagnation and diversion of flow to collateral pathways. PMID:27419615

Design and verification of a shape memory polymer peripheral occlusion device.

PubMed

Landsman, Todd L; Bush, Ruth L; Glowczwski, Alan; Horn, John; Jessen, Staci L; Ungchusri, Ethan; Diguette, Katelin; Smith, Harrison R; Hasan, Sayyeda M; Nash, Daniel; Clubb, Fred J; Maitland, Duncan J

2016-10-01

Shape memory polymer foams have been previously investigated for their safety and efficacy in treating a porcine aneurysm model. Their biocompatibility, rapid thrombus formation, and ability for endovascular catheter-based delivery to a variety of vascular beds makes these foams ideal candidates for use in numerous embolic applications, particularly within the peripheral vasculature. This study sought to investigate the material properties, safety, and efficacy of a shape memory polymer peripheral embolization device in vitro. The material characteristics of the device were analyzed to show tunability of the glass transition temperature (Tg) and the expansion rate of the polymer to ensure adequate time to deliver the device through a catheter prior to excessive foam expansion. Mechanical analysis and flow migration studies were performed to ensure minimal risk of vessel perforation and undesired thromboembolism upon device deployment. The efficacy of the device was verified by performing blood flow studies that established affinity for thrombus formation and blood penetration throughout the foam and by delivery of the device in an ultrasound phantom that demonstrated flow stagnation and diversion of flow to collateral pathways. Copyright © 2016 Elsevier Ltd. All rights reserved.

Shape memory polymer foams for endovascular therapies

DOEpatents

Wilson, Thomas S.; Maitland, Duncan J.

2017-03-21

A system for occluding a physical anomaly. One embodiment comprises a shape memory material body wherein the shape memory material body fits within the physical anomaly occluding the physical anomaly. The shape memory material body has a primary shape for occluding the physical anomaly and a secondary shape for being positioned in the physical anomaly.

Shape memory polymer foams for endovascular therapies

DOEpatents

Wilson, Thomas S [Castro Valley, CA; Maitland, Duncan J [Pleasant Hill, CA

2012-03-13

A system for occluding a physical anomaly. One embodiment comprises a shape memory material body wherein the shape memory material body fits within the physical anomaly occluding the physical anomaly. The shape memory material body has a primary shape for occluding the physical anomaly and a secondary shape for being positioned in the physical anomaly.

Shape memory polymer foams for endovascular therapies

DOEpatents

Wilson, Thomas S.; Maitland, Duncan J.

2015-05-26

A system for occluding a physical anomaly. One embodiment comprises a shape memory material body wherein the shape memory material body fits within the physical anomaly occluding the physical anomaly. The shape memory material body has a primary shape for occluding the physical anomaly and a secondary shape for being positioned in the physical anomaly.

TOPICAL REVIEW: Pneumatic and hydraulic microactuators: a review

NASA Astrophysics Data System (ADS)

De Volder, Michaël; Reynaerts, Dominiek

2010-04-01

The development of MEMS actuators is rapidly evolving and continuously new progress in terms of efficiency, power and force output is reported. Pneumatic and hydraulic are an interesting class of microactuators that are easily overlooked. Despite the 20 years of research, and hundreds of publications on this topic, these actuators are only popular in microfluidic systems. In other MEMS applications, pneumatic and hydraulic actuators are rare in comparison with electrostatic, thermal or piezo-electric actuators. However, several studies have shown that hydraulic and pneumatic actuators deliver among the highest force and power densities at microscale. It is believed that this asset is particularly important in modern industrial and medical microsystems, and therefore, pneumatic and hydraulic actuators could start playing an increasingly important role. This paper shows an in-depth overview of the developments in this field ranging from the classic inflatable membrane actuators to more complex piston-cylinder and drag-based microdevices.

Low-Actuation Voltage MEMS Digital-to-Analog Converter with Parylene Spring Structures

PubMed Central

Ma, Cheng-Wen; Lee, Fu-Wei; Liao, Hsin-Hung; Kuo, Wen-Cheng; Yang, Yao-Joe

2015-01-01

We propose an electrostatically-actuated microelectromechanical digital-to-analog converter (M-DAC) device with low actuation voltage. The spring structures of the silicon-based M-DAC device were monolithically fabricated using parylene-C. Because the Young’s modulus of parylene-C is considerably lower than that of silicon, the electrostatic microactuators in the proposed device require much lower actuation voltages. The actuation voltage of the proposed M-DAC device is approximately 6 V, which is less than one half of the actuation voltages of a previously reported M-DAC equipped with electrostatic microactuators. The measured total displacement of the proposed three-bit M-DAC is nearly 504 nm, and the motion step is approximately 72 nm. Furthermore, we demonstrated that the M-DAC can be employed as a mirror platform with discrete displacement output for a noncontact surface profiling system. PMID:26343682

Responsive Biomaterials: Advances in Materials Based on Shape-Memory Polymers.

PubMed

Hardy, John G; Palma, Matteo; Wind, Shalom J; Biggs, Manus J

2016-07-01

Shape-memory polymers (SMPs) are morphologically responsive materials with potential for a variety of biomedical applications, particularly as devices for minimally invasive surgery and the delivery of therapeutics and cells for tissue engineering. A brief introduction to SMPs is followed by a discussion of the current progress toward the development of SMP-based biomaterials for clinically relevant biomedical applications. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Damage healing ability of a shape-memory-polymer-based particulate composite with small thermoplastic contents

NASA Astrophysics Data System (ADS)

Nji, Jones; Li, Guoqiang

2012-02-01

The purpose of this study is to investigate the potential of a shape-memory-polymer (SMP)-based particulate composite to heal structural-length scale damage with small thermoplastic additive contents through a close-then-heal (CTH) self-healing scheme that was introduced in a previous study (Li and Uppu 2010 Comput. Sci. Technol. 70 1419-27). The idea is to achieve reasonable healing efficiencies with minimal sacrifice in structural load capacity. By first closing cracks, the gap between two crack surfaces is narrowed and a lesser amount of thermoplastic particles is required to achieve healing. The particulate composite was fabricated by dispersing copolyester thermoplastic particles in a shape memory polymer matrix. It is found that, for small thermoplastic contents of less than 10%, the CTH scheme followed in this study heals structural-length scale damage in the SMP particulate composite to a meaningful extent and with less sacrifice of structural capacity.

Direct Writing of Three-Dimensional Macroporous Photonic Crystals on Pressure-Responsive Shape Memory Polymers.

PubMed

Fang, Yin; Ni, Yongliang; Leo, Sin-Yen; Wang, Bingchen; Basile, Vito; Taylor, Curtis; Jiang, Peng

2015-10-28

Here we report a single-step direct writing technology for making three-dimensional (3D) macroporous photonic crystal patterns on a new type of pressure-responsive shape memory polymer (SMP). This approach integrates two disparate fields that do not typically intersect: the well-established templating nanofabrication and shape memory materials. Periodic arrays of polymer macropores templated from self-assembled colloidal crystals are squeezed into disordered arrays in an unusual shape memory "cold" programming process. The recovery of the original macroporous photonic crystal lattices can be triggered by direct writing at ambient conditions using both macroscopic and nanoscopic tools, like a pencil or a nanoindenter. Interestingly, this shape memory disorder-order transition is reversible and the photonic crystal patterns can be erased and regenerated hundreds of times, promising the making of reconfigurable/rewritable nanooptical devices. Quantitative insights into the shape memory recovery of collapsed macropores induced by the lateral shear stresses in direct writing are gained through fundamental investigations on important process parameters, including the tip material, the critical pressure and writing speed for triggering the recovery of the deformed macropores, and the minimal feature size that can be directly written on the SMP membranes. Besides straightforward applications in photonic crystal devices, these smart mechanochromic SMPs that are sensitive to various mechanical stresses could render important technological applications ranging from chromogenic stress and impact sensors to rewritable high-density optical data storage media.

Microactuators as driving units for microbotic systems

NASA Astrophysics Data System (ADS)

Lehr, Heinz; Abel, S.; Doepper, J.; Ehrfeld, Wolfgang; Hagemann, B.; Kaemper, Klaus P.; Michel, Frank; Schulz, Ch.; Theurigen, C.

1996-12-01

The trend towards the integration of a multitude of functions in e.g. data end-, medical- and communication systems pushes the miniaturization of actuators for linear or rotational motions. Technical advantages of these devices are their low energy consumption, their potential for high precision positioning and their low inertial masses, which allow e.g. huge rotational frequencies. Appreciable forces and torques as well as appropriate mechanical interfaces to integrate these drive units into complete systems are necessary prerequisites for robotic applications, but rarely found up to now. Most of these difficulties arise due to the application of monolithic fabrication techniques, leading to structures of essentially planar nature and severe material restrictions. It turned out that only hybrid concepts and the assembly of components made from the most appropriate material open the chance to build up microactuators which are well suited for microrobotic systems. The contribution starts with a short description of the LIGA technique, which constitutes the major 3-D microfabrication method for the production of individual actuator components with structural heights of up to several millimeters made from a variety of function adapted materials. The assembling of these components results in microactuators with typical dimensions in the millimeter range. Examples are powerful electromagnetic micromotors, delivering torques much larger than one (mu) Nm and high rotational speeds which may be converted by use of LIGA fabricated gear-wheels to furthermore increase the torque. Huge forces are obtained in addition by use of microfabricated fluidic systems. Although small in size, the actuators still offer good handling opportunities and interfacing facilities to build up more complicated robotic systems.

Four-Point-Latching Microactuator

NASA Technical Reports Server (NTRS)

Toda, Risaku; Yang, Eui-Hyeok

2008-01-01

An experimental inchworm-type linear microactuator is depicted. This microactuator is a successor to one described in "MEMS-Based Piezoelectric/Electrostatic Inchworm Actuator" (NPO-30672), NASA Tech Briefs, Vol. 27, No. 6 (June 2003), page 68. Both actuators are based on the principle of using a piezoelectric transducer operated in alternation with electrostatically actuated clutches to cause a slider to move in small increments. However, the design of the present actuator incorporates several improvements over that of the previous one. The most readily apparent improvement is in geometry and, consequently, in fabrication: In the previous actuator, the inchworm motion was perpendicular to the broad faces of a flat silicon wafer on which the actuator was fabricated, and fabrication involved complex processes to form complex three-dimensional shapes in and on the wafer. In the present actuator, the inchworm motion is parallel to the broad faces of a wafer on which it is fabricated. The components needed to produce the in-plane motion are nearly planar in character and, consequently, easier to fabricate. Other advantages of the present design are described, including that the previous actuator contained two clutches (denoted 'holders' in the cited prior article), the present actuator contains four clutches. The operational sequence of the previous two-clutch actuator is similar. However, the two-clutch configuration is susceptible to tilt of the slider and a consequent large increase in drag. Hence, the primary operational advantages of the present four-point-latching design over the prior two-point-latching design are less drag and greater control robustness arising from greater stability of the orientation of the slider.

An approach to predict the shape-memory behavior of amorphous polymers from Dynamic Mechanical Analysis (DMA) data

NASA Astrophysics Data System (ADS)

Kuki, Ákos; Czifrák, Katalin; Karger-Kocsis, József; Zsuga, Miklós; Kéki, Sándor

2015-02-01

The prediction of shape-memory behavior is essential regarding the design of a smart material for different applications. This paper proposes a simple and quick method for the prediction of shape-memory behavior of amorphous shape memory polymers (SMPs) on the basis of a single dynamic mechanical analysis (DMA) temperature sweep at constant frequency. All the parameters of the constitutive equations for linear viscoelasticity are obtained by fitting the DMA curves. The change with the temperature of the time-temperature superposition shift factor ( a T ) is expressed by the Williams-Landel-Ferry (WLF) model near and above the glass transition temperature ( T g ), and by the Arrhenius law below T g . The constants of the WLF and Arrhenius equations can also be determined. The results of our calculations agree satisfactorily with the experimental free recovery curves from shape-memory tests.

Mechanical properties and shape memory effect of thermal-responsive polymer based on PVA

NASA Astrophysics Data System (ADS)

Lin, Liulan; Zhang, Lingfeng; Guo, Yanwei

2018-01-01

In this study, the effect of content of glutaraldehyde (GA) on the shape memory behavior of a shape memory polymer based on polyvinyl alcohol chemically cross-linked with GA was investigated. Thermal-responsive shape memory composites with three different GA levels, GA-PVA (3 wt%, 5 wt%, 7 wt%), were prepared by particle melting, mold forming and freeze-drying technique. The mechanical properties, thermal properties and shape memory behavior were measured by differential scanning calorimeter, physical bending test and cyclic thermo-mechanical test. The addition of GA to PVA led to a steady shape memory transition temperature and an improved mechanical compressive strength. The composite with 5 wt% of GA exhibited the best shape recoverability. Further increase in the crosslinking agent content of GA would reduce the recovery force and prolong the recovery time due to restriction in the movement of the soft PVA chain segments. These results provide important information for the study on materials in 4D printing.

Strategic design and fabrication of acrylic shape memory polymers

NASA Astrophysics Data System (ADS)

Park, Ju Hyuk; Kim, Hansu; Ryoun Youn, Jae; Song, Young Seok

2017-08-01

Modulation of thermomechanics nature is a critical issue for an optimized use of shape memory polymers (SMPs). In this study, a strategic approach was proposed to control the transition temperature of SMPs. Free radical vinyl polymerization was employed for tailoring and preparing acrylic SMPs. Transition temperatures of the shape memory tri-copolymers were tuned by changing the composition of monomers. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy analyses were carried out to evaluate the chemical structures and compositions of the synthesized SMPs. The thermomechanical properties and shape memory performance of the SMPs were also examined by performing dynamic mechanical thermal analysis. Numerical simulation based on a finite element method provided consistent results with experimental cyclic shape memory tests of the specimens. Transient shape recovery tests were conducted and optical transparence of the samples was identified. We envision that the materials proposed in this study can help develop a new type of shape-memory devices in biomedical and aerospace engineering applications.

Shape memory alloy/shape memory polymer tools

DOEpatents

Seward, Kirk P.; Krulevitch, Peter A.

2005-03-29

Micro-electromechanical tools for minimally invasive techniques including microsurgery. These tools utilize composite shape memory alloy (SMA), shape memory polymer (SMP) and combinations of SMA and SMP to produce catheter distal tips, actuators, etc., which are bistable. Applications for these structures include: 1) a method for reversible fine positioning of a catheter tip, 2) a method for reversible fine positioning of tools or therapeutic catheters by a guide catheter, 3) a method for bending articulation through the body's vasculature, 4) methods for controlled stent delivery, deployment, and repositioning, and 5) catheters with variable modulus, with vibration mode, with inchworm capability, and with articulated tips. These actuators and catheter tips are bistable and are opportune for in vivo usage because the materials are biocompatible and convenient for intravascular use as well as other minimal by invasive techniques.

Triple-Shape Memory Polymers Based on Self-Complementary Hydrogen Bonding

PubMed Central

Ware, Taylor; Hearon, Keith; Lonnecker, Alexander; Wooley, Karen L.; Maitland, Duncan J.; Voit, Walter

2012-01-01

Triple shape memory polymers (TSMPs) are a growing subset of a class of smart materials known as shape memory polymers, which are capable of changing shape and stiffness in response to a stimulus. A TSMP can change shapes twice and can fix two metastable shapes in addition to its permanent shape. In this work, a novel TSMP system comprised of both permanent covalent cross-links and supramolecular hydrogen bonding cross-links has been synthesized via a one-pot method. Triple shape properties arise from the combination of the glass transition of (meth)acrylate copolymers and the dissociation of self-complementary hydrogen bonding moieties, enabling broad and independent control of both glass transition temperature (Tg) and cross-link density. Specifically, ureidopyrimidone methacrylate and a novel monomer, ureidopyrimidone acrylate, were copolymerized with various alkyl acrylates and bisphenol A ethoxylate diacrylate. Control of Tg from 0 to 60 °C is demonstrated: concentration of hydrogen bonding moieties is varied from 0 to 40 wt %; concentration of the diacrylate is varied from 0 to 30 wt %. Toughness ranges from 0.06 to 0.14 MPa and is found to peak near 20 wt % of the supramolecular cross-linker. A widely tunable class of amorphous triple-shape memory polymers has been developed and characterized through dynamic and quasi-static thermomechanical testing to gain insights into the dynamics of supramolecular networks. PMID:22287811

Electro-Optic Properties of Holographically Patterned, Polymer Stabilized Cholesteric Liquid Crystals (Preprint)

DTIC Science & Technology

2007-01-01

Electro - optic properties of cholesteric liquid crystals with holographically patterned polymer stabilization were examined. It is hypothesized that...enhanced electro - optic properties of the final device. Prior to holographic patterning, polymer stabilization with large elastic memory was generated by way... electro - optic properties appear to stem from a single dimension domain size increase, which allows for a reduction in the LC/polymer interaction.

Note: A simple picture of subdiffusive polymer motion from stochastic simulations

NASA Astrophysics Data System (ADS)

Gniewek, Pawel; Kolinski, Andrzej

2011-02-01

Entangled polymer solutions and melts exhibit unusual frictional properties. In the entanglement limit self-diffusion coefficient of long flexible polymers decays with the second power of chain length and viscosity increases with 3-3.5 power of chain length.1 It is very difficult to provide detailed molecular-level explanation of the entanglement effect.2 Perhaps, the problem of many entangled polymer chains is the most complex multibody issue of classical physics. There are different approaches to polymer melt dynamics. Some of these recognize hydrodynamic interactions as a dominant term, while topological constraints for polymer chains are assumed as a secondary factor. Other theories consider the topological constraints as the most important factors controlling polymer dynamics. Herman and co-workers describe polymer dynamics in melts, as a lateral sliding of a chain along other chains until complete mutual disentanglement. Despite the success in explaining the power-laws for viscosity, the model has some limitations. First of all, memory effects are ignored, that is, polymer segments are treated independently. Also, each entanglement/obstacle is treated as a separate entity, which is certainly a simplification of the memory effect problem. In addition to that, correlated motions of segments are addressed within the framework of renormalized Rouse-chain theory,7 without calling any topological entanglements in advance. This approach leads to the generalized Langevin equation characterized by distinct memory kernels describing local and nonlocal segment correlations or to the Smoluchowski equation in which the segments' mobility is treated as a stochastic variable.11 Both models describe the polymer segments motion at a microscopic level. An interesting alternative is to solve the integrodifferential equation for the chain relaxation with a sophisticated kernel function.12 The design of the kernel function is based on a mesoscopic description of the polymer melt. These theories explain some experimental data, although the description of the crossover between the Rouse and non-Rouse behavior is not satisfactory. Obviously, within the scope of a short note we cannot review all theoretical concepts of the polymer melt dynamics. Here we focus just on the interpretation of the observed single segment autocorrelation function.

An investigation of a thermally steerable electroactive polymer/shape memory polymer hybrid actuator

NASA Astrophysics Data System (ADS)

Ren, Kailiang; Bortolin, Robert S.; Zhang, Q. M.

2016-02-01

This paper investigates the thermal response of a hybrid actuator composed of an electroactive polymer (EAP) and a shape memory polymer (SMP). This study introduces the concept of using the large strain from a phase transition (ferroelectric to paraelectric phase) induced by temperature change in a poly(vinylidene fluoride-trifluoroethylene) film to tune the shape of an SMP film above its glass transition temperature (Tg). Based on the material characterization data, it is revealed that the thickness ratio of the EAP/SMP films plays a critical role in the displacement of the actuator. Further, it is also demonstrated that the displacement of the hybrid actuator can be tailored by varying the temperature, and finite element method simulation results fit well with the measurement data. This specially designed hybrid actuator shows great promise for future morphing aircraft applications.

Stretchable degradable and electroactive shape memory copolymers with tunable recovery temperature enhance myogenic differentiation.

PubMed

Deng, Zexing; Guo, Yi; Zhao, Xin; Li, Longchao; Dong, Ruonan; Guo, Baolin; Ma, Peter X

2016-12-01

Development of flexible degradable electroactive shape memory polymers (ESMPs) with tunable switching temperature (around body temperature) for tissue engineering is still a challenge. Here we designed and synthesized a series of shape memory copolymers with electroactivity, super stretchability and tunable recovery temperature based on poly(ε-caprolactone) (PCL) with different molecular weight and conductive amino capped aniline trimer, and demonstrated their potential to enhance myogenic differentiation from C2C12 myoblast cells. We characterized the copolymers by Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance ( 1 H NMR), cyclic voltammetry (CV), ultraviolet-visible spectroscopy (UV-vis), differential scanning calorimetry (DSC), shape memory test, tensile test and in vitro enzymatic degradation study. The electroactive biodegradable shape memory copolymers showed great elasticity, tunable recovery temperature around 37°C, and good shape memory properties. Furthermore, proliferation and differentiation of C2C12 myoblasts were investigated on electroactive copolymers films, and they greatly enhanced the proliferation, myotube formation and related myogenic differentiation genes expression of C2C12 myoblasts compared to the pure PCL with molecular weight of 80,000. Our study suggests that these electroactive, highly stretchable, biodegradable shape memory polymers with tunable recovery temperature near the body temperature have great potential in skeletal muscle tissue engineering application. Conducting polymers can regulate cell behavior such cell adhesion, proliferation, and differentiation with or without electrical stimulation. Therefore, they have great potential for electrical signal sensitive tissue regeneration. Although conducting biomaterials with degradability have been developed, highly stretchable and electroactive degradable copolymers for soft tissue engineering have been rarely reported. On the other hand, shape memory polymers (SMPs) have been widely used in biomedical fields. However, SMPs based on polyesters usually are biologically inert. This work reported the design of super stretchable electroactive degradable SMPs based on polycaprolactone and aniline trimer with tunable recovery temperature around body temperature. These flexible electroactive SMPs facilitated the proliferation and differentiation of C2C12 myoblast cells compared with polycaprolactone, indicating that they are excellent scaffolding biomaterials in tissue engineering to repair skeletal muscle and possibly other tissues. Copyright © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Porous Shape Memory Polymers

PubMed Central

Hearon, Keith; Singhal, Pooja; Horn, John; Small, Ward; Olsovsky, Cory; Maitland, Kristen C.; Wilson, Thomas S.; Maitland, Duncan J.

2013-01-01

Porous shape memory polymers (SMPs) include foams, scaffolds, meshes, and other polymeric substrates that possess porous three-dimensional macrostructures. Porous SMPs exhibit active structural and volumetric transformations and have driven investigations in fields ranging from biomedical engineering to aerospace engineering to the clothing industry. The present review article examines recent developments in porous SMPs, with focus given to structural and chemical classification, methods of characterization, and applications. We conclude that the current body of literature presents porous SMPs as highly interesting smart materials with potential for industrial use. PMID:23646038

Deformation behavior of carbon-fiber reinforced shape-memory-polymer composites used for deployable structures (Conference Presentation)

NASA Astrophysics Data System (ADS)

Lan, Xin; Liu, Liwu; Li, Fengfeng; Pan, Chengtong; Liu, Yanju; Leng, Jinsong

2017-04-01

Shape memory polymers (SMPs) are a new type of smart material, they perform large reversible deformation with a certain external stimulus (e.g., heat and electricity). The properties (e.g., stiffness, strength and other mechanically static or quasi-static load-bearing capacity) are primarily considered for conventional resin-based composite materials which are mainly used for structural materials. By contrast, the mechanical actuating performance with finite deformation is considered for the shape memory polymers and their composites which can be used for both structural materials and functional materials. For shape memory polymers and their composites, the performance of active deformation is expected to further promote the development in smart active deformation structures, such as deployable space structures and morphing wing aircraft. The shape memory polymer composites (SMPCs) are also one type of High Strain Composite (HSC). The space deployable structures based on carbon fiber reinforced shape memory polymer composites (SMPCs) show great prospects. Considering the problems that SMPCs are difficult to meet the practical applications in space deployable structures in the recent ten years, this paper aims to research the mechanics of deformation, actuation and failure of SMPCs. In the overall view of the shape memory polymer material's nonlinearity (nonlinearity and stress softening in the process of pre-deformation and recovery, relaxation in storage process, irreversible deformation), by the multiple verifications among theory, finite element and experiments, one obtains the deformation and actuation mechanism for the process of "pre-deformation, energy storage and actuation" and its non-fracture constraint domain. Then, the parameters of SMPCs will be optimized. Theoretical analysis is realized by the strain energy function, additionally considering the interaction strain energy between the fiber and the matrix. For the common resin-based or soft-material-based composites under pure bending deformation, we expect to uniformly explain the whole process of buckling occurrence, evolution and finally failure, especially for the early evolution characteristics of fiber microbuckling inside the microstructures. The research results are meaningful for the practical applications for SMPC deployable structures in space. Considering the deformation mechanisms of SMPCs, the local post-microbuckling is required for the unidirectional fiber reinforced composite materials, at the conditions of its large geometrical deflection. The cross section of SMPC is divided into three areas: non-buckling stretching area, non-buckling compressive area, and buckling compressive area. Three variables are considered: critical buckling position, and neutral plane, the fiber buckling half-wavelength. Considering the condition of the small strain and large displacement, the strain energy expression of the SMP/fiber system was derived, which contains two types, e.g., strain energy of SMP and fiber. According to the minimum energy principle, the expression for all key parameters were derived, including the critical buckling curvature, neutral plane position, the buckling half-wavelength, fiber buckling amplitude, and strain.

Polydopamine Particle-Filled Shape-Memory Polyurethane Composites with Fast Near-Infrared Light Responsibility.

PubMed

Yang, Li; Tong, Rui; Wang, Zhanhua; Xia, Hesheng

2018-03-25

A new kind of fast near-infrared (NIR) light-responsive shape-memory polymer composites was prepared by introducing polydopamine particles (PDAPs) into commercial shape-memory polyurethane (SMPU). The toughness and strength of the polydopamine-particle-filled polyurethane composites (SMPU-PDAPs) were significantly enhanced with the addition of PDAPs due to the strong interface interaction between PDAPs and polyurethane segments. Owing to the outstanding photothermal effect of PDAPs, the composites exhibit a rapid light-responsive shape-memory process in 60 s with a PDAPs content of 0.01 wt%. Due to the excellent dispersion and convenient preparation method, PDAPs have great potential to be used as high-efficiency and environmentally friendly fillers to obtain novel photoactive functional polymer composites. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

The Characterization of Thin Film Nickel Titanium Shape Memory Alloys

NASA Astrophysics Data System (ADS)

Harris Odum, Nicole Latrice

Shape memory alloys (SMA) are able to recover their original shape through the appropriate heat or stress exposure after enduring mechanical deformation at a low temperature. Numerous alloy systems have been discovered which produce this unique feature like TiNb, AgCd, NiAl, NiTi, and CuZnAl. Since their discovery, bulk scale SMAs have undergone extensive material property investigations and are employed in real world applications. However, its thin film counterparts have been modestly investigated and applied. Researchers have introduced numerous theoretical microelectromechanical system (MEMS) devices; yet, the research community's overall unfamiliarity with the thin film properties has delayed growth in this area. In addition, it has been difficult to outline efficient thin film processing techniques. In this dissertation, NiTi thin film processing and characterization techniques will be outlined and discussed. NiTi thin films---1 mum thick---were produced using sputter deposition techniques. Substrate bound thin films were deposited to analysis the surface using Scanning Electron Microscopy; the film composition was obtained using Energy Dispersive Spectroscopy; the phases were identified using X-ray diffraction; and the transformation temperatures acquired using resistivity testing. Microfabrication processing and sputter deposition were employed to develop tensile membranes for membrane deflection experimentation to gain insight on the mechanical properties of the thin films. The incorporation of these findings will aid in the movement of SMA microactuation devices from theory to fruition and greatly benefit industries such as medicinal and aeronautical.

A Structural Approach to Establishing a Platform Chemistry for the Tunable, Bulk Electron Beam Cross-Linking of Shape Memory Polymer Systems

PubMed Central

Hearon, Keith; Besset, Celine J.; Lonnecker, Alexander T.; Ware, Taylor; Voit, Walter E.; Wilson, Thomas S.; Wooley, Karen L.; Maitland, Duncan J.

2014-01-01

The synthetic design and thermomechanical characterization of shape memory polymers (SMPs) built from a new polyurethane chemistry that enables facile, bulk and tunable cross-linking of low-molecular weight thermoplastics by electron beam irradiation is reported in this study. SMPs exhibit stimuli-induced geometry changes and are being proposed for applications in numerous fields. We have previously reported a polyurethane SMP system that exhibits the complex processing capabilities of thermoplastic polymers and the mechanical robustness and tunability of thermomechanical properties that are often characteristic of thermoset materials. These previously reported polyurethanes suffer practically because the thermoplastic molecular weights needed to achieve target cross-link densities severely limit high-throughput thermoplastic processing and because thermally unstable radiation-sensitizing additives must be used to achieve high enough cross-link densities to enable desired tunable shape memory behavior. In this study, we demonstrate the ability to manipulate cross-link density in low-molecular weight aliphatic thermoplastic polyurethane SMPs (Mw as low as ~1.5 kDa) without radiation-sensitizing additives by incorporating specific structural motifs into the thermoplastic polymer side chains that we hypothesized would significantly enhance susceptibility to e-beam cross-linking. A custom diol monomer was first synthesized and then implemented in the synthesis of neat thermoplastic polyurethane SMPs that were irradiated at doses ranging from 1 to 500 kGy. Dynamic mechanical analysis (DMA) demonstrated rubbery moduli to be tailorable between 0.1 and 55 MPa, and both DMA and sol/gel analysis results provided fundamental insight into our hypothesized mechanism of electron beam cross-linking, which enables controllable bulk cross-linking to be achieved in highly processable, low-molecular weight thermoplastic shape memory polymers without sensitizing additives. PMID:25411511

New design strategy for reversible plasticity shape memory polymers with deformable glassy aggregates.

PubMed

Lin, Tengfei; Tang, Zhenghai; Guo, Baochun

2014-12-10

Reversible plasticity shape memory (RPSM) is a new concept in the study of shape memory performance behavior and describes a phenomenon in which shape memory polymers (SMPs) can undergo a large plastic deformation at room temperature and subsequently recover their original shape upon heating. To date, RPSM behavior has been demonstrated in only a few polymers. In the present study, we implement a new design strategy, in which deformable glassy hindered phenol (AO-80) aggregates are incorporated into an amorphous network of epoxidized natural rubber (ENR) cured with zinc diacrylate (ZDA), in order to achieve RPSM properties. We propose that AO-80 continuously tunes the glass transition temperature (Tg) and improves the chain mobility of the SMP, providing traction and anchoring the ENR chains by intermolecular hydrogen bonding interactions. The RPSM behavior of the amorphous SMPs is characterized, and the results demonstrate good fixity at large deformations (up to 300%) and excellent recovery upon heating. Large energy storage capacities at Td in these RPSM materials are demonstrated compared with those achieved at elevated temperature in traditional SMPs. Interestingly, the further revealed self-healing properties of these materials are closely related to their RPSM behavior.

Shape memory polymer sensors for tracking cumulative environmental exposure

NASA Astrophysics Data System (ADS)

Snyder, Ryan; Rauscher, Michael; Vining, Ben; Havens, Ernie; Havens, Teresa; McFerran, Jace

2010-04-01

Cornerstone Research Group Inc. (CRG) has developed environmental exposure tracking (EET) sensors using shape memory polymers (SMP) to monitor the degradation of perishable items, such as munitions, foods and beverages, or medicines, by measuring the cumulative exposure to temperature and moisture. SMPs are polymers whose qualities have been altered to give them dynamic shape "memory" properties. Under thermal or moisture stimuli, the SMP exhibits a radical change from a rigid thermoset to a highly flexible, elastomeric state. The dynamic response of the SMP can be tailored to match the degradation profile of the perishable item. SMP-based EET sensors require no digital memory or internal power supply and provide the capability of inexpensive, long-term life cycle monitoring of thermal and moisture exposure over time. This technology was developed through Phase I and Phase II SBIR efforts with the Navy. The emphasis of current research centers on transitioning SMP materials from the lab bench to a production environment. Here, CRG presents the commercialization progress of thermally-activated EET sensors, focusing on fabrication scale-up, process refinements, and quality control. In addition, progress on the development of vapor pressure-responsive SMP (VPR-SMP) will be discussed.

Four-Dimensional Printing Hierarchy Scaffolds with Highly Biocompatible Smart Polymers for Tissue Engineering Applications.

PubMed

Miao, Shida; Zhu, Wei; Castro, Nathan J; Leng, Jinsong; Zhang, Lijie Grace

2016-10-01

The objective of this study was to four-dimensional (4D) print novel biomimetic gradient tissue scaffolds with highly biocompatible naturally derived smart polymers. The term "4D printing" refers to the inherent smart shape transformation of fabricated constructs when implanted minimally invasively for seamless and dynamic integration. For this purpose, a series of novel shape memory polymers with excellent biocompatibility and tunable shape changing effects were synthesized and cured in the presence of three-dimensional printed sacrificial molds, which were subsequently dissolved to create controllable and graded porosity within the scaffold. Surface morphology, thermal, mechanical, and biocompatible properties as well as shape memory effects of the synthesized smart polymers and resultant porous scaffolds were characterized. Fourier transform infrared spectroscopy and gel content analysis confirmed the formation of chemical crosslinking by reacting polycaprolactone triol and castor oil with multi-isocyanate groups. Differential scanning calorimetry revealed an adjustable glass transition temperature in a range from -8°C to 35°C. Uniaxial compression testing indicated that the obtained polymers, possessing a highly crosslinked interpenetrating polymeric networks, have similar compressive modulus to polycaprolactone. Shape memory tests revealed that the smart polymers display finely tunable recovery speed and exhibit greater than 92% shape fixing at -18°C or 0°C and full shape recovery at physiological temperature. Scanning electron microscopy analysis of fabricated scaffolds revealed a graded microporous structure, which mimics the nonuniform distribution of porosity found within natural tissues. With polycaprolactone serving as a control, human bone marrow-derived mesenchymal stem cell adhesion, proliferation, and differentiation greatly increased on our novel smart polymers. The current work will significantly advance the future design and development of novel and functional biomedical scaffolds with advanced 4D printing technology and highly biocompatible smart biomaterials.

Four-Dimensional Printing Hierarchy Scaffolds with Highly Biocompatible Smart Polymers for Tissue Engineering Applications

PubMed Central

Miao, Shida; Zhu, Wei; Castro, Nathan J.; Leng, Jinsong

2016-01-01

The objective of this study was to four-dimensional (4D) print novel biomimetic gradient tissue scaffolds with highly biocompatible naturally derived smart polymers. The term “4D printing” refers to the inherent smart shape transformation of fabricated constructs when implanted minimally invasively for seamless and dynamic integration. For this purpose, a series of novel shape memory polymers with excellent biocompatibility and tunable shape changing effects were synthesized and cured in the presence of three-dimensional printed sacrificial molds, which were subsequently dissolved to create controllable and graded porosity within the scaffold. Surface morphology, thermal, mechanical, and biocompatible properties as well as shape memory effects of the synthesized smart polymers and resultant porous scaffolds were characterized. Fourier transform infrared spectroscopy and gel content analysis confirmed the formation of chemical crosslinking by reacting polycaprolactone triol and castor oil with multi-isocyanate groups. Differential scanning calorimetry revealed an adjustable glass transition temperature in a range from −8°C to 35°C. Uniaxial compression testing indicated that the obtained polymers, possessing a highly crosslinked interpenetrating polymeric networks, have similar compressive modulus to polycaprolactone. Shape memory tests revealed that the smart polymers display finely tunable recovery speed and exhibit greater than 92% shape fixing at −18°C or 0°C and full shape recovery at physiological temperature. Scanning electron microscopy analysis of fabricated scaffolds revealed a graded microporous structure, which mimics the nonuniform distribution of porosity found within natural tissues. With polycaprolactone serving as a control, human bone marrow-derived mesenchymal stem cell adhesion, proliferation, and differentiation greatly increased on our novel smart polymers. The current work will significantly advance the future design and development of novel and functional biomedical scaffolds with advanced 4D printing technology and highly biocompatible smart biomaterials. PMID:28195832

Design and fabrication of a large vertical travel silicon inchworm microactuator for advanced segmented silicon space telescope (ASSIST)

NASA Technical Reports Server (NTRS)

Yang, E.; Dekany, R.; Padin, S.

2003-01-01

The goal of this research is to develop inchworm motor systems capable of simultaneously providing nanometer resolution, high stiffness, large output force, long travel range, and compactness for ultraprecision positioning applications in space.

Ultra Low Density Shape Memory Polymer Foams With Tunable Physicochemical Properties for Treatment of intracranial Aneurysms

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

Singhal, Pooja

Shape memory polymers (SMPs) are a rapidly emerging class of smart materials that can be stored in a deformed temporary shape, and can actively return to their original shape upon application of an external stimulus such as heat, pH or light. This behavior is particularly advantageous for minimally invasive biomedical applications comprising embolic/regenerative scaffolds, as it enables a transcatheter delivery of the device to the target site. The focus of this work was to exploit this shape memory behavior of polyurethanes, and develop an efficient embolic SMP foam device for the treatment of intracranial aneurysms.In summary, this work reports amore » novel family of ultra low density polymer foams which can be delivered via a minimally invasive surgery to the aneurysm site, actuated in a controlled manner to efficiently embolize the aneurysm while promoting physiological fluid/blood flow through the reticulated/open porous structure, and eventually biodegrade leading to complete healing of the vasculature.« less

Porous inorganic-organic shape memory polymers.

PubMed

Zhang, Dawei; Burkes, William L; Schoener, Cody A; Grunlan, Melissa A

2012-06-21

Thermoresponsive shape memory polymers (SMPs) are a type of stimuli-sensitive materials that switch from a temporary shape back to their permanent shape upon exposure to heat. While the majority of SMPs have been fabricated in the solid form, porous SMP foams exhibit distinct properties and are better suited for certain applications, including some in the biomedical field. Like solid SMPs, SMP foams have been restricted to a limited group of organic polymer systems. In this study, we prepared inorganic-organic SMP foams based on the photochemical cure of a macromer comprised of inorganic polydimethylsiloxane (PDMS) segments and organic poly(ε-caprolactone) (PCL) segments, diacrylated PCL(40)-block-PDMS(37)-block-PCL(40). To achieve tunable pore size with high interconnectivity, the SMP foams were prepared via a refined solvent-casting/particulate-leaching (SCPL) method. By varying design parameters such as degree of salt fusion, macromer concentration in the solvent and salt particle size, the SMP foams with excellent shape memory behavior and tunable pore size, pore morphology, and modulus were obtained.

Research on characteristics of symmetric optothermal microactuators.

PubMed

Wang, Y D; You, Q Y; Chen, J J; Zhang, H J

2018-04-01

This paper proposes and studies symmetric optothermal microactuators (OTMAs) which are directly controlled by a laser beam. Based on the principle of thermal flux, a theoretical model is established to describe the laser-induced temperature rises and optothermal expansions of the OTMAs' expansion arms. Temperature rise distributions of the arms with lengths of 590, 990, and 2260 μm are simulated separately, which reveals that, under 2 mW laser irradiation, the maximum temperature rises are invariably less than 75.9°C. Simulations are also made to consider optothermal expansions of the arms caused by laser irradiation, which turns out that expansion increases considerably when the arm's length increases from 250 to 1000 μm, while insignificantly between 1250 and 2500 μm. Under a laser beam of 2 mW power, experiments on three microfabricated OTMAs have been further conducted, which demonstrate that the OTMAs are capable of generating maximum deflections of 7.3, 11.3, and 13.6 μm, and that the growth of deflection is comparatively obvious in the case when the total length changes from 750 to 1200 μm, while insignificant for the range between 1200 and 2380 μm. With regard to simulations and experiments, it has been proved that the OTMAs are capable of implementing direct laser-controlled microactuation in which only about 2 mW laser power is demanded. Moreover, it has been proved that twofold total length or arm length does not correspondingly result in doubling the deflection, nor the expansion. Therefore, total length/expansion arm's length around or less than 1200/1000 μm is more appropriate for obtaining satisfactory characteristics of OTMAs, which may be potentially applied in MEMS/MOEMS and micro-/nano-technology.

A three-degree-of-freedom thin-film PZT-actuated microactuator with large out-of-plane displacement.

PubMed

Choi, Jongsoo; Qiu, Zhen; Rhee, Choong-Ho; Wang, Thomas; Oldham, Kenn

2014-07-01

A novel three degree-of-freedom microactuator based on thin-film lead-zirconate-titanate (PZT) is described with its detailed structural model. Its central rectangular-shaped mirror platform, also referred to as the stage, is actuated by four symmetric PZT bending legs such that each leg provides vertical translation for one corner of the stage. It has been developed to support real-time in vivo vertical cross-sectional imaging with a dual axes confocal endomicroscope for early cancer detection, having large displacements in three axes (z, θ x , θ y ) and a relatively high bandwidth in the z-axis direction. Prototype microactuators closely meet the performance requirements for this application; in the out-of-plane (z-axis) direction, it has shown more than 177 μ m of displacement and about 84 Hz of structural natural frequency, when two diagonal legs are actuated at 14V. With all four legs, another prototype of the same design with lighter stage mass has achieved more than 430 μ m of out-of-plane displacement at 15V and about 200 Hz of bandwidth. The former design has shown approximately 6.4° and 2.9° of stage tilting about the x-axis and y-axis, respectively, at 14V. This paper also presents a modeling technique that uses experimental data to account for the effects of fabrication uncertainties in residual stress and structural dimensions. The presented model predicts the static motion of the stage within an average absolute error of 14.6 μ m, which approaches the desired imaging resolution, 5 μ m, and also reasonably anticipates the structural dynamic behavior of the stage. The refined model will support development of a future trajectory tracking controller for the system.

A three-degree-of-freedom thin-film PZT-actuated microactuator with large out-of-plane displacement

PubMed Central

Choi, Jongsoo; Qiu, Zhen; Rhee, Choong-Ho; Wang, Thomas; Oldham, Kenn

2014-01-01

A novel three degree-of-freedom microactuator based on thin-film lead-zirconate-titanate (PZT) is described with its detailed structural model. Its central rectangular-shaped mirror platform, also referred to as the stage, is actuated by four symmetric PZT bending legs such that each leg provides vertical translation for one corner of the stage. It has been developed to support real-time in vivo vertical cross-sectional imaging with a dual axes confocal endomicroscope for early cancer detection, having large displacements in three axes (z, θx, θy) and a relatively high bandwidth in the z-axis direction. Prototype microactuators closely meet the performance requirements for this application; in the out-of-plane (z-axis) direction, it has shown more than 177 μm of displacement and about 84 Hz of structural natural frequency, when two diagonal legs are actuated at 14V. With all four legs, another prototype of the same design with lighter stage mass has achieved more than 430 μm of out-of-plane displacement at 15V and about 200 Hz of bandwidth. The former design has shown approximately 6.4° and 2.9° of stage tilting about the x-axis and y-axis, respectively, at 14V. This paper also presents a modeling technique that uses experimental data to account for the effects of fabrication uncertainties in residual stress and structural dimensions. The presented model predicts the static motion of the stage within an average absolute error of 14.6 μm, which approaches the desired imaging resolution, 5 μm, and also reasonably anticipates the structural dynamic behavior of the stage. The refined model will support development of a future trajectory tracking controller for the system. PMID:25506131

Two-way shape memory behavior of semi-crystalline elastomer under stress-free condition

NASA Astrophysics Data System (ADS)

Qian, Chen; Dong, Yubing; Zhu, Yaofeng; Fu, Yaqin

2016-08-01

Semi-crystalline shape memory polymers exhibit two-way shape memory effect (2W-SME) under constant stresses through crystallization-induced elongation upon cooling and melting-induced constriction upon heating. The applied constant stress influenced the prediction and usability of 2W-SME in practical applications without any external force. Here the reversible shape transition in EVA-shaped memory polymer was quantitative analyzed under a suitable temperature range and external stress-free condition. The fraction of reversible strain increased with increasing upper temperature (T high) within the temperature range and reached the maximum value of 13.62% at 70 °C. However, reversible strain transition was almost lost when T high exceeded 80 °C because of complete melting of crystalline scaffold, known as the latent recrystallization template. The non-isothermal annealing of EVA 2W-SMP under changing circulating temperatures was confirmed. Moreover, the orientation of crystallization was retained at high temperatures. These findings may contribute to design an appropriate shape memory protocol based on application-specific requirements.

Photonic Shape Memory Polymer with Stable Multiple Colors

PubMed Central

2017-01-01

A photonic shape memory polymer film that shows large color response (∼155 nm) in a wide temperature range has been fabricated from a semi-interpenetrating network of a cholesteric polymer and poly(benzyl acrylate). The large color response is achieved by mechanical embossing of the photonic film above its broad glass transition temperature. The embossed film, as it recovers to its original shape on heating through the broad thermal transition, exhibits multiple structural colors ranging from blue to orange. The relaxation behavior of the embossed film can be fully described using a Kelvin–Voigt model, which reveals that the influence of temperature on the generation of colors is much stronger than that of time, thereby producing stable multiple colors. PMID:28840717

Thiol-vinyl systems as shape memory polymers and novel two-stage reactive polymer systems

NASA Astrophysics Data System (ADS)

Nair, Devatha P.

2011-12-01

The focus of this research was to formulate, characterize and tailor the reaction methodologies and material properties of thiol-vinyl systems to develop novel polymer platforms for a range of engineering applications. Thiol-ene photopolymers were demonstrated to exhibit several advantageous characteristics for shape memory polymer systems for a range of biomedical applications. The thiol-ene shape memory polymer systems were tough and flexible as compared to the acrylic control systems with glass transition temperatures between 30 and 40 °C; ideal for actuation at body temperature. The thiol-ene polymers also exhibited excellent shape fixity and a rapid and distinct shape memory actuation response along with free strain recoveries of greater than 96% and constrained stress recoveries of 100%. Additionally, two-stage reactive thiol-acrylate systems were engineered as a polymer platform technology enabling two independent sets of polymer processing and material properties. There are distinct advantages to designing polymer systems that afford two distinct sets of material properties -- an intermediate polymer that would enable optimum handling and processing of the material (stage 1), while maintaining the ability to tune in different, final properties that enable the optimal functioning of the polymeric material (stage 2). To demonstrate the range of applicability of the two-stage reactive systems, three specific applications were demonstrated; shape memory polymers, lithographic impression materials, and optical materials. The thiol-acrylate reactions exhibit a wide range of application versatility due to the range of available thiol and acrylate monomers as well as reaction mechanisms such as Michael Addition reactions and free radical polymerizations. By designing a series of non-stoichiometeric thiol-acrylate systems, a polymer network is initially formed via a base catalyzed 'click' Michael addition reaction. This self-limiting reaction results in a Stage 1 polymer with excess acrylic functional groups within the network. At a later point in time, the photoinitiated, free radical polymerization of the excess acrylic functional groups results in a highly crosslinked, robust material system. By varying the monomers within the system as well as the stoichiometery of thiol to acrylate functional groups, the ability of the two-stage reactive systems to encompass a wide range of properties at the end of both the stage 1 and stage 2 polymerizations was demonstrated. The thiol-acrylate networks exhibited intermediate Stage 1 rubbery moduli and glass transition temperatures that range from 0.5 MPa and -10 ºC to 22 MPa and 22 ºC respectively. The same polymer networks can then attain glass transition temperatures that range from 5 ºC to 195 ºC and rubbery moduli of up to 200 MPa after the subsequent photocure stage. Two-stage reactive polymer composite systems were also formulated and characterized for thermomechanical and mechanical properties. Thermomechanical analysis showed that the fillers resulted in a significant increase in the modulus at both stage 1 and stage 2 polymerizations without a significant change in the glass transition temperatures (Tg). The two-stage reactive matrix composite formed with a hexafunctional acrylate matrix and 20 volume % silica particles showed a 125% increase in stage 1 modulus and 101% increase in stage 2 modulus, when compared with the modulus of the neat matrix. Finally, the two-stage reactive polymeric devices were formulated and designed as orthopedic suture anchors for arthroscopic surgeries and mechanically characterized. The Stage 1 device was designed to exhibit properties ideal for arthroscopic delivery and device placement with glass transition temperatures 25 -- 30 °C and rubbery moduli ˜ 95 MPa. The subsequent photopolymerization generated Stage 2 polymers designed to match the local bone environment with moduli ranging up to 2 GPa. Additionally, pull-out strengths of 140 N were demonstrated and are equivalent to the pull-strengths achieved by other commercially available suture anchors.

Acceleration Techniques for Recombination of Gases in Electrolysis Microactuators with Nafion®-Coated Electrocatalyst

PubMed Central

Sheybani, Roya; Meng, Ellis

2015-01-01

Recombination of electrolysis gases (oxidation of hydrogen and reduction of oxygen) is an important factor in operation efficiency of devices employing electrolysis such as actuators and also unitized regenerative fuel cells. Several methods of improving recombination speed and repeatability were developed for application to electrolysis microactuators with Nafion®-coated catalytic electrodes. Decreasing the electrolysis chamber volume increased the speed, consistency, and repeatability of the gas recombination rate. To further improve recombination performance, methods to increase the catalyst surface area, hydrophobicity, and availability were developed and evaluated. Of these, including in the electrolyte pyrolyzed-Nafion®-coated Pt segments contained in the actuator chamber accelerated recombination by increasing the catalyst surface area and decreasing the gas transport diffusion path. This approach also reduced variability in recombination encountered under varying actuator orientation (resulting in differing catalyst/gas bubble proximity) and increased the rate of recombination by 2.3 times across all actuator orientations. Repeatability of complete recombination for different generated gas volumes was studied through cycling. PMID:26251561

Analysis of out-of-plane thermal microactuators

NASA Astrophysics Data System (ADS)

Atre, Amarendra

2006-02-01

Out-of-plane thermal microactuators find applications in optical switches to motivate micromirrors. Accurate analysis of such actuators is beneficial for improving existing designs and constructing more energy efficient actuators. However, the analysis is complicated by the nonlinear deformation of the thermal actuators along with temperature-dependent properties of polysilicon. This paper describes the development, modeling issues and results of a three-dimensional multiphysics nonlinear finite element model of surface micromachined out-of-plane thermal actuators. The model includes conductive and convective cooling effects and takes into account the effect of variable air gap on the response of the actuator. The model is implemented to investigate the characteristics of two diverse MUMPs fabricated out-of-plane thermal actuators. Reasonable agreement is observed between simulated and measured results for the model that considers the influence of air gap on actuator response. The usefulness of the model is demonstrated by implementing it to observe the effect of actuator geometry variation on steady-state deflection response.

Design and simulation of a MEM pressure microgripper based on electrothermal microactuators

NASA Astrophysics Data System (ADS)

Tecpoyotl-T., Margarita; Vargas Ch., Pedro; Koshevaya, Svetlana; Cabello-R., Ramón; Ocampo-D., Alejandra; Vera-D., J. Gerardo

2016-09-01

Design and simulation of a novel pressure microgripper based on Microelectromechanical, MEM technology, and composed by several electrothermal microactuators were carried out in order to increment the displacement and the cutoff force. The implementation of an element of press or gripping in the arrow of chevron actuator was implemented to supply stability in the manipulation of micro-objects. Each device of the microgripper and its fundamental equations will be described. The fundamental parameters to understand the operation and behaviour of the device are analyzed through sweeps of temperature (from 30 °C up to 100 °C) and voltage (from 0.25 V up to 5 V), showing the feasibility to operate the microgripper with electrical or thermal feeding. The design and simulation were development with Finite Element Method (FEM) in Ansys-Workbench 16.0. In this work, the fundamental parameters were calculated in Ansys-Workbench. It is shown, that structural modifications have great impact in the displacement and the cut-off force of the microgripper.

High Performance Transparent Transistor Memory Devices Using Nano-Floating Gate of Polymer/ZnO Nanocomposites

NASA Astrophysics Data System (ADS)

Shih, Chien-Chung; Lee, Wen-Ya; Chiu, Yu-Cheng; Hsu, Han-Wen; Chang, Hsuan-Chun; Liu, Cheng-Liang; Chen, Wen-Chang

2016-02-01

Nano-floating gate memory devices (NFGM) using metal nanoparticles (NPs) covered with an insulating polymer have been considered as a promising electronic device for the next-generation nonvolatile organic memory applications NPs. However, the transparency of the device with metal NPs is restricted to 60~70% due to the light absorption in the visible region caused by the surface plasmon resonance effects of metal NPs. To address this issue, we demonstrate a novel NFGM using the blends of hole-trapping poly (9-(4-vinylphenyl) carbazole) (PVPK) and electron-trapping ZnO NPs as the charge storage element. The memory devices exhibited a remarkably programmable memory window up to 60 V during the program/erase operations, which was attributed to the trapping/detrapping of charge carriers in ZnO NPs/PVPK composite. Furthermore, the devices showed the long-term retention time (>105 s) and WRER test (>200 cycles), indicating excellent electrical reliability and stability. Additionally, the fabricated transistor memory devices exhibited a relatively high transparency of 90% at the wavelength of 500 nm based on the spray-coated PEDOT:PSS as electrode, suggesting high potential for transparent organic electronic memory devices.

Effects of programming and healing temperatures on the healing efficiency of a confined healable polymer composite

NASA Astrophysics Data System (ADS)

Yougoubare, Y. Quentin; Pang, Su-Seng

2014-02-01

In previous work, a biomimetic close-then-heal (CTH) healing mechanism was proposed and validated to repeatedly heal wide-open cracks in load carrying engineering structures by using constrained expansion of compression programmed thermoset shape memory polymers (SMPs). In this study, the effects on healing efficiencies of variation of temperature during both thermomechanical programming and shape recovery (healing) under three-dimensional (3D) confinement are evaluated. The polymer considered is a polystyrene shape memory polymer with 6% by volume of thermoplastic particle additives (copolyester) dispersed in the matrix. In addition to the programming and healing temperatures, some of the parameters investigated include the flexural strength, crack width and elemental composition at the crack interface. It is observed that while increase of the programming temperature is slightly beneficial to strength recovery, most of the strength recovered and damage repair are strongly dependent on the healing temperature. The best healing efficiency (63%) is achieved by a combination of a programming temperature above the glass transition temperature of the polymer and a healing temperature above the bonding point of the copolyester.

Influence of mechanically-induced dilatation on the shape memory behavior of amorphous polymers at large deformation

NASA Astrophysics Data System (ADS)

Hanzon, Drew W.; Lu, Haibao; Yakacki, Christopher M.; Yu, Kai

2018-01-01

In this study, we explore the influence of mechanically-induced dilatation on the thermomechanical and shape memory behavior of amorphous shape memory polymers (SMPs) at large deformation. The uniaxial tension, glass transition, stress relaxation and free recovery behaviors are examined with different strain levels (up to 340% engineering strain). A multi-branched constitutive model that incorporates dilatational effects on the polymer relaxation time is established and applied to assist in discussions and understand the nonlinear viscoelastic behaviors of SMPs. It is shown that the volumetric dilatation results in an SMP network with lower viscosity, faster relaxation, and lower Tg. The influence of the dilatational effect on the thermomechanical behaviors is significant when the polymers are subject to large deformation or in a high viscosity state. The dilation also increases the free recovery rate of SMP at a given recovery temperature. Even though the tested SMPs are far beyond their linear viscoelastic region when a large programming strain is applied, the free recovery behavior still follows the time-temperature superposition (TTSP) if the dilatational effect is considered during the transformation of time scales; however, if the programming strain is different, TTSP fails in predicting the recovery behavior of SMPs because the network has different entropy state and driving force during shape recovery. Since most soft active polymers are subject to large deformation in practice, this study provides a theoretical basis to better understand their nonlinear viscoelastic behaviors, and optimize their performance in engineering applications.

Field enhanced charge carrier reconfiguration in electronic and ionic coupled dynamic polymer resistive memory.

PubMed

Zhao, Jun Hui; Thomson, Douglas J; Pilapil, Matt; Pillai, Rajesh G; Rahman, G M Aminur; Freund, Michael S

2010-04-02

Dynamic resistive memory devices based on a conjugated polymer composite (PPy(0)DBS(-)Li(+) (PPy: polypyrrole; DBS(-): dodecylbenzenesulfonate)), with field-driven ion migration, have been demonstrated. In this work the dynamics of these systems has been investigated and it has been concluded that increasing the applied field can dramatically increase the rate at which information can be 'written' into these devices. A conductance model using space charge limited current coupled with an electric field induced ion reconfiguration has been successfully utilized to interpret the experimentally observed transient conducting behaviors. The memory devices use the rising and falling transient current states for the storage of digital states. The magnitude of these transient currents is controlled by the magnitude and width of the write/read pulse. For the 500 nm length devices used in this work an increase in 'write' potential from 2.5 to 5.5 V decreased the time required to create a transient conductance state that can be converted into the digital signal by 50 times. This work suggests that the scaling of these devices will be favorable and that 'write' times for the conjugated polymer composite memory devices will decrease rapidly as ion driving fields increase with decreasing device size.

Preparation and characterization of triple shape memory composite foams.

PubMed

Nejad, Hossein Birjandi; Baker, Richard M; Mather, Patrick T

2014-10-28

Foams prepared from shape memory polymers (SMPs) offer the potential for low density materials that can be triggered to deploy with a large volume change, unlike their solid counterparts that do so at near-constant volume. While examples of shape memory foams have been reported in the past, they have been limited to dual SMPs: those polymers featuring one switching transition between an arbitrarily programmed shape and a single permanent shape established by constituent crosslinks. Meanwhile, advances by SMP researchers have led to several approaches toward triple- or multi-shape polymers that feature more than one switching phase and thus a multitude of temporary shapes allowing for a complex sequence of shape deployments. Here, we report the design, preparation, and characterization of a triple shape memory polymeric foam that is open cell in nature and features a two phase, crosslinked SMP with a glass transition temperature of one phase at a temperature lower than a melting transition of the second phase. The soft materials were observed to feature high fidelity, repeatable triple shape behavior, characterized in compression and demonstrated for complex deployment by fixing a combination of foam compression and bending. We further explored the wettability of the foams, revealing composition-dependent behavior favorable for future work in biomedical investigations.

Implementation of a finite element analysis procedure for structural analysis of shape memory behaviour of fibre reinforced shape memory polymer composites

NASA Astrophysics Data System (ADS)

Azzawi, Wessam Al; Epaarachchi, J. A.; Islam, Mainul; Leng, Jinsong

2017-12-01

Shape memory polymers (SMPs) offer a unique ability to undergo a substantial shape deformation and subsequently recover the original shape when exposed to a particular external stimulus. Comparatively low mechanical properties being the major drawback for extended use of SMPs in engineering applications. However the inclusion of reinforcing fibres in to SMPs improves mechanical properties significantly while retaining intrinsic shape memory effects. The implementation of shape memory polymer composites (SMPCs) in any engineering application is a unique task which requires profound materials and design optimization. However currently available analytical tools have critical limitations to undertake accurate analysis/simulations of SMPC structures and slower derestrict transformation of breakthrough research outcomes to real-life applications. Many finite element (FE) models have been presented. But majority of them require a complicated user-subroutines to integrate with standard FE software packages. Furthermore, those subroutines are problem specific and difficult to use for a wider range of SMPC materials and related structures. This paper presents a FE simulation technique to model the thermomechanical behaviour of the SMPCs using commercial FE software ABAQUS. Proposed technique incorporates material time-dependent viscoelastic behaviour. The ability of the proposed technique to predict the shape fixity and shape recovery was evaluated by experimental data acquired by a bending of a SMPC cantilever beam. The excellent correlation between the experimental and FE simulation results has confirmed the robustness of the proposed technique.

Low density biodegradable shape memory polyurethane foams for embolic biomedical applications

PubMed Central

Singhal, Pooja; Small, Ward; Cosgriff-Hernandez, Elizabeth; Maitland, Duncan J; Wilson, Thomas S

2014-01-01

Low density shape memory polymer foams hold significant interest in the biomaterials community for their potential use in minimally invasive embolic biomedical applications. The unique shape memory behavior of these foams allows them to be compressed to a miniaturized form, which can be delivered to an anatomical site via a transcatheter process, and thereafter actuated to embolize the desired area. Previous work in this field has described the use of a highly covalently crosslinked polymer structure for maintaining excellent mechanical and shape memory properties at the application-specific ultra low densities. This work is aimed at further expanding the utility of these biomaterials, as implantable low density shape memory polymer foams, by introducing controlled biodegradability. A highly covalently crosslinked network structure was maintained by use of low molecular weight, symmetrical and polyfunctional hydroxyl monomers such as Polycaprolactone triol (PCL-t, Mn 900 g), N,N,N0,N0-Tetrakis (hydroxypropyl) ethylenediamine (HPED), and Tris (2-hydroxyethyl) amine (TEA). Control over the degradation rate of the materials was achieved by changing the concentration of the degradable PCL-t monomer, and by varying the material hydrophobicity. These porous SMP materials exhibit a uniform cell morphology and excellent shape recovery, along with controllable actuation temperature and degradation rate. We believe that they form a new class of low density biodegradable SMP scaffolds that can potentially be used as “smart” non-permanent implants in multiple minimally invasive biomedical applications. PMID:24090987

A multiple-shape memory polymer-metal composite actuator capable of programmable control, creating complex 3D motion of bending, twisting, and oscillation

NASA Astrophysics Data System (ADS)

Shen, Qi; Trabia, Sarah; Stalbaum, Tyler; Palmre, Viljar; Kim, Kwang; Oh, Il-Kwon

2016-04-01

Development of biomimetic actuators has been an essential motivation in the study of smart materials. However, few materials are capable of controlling complex twisting and bending deformations simultaneously or separately using a dynamic control system. Here, we report an ionic polymer-metal composite actuator having multiple-shape memory effect, and is able to perform complex motion by two external inputs, electrical and thermal. Prior to the development of this type of actuator, this capability only could be realized with existing actuator technologies by using multiple actuators or another robotic system. This paper introduces a soft multiple-shape-memory polymer-metal composite (MSMPMC) actuator having multiple degrees-of-freedom that demonstrates high maneuverability when controlled by two external inputs, electrical and thermal. These multiple inputs allow for complex motions that are routine in nature, but that would be otherwise difficult to obtain with a single actuator. To the best of the authors’ knowledge, this MSMPMC actuator is the first solitary actuator capable of multiple-input control and the resulting deformability and maneuverability.

Phase-Change Thermoplastic Elastomer Blends for Tunable Shape Memory by Physical Design

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

Mineart, Kenneth P.; Tallury, Syamal S.; Li, Tao

Shape-memory polymers (SMPs) change shape upon exposure to an environmental stimulus.1-3 They are of considerable importance in the ongoing development of stimuli-responsive biomedical4,5 and deployable6 devices, and their function depends on the presence of two components.7 The first provides mechanical rigidity to ensure retention of one or more temporary strain states and also serves as a switch capable of releasing a temporary strain state. The second, a network-forming component, is required to restore the polymer to a prior strain state upon stimulation. In thermally-activated SMPs, the switching element typically relies on a melting or glass transition temperature,1-3,7 and broad ormore » multiple switches permit several temporary strain states.8-10 Chemical integration of network-forming and switching species endows SMPs with specific properties.8,10,11 Here, we demonstrate that phase-change materials incorporated into network-forming macromolecules yield shape-memory polymer blends (SMPBs) with physically tunable switching temperatures and recovery kinetics for use in multi-responsive laminates and shape-change electronics.« less

A multiple-shape memory polymer-metal composite actuator capable of programmable control, creating complex 3D motion of bending, twisting, and oscillation

PubMed Central

Shen, Qi; Trabia, Sarah; Stalbaum, Tyler; Palmre, Viljar; Kim, Kwang; Oh, Il-Kwon

2016-01-01

Development of biomimetic actuators has been an essential motivation in the study of smart materials. However, few materials are capable of controlling complex twisting and bending deformations simultaneously or separately using a dynamic control system. Here, we report an ionic polymer-metal composite actuator having multiple-shape memory effect, and is able to perform complex motion by two external inputs, electrical and thermal. Prior to the development of this type of actuator, this capability only could be realized with existing actuator technologies by using multiple actuators or another robotic system. This paper introduces a soft multiple-shape-memory polymer-metal composite (MSMPMC) actuator having multiple degrees-of-freedom that demonstrates high maneuverability when controlled by two external inputs, electrical and thermal. These multiple inputs allow for complex motions that are routine in nature, but that would be otherwise difficult to obtain with a single actuator. To the best of the authors’ knowledge, this MSMPMC actuator is the first solitary actuator capable of multiple-input control and the resulting deformability and maneuverability. PMID:27080134

A multiple-shape memory polymer-metal composite actuator capable of programmable control, creating complex 3D motion of bending, twisting, and oscillation.

PubMed

Shen, Qi; Trabia, Sarah; Stalbaum, Tyler; Palmre, Viljar; Kim, Kwang; Oh, Il-Kwon

2016-04-15

Development of biomimetic actuators has been an essential motivation in the study of smart materials. However, few materials are capable of controlling complex twisting and bending deformations simultaneously or separately using a dynamic control system. Here, we report an ionic polymer-metal composite actuator having multiple-shape memory effect, and is able to perform complex motion by two external inputs, electrical and thermal. Prior to the development of this type of actuator, this capability only could be realized with existing actuator technologies by using multiple actuators or another robotic system. This paper introduces a soft multiple-shape-memory polymer-metal composite (MSMPMC) actuator having multiple degrees-of-freedom that demonstrates high maneuverability when controlled by two external inputs, electrical and thermal. These multiple inputs allow for complex motions that are routine in nature, but that would be otherwise difficult to obtain with a single actuator. To the best of the authors' knowledge, this MSMPMC actuator is the first solitary actuator capable of multiple-input control and the resulting deformability and maneuverability.

Programmable, reversible and repeatable wrinkling of shape memory polymer thin films on elastomeric substrates for smart adhesion.

PubMed

Wang, Yu; Xiao, Jianliang

2017-08-09

Programmable, reversible and repeatable wrinkling of shape memory polymer (SMP) thin films on elastomeric polydimethylsiloxane (PDMS) substrates is realized, by utilizing the heat responsive shape memory effect of SMPs. The dependencies of wrinkle wavelength and amplitude on program strain and SMP film thickness are shown to agree with the established nonlinear buckling theory. The wrinkling is reversible, as the wrinkled SMP thin film can be recovered to the flat state by heating up the bilayer system. The programming cycle between wrinkle and flat is repeatable, and different program strains can be used in different programming cycles to induce different surface morphologies. Enabled by the programmable, reversible and repeatable SMP film wrinkling on PDMS, smart, programmable surface adhesion with large tuning range is demonstrated.

3D Printed Silicones with Shape Memory

DOE PAGES

Wu, Amanda S.; Small IV, Ward; Bryson, Taylor M.; ...

2017-07-05

Direct ink writing enables the layer-by-layer manufacture of ordered, porous structures whose mechanical behavior is driven by architecture and material properties. Here, we incorporate two different gas filled microsphere pore formers to evaluate the effect of shell stiffness and T g on compressive behavior and compression set in siloxane matrix printed structures. The lower T g microsphere structures exhibit substantial compression set when heated near and above T g, with full structural recovery upon reheating without constraint. By contrast, the higher T g microsphere structures exhibit reduced compression set with no recovery upon reheating. Aside from their role in tuningmore » the mechanical behavior of direct ink write structures, polymer microspheres are good candidates for shape memory elastomers requiring structural complexity, with potential applications toward tandem shape memory polymers.« less

Application of graphene oxide-poly (vinyl alcohol) polymer nanocomposite for memory devices

NASA Astrophysics Data System (ADS)

Kaushal, Jyoti; Kaur, Ravneet; Sharma, Jadab; Tripathi, S. K.

2018-05-01

Significant attention has been gained by polymer nanocomposites because of their possible demands in future electronic memory devices. In the present work, device based on Graphene Oxide (GO) and polyvinyl alcohol (PVA) has been made and examined for the memory device application. The prepared Graphene oxide (GO) and GO-PVA nanocomposite (NC) has been characterized by X-ray Diffraction (XRD). GO nanosheets show the diffraction peak at 2θ = 11.60° and the interlayer spacing of 0.761 nm. The XRD of GO-PVA NC shows the diffraction peak at 2θ =18.56°. The fabricated device shows bipolar switching behavior having ON/OFF current ratio ˜102. The Write-Read-Erase-Read (WRER) cycles test shows that the Al/GO-PVA/Ag device has good stability and repeatability.

3D Printed Silicones with Shape Memory

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

Wu, Amanda S.; Small IV, Ward; Bryson, Taylor M.

Direct ink writing enables the layer-by-layer manufacture of ordered, porous structures whose mechanical behavior is driven by architecture and material properties. Here, we incorporate two different gas filled microsphere pore formers to evaluate the effect of shell stiffness and T g on compressive behavior and compression set in siloxane matrix printed structures. The lower T g microsphere structures exhibit substantial compression set when heated near and above T g, with full structural recovery upon reheating without constraint. By contrast, the higher T g microsphere structures exhibit reduced compression set with no recovery upon reheating. Aside from their role in tuningmore » the mechanical behavior of direct ink write structures, polymer microspheres are good candidates for shape memory elastomers requiring structural complexity, with potential applications toward tandem shape memory polymers.« less

Shape Memory Polyurethane Materials Containing Ferromagnetic Iron Oxide and Graphene Nanoplatelets

PubMed Central

Urban, Magdalena

2017-01-01

Intelligent materials, such as memory shape polymers, have attracted considerable attention due to wide range of possible applications. Currently, intensive research is underway, in matters of obtaining memory shape materials that can be actuated via inductive methods, for example with help of magnetic field. In this work, an attempt was made to develop a new polymer composite—polyurethane modified with graphene nanoplates and ferromagnetic iron oxides—with improved mechanical properties and introduced magnetic and memory shape properties. Based on the conducted literature review, gathered data were compared to the results of similar materials. Obtained materials were tested for their thermal, rheological, mechanical and shape memory properties. Structure of both fillers and composites were also analyzed using various spectroscopic methods. The addition of fillers to the polyurethane matrix improved the mechanical and shape memory properties, without having a noticeable impact on thermal properties. As it was expected, the high content of fillers caused a significant change in viscosity of filled prepolymers (during the synthesis stage). Each of the studied composites showed better mechanical properties than the unmodified polyurethanes. The addition of magnetic particles introduced additional properties to the composite, which could significantly expand the functionality of the materials developed in this work. PMID:28906445

Shape Memory Polyurethane Materials Containing Ferromagnetic Iron Oxide and Graphene Nanoplatelets.

PubMed

Urban, Magdalena; Strankowski, Michał

2017-09-14

Intelligent materials, such as memory shape polymers, have attracted considerable attention due to wide range of possible applications. Currently, intensive research is underway, in matters of obtaining memory shape materials that can be actuated via inductive methods, for example with help of magnetic field. In this work, an attempt was made to develop a new polymer composite-polyurethane modified with graphene nanoplates and ferromagnetic iron oxides-with improved mechanical properties and introduced magnetic and memory shape properties. Based on the conducted literature review, gathered data were compared to the results of similar materials. Obtained materials were tested for their thermal, rheological, mechanical and shape memory properties. Structure of both fillers and composites were also analyzed using various spectroscopic methods. The addition of fillers to the polyurethane matrix improved the mechanical and shape memory properties, without having a noticeable impact on thermal properties. As it was expected, the high content of fillers caused a significant change in viscosity of filled prepolymers (during the synthesis stage). Each of the studied composites showed better mechanical properties than the unmodified polyurethanes. The addition of magnetic particles introduced additional properties to the composite, which could significantly expand the functionality of the materials developed in this work.

Wireless Displacement Sensing of Micromachined Spiral-Coil Actuator Using Resonant Frequency Tracking

PubMed Central

Ali, Mohamed Sultan Mohamed; AbuZaiter, Alaa; Schlosser, Colin; Bycraft, Brad; Takahata, Kenichi

2014-01-01

This paper reports a method that enables real-time displacement monitoring and control of micromachined resonant-type actuators using wireless radiofrequency (RF). The method is applied to an out-of-plane, spiral-coil microactuator based on shape-memory-alloy (SMA). The SMA spiral coil forms an inductor-capacitor resonant circuit that is excited using external RF magnetic fields to thermally actuate the coil. The actuation causes a shift in the circuit's resonance as the coil is displaced vertically, which is wirelessly monitored through an external antenna to track the displacements. Controlled actuation and displacement monitoring using the developed method is demonstrated with the microfabricated device. The device exhibits a frequency sensitivity to displacement of 10 kHz/μm or more for a full out-of-plane travel range of 466 μm and an average actuation velocity of up to 155 μm/s. The method described permits the actuator to have a self-sensing function that is passively operated, thereby eliminating the need for separate sensors and batteries on the device, thus realizing precise control while attaining a high level of miniaturization in the device. PMID:25014100

Focused ion beam micromachining of TiNi film on Si( 1 1 1 )

NASA Astrophysics Data System (ADS)

Xie, D. Z.; Ngoi, B. K. A.; Ong, A. S.; Fu, Y. Q.; Lim, B. H.

2003-11-01

Having an excellent shape memory effect, titanium-nickel (TiNi) thin films are often used for fabrication of microactuators in microelectromechanical systems. In this work, the Ga + focused ion beam (FIB) etching characteristics of TiNi thin films has been investigated. The thin films were deposited on Si(1 1 1) wafers by co-sputtering NiTi and Ti targets using a magnetron-sputtering system. Some patterns have been etched on the surface of the films by FIB. Atomic force microscopy has been used to analyze the surface morphology of the etched areas. It is found that the etched depth depends linearly on the ion dose per area with a slope of 0.259 μm/(nC/μm 2). However, the etching depth decreases with increasing the ion beam current. The root-mean-square (RMS) surface roughness changes nonlinearly with ion dose and reaches a minimum of about 5.00 nm at a dose of about 0.45 nC/μm 2. The RMS decreases with increasing ion beam current and reaches about 4.00 nm as the ion beam current is increased to 2 nA.

A low switching voltage organic-on-inorganic heterojunction memory element utilizing a conductive polymer fuse on a doped silicon substrate

NASA Astrophysics Data System (ADS)

Smith, Shawn; Forrest, Stephen R.

2004-06-01

We present a simple, nonvolatile, write-once-read-many-times (WORM) memory device utilizing an organic-on-inorganic heterojunction (OI-HJ) diode with a conductive polymer fuse consisting of polyethylene dioxythiophene:polysterene sulfonic acid (PEDOT:PSS) forming one side of the rectifying junction. Current transients are used to change the fuse from a conducting to a nonconducting state to record a logical "1" or "0", while the nonlinearity of the OI-HJ allows for passive matrix memory addressing. The device switches at 2 and 4 V for 50 nm thick PEDOT:PSS films on p-type Si and n-type Si, respectively. This is significantly lower than the switching voltage used in PEDOT:PSS/p-i-n Si memory elements [J. Appl Phys. 94, 7811 (2003)]. The switching results in a permanent reduction of forward-bias current by approximately five orders of magnitude. These results suggest that the OI-HJ structure has potential for use in low-cost passive matrix WORM memories for archival storage applications.

Nanoscale Design of Nano-Sized Particles in Shape-Memory Polymer Nanocomposites Driven by Electricity

PubMed Central

Lu, Haibao; Huang, Wei Min; Liang, Fei; Yu, Kai

2013-01-01

In the last few years, we have witnessed significant progress in developing high performance shape memory polymer (SMP) nanocomposites, in particular, for shape recovery activated by indirect heating in the presence of electricity, magnetism, light, radio frequency, microwave and radiation, etc. In this paper, we critically review recent findings in Joule heating of SMP nanocomposites incorporated with nanosized conductive electromagnetic particles by means of nanoscale control via applying an electro- and/or magnetic field. A few different nanoscale design principles to form one-/two-/three- dimensional conductive networks are discussed. PMID:28788303

Mechanical properties of shape memory polymers for morphing aircraft applications

NASA Astrophysics Data System (ADS)

Keihl, Michelle M.; Bortolin, Robert S.; Sanders, Brian; Joshi, Shiv; Tidwell, Zeb

2005-05-01

This investigation addresses basic characterization of a shape memory polymer (SMP) as a suitable structural material for morphing aircraft applications. Tests were performed for monotonic loading in high shear at constant temperature, well below, or just above the glass transition temperature. The SMP properties were time-and temperature-dependent. Recovery by the SMP to its original shape needed to be unfettered. Based on the testing SMPs appear to be an attractive and promising component in the solution for a skin material of a morphing aircraft. Their multiple state abilities allow them to easily change shape and, once cooled, resist large loads.

Frequency-dependent learning achieved using semiconducting polymer/electrolyte composite cells

NASA Astrophysics Data System (ADS)

Dong, W. S.; Zeng, F.; Lu, S. H.; Liu, A.; Li, X. J.; Pan, F.

2015-10-01

Frequency-dependent learning has been achieved using semiconducting polymer/electrolyte composite cells. The cells composed of polymer/electrolyte double layers realized the conventional spike-rate-dependent plasticity (SRDP) learning model. These cells responded to depression upon low-frequency stimulation and to potentiation upon high-frequency stimulation and presented long-term memory. The transition threshold θm from depression to potentiation varied depending on the previous stimulations. A nanostructure resembling a bio-synapse in its transport passages was demonstrated and a random channel model was proposed to describe the ionic kinetics at the polymer/electrolyte interface during and after stimulations with various frequencies, accounting for the observed SRDP.Frequency-dependent learning has been achieved using semiconducting polymer/electrolyte composite cells. The cells composed of polymer/electrolyte double layers realized the conventional spike-rate-dependent plasticity (SRDP) learning model. These cells responded to depression upon low-frequency stimulation and to potentiation upon high-frequency stimulation and presented long-term memory. The transition threshold θm from depression to potentiation varied depending on the previous stimulations. A nanostructure resembling a bio-synapse in its transport passages was demonstrated and a random channel model was proposed to describe the ionic kinetics at the polymer/electrolyte interface during and after stimulations with various frequencies, accounting for the observed SRDP. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr02891d

Long-time dynamics of Rouse-Zimm polymers in dilute solutions with hydrodynamic memory.

PubMed

Lisy, V; Tothova, J; Zatovsky, A V

2004-12-01

The dynamics of flexible polymers in dilute solutions is studied taking into account the hydrodynamic memory, as a consequence of fluid inertia. As distinct from the Rouse-Zimm (RZ) theory, the Boussinesq friction force acts on the monomers (beads) instead of the Stokes force, and the motion of the solvent is governed by the nonstationary Navier-Stokes equations. The obtained generalized RZ equation is solved approximately using the preaveraging of the Oseen tensor. It is shown that the time correlation functions describing the polymer motion essentially differ from those in the RZ model. The mean-square displacement (MSD) of the polymer coil is at short times approximately t(2) (instead of approximately t). At long times the MSD contains additional (to the Einstein term) contributions, the leading of which is approximately t. The relaxation of the internal normal modes of the polymer differs from the traditional exponential decay. It is displayed in the long-time tails of their correlation functions, the longest lived being approximately t(-3/2) in the Rouse limit and t(-5/2) in the Zimm case, when the hydrodynamic interaction is strong. It is discussed that the found peculiarities, in particular, an effectively slower diffusion of the polymer coil, should be observable in dynamic scattering experiments. (c) 2004 American Institute of Physics

Multilevel non-volatile data storage utilizing common current hysteresis of networked single walled carbon nanotubes

NASA Astrophysics Data System (ADS)

Hwang, Ihn; Wang, Wei; Hwang, Sun Kak; Cho, Sung Hwan; Kim, Kang Lib; Jeong, Beomjin; Huh, June; Park, Cheolmin

2016-05-01

The characteristic source-drain current hysteresis frequently observed in field-effect transistors with networked single walled carbon-nanotube (NSWNT) channels is problematic for the reliable switching and sensing performance of devices. But the two distinct current states of the hysteresis curve at a zero gate voltage can be useful for memory applications. In this work, we demonstrate a novel non-volatile transistor memory with solution-processed NSWNTs which are suitable for multilevel data programming and reading. A polymer passivation layer with a small amount of water employed on the top of the NSWNT channel serves as an efficient gate voltage dependent charge trapping and de-trapping site. A systematic investigation evidences that the water mixed in a polymer passivation solution is critical for reliable non-volatile memory operation. The optimized device is air-stable and temperature-resistive up to 80 °C and exhibits excellent non-volatile memory performance with an on/off current ratio greater than 104, a switching time less than 100 ms, data retention longer than 4000 s, and write/read endurance over 100 cycles. Furthermore, the gate voltage dependent charge injection mediated by water in the passivation layer allowed for multilevel operation of our memory in which 4 distinct current states were programmed repetitively and preserved over a long time period.The characteristic source-drain current hysteresis frequently observed in field-effect transistors with networked single walled carbon-nanotube (NSWNT) channels is problematic for the reliable switching and sensing performance of devices. But the two distinct current states of the hysteresis curve at a zero gate voltage can be useful for memory applications. In this work, we demonstrate a novel non-volatile transistor memory with solution-processed NSWNTs which are suitable for multilevel data programming and reading. A polymer passivation layer with a small amount of water employed on the top of the NSWNT channel serves as an efficient gate voltage dependent charge trapping and de-trapping site. A systematic investigation evidences that the water mixed in a polymer passivation solution is critical for reliable non-volatile memory operation. The optimized device is air-stable and temperature-resistive up to 80 °C and exhibits excellent non-volatile memory performance with an on/off current ratio greater than 104, a switching time less than 100 ms, data retention longer than 4000 s, and write/read endurance over 100 cycles. Furthermore, the gate voltage dependent charge injection mediated by water in the passivation layer allowed for multilevel operation of our memory in which 4 distinct current states were programmed repetitively and preserved over a long time period. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr00505e

Light-Induced Temperature Transitions in Biodegradable Polymer and Nanorod Composites**

PubMed Central

Hribar, Kolin C.; Metter, Robert B.; Ifkovits, Jamie L.; Troxler, Thomas

2010-01-01

Shape-memory materials (including polymers, metals, and ceramics) are those that are processed into a temporary shape and respond to some external stimuli (e.g., temperature) to undergo a transition back to a permanent shape.[1, 2] Shape memory polymers are finding use in a range of applications from aerospace to fabrics, to biomedical devices and microsystem components.[3–5] For many applications, it would be beneficial to initiate heating with an external trigger (e.g., transdermal light exposure). In this work, we formulated composites of gold nanorods (<1% by volume) and biodegradable networks, where exposure to infrared light induced heating and consequently, shape transitions. The heating is repeatable and tunable based on nanorod concentration and light intensity and the nanorods did not alter the cytotoxicity or in vivo tissue response to the networks. PMID:19408258

Parametric analysis and temperature effect of deployable hinged shells using shape memory polymers

NASA Astrophysics Data System (ADS)

Tao, Ran; Yang, Qing-Sheng; He, Xiao-Qiao; Liew, Kim-Meow

2016-11-01

Shape memory polymers (SMPs) are a class of intelligent materials, which are defined by their capacity to store a temporary shape and recover an original shape. In this work, the shape memory effect of SMP deployable hinged shell is simulated by using compiled user defined material subroutine (UMAT) subroutine of ABAQUS. Variations of bending moment and strain energy of the hinged shells with different temperatures and structural parameters in the loading process are given. The effects of the parameters and temperature on the nonlinear deformation process are emphasized. The entire thermodynamic cycle of SMP deployable hinged shell includes loading at high temperature, load carrying with cooling, unloading at low temperature and recovering the original shape with heating. The results show that the complicated thermo-mechanical deformation and shape memory effect of SMP deployable hinge are influenced by the structural parameters and temperature. The design ability of SMP smart hinged structures in practical application is prospected.

New trends in the optical and electronic applications of polymers containing transition-metal complexes.

PubMed

Liu, Shu-Juan; Chen, Yang; Xu, Wen-Juan; Zhao, Qiang; Huang, Wei

2012-04-13

Polymers containing transition-metal complexes exhibit excellent optical and electronic properties, which are different from those of polymers with a pure organic skeleton and combine the advantages of both polymers and metal complexes. Hence, research about this class of polymers has attracted more and more interest in recent years. Up to now, a number of novel polymers containing transition-metal complexes have been exploited, and significant advances in their optical and electronic applications have been achieved. In this article, we summarize some new research trends in the applications of this important class of optoelectronic polymers, such as chemo/biosensors, electronic memory devices and photovoltaic devices. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

High energy microelectromechanical oscillator based on the electrostatic microactuator

NASA Astrophysics Data System (ADS)

Baginsky, I.; Kostsov, Edvard; Sobolev, Victor

2008-03-01

Electrostatic high energy micromotor based on the ferroelectric films is studied as applied to microelectromechanical devices operating in vibrational mode. It is shown that the micromotor can be efficiently used in high frequency micromechanical vibrators that are used in high energy MEMS devices, such as micropumps, microvalves, microinjectors, adaptive microoptic devices etc.

Development of a flexible microfluidic system integrating magnetic micro-actuators for trapping biological species

NASA Astrophysics Data System (ADS)

Fulcrand, R.; Jugieu, D.; Escriba, C.; Bancaud, A.; Bourrier, D.; Boukabache, A.; Gué, A. M.

2009-10-01

A flexible microfluidic system embedding microelectromagnets has been designed, modeled and fabricated by using a photosensitive resin as structural material. The fabrication process involves the integration of micro-coils in a multilayer SU-8 microfluidic system by combining standard electroplating and dry films lamination. This technique offers numerous advantages in terms of integration, biocompatibility and chemical resistance. Various designs of micro-coils, including spiral, square or serpentine wires, have been simulated and experimentally tested. It has been established that thermal dissipation in micro-coils depends strongly on the number of turns and current density but remains compatible with biological applications. Real-time experimentations show that these micro-actuators are efficient in trapping magnetic micro-beads without any external field source or a permanent magnet and highlight that the size of microfluidic channels has been adequately designed for optimal trapping. Moreover, we trap magnetic beads in less than 2 s and release them instantaneously into the micro-channel. The actuation solely relies on electric fields, which are easier to control than standard magneto-fluidic modules.

Detailed study of scratch drive actuator characteristics using high-speed imaging

NASA Astrophysics Data System (ADS)

Li, Lijie; Brown, James G.; Uttamchandani, Deepak G.

2001-10-01

Microactuators are one of the key components in MEMS and Microsystems technology, and various designs have been realized through different fabrication processes. One type of microactuator commonly used is the scratch drive actuator (SDA) that is frequently fabricated by surface micromachining processes. An experimental investigation has been conducted on the characteristics of SDAs fabricated using the Cronos Microsystems MUMPs process. The motivation is to compare the response of SDAs located on the same die, and SDAs located on the different dies from the same fabrication batch. A high-speed imaging camera has been used to precisely determine important SDA characteristics such as step size, velocity, maximum velocity, and acceleration over long travel distance. These measurements are important from a repeatability point of view, and in order to fully exploit the potential of the SDA as a precise positioning mechanism. 2- and 3-stage SDAs have been designed and fabricated for these experiments. Typical step sizes varying from 7 nm at a driving voltage of 60 V to 23 nm at 290 V have been obtained.

Design and modeling of an efficiency horizontal thermal micro-actuator with integrated piezoresistors for precise control.

PubMed

Zhang, Yan; Lee, Dong-Weon

2010-05-01

An integrated system made up of a double-hot arm electro-thermal microactuator and a piezoresistor embedded at the base of the 'cold arm' is proposed. The electro-thermo-mechanical modeling and optimization is developed to elaborate the operation mechanism of the hybrid system through numerical simulations. For given materials, the geometry design mostly influences the performance of the sensor and actuator, which can be considered separately. That is because thermal expansion induced heating energy has less influence on the base area of the 'cold arm,' where is the maximum stress. The piezoresistor is positioned here for large sensitivity to monitor the in-plane movement of the system and characterize the actuator response precisely in real time. Force method is used to analyze the thermal induced mechanical expansion in the redundant structure. On the other hand, the integrated actuating mechanism is designed for high speed imaging. Based on the simulation results, the actuator operates at levels below 5 mA appearing to be very reliable, and the stress sensitivity is about 40 MPa per micron.

Effects of fiber pre-strain on the healing efficiency of thermoset polymers

NASA Astrophysics Data System (ADS)

Ajisafe, Oludayo

One major challenge that has been facing material self healing is how to heal bigger macroscopic or structural scale damage autonomously, repeatedly, efficiently and at molecular length scale. Different approaches have been used to heal materials. However, none of them can heal macroscopic cracks. Our research group has proposed a novel shape-memory polymer (SMP) based, bio-inspired Close-Then-Heal (CTH) scheme to heal macroscopic cracks in SMP matrix. The most recent development in our group is to use SMP fibers to heal conventional thermosetting polymers according to the CTH scheme. The aim of this study is to further investigate the effect of pre-tension of SMP fibers during the cold-drawing programming on the self-healing efficiency of the conventional thermosetting polymer composites. This was done by fabricating a composite with thermoplastic particles (polycaprolactone) dispersed in a thermosetting polymer matrix (Epon 828). Shape memory fiber pre-tensioned into 3 different groups of 0%, 50% and 100% prestrain, was also embedded into the composite in the longitudinal direction. In this composite, the shape memory effect of the shape memory fibers is utilized for sealing (closing) the cracks and the thermoplastic particles are used for molecular-length scale healing. In this study, 7% by volume of thermoplastic particles was used. Beam specimens were prepared and controlled structural length scale damage was created prior to curing by inserting an aluminum foil of designed thickness in a perpendicular direction to the shape memory fibers before the matrix was allowed to cure. The aluminum sheet was removed post cure to leave a controlled damage. The specimen was healed by fixing the two ends of the beam and heating the sample above the Tg of the shape memory fiber. The recovery force of the sample was recorded and then the beam was tested again to fracture. This fracture healing cycle lasted 7 times. The healing efficiency was evaluated per the peak-tensile load. The Ultrasonic C-scan and SEM were used to examine the healed cracks. It was found that the beams with 100% pre-strained fiber were able to recover repeatedly about 50% of its peak tensile strength; the beams with 50% pre-strained fiber, 43%; and the beams with un-stretched fibers were able to recover about 21% of its original peak tensile strength. Also it was found that the higher the pre-tension the higher the recovery stress seen during the healing cycle.

Propulsion of swimming microrobots inspired by metachronal waves in ciliates: from biology to material specifications.

PubMed

Palagi, Stefano; Jager, Edwin W H; Mazzolai, Barbara; Beccai, Lucia

2013-12-01

The quest for swimming microrobots originates from possible applications in medicine, especially involving navigation in bodily fluids. Swimming microorganisms have become a source of inspiration because their propulsion mechanisms are effective in the low-Reynolds number regime. In this study, we address a propulsion mechanism inspired by metachronal waves, i.e. the spontaneous coordination of cilia leading to the fast swimming of ciliates. We analyse the biological mechanism (referring to its particular embodiment in Paramecium caudatum), and we investigate the contribution of its main features to the swimming performance, through a three-dimensional finite-elements model, in order to develop a simplified, yet effective artificial design. We propose a bioinspired propulsion mechanism for a swimming microrobot based on a continuous cylindrical electroactive surface exhibiting perpendicular wave deformations travelling longitudinally along its main axis. The simplified propulsion mechanism is conceived specifically for microrobots that embed a micro-actuation system capable of executing the bioinspired propulsion (self-propelled microrobots). Among the available electroactive polymers, we select polypyrrole as the possible actuation material and we assess it for this particular embodiment. The results are used to appoint target performance specifications for the development of improved or new electroactive materials to attain metachronal-waves-like propulsion.

Optimized Mixing in Microchannels with Integrated Microactuators

NASA Astrophysics Data System (ADS)

Folk, Christopher Richard

Microscale valves and pumps have been designed and fabricated for integration into a microfluidic circuit. Furthermore, a micromixer for this circuit has been designed and optimized. N-isopropylacrylamide (NIPA) gels have been fabricated and actuated directly with heat and indirectly by laser. A new method for photopatterning these gels based on photoinitiation has been used to fabricate hydrogel valves down to 50 mum in diameter. Hydrogel valves have been fabricated in situ in a microfluidic network. The valves open in 27 seconds and close via diffusion of water into the gel in 128 seconds, which is faster than other optically-driven polymers used for large displacements. In this research, azobis-isobutyronitrile (AIBN) is incorporated into a variety of polydimethylsiloxane (PDMS) pump chambers. The AIBN is heated via integrated resistive heaters and decomposes to release nitrogen gas. The nitrogen gas provides impulse power to a PDMS diaphragm to displace the fluid. The pump devices have been built and characterized. Lastly, in this work, we describe the use of combined fluid dynamic and diffusion modeling to simulate a micromixer based on the elements above. The micromixer is optimized via Design of Experiments to produce an optimized geometry for mixing. The optimization is validated via comparison to previous work through the Strouhal number.

Humidity-activated shape memory effect on plasticized starch-based biomaterials.

PubMed

Sessini, Valentina; Arrieta, Marina P; Fernández-Torres, Alberto; Peponi, Laura

2018-01-01

Humidity-activated shape memory behavior of plasticized starch-based films reinforced with the innovative combination of starch nanocrystals (SNCs) and catechin as antioxidant were studied. In a previous work, we reported the processing of gelatinized starch-based films filled with SNCs and catechin as antioxidant agent, and we observed that this novel combination leads to starch-based film with enhanced thermal and mechanical performance. In this work, the humidity-activated shape memory behavior of the previous developed starch-based films was characterized. The moisture loss as well as the moisture absorption were studied since they are essential parameters in humidity-activated shape memory polymers to fix the temporary shape and to recover the original shape, respectively. Therefore, the effect of the incorporation of SNCs and catechin on the humidity-activated shape memory properties of plasticized starch was also studied. Moreover, the effectiveness of catechin to increase the polymer stability under oxidative atmosphere and the thermo-mechanical relaxation of all the starch-based materials were studied. The combination of plasticized starch matrix loaded with both, SNCs and catechin, leads to a multifunctional starch-based films with increased hydrophilicity and with excellent humidity-activated shape memory behavior with interest for potential biomedical applications. Copyright © 2017 Elsevier Ltd. All rights reserved.

A preliminary study on shape recovery speed of a styrene-based shape memory polymer composite actuated by different heating methods

NASA Astrophysics Data System (ADS)

Wu, Xuelian; Zhang, Wuyi; Liu, Yanju; Leng, Jinsong

2007-07-01

Thermally activated shape memory polymers (SMPs) receive increasing attention in recent years. Different from those reported in the literature, in this paper we propose a new approach, i.e., using infrared light, for heating SMPs for shape recovery. We compare this approach with the traditional water bath method in terms of shape recovery speed in bending at both vacuum and no vacuum conditions. The results reveal that the shape recovery speed in infrared heating at vacuum condition is about eight times slower than that by hot water. However, the recovery time is more than doubled if without vacuum.

Shape-Memory Polymers for Biomedical Applications

NASA Astrophysics Data System (ADS)

Yakacki, Christopher M.; Gall, Ken

Shape-memory polymers (SMPs) are a class of mechanically functional "smart" materials that have generated substantial interest for biomedical applications. SMPs offer the ability to promote minimally invasive surgery, provide structural support, exert stabilizing forces, elute therapeutic agents, and biodegrade. This review focuses on several areas of biomedicine including vascular, orthopedic, and neuronal applications with respect to the progress and potential for SMPs to improve the standard of treatment in these areas. Fundamental studies on proposed biomedical SMP systems are discussed with regards to biodegradability, tailorability, sterilization, and biocompatibility. Lastly, a proposed research and development pathway for SMP-based biomedical devices is proposed based on trends in the recent literature.

Three-Dimensional Flexible Electronics Enabled by Shape Memory Polymer Substrates for Responsive Neural Interfaces.

PubMed

Ware, Taylor; Simon, Dustin; Hearon, Keith; Liu, Clive; Shah, Sagar; Reeder, Jonathan; Khodaparast, Navid; Kilgard, Michael P; Maitland, Duncan J; Rennaker, Robert L; Voit, Walter E

2012-12-01

Planar electronics processing methods have enabled neural interfaces to become more precise and deliver more information. However, this processing paradigm is inherently 2D and rigid. The resulting mechanical and geometrical mismatch at the biotic-abiotic interface can elicit an immune response that prevents effective stimulation. In this work, a thiol-ene/acrylate shape memory polymer is utilized to create 3D softening substrates for stimulation electrodes. This substrate system is shown to soften in vivo from more than 600 to 6 MPa. A nerve cuff electrode that coils around the vagus nerve in a rat and that drives neural activity is demonstrated.

Feasibility study of polyurethane shape-memory polymer actuators for pressure bandage application.

PubMed

Ahmad, Manzoor; Luo, Jikui; Miraftab, Mohsen

2012-02-01

The feasibility of laboratory-synthesized polyurethane-based shape-memory polymer (SMPU) actuators has been investigated for possible application in medical pressure bandages where gradient pressure is required between the ankle and the knee for treatment of leg ulcers. In this study, using heat as the stimulant, SMPU strip actuators have been subjected to gradual and cyclic stresses; their recovery force, reproducibility and reusability have been monitored with respect to changes in temperature and circumference of a model leg, and the stress relaxation at various temperatures has been investigated. The findings suggest that SMPU actuators can be used for the development of the next generation of pressure bandages.

Electroactive polymer and shape memory alloy actuators in biomimetics and humanoids

NASA Astrophysics Data System (ADS)

Tadesse, Yonas

2013-04-01

There is a strong need to replicate natural muscles with artificial materials as the structure and function of natural muscle is optimum for articulation. Particularly, the cylindrical shape of natural muscle fiber and its interconnected structure promote the critical investigation of artificial muscles geometry and implementation in the design phase of certain platforms. Biomimetic robots and Humanoid Robot heads with Facial Expressions (HRwFE) are some of the typical platforms that can be used to study the geometrical effects of artificial muscles. It has been shown that electroactive polymer and shape memory alloy artificial muscles and their composites are some of the candidate materials that may replicate natural muscles and showed great promise for biomimetics and humanoid robots. The application of these materials to these systems reveals the challenges and associated technologies that need to be developed in parallel. This paper will focus on the computer aided design (CAD) models of conductive polymer and shape memory alloys in various biomimetic systems and Humanoid Robot with Facial Expressions (HRwFE). The design of these systems will be presented in a comparative manner primarily focusing on three critical parameters: the stress, the strain and the geometry of the artificial muscle.

Thermally driven microfluidic pumping via reversible shape memory polymers

NASA Astrophysics Data System (ADS)

Robertson, J. M.; Rodriguez, R. X.; Holmes, L. R., Jr.; Mather, P. T.; Wetzel, E. D.

2016-08-01

The need exists for autonomous microfluidic pumping systems that utilize environmental cues to transport fluid within a network of channels for such purposes as heat distribution, self-healing, or optical reconfiguration. Here, we report on reversible thermally driven microfluidic pumping enabled by two-way shape memory polymers. After developing a suitable shape memory polymer (SMP) through variation in the crosslink density, thin and flexible microfluidic devices were constructed by lamination of plastic films with channels defined by laser-cutting of double-sided adhesive film. SMP blisters integrated into the devices provide thermally driven pumping, while opposing elastic blisters are used to generate backpressure for reversible operation. Thermal cycling of the device was found to drive reversible fluid flow: upon heating to 60 °C, the SMP rapidly contracted to fill the surface channels with a transparent fluid, and upon cooling to 8 °C the flow reversed and the channel re-filled with black ink. Combined with a metallized backing layer, this device results in refection of incident light at high temperatures and absorption of light (at the portions covered with channels) at low temperatures. We discuss power-free, autonomous applications ranging from thermal regulation of structures to thermal indication via color change.

Synthesis of ZnO nanorods and observation of resistive switching memory in ZnO based polymer nanocomposites

NASA Astrophysics Data System (ADS)

Nair, Manjula G.; Malakar, Meenakshi; Mohapatra, Saumya R.; Chowdhury, Avijit

2018-05-01

This research reports the observation of bipolar resistive switching memory in ZnO nanorod based polymer nanocomposites. We synthesized ZnO nanorods by wet-chemical method and characterized them using XRD, UV-VIS spectroscopy and SEM. The synthesized materials have hexagonal ZnO phase with grain size of 24 nm and having strong orientation along (101) direction as observed from XRD. The SEM micrograph confirms the formation of ZnO nanorods with diameter in the range of 10 to 20 nm and length of the order of 1 µm. From optical absorption spectra the band gap is estimated to be 2.42 eV. ZnO nanorods were dispersed in PVDF-HFP polymer matrix to prepare the nanocomposite. This nanocomposite was used as active layer in the devices having sandwich structure of ITO/PVDF-HFP+ZnO nanorods/Al. Bipolar non-volatile memory was observed with ON-OFF resistance ratio of the order of 103 and with a wide voltage window of 2.3V. The switching mechanism could be due to the trapping and de-trapping of electrons by the ZnO nanorods in the nanocomposite during ON and OFF states respectively.

Multimaterial 4D Printing with Tailorable Shape Memory Polymers

PubMed Central

Ge, Qi; Sakhaei, Amir Hosein; Lee, Howon; Dunn, Conner K.; Fang, Nicholas X.; Dunn, Martin L.

2016-01-01

We present a new 4D printing approach that can create high resolution (up to a few microns), multimaterial shape memory polymer (SMP) architectures. The approach is based on high resolution projection microstereolithography (PμSL) and uses a family of photo-curable methacrylate based copolymer networks. We designed the constituents and compositions to exhibit desired thermomechanical behavior (including rubbery modulus, glass transition temperature and failure strain which is more than 300% and larger than any existing printable materials) to enable controlled shape memory behavior. We used a high resolution, high contrast digital micro display to ensure high resolution of photo-curing methacrylate based SMPs that requires higher exposure energy than more common acrylate based polymers. An automated material exchange process enables the manufacture of 3D composite architectures from multiple photo-curable SMPs. In order to understand the behavior of the 3D composite microarchitectures, we carry out high fidelity computational simulations of their complex nonlinear, time-dependent behavior and study important design considerations including local deformation, shape fixity and free recovery rate. Simulations are in good agreement with experiments for a series of single and multimaterial components and can be used to facilitate the design of SMP 3D structures. PMID:27499417

A Thrombus Generation Model Applied to Aneurysms Treated with Shape Memory Polymer Foam and Metal Coils

NASA Astrophysics Data System (ADS)

Horn, John; Ortega, Jason; Hartman, Jonathan; Maitland, Duncan

2015-11-01

To prevent their rupture, intracranial aneurysms are often treated with endovascular metal coils which fill the aneurysm sac and isolate it from the arterial flow. Despite its widespread use, this method can result in suboptimal outcomes leading to aneurysm recurrence. Recently, shape memory polymer foam has been proposed as an alternative aneurysm filler. In this work, a computational model has been developed to predict thrombus formation in blood in response to such cardiovascular implantable devices. The model couples biofluid and biochemical phenomena present as the blood interacts with a device and stimulates thrombus formation. This model is applied to simulations of both metal coil and shape memory polymer foam treatments within an idealized 2D aneurysm geometry. Using the predicted thrombus responses, the performance of these treatments is evaluated and compared. The results suggest that foam-treated aneurysms may fill more quickly and more completely with thrombus than coil-filled aneurysms, potentially leading to improved long-term aneurysm healing. This work was performed in part under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Thermomechanical behavior of shape memory elastomeric composites

NASA Astrophysics Data System (ADS)

Ge, Qi; Luo, Xiaofan; Rodriguez, Erika D.; Zhang, Xiao; Mather, Patrick T.; Dunn, Martin L.; Qi, H. Jerry

2012-01-01

Shape memory polymers (SMPs) can fix a temporary shape and recover their permanent shape in response to environmental stimuli such as heat, electricity, or irradiation. Most thermally activated SMPs use the macromolecular chain mobility change around the glass transition temperature ( Tg) to achieve the shape memory (SM) effects. During this process, the stiffness of the material typically changes by three orders of magnitude. Recently, a composite materials approach was developed to achieve thermally activated shape memory effect where the material exhibits elastomeric response in both the temporary and the recovered configurations. These shape memory elastomeric composites (SMECs) consist of an elastomeric matrix reinforced by a semicrystalline polymer fiber network. The matrix provides background rubber elasticity while the fiber network can transform between solid crystals and melt phases over the operative temperature range. As such it serves as a reversible "switching phase" that enables shape fixing and recovery. Shape memory elastomeric composites provide a new paradigm for the development of a wide array of active polymer composites that utilize the melt-crystal transition to achieve the shape memory effect. This potentially allows for material systems with much simpler chemistries than most shape memory polymers and thus can facilitate more rapid material development and insertion. It is therefore important to understand the thermomechanical behavior and to develop corresponding material models. In this paper, a 3D finite-deformation constitutive modeling framework was developed to describe the thermomechanical behavior of SMEC. The model is phenomenological, although inspired by micromechanical considerations of load transfer between the matrix and fiber phases of a composite system. It treats the matrix as an elastomer and the fibers as a complex solid that itself is an aggregate of melt and crystal phases that evolve from one to the other during a temperature change. As such, the composite consists of an elastomer reinforced by a soft liquid at high temperature and a stiff solid at low temperature. The model includes a kinetic description of the non-isothermal crystallization and melting of the fibers during a temperature change. As the fibers transform from melt to crystal during cooling it is assumed that new crystals are formed in an undeformed state, which requires careful tracking of the kinematics of the evolving phases which comes at a significant computational cost. In order to improve the computational efficiency, an effective phase model (EPM) is adopted to treat the evolving crystal phases as an effective medium. A suite of careful thermomechanical experiments with a SMEC was carried out to calibrate various model parameters, and then to demonstrate the ability of the model to accurately capture the shape memory behavior of the SMEC system during complex thermomechanical loading scenarios. The model also identifies the effects of microstructural design parameters such as the fiber volume fraction.

Electrical memory characteristics of a nondoped pi-conjugated polymer bearing carbazole moieties.

PubMed

Park, Samdae; Lee, Taek Joon; Kim, Dong Min; Kim, Jin Chul; Kim, Kyungtae; Kwon, Wonsang; Ko, Yong-Gi; Choi, Heungyeal; Chang, Taihyun; Ree, Moonhor

2010-08-19

Poly[bis(9H-carbazole-9-ethyl)dipropargylmalonate] (PCzDPM) is a novel pi-conjugated polymer bearing carbazole moieties that has been synthesized by polymerization of bis(9H-carbazole-9-ethyl)dipropargylmalonate with the aid of molybdenum chloride solution as the catalyst. This polymer is thermally stable up to 255 degrees C under a nitrogen atmosphere and 230 degrees C in air ambient; its glass-transition temperature is 147 or 128 degrees C, depending on the polymer chain conformation (helical or planar structure). The charge-transport characteristics of PCzDPM in nanometer-scaled thin films were studied as a function of temperature and film thickness. PCzDPM films with a thickness of 15-30 nm were found to exhibit very stable dynamic random access memory (DRAM) characteristics without polarity. Furthermore, the polymer films retain DRAM characteristics up to 180 degrees C. The ON-state current is dominated by Ohmic conduction, and the OFF-state current appears to undergo a transition from Ohmic to space-charge-limited conduction with a shallow-trap distribution. The ON/OFF switching of the devices is mainly governed by filament formation. The filament formation mechanism for the switching process is supported by the metallic properties of the PCzDPM film, which result in the temperature dependence of the ON-state current. In addition, the structure of this pi-conjugated polymer was found to vary with its thermal history; this change in structure can affect filament formation in the polymer film.

Reconfigurable Photonic Crystals Enabled by Multistimuli-Responsive Shape Memory Polymers Possessing Room Temperature Shape Processability.

PubMed

Fang, Yin; Leo, Sin-Yen; Ni, Yongliang; Wang, Junyu; Wang, Bingchen; Yu, Long; Dong, Zhe; Dai, Yuqiong; Basile, Vito; Taylor, Curtis; Jiang, Peng

2017-02-15

Traditional shape memory polymers (SMPs) are mostly thermoresponsive, and their applications in nano-optics are hindered by heat-demanding programming and recovery processes. By integrating a polyurethane-based shape memory copolymer with templating nanofabrication, reconfigurable/rewritable macroporous photonic crystals have been demonstrated. This SMP coupled with the unique macroporous structure enables unusual all-room-temperature shape memory cycles. "Cold" programming involving microscopic order-disorder transitions of the templated macropores is achieved by mechanically deforming the macroporous SMP membranes. The rapid recovery of the permanent, highly ordered photonic crystal structure from the temporary, disordered configuration can be triggered by multiple stimuli including a large variety of vapors and solvents, heat, and microwave radiation. Importantly, the striking chromogenic effects associated with these athermal and thermal processes render a sensitive and noninvasive optical methodology for quantitatively characterizing the intriguing nanoscopic shape memory effects. Some critical parameters/mechanisms that could significantly affect the final performance of SMP-based reconfigurable photonic crystals including strain recovery ratio, dynamics and reversibility of shape recovery, as well as capillary condensation of vapors in macropores, which play a crucial role in vapor-triggered recovery, can be evaluated using this new optical technology.

Variable-Resistivity Material For Memory Circuits

NASA Technical Reports Server (NTRS)

Nagasubramanian, Ganesan; Distefano, Salvador; Moacanin, Jovan

1989-01-01

Nonvolatile memory elements packed densely. Electrically-erasable, programmable, read-only memory matrices made with newly-synthesized organic material of variable electrical resistivity. Material, polypyrrole doped with tetracyanoquinhydrone (TCNQ), changes reversibly between insulating or higher-resistivity state and conducting or low-resistivity state. Thin film of conductive polymer separates layer of row conductors from layer of column conductors. Resistivity of film at each intersection and, therefore, resistance of memory element defined by row and column, increased or decreased by application of suitable switching voltage. Matrix circuits made with this material useful for experiments in associative electronic memories based on models of neural networks.

Characterizing Effects of Nitric Oxide Sterilization on tert-Butyl Acrylate Shape Memory Polymers

NASA Astrophysics Data System (ADS)

Phillippi, Ben

As research into the potential uses of shape memory polymers (SMPs) as implantable medical devices continues to grow and expand, so does the need for an accurate and reliable sterilization mechanism. The ability of an SMP to precisely undergo a programmed shape change will define its ability to accomplish a therapeutic task. To ensure proper execution of the in vivo shape change, the sterilization process must not negatively affect the shape memory behavior of the material. To address this need, this thesis investigates the effectiveness of a benchtop nitric oxide (NOx) sterilization process and the extent to which the process affects the shape memory behavior of a well-studied tert-Butyl Acrylate (tBA) SMP. Quantifying the effects on shape memory behavior was performed using a two-tiered analysis. A two-tiered study design was used to determine if the sterilization process induced any premature shape recovery and to identify any effects that NOx has on the overall shape memory behavior of the foams. Determining the effectiveness of the NOx system--specially, whether the treated samples are more sterile/less contaminated than untreated--was also performed with a two-tiered analysis. In this case, the two-tiered analysis was employed to have a secondary check for contamination. To elaborate, all of the samples that were deemed not contaminated from the initial test were put through a second sterility test to check for contamination a second time. The results of these tests indicated the NOx system is an effective sterilization mechanism and the current protocol does not negatively impact the shape memory behavior of the tBA SMP. The samples held their compressed shape throughout the entirety of the sterilization process. Additionally, there were no observable impacts on the shape memory behavior induced by NOx. Lastly, the treated samples demonstrated lower contamination than the untreated. This thesis demonstrates the effectiveness of NOx as a laboratory scale sterilization mechanism for heat triggered shape memory polymers. The shape memory analysis indicated that the magnitude of the length changes induced by NOx is small enough that it does not make a statistically significant impact on the shape memory behavior of the foams. Additionally, there were no observable effects on the shape memory behavior induced by NOx. The results further indicated the NOx system is effective at sterilizing porous scaffolds, as none of the sterilized samples showed contamination. Testing methods proved to be effective because the initial sterility test was able to identify all of the contaminated samples and preliminary results indicated that NOx sterilization improves the sterility of the foams.

A phenomenological model for simulating the chemo-responsive shape memory effect in polymers undergoing a permeation transition

NASA Astrophysics Data System (ADS)

Lu, Haibao; Huang, Wei Min; Leng, Jinsong

2014-04-01

We present a phenomenological model for studying the constitutive relations and working mechanism of the chemo-responsive shape memory effect (SME) in shape memory polymers (SMPs). On the basis of the solubility parameter equation, diffusion model and permeation transition model, a phenomenological model is derived for quantitatively identifying the influential factors in the chemically induced SME in SMPs. After this, a permeability parallel model and series model are implemented in order to couple the constitutive relations of the permeability coefficient, stress and relaxation time as a function of stretch, separately. The inductive effect of the permeability transition on the transition temperature is confirmed as the driving force for the chemo-responsive SME. Furthermore, the analytical result from the phenomenological model is compared with the available experimental results and the simulation of a semi-empirical model reported in the literature for verification.

Reticulation of low density shape memory polymer foam with an in vivo demonstration of vascular occlusion

PubMed Central

Rodriguez, Jennifer N.; Miller, Matthew W.; Boyle, Anthony; Horn, John; Yang, Cheng-Kang; Wilson, Thomas S.; Ortega, Jason M.; Small, Ward; Nash, Landon; Skoog, Hunter; Maitland, Duncan J.

2014-01-01

Predominantly closed-cell low density shape memory polymer (SMP) foam was recently reported to be an effective aneurysm filling device in a porcine model (Rodriguez et al., Journal of Biomedical Materials Research Part A 2013: (http://dx.doi.org/10.1002/jbm.a.34782)). Because healing involves blood clotting and cell migration throughout the foam volume, a more open-cell structure may further enhance the healing response. This research sought to develop a non-destructive reticulation process for this SMP foam to disrupt the membranes between pore cells. Non-destructive mechanical reticulation was achieved using a gravity-driven floating nitinol pin array coupled with vibratory agitation of the foam and supplemental chemical etching. Reticulation resulted in a reduced elastic modulus and increased permeability, but did not impede shape memory behavior. Reticulated foams were capable of achieving rapid vascular occlusion in an in vivo porcine model. PMID:25222869

Thermorheological characteristics and comparison of shape memory polymers fabricated by novel 3D printing technique

NASA Astrophysics Data System (ADS)

Hassan, Rizwan Ul; Jo, Soohwan; Seok, Jongwon

The feasibility of fabrication of shape memory polymers (SMPs) was investigated using a customized 3-dimensional (3D) printing technique with an excellent resolution that could be less than 100 microns. The thermorheological effects of SMPs were adjusted by contact and non-contact triggering, which led to the respective excellent shape recoveries of 100% and 99.89%. Thermogravimetric analyses of SMPs resulted in a minor weight loss, thereby revealing good thermal stability at higher temperatures. The viscoelastic properties of SMPs were measured using dynamic mechanical analyses, exhibiting increased viscous and elastic characteristics. Mechanical strength, thermal stability and viscoelastic properties, of the two SMPs were compared [di(ethylene) glycol dimethacrylate (DEGDMA) and poly (ethylene glycol) dimethacrylate (PEGDMA)] to investigate the shape memory behavior. This novel 3D printing technique can be used as a promising method for fabricating smart materials with increased accuracy in a cost-effective manner.

Recovery behaviour of shape memory polyurethane based laminates after thermoforming

NASA Astrophysics Data System (ADS)

Wu, Shuiliang; Xu, Wensen; Prasath Balamurugan, G.; Thompson, Michael R.; Nielsen, Kent E.; Brandys, Frank A.

2017-11-01

Shape memory polymers (SMPs) can be used to produce a new class of decorative films capable of improved formability and shape recovery in polymer laminates, which are increasingly being used for automotive, aerospace, construction and commercial applications. As a relatively new field there is little knowledge on the shape recovery behaviour of laminates with a SMP film and few methods of quantify that behaviour. The influences of different variables that affect the recovery behaviour of thermoplastic shape memory polyurethanes based laminates including ambient temperature (45 °C and 65 °C), material modulus, and adhesive strength were investigated after thermoforming, through both experimental and modelling methods. The empirical model assisted in identifying the contributions of the adhesive to transfer stresses, which dampened the recovery of the laminate with lower shear strength adhesives. Increasing ambient temperature and the film modulus increased both the final angle recovery ratios and recovery rates.

Characterization of Nonlinear Rate Dependent Response of Shape Memory Polymers

NASA Technical Reports Server (NTRS)

Volk, Brent; Lagoudas, Dimitris C.; Chen, Yi-Chao; Whitley, Karen S.

2007-01-01

Shape Memory Polymers (SMPs) are a class of polymers, which can undergo deformation in a flexible state at elevated temperatures, and when cooled below the glass transition temperature, while retaining their deformed shape, will enter and remain in a rigid state. Upon heating above the glass transition temperature, the shape memory polymer will return to its original, unaltered shape. SMPs have been reported to recover strains of over 400%. It is important to understand the stress and strain recovery behavior of SMPs to better develop constitutive models which predict material behavior. Initial modeling efforts did not account for large deformations beyond 25% strain. However, a model under current development is capable of describing large deformations of the material. This model considers the coexisting active (rubber) and frozen (glass) phases of the polymer, as well as the transitions between the material phases. The constitutive equations at the continuum level are established with internal state variables to describe the microstructural changes associated with the phase transitions. For small deformations, the model reduces to a linear model that agrees with those reported in the literature. Thermomechanical characterization is necessary for the development, calibration, and validation of a constitutive model. The experimental data reported in this paper will assist in model development by providing a better understanding of the stress and strain recovery behavior of the material. This paper presents the testing techniques used to characterize the thermomechanical material properties of a shape memory polymer (SMP) and also presents the resulting data. An innovative visual-photographic apparatus, known as a Vision Image Correlation (VIC) system was used to measure the strain. The details of this technique will also be presented in this paper. A series of tensile tests were performed on specimens such that strain levels of 10, 25, 50, and 100% were applied to the material while it was above its glass transition temperature. After deforming the material to a specified applied strain, the material was then cooled to below the glass transition temperature (Tg) while retaining the deformed shape. Finally, the specimen was heated again to above the transition temperature, and the resulting shape recovery profile was measured. Results show that strain recovery occurs at a nonlinear rate with respect to time. Results also indicate that the ratio of recoverable strain/applied strain increases as the applied strain increases.

Biodegradable shape-memory block co-polymers for fast self-expandable stents.

PubMed

Xue, Liang; Dai, Shiyao; Li, Zhi

2010-11-01

Block co-polymers PCTBVs (M(n) of 36,300-65,300 g/mol, T(m) of 39-40 and 142 degrees C) containing hyperbranched three-arm poly(epsilon-caprolactone) (PCL) as switching segment and microbial polyester PHBV as crystallizable hard segment were designed as biodegradable shape-memory polymer (SMP) for fast self-expandable stent and synthesized in 96% yield by the reaction of three-arm PCL-triol (M(n) of 4200 g/mol, T(m) of 47 degrees C) with methylene diphenyl 4,4'-diisocyanate isocynate (MDI) to form the hyperbrached MDI-linked PCL (PTCM; M(n) of 25,400 g/mol and a T(m) of 38 degrees C), followed by further polymerization with PHBV-diol (M(n) of 2200 g/mol, T(m) of 137 and 148 degrees C). The polymers were characterized by (1)H NMR, GPC, DSC, tensile test, and cyclic thermomechanical tensile test. PCTBVs showed desired thermal properties, mechanical properties, and ductile nature. PCTBV containing 25 wt% PHBV (PCTBV-25) demonstrated excellent shape-memory property at 40 degrees C, with R(f) of 94%, R(r) of 98%, and shape recovery within 25s. PCTBV-25 was also shown as a safe material with good biocompatibility by cytotoxicity tests and cell growth experiments. The stent made from PCTBV-25 film showed nearly complete self-expansion at 37 degrees C within only 25 s, which is much better and faster than the best known self-expandable stents. Copyright (c) 2010 Elsevier Ltd. All rights reserved.

Soluble porphyrin polymers

DOEpatents

Gust, Jr., John Devens; Liddell, Paul Anthony

2015-07-07

Porphyrin polymers of Structure 1, where n is an integer (e.g., 1, 2, 3, 4, 5, or greater) ##STR00001## are synthesized by the method shown in FIGS. 2A and 2B. The porphyrin polymers of Structure 1 are soluble in organic solvents such as 2-MeTHF and the like, and can be synthesized in bulk (i.e., in processes other than electropolymerization). These porphyrin polymers have long excited state lifetimes, making the material suitable as an organic semiconductor for organic electronic devices including transistors and memories, as well as solar cells, sensors, light-emitting devices, and other opto-electronic devices.

3D Printing of a Thermoplastic Shape Memory Polymer using FDM

NASA Astrophysics Data System (ADS)

Zhao, Zhiyang; Weiss, R. A.; Vogt, Bryan

Shape memory polymers (SMPs) change from a temporary shape to its permanent shape when exposed to an external stimulus. The shape memory relies on the presence of two independent networks. 3D printing provides a facile method to fabricate complex shapes with high degrees of customizability. The most common consumer 3D printing technology is fused deposition modeling (FDM), which relies on the extrusion of a thermoplastic filament to build-up the part in a layer by layer fashion. The material choices for FDM are limited, but growing. The generation of an SMP that is printable by FDM could open SMPs to many new potential applications. In this work, we demonstrate printing of thermally activated SMP using FDM. Partially neutralized poly(ethylene-co-r-methacrylic acid) ionomers (Surlyn by Dupont) was extruded into filaments and used as a model thermoplastic shape memory material. The properties of the SMP part can be readily tuned by print parameters, such as infill density or infill direction without changing the base material. We discuss the performance and characteristics of 3D printed shapes compared to their compression molded analogs.

Designing multifunctional polymers for cardiovascular implants.

PubMed

Wischke, Christian; Lendlein, Andreas

2011-01-01

Polymer-based biomaterials are extensively used in all disciplines of clinical medicine and innovations in biomaterial science are building a product pipeline, e.g., of future cardiovascular implants. Still, cardiovascular applications demand a number of extensive requirements of properties and functions to be fulfilled by the polymer matrix. This report provides an overview on some of these issues and how they can be addressed by a tailored design of novel polymer-based biomaterials. Multifunctional shape-memory polymers are highlighted as a class of materials that combine biocompatibility and the capability for stimuli-induced active movements for anchoring of implants with a controlled degradation and drug release profile to enable a functional regeneration of the tissue at the application site.

Understanding Melt-Memory of Commercial Polyolefins

NASA Astrophysics Data System (ADS)

Alamo, Rufina

Self-nucleation (SN) or controlling self-generated seeds in a polymer melt is an avenue to increase the rate of solidification of semicrystalline polymers of commercial relevance. Self-nuclei are remains in the melt of the segmental self-assembly to form polymer crystallites providing a path to enhance primary crystal nucleation. SN has been extensively studied in homopolymers such as iPP. Recently, a strong memory effect of crystallization has been observed in melts of random ethylene copolymers well above the equilibrium melting temperature. The melt memory is associated with clusters or seeds that remain in the melt from the copolymer's sequence length partitioning. Cooling from progressively lower self-seeded melt temperatures, ethylene copolymers with a broad inter-chain comonomer composition (1 - 15 mol%) display first the expected accelerated crystallization, followed by a decrease in the rate in a range of melt temperatures where narrow copolymers show a continuous acceleration of the rate. This unusual inversion of the crystallization rate was postulated to arise from the onset of liquid-liquid phase separation (LLPS) between comonomer-rich and comonomer-poor components of the broad copolymer. The UCST type phase diagram of these commercial copolymers has been documented via SANS using a blend of components, some deuterated, to reproduce the broad distribution. Furthermore, the components that contribute to LLPS have been identified by the crystallization behavior of molar mass fractions. The influence of long chain branching on the topology of copolymer melts has been analyzed using model 3-arm stars hydrogenated polybutadienes. The effect of melt viscosity on strength of melt memory is also evident when SN data of random ethylene copolymers are compared with those of propylene-ethylene copolymers. The strong dependence of melt viscosity on melt memory, and a critical threshold crystallinity level to observe the effect of melt memory on crystallization rate, support the kinetic nature of the SN phenomenon. Support from NSF, DMR-1105129 and DMR-1607786 is gratefully acknowledged.

Feasibility study of polyurethane shape-memory polymer actuators for pressure bandage application

PubMed Central

Ahmad, Manzoor; Luo, Jikui; Miraftab, Mohsen

2012-01-01

The feasibility of laboratory-synthesized polyurethane-based shape-memory polymer (SMPU) actuators has been investigated for possible application in medical pressure bandages where gradient pressure is required between the ankle and the knee for treatment of leg ulcers. In this study, using heat as the stimulant, SMPU strip actuators have been subjected to gradual and cyclic stresses; their recovery force, reproducibility and reusability have been monitored with respect to changes in temperature and circumference of a model leg, and the stress relaxation at various temperatures has been investigated. The findings suggest that SMPU actuators can be used for the development of the next generation of pressure bandages. PMID:27877473

A Kirigami shape memory polymer honeycomb concept for deployment

NASA Astrophysics Data System (ADS)

Neville, Robin M.; Chen, Jianguo; Guo, Xiaogang; Zhang, Fenghua; Wang, Wenxin; Dobah, Yousef; Scarpa, Fabrizio; Leng, Jinsong; Peng, Hua-Xin

2017-05-01

We present a shape memory polymer (SMP) honeycomb with tuneable and shape morphing mechanical characteristics. Kirigami (Origami with cutting allowed) techniques have been used to design and manufacture the honeycomb. The cellular structure described in this work has styrene SMP hinges that create the shape change and the deployment actuation. To create a large volumetric deployment, the Kirigami open honeycomb configuration has been designed by setting an initial three-dimensional re-entrant auxetic (negative Poisson’s ratio) configuration, while the final honeycomb shape assume a convex (positive Poisson’s ratio) layout. A model was developed to predict the shape change of the structure, and compared to experimental results from a demonstrator honeycomb deployment test.

Hysteresis mechanism and control in pentacene organic field-effect transistors with polymer dielectric

NASA Astrophysics Data System (ADS)

Huang, Wei; Shi, Wei; Han, Shijiao; Yu, Junsheng

2013-05-01

Hysteresis mechanism of pentacene organic field-effect transistors (OFETs) with polyvinyl alcohol (PVA) and/or polymethyl methacrylate (PMMA) dielectrics is studied. Through analyzing the electrical characteristics of OFETs with various PVA/PMMA arrangements, it shows that charge, which is trapped in PVA bulk and at the interface of pentacene/PVA, is one of the origins of hysteresis. The results also show that memory window is proportional to both trap amount in PVA and charge density at the gate/PVA or PVA/pentacene interfaces. Hence, the controllable memory window of around 0 ˜ 10 V can be realized by controlling the thickness and combination of triple-layer polymer dielectrics.

In vitro and in vivo Evaluation of a Shape Memory Polymer Foam-over-Wire Embolization Device Delivered in Saccular Aneurysm Models

PubMed Central

Boyle, Anthony J.; Landsman, Todd L.; Wierzbicki, Mark A.; Nash, Landon D.; Hwang, Wonjun; Miller, Matthew W.; Tuzun, Egemen; Hasan, Sayyeda M.; Maitland, Duncan J.

2015-01-01

Current endovascular therapies for intracranial saccular aneurysms result in high recurrence rates due to poor tissue healing, coil compaction, and aneurysm growth. We propose treatment of saccular aneurysms using shape memory polymer (SMP) foam to improve clinical outcomes. SMP foam-over-wire (FOW) embolization devices were delivered to in vitro and in vivo porcine saccular aneurysm models to evaluate device efficacy, aneurysm occlusion, and acute clotting. FOW devices demonstrated effective delivery and stable implantation in vitro. In vivo porcine aneurysms were successfully occluded using FOW devices with theoretical volume occlusion values greater than 72% and rapid, stable thrombus formation. PMID:26227115

A New Strategy to Prepare Polymer-based Shape Memory Elastomers.

PubMed

Song, Shijie; Feng, Jiachun; Wu, Peiyi

2011-10-04

A new strategy that utilizes the microphase separation of block copolymer and phase transition of small molecules for preparing polymer-based shape memory elastomer has been proposed. According to this strategy, a novel kind of shape memory elastomer comprising styrene-b-(ethylene-co-butylene)-b-styrene (SEBS) and paraffin has been prepared. Because paraffins are midblock-selective molecules for SEBS, they will preferentially enter and swell EB blocks supporting paraffins as an excellent switch phase for shape memory effect. Microstructures of SEBS/paraffin composites have been characterized by transmission electron microscopy, polarized light microscopy, and differential scanning calorimetry. The composites demonstrate various phase morphologies with regard to different paraffin loading. It has been found that under low paraffin loading, all the paraffins precisely embed in and swell EB-rich domains. While under higher loading, part of the paraffins become free and a larger-scaled phase separation has been observed. However, within wide paraffin loadings, all composites show good shape fixing, shape recovery performances, and improved tensile properties. Compared to the reported methods for shape memory elastomers preparation, this method not only simplifies the fabrication procedure from raw materials to processing but also offers a controllable approach for the optimization of shape memory properties as well as balancing the rigidity and softness of the material. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Progress and opportunities in high-voltage microactuator powering technology towards one-chip MEMS

NASA Astrophysics Data System (ADS)

Mita, Yoshio; Hirakawa, Atsushi; Stefanelli, Bruno; Mori, Isao; Okamoto, Yuki; Morishita, Satoshi; Kubota, Masanori; Lebrasseur, Eric; Kaiser, Andreas

2018-04-01

In this paper, we address issues and solutions for micro-electro-mechanical-systems (MEMS) powering through semiconductor devices towards one-chip MEMS, especially those with microactuators that require high voltage (HV, which is more than 10 V, and is often over 100 V) for operation. We experimentally and theoretically demonstrated that the main reason why MEMS actuators need such HV is the tradeoff between resonant frequency and displacement amplitude. Indeed, the product of frequency and displacement is constant regardless of the MEMS design, but proportional to the input energy, which is the square of applied voltage in an electrostatic actuator. A comprehensive study on the principles of HV device technology and associated circuit technologies, especially voltage shifter circuits, was conducted. From the viewpoint of on-chip energy source, series-connected HV photovoltaic cells have been discussed. Isolation and electrical connection methods were identified to be key enabling technologies. Towards future rapid development of such autonomous devices, a technology to convert standard 5 V CMOS devices into HV circuits using SOI substrate and a MEMS postprocess is presented. HV breakdown experiments demonstrated this technology can hold over 700 to 1000 V, depending on the layout.

Low-voltage operating flexible ferroelectric organic field-effect transistor nonvolatile memory with a vertical phase separation P(VDF-TrFE-CTFE)/PS dielectric

NASA Astrophysics Data System (ADS)

Xu, Meili; Xiang, Lanyi; Xu, Ting; Wang, Wei; Xie, Wenfa; Zhou, Dayu

2017-10-01

Future flexible electronic systems require memory devices combining low-power operation and mechanical bendability. However, high programming/erasing voltages, which are universally needed to switch the storage states in previously reported ferroelectric organic field-effect transistor (Fe-OFET) nonvolatile memories (NVMs), severely prevent their practical applications. In this work, we develop a route to achieve a low-voltage operating flexible Fe-OFET NVM. Utilizing vertical phase separation, an ultrathin self-organized poly(styrene) (PS) buffering layer covers the surface of the ferroelectric polymer layer by one-step spin-coating from their blending solution. The ferroelectric polymer with a low coercive field contributes to low-voltage operation in the Fe-OFET NVM. The polymer PS contributes to the improvement of mobility, attributing to screening the charge scattering and decreasing the surface roughness. As a result, a high performance flexible Fe-OFET NVM is achieved at the low P/E voltages of ±10 V, with a mobility larger than 0.2 cm2 V-1 s-1, a reliable P/E endurance over 150 cycles, stable data storage retention capability over 104 s, and excellent mechanical bending durability with a slight performance degradation after 1000 repetitive tensile bending cycles at a curvature radius of 5.5 mm.

Sequential Self-Folding Structures by 3D Printed Digital Shape Memory Polymers

NASA Astrophysics Data System (ADS)

Mao, Yiqi; Yu, Kai; Isakov, Michael S.; Wu, Jiangtao; Dunn, Martin L.; Jerry Qi, H.

2015-09-01

Folding is ubiquitous in nature with examples ranging from the formation of cellular components to winged insects. It finds technological applications including packaging of solar cells and space structures, deployable biomedical devices, and self-assembling robots and airbags. Here we demonstrate sequential self-folding structures realized by thermal activation of spatially-variable patterns that are 3D printed with digital shape memory polymers, which are digital materials with different shape memory behaviors. The time-dependent behavior of each polymer allows the temporal sequencing of activation when the structure is subjected to a uniform temperature. This is demonstrated via a series of 3D printed structures that respond rapidly to a thermal stimulus, and self-fold to specified shapes in controlled shape changing sequences. Measurements of the spatial and temporal nature of self-folding structures are in good agreement with the companion finite element simulations. A simplified reduced-order model is also developed to rapidly and accurately describe the self-folding physics. An important aspect of self-folding is the management of self-collisions, where different portions of the folding structure contact and then block further folding. A metric is developed to predict collisions and is used together with the reduced-order model to design self-folding structures that lock themselves into stable desired configurations.

Hybrid macro-micro fluidics system for a chip-based biosensor

NASA Astrophysics Data System (ADS)

Tamanaha, C. R.; Whitman, L. J.; Colton, R. J.

2002-03-01

We describe the engineering of a hybrid fluidics platform for a chip-based biosensor system that combines high-performance microfluidics components with powerful, yet compact, millimeter-scale pump and valve actuators. The microfluidics system includes channels, valveless diffuser-based pumps, and pinch-valves that are cast into a poly(dimethylsiloxane) (PDMS) membrane and packaged along with the sensor chip into a palm-sized plastic cartridge. The microfluidics are driven by pump and valve actuators contained in an external unit (with a volume ~30 cm3) that interfaces kinematically with the PDMS microelements on the cartridge. The pump actuator is a simple-lever, flexure-hinge displacement amplifier that increases the motion of a piezoelectric stack. The valve actuators are an array of cantilevers operated by shape memory alloy wires. All components can be fabricated without the need for complex lithography or micromachining, and can be used with fluids containing micron-sized particulates. Prototypes have been modeled and tested to ensure the delivery of microliter volumes of fluid and the even dispersion of reagents over the chip sensing elements. With this hybrid approach to the fluidics system, the biochemical assay benefits from the many advantages of microfluidics yet we avoid the complexity and unknown reliability of immature microactuator technologies.

Tunable thiol-epoxy shape memory polymer foams

NASA Astrophysics Data System (ADS)

Ellson, Gregory; Di Prima, Matthew; Ware, Taylor; Tang, Xiling; Voit, Walter

2015-05-01

Shape memory polymers (SMPs) are uniquely suited to a number of applications due to their shape storage and recovery abilities and the wide range of available chemistries. However, many of the desired performance properties are tied to the polymer chemistry which can make optimization difficult. The use of foaming techniques is one way to tune mechanical response of an SMP without changing the polymer chemistry. In this work, a novel thiol-epoxy SMP was foamed using glass microspheres (40 and 50% by volume Q-Cel 6019), using expandable polymer microspheres (1% 930 DU 120), and by a chemical blowing agent (1% XOP-341). Each approach created SMP foam with a differing density and microstructure from the others. Thermal and thermomechanical analysis was performed to observe the behavioral difference between the foaming techniques and to confirm that the glass transition (Tg) was relatively unchanged near 50 °C while the glassy modulus varied from 19.1 to 345 MPa and the rubbery modulus varied from 0.04 to 2.2 MPa. The compressive behavior of the foams was characterized through static compression testing at different temperatures, and cyclic compression testing at Tg. Constrained shape recovery testing showed a range of peak recovery stress from 5 MPa for the syntactic Q-Cel foams to ˜0.1 MPa for the chemically blown XOP-341 foam. These results showed that multiple foaming approaches can be used with a novel SMP to vary the mechanical response independent of Tg and polymer chemistry.

Interplay of non-Markov and internal friction effects in the barrier crossing kinetics of biopolymers: insights from an analytically solvable model.

PubMed

Makarov, Dmitrii E

2013-01-07

Conformational rearrangements in biomolecules (such as protein folding or enzyme-ligand binding) are often interpreted in terms of low-dimensional models of barrier crossing such as Kramers' theory. Dimensionality reduction, however, entails memory effects; as a result, the effective frictional drag force along the reaction coordinate nontrivially depends on the time scale of the transition. Moreover, when both solvent and "internal" friction effects are important, their interplay results in a highly nonlinear dependence of the effective friction on solvent viscosity that is not captured by common phenomenological models of barrier crossing. Here, these effects are illustrated using an analytically solvable toy model of an unstructured polymer chain involved in an inter- or intramolecular transition. The transition rate is calculated using the Grote-Hynes and Langer theories, which--unlike Kramers' theory--account for memory. The resulting effective frictional force exerted by the polymer along the reaction coordinate can be rationalized in terms of the effective number of monomers engaged in the transition. Faster transitions (relative to the polymer reconfiguration time scale) involve fewer monomers and, correspondingly, lower friction forces, because the polymer chain does not have enough time to reconfigure in response to the transition.

Mechanisms of charge transport and resistive switching in composite films of semiconducting polymers with nanoparticles of graphene and graphene oxide

NASA Astrophysics Data System (ADS)

Berestennikov, A. S.; Aleshin, A. N.

2017-11-01

We have investigated the effect of the resistive switching in the composite films based on polyfunctional polymers - PVK, PFD and PVC mixed with particles of Gr and GO with the concentration of ˜ 1 - 3 wt.%. We have developed the solution processed hybrid memory structures based on PVK and GO particles composite films. The effect of the resistive switching in Al/PVK(PFD; PVC):Gr(GO)/ITO/PET structures manifests itself as a sharp change of the electrical resistance from a low-conducting state to a relatively high-conducting state when applying a bias to Al-ITO electrodes of ˜ 0.2-0.4 V. It has been established that a sharp conductivity jump characterized by S-shaped current-voltage curves and the presence of their hysteresis occurs upon applying a voltage pulse to the Au/PVK(PFD; PVC):Gr(GO)/ITO/PET structures, with the switching time in the range from 1 to 30 μs. The mechanism of resistive switching associated with the processes of capture and accumulation of charge carriers by Gr(GO) particles introduced into the matrixes of the PVK polymer due to the reduction/oxidation processes. The possible mechanisms of energy transfer between organic and inorganic components in PVK(PFD; PVC):GO(Gr) films causes increase mobility are discussed. Incorporating of Gr (GO) particles into the polymer matrix is a promising route to enhance the performance of hybrid memory structures, as well as it is an effective medium for memory cells.

Direct 4D printing via active composite materials.

PubMed

Ding, Zhen; Yuan, Chao; Peng, Xirui; Wang, Tiejun; Qi, H Jerry; Dunn, Martin L

2017-04-01

We describe an approach to print composite polymers in high-resolution three-dimensional (3D) architectures that can be rapidly transformed to a new permanent configuration directly by heating. The permanent shape of a component results from the programmed time evolution of the printed shape upon heating via the design of the architecture and process parameters of a composite consisting of a glassy shape memory polymer and an elastomer that is programmed with a built-in compressive strain during photopolymerization. Upon heating, the shape memory polymer softens, releases the constraint on the strained elastomer, and allows the object to transform into a new permanent shape, which can then be reprogrammed into multiple subsequent shapes. Our key advance, the markedly simplified creation of high-resolution complex 3D reprogrammable structures, promises to enable myriad applications across domains, including medical technology, aerospace, and consumer products, and even suggests a new paradigm in product design, where components are simultaneously designed to inhabit multiple configurations during service.

Direct 4D printing via active composite materials

PubMed Central

Ding, Zhen; Yuan, Chao; Peng, Xirui; Wang, Tiejun; Qi, H. Jerry; Dunn, Martin L.

2017-01-01

We describe an approach to print composite polymers in high-resolution three-dimensional (3D) architectures that can be rapidly transformed to a new permanent configuration directly by heating. The permanent shape of a component results from the programmed time evolution of the printed shape upon heating via the design of the architecture and process parameters of a composite consisting of a glassy shape memory polymer and an elastomer that is programmed with a built-in compressive strain during photopolymerization. Upon heating, the shape memory polymer softens, releases the constraint on the strained elastomer, and allows the object to transform into a new permanent shape, which can then be reprogrammed into multiple subsequent shapes. Our key advance, the markedly simplified creation of high-resolution complex 3D reprogrammable structures, promises to enable myriad applications across domains, including medical technology, aerospace, and consumer products, and even suggests a new paradigm in product design, where components are simultaneously designed to inhabit multiple configurations during service. PMID:28439560

Large energy absorption in Ni-Mn-Ga/polymer composites

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

Feuchtwanger, Jorge; Richard, Marc L.; Tang, Yun J.

2005-05-15

Ferromagnetic shape memory alloys can respond to a magnetic field or applied stress by the motion of twin boundaries and hence they show large hysteresis or energy loss. Ni-Mn-Ga particles made by spark erosion have been dispersed and oriented in a polymer matrix to form pseudo 3:1 composites which are studied under applied stress. Loss ratios have been determined from the stress-strain data. The loss ratios of the composites range from 63% to 67% compared to only about 17% for the pure, unfilled polymer samples.

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

Wuttig, Manfred

The research was directed towards finding new functional materials, mainly polymeric. Main accomplishment consisit of indentifying mulktiferroic polymers and a shape memory alloy featuring an ultralong fatigue life of 10 million cycles.

Transparent photostable ZnO nonvolatile memory transistor with ferroelectric polymer and sputter-deposited oxide gate

NASA Astrophysics Data System (ADS)

Park, C. H.; Im, Seongil; Yun, Jungheum; Lee, Gun Hwan; Lee, Byoung H.; Sung, Myung M.

2009-11-01

We report on the fabrication of transparent top-gate ZnO nonvolatile memory thin-film transistors (NVM-TFTs) with 200 nm thick poly(vinylidene fluoride/trifluoroethylene) ferroelectric layer; semitransparent 10 nm thin AgOx and transparent 130 nm thick indium-zinc oxide (IZO) were deposited on the ferroelectric polymer as gate electrode by rf sputtering. Our semitransparent NVM-TFT with AgOx gate operates under low voltage write-erase (WR-ER) pulse of ±20 V, but shows some degradation in retention property. In contrast, our transparent IZO-gated device displays very good retention properties but requires anomalously higher pulse of ±70 V for WR and ER states. Both devices stably operated under visible illuminations.

Organic nonvolatile resistive memory devices based on thermally deposited Au nanoparticle

NASA Astrophysics Data System (ADS)

Jin, Zhiwen; Liu, Guo; Wang, Jizheng

2013-05-01

Uniform Au nanoparticles (NPs) are formed by thermally depositing nominal 2-nm thick Au film on a 10-nm thick polyimide film formed on a Al electrode, and then covered by a thin polymer semiconductor film, which acts as an energy barrier for electrons to be injected from the other Al electrode (on top of polymer film) into the Au NPs, which are energetically electron traps in such a resistive random access memory (RRAM) device. The Au NPs based RRAM device exhibits estimated retention time of 104 s, cycle times of more than 100, and ON-OFF ratio of 102 to 103. The carrier transport properties are also analyzed by fitting the measured I-V curves with several conduction models.

Fabrication and characterization of cylindrical light diffusers comprised of shape memory polymer.

PubMed

Small, Ward; Buckley, Patrick R; Wilson, Thomas S; Loge, Jeffrey M; Maitland, Kristen D; Maitland, Duncan J

2008-01-01

We developed a technique for constructing light diffusing devices comprised of a flexible shape memory polymer (SMP) cylindrical diffuser attached to the tip of an optical fiber. The devices are fabricated by casting an SMP rod over the cleaved tip of an optical fiber and media blasting the SMP rod to create a light diffusing surface. The axial and polar emission profiles and circumferential (azimuthal) uniformity are characterized for various blasting pressures, nozzle-to-sample distances, and nozzle translation speeds. The diffusers are generally strongly forward-directed and consistently withstand over 8 W of incident IR laser light without suffering damage when immersed in water. These devices are suitable for various endoluminal and interstitial biomedical applications.

Fabrication and characterization of cylindrical light diffusers comprised of shape memory polymer

PubMed Central

Small, Ward; Buckley, Patrick R.; Wilson, Thomas S.; Loge, Jeffrey M.; Maitland, Kristen D.; Maitland, Duncan J.

2009-01-01

We developed a technique for constructing light diffusing devices comprised of a flexible shape memory polymer (SMP) cylindrical diffuser attached to the tip of an optical fiber. The devices are fabricated by casting an SMP rod over the cleaved tip of an optical fiber and media blasting the SMP rod to create a light diffusing surface. The axial and polar emission profiles and circumferential (azimuthal) uniformity are characterized for various blasting pressures, nozzle-to-sample distances, and nozzle translation speeds. The diffusers are generally strongly forward-directed and consistently withstand over 8 W of incident IR laser light without suffering damage when immersed in water. These devices are suitable for various endoluminal and interstitial biomedical applications. PMID:18465981

Reticulation of low density shape memory polymer foam with an in vivo demonstration of vascular occlusion

DOE PAGES

Rodriguez, Jennifer N.; Miller, Matthew W.; Boyle, Anthony; ...

2014-08-11

Recently, predominantly closed-cell low density shape memory polymer (SMP) foam was reported to be an effective aneurysm filling device in a porcine model (Rodriguez et al., Journal of Biomedical Materials Research Part A 2013: (http://dx.doi.org/10.1002/jbm.a.34782)). Because healing involves blood clotting and cell migration throughout the foam volume, a more open-cell structure may further enhance the healing response. This research sought to develop a non-destructive reticulation process for this SMP foam to disrupt the membranes between pore cells. Non-destructive mechanical reticulation was achieved using a gravity-driven floating nitinol pin array coupled with vibratory agitation of the foam and supplemental chemical etching.more » Lastly, reticulation resulted in a reduced elastic modulus and increased permeability, but did not impede the shape memory behavior. Reticulated foams were capable of achieving rapid vascular occlusion in an in vivo porcine model.« less

Influence of Thin-Film Adhesives in Pullout Tests Between Nickel-Titanium Shape Memory Alloy and Carbon Fiber-Reinforced Polymer Matrix Composites

NASA Technical Reports Server (NTRS)

Quade, Derek J.; Jana, Sadhan; McCorkle, Linda S.

2018-01-01

Strips of nickel-titanium (NiTi) shape memory alloy (SMA) and carbon fiber-reinforced polymer matrix composite (PMC) were bonded together using multiple thin film adhesives and their mechanical strengths were evaluated under pullout test configuration. Tensile and lap shear tests were conducted to confirm the deformation of SMAs at room temperature and to evaluate the adhesive strength between the NiTi strips and the PMC. Optical and scanning electron microscopy techniques were used to examine the interfacial bonding after failure. Simple equations on composite tensile elongation were used to fit the experimental data on tensile properties. ABAQUS models were generated to show the effects of enhanced bond strength and the distribution of stress in SMA and PMC. The results revealed that the addition of thin film adhesives increased the average adhesive strength between SMA and PMC while halting the room temperature shape memory effect within the pullout specimen.

Ultra low density biodegradable shape memory polymer foams with tunable physical properties

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

Singhal, Pooja; Wilson, Thomas S.; Cosgriff-Hernandez, Elizabeth

Compositions and/or structures of degradable shape memory polymers (SMPs) ranging in form from neat/unfoamed to ultra low density materials of down to 0.005 g/cc density. These materials show controllable degradation rate, actuation temperature and breadth of transitions along with high modulus and excellent shape memory behavior. A method of m ly low density foams (up to 0.005 g/cc) via use of combined chemical and physical aking extreme blowing agents, where the physical blowing agents may be a single compound or mixtures of two or more compounds, and other related methods, including of using multiple co-blowing agents of successively higher boilingmore » points in order to achieve a large range of densities for a fixed net chemical composition. Methods of optimization of the physical properties of the foams such as porosity, cell size and distribution, cell openness etc. of these materials, to further expand their uses and improve their performance.« less

The effects of heterogeneities on memory-dependent diffusion

NASA Astrophysics Data System (ADS)

Adib, Farhad; Neogi, P.

1993-07-01

Case II diffusion is often seen in glassy polymers, where the mass uptake in sorption is proportional to time t instead of sqrt{t}. A memory dependent diffusion is needed to explain such effects, where the relaxation function used to describe the memory effect has a characteristic time. The ratio of this time to the overall diffusion times is the diffusional Deborah number. Simple models show that case II results when the Deborah number is around one, that is, when the two time scales are comparable. Under investigation are the possible effects of the fact that the glassy polymers are heterogeneous over molecular scales. The averaging form given by DiMarzio and Sanchez has been used to obtain the averaged response. The calculated dynamics of sorption show that whereas case II is still observed, the long term tails change dramatically from the oscillatory to torpid, to chaotic, which are all observed in the experiments. The Deborah number defined here in a self-consistent manner collapses in those cases, but causes no other ill-effects.

Development of a smart, anti-water polyurethane polymer hair coating for style setting.

PubMed

Liu, Y; Liu, Y J; Hu, J; Ji, F L; Lv, J; Chen, S J; Zhu, Y

2016-06-01

The goal of this work was to develop a novel polyurethane polymer coating for the surface of the hair that could be used for style setting via the shape memory effect (SME). The features of the films are in accordance with conventional hair styling methods used in the laboratory. In this study, a new polyurethane polymer was synthesized; the morphology and mechanical behaviour of the coated hair were systematically investigated using a scanning electron microscope (SEM) and an Instron 5566 (with a temperature oven). The SME of the hair was tested using a 35-g weight and over five washing and drying cycles. The experimental result shows that the polyurethane polymer has effects on the mechanical behaviour of the hair. It indicates that the fixed shape (at 22°C) and recover rate (at 60°C) of different casted thickness films are similar. And the stress of the film becomes larger with increasing film thickness. Furthermore, the shape memory ability could be endowed with the hair styling using this polymer; the hair fibre could recover to the 65% of its original shape after five cycle deformation by 35 g mass under the heat-treated condition; it could recover its original setting styling even after 5th water washing and drying. The SEM results indicated that the microsurface of the hair is coated with the polymer membrane; it contributes to the shape memory ability of the coated hair to keep and recover to the original setting styling. The styling hair can return to the original hair because the polyurethane polymer can be washed out by water with suitable strength and shampoo totally which does not leave any flake. The polyurethane polymer-based hair setting agent has been developed successfully, and it could be coated evenly on the human hair with good hand feeling and SMEs. The SME is highly related to the quantity of polyurethane polymer solution, and the effect could be improved by increasing the solution quantity. The maximum deformation of the coated hair could be recovered 94% at 75°C, once its shape is changed by an external force. The treated hair can withstand warm water rinsing for at least five cycles, and it can keep 65% of its original setting style after water rinsing. The polyurethane polymer could be totally removed by shampooing the hair and hot towel covering for 5-10 min. This research provides an effective way for the development of new intelligent shaping agents. © 2015 Society of Cosmetic Scientists and the Société Française de Cosmétologie.

A Rotary Microactuator Supported on Encapsulated Microball Bearings using an Electro-Pneumatic Thrust Balance

DTIC Science & Technology

2009-01-01

Additionally, high-speed air bearings have been demonstrated in micromotors (55 000 rpm) and micro-turbomachinery (2 million rpm) [7, 8]. While...without thrust balances [11]. For applications requiring continuous rotation ( micromotors and micropumps) this hydrostatic balancing force can be...conditions for stable actuation of the micromotor leading to maximum speeds. In addition to increased speed, this device demonstrates a substantial

A Vertical Organic Transistor Architecture for Fast Nonvolatile Memory.

PubMed

She, Xiao-Jian; Gustafsson, David; Sirringhaus, Henning

2017-02-01

A new device architecture for fast organic transistor memory is developed, based on a vertical organic transistor configuration incorporating high-performance ambipolar conjugated polymers and unipolar small molecules as the transport layers, to achieve reliable and fast programming and erasing of the threshold voltage shift in less than 200 ns. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Surface Control of Cold Hibernated Elastic Memory Self-Deployable Structure

NASA Technical Reports Server (NTRS)

Sokolowski, Witold M.; Ghaffarian, Reza

2006-01-01

A new class of simple, reliable, lightweight, low packaging volume and cost, self-deployable structures has been developed for use in space and commercial applications. This technology called 'cold hibernated elastic memory' (CHEM) utilizes shape memory polymers (SMP)in open cellular (foam) structure or sandwich structures made of shape memory polymer foam cores and polymeric composite skins. Some of many potential CHEM space applications require a high precision deployment and surface accuracy during operation. However, a CHEM structure could be slightly distorted by the thermo-mechanical processing as well as by thermal space environment Therefore, the sensor system is desirable to monitor and correct the potential surface imperfection. During these studies, the surface control of CHEM smart structures was demonstrated using a Macro-Fiber Composite (MFC) actuator developed by the NASA LaRC and US Army ARL. The test results indicate that the MFC actuator performed well before and after processing cycles. It reduced some residue compressive strain that in turn corrected very small shape distortion after each processing cycle. The integrated precision strain gages were detecting only a small flat shape imperfection indicating a good recoverability of original shape of the CHEM test structure.

Biodegradable polydepsipeptides.

PubMed

Feng, Yakai; Guo, Jintang

2009-02-01

This paper reviews the synthesis, characterization, biodegradation and usage of bioresorbable polymers based on polydepsipeptides. The ring-opening polymerization of morpholine-2,5-dione derivatives using organic Sn and enzyme lipase is discussed. The dependence of the macroscopic properties of the block copolymers on their structure is also presented. Bioresorbable polymers based on polydepsipeptides could be used as biomaterials in drug controlled release, tissue engineering scaffolding and shape-memory materials.

Memory Device and Nanofabrication Techniques Using Electrically Configurable Materials

NASA Astrophysics Data System (ADS)

Ascenso Simões, Bruno

Development of novel nanofabrication techniques and single-walled carbon nanotubes field configurable transistor (SWCNT-FCT) memory devices using electrically configurable materials is presented. A novel lithographic technique, electric lithography (EL), that uses electric field for pattern generation has been demonstrated. It can be used for patterning of biomolecules on a polymer surface and patterning of resist as well. Using electrical resist composed of a polymer having Boc protected amine group and iodonium salt, Boc group on the surface of polymer was modified to free amine by applying an electric field. On the modified surface of the polymer, Streptavidin pattern was fabricated with a sub-micron scale. Also patterning of polymer resin composed of epoxy monomers and diaryl iodonium salt by EL has been demonstrated. Reaction mechanism for electric resist configuration is believed to be induced by an acid generation via electrochemical reduction in the resist. We show a novel field configurable transistor (FCT) based on single-walled carbon nanotube network field-effect transistors in which poly (ethylene glycol) crosslinked by electron-beam is incorporated into the gate. The device conductance can be configured to arbitrary states reversibly and repeatedly by applying external gate voltages. Raman spectroscopy revealed that evolution of the ratio of D- to G-band intensity in the SWCNTs of the FCT progressively increases as the device is configured to lower conductance states. Electron transport studies at low temperatures showed a strong temperature dependence of the resistance. Band gap widening of CNTs up to ˜ 4 eV has been observed by examining the differential conductance-gate voltage-bias voltage relationship. The switching mechanism of the FCT is attributed a structural transformation of CNTs via reversible hydrogenation and dehydrogenations induced by gate voltages, which tunes the CNT bandgap continuously and reversibly to non-volatile analog values. The CNT transistors with field tunable band gaps would facilitate field programmable circuits based on the self-organized CNTs, and might also lead to novel analog memory, neuromorphic, and photonic devices.

High-Temperature Shape Memory Polymers

NASA Technical Reports Server (NTRS)

Yoonessi, Mitra; Weiss, Robert A.

2012-01-01

physical conformation changes when exposed to an external stimulus, such as a change in temperature. Such materials have a permanent shape, but can be reshaped above a critical temperature and fixed into a temporary shape when cooled under stress to below the critical temperature. When reheated above the critical temperature (Tc, also sometimes called the triggering or switching temperature), the materials revert to the permanent shape. The current innovation involves a chemically treated (sulfonated, carboxylated, phosphonated, or other polar function group), high-temperature, semicrystalline thermoplastic poly(ether ether ketone) (Tg .140 C, Tm = 340 C) mix containing organometallic complexes (Zn++, Li+, or other metal, ammonium, or phosphonium salts), or high-temperature ionic liquids (e.g. hexafluorosilicate salt with 1-propyl-3- methyl imidazolium, Tm = 210 C) to form a network where dipolar or ionic interactions between the polymer and the low-molecular-weight or inorganic compound forms a complex that provides a physical crosslink. Hereafter, these compounds will be referred to as "additives". The polymer is semicrystalline, and the high-melt-point crystals provide a temporary crosslink that acts as a permanent crosslink just so long as the melting temperature is not exceeded. In this example case, the melting point is .340 C, and the shape memory critical temperature is between 150 and 250 C. PEEK is an engineering thermoplastic with a high Young fs modulus, nominally 3.6 GPa. An important aspect of the invention is the control of the PEEK functionalization (in this example, the sulfonation degree), and the thermal properties (i.e. melting point) of the additive, which determines the switching temperature. Because the compound is thermoplastic, it can be formed into the "permanent" shape by conventional plastics processing operations. In addition, the compound may be covalently cross - linked after forming the permanent shape by S-PEEK by applying ionizing radiation ( radiation, neutrons), or by chemical crosslinking to form a covalent permanent network. With respect to other shape memory polymers, this invention is novel in that it describes the use of a thermoplastic composition that can be thermally molded or solution-cast into complex "permanent" shapes, and then reheated or redissolved and recast from solution to prepare another shape. It is also unique in that the shape memory behavior is provided by a non-polymer additive.

Self-healing nanocomposite using shape memory polymer and carbon nanotubes

NASA Astrophysics Data System (ADS)

Liu, Yingtao; Rajadas, Abhishek; Chattopadhyay, Aditi

2013-04-01

Carbon fiber reinforced composites are used in a wide range of applications in aerospace, mechanical, and civil structures. Due to the nature of material, most damage in composites, such as delaminations, are always barely visible to the naked eye, which makes it difficult to detect and repair. The investigation of biological systems has inspired the development and characterization of self-healing composites. This paper presents the development of a new type of self-healing material in order to impede damage progression and conduct in-situ damage repair in composite structures. Carbon nanotubes, which are highly conductive materials, are mixed with shape memory polymer to develop self-healing capability. The developed polymeric material is applied to carbon fiber reinforced composites to automatically heal the delamination between different layers. The carbon fiber reinforced composite laminates are manufactured using high pressure molding techniques. Tensile loading is applied to double cantilever beam specimens using an MTS hydraulic test frame. A direct current power source is used to generate heat within the damaged area. The application of thermal energy leads to re-crosslinking in shape memory polymers. Experimental results showed that the developed composite materials are capable of healing the matrix cracks and delaminations in the bonded areas of the test specimens. The developed self-healing material has the potential to be used as a novel structural material in mechanical, civil, aerospace applications.

Tuning the Electrical Memory Behavior from Nonvolatile to Volatile in Functional Copolyimides Bearing Varied Fluorene and Pyrene Moieties

NASA Astrophysics Data System (ADS)

Jia, Nanfang; Qi, Shengli; Tian, Guofeng; Wang, Xiaodong; Wu, Dezhen

2017-04-01

For producing polymer based electronics with good memory behavior, a series of functional copolyimides were designed and synthesized in this work by copolymerizing 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride (DSDA) with (9,9'-bis(4-aminophenyl)fluorene) (BAPF) and N, N-bis(4-aminophenyl) aminopyrene (DAPAP) diamines. The synthesized copolyimides DSDA/(DAPAP/BAPF) were denoted as coPI-DAPAP x ( x = 100, 50, 20, 10, 5, 1, 0), where x% represents the molar fraction of the DAPAP unit in the diamines. Characterization results indicate that the coPI-DAPAP x exhibits tunable electrical switching behaviors from write once read many times (WORM, nonvolatile, coPI-DAPAP100, coPI-DAPAP50, coPI-DAPAP20, coPI-DAPAP10) to the static random access memory (SRAM, volatile, coPI-DAPAP5, coPI-DAPAP1) with the variation of the DAPAP content. Optical and electrochemical characterization show gradually decreasing highest occupied molecular orbital levels and enlarged energy gap with the decrease of the DAPAP moiety, suggesting decreasing charge-transfer effect in the copolyimides, which can account for the observed WORM-SRAM memory conversion. Meanwhile, the charge transfer process was elucidated by quantum chemical calculation at B3LYP/6-31G(d) theory level. This work shows the effect of electron donor content on the memory behavior of polymer electronic materials.

Release mechanism utilizing shape memory polymer material

DOEpatents

Lee, Abraham P.; Northrup, M. Allen; Ciarlo, Dino R.; Krulevitch, Peter A.; Benett, William J.

2000-01-01

Microfabricated therapeutic actuators are fabricated using a shape memory polymer (SMP), a polyurethane-based material that undergoes a phase transformation at a specified temperature (Tg). At a temperature above temperature Tg material is soft and can be easily reshaped into another configuration. As the temperature is lowered below temperature Tg the new shape is fixed and locked in as long as the material stays below temperature Tg. Upon reheating the material to a temperature above Tg, the material will return to its original shape. By the use of such SMP material, SMP microtubing can be used as a release actuator for the delivery of embolic coils through catheters into aneurysms, for example. The microtubing can be manufactured in various sizes and the phase change temperature Tg is determinate for an intended temperature target and intended use.

Electrokinetic Microactuator Arrays for Control of Vehicles

DTIC Science & Technology

2002-08-01

programmable logic array (PLA) content in each unit cell....................46 Chapter 4 4.1 Schematic showing electroosmotic flow induced by an...control situations involved in propulsion systems, spanning from con- trol of mixing in advanced gas turbine combustors, to active control of surge and... electroosmotic flow, shown schematically in Fig. 4.1, results when an electric field is applied to a liquid electrolyte in contact with a charged solid

Fabrication of an electromagnetic actuator with the planar coil

NASA Astrophysics Data System (ADS)

Jeong, HyunKu; Jeong, OkChan; Yang, Sang S.

2000-06-01

This paper first presents the fabrication of an electromagnetic microactuator using an electroplated spiral copper coil on a parylene C diaphragm. The parylene is a bio-compatible material and has a very low Young's modulus less than 2.8 Gpa, which makes the large deflection for the low power consumption. The actuator consists of an electroplated coil on the parylene C diaphragm, a small-size permanent magnet and a core. The diaphragm is actuated by the Lorenz force generated by the current through the coil in the magnetic field of the magnet. The size of the actuator diaphragm is 4 by 4 mm2 and 5 micrometers thick. The resistance and inductance of the copper spiral coil are 2 (Omega) and 11 (mu) H at 100 Hz, respectively. The center deflection of the actuator diaphragm is measured with the laser vibrometer. Whenthe current through the coil is 380 mA, the peak-to-peak deflection of the actuator is 143 micrometers below the resonant frequency of 35 Hz. The mechanical sensitivity of the actuator diaphragm is 900 micrometers /A at 10 Hz and 35 Hz, respectively. An electromagnetic microactuator using the electroplated copper coil on the parylene diaphragm is expected to be useful in making a micropump for the bio-medical use.

High-Temperature Shape Memory Behavior of Semicrystalline Polyamide Thermosets.

PubMed

Li, Ming; Guan, Qingbao; Dingemans, Theo J

2018-05-21

We have explored semicrystalline poly(decamethylene terephthalamide) (PA 10T) based thermosets as single-component high-temperature (>200 °C) shape memory polymers (SMPs). The PA 10T thermosets were prepared from reactive thermoplastic precursors. Reactive phenylethynyl (PE) functionalities were either attached at the chain termini or placed as side groups along the polymer main chain. The shape fixation and recovery performance of the thermoset films were investigated using a rheometer in torsion mode. By controlling the M n of the reactive oligomers, or the PE concentration of the PE side-group functionalized copolyamides, we were able to design dual-shape memory PA 10T thermosets with a broad recovery temperature range of 227-285 °C. The thermosets based on the 1000 g mol -1 reactive PE precursor and the copolyamide with 15 mol % PE side groups show the highest fixation rate (99%) and recovery rate (≥90%). High temperature triple-shape memory behavior can be achieved as well when we use the melt transition ( T m ≥ 200 °C) and the glass transition ( T g = ∼125 °C) as the two switches. The recovery rate of the two recovery steps are highly dependent on the crystallinity of the thermosets and vary within a wide range of 74%-139% and 40-82% for the two steps, respectively. Reversible shape memory events could also be demonstrated when we perform a forward and backward deformation in a triple shape memory cycle. We also studied the angular recovery velocity as a function of temperature, which provides a thermokinematic picture of the shape recovery process and helps to program for desired shape memory behavior.

High-Temperature Shape Memory Behavior of Semicrystalline Polyamide Thermosets

PubMed Central

2018-01-01

We have explored semicrystalline poly(decamethylene terephthalamide) (PA 10T) based thermosets as single-component high-temperature (>200 °C) shape memory polymers (SMPs). The PA 10T thermosets were prepared from reactive thermoplastic precursors. Reactive phenylethynyl (PE) functionalities were either attached at the chain termini or placed as side groups along the polymer main chain. The shape fixation and recovery performance of the thermoset films were investigated using a rheometer in torsion mode. By controlling the Mn of the reactive oligomers, or the PE concentration of the PE side-group functionalized copolyamides, we were able to design dual-shape memory PA 10T thermosets with a broad recovery temperature range of 227–285 °C. The thermosets based on the 1000 g mol–1 reactive PE precursor and the copolyamide with 15 mol % PE side groups show the highest fixation rate (99%) and recovery rate (≥90%). High temperature triple-shape memory behavior can be achieved as well when we use the melt transition (Tm ≥ 200 °C) and the glass transition (Tg = ∼125 °C) as the two switches. The recovery rate of the two recovery steps are highly dependent on the crystallinity of the thermosets and vary within a wide range of 74%–139% and 40–82% for the two steps, respectively. Reversible shape memory events could also be demonstrated when we perform a forward and backward deformation in a triple shape memory cycle. We also studied the angular recovery velocity as a function of temperature, which provides a thermokinematic picture of the shape recovery process and helps to program for desired shape memory behavior. PMID:29742899

The impact of shape memory test on degradation profile of a bioresorbable polymer.

PubMed

Musioł, Marta; Jurczyk, Sebastian; Kwiecień, Michał; Smola-Dmochowska, Anna; Domański, Marian; Janeczek, Henryk; Włodarczyk, Jakub; Klim, Magdalena; Rydz, Joanna; Kawalec, Michał; Sobota, Michał

2018-05-01

The semicrystalline poly(L-lactide) (PLLA) belongs to the materials with shape memory effect (SME) and as a bioresorbable and biocompatible polymer it have found many applications in medical and pharmaceutical field. Assessment of the SME impact on the polymer degradation profile plays crucial role in applications such as drug release systems or in regenerative medicine. Herein, the results of in vitro degradation studies of PLLA samples after SME full test cycle are presented. The samples were loaded and deformed in two manners: progressive and non-progressive. The performed experiments illustrate also influence of the material mechanical damages, caused e.g. during incorrect implantation of PLLA product, on hydrolytic degradation profile. Apparently, degradation profiles are significantly different for the material which was not subjected to the deformation and the deformed ones. The materials after deformation of 50% (in SME cycle) was characterized by non-reversible morphology changes. The effect was observed in deformed samples during the SME test which were carried out ten times. Copyright © 2018 Elsevier Ltd. All rights reserved.

Advancing reversible shape memory by tuning the polymer network architecture

DOE PAGES

Li, Qiaoxi; Zhou, Jing; Vatankhah-Varnoosfaderani, Mohammad; ...

2016-02-02

Because of counteraction of a chemical network and a crystalline scaffold, semicrystalline polymer networks exhibit a peculiar behavior—reversible shape memory (RSM), which occurs naturally without applying any external force and particular structural design. There are three RSM properties: (i) range of reversible strain, (ii) rate of strain recovery, and (iii) decay of reversibility with time, which can be improved by tuning the architecture of the polymer network. Different types of poly(octylene adipate) networks were synthesized, allowing for control of cross-link density and network topology, including randomly cross-linked network by free-radical polymerization, thiol–ene clicked network with enhanced mesh uniformity, and loosemore » network with deliberately incorporated dangling chains. It is shown that the RSM properties are controlled by average cross-link density and crystal size, whereas topology of a network greatly affects its extensibility. In conclusion, we have achieved 80% maximum reversible range, 15% minimal decrease in reversibility, and fast strain recovery rate up to 0.05 K –1, i.e., ca. 5% per 10 s at a cooling rate of 5 K/min.« less

Transition state analogue imprinted polymers as artificial amidases for amino acid p-nitroanilides: morphological effects of polymer network on catalytic efficiency.

PubMed

Mathew, Divya; Thomas, Benny; Devaky, K S

2017-11-13

The morphology of the polymer network - porous/less porous - plays predominant role in the amidase activities of the polymer catalysts in the hydrolytic reactions of amino acid p-nitroanilides. Polymers with the imprints of stable phosphonate analogue of the intermediate of hydrolytic reactions were synthesized as enzyme mimics. Molecular imprinting was carried out in thermodynamically stable porogen dimethyl sulphoxide and unstable porogen chloroform, to investigate the morphological effects of polymers on catalytic amidolysis. It was found that the medium of polymerization has vital influence in the amidase activities of the enzyme mimics. The morphological studies of the polymer catalysts were carried out by scanning electron microscopy and Bruner-Emmett-Teller analysis. The morphology of the polymer catalysts and their amidase activities are found to be dependent on the composition of reaction medium. The polymer catalyst prepared in dimethyl sulphoxide is observed to be efficient in 1:9 acetonitrile (ACN)-Tris HCl buffer and that prepared in chloroform is noticed to be stereo specifically and shape-selectively effective in 9:1 ACN-Tris HCl buffer. The solvent memory effect in catalytic amidolysis was investigated using the polymer prepared in acetonitrile.

Multi-shape memory polymers achieved by the spatio-assembly of 3D printable thermoplastic building blocks.

PubMed

Li, Hongze; Gao, Xiang; Luo, Yingwu

2016-04-07

Multi-shape memory polymers were prepared by the macroscale spatio-assembly of building blocks in this work. The building blocks were methyl acrylate-co-styrene (MA-co-St) copolymers, which have the St-block-(St-random-MA)-block-St tri-block chain sequence. This design ensures that their transition temperatures can be adjusted over a wide range by varying the composition of the middle block. The two St blocks at the chain ends can generate a crosslink network in the final device to achieve strong bonding force between building blocks and the shape memory capacity. Due to their thermoplastic properties, 3D printing was employed for the spatio-assembly to build devices. This method is capable of introducing many transition phases into one device and preparing complicated shapes via 3D printing. The device can perform a complex action via a series of shape changes. Besides, this method can avoid the difficult programing of a series of temporary shapes. The control of intermediate temporary shapes was realized via programing the shapes and locations of building blocks in the final device.

Biosmart Materials: Breaking New Ground in Dentistry

PubMed Central

Badami, Vijetha; Ahuja, Bharat

2014-01-01

By definition and general agreement, smart materials are materials that have properties which may be altered in a controlled fashion by stimuli, such as stress, temperature, moisture, pH, and electric or magnetic fields. There are numerous types of smart materials, some of which are already common. Examples include piezoelectric materials, which produce a voltage when stress is applied or vice versa, shape memory alloys or shape memory polymers which are thermoresponsive, and pH sensitive polymers which swell or shrink as a response to change in pH. Thus, smart materials respond to stimuli by altering one or more of their properties. Smart behaviour occurs when a material can sense some stimulus from its environment and react to it in a useful, reliable, reproducible, and usually reversible manner. These properties have a beneficial application in various fields including dentistry. Shape memory alloys, zirconia, and smartseal are examples of materials exhibiting a smart behavior in dentistry. There is a strong trend in material science to develop and apply these intelligent materials. These materials would potentially allow new and groundbreaking dental therapies with a significantly enhanced clinical outcome of treatments. PMID:24672407

Fabrication of a Bioactive, PCL-based "Self-fitting" Shape Memory Polymer Scaffold.

PubMed

Nail, Lindsay N; Zhang, Dawei; Reinhard, Jessica L; Grunlan, Melissa A

2015-10-23

Tissue engineering has been explored as an alternative strategy for the treatment of critical-sized cranio-maxillofacial (CMF) bone defects. Essential to the success of this approach is a scaffold that is able to conformally fit within an irregular defect while also having the requisite biodegradability, pore interconnectivity and bioactivity. By nature of their shape recovery and fixity properties, shape memory polymer (SMP) scaffolds could achieve defect "self-fitting." In this way, following exposure to warm saline (~60 ºC), the SMP scaffold would become malleable, permitting it to be hand-pressed into an irregular defect. Subsequent cooling (~37 ºC) would return the scaffold to its relatively rigid state within the defect. To meet these requirements, this protocol describes the preparation of SMP scaffolds prepared via the photochemical cure of biodegradable polycaprolactone diacrylate (PCL-DA) using a solvent-casting particulate-leaching (SCPL) method. A fused salt template is utilized to achieve pore interconnectivity. To realize bioactivity, a polydopamine coating is applied to the surface of the scaffold pore walls. Characterization of self-fitting and shape memory behaviors, pore interconnectivity and in vitro bioactivity are also described.

Dually actuated triple shape memory polymers of cross-linked polycyclooctene-carbon nanotube/polyethylene nanocomposites.

PubMed

Wang, Zhenwen; Zhao, Jun; Chen, Min; Yang, Minhao; Tang, Luyang; Dang, Zhi-Min; Chen, Fenghua; Huang, Miaoming; Dong, Xia

2014-11-26

In this work, electrically and thermally actuated triple shape memory polymers (SMPs) of chemically cross-linked polycyclooctene (PCO)-multiwalled carbon nanotube (MWCNT)/polyethylene (PE) nanocomposites with co-continuous structure and selective distribution of fillers in PCO phase are prepared. We systematically studied not only the microstructure including morphology and fillers' selective distribution in one phase of the PCO/PE blends, but also the macroscopic properties including thermal, mechanical, and electrical properties. The co-continuous window of the immiscible PCO/PE blends is found to be the volume fraction of PCO (vPCO) of ca. 40-70 vol %. The selective distribution of fillers in one phase of co-continuous blends is obtained by a masterbatch technique. The prepared triple SMP materials show pronounced triple shape memory effects (SMEs) on the dynamic mechanical thermal analysis (DMTA) and the visual observation by both thermal and electric actuations. Such polyolefin samples with well-defined microstructure, electrical actuation, and triple SMEs might have potential applications as, for example, multiple autochoke elements for engines, self-adjusting orthodontic wires, and ophthalmic devices.

Shape memory polymeric composites sensing by optic fibre Bragg gratings: A very first approach

NASA Astrophysics Data System (ADS)

Quadrini, Fabrizio; Santo, Loredana; Ciminello, Monica; Concilio, Antonio; Volponi, Ruggero; Spena, Paola

2016-05-01

Shape memory polymer composites (SMPCs) have the potential for many applications in aerospace, spanning from self-repairing of structures to self-deploying of antennas, solar sails, or functional devices (e.g. for grabbing small space debris). In all these cases, it may be essential to have information about their configuration at different stages of shape recovery. In this study, the strain history of a prepreg carbon fibre system, cured with a shape memory polymer (SMP) interlayer, is monitored through a Fibre Bragg Grating (FBG), a fibre optic sensor device. SMPC has been manufactured by using traditional technologies for aerospace. After manufacturing cylindrical shape samples, an external fibre optic system is added to the composite structure; this system is especially suited for high temperatures which are necessary for SMP recovery and composite softening. Sensor functionality is checked before and after each strain history path. Optic fibre arrangement is optimized to avoid unwanted breakings whereas strains are limited by fibre collapsing, i.e. within nominal 2% of deformation. Dynamic information about shape recovery gives fundamental insights about strain evolution during time as well as its spatial distribution.

Formation of holographic memory for optically reconfigurable gate array by angle-multiplexing recording of multi-circuit information in liquid crystal composites

NASA Astrophysics Data System (ADS)

Ogiwara, Akifumi; Maekawa, Hikaru; Watanabe, Minoru; Moriwaki, Retsu

2014-02-01

A holographic polymer-dispersed liquid crystal (HPDLC) memory to record multi-context information for an optically reconfigurable gate array is formed by the angle-multiplexing recording using a successive laser exposure in liquid crystal (LC) composites. The laser illumination system is constructed using the half mirror and photomask written by the different configuration contexts placed on the motorized stages under the control of a personal computer. The fabricated holographic memory implements a precise reconstruction of configuration contexts corresponding to the various logical circuits such as OR circuit and NOR circuit by the laser illumination at different incident angle in the HPDLC memory.

Fabrication and Electromechanical Performance of a Novel High Modulus Ionogen Micro-Actuator

DTIC Science & Technology

2011-09-01

are molten organic salts . Due to their high ionic conductivity and large electrochemical potential window (up to 5.7 V between platinium electrodes...13402 Gokhan Hatipoglu/ Procedia Engineering 00 (2011) 000–000 ILs are widely used in applications such as lithium batteries [2], dye synthesized solar...aliphatic onium cations and asymmetric amide anions and their electrochemical properties as a lithium battery electrolyte. Journal of Power Sources, 2005

Mechanical Adaptivity as a Process: Implications to New Materials and Material System Design

DTIC Science & Technology

2012-08-01

Deliver. Rev. 2004 Microactuators and valves Uses: • Drug delivery • Microfluidic actuators, valves , and pumps • Chemical and biological Sensors... paper where they did a study with f the stoichiometric parameter involved in the reduction step, and they looked at 2 X* - both far away from the...through strain? How do varying material properties affect behavior? Smith, Vaia et al. submitted 2012 23 Fibrous Paper Next Step: Heterogeneous

Preparation and characterization of shape memory polymer scaffolds via solvent casting/particulate leaching.

PubMed

De Nardo, Luigi; Bertoldi, Serena; Cigada, Alberto; Tanzi, Maria Cristina; Haugen, Håvard Jostein; Farè, Silvia

2012-09-27

Porous Shape Memory Polymers (SMPs) are ideal candidates for the fabrication of defect fillers, able to support tissue regeneration via minimally invasive approaches. In this regard, control of pore size, shape and interconnection is required to achieve adequate nutrient transport and cell ingrowth. Here, we assessed the feasibility of the preparation of SMP porous structures and characterized their chemico-physical properties and in vitro cell response. SMP scaffolds were obtained via solvent casting/particulate leaching of gelatin microspheres, prepared via oil/water emulsion. A solution of commercial polyether-urethane (MM-4520, Mitsubishi Heavy Industries) was cast on compacted microspheres and leached-off after polymer solvent evaporation. The obtained structures were characterized in terms of morphology (SEM and micro-CT), thermo-mechanical properties (DMTA), shape recovery behavior in compression mode, and in vitro cytocompatibility (MG63 Osteoblast-like cell line). The fabrication process enabled easy control of scaffold morphology, pore size, and pore shape by varying the gelatin microsphere morphology. Homogeneous spherical and interconnected pores have been achieved together with the preservation of shape memory ability, with recovery rate up to 90%. Regardless of pore dimensions, MG63 cells were observed adhering and spreading onto the inner surface of the scaffolds obtained for up to seven days of static in vitro tests. A new class of SMP porous structures has been obtained and tested in vitro: according to these preliminary results reported, SMP scaffolds can be further exploited in the design of a new class of implantable devices.

Biomedical applications of thermally activated shape memory polymers†

PubMed Central

Small, Ward; Singhal, Pooja; Wilson, Thomas S.

2011-01-01

Shape memory polymers (SMPs) are smart materials that can remember a primary shape and can return to this primary shape from a deformed secondary shape when given an appropriate stimulus. This property allows them to be delivered in a compact form via minimally invasive surgeries in humans, and deployed to achieve complex final shapes. Here we review the various biomedical applications of SMPs and the challenges they face with respect to actuation and biocompatibility. While shape memory behavior has been demonstrated with heat, light and chemical environment, here we focus our discussion on thermally stimulated SMPs. PMID:21258605

Bistable resistive memory behavior in gelatin-CdTe quantum dot composite film

NASA Astrophysics Data System (ADS)

Vallabhapurapu, Sreedevi; Rohom, Ashwini; Chaure, N. B.; Du, Shengzhi; Srinivasan, Ananthakrishnan

2018-05-01

Bistable memory behavior has been observed for the first time in gelatin type A thin film dispersed with functionalized CdTe quantum dots. The two terminal device with the polymer nanocomposite layer sandwiched between an indium tin oxide coated glass plate and an aluminium top electrode performs as a bistable resistive random access memory module. Butterfly shaped (O-shaped with a hysteresis in forward and reverse sweeps) current-voltage response is observed in this device. The conduction mechanism leading to the bistable electrical switching has been deduced to be a combination of ohmic and electron hopping.

Multiblock thermoplastic polyurethanes for biomedical and shape memory applications

NASA Astrophysics Data System (ADS)

Gu, Xinzhu

Polyurethanes are a class of polymers that are capable of tailoring the overall polymer structure and thus final properties by many factors. The great potential in tailoring polymer structures imparts PUs unique mechanical properties and good cytocompatibility, which make them good candidates for many biomedical devices. In this dissertation, three families of multiblock thermoplastic polyurethanes are synthesized and characterized for biomedical and shape memory applications. In the first case described in Chapters 2, 3 and 4, a novel family of multiblock thermoplastic polyurethanes consisting of poly(ɛ-caprolactone) (PCL) and poly(ethylene glycol) (PEG) are presented. These materials were discovered to be very durable, with strain-to-break higher than 1200%. Heat-triggered reversible plasticity shape memory (RPSM) was observed, where the highly deformed samples completely recovered their as-cast shape within one minute when heating above the transition temperature. Instead of conventional "hard" blocks, entanglements, which result from high molecular weight, served as the physical crosslinks in this system, engendering shape recovery and preventing flow. Moreover, water-triggered shape memory effect of PCL-PEG TPUs is explored, wherein water permeated into the initially oriented PEG domains, causing rapid shape recovery toward the equilibrium shape upon contact with liquid water. The recovery behavior is found to be dependent on PEG weight percentage in the copolymers. By changing the material from bulk film to electrospun fibrous mat, recovery speed was greatly accelerated. The rate of water recovery was manipulated through structural variables, including thickness of bulk film and diameter of e-spun webs. A new, yet simple shape memory cycle, "wet-fixing" is also reported, where both the fixing and recovery ratios can be greatly improved. A detailed microstructural study on one particular composition is presented, revealing the evolution of microphase morphology during the shape memory cycle. Then, in Chapter 5, the role of Polyhedral oligosilsesquioxane (POSS) in suppressing enzymatic degradation of PCL-PEG TPUs is investigated. In vitro enzymatic hydrolytic biodegradation revealed that POSS incorporation significantly suppressed degradation of PCL-PEG TPUs. All TPUs were surface-eroded by enzymatic attack in which the chemical composition and the bulk mechanical properties exhibited little changes. A surface passivation mechanism is proposed to explain the protection of POSS-containing TPUs from enzymatic degradation. Finally, Chapter 6 presents another POSS-based TPUs system with PLA-based polyol as the glassy soft block. Manipulation of the final thermal and mechanical properties is discussed in terms of different polyols and POSS used. The free recovery and the constrained recovery responses of the polymer films were demonstrated as a function of the prior "fixing" deformation temperature. In addition, this family of materials was capable of memorizing their T g., where optimal recovery breadth and recovery stress were achieved when pre-deformation occurred right at Tg.

Soft Polymers for Building up Small and Smallest Blood Supplying Systems by Stereolithography

PubMed Central

Meyer, Wolfdietrich; Engelhardt, Sascha; Novosel, Esther; Elling, Burkhard; Wegener, Michael; Krüger, Hartmut

2012-01-01

Synthesis of a homologous series of photo-polymerizable α,ω-polytetrahydrofuranether-diacrylate (PTHF-DA) resins is described with characterization by NMR, GPC, DSC, soaking and rheometrical measurements. The curing speeds of the resins are determined under UV light exposure. Young’s modulus and tensile strength of fully cured resins show flexible to soft material attributes dependent on the molar mass of the used linear PTHF-diacrylates. Structuring the materials by stereo lithography (SL) and multiphoton polymerization (MPP) leads to tubes and bifurcated tube systems with a diameter smaller than 2 mm aimed at small to smallest supplying systems with capillary dimensions. WST-1 biocompatibility tests ofm polymer extracts show nontoxic characteristics of the adapted polymers after a washing process. Some polymers show shape memory effect (SME). PMID:24955530

Supramolecular Polymer Nanocomposites - Improvement of Mechanical Properties

NASA Astrophysics Data System (ADS)

Hinricher, Jesse; Neikirk, Colin; Priestley, Rodney

2015-03-01

Supramolecular polymers differ from traditional polymers in that their repeat units are connected by hydrogen bonds that can reversibly break and form under various stimuli. They can be more easily recycled than conventional materials, and their highly temperature dependent viscosities result in reduced energy consumption and processing costs. Furthermore, judicious selection of supramolecular polymer architecture and functionality allows the design of advanced materials including shape memory and self-healing materials. Supramolecular polymers have yet to see widespread use because they can't support much weight due to their inherent mechanical weakness. In order to address this issue, the mechanical strength of supramolecular polymer nanocomposites based on ureidopyrmidinone (UPy) telechelic poly(caprolactone) doped with surface activated silica nanoparticles was investigated by tensile testing and dynamic mechanical analysis. The effects of varying amounts and types of nanofiller surface functionality were investigated to glean insight into the contributions of filler-filler and filler-matrix interactions to mechanical reinforcement in supramolecular polymer nanocomposites. MRSEC NSF DMR 0819860 (PI: Prof. N. Phuan Ong) REU Site Grant: NSF DMR-1156422 (PI: Prof. Mikko Haataja)

High-strain slide-ring shape-memory polycaprolactone-based polyurethane.

PubMed

Wu, Ruiqing; Lai, Jingjuan; Pan, Yi; Zheng, Zhaohui; Ding, Xiaobin

2018-06-06

To enable shape-memory polymer networks to achieve recoverable high deformability with a simultaneous high shape-fixity ratio and shape-recovery ratio, novel semi-crystalline slide-ring shape-memory polycaprolactone-based polyurethane (SR-SMPCLU) with movable net-points constructed by a topologically interlocked slide-ring structure was designed and fabricated. The SR-SMPCLU not only exhibited good shape fixity, almost complete shape recovery, and a fast shape-recovery speed, it also showed an outstanding recoverable high-strain capacity with 95.83% Rr under a deformation strain of 1410% due to the pulley effect of the topological slide-ring structure. Furthermore, the SR-SMPCLU system maintained excellent shape-memory performance with increasing the training cycle numbers at 45% and even 280% deformation strain. The effects of the slide-ring cross-linker content, deformation strain, and successive shape-memory cycles on the shape-memory performance were investigated. A possible mechanism for the shape-memory effect of the SR-SMPCLU system is proposed.

Electrothermal Microactuators With Peg Drive Improve Performance for Brain Implant Applications

PubMed Central

Anand, Sindhu; Sutanto, Jemmy; Baker, Michael S.; Okandan, Murat; Muthuswamy, Jit

2013-01-01

This paper presents a new actuation scheme for in-plane bidirectional translation of polysilicon microelectrodes. The new Chevron-peg actuation scheme uses microelectromechanical systems (MEMS) based electrothermal microactuators to move microelectrodes for brain implant applications. The design changes were motivated by specific needs identified by the in vivo testing of an earlier generation of MEMS microelectrodes that were actuated by the Chevron-latch type of mechanism. The microelectrodes actuated by the Chevron-peg mechanism discussed here show improved performance in the following key areas: higher force generation capability (111 μN per heat strip compared to 50 μN), reduced power consumption (91 mW compared to 360 mW), and reliable performance with consistent forward and backward movements of microelectrodes. Failure analysis of the Chevron-latch and the Chevron-peg type of actuation schemes showed that the latter is more robust to wear over four million cycles of operation. The parameters for the activation waveforms for Chevron-peg actuators were optimized using statistical analysis. Waveforms with a 1-ms time period and a 1-Hz frequency of operation showed minimal error between the expected and the actual movement of the microelectrodes. The new generation of Chevron-peg actuators and microelectrodes are therefore expected to enhance the longevity and performance of implanted microelectrodes in the brain.  [2011-0341] PMID:24431926

Direct Intracochlear Acoustic Stimulation Using a PZT Microactuator.

PubMed

Luo, Chuan; Omelchenko, Irina; Manson, Robert; Robbins, Carol; Oesterle, Elizabeth C; Cao, Guo Zhong; Shen, I Y; Hume, Clifford R

2015-12-01

Combined electric and acoustic stimulation has proven to be an effective strategy to improve hearing in some cochlear implant users. We describe an acoustic microactuator to directly deliver stimuli to the perilymph in the scala tympani. The 800 µm by 800 µm actuator has a silicon diaphragm driven by a piezoelectric thin film (e.g., lead-zirconium-titanium oxide or PZT). This device could also be used as a component of a bimodal acoustic-electric electrode array. In the current study, we established a guinea pig model to test the actuator for its ability to deliver auditory signals to the cochlea in vivo. The actuator was placed through the round window of the cochlea. Auditory brainstem response (ABR) thresholds, peak latencies, and amplitude growth were calculated for an ear canal speaker versus the intracochlear actuator for tone burst stimuli at 4, 8, 16, and 24 kHz. An ABR was obtained after removal of the probe to assess loss of hearing related to the procedure. In some animals, the temporal bone was harvested for histologic analysis of cochlear damage. We show that the device is capable of stimulating ABRs in vivo with latencies and growth functions comparable to stimulation in the ear canal. Further experiments will be necessary to evaluate the efficiency and safety of this modality in long-term auditory stimulation and its ability to be integrated with conventional cochlear implant arrays. © The Author(s) 2015.

High-resolution inchworm linear motor based on electrostatic twisting microactuators

NASA Astrophysics Data System (ADS)

Kim, Sang-Ho; Hwang, Il-Han; Jo, Kyoung-Woo; Yoon, Eui-Sung; Lee, Jong-Hyun

2005-09-01

A new inchworm micromotor using new electrostatic in-plane twisting microactuators has been designed, fabricated and characterized for nano-resolution manipulators. The proposed twisting mechanism was implemented employing a pair of differential electrostatic actuators with a high stiffness in the driving direction for stable positioning. The electromechanically coupled motion of the voltage-displacement relation was analyzed using a finite element method (FEM), confirming that the twisting actuator makes a tiny step movement efficiently. The proposed actuator was fabricated on a silicon-on-insulator (SOI) wafer with the device footprint of 2.2 × 2.8 mm2, and its nano-stepping characteristics were measured by an optical interferometer consisting of an integrated micromirror and optical fiber. The fabricated inchworm motor showed a minimum step displacement of 5.2 ± 3.8 nm (2σ) and 4.1 ± 2.9 nm (2σ) for cyclic motion in the +y- and the -y-directions, respectively, with the gripping voltage of 15 V and differential voltage of 1 V. As a result, the proposed inchworm micromotor could operate with a stroke of 3 µm and a bi-directional step displacement of less than 10 nm. The step displacement is the smallest value of in-plane-type micromotors so far, and its magnitude was controllable up to 120 nm/cycle by changing the differential voltage.

Pre-stressed piezoelectric bimorph micro-actuators based on machined 40 µm PZT thick films: batch scale fabrication and integration with MEMS

NASA Astrophysics Data System (ADS)

Wilson, S. A.; Jourdain, R. P.; Owens, S.

2010-09-01

The projected force-displacement capability of piezoelectric ceramic films in the 20-50 µm thickness range suggests that they are well suited to many micro-fluidic and micro-pneumatic applications. Furthermore when they are configured as bending actuators and operated at ~ 1 V µm - 1 they do not necessarily conform to the high-voltage, very low-displacement piezoelectric stereotype. Even so they are rarely found today in commercial micro-electromechanical devices, such as micro-pumps and micro-valves, and the main barriers to making them much more widely available would appear to be processing incompatibilities rather than commercial desirability. In particular, the issues associated with integration of these devices into MEMS at the production level are highly significant and they have perhaps received less attention in the mainstream than they deserve. This paper describes a fabrication route based on ultra-precision ceramic machining and full-wafer bonding for cost-effective batch scale production of thick film PZT bimorph micro-actuators and their integration with MEMS. The resulting actuators are pre-stressed (ceramic in compression) which gives them added performance, they are true bimorphs with bi-directional capability and they exhibit full bulk piezoelectric ceramic properties. The devices are designed to integrate with ancillary systems components using transfer-bonding techniques. The work forms part of the European Framework 6 Project 'Q2M—Quality to Micro'.

Current-voltage characteristics of organic semiconductors: Interfacial control between organic layers and electrodes

NASA Astrophysics Data System (ADS)

Kondo, Takeshi

2007-12-01

Current-voltage (I-V) characteristics of organic molecular glasses and solution processable materials embedded between two electrodes were studied to find materials possessing high charge-carrier mobilities and to design organic memory devices. The comparison studies between TOF, FET and SCLC measurements confirm the validity of using analyses of I-V characteristics to determine the mobility of organic semiconductors. Hexaazatrinaphthylene derivatives tri-substituted by electron withdrawing groups were characterized as potential electron transporting molecular glasses. The presence of two isomers has important implications for film morphology and effective mobility. The statistical isomer mixture of hexaazatrinaphthylene derivatized with pentafluoro-phenylmethyl ester is able to form amorphous films, and electron mobilities with the range of 10--2 cm2/Vs are observed in their I-V characteristics. Single-layer organic memory devices consisting of a polymer layer embedded between an Al electrode and ITO modified with Ag nanodots (Ag-NDs) prepared by a solution-based surface assembly demonstrated a potential capability as nonvolatile organic memory device with high ON/OFF switching ratios of 10 4. This level of performance could be achieved by modifying the ITO electrodes with some Ag-NDs that act as trapping sites, reducing the current in the OFF state. Based upon the observed electrical characteristics, the currents of the low-resistance state can be attributed to a tunneling through low-resistance pathways of metal particles originating from the metal top electrode in the organic layer and that the high-resistance state is controlled by charge trapping by the metal particles including Ag-NDs. In an alternative approach, complex films of AgNO3: hexaazatrinaphthylene derivatives were studied as the active layers for all-solution processed and air-stable organic memory devices. Rewritable memory effects were observed in the devices comprised of a thin polymer dielectric layer deposited on the bottom electrode, the complex film, and a conducting polymer film as the top electrode. The electrical characteristics indicate that the accumulation of Ag+ ions at the interface of the complex film and the top electrode may contribute to the switching effect.

PCL-based Shape Memory Polymers with Variable PDMS Soft Segment Lengths

PubMed Central

Zhang, Dawei; Giese, Melissa L.; Prukop, Stacy L.; Grunlan, Melissa A.

2012-01-01

Thermoresponsive shape memory polymers (SMPs) are stimuli-responsive materials that return to their permanent shape from a temporary shape in response to heating. The design of new SMPs which obtain a broader range of properties including mechanical behavior is critical to realize their potential in biomedical as well as industrial and aerospace applications. To tailor the properties of SMPs, “AB networks” comprised of two distinct polymer components have been investigated but are overwhelmingly limited to those in which both components are organic. In this present work, we prepared inorganic-organic SMPs comprised of inorganic polydimethyl-siloxane (PDMS) segments of varying lengths and organic poly(ε-caprolactone) (PCL) segments. PDMS has a particularly low Tg (−125 °C) which makes it a particularly effective soft segment to tailor the mechanical properties of PCL-based SMPs. The SMPs were prepared via the rapid photocure of solutions of diacrylated PCL40-block-PDMSm-block-PCL40 macromers (m = 20, 37, 66 and 130). The resulting inorganic-organic SMP networks exhibited excellent shape fixity and recovery. By changing the PDMS segment length, the thermal, mechanical, and surface properties were systematically altered. PMID:22904597

Silicone Membranes to Inhibit Water Uptake into Thermoset Polyurethane Shape-Memory Polymer Conductive Composites

PubMed Central

Yu, Ya-Jen; Infanger, Stephen; Grunlan, Melissa A.; Maitland, Duncan J.

2014-01-01

Electroactive shape memory polymer (SMP) composites capable of shape actuation via resistive heating are of interest for various biomedical applications. However, water uptake into SMPs will produce a depression of the glass transition temperature (Tg) resulting in shape recovery in vivo. While water actuated shape recovery may be useful, it is foreseen to be undesirable during early periods of surgical placement into the body. Silicone membranes have been previously reported to prevent release of conductive filler from an electroactive polymer composite in vivo. In this study, a silicone membrane was used to inhibit water uptake into a thermoset SMP composite containing conductive filler. Thermoset polyurethane (PU) SMPs were loaded with either 5 wt% carbon black (CB) or 5 wt% carbon nanotubes (CNT) and subsequently coated with either an Al2O3- or silica-filled silicone membrane. It was observed that the silicone membranes, particularly the silica-filled membrane, reduced the rate of water absorption (37 °C) and subsequent Tg depression versus uncoated composites. In turn, this led to a reduction in the rate of recovery of the permanent shape when exposed to water at 37 °C. PMID:25663711

Silicone Membranes to Inhibit Water Uptake into Thermoset Polyurethane Shape-Memory Polymer Conductive Composites.

PubMed

Yu, Ya-Jen; Infanger, Stephen; Grunlan, Melissa A; Maitland, Duncan J

2015-01-05

Electroactive shape memory polymer (SMP) composites capable of shape actuation via resistive heating are of interest for various biomedical applications. However, water uptake into SMPs will produce a depression of the glass transition temperature ( T g ) resulting in shape recovery in vivo . While water actuated shape recovery may be useful, it is foreseen to be undesirable during early periods of surgical placement into the body. Silicone membranes have been previously reported to prevent release of conductive filler from an electroactive polymer composite in vivo . In this study, a silicone membrane was used to inhibit water uptake into a thermoset SMP composite containing conductive filler. Thermoset polyurethane (PU) SMPs were loaded with either 5 wt% carbon black (CB) or 5 wt% carbon nanotubes (CNT) and subsequently coated with either an Al 2 O 3 - or silica-filled silicone membrane. It was observed that the silicone membranes, particularly the silica-filled membrane, reduced the rate of water absorption (37 °C) and subsequent T g depression versus uncoated composites. In turn, this led to a reduction in the rate of recovery of the permanent shape when exposed to water at 37 °C.

Shape Recovery with Concomitant Mechanical Strengthening of Amphiphilic Shape Memory Polymers in Warm Water

DOE PAGES

Zhang, Ben; DeBartolo, Janae E.; Song, Jie

2017-01-26

Maintaining adequate or enhancing mechanical properties of shape memory polymers (SMPs) after shape recovery in an aqueous environment are greatly desired for biomedical applications of SMPs as self-fitting tissue scaffolds or minimally invasive surgical implants. Here we report stable temporary shape fixing and facile shape recovery of biodegradable triblock amphiphilic SMPs containing a poly(ethylene glycol) (PEG) center block and flanking poly(lactic acid) or poly(lactic-co-glycolic acid) blocks in warm water, accompanied with concomitant enhanced mechanical strengths. Differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WXRD) and small-angle X-ray scattering (SAXS) analyses revealed that the unique stiffening of the amphiphilic SMPs upon hydrationmore » was due to hydration-driven microphase separation and PEG crystallization. We further demonstrated that the chemical composition of degradable blocks in these SMPs could be tailored to affect the persistence of hydration-induced stiffening upon subsequent dehydration. These properties combined open new horizons for these amphiphilic SMPs for smart weight-bearing in vivo applications (e.g. as self-fitting intervertebral discs). In conclusion, this study also provides a new material design strategy to strengthen polymers in aqueous environment in general.« less

Mechanical and Infrared Thermography Analysis of Shape Memory Polyurethane

NASA Astrophysics Data System (ADS)

Pieczyska, Elzbieta Alicja; Maj, Michal; Kowalczyk-Gajewska, Katarzyna; Staszczak, Maria; Urbanski, Leszek; Tobushi, Hisaaki; Hayashi, Shunichi; Cristea, Mariana

2014-07-01

Multifunctional new material—polyurethane shape memory polymer (PU-SMP)—was subjected to tension carried out at room temperature at various strain rates. The influence of effects of thermomechanical couplings on the SMP mechanical properties was studied, based on the sample temperature changes, measured by a fast and sensitive infrared camera. It was found that the polymer deformation process strongly depends on the strain rate applied. The initial reversible strain is accompanied by a small drop in temperature, called thermoelastic effect. Its maximal value is related to the SMP yield point and increases upon increase of the strain rate. At higher strains, the stress and temperature significantly increase, caused by reorientation of the polymer molecular chains, followed by the stress drop and its subsequent increase accompanying the sample rupture. The higher strain rate, the higher stress, and temperature changes were obtained, since the deformation process was more dynamic and has occurred in almost adiabatic conditions. The constitutive model of SMP valid in finite strain regime was developed. In the proposed approach, SMP is described as a two-phase material composed of hyperelastic rubbery phase and elastic-viscoplastic glassy phase, while the volume content of phases is specified by the current temperature.

Silicone membranes to inhibit water uptake into thermoset polyurethane shape-memory polymer conductive composites

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

Yu, Ya-Jen; Infanger, Stephen; Grunlan, Melissa A.

Electroactive shape memory polymer (SMP) composites capable of shape actuation via resistive heating are of interest for various biomedical applications. However, water uptake into SMPs will produce a depression of the glass transition temperature (T g) resulting in shape recovery in vivo. While water actuated shape recovery may be useful, it is foreseen to be undesirable during early periods of surgical placement into the body. Silicone membranes have been previously reported to prevent release of conductive filler from an electroactive polymer composite in vivo. In this paper, a silicone membrane was used to inhibit water uptake into a thermoset SMPmore » composite containing conductive filler. Thermoset polyurethane SMPs were loaded with either 5 wt % carbon black or 5 wt % carbon nanotubes, and subsequently coated with either an Al 2O 3- or silica-filled silicone membrane. It was observed that the silicone membranes, particularly the silica-filled membrane, reduced the rate of water absorption (37°C) and subsequent T g depression versus uncoated composites. Finally, in turn, this led to a reduction in the rate of recovery of the permanent shape when exposed to water at 37°C.« less

Silicone membranes to inhibit water uptake into thermoset polyurethane shape-memory polymer conductive composites

DOE PAGES

Yu, Ya-Jen; Infanger, Stephen; Grunlan, Melissa A.; ...

2014-07-24

Electroactive shape memory polymer (SMP) composites capable of shape actuation via resistive heating are of interest for various biomedical applications. However, water uptake into SMPs will produce a depression of the glass transition temperature (T g) resulting in shape recovery in vivo. While water actuated shape recovery may be useful, it is foreseen to be undesirable during early periods of surgical placement into the body. Silicone membranes have been previously reported to prevent release of conductive filler from an electroactive polymer composite in vivo. In this paper, a silicone membrane was used to inhibit water uptake into a thermoset SMPmore » composite containing conductive filler. Thermoset polyurethane SMPs were loaded with either 5 wt % carbon black or 5 wt % carbon nanotubes, and subsequently coated with either an Al 2O 3- or silica-filled silicone membrane. It was observed that the silicone membranes, particularly the silica-filled membrane, reduced the rate of water absorption (37°C) and subsequent T g depression versus uncoated composites. Finally, in turn, this led to a reduction in the rate of recovery of the permanent shape when exposed to water at 37°C.« less

Revealing the glass transition in shape memory polymers using Brillouin spectroscopy.

PubMed

Steelman, Zachary A; Weems, Andrew C; Traverso, Andrew J; Szafron, Jason M; Maitland, Duncan J; Yakovlev, Vladislav V

2017-12-11

Emerging medical devices which employ shape memory polymers (SMPs) require precise measurements of the glass transition temperature (T g ) to ensure highly controlled shape recovery kinetics. Conventional techniques like differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) have limitations that prevent utilization for certain devices, including limited accuracy and the need for sacrificial samples. In this report, we employ an approach based on Brillouin spectroscopy to probe the glass transition of SMPs rapidly, remotely, and nondestructively. Further, we compare the T g obtained from Brillouin scattering with DMA- and DSC-measured T g to demonstrate the accuracy of Brillouin scattering for this application. We conclude that Brillouin spectroscopy is an accurate technique for obtaining the glass transition temperature of SMPs, aligning closely with the most common laboratory standards while providing a rapid, remote, and nondestructive method for the analysis of unique polymeric medical devices.

A constitutive theory for shape memory polymers: coupling of small and large deformation

NASA Astrophysics Data System (ADS)

Tan, Qiao; Liu, Liwu; Liu, Yanju; Leng, Jinsong; Yan, Xiangqiao; Wang, Haifang

2013-04-01

At high temperatures, SMPs share attributes like rubber and exhibit long-range reversibility. In contrast, at low temperatures they become very rigid and are susceptible to plastic, only small strains are allowable. But there relatively little literature has considered the unique small stain (rubber phase) and large stain (glass phase) coupling in SMPs when developing the constitutive modeling. In this work, we present a 3D constitutive model for shape memory polymers in both low temperature small strain regime and high temperature large strain regime. The theory is based on the work of Liu et al. [15]. Four steps of SMP's thermomechanical loadings cycle are considered in the constitutive model completely. The linear elastic and hyperelastic effects of SMP in different temperatures are also fully accounted for in the proposed model by adopt the neo-Hookean model and the Generalized Hooke's laws.

Development of high shrinkage polyethylene terephthalate (PET) shape memory polymer tendons for concrete crack closure

NASA Astrophysics Data System (ADS)

Teall, Oliver; Pilegis, Martins; Sweeney, John; Gough, Tim; Thompson, Glen; Jefferson, Anthony; Lark, Robert; Gardner, Diane

2017-04-01

The shrinkage force exerted by restrained shape memory polymers (SMPs) can potentially be used to close cracks in structural concrete. This paper describes the physical processing and experimental work undertaken to develop high shrinkage die-drawn polyethylene terephthalate (PET) SMP tendons for use within a crack closure system. The extrusion and die-drawing procedure used to manufacture a series of PET tendon samples is described. The results from a set of restrained shrinkage tests, undertaken at differing activation temperatures, are also presented along with the mechanical properties of the most promising samples. The stress developed within the tendons is found to be related to the activation temperature, the cross-sectional area and to the draw rate used during manufacture. Comparisons with commercially-available PET strip samples used in previous research are made, demonstrating an increase in restrained shrinkage stress by a factor of two for manufactured PET filament samples.

Revealing the glass transition in shape memory polymers using Brillouin spectroscopy

NASA Astrophysics Data System (ADS)

Steelman, Zachary A.; Weems, Andrew C.; Traverso, Andrew J.; Szafron, Jason M.; Maitland, Duncan J.; Yakovlev, Vladislav V.

2017-12-01

Emerging medical devices which employ shape memory polymers (SMPs) require precise measurements of the glass transition temperature (Tg) to ensure highly controlled shape recovery kinetics. Conventional techniques like differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) have limitations that prevent utilization for certain devices, including limited accuracy and the need for sacrificial samples. In this report, we employ an approach based on Brillouin spectroscopy to probe the glass transition of SMPs rapidly, remotely, and nondestructively. Further, we compare the Tg obtained from Brillouin scattering with DMA- and DSC-measured Tg to demonstrate the accuracy of Brillouin scattering for this application. We conclude that Brillouin spectroscopy is an accurate technique for obtaining the glass transition temperature of SMPs, aligning closely with the most common laboratory standards while providing a rapid, remote, and nondestructive method for the analysis of unique polymeric medical devices.

Effect of Biodegradable Shape-Memory Polymers on Proliferation of 3T3 Cells

NASA Astrophysics Data System (ADS)

Xu, Shuo-Gui; Zhang, Peng; Zhu, Guang-Ming; Jiang, Ying-Ming

2011-07-01

This article evaluates the in vitro biocompatibility for biodegradable shape-memory polymers (BSMP) invented by the authors. 3T3 cells (3T3-Swiss albino GNM 9) of primary and passaged cultures were inoculated into two kinds of carriers: the BSMP carrier and the control group carrier. Viability, proliferation, and DNA synthesis (the major biocompatibility parameters), were measured and evaluated for both the BSMP and naked carrier via cell growth curve analysis, MTT colorimetry and addition of 3H-TdR to culture media. The results showed that there was no difference between the BSMP carrier and the control dish in terms of viability, proliferation, and metabolism of the 3T3 cells. Overall, the BSMP carrier provides good biocompatibility and low toxicity to cells in vitro, and could indicate future potential for this medium as a biological material for implants in vivo.

The effect of bacterial cellulose on the shape memory behavior of polyvinyl alcohol nanocomposite hydrogel

NASA Astrophysics Data System (ADS)

Pirahmadi, Pegah; Kokabi, Mehrdad

2018-01-01

Most research on shape memory polymers has been confined to neat polymers in their dry state, while, some hydrogel networks are known for their shape memory properties. Hydrogels have low glass transition temperatures which are below 100°C depend on the content of water. But they are usually weak and brittle, and not suitable for structural applications due to their low mechanical strengths because of these materials have large amount of water (>50%), so they could not remember original shape perfectly. Bacterial cellulose nanofibers with perfect properties such as high water holding capacity, high crystallinity, high tensile strength and good biocompatibility can dismiss all the drawbacks. In the present study, polyvinyl alcohol/bacterial cellulose nanocomposite hydrogel prepared by repetitive freezing-thawing method. The bacterial cellulose was used as reinforcement to improve the mechanical properties and stimuli response. Differential scanning calorimetry was employed to obtain the glass transition temperature. Nanocomposite morphology was characterized by field-emission scanning electron microscopy and mechanical properties were investigated by standard tensile test. Finally, the effect of bacterial cellulose nanofiber on shape memory behavior of polyvinyl alcohol/bacterial cellulose nanocomposite hydrogel was investigated. It is found that switching temperature of this system is the glass transition temperature of the nano domains formed within the system. The results also show increase of shape recovery, and shape recovery speed due to presence of bacterial cellulose.

Inter-crosslinking network gels having both shape memory and high ductility

NASA Astrophysics Data System (ADS)

Amano, Yoshitaka; Hidema, Ruri; Furukawa, Hidemitsu

2012-04-01

Medical treatment for injuries should be easy and quick in many accidents. Plasters or bandages are frequently used to wrap and fix injured parts. If plasters or bandages have additional smart functions, such as cooling, removability and repeatability, they will be much more useful and effective. Here we propose innovative biocompatible materials, that is, nontoxic high-strength shape-memory gels as novel smart medical materials. These smart gels were prepared from two monomers (DMAAm and SA), a polymer (HPC), and an inter-crosslinking agent (Karenz-MOI). In the synthesis of the gels, 1) a shape-memory copolymer network is made from the DMAAm and the SA, and 2) the copolymer and the HPC are crosslinked by the Karenz-MOI. Thus the crosslinking points are connected only between the different polymers. This is our original technique of developing a new network structure of gels, named Inter-Crosslinking Network (ICN). The ICN gels achieve high ductility, going up to 700% strain in tensile tests, while the ICN gels contain about 44% water. Moreover the SA has temperature dependence due to its crystallization properties; thus the ICN gels obtain shape memory properties and are named ICN-SMG. While the Young's modulus of the ICN-SMG is large below their crystallization temperature and the gels behave like plastic materials, the modulus becomes smaller above the temperature and the gels turn back to their original shape.

A Very Simple Strategy for Preparing External Stress-Free Two-Way Shape Memory Polymers by Making Use of Hydrogen Bonds.

PubMed

Fan, Long Fei; Rong, Min Zhi; Zhang, Ming Qiu; Chen, Xu Dong

2018-05-11

Development of two-way shape memory polymers that operate free of external force remains a great challenge. Here, the design criteria for this type of material are proposed, deriving a novel fabrication strategy accordingly, which employs conventional crosslinked polyurethane (PU) containing crystalline poly(ε-caprolactone) (PCL) as the proof-of-concept material. Having been simply trained by stretching and thermal treatment without additional ingredients and chemicals, the PU is coupled with a two-way shape memory effect. The core advancement of this study lies in the successful conversion of the inherent hydrogen bond network, which is often the easiest to overlook, into an internal stress provider. The temperature-dependent reversible melting/recrystallization of the crystalline phases elaborately works with the tensed hydrogen bond network, leading to implementation of the two-way shape memory effect. An average reversible strain of as high as ≈20% along the stretch direction is obtained through cooperation adjustment of chemical crosslinking density, crystallinity, and concentration of hydrogen bonds. Meanwhile, the highest internal tension offered by the hydrogen bond network is determined to be 0.10 MPa. Owing to the great convenience characterized by material selection, preparation, programming, and application, the current work may open up an avenue for production and usage of the smart material. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Geometry- and Length Scale-Dependent Deformation and Recovery on Micro- and Nanopatterned Shape Memory Polymer Surfaces

PubMed Central

Lee, Wei Li; Low, Hong Yee

2016-01-01

Micro- and nanoscale surface textures, when optimally designed, present a unique approach to improve surface functionalities. Coupling surface texture with shape memory polymers may generate reversibly tuneable surface properties. A shape memory polyetherurethane is used to prepare various surface textures including 2 μm- and 200 nm-gratings, 250 nm-pillars and 200 nm-holes. The mechanical deformation via stretching and recovery of the surface texture are investigated as a function of length scales and shapes. Results show the 200 nm-grating exhibiting more deformation than 2 μm-grating. Grating imparts anisotropic and surface area-to-volume effects, causing different degree of deformation between gratings and pillars under the same applied macroscopic strain. Full distribution of stress within the film causes the holes to deform more substantially than the pillars. In the recovery study, unlike a nearly complete recovery for the gratings after 10 transformation cycles, the high contribution of surface energy impedes the recovery of holes and pillars. The surface textures are shown to perform a switchable wetting function. This study provides insights into how geometric features of shape memory surface patterns can be designed to modulate the shape programming and recovery, and how the control of reversibly deformable surface textures can be applied to transfer microdroplets. PMID:27026290

One-Way Multishape-Memory Effect and Tunable Two-Way Shape Memory Effect of Ionomer Poly(ethylene-co-methacrylic acid).

PubMed

Lu, Lu; Li, Guoqiang

2016-06-15

Reversible elongation by cooling and contraction by heating, without the need for repeated programming, is well-known as the two-way shape-memory effect (2W-SME). This behavior is contrary to the common physics-contraction when cooling and expansion when heating. Materials with such behavior may find many applications in real life, such as self-sufficient grippers, fastening devices, optical gratings, soft actuators, and sealant. Here, it is shown that ionomer Surlyn 8940, a 50-year old polymer, exhibits both one-way multishape-memory effects and tunable two-way reversible actuation. The required external tensile stress to trigger the tunable 2W-SME is very low when randomly jumping the temperatures within the melting transition window. With a proper one-time programming, "true" 2W-SME (i.e., 2W-SME without the need for an external tensile load) is also achieved. A long training process is not needed to trigger the tunable 2W-SME. Instead, a proper one-time tensile programming is sufficient to trigger repeated and tunable 2W-SME. Because the 2W-SME of the ionomer Surlyn is driven by the thermally reversible network, here crystallization and melting transitions of the semicrystalline poly(ethylene-co-methacrylic acid), it is believed that a class of thermally reversible polymers should also exhibit tunable 2W-SMEs.

Spatial light modulators and applications III; Proceedings of the Meeting, San Diego, CA, Aug. 7, 8, 1989

NASA Astrophysics Data System (ADS)

Efron, Uzi

Recent advances in the technology and applications of spatial light modulators (SLMs) are discussed in review essays by leading experts. Topics addressed include materials for SLMs, SLM devices and device technology, applications to optical data processing, and applications to artificial neural networks. Particular attention is given to nonlinear optical polymers, liquid crystals, magnetooptic SLMs, multiple-quantum-well SLMs, deformable-mirror SLMs, three-dimensional optical memories, applications of photorefractive devices to optical computing, photonic neurocomputers and learning machines, holographic associative memories, SLMs as parallel memories for optoelectronic neural networks, and coherent-optics implementations of neural-network models.

Spatial profile of charge storage in organic field-effect transistor nonvolatile memory using polymer electret

NASA Astrophysics Data System (ADS)

She, Xiao-Jian; Liu, Jie; Zhang, Jing-Yu; Gao, Xu; Wang, Sui-Dong

2013-09-01

Spatial profile of the charge storage in the pentacene-based field-effect transistor nonvolatile memories using poly(2-vinyl naphthalene) electret is probed. The electron trapping into the electret after programming can be space dependent with more electron storage in the region closer to the contacts, and reducing the channel length is an effective approach to improve the memory performance. The deficient electron supply in pentacene is proposed to be responsible for the inhomogeneous electron storage in the electret. The hole trapping into the electret after erasing is spatially homogeneous, arising from the sufficient hole accumulation in the pentacene channel.

Spatial light modulators and applications III; Proceedings of the Meeting, San Diego, CA, Aug. 7, 8, 1989

NASA Technical Reports Server (NTRS)

Efron, Uzi (Editor)

1990-01-01

Recent advances in the technology and applications of spatial light modulators (SLMs) are discussed in review essays by leading experts. Topics addressed include materials for SLMs, SLM devices and device technology, applications to optical data processing, and applications to artificial neural networks. Particular attention is given to nonlinear optical polymers, liquid crystals, magnetooptic SLMs, multiple-quantum-well SLMs, deformable-mirror SLMs, three-dimensional optical memories, applications of photorefractive devices to optical computing, photonic neurocomputers and learning machines, holographic associative memories, SLMs as parallel memories for optoelectronic neural networks, and coherent-optics implementations of neural-network models.

Laser Fabrication of Polymer Ferroelectric Nanostructures for Nonvolatile Organic Memory Devices.

PubMed

Martínez-Tong, Daniel E; Rodríguez-Rodríguez, Álvaro; Nogales, Aurora; García-Gutiérrez, Mari-Cruz; Pérez-Murano, Francesc; Llobet, Jordi; Ezquerra, Tiberio A; Rebollar, Esther

2015-09-09

Polymer ferroelectric laser-induced periodic surface structures (LIPSS) have been prepared on ferroelectric thin films of a poly(vinylidene fluoride-trifluoroethylene) copolymer. Although this copolymer does not absorb light at the laser wavelength, LIPSS on the copolymer can be obtained by forming a bilayer with other light-absorbing polymers. The ferroelectric nature of the structured bilayer was proven by piezoresponse force microscopy measurements. Ferroelectric hysteresis was found on both the bilayer and the laser-structured bilayer. We show that it is possible to write ferroelectric information at the nanoscale. The laser-structured ferroelectric bilayer showed an increase in the information storage density of an order of magnitude, in comparison to the original bilayer.

Ion conducting organic/inorganic hybrid polymers

NASA Technical Reports Server (NTRS)

Meador, Maryann B. (Inventor); Kinder, James D. (Inventor)

2010-01-01

This invention relates to a series of organic/inorganic hybrid polymers that are easy to fabricate into dimensionally stable films with good ion-conductivity over a wide range of temperatures for use in a variety of applications. The polymers are prepared by the reaction of amines, preferably diamines and mixtures thereof with monoamines with epoxy-functionalized alkoxysilanes. The products of the reaction are polymerized by hydrolysis of the alkoxysilane groups to produce an organic-containing silica network. Suitable functionality introduced into the amine and alkoxysilane groups produce solid polymeric membranes which conduct ions for use in fuel cells, high-performance solid state batteries, chemical sensors, electrochemical capacitors, electro-chromic windows or displays, analog memory devices and the like.

Development of a self-stressing NiTiNb shape memory alloy (SMA)/fiber reinforced polymer (FRP) patch

NASA Astrophysics Data System (ADS)

El-Tahan, M.; Dawood, M.; Song, G.

2015-06-01

The objective of this research is to develop a self-stressing patch using a combination of shape memory alloys (SMAs) and fiber reinforced polymer (FRP) composites. Prestressed carbon FRP patches are emerging as a promising alternative to traditional methods to repair cracked steel structures and civil infrastructure. However, prestressing these patches typically requires heavy and complex fixtures, which is impractical in many applications. This paper presents a new approach in which the prestressing force is applied by restraining the shape memory effect of NiTiNb SMA wires. The wires are subsequently embedded in an FRP overlay patch. This method overcomes the practical challenges associated with conventional prestressing. This paper presents the conceptual development of the self-stressing patch with the support of experimental observations. The bond between the SMA wires and the FRP is evaluated using pull-out tests. The paper concludes with an experimental study that evaluates the patch response during activation subsequent monotonic tensile loading. The results demonstrate that the self-stressing patch with NiTiNb SMA is capable of generating a significant prestressing force with minimal tool and labor requirements.

Effect of Cross-linking Density on Creep and Recovery Behavior in Epoxy-Based Shape Memory Polymers (SMEPs) for Structural Applications

NASA Astrophysics Data System (ADS)

Rao, Kavitha V.; Ananthapadmanabha, G. S.; Dayananda, G. N.

2016-12-01

Epoxy-based shape memory polymers (SMEPs) are gaining importance in the area of aerospace structures due to their high strength and stiffness which is a primary requirement for an SMEP in structural applications. The understanding of viscoelastic behavior of SMEPs is very essential to assess their shape memory effect. In the present work, three types of SMEPs with varying cross-linking densities were developed by curing an aromatic epoxy resin with aliphatic amines. Glass transition temperature ( T g) was measured for these SMEPs using advanced rheometric expansion system, and from the T g measurements, a range of temperatures from glassy to rubbery regimes were chosen. At selected temperatures, creep-recovery tests were performed in order to evaluate the viscoelastic behavior of SMEPs and also to investigate the effect of temperature on creep-recovery. Further, a three-parameter viscoelastic model (Zener) was used to fit the data obtained from experiments. Model parameters like moduli of the springs and viscosity of the dashpot were evaluated by curve fitting. Results revealed that Zener model was well suited to describe the viscoelastic behavior of SMEPs as a function of test temperatures.

Variable stiffness corrugated composite structure with shape memory polymer for morphing skin applications

NASA Astrophysics Data System (ADS)

Gong, Xiaobo; Liu, Liwu; Scarpa, Fabrizio; Leng, Jinsong; Liu, Yanju

2017-03-01

This work presents a variable stiffness corrugated structure based on a shape memory polymer (SMP) composite with corrugated laminates as reinforcement that shows smooth aerodynamic surface, extreme mechanical anisotropy and variable stiffness for potential morphing skin applications. The smart composite corrugated structure shows a low in-plane stiffness to minimize the actuation energy, but also possess high out-of-plane stiffness to transfer the aerodynamic pressure load. The skin provides an external smooth aerodynamic surface because of the one-sided filling with the SMP. Due to variable stiffness of the shape memory polymer the morphing skin exhibits a variable stiffness with a change of temperature, which can help the skin adjust its stiffness according different service environments and also lock the temporary shape without external force. Analytical models related to the transverse and bending stiffness are derived and validated using finite element techniques. The stiffness of the morphing skin is further investigated by performing a parametric analysis against the geometry of the corrugation and various sets of SMP fillers. The theoretical and numerical models show a good agreement and demonstrate the potential of this morphing skin concept for morphing aircraft applications. We also perform a feasibility study of the use of this morphing skin in a variable camber morphing wing baseline. The results show that the morphing skin concept exhibits sufficient bending stiffness to withstand the aerodynamic load at low speed (less than 0.3 Ma), while demonstrating a large transverse stiffness variation (up to 191 times) that helps to create a maximum mechanical efficiency of the structure under varying external conditions.

Polymer and ceramic nanocomposites for aerospace applications

NASA Astrophysics Data System (ADS)

Rathod, Vivek T.; Kumar, Jayanth S.; Jain, Anjana

2017-11-01

This paper reviews the potential of polymer and ceramic matrix composites for aerospace/space vehicle applications. Special, unique and multifunctional properties arising due to the dispersion of nanoparticles in ceramic and metal matrix are briefly discussed followed by a classification of resulting aerospace applications. The paper presents polymer matrix composites comprising majority of aerospace applications in structures, coating, tribology, structural health monitoring, electromagnetic shielding and shape memory applications. The capabilities of the ceramic matrix nanocomposites to providing the electromagnetic shielding for aircrafts and better tribological properties to suit space environments are discussed. Structural health monitoring capability of ceramic matrix nanocomposite is also discussed. The properties of resulting nanocomposite material with its disadvantages like cost and processing difficulties are discussed. The paper concludes after the discussion of the possible future perspectives and challenges in implementation and further development of polymer and ceramic nanocomposite materials.

Coarse-grained simulation of molecular mechanisms of recovery in thermally activated shape-memory polymers

NASA Astrophysics Data System (ADS)

Abberton, Brendan C.; Liu, Wing Kam; Keten, Sinan

2013-12-01

Thermally actuated shape-memory polymers (SMPs) are capable of being programmed into a temporary shape and then recovering their permanent reference shape upon exposure to heat, which facilitates a phase transition that allows dramatic increase in molecular mobility. Experimental, analytical, and computational studies have established empirical relations of the thermomechanical behavior of SMPs that have been instrumental in device design. However, the underlying mechanisms of the recovery behavior and dependence on polymer microstructure remain to be fully understood for copolymer systems. This presents an opportunity for bottom-up studies through molecular modeling; however, the limited time-scales of atomistic simulations prohibit the study of key performance metrics pertaining to recovery. In order to elucidate the effects of phase fraction, recovery temperature, and deformation temperature on shape recovery, here we investigate the shape-memory behavior in a copolymer model with coarse-grained potentials using a two-phase molecular model that reproduces physical crosslinking. Our simulation protocol allows observation of upwards of 90% strain recovery in some cases, at time-scales that are on the order of the timescale of the relevant relaxation mechanism (stress relaxation in the unentangled soft-phase). Partial disintegration of the glassy phase during mechanical deformation is found to contribute to irrecoverable strain. Temperature dependence of the recovery indicates nearly full elastic recovery above the trigger temperature, which is near the glass-transition temperature of the rubbery switching matrix. We find that the trigger temperature is also directly correlated with the deformation temperature, indicating that deformation temperature influences the recovery temperatures required to obtain a given amount of shape recovery, until the plateau regions overlap above the transition region. Increasing the fraction of glassy phase results in higher strain recovery at low to intermediate temperatures, a widening of the transition region, and an eventual crossover at high temperatures. Our results corroborate experimental findings on shape-memory behavior and provide new insight into factors governing deformation recovery that can be leveraged in biomaterials design. The established computational methodology can be extended in straightforward ways to investigate the effects of monomer chemistry, low-molecular-weight solvents, physical and chemical crosslinking, different phase-separation morphologies, and more complicated mechanical deformation toward predictive modeling capabilities for stimuli-responsive polymers.

Analysis of intelligent hinged shell structures: deployable deformation and shape memory effect

NASA Astrophysics Data System (ADS)

Shi, Guang-Hui; Yang, Qing-Sheng; He, X. Q.

2013-12-01

Shape memory polymers (SMPs) are a class of intelligent materials with the ability to recover their initial shape from a temporarily fixable state when subjected to external stimuli. In this work, the thermo-mechanical behavior of a deployable SMP-based hinged structure is modeled by the finite element method using a 3D constitutive model with shape memory effect. The influences of hinge structure parameters on the nonlinear loading process are investigated. The total shape memory of the processes the hinged structure goes through, including loading at high temperature, decreasing temperature with load carrying, unloading at low temperature and recovering the initial shape with increasing temperature, are illustrated. Numerical results show that the present constitutive theory and the finite element method can effectively predict the complicated thermo-mechanical deformation behavior and shape memory effect of SMP-based hinged shell structures.

Shape Memory Properties and Enzymatic Degradability of Poly(ε-caprolactone)-Based Polyurethane Urea Containing Phenylalanine-Derived Chain Extender.

PubMed

Wang, Rong; Zhang, Fanjun; Lin, Weiwei; Liu, Wenkai; Li, Jiehua; Luo, Feng; Wang, Yaning; Tan, Hong

2018-06-01

Biodegradable shape memory polymers are promising biomaterials for minimally invasive surgical procedures. Herein, a series of linear biodegradable shape memory poly(ε-caprolactone) (PCL)-based polyurethane ureas (PUUs) containing a novel phenylalanine-derived chain extender is synthesized. The phenylalanine-derived chain extender, phenylalanine-hexamethylenediamine-phenylalanine (PHP), contains two chymotrypsin cleaving sites to enhance the enzymatic degradation of PUUs. The degradation rate, the crystallinity, and mechanical properties of PUUs are tailored by the content of PHP. Meanwhile, semicrystalline PCL is not only hydrolytically degradable but also vital for shape memory. Good shape memory ability under body temperature is achieved for PUUs due to the strong interactions in hard segments for permanent crosslinking and the crystallization-melt transition of PCL to switch temporary shape. The PUUs would have a great potential in application as implanting stent. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Lateral-deflection-controlled friction force microscopy

NASA Astrophysics Data System (ADS)

Fukuzawa, Kenji; Hamaoka, Satoshi; Shikida, Mitsuhiro; Itoh, Shintaro; Zhang, Hedong

2014-08-01

Lateral-deflection-controlled dual-axis friction force microscopy (FFM) is presented. In this method, an electrostatic force generated with a probe-incorporated micro-actuator compensates for friction force in real time during probe scanning using feedback control. This equivalently large rigidity can eliminate apparent boundary width and lateral snap-in, which are caused by lateral probe deflection. The method can evolve FFM as a method for quantifying local frictional properties on the micro/nanometer-scale by overcoming essential problems to dual-axis FFM.

Missile Flight Control Using micro-Actuated Flow Effectors - Review of Fiscal Year 2005/2006 Progress

DTIC Science & Technology

2006-08-01

be developed. A common analysis model covering the aerodynamic-flow effector interaction, the compliant mechanism-SMA dynamics and the control...additional CFD analysis for the finless DRDC-B1AC2R between 15 deg. to 20 deg. to determine where the peak side force is situated. Compare pressure...Carry out CFD study on DRDC-B1AC2R with fins. Decide on analysis matrix. Coordinate with wind tunnel test matrix. Action: DRDC-nh Y0405-7. Decide

Fabrication of nylon/fullerene polymer memory

NASA Astrophysics Data System (ADS)

Jayan, Manuvel; Davis, Rosemary; Karthik, M. P.; Devika, K.; Kumar, G. Vijay; Sriraj, B.; Predeep, P.

2017-06-01

Two terminal Organic memories in passive matrix array form with device structure, Al/Nylon/ (Nylon+C60)/Nylon/ Al are fabricated. The current-voltage measurements showed hysteresis and the devices are thoroughly characterized for write-read-erase-read cycles. The control over the dispersion concentration, capacity of fullerene to readily accept electrons and the constant diameter of fullerene made possible uniform device fabrication with reproducible results. Scanning electron micrographs indicated that the device thickness remained uniform in the range of 19 micrometers.

Effective thermo-mechanical properties and shape memory effect of CNT/SMP composites

NASA Astrophysics Data System (ADS)

Yang, Qingsheng; Liu, Xia; Leng, Fangfang

2009-07-01

Shape memory polymer (SMP) has been applied in many fields as intelligent sensors and actuators. In order to improve the mechanical properties and recovery force of SMP, the addition of minor amounts of carbon nanotubes (CNT) into SMP has attracted wide attention. A micromechanical model and thermo-mechanical properties of CNT/SMP composites were studied in this paper. The thermo-mechanical constitutive relation of intellectual composites with isotropic and transversely isotropic CNT was obtained. Moreover, the shape memory effect of CNT/SMP composites and the effect of temperature and the volume fraction of CNT were discussed. The work shows that CNT/SMP composites exhibit excellent macroscopic thermo-mechanical properties and shape memory effect, while both of them can be affected remarkably by temperature and the microstructure parameters.

Thermomechanical behavior of a two-way shape memory composite actuator

NASA Astrophysics Data System (ADS)

Ge, Qi; Westbrook, Kristofer K.; Mather, Patrick T.; Dunn, Martin L.; Qi, H. Jerry

2013-05-01

Shape memory polymers (SMPs) are a class of smart materials that can fix a temporary shape and recover to their permanent (original) shape in response to an environmental stimulus such as heat, electricity, or irradiation, among others. Most SMPs developed in the past can only demonstrate the so-called one-way shape memory effect; i.e., one programming step can only yield one shape memory cycle. Recently, one of the authors (Mather) developed a SMP that exhibits both one-way shape memory (1W-SM) and two-way shape memory (2W-SM) effects (with the assistance of an external load). This SMP was further used to develop a free-standing composite actuator with a nonlinear reversible actuation under thermal cycling. In this paper, a theoretical model for the PCO SMP based composite actuator was developed to investigate its thermomechanical behavior and the mechanisms for the observed phenomena during the actuation cycles, and to provide insight into how to improve the design.

Flexible non-volatile memory devices based on organic semiconductors

NASA Astrophysics Data System (ADS)

Cosseddu, Piero; Casula, Giulia; Lai, Stefano; Bonfiglio, Annalisa

2015-09-01

The possibility of developing fully organic electronic circuits is critically dependent on the ability to realize a full set of electronic functionalities based on organic devices. In order to complete the scene, a fundamental element is still missing, i.e. reliable data storage. Over the past few years, a considerable effort has been spent on the development and optimization of organic polymer based memory elements. Among several possible solutions, transistor-based memories and resistive switching-based memories are attracting a great interest in the scientific community. In this paper, a route for the fabrication of organic semiconductor-based memory devices with performances beyond the state of the art is reported. Both the families of organic memories will be considered. A flexible resistive memory based on a novel combination of materials is presented. In particular, high retention time in ambient conditions are reported. Complementary, a low voltage transistor-based memory is presented. Low voltage operation is allowed by an hybrid, nano-sized dielectric, which is also responsible for the memory effect in the device. Thanks to the possibility of reproducibly fabricating such device on ultra-thin substrates, high mechanical stability is reported.

Holographic Recording Materials Development

NASA Technical Reports Server (NTRS)

Verber, C. M.; Schwerzel, R. E.; Perry, P. J.; Craig, R. A.

1976-01-01

Organic photorefractive materials were evaluated for application in a reversible holographic memory system. Representative indigo and thioindigo derivatives and several stilbene derivatives were studied as well as 15, 16-dialkyldihydropyrene derivatives the following goals were achieved: (1) the successful writing of phase holograms in a thioindigo/polymer gel system, (2) the successful writing and erasing of phase holograms in a variety of indigo/polymer gel and indigo/solid polymer systems, and (3) the identification of indigoid dyes and 15, 16-dialkyldihydropyrene derivatives as materials potentially suitable for utilization in an operational system. Photochemical studies of the stilbene, indigo, thioindigo, and dialkyldihydropyrene derivatives in solution and in a variety of polymer matrix materials were conducted with the goal of optimizing the photorefractive behavior of the chemical system as a whole. The spectroscopic properties required of optimal photorefractive materials were identified, and it was shown that both the indigoid dyes and the dialkyldihydropyrenes closely match the required properties.

Amorphous blue phase III polymer scaffold as a sub-millisecond switching electro-optical memory device

NASA Astrophysics Data System (ADS)

Gandhi, Sahil Sandesh; Kim, Min Su; Hwang, Jeoung-Yeon; Chien, Liang-Chy

2017-02-01

We demonstrate the application of the nanostructured scaffold of BPIII as a resuable EO device that retains the BPIII ordering and sub-millisecond EO switching characteristics, that is, "EO-memory" of the original BPIII even after removal of the cholesteric blue phase liquid crystal (LC) and subsequent refilling with different nematic LCs. We also fabricate scaffolds mimicking the isotropic phase and cubic blue phase I (BPI) to demonstrate the versatility of our material system to nano-engineer EO-memory scaffolds of various structures. We envisage that this work will promote new experimental investigations of the mysterious BPIII and the development of novel device architectures and optically functional nanomaterials.

Chemical cross-linking of polypropylenes towards new shape memory polymers.

PubMed

Raidt, Thomas; Hoeher, Robin; Katzenberg, Frank; Tiller, Joerg C

2015-04-01

In this work, syndiotactic polypropylene (sPP) as well as isotactic polypropylene (iPP) are cross-linked to gain a shape memory effect. Both prepared PP networks exhibit maximum strains of 700%, stored strains of up to 680%, and recoveries of nearly 100%. While x-iPP is stable for many cycles, x-sPP ruptures after the first shape-memory cycle. It is shown by wide-angle X-ray scattering (WAXS) experiments that cross-linked iPP exhibits homoepitaxy in the temporary, stretched shape but in contrast to previous reports it contains a higher amount of daughter than mother crystals. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Femtosecond laser microfabrication in polymers towards memory devices and microfluidic applications

NASA Astrophysics Data System (ADS)

Deepak, K. L. N.; Venugopal Rao, S.; Narayana Rao, D.

2011-12-01

We have investigated femtosecond laser induced microstructures, gratings, and craters in four different polymers: poly methyl methacrylate (PMMA), poly dimethyl siloxane (PDMS), polystyrene (PS) and poly vinyl alcohol (PVA) using Ti:sapphire laser delivering 800 nm, 100 femtosecond (fs) pulses at 1 kHz repetition rate with a maximum pulse energy of 1 mJ. Local chemical modifications leading to the formation of optical centers and peroxide radicals which were studied using UV-Visible absorption and emission, confocal micro-Raman and Electron Spin Resonance (ESR) spectroscopic techniques.

Bistable electroactive polymer for refreshable Braille display with improved actuation stability

NASA Astrophysics Data System (ADS)

Niu, Xiaofan; Brochu, Paul; Stoyanov, Hristiyan; Yun, Sung Ryul; Pei, Qibing

2012-04-01

Poly(t-butyl acrylate) is a bistable electroactive polymer (BSEP) capable of rigid-to-rigid actuation. The BSEP combines the large-strain actuation of dielectric elastomers with shape memory property. We have introduced a material approach to overcome pull-in instability in poly(t-butyl acrylate) that significantly improves the actuation lifetime at strains greater than 100%. Refreshable Braille display devices with size of a smartphone screen have been fabricated to manifest a potential application of the BSEP. We will report the testing results of the devices by a Braille user.

Direct-write fabrication of 4D active shape-changing behavior based on a shape memory polymer and its nanocomposite (Conference Presentation)

NASA Astrophysics Data System (ADS)

Wei, Hongqiu; Zhang, Qiwei; Yao, Yongtao; Liu, Liwu; Liu, Yanju; Leng, Jinsong

2017-04-01

Shape memory polymers (SMPs), a typical class of smart materials, have been witnessed significant advances in the past decades. Based on the unique performance to recover the initial shape after going through a shape deformation, the applications of SMPs have aroused growing interests. However, most of the researches are hindered by traditional processing technologies which limit the design space of SMPs-based structures. Three-dimension (3D) printing as an emerging technology endows design freedom to manufacture materials with complex structures. In present article, we show that by employing direct-write printing method; one can realize the printing of SMPs to achieve 4D active shape-changing structures. We first fabricated a kind of 3D printable polylactide (PLA)-based SMPs and characterized the overall properties of such materials. Results demonstrated the prepared PLA-based SMPs presenting excellent shape memory effect. In what follows, the rheological properties of such PLA-based SMP ink during printing process were discussed in detail. Finally, we designed and printed several 3D configurations for investigation. By combining 3D printing with shape memory behavior, these printed structures achieve 4D active shape-changing performance under heat stimuli. This research presents a high flexible method to realize the fabrication of SMP-based 4D active shape-changing structures, which opens the way for further developments and improvements of high-tech fields like 4D printing, soft robotics, micro-systems and biomedical devices.

A stress-induced phase transition model for semi-crystallize shape memory polymer

NASA Astrophysics Data System (ADS)

Guo, Xiaogang; Zhou, Bo; Liu, Liwu; Liu, Yanju; Leng, Jinsong

2014-03-01

The developments of constitutive models for shape memory polymer (SMP) have been motivated by its increasing applications. During cooling or heating process, the phase transition which is a continuous time-dependent process happens in semi-crystallize SMP and the various individual phases form at different temperature and in different configuration. Then, the transformation between these phases occurred and shape memory effect will emerge. In addition, stress applied on SMP is an important factor for crystal melting during phase transition. In this theory, an ideal phase transition model considering stress or pre-strain is the key to describe the behaviors of shape memory effect. So a normal distributed model was established in this research to characterize the volume fraction of each phase in SMP during phase transition. Generally, the experiment results are partly backward (in heating process) or forward (in cooling process) compared with the ideal situation considering delay effect during phase transition. So, a correction on the normal distributed model is needed. Furthermore, a nonlinear relationship between stress and phase transition temperature Tg is also taken into account for establishing an accurately normal distributed phase transition model. Finally, the constitutive model which taking the stress as an influence factor on phase transition was also established. Compared with the other expressions, this new-type model possesses less parameter and is more accurate. For the sake of verifying the rationality and accuracy of new phase transition and constitutive model, the comparisons between the simulated and experimental results were carried out.

Effects of thermo-mechanical behavior and hinge geometry on folding response of shape memory polymer sheets

NASA Astrophysics Data System (ADS)

Mailen, Russell W.; Dickey, Michael D.; Genzer, Jan; Zikry, Mohammed

2017-11-01

Shape memory polymer (SMP) sheets patterned with black ink hinges change shape in response to external stimuli, such as absorbed thermal energy from an infrared (IR) light. The geometry of these hinges, including size, orientation, and location, and the applied thermal loads significantly influence the final folded shape of the sheet, but these variables have not been fully investigated. We perform a systematic study on SMP sheets to fundamentally understand the effects of single and double hinge geometries, hinge orientation and spacing, initial temperature, heat flux intensity, and pattern width on the folding behavior. We have developed thermo-viscoelastic finite element models to characterize and quantify the stresses, strains, and temperatures as they relate to SMP shape changes. Our predictions indicate that hinge orientation can be used to reduce the total bending angle, which is the angle traversed by the folding face of the sheet. Two parallel hinges increase the total bending angle, and heat conduction between the hinges affects the transient folding response. IR intensity and initial temperatures can also influence the transient folding behavior. These results can provide guidelines to optimize the transient folding response and the three-dimensional folded structure obtained from self-folding polymer origami sheets that can be applied for myriad applications.

Direct Intracochlear Acoustic Stimulation Using a PZT Microactuator

PubMed Central

Luo, Chuan; Omelchenko, Irina; Manson, Robert; Robbins, Carol; Oesterle, Elizabeth C.; Cao, Guo Zhong; Hume, Clifford R.

2015-01-01

Combined electric and acoustic stimulation has proven to be an effective strategy to improve hearing in some cochlear implant users. We describe an acoustic microactuator to directly deliver stimuli to the perilymph in the scala tympani. The 800 µm by 800 µm actuator has a silicon diaphragm driven by a piezoelectric thin film (e.g., lead-zirconium-titanium oxide or PZT). This device could also be used as a component of a bimodal acoustic-electric electrode array. In the current study, we established a guinea pig model to test the actuator for its ability to deliver auditory signals to the cochlea in vivo. The actuator was placed through the round window of the cochlea. Auditory brainstem response (ABR) thresholds, peak latencies, and amplitude growth were calculated for an ear canal speaker versus the intracochlear actuator for tone burst stimuli at 4, 8, 16, and 24 kHz. An ABR was obtained after removal of the probe to assess loss of hearing related to the procedure. In some animals, the temporal bone was harvested for histologic analysis of cochlear damage. We show that the device is capable of stimulating ABRs in vivo with latencies and growth functions comparable to stimulation in the ear canal. Further experiments will be necessary to evaluate the efficiency and safety of this modality in long-term auditory stimulation and its ability to be integrated with conventional cochlear implant arrays. PMID:26631107

Microfabrication and characterization of an array of dielectric elastomer actuators generating uniaxial strain to stretch individual cells

NASA Astrophysics Data System (ADS)

Akbari, S.; Shea, H. R.

2012-04-01

Cells regulate their behavior in response to mechanical strains. Cell cultures to study mechanotransuction are typically cm2 in area, far too large to monitor single cell response. We have developed an array of dielectric elastomer microactuators as a tool to study mechanotransduction of individual cells. The array consists of 72 100 µm × 200 µm electroactive polymer actuators which expand uniaxially when a voltage is applied. Single cells will be attached on each actuator to study their response to periodic mechanical strains. The device is fabricated by patterning compliant microelectrodes on both sides of a 30 µm thick polydimethylsiloxane membrane, which is bonded to a Pyrex chip with 200 µm wide trenches. Low-energy metal ion implantation is used to make stretchable electrodes and we demonstrate here the successful miniaturization of such ion-implanted electrodes. The top electrode covers the full membrane area, while the bottom electrodes are 100 µm wide parallel lines, perpendicular to the trenches. Applying a voltage between the top and bottom electrodes leads to uniaxial expansion of the membrane at the intersection of the bottom electrodes and the trenches. To characterize the in-plane strain, an array of 4 µm diameter aluminum dots is deposited on each actuator. The position of each dot is tracked, allowing displacement and strain profiles to be measured as a function of voltage. The uniaxial strain reaches 4.7% at 2.9 kV with a 0.2 s response time, sufficient to stimulate most cells with relevant biological strains and frequencies.

Multi-shape active composites by 3D printing of digital shape memory polymers

NASA Astrophysics Data System (ADS)

Wu, Jiangtao; Yuan, Chao; Ding, Zhen; Isakov, Michael; Mao, Yiqi; Wang, Tiejun; Dunn, Martin L.; Qi, H. Jerry

2016-04-01

Recent research using 3D printing to create active structures has added an exciting new dimension to 3D printing technology. After being printed, these active, often composite, materials can change their shape over time; this has been termed as 4D printing. In this paper, we demonstrate the design and manufacture of active composites that can take multiple shapes, depending on the environmental temperature. This is achieved by 3D printing layered composite structures with multiple families of shape memory polymer (SMP) fibers - digital SMPs - with different glass transition temperatures (Tg) to control the transformation of the structure. After a simple single-step thermomechanical programming process, the fiber families can be sequentially activated to bend when the temperature is increased. By tuning the volume fraction of the fibers, bending deformation can be controlled. We develop a theoretical model to predict the deformation behavior for better understanding the phenomena and aiding the design. We also design and print several flat 2D structures that can be programmed to fold and open themselves when subjected to heat. With the advantages of an easy fabrication process and the controllable multi-shape memory effect, the printed SMP composites have a great potential in 4D printing applications.

Lightweight, Self-Deployable Wheels

NASA Technical Reports Server (NTRS)

Chmielewski, Artur; Sokolowski, Witold; Rand, Peter

2003-01-01

Ultra-lightweight, self-deployable wheels made of polymer foams have been demonstrated. These wheels are an addition to the roster of cold hibernated elastic memory (CHEM) structural applications. Intended originally for use on nanorovers (very small planetary-exploration robotic vehicles), CHEM wheels could also be used for many commercial applications, such as in toys. The CHEM concept was reported in "Cold Hibernated Elastic Memory (CHEM) Expandable Structures" (NPO-20394), NASA Tech Briefs, Vol. 23, No. 2 (February 1999), page 56. To recapitulate: A CHEM structure is fabricated from a shape-memory polymer (SMP) foam. The structure is compressed to a very small volume while in its rubbery state above its glass-transition temperature (Tg). Once compressed, the structure can be cooled below Tg to its glassy state. As long as the temperature remains

Multi-shape active composites by 3D printing of digital shape memory polymers.

PubMed

Wu, Jiangtao; Yuan, Chao; Ding, Zhen; Isakov, Michael; Mao, Yiqi; Wang, Tiejun; Dunn, Martin L; Qi, H Jerry

2016-04-13

Recent research using 3D printing to create active structures has added an exciting new dimension to 3D printing technology. After being printed, these active, often composite, materials can change their shape over time; this has been termed as 4D printing. In this paper, we demonstrate the design and manufacture of active composites that can take multiple shapes, depending on the environmental temperature. This is achieved by 3D printing layered composite structures with multiple families of shape memory polymer (SMP) fibers - digital SMPs - with different glass transition temperatures (Tg) to control the transformation of the structure. After a simple single-step thermomechanical programming process, the fiber families can be sequentially activated to bend when the temperature is increased. By tuning the volume fraction of the fibers, bending deformation can be controlled. We develop a theoretical model to predict the deformation behavior for better understanding the phenomena and aiding the design. We also design and print several flat 2D structures that can be programmed to fold and open themselves when subjected to heat. With the advantages of an easy fabrication process and the controllable multi-shape memory effect, the printed SMP composites have a great potential in 4D printing applications.

Multi-shape active composites by 3D printing of digital shape memory polymers

PubMed Central

Wu, Jiangtao; Yuan, Chao; Ding, Zhen; Isakov, Michael; Mao, Yiqi; Wang, Tiejun; Dunn, Martin L.; Qi, H. Jerry

2016-01-01

Recent research using 3D printing to create active structures has added an exciting new dimension to 3D printing technology. After being printed, these active, often composite, materials can change their shape over time; this has been termed as 4D printing. In this paper, we demonstrate the design and manufacture of active composites that can take multiple shapes, depending on the environmental temperature. This is achieved by 3D printing layered composite structures with multiple families of shape memory polymer (SMP) fibers – digital SMPs - with different glass transition temperatures (Tg) to control the transformation of the structure. After a simple single-step thermomechanical programming process, the fiber families can be sequentially activated to bend when the temperature is increased. By tuning the volume fraction of the fibers, bending deformation can be controlled. We develop a theoretical model to predict the deformation behavior for better understanding the phenomena and aiding the design. We also design and print several flat 2D structures that can be programmed to fold and open themselves when subjected to heat. With the advantages of an easy fabrication process and the controllable multi-shape memory effect, the printed SMP composites have a great potential in 4D printing applications. PMID:27071543

Temperature dependent evolution of wrinkled single-crystal silicon ribbons on shape memory polymers.

PubMed

Wang, Yu; Yu, Kai; Qi, H Jerry; Xiao, Jianliang

2017-10-25

Shape memory polymers (SMPs) can remember two or more distinct shapes, and thus can have a lot of potential applications. This paper presents combined experimental and theoretical studies on the wrinkling of single-crystal Si ribbons on SMPs and the temperature dependent evolution. Using the shape memory effect of heat responsive SMPs, this study provides a method to build wavy forms of single-crystal silicon thin films on top of SMP substrates. Silicon ribbons obtained from a Si-on-insulator (SOI) wafer are released and transferred onto the surface of programmed SMPs. Then such bilayer systems are recovered at different temperatures, yielding well-defined, wavy profiles of Si ribbons. The wavy profiles are shown to evolve with time, and the evolution behavior strongly depends on the recovery temperature. At relatively low recovery temperatures, both wrinkle wavelength and amplitude increase with time as evolution progresses. Finite element analysis (FEA) accounting for the thermomechanical behavior of SMPs is conducted to study the wrinkling of Si ribbons on SMPs, which shows good agreement with experiment. Merging of wrinkles is observed in FEA, which could explain the increase of wrinkle wavelength observed in the experiment. This study can have important implications for smart stretchable electronics, wrinkling mechanics, stimuli-responsive surface engineering, and advanced manufacturing.

Nondegradable magnetic poly (carbonate urethane) microspheres with good shape memory as a proposed material for vascular embolization.

PubMed

Liu, Rongrong; Zhang, Qian; Zhou, Qian; Zhang, Ping; Dai, Honglian

2018-06-01

In this study, nondegradable poly (carbonate urethane) (PCU) and poly (carbonate urethane) incorporated variable Fe 3 O 4 content microspheres (PCU/Fe 3 O 4 ) were synthesized using pre-polymerization and suspension polymerization. Synthesis was confirmed through Fourier transform infrared spectroscopy (FTIR). The effect of Fe 3 O 4 incorporation was investigated on crystalline, thermal, shape memory and degradation properties by X-Ray diffraction (XRD), Differential scanning calorimetery (DSC), compression test and degradation in vitro, respectively. Otherwise, the assessment of magnetic characteristics by vibrational sample magnetometry (VSM) disclosed superparamagnetic behavior. The tunable superparamagnetic behavior depends on the amount of magnetic particles incorporated within the networks. The biological study results of as-synthesized polymers from the platelet adhesion test and the cell proliferation inhibition test indicated they were biocompatible in vitro. Fe 3 O 4 incorporation was conductive to reducing platelet adhesion in blood contacting test and promotion of rat vascular smooth muscle cell proliferation and growth. These nondegradable, superparamagnetic, biocompatible polymers, combined with their good shape memory properties may allow for their future exploitation in the biomedical field, such as, in cardiovascular implants, targeted tumor treatment, tissue engineering and artificial organ's engineering. Copyright © 2018. Published by Elsevier Ltd.

A shape memory polymer concrete crack closure system activated by electrical current

NASA Astrophysics Data System (ADS)

Teall, Oliver; Pilegis, Martins; Davies, Robert; Sweeney, John; Jefferson, Tony; Lark, Robert; Gardner, Diane

2018-07-01

The presence of cracks has a negative impact on the durability of concrete by providing paths for corrosive materials to the embedded steel reinforcement. Cracks in concrete can be closed using shape memory polymers (SMP) which produce a compressive stress across the crack faces. This stress has been previously found to enhance the load recovery associated with autogenous self-healing. This paper details the experiments undertaken to incorporate SMP tendons containing polyethylene terephthalate (PET) filaments into reinforced and unreinforced 500 × 100 × 100 mm structural concrete beam samples. These tendons are activated via an electrical supply using a nickel-chrome resistance wire heating system. The set-up, methodology and results of restrained shrinkage stress and crack closure experiments are explained. Crack closure of up to 85% in unreinforced beams and 26%–39% in reinforced beams is measured using crack-mouth opening displacement, microscope and digital image correlation equipment. Conclusions are made as to the effectiveness of the system and its potential for application within industry.

Use of the shape memory polymer polystyrene in the creation of thin film stretchable sensors for wearable applications

NASA Astrophysics Data System (ADS)

Van Volkinburg, Kyle R.; Nguyen, Thao; Pegan, Jonathan D.; Khine, Michelle; Washington, Gregory N.

2016-04-01

The shape memory polymer polystyrene (PS) has been used to create complex hierarchical wrinkling in the fabrication of stretchable thin film bimetallic sensors ideal for wearable based gesture monitoring applications. The film has been bonded to the elastomer polydimethylsiloxane (PDMS) and operates as a strain gauge under the general notion of geometric piezoresistivity. The film was subject to tensile, cyclic, and step loading conditions in order to characterize its dynamic behavior. To measure the joint angle of the metacarpophalangeal (MCP) joint on the right index finger, the sensor was adhered to a fitted golf glove above said joint and a motion study was conducted. At maximum joint angle the sensor experienced roughly 23.5% strain. From the study it was found that two simple curves, one while the finger was in flexion and the other while the finger was in extension, were able to predict the joint angle from measured voltage with an average error of 2.99 degrees.

Implementation of poly(ε-caprolactone) sheet-based shape-memory polymer microvalves into plastic-based microfluidic devices

NASA Astrophysics Data System (ADS)

Jiang, Chenyang; Uto, Koichiro; Ebara, Mitsuhiro; Aoyagi, Takao; Ichiki, Takanori

2015-06-01

Implementation of shape-memory polymer (SMP) sheet-based microvalves into plastic-based microfluidic devices has been studied toward the use in disposable and mass producible micro total analysis devices. Poly(ε-caprolactone) (PCL) and poly(methyl methacrylate-co-styrene) (MS) were used as SMP and main substrate materials, respectively. Bonding between PCL sheets and MS plates was the critical issue in the practical implementation. We found the pristine PCL sheet has relatively rough surface with Ra of 85.14 nm, which is the cause of poor bonding. Hence, by introducing the post-anneal treatment with sandwiched between two flat glass plates, the PCL surface could be smoothed to Ra of 12.50 nm, and tight bonding could be obtained. Consequently, microfluidic devices consisting of plastic/PCL/plastic layers were successfully fabricated and therein the actuation of SMP valves without any leakage was demonstrated. The present technology is expected to be applicable to disposable microfluidic devices as required for point-of-care testing.

Artificial muscles made of chiral two-way shape memory polymer fibers

NASA Astrophysics Data System (ADS)

Yang, Qianxi; Fan, Jizhou; Li, Guoqiang

2016-10-01

In this work, we demonstrate the unusual improvement of the tensile actuation of hierarchically chiral structured artificial muscle made of two-way shape memory polymer (2W-SMP) fiber. Experimental results show that the chemically cross-linked poly(ethylene-co-vinyl acetate) 2W-SMP fibers possess an average negative coefficient of thermal expansion (NCTE) that is at least one order higher than that of the polyethylene fiber used previously. As expected, the increase in axial thermal contraction of the precursor fiber leads to an increase in the recovered torque ( 4.4 Nmm ) of the chiral fiber and eventually in the tensile actuation of the twisted-then-coiled artificial muscle ( 67.81 ±1.82 % ). A mechanical model based on Castigliano's second theorem is proposed, and the calculated result is consistent with the experimental result (64.17% tensile stroke). The model proves the significance of the NCTE and the recovered torque on tensile actuation of the artificial muscle and can be used as a guidance for the future design.

A 1D thermomechanical network transition constitutive model coupled with multiple structural relaxation for shape memory polymers

NASA Astrophysics Data System (ADS)

Zeng, Hao; Xie, Zhimin; Gu, Jianping; Sun, Huiyu

2018-03-01

A new thermomechanical network transition constitutive model is proposed in the study to describe the viscoelastic behavior of shape memory polymers (SMPs). Based on the microstructure of semi-crystalline SMPs, a new simplified transformation equation is proposed to describe the transform of transient networks. And the generalized fractional Maxwell model is introduced in the paper to estimate the temperature-dependent storage modulus. In addition, a neo-KAHR theory with multiple discrete relaxation processes is put forward to study the structural relaxation of the nonlinear thermal strain in cooling/heating processes. The evolution equations of the time- and temperature-dependent stress and strain response are developed. In the model, the thermodynamical and mechanical characteristics of SMPs in the typical thermomechanical cycle are described clearly and the irreversible deformation is studied in detail. Finally, the typical thermomechanical cycles are simulated using the present constitutive model, and the simulation results agree well with the experimental results.

A new bistable electroactive polymer for prolonged cycle lifetime of refreshable Braille displays

NASA Astrophysics Data System (ADS)

Ren, Zhi; Niu, Xiaofan; Chen, Dustin; Hu, Wei; Pei, Qibing

2014-03-01

ABSTRACT: Bistable electroactive polymers (BSEP) amalgamating electrically induced large-strain actuation and shape memory effect present a unique opportunity for refreshable Braille displays. A new BSEP material with long-chain crosslinkers to achieve prolonged cycle lifetime of refreshable Braille displays is reported here. The modulus of the BSEP material decreases by more than three orders of magnitude from a rigid, plastic state to a rubbery state when heated above the polymer's glass transition temperature. In its rubbery state, the polymer film can be electrically actuated to buckle convexly when a high voltage is applied across a circular active area. Modifying the concentration of long-chain crosslinkers in the polymer allows not only for fine-tuning of the polymer's glass transition temperature and elasticity in the rubbery state, but also enhancement of the actuation stability. For a raised height of 0.4 mm by a Braille dot with a 1.3 mm diameter, actuation can be repeated over 2000 cycles at 70°C in the rubbery state. The actuated dome shape can be fixed by cooling the polymer below the glass transition temperature. This refreshable rigid-to-rigid actuation simultaneously provides large-strain actuation and large force support. Devices capable of displaying Braille characters over a page-size area consisting of 324 Braille cells have been fabricated.

On a novel self-regulating shape memory polymer composite

NASA Astrophysics Data System (ADS)

Gao, Fei; Son, Seyul; Park, Kyungmook; Biggs, David; Andrews, Courtney; Mockensturm, Eric M.; Goulbourne, Nakhiah C.

2011-04-01

Polyurethane shape memory polymers (PU-SMPs) are active materials that can be transformed into complex shapes with the ability to recover their original shape even after undergoing large deformations. Because of their light weight, large recoverability, low cost, and high compliance, SMPs can be potentially employed as actuators, MEMS devices, temperature sensors, and damping elements to name a few. One of the key challenges in implementing SMPs is the response time which is limited by the method of heating and cooling and the material. Unlike shape memory alloys, SMPs can be activated by multiple stimuli including lasers, resistive heating, electric fields, and magnetic fields. While these methods may provide an efficient way of heating the SMP, they rely on the slow process of passive conduction for cooling. In this paper, a self regulating SMP (SR-SMP) composite is introduced, whereby a novel heating and cooling system consisting of embedded silica capillary tubes in the SMP (DiAPLEX® MP4510: SMP Technologies, Inc.) has been developed. The tubes are used to pump hot/cold fluid through the SMP membrane and hence provide a local temperature source. In order to show the effectiveness and efficiency of the mechanism, the thermomechanical response of the SR-SMP is compared experimentally to a SMP with "conventional" i.e. global heating and cooling mechanisms. It is shown that the SR-SMP has a faster thermomechanical response. It has been demonstrated previously that soft SMPs can be controlled by an electric field while in the rubbery phase, thus taking advantage of the Maxwell stress or electrostatic stress effect. Thermomechanical characterization of PU-SMPs is described for different weight percentages of resin (Diphenylmethane-4, 4'-diisocyanate) and hardener (1,4-Butanediol). Varying the percent hardener reduced the effective cross-link density of the polymer and hence the thermomechanical properties. The electromechanical response of pure SMP and SR-SMP is predicted numerically. The numerical computation indicates that the softer SMPs (resin:hardener = 5:4, 8:7, and 9:8) could be used as electroactive polymers.

Thermo-mechanical behavior and structure of melt blown shape-memory polyurethane nonwovens.

PubMed

Safranski, David L; Boothby, Jennifer M; Kelly, Cambre N; Beatty, Kyle; Lakhera, Nishant; Frick, Carl P; Lin, Angela; Guldberg, Robert E; Griffis, Jack C

2016-09-01

New processing methods for shape-memory polymers allow for tailoring material properties for numerous applications. Shape-memory nonwovens have been previously electrospun, but melt blow processing has yet to be evaluated. In order to determine the process parameters affecting shape-memory behavior, this study examined the effect of air pressure and collector speed on the mechanical behavior and shape-recovery of shape-memory polyurethane nonwovens. Mechanical behavior was measured by dynamic mechanical analysis and tensile testing, and shape-recovery was measured by unconstrained and constrained recovery. Microstructure changes throughout the shape-memory cycle were also investigated by micro-computed tomography. It was found that increasing collector speed increases elastic modulus, ultimate strength and recovery stress of the nonwoven, but collector speed does not affect the failure strain or unconstrained recovery. Increasing air pressure decreases the failure strain and increases rubbery modulus and unconstrained recovery, but air pressure does not influence recovery stress. It was also found that during the shape-memory cycle, the connectivity density of the fibers upon recovery does not fully return to the initial values, accounting for the incomplete shape-recovery seen in shape-memory nonwovens. With these parameter to property relationships identified, shape-memory nonwovens can be more easily manufactured and tailored for specific applications. Copyright © 2016 Elsevier Ltd. All rights reserved.

Space micro-guidance and control - Applications and architectures

NASA Technical Reports Server (NTRS)

Mettler, Edward; Hadaegh, Fred Y.

1992-01-01

The features and the components of a new microscale guidance, navigation, and control (GN&C) system for future space systems are discussed. An approach is described for the utilization of new microengineering technologies for achieving major reductions in the GN&C system's mass, size, power, and costs. The micro-GN&C system and the component concepts include microactuated adaptive optics, micromachined inertial sensors, fiberoptic data nets with light-power transmission, and VLSI microcomputers. The GN&C system will be applied in microspacecraft, microlanders, microrovers, remote sensing platforms, interferometers, and deployable reflectors.

Space micro-guidance and control - Applications and architectures

NASA Astrophysics Data System (ADS)

Mettler, Edward; Hadaegh, Fred Y.

1992-07-01

The features and the components of a new microscale guidance, navigation, and control (GN&C) system for future space systems are discussed. An approach is described for the utilization of new microengineering technologies for achieving major reductions in the GN&C system's mass, size, power, and costs. The micro-GN&C system and the component concepts include microactuated adaptive optics, micromachined inertial sensors, fiberoptic data nets with light-power transmission, and VLSI microcomputers. The GN&C system will be applied in microspacecraft, microlanders, microrovers, remote sensing platforms, interferometers, and deployable reflectors.

Review of Adaptive Programmable Materials and Their Bioapplications.

PubMed

Fan, Xiaoshan; Chung, Jing Yang; Lim, Yong Xiang; Li, Zibiao; Loh, Xian Jun

2016-12-14

Adaptive programmable materials have attracted increasing attention due to their high functionality, autonomous behavior, encapsulation, and site-specific confinement capabilities in various applications. Compared to conventional materials, adaptive programmable materials possess unique single-material architecture that can maintain, respond, and change their shapes and dimensions when they are subjected to surrounding environment changes, such as alternation in temperature, pH, and ionic strength. In this review, the most-recent advances in the design strategies of adaptive programmable materials are presented with respect to different types of architectural polymers, including stimuli-responsive polymers and shape-memory polymers. The diverse functions of these sophisticated materials and their significance in therapeutic agent delivery systems are also summarized in this review. Finally, the challenges for facile fabrication of these materials and future prospective are also discussed.

Monomeric and polymeric forms of ependymin: a brain extracellular glycoprotein implicated in memory consolidation processes.

PubMed

Shashoua, V E

1988-07-01

Ependymin, a brain extracellular glycoprotein that appears to be implicated in neural circuit modifications associated with the process of memory consolidation, can rapidly polymerize into fibrous aggregates when the Ca2+ concentration in solution is reduced by the addition of EGTA or by dialysis. Such aggregates, once formed, could not be redissolved in boiling 1% SDS in 6 M urea, acetic acid, saturated aqueous potassium thiocyanate, and trifluoroacetic acid. They were, however, soluble in formic acid. Investigations of the immunological properties of ependymin indicated that various monomers, oligomers and polymers of the molecule with differing carbohydrate contents can be obtained. The polymerization properties of the ependymins may play an important role in their functions in memory consolidation mechanisms.

Direct Observation of a Carbon Filament in Water-Resistant Organic Memory.

PubMed

Lee, Byung-Hyun; Bae, Hagyoul; Seong, Hyejeong; Lee, Dong-Il; Park, Hongkeun; Choi, Young Joo; Im, Sung-Gap; Kim, Sang Ouk; Choi, Yang-Kyu

2015-07-28

The memory for the Internet of Things (IoT) requires versatile characteristics such as flexibility, wearability, and stability in outdoor environments. Resistive random access memory (RRAM) to harness a simple structure and organic material with good flexibility can be an attractive candidate for IoT memory. However, its solution-oriented process and unclear switching mechanism are critical problems. Here we demonstrate iCVD polymer-intercalated RRAM (i-RRAM). i-RRAM exhibits robust flexibility and versatile wearability on any substrate. Stable operation of i-RRAM, even in water, is demonstrated, which is the first experimental presentation of water-resistant organic memory without any waterproof protection package. Moreover, the direct observation of a carbon filament is also reported for the first time using transmission electron microscopy, which puts an end to the controversy surrounding the switching mechanism. Therefore, reproducibility is feasible through comprehensive modeling. Furthermore, a carbon filament is superior to a metal filament in terms of the design window and selection of the electrode material. These results suggest an alternative to solve the critical issues of organic RRAM and an optimized memory type suitable for the IoT era.

Superhydrophobic Surface With Shape Memory Micro/Nanostructure and Its Application in Rewritable Chip for Droplet Storage.

PubMed

Lv, Tong; Cheng, Zhongjun; Zhang, Dongjie; Zhang, Enshuang; Zhao, Qianlong; Liu, Yuyan; Jiang, Lei

2016-09-21

Recently, superhydrophobic surfaces with tunable wettability have aroused much attention. Noticeably, almost all present smart performances rely on the variation of surface chemistry on static micro/nanostructure, to obtain a surface with dynamically tunable micro/nanostructure, especially that can memorize and keep different micro/nanostructures and related wettabilities, is still a challenge. Herein, by creating micro/nanostructured arrays on shape memory polymer, a superhydrophobic surface that has shape memory ability in changing and recovering its hierarchical structures and related wettabilities was reported. Meanwhile, the surface was successfully used in the rewritable functional chip for droplet storage by designing microstructure-dependent patterns, which breaks through current research that structure patterns cannot be reprogrammed. This article advances a superhydrophobic surface with shape memory hierarchical structure and the application in rewritable functional chip, which could start some fresh ideas for the development of smart superhydrophobic surface.

Shape-memory effect of nanocomposites based on liquid-crystalline elastomers

NASA Astrophysics Data System (ADS)

Marotta, A.; Lama, G. C.; Gentile, G.; Cerruti, P.; Carfagna, C.; Ambrogi, V.

2016-05-01

In this work, nanocomposites based on liquid crystalline (LC) elastomers were prepared and characterized in their shape memory properties. For the synthesis of materials, p-bis(2,3-epoxypropoxy)-α-methylstilbene (DOMS) was used as mesogenic epoxy monomer, sebacic acid (SA) as curing agent and multi-walled carbon nanotubes (MWCNT) and graphene oxide (GO) as fillers. First, an effective compatibilization methodology was set up to improve the interfacial adhesion between the matrix and the carbonaceous nanofillers, thus obtaining homogeneous distribution and dispersion of the nanofillers within the polymer phase. Then, the obtained nanocomposite films were characterized in their morphological and thermal properties. In particular, the effect of the addition of the nanofillers on liquid crystalline behavior, as well as on shape-memory properties of the realized materials was investigated. It was found that both fillers were able to enhance the thermomechanical response of the LC elastomers, making them good candidates as shape memory materials.

Achievement of two logical states through a polymer/silicon interface for organic-inorganic hybrid memory

NASA Astrophysics Data System (ADS)

Chen, Jianhui; Chen, Bingbing; Shen, Yanjiao; Guo, Jianxin; Liu, Baoting; Dai, Xiuhong; Xu, Ying; Mai, Yaohua

2017-11-01

A hysteresis loop of minority carrier lifetime vs voltage is found in polystyrenesulfonate (PSS)/Si organic-inorganic hybrid heterojunctions, implying an interfacial memory effect. Capacitance-voltage and conductance-voltage hysteresis loops are observed and reveal a memory window. A switchable interface state, which can be controlled by charge transfer based on an electrochemical oxidation/deoxidation process, is suggested to be responsible for this hysteresis effect. We perform first-principle total-energy calculations on the influence of external electric fields and electrons or holes, which are injected into interface states on the adsorption energy of PSS on Si. It is demonstrated that the dependence of the interface adsorption energy difference on the electric field is the origin of this two-state switching. These results offer a concept of organic-inorganic hybrid interface memory being optically or electrically readable, low-cost, and compatible with the flexible organic electronics.

Manifestation of the shape-memory effect in polyetherurethane cellular plastics, fabric composites, and sandwich structures under microgravity

NASA Astrophysics Data System (ADS)

Babaevskii, P. G.; Kozlov, N. A.; Agapov, I. G.; Reznichenko, G. M.; Churilo, N. V.; Churilo, I. V.

2016-09-01

The results of experiments that were performed to test the feasibility of creating sandwich structures (consisting of thin-layer sheaths of polymer composites and a cellular polymer core) with the shapememory effect as models of the transformable components of space structures have been given. The data obtained indicate that samples of sandwich structures under microgravity conditions on board the International Space Station have recovered their shape to almost the same degree as under terrestrial conditions, which makes it possible to recommend them for creating components of transformable space structures on their basis.

Characterizing filamentary switching in resistive memories (Presentation Recording)

NASA Astrophysics Data System (ADS)

Busby, Yan; Pireaux, Jean-Jacques

2015-09-01

Characterizing filamentary switching in resistive memories For many organic, inorganic and hybrid memory devices the resistive switching mechanism is well known to rely on filament formation [1]. This implies that localized conductive paths are established between the two terminal electrodes during the forming step. This filaments sustain the current flow when the memory is in the low conductive state and they can be ruptured and possibly re-formed for more than hundreds of I-V cycles. The nature and morphology of filaments has been long time debated especially for organic memories. The filament size, density and formation mechanism have been very challenging to be characterized, and need appropriate experimental techniques. However, filaments in organic memories have been recently identified and characterized by cross-section transmission electron microscopy (TEM), conductive-AFM, AFM-tomography and through depth profile analysis combining Time-of-flight secondary ions mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS). In particular, 3D spectroscopic images obtained with ToF-SIMS give access for the first time to filament formation process and rupture mechanism. From these results, a clear picture of the filament(s) dynamics during memory operation can be drawn. In this contribution, recent results showing filaments in memories based on different structures and architectures will be discussed. The memories are based on insulating polymers (polystyrene [2] and poly methyl methacrylate [3]), conductive polymers/nanocomposites (polyera N1400 with metal NPs [4]), and small semiconducting molecules (Tris(8-hydroxyquinolinato)aluminium - Alq3 [5]). The results show that resistive switching clearly involves the inhomogeneous metal diffusion in the organic layer taking place during the top electrode deposition and during memory operation. This may be of great relevance in many other organic electronics applications. REFERENCES [1] S. Nau, S. Sax, E.J.W. List-Kratochvil, Adv. Mater. 2014, 26, 2508-2513. [2] Y. Busby, N. Crespo-Monteiro, M. Girleanu, M. Brinkmann, O. Ersen, J.-J. Pireaux, Organic Electronics 2015, 16, 40-45. [3] C. Wolf, S. Nau, S. Sax, Y. Busby, J.-J. Pireaux, E.J.W. List-Kratochvil (under submission). [4] G. Casula, P. Cosseddu, Y. Busby, J.-J. Pireaux, M. Rosowski, B. Tkacz Szczesna, K. Soliwoda, G. Celichowski, J. Grobelny, J. Novák, R. Banerjee, F. Schreiber, A. Bonfiglio, Organic Electronics, 2015, 18, 17-23. [5] Y. Busby, S. Nau, S. Sax, E.J.W. List- Kratochvil, J. Novak, R. Banerjee, F. Schreiber, J.-J. Pireaux, (under submission)

A Summary of the Third Persh Conference: Strategic Issues in Materials for National Defense

DTIC Science & Technology

2012-12-01

addresses a distinct materials-related topic of strategic importance, ranging from thermal management materials to data mining, and from...such as aerogels, shape-memory alloys, polymers, electronic ink, and zeolites . The second demonstration kit, “Zoom in on Life,” investigates how the

Self-Positioned Nanosized Mask for Transparent and Flexible Ferroelectric Polymer Nanodiodes Array.

PubMed

Hyun, Seung; Kwon, Owoong; Choi, Chungryong; Vincent Joseph, Kanniyambatti L; Kim, Yunseok; Kim, Jin Kon

2016-10-12

High density arrays of ferroelectric polymer nanodiodes have gained strong attention for next-generation transparent and flexible nonvolatile resistive memory. Here, we introduce a facile and innovative method to fabricate ferroelectric polymer nanodiode array on an ITO-coated poly(ethylene terephthalate) (PET) substrate by using block copolymer self-assembly and oxygen plasma etching. First, polystyrene-block-poly(2-vinylpyridine) copolymer (PS-b-P2VP) micelles were spin-coated on poly(vinylidene fluoride-ran-trifluoroethylene) copolymer (P(VDF-TrFE)) film/ITO-coated PET substrate. After the sample was immersed in a gold precursor (HAuCl 4 ) containing solution, which strongly coordinates with nitrogen group in P2VP, oxygen plasma etching was performed. During the plasma etching, coordinated gold precursors became gold nanoparticles (GNPs), which successfully acted as self-positioned etching mask to fabricate a high density array of P(VDF-TrFE)) nanoislands with GNP at the top. Each nanoisland shows clearly individual diode property, as confirmed by current-voltage (I-V) curve. Furthermore, due to the transparent and flexible nature of P(VDF-TrFE)) nanoisland as well as the substrate, the P(VDF-TrFE) nanodiode array was highly tranparent, and the diode property was maintained even after a large number of bendings (for instance, 1000 times). The array could be used as the next-generation tranparent and flexible nonvolatile memory device.

Fire-Retardant, Self-Extinguishing Inorganic/Polymer Composite Memory Foams.

PubMed

Chatterjee, Soumyajyoti; Shanmuganathan, Kadhiravan; Kumaraswamy, Guruswamy

2017-12-27

Polymeric foams used in furniture and automotive and aircraft seating applications rely on the incorporation of environmentally hazardous fire-retardant additives to meet fire safety norms. This has occasioned significant interest in novel approaches to the elimination of fire-retardant additives. Foams based on polymer nanocomposites or based on fire-retardant coatings show compromised mechanical performance and require additional processing steps. Here, we demonstrate a one-step preparation of a fire-retardant ice-templated inorganic/polymer hybrid that does not incorporate fire-retardant additives. The hybrid foams exhibit excellent mechanical properties. They are elastic to large compressional strain, despite the high inorganic content. They also exhibit tunable mechanical recovery, including viscoelastic "memory". These hybrid foams are prepared using ice-templating that relies on a green solvent, water, as a porogen. Because these foams are predominantly comprised of inorganic components, they exhibit exceptional fire retardance in torch burn tests and are self-extinguishing. After being subjected to a flame, the foam retains its porous structure and does not drip or collapse. In micro-combustion calorimetry, the hybrid foams show a peak heat release rate that is only 25% that of a commercial fire-retardant polyurethanes. Finally, we demonstrate that we can use ice-templating to prepare hybrid foams with different inorganic colloids, including cheap commercial materials. We also demonstrate that ice-templating is amenable to scale up, without loss of mechanical performance or fire-retardant properties.

Active origami by 4D printing

NASA Astrophysics Data System (ADS)

Ge, Qi; Dunn, Conner K.; Qi, H. Jerry; Dunn, Martin L.

2014-09-01

Recent advances in three dimensional (3D) printing technology that allow multiple materials to be printed within each layer enable the creation of materials and components with precisely controlled heterogeneous microstructures. In addition, active materials, such as shape memory polymers, can be printed to create an active microstructure within a solid. These active materials can subsequently be activated in a controlled manner to change the shape or configuration of the solid in response to an environmental stimulus. This has been termed 4D printing, with the 4th dimension being the time-dependent shape change after the printing. In this paper, we advance the 4D printing concept to the design and fabrication of active origami, where a flat sheet automatically folds into a complicated 3D component. Here we print active composites with shape memory polymer fibers precisely printed in an elastomeric matrix and use them as intelligent active hinges to enable origami folding patterns. We develop a theoretical model to provide guidance in selecting design parameters such as fiber dimensions, hinge length, and programming strains and temperature. Using the model, we design and fabricate several active origami components that assemble from flat polymer sheets, including a box, a pyramid, and two origami airplanes. In addition, we directly print a 3D box with active composite hinges and program it to assume a temporary flat shape that subsequently recovers to the 3D box shape on demand.

Synergistic High Charge-Storage Capacity for Multi-level Flexible Organic Flash Memory

NASA Astrophysics Data System (ADS)

Kang, Minji; Khim, Dongyoon; Park, Won-Tae; Kim, Jihong; Kim, Juhwan; Noh, Yong-Young; Baeg, Kang-Jun; Kim, Dong-Yu

2015-07-01

Electret and organic floating-gate memories are next-generation flash storage mediums for printed organic complementary circuits. While each flash memory can be easily fabricated using solution processes on flexible plastic substrates, promising their potential for on-chip memory organization is limited by unreliable bit operation and high write loads. We here report that new architecture could improve the overall performance of organic memory, and especially meet high storage for multi-level operation. Our concept depends on synergistic effect of electrical characterization in combination with a polymer electret (poly(2-vinyl naphthalene) (PVN)) and metal nanoparticles (Copper). It is distinguished from mostly organic nano-floating-gate memories by using the electret dielectric instead of general tunneling dielectric for additional charge storage. The uniform stacking of organic layers including various dielectrics and poly(3-hexylthiophene) (P3HT) as an organic semiconductor, followed by thin-film coating using orthogonal solvents, greatly improve device precision despite easy and fast manufacture. Poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] as high-k blocking dielectric also allows reduction of programming voltage. The reported synergistic organic memory devices represent low power consumption, high cycle endurance, high thermal stability and suitable retention time, compared to electret and organic nano-floating-gate memory devices.

Low-voltage-operated organic one-time programmable memory using printed organic thin-film transistors and antifuse capacitors.

PubMed

Jung, Soon-Won; Na, Bock Soon; Park, Chan Woo; Koo, Jae Bon

2014-11-01

We demonstrate an organic one-time programmable memory cell formed entirely at plastic-compatible temperatures. All the processes are performed at below 130 degrees C. Our memory cell consists of a printed organic transistor and an organic capacitor. Inkjet-printed organic transistors are fabricated by using high-k polymer dielectric blends comprising poly(vinylidenefluoride-trifluoroethylene) [P(VDF-TrFE)] and poly(methyl methacrylate) (PMMA) for low-voltage operation. P(NDI2OD-T2) transistors have a high field-effect mobility of 0.2 cm2/Vs and a low operation gate voltage of less than 10 V. The operation voltage effectively decreases owing to the high permittivity of the P(VDF-TrFE):PMMA blended film. The data in the memory cell are programmed by electrically breaking the organic capacitor. The organic capacitor acts like an antifuse capacitor, because it is initially open, and it becomes permanently short-circuited by applying a high voltage. The organic memory cells are programmed with 4 V, and they are read out with 2 V. The memory data are read out by sensing the current in the memory cell. The printed organic one-time programmable memory is suitable for applications storing small amount of data, such as low-cost radio-frequency identification (RFID) tag.

Synergistic High Charge-Storage Capacity for Multi-level Flexible Organic Flash Memory.

PubMed

Kang, Minji; Khim, Dongyoon; Park, Won-Tae; Kim, Jihong; Kim, Juhwan; Noh, Yong-Young; Baeg, Kang-Jun; Kim, Dong-Yu

2015-07-23

Electret and organic floating-gate memories are next-generation flash storage mediums for printed organic complementary circuits. While each flash memory can be easily fabricated using solution processes on flexible plastic substrates, promising their potential for on-chip memory organization is limited by unreliable bit operation and high write loads. We here report that new architecture could improve the overall performance of organic memory, and especially meet high storage for multi-level operation. Our concept depends on synergistic effect of electrical characterization in combination with a polymer electret (poly(2-vinyl naphthalene) (PVN)) and metal nanoparticles (Copper). It is distinguished from mostly organic nano-floating-gate memories by using the electret dielectric instead of general tunneling dielectric for additional charge storage. The uniform stacking of organic layers including various dielectrics and poly(3-hexylthiophene) (P3HT) as an organic semiconductor, followed by thin-film coating using orthogonal solvents, greatly improve device precision despite easy and fast manufacture. Poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] as high-k blocking dielectric also allows reduction of programming voltage. The reported synergistic organic memory devices represent low power consumption, high cycle endurance, high thermal stability and suitable retention time, compared to electret and organic nano-floating-gate memory devices.

Thin Rechargeable Batteries for CMOS SRAM Memory Protection

NASA Technical Reports Server (NTRS)

Crouse, Dennis N.

1993-01-01

New rechargeable battery technology is described and compared with classical primary battery back-up of SRAM PC cards. Thin solid polymer electrolyte cells with the thickness of TSOP memory components (1 mm nominal, 1.1 mm max) and capacities of 14 mAh/sq cm can replace coin cells. The SRAM PC cards with permanently installed rechargeable cells and optional electrochromic low battery voltage indicators will free the periodic PC card user from having to 'feed' their PC cards with coin cells and will allow a quick visual check of stored cards for their battery voltage status.

Hysteresis and memory factor of the Kerr effect in blue phases

NASA Astrophysics Data System (ADS)

Nordendorf, Gaby; Lorenz, Alexander; Hoischen, Andreas; Schmidtke, Jürgen; Kitzerow, Heinz; Wilkes, David; Wittek, Michael

2013-11-01

The performance of a polymer-stabilized blue phase system based on a nematic host with large dielectric anisotropy and a chiral dopant with high helical twisting power is investigated and the influence of the reactive monomer composition on the electro-optic characteristics is studied. Field-induced birefringence with a Kerr coefficient greater than 1 nm V-2 can be achieved in a large temperature range from well below 20 °C to above 55 °C. The disturbing influences of electro-optic hysteresis and memory effects can be reduced by diligent choice of the composition and appropriate electric addressing.

Dynamically Cross-linked Elastomer Hybrids with Light-Induced Rapid and Efficient Self-Healing Ability and Reprogrammable Shape Memory Behavior.

PubMed

Bai, Jing; Shi, Zixing

2017-08-16

Pristine carbon nanotubes (CNTs) were activated to exhibit Diels-Alder (DA) reactivity in a polymer matrix, which was modified with monomers containing furan groups. The DA-active polymer matrix was transferred into a dynamic reversible cross-linked inorganic-organic network via a Diels-Alder reaction with CNTs, where pristine CNTs were used as dienophile chemicals and furan-modified SBS acted as the macromolecular diene. In this system, the mechanical properties as well as resilience and solvent resistance were greatly improved even with the presence of only 1 wt % CNTs. Meanwhile, the hybrids retained recyclability and exhibited some smart behaviors, including self-healing and reprogrammable shape memory properties. Furthermore, due to the photothermal effect of CNTs, a retro-Diels-Alder (rDA) reaction was activated under laser irradiation, and healing of a crack on the hybrid surface was demonstrated in approximately 10 s with almost complete recovery of the mechanical properties. Such fast and efficient self-healing performance provides a new concept in designing self-healing nanocomposites with tunable structures and mechanical properties. Furthermore, the DA and rDA reactions could be combined to reprogram the shape memory behavior under laser irradiation or thermal treatment, wherein the temporary shape of the sample could be transferred to a permanent shape via the rDA reaction at high temperature.

Reflexive composites: self-healing composite structures

NASA Astrophysics Data System (ADS)

Margraf, Thomas W., Jr.; Barnell, Thomas J.; Havens, Ernie; Hemmelgarn, Christopher D.

2008-03-01

Cornerstone Research Group Inc. has developed reflexive composites achieving increased vehicle survivability through integrated structural awareness and responsiveness to damage. Reflexive composites can sense damage through integrated piezoelectric sensing networks and respond to damage by heating discrete locations to activate the healable polymer matrix in areas of damage. The polymer matrix is a modified thermoset shape memory polymer that heals based on phenomena known as reptation. In theory, the reptation healing phenomena should occur in microseconds; however, during experimentation, it has been observed that to maximize healing and restore up to 85 % of mechanical properties a healing cycle of at least three minutes is required. This paper will focus on work conducted to determine the healing mechanisms at work in CRG's reflexive composites, the optimal healing cycles, and an explanation of the difference between the reptation model and actual healing times.

Aging, memory, and nonhierarchical energy landscape of spin jam

NASA Astrophysics Data System (ADS)

Samarakoon, Anjana; Sato, Taku J.; Chen, Tianran; Chern, Gai-Wei; Yang, Junjie; Klich, Israel; Sinclair, Ryan; Zhou, Haidong; Lee, Seung-Hun

2016-10-01

The notion of complex energy landscape underpins the intriguing dynamical behaviors in many complex systems ranging from polymers, to brain activity, to social networks and glass transitions. The spin glass state found in dilute magnetic alloys has been an exceptionally convenient laboratory frame for studying complex dynamics resulting from a hierarchical energy landscape with rugged funnels. Here, we show, by a bulk susceptibility and Monte Carlo simulation study, that densely populated frustrated magnets in a spin jam state exhibit much weaker memory effects than spin glasses, and the characteristic properties can be reproduced by a nonhierarchical landscape with a wide and nearly flat but rough bottom. Our results illustrate that the memory effects can be used to probe different slow dynamics of glassy materials, hence opening a window to explore their distinct energy landscapes.

Nonvolatile Ferroelectric Memory Circuit Using Black Phosphorus Nanosheet-Based Field-Effect Transistors with P(VDF-TrFE) Polymer.

PubMed

Lee, Young Tack; Kwon, Hyeokjae; Kim, Jin Sung; Kim, Hong-Hee; Lee, Yun Jae; Lim, Jung Ah; Song, Yong-Won; Yi, Yeonjin; Choi, Won-Kook; Hwang, Do Kyung; Im, Seongil

2015-10-27

Two-dimensional van der Waals (2D vdWs) materials are a class of new materials that can provide important resources for future electronics and materials sciences due to their unique physical properties. Among 2D vdWs materials, black phosphorus (BP) has exhibited significant potential for use in electronic and optoelectronic applications because of its allotropic properties, high mobility, and direct and narrow band gap. Here, we demonstrate a few-layered BP-based nonvolatile memory transistor with a poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)) ferroelectric top gate insulator. Experiments showed that our BP-based ferroelectric transistors operate satisfactorily at room temperature in ambient air and exhibit a clear memory window. Unlike conventional ambipolar BP transistors, our ferroelectric transistors showed only p-type characteristics due to the carbon-fluorine (C-F) dipole effect of the P(VDF-TrFE) layer, as well as the highest linear mobility value of 1159 cm(2) V(-1) s(-1) with a 10(3) on/off current ratio. For more advanced memory applications beyond unit memory devices, we implemented two memory inverter circuits, a resistive-load inverter circuit and a complementary inverter circuit, combined with an n-type molybdenum disulfide (MoS2) nanosheet. Our memory inverter circuits displayed a clear memory window of 15 V and memory output voltage efficiency of 95%.

Self-healing polymers and composites based on thermal activation

NASA Astrophysics Data System (ADS)

Wang, Ying; Bolanos, Ed; Wudl, Fred; Hahn, Thomas; Kwok, Nathan

2007-04-01

Structural polymer composites are susceptible to premature failure in the form of microcracks in the matrix. Although benign initially when they form, these matrix cracks tend to coalesce and lead in service to critical damage modes such as ply delamination. The matrix cracks are difficult to detect and almost impossible to repair because they form inside the composite laminate. Therefore, polymers with self-healing capability would provide a promising potential to minimize maintenance costs while extending the service lifetime of composite structures. In this paper we report on a group of polymers and their composites which exhibit mendable property upon heating. The failure and healing mechanisms of the polymers involve Diels-Alder (DA) and retro-Diels-Alder (RDA) reactions on the polymer back-bone chain, which are thermally reversible reactions requiring no catalyst. The polymers exhibited good healing property in bulk form. Composite panels were prepared by sandwiching the monomers between carbon fiber fabric layers and cured in autoclave. Microcracks were induced on the resin-rich surface of composite with Instron machine at room temperature by holding at 1% strain for 1 min. The healing ability of the composite was also demonstrated by the disappearance of microcracks after heating. In addition to the self-healing ability, the polymers and composites also exhibited shape memory property. These unique properties may provide the material multi-functional applications. Resistance heating of traditional composites and its applicability in self-healing composites is also studied to lay groundwork for a fully integrated self-healing composite.

Toward Self-Control Systems for Neurogenic Underactive Bladder: A Triboelectric Nanogenerator Sensor Integrated with a Bistable Micro-Actuator.

PubMed

Arab Hassani, Faezeh; Mogan, Roshini P; Gammad, Gil G L; Wang, Hao; Yen, Shih-Cheng; Thakor, Nitish V; Lee, Chengkuo

2018-04-24

Aging, neurologic diseases, and diabetes are a few risk factors that may lead to underactive bladder (UAB) syndrome. Despite all of the serious consequences of UAB, current solutions, the most common being ureteric catheterization, are all accompanied by serious shortcomings. The necessity of multiple catheterizations per day for a physically able patient not only reduces the quality of life with constant discomfort and pain but also can end up causing serious complications. Here, we present a bistable actuator to empty the bladder by incorporating shape memory alloy components integrated on flexible polyvinyl chloride sheets. The introduction of two compression and restoration phases for the actuator allows for repeated actuation for a more complete voiding of the bladder. The proposed actuator exhibits one of the highest reported voiding percentages of up to 78% of the bladder volume in an anesthetized rat after only 20 s of actuation. This amount of voiding is comparable to the common catheterization method, and its one time implantation onto the bladder rectifies the drawbacks of multiple catheterizations per day. Furthermore, the scaling of the device for animal models larger than rats can be easily achieved by adjusting the number of nitinol springs. For neurogenic UAB patients with degraded nerve function as well as degenerated detrusor muscle, we integrate a flexible triboelectric nanogenerator sensor with the actuator to detect the fullness of the bladder. The sensitivity of this sensor to the filling status of the bladder shows its capability for defining a self-control system in the future that would allow autonomous micturition.

Shape Memory Polymers: A Joint Chemical and Materials Engineering Hands-On Experience

ERIC Educational Resources Information Center

Seif, Mujan; Beck, Matthew

2018-01-01

Hands-on experiences are excellent tools for increasing retention of first year engineering students. They also encourage interdisciplinary collaboration, a critical skill for modern engineers. In this paper, we describe and evaluate a joint Chemical and Materials Engineering hands-on lab that explores cross-linking and glass transition in…

A simplified constitutive model for predicting shape memory polymers deformation behavior

NASA Astrophysics Data System (ADS)

Li, Yunxin; Guo, Siu-Siu; He, Yuhao; Liu, Zishun

2015-12-01

Shape memory polymers (SMPs) can keep a temporary shape after pre-deformation at a higher temperature and subsequent cooling. When they are reheated, their original shapes can be recovered. Such special characteristics of SMPs make them widely used in aerospace structures, biomedical devices, functional textiles and other devices. Increasing usefulness of SMPs motivates us to further understand their thermomechanical properties and deformation behavior, of which the development of appropriate constitutive models for SMPs is imperative. There is much work in literatures that address constitutive models of the thermo-mechanical coupling in SMPs. However, due to their complex forms, it is difficult to apply these constitutive models in the real world. In this paper, a three-element model with simple form is proposed to investigate the thermo-mechanical small strain (within 10%) behavior of polyurethane under uniaxial tension. Two different cases of heated recovery are considered: (1) unconstrained free strain recovery and (2) stress recovery under full constraint at a strain level fixed during low temperature unloading. To validate the model, simulated and predicted results are compared with Tobushi's experimental results and good agreement can be observed.

3D Printing of Highly Stretchable, Shape-Memory, and Self-Healing Elastomer toward Novel 4D Printing.

PubMed

Kuang, Xiao; Chen, Kaijuan; Dunn, Conner K; Wu, Jiangtao; Li, Vincent C F; Qi, H Jerry

2018-02-28

The three-dimensional (3D) printing of flexible and stretchable materials with smart functions such as shape memory (SM) and self-healing (SH) is highly desirable for the development of future 4D printing technology for myriad applications, such as soft actuators, deployable smart medical devices, and flexible electronics. Here, we report a novel ink that can be used for the 3D printing of highly stretchable, SM, and SH elastomer via UV-light-assisted direct-ink-write printing. An ink containing urethane diacrylate and a linear semicrystalline polymer is developed for the 3D printing of a semi-interpenetrating polymer network elastomer that can be stretched by up to 600%. The 3D-printed complex structures show interesting functional properties, such as high strain SM and SM -assisted SH capability. We demonstrate that such a 3D-printed SM elastomer has the potential application for biomedical devices, such as vascular repair devices. This research paves a new way for the further development of novel 4D printing, soft robotics, and biomedical devices.

Characterizing and modeling the free recovery and constrained recovery behavior of a polyurethane shape memory polymer

NASA Astrophysics Data System (ADS)

Volk, Brent L.; Lagoudas, Dimitris C.; Maitland, Duncan J.

2011-09-01

In this work, tensile tests and one-dimensional constitutive modeling were performed on a high recovery force polyurethane shape memory polymer that is being considered for biomedical applications. The tensile tests investigated the free recovery (zero load) response as well as the constrained displacement recovery (stress recovery) response at extension values up to 25%, and two consecutive cycles were performed during each test. The material was observed to recover 100% of the applied deformation when heated at zero load in the second thermomechanical cycle, and a stress recovery of 1.5-4.2 MPa was observed for the constrained displacement recovery experiments. After the experiments were performed, the Chen and Lagoudas model was used to simulate and predict the experimental results. The material properties used in the constitutive model—namely the coefficients of thermal expansion, shear moduli, and frozen volume fraction—were calibrated from a single 10% extension free recovery experiment. The model was then used to predict the material response for the remaining free recovery and constrained displacement recovery experiments. The model predictions match well with the experimental data.

Solvent stimulated actuation of polyurethane-based shape memory polymer foams using dimethyl sulfoxide and ethanol

NASA Astrophysics Data System (ADS)

Boyle, A. J.; Weems, A. C.; Hasan, S. M.; Nash, L. D.; Monroe, M. B. B.; Maitland, D. J.

2016-07-01

Solvent exposure has been investigated to trigger actuation of shape memory polymers (SMPs) as an alternative to direct heating. This study aimed to investigate the feasibility of using dimethyl sulfoxide (DMSO) and ethanol (EtOH) to stimulate polyurethane-based SMP foam actuation and the required solvent concentrations in water for rapid actuation of hydrophobic SMP foams. SMP foams exhibited decreased T g when submerged in DMSO and EtOH when compared to water submersion. Kinetic DMA experiments showed minimal or no relaxation for all SMP foams in water within 30 min, while SMP foams submerged in EtOH exhibited rapid relaxation within 1 min of submersion. SMP foams expanded rapidly in high concentrations of DMSO and EtOH solutions, where complete recovery over 30 min was observed in DMSO concentrations greater than 90% and in EtOH concentrations greater than 20%. This study demonstrates that both DMSO and EtOH are effective at triggering volume recovery of polyurethane-based SMP foams, including in aqueous environments, and provides promise for use of this actuation technique in various applications.

Shape forming by thermal expansion mismatch and shape memory locking in polymer/elastomer laminates

NASA Astrophysics Data System (ADS)

Yuan, Chao; Ding, Zhen; Wang, T. J.; Dunn, Martin L.; Qi, H. Jerry

2017-10-01

This paper studies a novel method to fabricate three-dimensional (3D) structure from 2D thermo-responsive shape memory polymer (SMP)/elastomer bilayer laminate. In this method, the shape change is actuated by the thermal mismatch strain between the SMP and the elastomer layers upon heating. However, the glass transition behavior of the SMP locks the material into a new 3D shape that is stable even upon cooling. Therefore, the second shape becomes a new permanent shape of the laminate. A theoretical model that accounts for the temperature-dependent thermomechanical behavior of the SMP material and thermal mismatch strain between the two layers is developed to better understand the underlying physics. Model predictions and experiments show good agreement and indicate that the theoretical model can well predict the bending behavior of the bilayer laminate. The model is then used in the optimal design of geometrical configuration and material selection. The latter also illustrates the requirement of thermomechanical behaviors of the SMP to lock the shape. Based on the fundamental understandings, several self-folding structures are demonstrated by the bilayer laminate design.

Effect of Graphene Addition on Shape Memory Behavior of Epoxy Resins

NASA Technical Reports Server (NTRS)

Williams, Tiffany; Meador, Michael; Miller, Sandi; Scheiman, Daniel

2011-01-01

Shape memory polymers (SMPs) and composites are a special class of smart materials known for their ability to change size and shape upon exposure to an external stimulus (e.g. light, heat, pH, or magnetic field). These materials are commonly used for biomedical applications; however, recent attempts have been made towards developing SMPs and composites for use in aircraft and space applications. Implementing SMPs and composites to create a shape change effect in some aircraft structures could potentially reduce drag, decrease fuel consumption, and improve engine performance. This paper discusses the development of suitable materials to use in morphing aircraft structures. Thermally responsive epoxy SMPs and nanocomposites were developed and the shape memory behavior and thermo-mechanical properties were studied. Overall, preliminary results from dynamic mechanical analysis (DMA) showed that thermally actuated shape memory epoxies and nanocomposites possessed Tgs near approximately 168 C. When graphene nanofiller was added, the storage modulus and crosslinking density decreased. On the other hand, the addition of graphene enhanced the recovery behavior of the shape memory nanocomposites. It was assumed that the addition of graphene improved shape memory recovery by reducing the crosslinking density and increasing the elasticity of the nanocomposites.

Modeling of grating formation in photopolymer that does not need scheduling (Conference Presentation)

NASA Astrophysics Data System (ADS)

Shimura, Tsutomu; Takeda, Yuki; Endo, Masao; Umegaki, Shinsuke; Fujimura, Ryushi

2016-09-01

Recently new photopolymers that does not require scheduled exposure in the multiple page writing for the holographic memory was introduced. Its sensitivity does not decrease throughout the multiple page writing process. We will explain why this photopolymer has such a property with our reaction model. The key is the existence of the molecules which make seeds of the polymers. At the first exposure process to record the page data, seeds are produced corresponding to the light intensity distribution. Then after writing the information of all multiplexed pages, the seeds are growing to be polymers under the spatially uniform light illumination.

Analysis of photonic band gap in novel piezoelectric photonic crystal

NASA Astrophysics Data System (ADS)

Malar Kodi, A.; Doni Pon, V.; Joseph Wilson, K. S.

2018-03-01

The transmission properties of one-dimensional novel photonic crystal having silver-doped novel piezoelectric superlattice and air as the two constituent layers have been investigated by means of transfer matrix method. By changing the appropriate thickness of the layers and filling factor of nanocomposite system, the variation in the photonic band gap can be studied. It is found that the photonic band gap increases with the filling factor of the metal nanocomposite and with the thickness of the layer. These structures possess unique characteristics enabling one to operate as optical waveguides, selective filters, optical switches, integrated piezoelectric microactuators, etc.

Detection of Brownian Torque in a Magnetically-Driven Rotating Microsystem

PubMed Central

Romodina, Maria N.; Lyubin, Evgeny V.; Fedyanin, Andrey A.

2016-01-01

Thermal fluctuations significantly affect the behavior of microscale systems rotating in shear flow, such as microvortexes, microbubbles, rotating micromotors, microactuators and other elements of lab-on-a-chip devices. The influence of Brownian torque on the motion of individual magnetic microparticles in a rotating magnetic field is experimentally determined using optical tweezers. Rotational Brownian motion induces the flattening of the breakdown transition between the synchronous and asynchronous modes of microparticle rotation. The experimental findings regarding microparticle rotation in the presence of Brownian torque are compared with the results of numerical Brownian dynamics simulations. PMID:26876334

Micro guidance and control synthesis: New components, architectures, and capabilities

NASA Technical Reports Server (NTRS)

Mettler, Edward; Hadaegh, Fred Y.

1993-01-01

New GN&C (guidance, navigation and control) system capabilities are shown to arise from component innovations that involve the synergistic use of microminiature sensors and actuators, microelectronics, and fiber optics. Micro-GN&C system and component concepts are defined that include micro-actuated adaptive optics, micromachined inertial sensors, fiber-optic data nets and light-power transmission, and VLSI microcomputers. The thesis is advanced that these micro-miniaturization products are capable of having a revolutionary impact on space missions and systems, and that GN&C is the pathfinder micro-technology application that can bring that about.

Control of microfabricated structures powered by flagellated bacteria using phototaxis

NASA Astrophysics Data System (ADS)

Steager, Edward; Kim, Chang-Beom; Patel, Jigarkumar; Bith, Socheth; Naik, Chandan; Reber, Lindsay; Kim, Min Jun

2007-06-01

Flagellated bacteria have been employed as microactuators in low Reynolds number fluidic environments. SU-8 microstructures have been fabricated and released on the surface of swarming Serratia marcescens, and the flagella propel the structures along the swarm surface. Phototactic control of these structures is demonstrated by exposing the localized regions of the swarm to ultraviolet light. The authors additionally discuss the control of microstructures in an open channel powered by bacteria which have been docked through a blotting technique. A tracking algorithm has been developed to analyze swarming patterns of the bacteria as well as the kinematics of the microstructures.

A ‘frozen volume’ transition model and working mechanism for the shape memory effect in amorphous polymers

NASA Astrophysics Data System (ADS)

Lu, Haibao; Wang, Xiaodong; Yao, Yongtao; Qing Fu, Yong

2018-06-01

Phenomenological models based on frozen volume parameters could well predict shape recovery behavior of shape memory polymers (SMPs), but the physical meaning of using the frozen volume parameters to describe thermomechanical properties has not been well-established. In this study, the fundamental working mechanisms of the shape memory effect (SME) in amorphous SMPs, whose temperature-dependent viscoelastic behavior follows the Eyring equation, have been established with the considerations of both internal stress and its resulted frozen volume. The stress-strain constitutive relation was initially modeled to quantitatively describe effects of internal stresses at the macromolecular scale based on the transient network theory. A phenomenological ‘frozen volume’ model was then established to characterize the macromolecule structure and SME of amorphous SMPs based on a two-site stress-relaxation model. Effects of the internal stress, frozen volume and strain rate on shape memory behavior and thermomechanical properties of the SMP were investigated. Finally, the simulation results were compared with the experimental results reported in the literature, and good agreements between the theoretical and experimental results were achieved. The novelty and key differences of our newly proposed model with respect to the previous reports are (1). The ‘frozen volume’ in our study is caused by the internal stress and governed by the two-site model theory, thus has a good physical meaning. (2). The model can be applied to characterize and predict both the thermal and thermomechanical behaviors of SMPs based on the constitutive relationship with internal stress parameters. It is expected to provide a power tool to investigate the thermomechanical behavior of the SMPs, of which both the macromolecular structure characteristics and SME could be predicted using this ‘frozen volume’ model.

An All-Organic Composite System for Resistive Change Memory via the Self-Assembly of Plastic-Crystalline Molecules.

PubMed

Cha, An-Na; Lee, Sang-A; Bae, Sukang; Lee, Sang Hyun; Lee, Dong Su; Wang, Gunuk; Kim, Tae-Wook

2017-01-25

An all-organic composite system was introduced as an active component for organic resistive memory applications. The active layer was prepared by mixing a highly polar plastic-crystalline organic molecule (succinonitrile, SN) into an insulating polymer (poly(methyl methacrylate), PMMA). As increasing concentrations of SN from 0 to 3.0 wt % were added to solutions of different concentrations of PMMA, we observed distinguishable microscopic surface structures on blended films of SN and PMMA at certain concentrations after the spin-casting process. The structures were organic dormant volcanos composed of micron-scale PMMA craters and disk type SN lava. Atomic force microscopy (AFM), cross-sectional transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy dispersive X-ray spectrometer (EDX) analysis showed that these structures were located in the middle of the film. Self-assembly of the plastic-crystalline molecules resulted in the phase separation of the SN:PMMA mixture during solvent evaporation. The organic craters remained at the surface after the spin-casting process, indicative of the formation of an all-organic composite film. Because one organic crater contains one SN disk, our system has a coplanar monolayer disk composite system, indicative of the simplest composite type of organic memory system. Current-voltage (I-V) characteristics of the composite films with organic craters revealed that our all-organic composite system showed unipolar type resistive switching behavior. From logarithmic I-V characteristics, we found that the current flow was governed by space charge limited current (SCLC). From these results, we believe that a plastic-crystalline molecule-polymer composite system is one of the most reliable ways to develop organic composite systems as potential candidates for the active components of organic resistive memory applications.

Biodegradable toughened nanohybrid shape memory polymer for smart biomedical applications.

PubMed

Biswas, Arpan; Singh, Akhand Pratap; Rana, Dipak; Aswal, Vinod K; Maiti, Pralay

2018-05-31

A polyurethane nanohybrid has been prepared through the in situ polymerization of an aliphatic diisocyanate, ester polyol and a chain extender in the presence of two-dimensional platelets. Polymerization within the platelet galleries helps to intercalate, generate diverse nanostructure and improve the nano to macro scale self-assembly, which leads to a significant enhancement in the toughness and thermal stability of the nanohybrid in comparison to pure polyurethane. The extensive interactions, the reason for property enhancement, between nanoplatelets and polymer chains are revealed through spectroscopic measurements and thermal studies. The nanohybrid exhibits significant improvement in the shape memory phenomena (91% recovery) at the physiological temperature, which makes it suitable for many biomedical applications. The structural alteration, studied through temperature dependent small angle neutron scattering and X-ray diffraction, along with unique crystallization behavior have extensively revealed the special shape memory behavior of this nanohybrid and facilitated the understanding of the molecular flipping in the presence of nanoplatelets. Cell line studies and subsequent imaging testify that this nanohybrid is a superior biomaterial that is suitable for use in the biomedical arena. In vivo studies on albino rats exhibit the potential of the shape memory effect of the nanohybrid as a self-tightening suture in keyhole surgery by appropriately closing the lips of the wound through the recovery of the programmed shape at physiological temperature with faster healing of the wound and without the formation of any scar. Further, the improved biodegradable nature along with the rapid self-expanding ability of the nanohybrid at 37 °C make it appropriate for many biomedical applications including a self-expanding stent for occlusion recovery due to its tough and flexible nature.

An annulus fibrosus closure device based on a biodegradable shape-memory polymer network.

PubMed

Sharifi, Shahriar; van Kooten, Theo G; Kranenburg, Hendrik-Jan C; Meij, Björn P; Behl, Marc; Lendlein, Andreas; Grijpma, Dirk W

2013-11-01

Injuries to the intervertebral disc caused by degeneration or trauma often lead to tearing of the annulus fibrosus (AF) and extrusion of the nucleus pulposus (NP). This can compress nerves and cause lower back pain. In this study, the characteristics of poly(D,L-lactide-co-trimethylene carbonate) networks with shape-memory properties have been evaluated in order to prepare biodegradable AF closure devices that can be implanted minimally invasively. Four different macromers with (D,L-lactide) to trimethylene carbonate (DLLA:TMC) molar ratios of 80:20, 70:30, 60:40 and 40:60 with terminal methacrylate groups and molecular weights of approximately 30 kg mol(-1) were used to prepare the networks by photo-crosslinking. The mechanical properties of the samples and their shape-memory properties were determined at temperatures of 0 °C and 40 °C by tensile tests- and cyclic, thermo-mechanical measurements. At 40 °C all networks showed rubber-like behavior and were flexible with elastic modulus values of 1.7-2.5 MPa, which is in the range of the modulus values of human annulus fibrosus tissue. The shape-memory characteristics of the networks were excellent with values of the shape-fixity and the shape-recovery ratio higher than 98 and 95%, respectively. The switching temperatures were between 10 and 39 °C. In vitro culture and qualitative immunocytochemistry of human annulus fibrosus cells on shape-memory films with DLLA:TMC molar ratios of 60:40 showed very good ability of the networks to support the adhesion and growth of human AF cells. When the polymer network films were coated by adsorption of fibronectin, cell attachment, cell spreading, and extracellular matrix production was further improved. Annulus fibrosus closure devices were prepared from these AF cell-compatible materials by photo-polymerizing the reactive precursors in a mold. Insertion of the multifunctional implant in the disc of a cadaveric canine spine showed that these shape-memory devices could be implanted through a small slit and to some extent deploy self-sufficiently within the disc cavity. © 2013 Elsevier Ltd. All rights reserved.

Fabrication and characterization of a magnetic micro-actuator based on deformable Fe-doped PDMS artificial cilium using 3D printing

NASA Astrophysics Data System (ADS)

Liu, Fengli; Alici, Gursel; Zhang, Binbin; Beirne, Stephen; Li, Weihua

2015-03-01

This paper proposes the use of a 3D extrusion printer to fabricate artificial magnetic cilium. The cilia are fabricated using polydimethylsiloxane (PDMS) doped with iron particles so that they remain slender and flexible. They can be driven by a magnetic field to closely mimic the behaviour of biological cilia. Doping iron particles to the polymers has already been done; however, to the best of our knowledge, printing such active and soft magnetic structures has not. The existing methods for manufacturing magnetic polymeric structures are complex and difficult to use for the fabrication of micro-sized high-aspect-ratio cilia. The 3D printing technique we propose here is simple and inexpensive compared to previously suggested fabrication methods. In this study, free-standing magnetic PDMS cilia were fabricated in different sizes up to 5 mm in length and 1 mm in width. The stress-strain curves of the PDMS cilia were experimentally obtained to quantify the effect of the concentration of the iron particles on the modulus of elasticity of the cilia. The higher the iron concentration, the higher the modulus of elasticity. We have quantified the characteristics of the cilia made of 40% w/w iron particles in PDMS. A single cilium (5 × 1 × 0.0035 mm) can output up to 27 μN blocking force under a magnetic field of 160 mT. These cilia can be used as a mixer in lap-on-chip applications and as the anchoring and propulsion legs of endoscopic capsule robots operating within the gastrointestinal tract of humans. Analytical expressions estimating the blocking force are established and compared with the experimental results.

Shape-Memory Hydrogels: Evolution of Structural Principles To Enable Shape Switching of Hydrophilic Polymer Networks.

PubMed

Löwenberg, Candy; Balk, Maria; Wischke, Christian; Behl, Marc; Lendlein, Andreas

2017-04-18

The ability of hydrophilic chain segments in polymer networks to strongly interact with water allows the volumetric expansion of the material and formation of a hydrogel. When polymer chain segments undergo reversible hydration depending on environmental conditions, smart hydrogels can be realized, which are able to shrink/swell and thus alter their volume on demand. In contrast, implementing the capacity of hydrogels to switch their shape rather than volume demands more sophisticated chemical approaches and structural concepts. In this Account, the principles of hydrogel network design, incorporation of molecular switches, and hydrogel microstructures are summarized that enable a spatially directed actuation of hydrogels by a shape-memory effect (SME) without major volume alteration. The SME involves an elastic deformation (programming) of samples, which are temporarily fixed by reversible covalent or physical cross-links resulting in a temporary shape. The material can reverse to the original shape when these molecular switches are affected by application of a suitable stimulus. Hydrophobic shape-memory polymers (SMPs), which are established with complex functions including multiple or reversible shape-switching, may provide inspiration for the molecular architecture of shape-memory hydrogels (SMHs), but cannot be identically copied in the world of hydrophilic soft materials. For instance, fixation of the temporary shape requires cross-links to be formed also in an aqueous environment, which may not be realized, for example, by crystalline domains from the hydrophilic main chains as these may dissolve in presence of water. Accordingly, dual-shape hydrogels have evolved, where, for example, hydrophobic crystallizable side chains have been linked into hydrophilic polymer networks to act as temperature-sensitive temporary cross-links. By incorporating a second type of such side chains, triple-shape hydrogels can be realized. Considering the typically given light permeability of hydrogels and the fully hydrated state with easy permeation by small molecules, other types of stimuli like light, pH, or ions can be employed that may not be easily used in hydrophobic SMPs. In some cases, those molecular switches can respond to more than one stimulus, thus increasing the number of opportunities to induce actuation of these synthetic hydrogels. Beyond this, biopolymer-based hydrogels can be equipped with a shape switching function when facilitating, for example, triple helix formation in proteins or ionic interactions in polysaccharides. Eventually, microstructured SMHs such as hybrid or porous structures can combine the shape-switching function with an improved performance by helping to overcome frequent shortcomings of hydrogels such as low mechanical strength or volume change upon temporary cross-link cleavage. Specifically, shape switching without major volume alteration is possible in porous SMHs by decoupling small volume changes of pore walls on the microscale and the macroscopic sample size. Furthermore, oligomeric rather than short aliphatic side chains as molecular switches allow stabilization of the sample volumes. Based on those structural principles and switching functionalities, SMHs have already entered into applications as soft actuators and are considered, for example, for cell manipulation in biomedicine. In the context of those applications, switching kinetics, switching forces, and reversibility of switching are aspects to be further explored.

Dynamic urea bond for the design of reversible and self-healing polymers

NASA Astrophysics Data System (ADS)

Ying, Hanze; Zhang, Yanfeng; Cheng, Jianjun

2014-02-01

Polymers bearing dynamic covalent bonds may exhibit dynamic properties, such as self-healing, shape memory and environmental adaptation. However, most dynamic covalent chemistries developed so far require either catalyst or change of environmental conditions to facilitate bond reversion and dynamic property change in bulk materials. Here we report the rational design of hindered urea bonds (urea with bulky substituent attached to its nitrogen) and the use of them to make polyureas and poly(urethane-urea)s capable of catalyst-free dynamic property change and autonomous repairing at low temperature. Given the simplicity of the hindered urea bond chemistry (reaction of a bulky amine with an isocyanate), incorporation of the catalyst-free dynamic covalent urea bonds to conventional polyurea or urea-containing polymers that typically have stable bulk properties may further broaden the scope of applications of these widely used materials.

Dynamic urea bond for the design of reversible and self-healing polymers

PubMed Central

Ying, Hanze; Zhang, Yanfeng; Cheng, Jianjun

2014-01-01

Polymers bearing dynamic covalent bonds may exhibit dynamic properties, such as self-healing, shape memory and environmental adaptation. However, most dynamic covalent chemistries developed so far require either catalyst or change of environmental conditions to facilitate bond reversion and dynamic property change in bulk materials. Here we report the rational design of hindered urea bonds (urea with bulky substituent attached to its nitrogen) and the use of them to make polyureas and poly(urethane-ureas) capable of catalyst-free dynamic property change and autonomous repairing at low temperature. Given the simplicity of the hindered urea bond chemistry (reaction of a bulky amine with an isocyanate), incorporation of the catalyst-free dynamic covalent urea bonds to conventional polyurea or urea-containing polymers that typically have stable bulk properties may further broaden the scope of applications of these widely used materials. PMID:24492620

Kirigami design and fabrication for biomimetic robotics

NASA Astrophysics Data System (ADS)

Rossiter, Jonathan; Sareh, Sina

2014-03-01

Biomimetics faces a continual challenge of how to bridge the gap between what Nature has so effectively evolved and the current tools and materials that engineers and scientists can exploit. Kirigami, from the Japanese `cut' and `paper', is a method of design where laminar materials are cut and then forced out-of-plane to yield 3D structures. Kirimimetic design provides a convenient and relatively closed design space within which to replicate some of the most interesting niche biological mechanisms. These include complex flexing organelles such as cilia in algae, energy storage and buckled structures in plants, and organic appendages that actuate out-of-plane such as the myoneme of the Vorticella protozoa. Where traditional kirigami employs passive materials which must be forced to transition to higher dimensions, we can exploit planar smart actuators and artificial muscles to create self-actuating kirigami structures. Here we review biomimetics with respect to the kirigami design and fabrication methods and examine how smart materials, including electroactive polymers and shape memory polymers, can be used to realise effective biomimetic components for robotic, deployable structures and engineering systems. One-way actuation, for example using shape memory polymers, can yield complete self-deploying structures. Bi-directional actuation, in contrast, can be exploited to mimic fundamental biological mechanisms such as thrust generation and fluid control. We present recent examples of kirigami robotic mechanisms and actuators and discuss planar fabrication methods, including rapid prototyping and 3D printing, and how current technologies, and their limitations, affect Kirigami robotics.

Plasma immersion ion implantation of polyurethane shape memory polymer: Surface properties and protein immobilization

NASA Astrophysics Data System (ADS)

Cheng, Xinying; Kondyurin, Alexey; Bao, Shisan; Bilek, Marcela M. M.; Ye, Lin

2017-09-01

Polyurethane-type shape memory polymers (SMPU) are promising biomedical implant materials due to their ability to recover to a predetermined shape from a temporary shape induced by thermal activation close to human body temperature and their advantageous mechanical properties including large recovery strains and low recovery stresses. Plasma Immersion Ion Implantation (PIII) is a surface modification process using energetic ions that generates radicals in polymer surfaces leading to carbonisation and oxidation and the ability to covalently immobilise proteins without the need for wet chemistry. Here we show that PIII treatment of SMPU significantly enhances its bioactivity making SMPU suitable for applications in permanent implantable biomedical devices. Scanning Electron Microscopy (SEM), contact angle measurements, surface energy measurements, attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to characterise the PIII modified surface, including its after treatment aging kinetics and its capability to covalently immobilise protein directly from solution. The results show a substantial improvement in wettability and dramatic changes of surface chemical composition dependent on treatment duration, due to the generation of radicals and subsequent oxidation. The SMPU surface, PIII treated for 200s, achieved a saturated level of covalently immobilized protein indicating that a full monolayer coverage was achieved. We conclude that PIII is a promising and efficient surface modification method to enhance the biocompatibility of SMPU for use in medical applications that demand bioactivity for tissue integration and stability in vivo.

Bio-based hyperbranched thermosetting polyurethane/triethanolamine functionalized multi-walled carbon nanotube nanocomposites as shape memory materials.

PubMed

Kalita, Hemjyoti; Karak, Niranjan

2014-07-01

Here, bio-based shape memory polymers have generated immense interest in recent times. Here, Bio-based hyperbranched polyurethane/triethanolamine functionalized multi-walled carbon nanotube (TEA-f-MWCNT) nanocomposites were prepared by in-situ pre-polymerization technique. The Fourier transform infrared spectroscopy and the transmission electron microscopic studies showed the strong interfacial adhesion and the homogeneous distribution of TEA-f-MWCNT in the polyurethane matrix. The prepared epoxy cured thermosetting nanocomposites exhibited enhanced tensile strength (6.5-34.5 MPa), scratch hardness (3.0-7.5 kg) and thermal stability (241-288 degrees C). The nanocomposites showed excellent shape fixity and shape recovery. The shape recovery time decreases (24-10 s) with the increase of TEA-f-MWCNT content in the nanocomposites. Thus the studied nanocomposites have potential to be used as advanced shape memory materials.

Aging, memory, and nonhierarchical energy landscape of spin jam

PubMed Central

Samarakoon, Anjana; Sato, Taku J.; Chen, Tianran; Chern, Gai-Wei; Yang, Junjie; Klich, Israel; Sinclair, Ryan; Zhou, Haidong; Lee, Seung-Hun

2016-01-01

The notion of complex energy landscape underpins the intriguing dynamical behaviors in many complex systems ranging from polymers, to brain activity, to social networks and glass transitions. The spin glass state found in dilute magnetic alloys has been an exceptionally convenient laboratory frame for studying complex dynamics resulting from a hierarchical energy landscape with rugged funnels. Here, we show, by a bulk susceptibility and Monte Carlo simulation study, that densely populated frustrated magnets in a spin jam state exhibit much weaker memory effects than spin glasses, and the characteristic properties can be reproduced by a nonhierarchical landscape with a wide and nearly flat but rough bottom. Our results illustrate that the memory effects can be used to probe different slow dynamics of glassy materials, hence opening a window to explore their distinct energy landscapes. PMID:27698141

Virtual Parts Engineering Research Center

DTIC Science & Technology

2010-05-20

engineering 10 materials. High strength alloys , composites (polymer composites and metallic composites), and the like cannot merely be replaced by...ceramics, smart materials, shape memory alloys , super plastic materials and nano- structured materials may be more appropriate substitutes in a reverse...molding process using thermosetting Bakelite. For remanufacturing the part in small quantities, machining has been identified as the most economical

Non-Markovian closure kinetics of flexible polymers with hydrodynamic interactions.

PubMed

Levernier, N; Dolgushev, M; Bénichou, O; Blumen, A; Guérin, T; Voituriez, R

2015-11-28

This paper presents a theoretical analysis of the closure kinetics of a polymer with hydrodynamic interactions. This analysis, which takes into account the non-Markovian dynamics of the end-to-end vector and relies on the preaveraging of the mobility tensor (Zimm dynamics), is shown to reproduce very accurately the results of numerical simulations of the complete nonlinear dynamics. It is found that Markovian treatments based on a Wilemski-Fixman approximation significantly overestimate cyclization times (up to a factor 2), showing the importance of memory effects in the dynamics. In addition, this analysis provides scaling laws of the mean first cyclization time (MFCT) with the polymer size N and capture radius b, which are identical in both Markovian and non-Markovian approaches. In particular, it is found that the scaling of the MFCT for large N is given by T ∼ N(3/2)ln(N/b(2)), which differs from the case of the Rouse dynamics where T ∼ N(2). The extension to the case of the reaction kinetics of a monomer of a Zimm polymer with an external target in a confined volume is also presented.

Epitaxy of Ferroelectric P(VDF-TrFE) Films via Removable PTFE Templates and Its Application in Semiconducting/Ferroelectric Blend Resistive Memory.

PubMed

Xia, Wei; Peter, Christian; Weng, Junhui; Zhang, Jian; Kliem, Herbert; Jiang, Yulong; Zhu, Guodong

2017-04-05

Ferroelectric polymer based devices exhibit great potentials in low-cost and flexible electronics. To meet the requirements of both low voltage operation and low energy consumption, thickness of ferroelectric polymer films is usually required to be less than, for example, 100 nm. However, decrease of film thickness is also accompanied by the degradation of both crystallinity and ferroelectricity and also the increase of current leakage, which surely degrades device performance. Here we report one epitaxy method based on removable poly(tetrafluoroethylene) (PTFE) templates for high-quality fabrication of ordered ferroelectric polymer thin films. Experimental results indicate that such epitaxially grown ferroelectric polymer films exhibit well improved crystallinity, reduced current leakage and good resistance to electrical breakdown, implying their applications in high-performance and low voltage operated ferroelectric devices. On the basis of this removable PTFE template method, we fabricated organic semiconducting/ferroelectric blend resistive films which presented record electrical performance with operation voltage as low as 5 V and ON/OFF ratio up to 10 5 .

Digital Microfluidics Sample Analyzer

NASA Technical Reports Server (NTRS)

Pollack, Michael G.; Srinivasan, Vijay; Eckhardt, Allen; Paik, Philip Y.; Sudarsan, Arjun; Shenderov, Alex; Hua, Zhishan; Pamula, Vamsee K.

2010-01-01

Three innovations address the needs of the medical world with regard to microfluidic manipulation and testing of physiological samples in ways that can benefit point-of-care needs for patients such as premature infants, for which drawing of blood for continuous tests can be life-threatening in their own right, and for expedited results. A chip with sample injection elements, reservoirs (and waste), droplet formation structures, fluidic pathways, mixing areas, and optical detection sites, was fabricated to test the various components of the microfluidic platform, both individually and in integrated fashion. The droplet control system permits a user to control droplet microactuator system functions, such as droplet operations and detector operations. Also, the programming system allows a user to develop software routines for controlling droplet microactuator system functions, such as droplet operations and detector operations. A chip is incorporated into the system with a controller, a detector, input and output devices, and software. A novel filler fluid formulation is used for the transport of droplets with high protein concentrations. Novel assemblies for detection of photons from an on-chip droplet are present, as well as novel systems for conducting various assays, such as immunoassays and PCR (polymerase chain reaction). The lab-on-a-chip (a.k.a., lab-on-a-printed-circuit board) processes physiological samples and comprises a system for automated, multi-analyte measurements using sub-microliter samples of human serum. The invention also relates to a diagnostic chip and system including the chip that performs many of the routine operations of a central labbased chemistry analyzer, integrating, for example, colorimetric assays (e.g., for proteins), chemiluminescence/fluorescence assays (e.g., for enzymes, electrolytes, and gases), and/or conductometric assays (e.g., for hematocrit on plasma and whole blood) on a single chip platform.

Dynamics of thin-film piezoelectric microactuators with large vertical stroke subject to multi-axis coupling and fabrication asymmetries

NASA Astrophysics Data System (ADS)

Choi, Jongsoo; Wang, Thomas; Oldham, Kenn

2018-01-01

The high performance and small size of MEMS based scanners has allowed various optical imaging techniques to be realized in a small form factor. Many such devices are resonant scanners, and thus their linear and nonlinear dynamic behaviors have been studied in the past. Thin-film piezoelectric materials, in contrast, provide sufficient energy density to achieve both large static displacements and high-frequency resonance, but large deformation can in turn influence dynamic scanner behavior. This paper reports on the influence of very large stroke translation of a piezoelectric vertical actuator on its resonant behavior, which may not be otherwise explained fully by common causes of resonance shift such as beam stiffening or nonlinear forcing. To examine the change of structural compliance over the course of scanner motion, a model has been developed that includes internal forces from residual stress and the resultant additional multi-axis coupling among actuator leg structures. Like some preceding vertical scanning micro-actuators, the scanner of this work has four legs, with each leg featuring four serially connected thin-film PZT unimorphs that allow the scanner to generate larger than 400 µm of vertical displacement at 14 V DC. Using an excitation near one or more resonances, the input voltage can be lowered, and complementary multi-axis rotations can be also generated, but change of the resonant frequencies with scanner height needs to be understood to maximize scanner performance. The presented model well predicts the experimental observation of the decrease of the resonant frequencies of the scanner with the increase of a dc bias voltage. Also, the effects of the magnitude and uniformity of residual stress across the scanner structure on the natural frequencies have been studied.

Fabrication of tough epoxy with shape memory effects by UV-assisted direct-ink write printing.

PubMed

Chen, Kaijuan; Kuang, Xiao; Li, Vincent; Kang, Guozheng; Qi, H Jerry

2018-03-07

3D printing of epoxy-based shape memory polymers with high mechanical strength, excellent thermal stability and chemical resistance is highly desirable for practical applications. However, thermally cured epoxy in general is difficult to print directly. There have been limited numbers of successes in printing epoxy but they suffer from relatively poor mechanical properties. Here, we present an ultraviolet (UV)-assisted 3D printing of thermally cured epoxy composites with high tensile toughness via a two-stage curing approach. The ink containing UV curable resin and epoxy oligomer is used for UV-assisted direct-ink write (DIW)-based 3D printing followed by thermal curing of the part containing the epoxy oligomer. The UV curable resin forms a network by photo polymerization after the 1st stage of UV curing, which can maintain the printed architecture at an elevated temperature. The 2nd stage thermal curing of the epoxy oligomer yields an interpenetrating polymer network (IPN) composite with highly enhanced mechanical properties. It is found that the printed IPN epoxy composites enabled by the two-stage curing show isotropic mechanical properties and high tensile toughness. We demonstrated that the 3D-printed high-toughness epoxy composites show good shape memory properties. This UV-assisted DIW 3D printing via a two-stage curing method can broaden the application of 3D printing to fabricate thermoset materials with enhanced tensile toughness and tunable properties for high-performance and functional applications.

An electrical-heating and self-sensing shape memory polymer composite incorporated with carbon fiber felt

NASA Astrophysics Data System (ADS)

Gong, Xiaobo; Liu, Liwu; Liu, Yanju; Leng, Jinsong

2016-03-01

Shape memory polymers (SMPs) have the ability to adjust their stiffness, lock a temporary shape, and recover the permanent shape upon imposing an appropriate stimulus. They have found their way into the field of morphing structures. The electrically Joule resistive heating of the conductive composite can be a desirable stimulus to activate the shape memory effect of SMPs without external heating equipment. Electro-induced SMP composites incorporated with carbon fiber felt (CFF) were explored in this work. The CFF is an excellent conductive filler which can easily spread throughout the composite. It has a huge advantage in terms of low cost, simple manufacturing process, and uniform and tunable temperature distribution while heating. A continuous and compact conductive network made of carbon fibers and the overlap joints among them was observed from the microscopy images, and this network contributes to the high conductive properties of the CFF/SMP composites. The CFF/SMP composites can be electrical-heated rapidly and uniformly, and its’ shape recovery effect can be actuated by the electrical resistance Joule heating of the CFF without an external heater. The CFF/SMP composite get higher modulus and higher strength than the pure SMP without losing any strain recovery property. The high dependence of temperature and strain on the electrical resistance also make the composite a good self-sensing material. In general, the CFF/SMP composite shows great prospects as a potential material for the future morphing structures.

Finite element analyses of a dual actuated prototype of a smart needle

NASA Astrophysics Data System (ADS)

Konh, Bardia; Podder, Tarun K.

2017-04-01

Brachytherapy is one of the most effective modalities for treating early stage prostate cancer. In this procedure, radioactive seeds are being placed in the prostate to kill the tumorous cells. Inaccurate placement of seeds can underdose the tumor and dangerously overdose the critical structures (urethra, rectum, bladder) and adjacent healthy tissues. It is very difficult, if not impossible, for the surgeons to compensate the needle misplacement errors while using the conventional passive straight needles. The smart needles actuated by shape memory alloy (SMA) wires are being developed to provide more actuation and control for the surgeons to achieve more geometric conformity. In our recent work, a prototype of a smart needle was developed where not only the actuation of SMA wires were incorporated, but also shape memory polymers (SMPs) were included in the design introducing a soft joint element to further assist the flexibility of the active surgical needles. The additional actuation of shape memory polymers provided the capability of reaching much high flexibility that was not achievable before. However, there are some disadvantages using this active SMP component compared to a passive Nylon joint component that are discussed in this work. The utilization of a heated SMP as a soft joint showed about 20% improvement in the final needle tip deflection. This work presents the finite element studies of the developed prototype. A finite element model that could accurately predict the behavior of the smart needle could be very valuable in analyzing and optimizing the future novel designs.

Triple shape memory polymers by 4D printing

NASA Astrophysics Data System (ADS)

Bodaghi, M.; Damanpack, A. R.; Liao, W. H.

2018-06-01

This article aims at introducing triple shape memory polymers (SMPs) by four-dimensional (4D) printing technology and shaping adaptive structures for mechanical/bio-medical devices. The main approach is based on arranging hot–cold programming of SMPs with fused decomposition modeling technology to engineer adaptive structures with triple shape memory effect (SME). Experiments are conducted to characterize elasto-plastic and hyper-elastic thermo-mechanical material properties of SMPs in low and high temperatures at large deformation regime. The feasibility of the dual and triple SMPs with self-bending features is demonstrated experimentally. It is advantageous in situations either where it is desired to perform mechanical manipulations on the 4D printed objects for specific purposes or when they experience cold programming inevitably before activation. A phenomenological 3D constitutive model is developed for quantitative understanding of dual/triple SME of SMPs fabricated by 4D printing in the large deformation range. Governing equations of equilibrium are established for adaptive structures on the basis of the nonlinear Green–Lagrange strains. They are then solved by developing a finite element approach along with an elastic-predictor plastic-corrector return map procedure accomplished by the Newton–Raphson method. The computational tool is applied to simulate dual/triple SMP structures enabled by 4D printing and explore hot–cold programming mechanisms behind material tailoring. It is shown that the 4D printed dual/triple SMPs have great potential in mechanical/bio-medical applications such as self-bending gripers/stents and self-shrinking/tightening staples.

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

Li, Yuzhan; Zhang, Yuehong; Rios, Orlando

The increasing demand for intelligent materials has driven the development of polymers with a variety of functionalities. However, combining multiple functionalities within one polymer is still challenging because of the difficulties encountered in coordinating different functional building blocks during fabrication. In this work, we demonstrate the fabrication of a multifunctional liquid crystalline epoxy network (LCEN) using the combination of thermotropic liquid crystals, photo-responsive azobenzene molecules, and exchangeable disulfide bonds. In addition to shape memory behavior enabled by the reversible liquid crystalline phase transition and photo-induced bending behavior resulting from the photo-responsive azobenzene molecules, the introduction of dynamic disulfide bonds intomore » the LCEN resulted in a structurally dynamic network, allowing the reshaping, repairing, and recycling of the material.« less

Conducting Polymeric Hydrogel Electrolyte Based on Carboxymethylcellulose and Polyacrylamide/Polyaniline for Supercapacitor Applications

NASA Astrophysics Data System (ADS)

Suganya, N.; Jaisankar, V.; Sivakumar, E. K. T.

Conducting polymer hydrogels represent a unique class of materials that possess enormous application in flexible electronic devices. In the present work, conducting carboxymethylcellulose (CMC)-co-polyacrylamide (PAAm)/polyaniline was synthesized by a two-step interpenetrating network solution polymerization technique. The synthesized CMC-co-PAAm/polyaniline with interpenetrating network structure was prepared by in situ polymerization of aniline to enhance conductivity. The molecular structure and morphology of the copolymer hydrogels were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. The novel conducting polymer hydrogels show good electrical and electrochemical behavior, which makes them potentially useful in electronic devices such as supercapacitors, biosensors, bioelectronics, solar cells and memory devices.

System for closure of a physical anomaly

DOEpatents

Bearinger, Jane P; Maitland, Duncan J; Schumann, Daniel L; Wilson, Thomas S

2014-11-11

Systems for closure of a physical anomaly. Closure is accomplished by a closure body with an exterior surface. The exterior surface contacts the opening of the anomaly and closes the anomaly. The closure body has a primary shape for closing the anomaly and a secondary shape for being positioned in the physical anomaly. The closure body preferably comprises a shape memory polymer.

Formation of Singularities for a Conservation Law with Memory.

DTIC Science & Technology

1983-04-01

respectively. Intetchanging the order of integration in the double integrals in (4.4) yields -10- I.I.... ..... , t su8 (0 + 011(011 ft JI) + SCOW)d + 64...molten polymers , meology 2 ory and pp lioatioona, 5 (1969), 57-92. Ovwi..’ " Is UsmIUTY CLANKFCATWN @’ TunS PA.. 010f bo~W _____________ WORT 0OOIM ATMO

Research on materials for advanced electronic and aerospace application. [including optical and magnetic data processing, stress corrosion and H2 interaction, and polymeric systems

NASA Technical Reports Server (NTRS)

1975-01-01

Development and understanding of materials most suitable for use in compact magnetic and optical memory systems are discussed. Suppression of metal deterioration by hydrogen is studied. Improvement of mechanical properties of polymers is considered, emphasizing low temperature ductility and compatibility with high modulus fiber materials.

Incorporation of memory effects in coarse-grained modeling via the Mori-Zwanzig formalism

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

Li, Zhen; Bian, Xin; Karniadakis, George Em, E-mail: george-karniadakis@brown.edu

2015-12-28

The Mori-Zwanzig formalism for coarse-graining a complex dynamical system typically introduces memory effects. The Markovian assumption of delta-correlated fluctuating forces is often employed to simplify the formulation of coarse-grained (CG) models and numerical implementations. However, when the time scales of a system are not clearly separated, the memory effects become strong and the Markovian assumption becomes inaccurate. To this end, we incorporate memory effects into CG modeling by preserving non-Markovian interactions between CG variables, and the memory kernel is evaluated directly from microscopic dynamics. For a specific example, molecular dynamics (MD) simulations of star polymer melts are performed while themore » corresponding CG system is defined by grouping many bonded atoms into single clusters. Then, the effective interactions between CG clusters as well as the memory kernel are obtained from the MD simulations. The constructed CG force field with a memory kernel leads to a non-Markovian dissipative particle dynamics (NM-DPD). Quantitative comparisons between the CG models with Markovian and non-Markovian approximations indicate that including the memory effects using NM-DPD yields similar results as the Markovian-based DPD if the system has clear time scale separation. However, for systems with small separation of time scales, NM-DPD can reproduce correct short-time properties that are related to how the system responds to high-frequency disturbances, which cannot be captured by the Markovian-based DPD model.« less

High Cycle-life Shape Memory Polymer at High Temperature

PubMed Central

Kong, Deyan; Xiao, Xinli

2016-01-01

High cycle-life is important for shape memory materials exposed to numerous cycles, and here we report shape memory polyimide that maintained both high shape fixity (Rf) and shape recovery (Rr) during the more than 1000 bending cycles tested. Its critical stress is 2.78 MPa at 250 °C, and the shape recovery process can produce stored energy of 0.218 J g−1 at the efficiency of 31.3%. Its high Rf is determined by the large difference in storage modulus at rubbery and glassy states, while the high Rr mainly originates from its permanent phase composed of strong π-π interactions and massive chain entanglements. Both difference in storage modulus and overall permanent phase were preserved during the bending deformation cycles, and thus high Rf and Rr were observed in every cycle and the high cycle-life will expand application areas of SMPs enormously. PMID:27641148

Reversible TAD Chemistry as a Convenient Tool for the Design of (Re)processable PCL-Based Shape-Memory Materials.

PubMed

Defize, Thomas; Riva, Raphaël; Thomassin, Jean-Michel; Alexandre, Michaël; Herck, Niels Van; Prez, Filip Du; Jérôme, Christine

2017-01-01

A chemically cross-linked but remarkably (re)processable shape-memory polymer (SMP) is designed by cross-linking poly(ε-caprolactone) (PCL) stars via the efficient triazolinedione click chemistry, based on the very fast and reversible Alder-ene reaction of 1,2,4-triazoline-3,5-dione (TAD) with indole compounds. Typically, a six-arm star-shaped PCL functionalized by indole moieties at the chain ends is melt-blended with a bisfunctional TAD, directly resulting in a cross-linked PCL-based SMP without the need of post-curing treatment. As demonstrated by the stress relaxation measurement, the labile character of the TAD-indole adducts under stress allows for the solid-state plasticity reprocessing of the permanent shape at will by compression molding of the raw cross-linked material, while keeping excellent shape-memory properties. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The Effects of Fiber Orientation and Adhesives on Tensile Properties of Carbon Fiber Reinforced Polymer Matrix Composite with Embedded Nickel-Titanium Shape Memory Alloys

NASA Technical Reports Server (NTRS)

Quade, Derek J.; Jana, Sadhan C.; Morscher, Gregory N.; Kannan, Manigandan; McCorkle, Linda S.

2017-01-01

Nickel-titanium (NiTi) shape memory alloy (SMA) sections were embedded within carbon fiber reinforced polymer matrix composite (CFRPPMC) laminates and their tensile properties were evaluated with simultaneous monitoring of modal acoustic emissions. The test specimens were fabricated in three different layup configurations and two different thin film adhesives were applied to bond the SMA with the PMC. A trio of acoustic sensors were attached to the specimens during tensile testing to monitor the modal acoustic emission (AE) as the materials experienced mechanical failure. The values of ultimate tensile strengths, strains, and moduli were obtained. Cumulative AE energy of events and specimen failure location were determined. In conjunction, optical and scanning electron microscopy techniques were used to examine the break areas of the specimens. The analysis of AE data revealed failure locations within the specimens which were validated from the microscopic images. The placement of 90 deg plies in the outer ply gave the strongest acoustic signals during break as well as the cleanest break of the samples tested. Overlapping 0 deg ply layers surrounding the SMA was found to be the best scenario to prevent failure of the specimen itself.

Micro devices using shape memory polymer patches for mated connections

DOEpatents

Lee, Abraham P.; Fitch, Joseph P.

2000-01-01

A method and micro device for repositioning or retrieving miniature devices located in inaccessible areas, such as medical devices (e.g., stents, embolic coils, etc.) located in a blood vessel. The micro repositioning or retrieving device and method uses shape memory polymer (SMP) patches formed into mating geometries (e.g., a hoop and a hook) for re-attachment of the deposited medical device to a catheter or guidewire. For example, SMP or other material hoops are formed on the medical device to be deposited in a blood vessel, and SMP hooks are formed on the micro device attached to a guidewire, whereby the hooks on the micro device attach to the hoops on the medical device, or vice versa, enabling deposition, movement, re-deposit, or retrieval of the medical device. By changing the temperature of the SMP hooks, the hooks can be attached to or released from the hoops located on the medical device. An exemplary method for forming the hooks and hoops involves depositing a sacrificial thin film on a substrate, patterning and processing the thin film to form openings therethrough, depositing or bonding SMP materials in the openings so as to be attached to the substrate, and removing the sacrificial thin film.

Hydrogels with a Memory: Dual-Responsive, Organometallic Poly(ionic liquid)s with Hysteretic Volume-Phase Transition

PubMed Central

2017-01-01

We report on the synthesis and structure–property relations of a novel, dual-responsive organometallic poly(ionic liquid) (PIL), consisting of a poly(ferrocenylsilane) backbone of alternating redox-active, silane-bridged ferrocene units and tetraalkylphosphonium sulfonate moieties in the side groups. This PIL is redox responsive due to the presence of ferrocene in the backbone and also exhibits a lower critical solution temperature (LCST)-type thermal responsive behavior. The LCST phase transition originates from the interaction between water molecules and the ionic substituents and shows a concentration-dependent, tunable transition temperature in aqueous solution. The PIL’s LCST-type transition temperature can also be influenced by varying the redox state of ferrocene in the polymer main chain. As the polymer can be readily cross-linked and is easily converted into hydrogels, it represents a new dual-responsive materials platform. Interestingly, the as-formed hydrogels display an unusual, strongly hysteretic volume-phase transition indicating useful thermal memory properties. By employing the dispersing abilities of this cationic PIL, CNT-hydrogel composites were successfully prepared. These hybrid conductive composite hydrogels showed bi-stable states and tunable resistance in heating–cooling cycles. PMID:28654756

Memory effects in annealed hybrid gold nanoparticles/block copolymer bilayers

PubMed Central

2011-01-01

We report on the use of the self-organization process of sputtered gold nanoparticles on a self-assembled block copolymer film deposited by horizontal precipitation Langmuir-Blodgett (HP-LB) method. The morphology and the phase-separation of a film of poly-n-butylacrylate-block-polyacrylic acid (PnBuA-b-PAA) were studied at the nanometric scale by using atomic force microscopy (AFM) and Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS). The templating capability of the PnBuA-b-PAA phase-separated film was studied by sputtering gold nanoparticles (NPs), forming a film of nanometric thickness. The effect of the polymer chain mobility onto the organization of gold nanoparticle layer was assessed by heating the obtained hybrid PnBuA-b-PAA/Au NPs bilayer at T >Tg. The nanoparticles' distribution onto the different copolymer domains was found strongly affected by the annealing treatment, showing a peculiar memory effect, which modifies the AFM phase response of the Au NPs layer onto the polar domains, without affecting their surfacial composition. The effect is discussed in terms of the peculiar morphological features induced by enhanced mobility of polymer chains on the Au NPs layer. PMID:21711674

Characterizing and modeling the free recovery and constrained recovery behavior of a polyurethane shape memory polymer

PubMed Central

Volk, Brent L; Lagoudas, Dimitris C; Maitland, Duncan J

2011-01-01

In this work, tensile tests and one-dimensional constitutive modeling are performed on a high recovery force polyurethane shape memory polymer that is being considered for biomedical applications. The tensile tests investigate the free recovery (zero load) response as well as the constrained displacement recovery (stress recovery) response at extension values up to 25%, and two consecutive cycles are performed during each test. The material is observed to recover 100% of the applied deformation when heated at zero load in the second thermomechanical cycle, and a stress recovery of 1.5 MPa to 4.2 MPa is observed for the constrained displacement recovery experiments. After performing the experiments, the Chen and Lagoudas model is used to simulate and predict the experimental results. The material properties used in the constitutive model – namely the coefficients of thermal expansion, shear moduli, and frozen volume fraction – are calibrated from a single 10% extension free recovery experiment. The model is then used to predict the material response for the remaining free recovery and constrained displacement recovery experiments. The model predictions match well with the experimental data. PMID:22003272

Modelling of loading, stress relaxation and stress recovery in a shape memory polymer.

PubMed

Sweeney, J; Bonner, M; Ward, I M

2014-09-01

A multi-element constitutive model for a lactide-based shape memory polymer has been developed that represents loading to large tensile deformations, stress relaxation and stress recovery at 60, 65 and 70°C. The model consists of parallel Maxwell arms each comprising neo-Hookean and Eyring elements. Guiu-Pratt analysis of the stress relaxation curves yields Eyring parameters. When these parameters are used to define the Eyring process in a single Maxwell arm, the resulting model yields at too low a stress, but gives good predictions for longer times. Stress dip tests show a very stiff response on unloading by a small strain decrement. This would create an unrealistically high stress on loading to large strain if it were modelled by an elastic element. Instead it is modelled by an Eyring process operating via a flow rule that introduces strain hardening after yield. When this process is incorporated into a second parallel Maxwell arm, there results a model that fully represents both stress relaxation and stress dip tests at 60°C. At higher temperatures a third arm is required for valid predictions. Crown Copyright © 2014. Published by Elsevier Ltd. All rights reserved.

Self-fitting shape memory polymer foam inducing bone regeneration: A rabbit femoral defect study.

PubMed

Xie, Ruiqi; Hu, Jinlian; Hoffmann, Oskar; Zhang, Yuanchi; Ng, Frankie; Qin, Tingwu; Guo, Xia

2018-04-01

Although tissue engineering has been attracted greatly for healing of critical-sized bone defects, great efforts for improvement are still being made in scaffold design. In particular, bone regeneration would be enhanced if a scaffold precisely matches the contour of bone defects, especially if it could be implanted into the human body conveniently and safely. In this study, polyurethane/hydroxyapatite-based shape memory polymer (SMP) foam was fabricated as a scaffold substrate to facilitate bone regeneration. The minimally invasive delivery and the self-fitting behavior of the SMP foam were systematically evaluated to demonstrate its feasibility in the treatment of bone defects in vivo. Results showed that the SMP foam could be conveniently implanted into bone defects with a compact shape. Subsequently, it self-matched the boundary of bone defects upon shape-recovery activation in vivo. Micro-computed tomography determined that bone ingrowth initiated at the periphery of the SMP foam with a constant decrease towards the inside. Successful vascularization and bone remodeling were also demonstrated by histological analysis. Thus, our results indicate that the SMP foam demonstrated great potential for bone regeneration. Copyright © 2018 Elsevier B.V. All rights reserved.

Virtual Treatment of Basilar Aneurysms Using Shape Memory Polymer Foam

PubMed Central

Ortega, J.M.; Hartman, J.; Rodriguez, J.N.; Maitland, D.J.

2013-01-01

Numerical simulations are performed on patient-specific basilar aneurysms that are treated with shape memory polymer (SMP) foam. In order to assess the post-treatment hemodynamics, two modeling approaches are employed. In the first, the foam geometry is obtained from a micro-CT scan and the pulsatile blood flow within the foam is simulated for both Newtonian and non-Newtonian viscosity models. In the second, the foam is represented as a porous media continuum, which has permeability properties that are determined by computing the pressure gradient through the foam geometry over a range of flow speeds comparable to those of in vivo conditions. Virtual angiography and additional post-processing demonstrate that the SMP foam significantly reduces the blood flow speed within the treated aneurysms, while eliminating the high-frequency velocity fluctuations that are present within the pre-treatment aneurysms. An estimation of the initial locations of thrombus formation throughout the SMP foam is obtained by means of a low fidelity thrombosis model that is based upon the residence time and shear rate of blood. The Newtonian viscosity model and the porous media model capture similar qualitative trends, though both yield a smaller volume of thrombus within the SMP foam. PMID:23329002

Virtual Treatment of Basilar Aneurysms Using Shape Memory Polymer Foam

NASA Astrophysics Data System (ADS)

Ortega, J. M.; Hartman, J.; Rodriguez, J. N.; Maitland, D. J.

2012-11-01

Numerical simulations are performed on patient-specific basilar aneurysms that are treated with shape memory polymer (SMP) foam. In order to assess the post-treatment hemodynamics, two modeling approaches are employed. In the first, the foam geometry is obtained from a micro-CT scan and the pulsatile blood flow within the foam is simulated for both Newtonian and non-Newtonian viscosity models. In the second, the foam is represented as a porous media continuum, which has permeability properties that are determined by computing the pressure gradient through the foam geometry over a range of flow speeds comparable to those of in vivo conditions. Virtual angiography and additional post-processing demonstrate that the SMP foam significantly reduces the blood flow speed within the treated aneurysms, while eliminating the high-frequency velocity fluctuations that are present prior to treatment. A prediction of the initial locations of thrombus formation throughout the SMP foam is obtained by means of a low fidelity thrombosis model that is based upon the residence time and shear rate of blood. The two modeling approaches capture similar qualitative trends for the initial locations of thrombus within the SMP foam.

Tunable-Porosity Membranes From Discrete Nanoparticles

PubMed Central

Marchetti, Patrizia; Mechelhoff, Martin; Livingston, Andrew G.

2015-01-01

Thin film composite membranes were prepared through a facile single-step wire-wound rod coating procedure in which internally crosslinked poly(styrene-co-butadiene) polymer nanoparticles self-assembled to form a thin film on a hydrophilic ultrafiltration support. This nanoparticle film provided a defect-free separation layer 130–150 nm thick, which was highly permeable and able to withstand aggressive pH conditions beyond the range of available commercial membranes. The nanoparticles were found to coalesce to form a rubbery film when heated above their glass transition temperature (Tg). The retention properties of the novel membrane were strongly affected by charge repulsion, due to the negative charge of the hydroxyl functionalized nanoparticles. Porosity was tuned by annealing the membranes at different temperatures, below and above the nanoparticle Tg. This enabled fabrication of membranes with varying performance. Nanofiltration properties were achieved with a molecular weight cut-off below 500 g mol−1 and a low fouling tendency. Interestingly, after annealing above Tg, memory of the interstitial spaces between the nanoparticles persisted. This memory led to significant water permeance, in marked contrast to the almost impermeable films cast from a solution of the same polymer. PMID:26626565

Magnetic field-induced strain and magnetoelectric effects in sandwich composite of ferromagnetic shape memory Ni-Mn-Ga crystal and piezoelectric PVDF polymer.

PubMed

Zeng, Min; Or, Siu Wing; Chan, Helen Lai Wa

2010-10-01

A sandwich composite consisting of one layer of ferromagnetic shape memory Ni-Mn-Ga crystal plate bonded between two layers of piezoelectric PVDF polymer film was fabricated, and its magnetic field-induced strain (MFIS) and magnetoelectric (ME) effects were investigated, together with a monolithic Ni-Mn-Ga crystal, as functions of magnetic fields and mechanical load. The load-free dc- and ac-MFISs were 0.35 and 0.05% in the composite, and 5.6 and 0.3% in the monolithic crystal, respectively. The relatively smaller load-free MFISs in the composite than the monolithic crystal resulted from the clamping of martensitic twin-boundary motion in the Ni-Mn-Ga plate by the PVDF films. The largest ME coefficient (α(E)) was 0.58 V/cm·Oe at a magnetic bias field (H(Bias)) of 8.35 kOe under load-free condition. The mechanism of the ME effect originated from the mechanically mediated MFIS effect in the Ni-Mn-Ga plate and piezoelectric effect in the PVDF films. The measured α(E)-H(Bias) responses under different loads showed good agreement with the model prediction.

Enhancements of the memory margin and the stability of an organic bistable device due to a graphene oxide:mica nanocomposite sandwiched between two polymer (9-vinylcarbazole) buffer layers

NASA Astrophysics Data System (ADS)

Kim, Woo Kyum; Wu, Chaoxing; Lee, Dea Uk; Kim, Hyoun Woo; Kim, Tae Whan

2018-01-01

Current-voltage (I-V) curves for the Al/polymer (9-vinylcarbazole) (PVK)/graphene oxide (GO):mica/PVK/indium-tin oxide (ITO) devices at 300 K showed a current bistability with a maximum high conductivity (ON)/low conductivity (OFF) ratio of 2 × 104, which was approximately 10 times larger than that of the device without a PVK layer. The endurance number of ON/OFF switchings for the Al/PVK/GO:mica/PVK/ITO device was 1 × 102 cycles, which was 20 times larger than that for the Al/GO:mica/ITO device. The ;erase; voltages were distributed between 2.3 and 3 V, and the ;write; voltages were distributed between -1.2 and -0.5 V. The retention time for the Al/PVK/GO:mica/PVK/ITO device was above 1 × 104 s, indicative of the memory stability of the device. The carrier transport mechanisms occurring in the Al/PVK/GO:mica/PVK/ITO and the Al/GO:mica/ITO devices are described on the basis of the I-V results and the energy band diagrams.

Method for loading shape memory polymer gripper mechanisms

DOEpatents

Lee, Abraham P.; Benett, William J.; Schumann, Daniel L.; Krulevitch, Peter A.; Fitch, Joseph P.

2002-01-01

A method and apparatus for loading deposit material, such as an embolic coil, into a shape memory polymer (SMP) gripping/release mechanism. The apparatus enables the application of uniform pressure to secure a grip by the SMP mechanism on the deposit material via differential pressure between, for example, vacuum within the SMP mechanism and hydrostatic water pressure on the exterior of the SMP mechanism. The SMP tubing material of the mechanism is heated to above the glass transformation temperature (Tg) while reshaping, and subsequently cooled to below Tg to freeze the shape. The heating and/or cooling may, for example, be provided by the same water applied for pressurization or the heating can be applied by optical fibers packaged to the SMP mechanism for directing a laser beam, for example, thereunto. At a point of use, the deposit material is released from the SMP mechanism by reheating the SMP material to above the temperature Tg whereby it returns to its initial shape. The reheating of the SMP material may be carried out by injecting heated fluid (water) through an associated catheter or by optical fibers and an associated beam of laser light, for example.

Portable Dextrous Force Feedback Master for robot telemanipulation (PDMFF)

NASA Technical Reports Server (NTRS)

Burdea, Grigore C.; Speeter, Thomas H.

1989-01-01

A major drawback of open loop masters is a lack of force feedback, limiting their ability to perform complex tasks such as assembly and repair. Researchers present a simple dextrous force feedback master for computer assisted telemanipulation. The device is compact, portable and can be held in the operator hand, without the need for a special joystick or console. The system is capable of both position feed forward and force feedback, using electronic position sensors and a pneumatic micro-actuator. The level of forces exercised by the pneumatic actuator is such that near rigidity may be attained. Experimental results showing good system linearity and small time lag are given.

Nonlinear damping for vibration isolation of microsystems using shear thickening fluid

NASA Astrophysics Data System (ADS)

Iyer, S. S.; Vedad-Ghavami, R.; Lee, H.; Liger, M.; Kavehpour, H. P.; Candler, R. N.

2013-06-01

This work reports the measurement and analysis of nonlinear damping of micro-scale actuators immersed in shear thickening fluids (STFs). A power-law damping term is added to the linear second-order model to account for the shear-dependent viscosity of the fluid. This nonlinear model is substantiated by measurements of oscillatory motion of a torsional microactuator. At high actuation forces, the vibration velocity amplitude saturates. The model accurately predicts the nonlinear damping characteristics of the STF using a power-law index extracted from independent rheology experiments. This result reveals the potential to use STFs as adaptive, passive dampers for vibration isolation of microelectromechanical systems.

Micro guidance and control technology overview

NASA Technical Reports Server (NTRS)

Kissel, Glen J.; Hadaegh, Fred Y.

1993-01-01

This paper gives an overview of micro-guidance and control technologies and in the process previews of the technology/user and systems issues presented in the guidance and control session at the workshop. We first present a discussion of the advantages of using micro-guidance and control components and then detail six micro-guidance and control thrusts that could have a revolutionary impact on space missions and systems. Specific technologies emerging in the micro-guidance and control field will be examined. These technologies fall into two broad categories: micro-attitude determination (inertial and celestial) and micro-actuation, control and sensing. Finally, the scope of the workshop's guidance and control panel are presented.

Stimuli-Responsive DNA-Based Hydrogels: From Basic Principles to Applications.

PubMed

Kahn, Jason S; Hu, Yuwei; Willner, Itamar

2017-04-18

The base sequence of nucleic acids encodes structural and functional information into the DNA biopolymer. External stimuli such as metal ions, pH, light, or added nucleic acid fuel strands provide triggers to reversibly switch nucleic acid structures such as metal-ion-bridged duplexes, i-motifs, triplex nucleic acids, G-quadruplexes, or programmed double-stranded hybrids of oligonucleotides (DNA). The signal-triggered oligonucleotide structures have been broadly applied to develop switchable DNA nanostructures and DNA machines, and these stimuli-responsive assemblies provide functional scaffolds for the rapidly developing area of DNA nanotechnology. Stimuli-responsive hydrogels undergoing signal-triggered hydrogel-to-solution transitions or signal-controlled stiffness changes attract substantial interest as functional matrices for controlled drug delivery, materials exhibiting switchable mechanical properties, acting as valves or actuators, and "smart" materials for sensing and information processing. The integration of stimuli-responsive oligonucleotides with hydrogel-forming polymers provides versatile means to exploit the functional information encoded in the nucleic acid sequences to yield stimuli-responsive hydrogels exhibiting switchable physical, structural, and chemical properties. Stimuli-responsive DNA-based nucleic acid structures are integrated in acrylamide polymer chains and reversible, switchable hydrogel-to-solution transitions of the systems are demonstrated by applying external triggers, such as metal ions, pH-responsive strands, G-quadruplex, and appropriate counter triggers that bridge and dissociate the polymer chains. By combining stimuli-responsive nucleic acid bridges with thermosensitive poly(N-isopropylacrylamide) (pNIPAM) chains, systems undergoing reversible solution ↔ hydrogel ↔ solid transitions are demonstrated. Specifically, by bridging acrylamide polymer chains by two nucleic acid functionalities, where one type of bridging unit provides a stimuli-responsive element and the second unit acts as internal "bridging memory", shape-memory hydrogels undergoing reversible and switchable transitions between shaped hydrogels and shapeless quasi-liquid states are demonstrated. By using stimuli-responsive hydrogel cross-linking units that can assemble the bridging units by two different input signals, the orthogonally-triggered functions of the shape-memory were shown. Furthermore, a versatile approach to assemble stimuli-responsive DNA-based acrylamide hydrogel films on surfaces is presented. The method involves the activation of the hybridization chain-reaction (HCR) by a surface-confined promoter strand, in the presence of acrylamide chains modified with two DNA hairpin structures and appropriate stimuli-responsive tethers. The resulting hydrogel-modified surfaces revealed switchable stiffness properties and signal-triggered catalytic functions. By applying the method to assemble the hydrogel microparticles, substrate-loaded, stimuli-responsive microcapsules are prepared. The signal-triggered DNA-based hydrogel microcapsules are applied as drug carriers for controlled release. The different potential applications and future perspectives of stimuli responsive hydrogels are discussed. Specifically, the use of these smart materials and assemblies as carriers for controlled drug release and as shape-memory matrices for information storage and inscription and the use of surface-confined stimuli-responsive hydrogels, exhibiting switchable stiffness properties, for catalysis and controlled growth of cells are discussed.

Antibody-functionalized polymer nanoparticle leading to memory recovery in Alzheimer's disease-like transgenic mouse model.

PubMed

Carradori, Dario; Balducci, Claudia; Re, Francesca; Brambilla, Davide; Le Droumaguet, Benjamin; Flores, Orfeu; Gaudin, Alice; Mura, Simona; Forloni, Gianluigi; Ordoñez-Gutierrez, Lara; Wandosell, Francisco; Masserini, Massimo; Couvreur, Patrick; Nicolas, Julien; Andrieux, Karine

2018-02-01

Alzheimer's disease (AD) is a neurodegenerative disorder related, in part, to the accumulation of amyloid-β peptide (Aβ) and especially the Aβ peptide 1-42 (Aβ 1-42 ). The aim of this study was to design nanocarriers able to: (i) interact with the Aβ 1-42 in the blood and promote its elimination through the "sink effect" and (ii) correct the memory defect observed in AD-like transgenic mice. To do so, biodegradable, PEGylated nanoparticles were surface-functionalized with an antibody directed against Aβ 1-42 . Treatment of AD-like transgenic mice with anti-Aβ 1-42 -functionalized nanoparticles led to: (i) complete correction of the memory defect; (ii) significant reduction of the Aβ soluble peptide and its oligomer level in the brain and (iii) significant increase of the Aβ levels in plasma. This study represents the first example of Aβ 1-42 monoclonal antibody-decorated nanoparticle-based therapy against AD leading to complete correction of the memory defect in an experimental model of AD. Copyright © 2017 Elsevier Inc. All rights reserved.

Elastic memory composites (EMC) for deployable industrial and commercial applications

NASA Astrophysics Data System (ADS)

Arzberger, Steven C.; Tupper, Michael L.; Lake, Mark S.; Barrett, Rory; Mallick, Kaushik; Hazelton, Craig; Francis, William; Keller, Phillip N.; Campbell, Douglas; Feucht, Sara; Codell, Dana; Wintergerst, Joe; Adams, Larry; Mallioux, Joe; Denis, Rob; White, Karen; Long, Mark; Munshi, Naseem A.; Gall, Ken

2005-05-01

The use of smart materials and multifunctional components has the potential to provide enhanced performance, improved economics, and reduced safety concerns for applications ranging from outer space to subterranean. Elastic Memory Composite (EMC) materials, based on shape memory polymers and used to produce multifunctional components and structures, are being developed and qualified for commercial use as deployable components and structures. EMC materials are similar to traditional fiber-reinforced composites except for the use of a thermoset shape memory resin that enables much higher packaging strains than traditional composites without damage to the fibers or the resin. This unique capability is being exploited in the development of very efficient EMC structural components for deployable spacecraft systems as well as capability enhancing components for use in other industries. The present paper is intended primarily to describe the transition of EMC materials as smart structure technologies into viable industrial and commercial products. Specifically, the paper discusses: 1) TEMBO EMC materials for deployable space/aerospace systems, 2) TEMBO EMC resins for terrestrial applications, 3) future generation EMC materials.

Controllable curvature from planar polymer sheets in response to light.

PubMed

Hubbard, Amber M; Mailen, Russell W; Zikry, Mohammed A; Dickey, Michael D; Genzer, Jan

2017-03-22

The ability to change shape and control curvature in 3D structures starting from planar sheets can aid in assembly and add functionality to an object. Herein, we convert planar sheets of shape memory polymers (SMPs) into 3D objects with controllable curvature by dictating where the sheets shrink. Ink patterned on the surface of the sheet absorbs infrared (IR) light, resulting in localized heating, and the material shrinks locally wherever the temperature exceeds the activation temperature, T a . We introduce two different mechanisms for controlling curvature within SMP sheets. The 'direct' mechanism uses localized shrinkage to induce curvature only in regions patterned with ink. The 'indirect' mechanism uses localized shrinkage in regions patterned with ink to induce curvature in neighboring regions without ink through a balance of internal stresses. Finite element analysis predicts the final shape of the polymer sheets with excellent qualitative agreement with experimental studies. Results from this study show that curvature can be controlled by the distribution and darkness of the ink pattern on the polymer sheet. Additionally, we utilize the direct and indirect curvature mechanisms to demonstrate the formation and actuation of gripper devices, which represent the potential utility of this approach.

Scalable fabrication of nanostructured devices on flexible substrates using additive driven self-assembly and nanoimprint lithography

NASA Astrophysics Data System (ADS)

Watkins, James

2013-03-01

Roll-to-roll (R2R) technologies provide routes for continuous production of flexible, nanostructured materials and devices with high throughput and low cost. We employ additive-driven self-assembly to produce well-ordered polymer/nanoparticle hybrid materials that can serve as active device layers, we use highly filled nanoparticle/polymer hybrids for applications that require tailored dielectric constant or refractive index, and we employ R2R nanoimprint lithography for device scale patterning. Specific examples include the fabrication of flexible floating gate memory and large area films for optical/EM management. Our newly constructed R2R processing facility includes a custom designed, precision R2R UV-assisted nanoimprint lithography (NIL) system and hybrid nanostructured materials coaters.

Local Displacements and Load Transfer of Shape Memory Alloys in Polymeric Matrices

DTIC Science & Technology

1997-01-01

plane displacements of room temperature cured SMA ribbon composites were obtained using moiré interferometry. Displacements due to thermal expansion ...141 Figure 6.10 Displacement profiles along SMA ribbon or different values of the coefficient of thermal expansion ...greater importance in polymer composites, which can have large coefficients of thermal expansion . Further, there is also a lack of experimental data

Polymer Coatings Degradation Properties

DTIC Science & Technology

1985-02-01

undertaken 124). The Box-Jenkins approach first evaluates the partial auto -correlation function and determines the order of the moving average memory function...78 - Tables 15 and 16 show the resalit- f- a, the partial auto correlation plots. Second order moving .-. "ra ;;th -he appropriate lags were...coated films. Kaempf, Guenter; Papenroth, Wolfgang; Kunststoffe Date: 1982 Volume: 72 Number:7 Pages: 424-429 Parameters influencing the accelerated

Novel Organic Phototransistor-Based Nonvolatile Memory Integrated with UV-Sensing/Green-Emissive Aggregation Enhanced Emission (AEE)-Active Aromatic Polyamide Electret Layer.

PubMed

Cheng, Shun-Wen; Han, Ting; Huang, Teng-Yung; Chang Chien, Yu-Hsin; Liu, Cheng-Liang; Tang, Ben Zhong; Liou, Guey-Sheng

2018-05-30

A novel aggregation enhanced emission (AEE)-active polyamide TPA-CN-TPE with a high photoluminesence characteristic was successfully synthesized by the direct polymerization of 4-cyanotriphenyl diamine (TPA-CN) and tetraphenylethene (TPE)-containing dicarboxylic acid. The obtained luminescent polyamide plays a significant role as the polymer electret layer in organic field-effect transistors (OFETs)-type memory. The strong green emission of TPA-CN-TPE under ultraviolet (UV) irradiation can be directly absorbed by the pentacene channel, displaying a light-induced programming and voltage-driven erasing organic phototransistor-based nonvolatile memory. Memory window can be effectively manipulated between the programming and erasing states by applying UV light illumination and electrical field, respectively. The photoinduced memory behavior can be maintained for over 10 4 s between these two states with an on/off ratio of 10 4 , and the memory switching can be steadily operated for many cycles. With high photoresponsivity ( R) and photosensitivity ( S), this organic phototransistor integrated with AEE-active polyamide electret layer could serve as an excellent candidate for UV photodetectors in optical applications. For comparison, an AEE-inactive aromatic polyimide TPA-PIS electret with much weaker solid-state emission was also applied in the same OFETs device architecture, but this device did not show any UV-sensitive and UV-induced memory characteristics, which further confirmed the significance of the light-emitting capability of the electret layer.

Effect of in vitro degradation of poly(D,L-lactide)/beta-tricalcium composite on its shape-memory properties.

PubMed

Zheng, Xiaotong; Zhou, Shaobing; Yu, Xiongjun; Li, Xiaohong; Feng, Bo; Qu, Shuxin; Weng, Jie

2008-07-01

The in vitro degradation characteristic and shape-memory properties of poly(D,L-lactide) (PDLLA)/beta-tricalcium phosphate (beta-TCP) composites were investigated because of their wide application in biomedical fields. In this article, PDLLA and crystalline beta-TCP were compounded and interesting shape-memory behaviors of the composite were first investigated. Then, in vitro degradation of the PDLLA/beta-TCP composites with weight ratios of 1:1, 2:1, and 3:1 was performed in phosphate buffer saline solution (PBS) (154 mM, pH 7.4) at 37 degrees C. The effect of in vitro degradation time for PDLLA/beta-TCP composites on shape-memory properties was studied by scanning electron microscopy, differential scanning calorimetry, gel permeation chromatography, X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The changes of structural morphology, glass transition temperature (T(g)), molecular weight, and weight loss of composites matrix and pH change of degradation medium indicated that shape-memory effects at different degradation time were nonlinearly influenced because of the breaking down of polymer chain and the formation of degradation products. Furthermore, the results from XRD and FTIR implied that the degradation products, for example, hydroxyapatite (HA), calcium hydrogen phosphate (CaHPO(4)), and calcium pyrophosphate (Ca(2)P(2)O(7)) phases also had some effects on shape-memory properties during the degradation. 2007 Wiley Periodicals, Inc.

Enhanced photomechanical response of a Ni-Ti shape memory alloy coated with polymer-based photothermal composites

NASA Astrophysics Data System (ADS)

Perez-Zúñiga, M. G.; Sánchez-Arévalo, F. M.; Hernández-Cordero, J.

2017-10-01

A simple way to enhance the activation of shape memory effects with light in a Ni-Ti alloy is demonstrated. Using polydimethylsiloxane-carbon nanopowder (PDMS+CNP) composites as coatings, the one-way shape memory effect (OWSME) of the alloy can be triggered using low power IR light from a laser diode. The PDMS+CNP coatings serve as photothermal materials capable to absorb light, and subsequently generate and dissipate heat in a highly efficient manner, thereby reducing the optical powers required for triggering the OWSME in the Ni-Ti alloy. Experimental results with a cantilever flexural test using both, bare Ni-Ti and coated samples, show that the PDMS+CNP coatings perform as thermal boosters, and therefore the temperatures required for phase transformation in the alloy can be readily obtained with low laser powers. It is also shown that the two-way shape memory effect (TWSME) can be set in the Ni-Ti alloy through cycling the TWSME by simply modulating the laser diode signal. This provides a simple means for training the material, yielding a light driven actuator capable to provide forces in the mN range. Hence, the use of photothermal coatings on Ni-Ti shape memory alloys may offer new possibilities for developing light-controlled smart actuators.

High reliable and stable organic field-effect transistor nonvolatile memory with a poly(4-vinyl phenol) charge trapping layer based on a pn-heterojunction active layer

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

Xiang, Lanyi; Ying, Jun; Han, Jinhua

2016-04-25

In this letter, we demonstrate a high reliable and stable organic field-effect transistor (OFET) based nonvolatile memory (NVM) with a polymer poly(4-vinyl phenol) (PVP) as the charge trapping layer. In the unipolar OFETs, the inreversible shifts of the turn-on voltage (V{sub on}) and severe degradation of the memory window (ΔV{sub on}) at programming (P) and erasing (E) voltages, respectively, block their application in NVMs. The obstacle is overcome by using a pn-heterojunction as the active layer in the OFET memory, which supplied a holes and electrons accumulating channel at the supplied P and E voltages, respectively. Both holes and electronsmore » transferring from the channels to PVP layer and overwriting the trapped charges with an opposite polarity result in the reliable bidirectional shifts of V{sub on} at P and E voltages, respectively. The heterojunction OFET exhibits excellent nonvolatile memory characteristics, with a large ΔV{sub on} of 8.5 V, desired reading (R) voltage at 0 V, reliable P/R/E/R dynamic endurance over 100 cycles and a long retention time over 10 years.« less

Kinetically driven self-assembly of a binary solute mixture with controlled phase separation via electro-hydrodynamic flow of corona discharge.

PubMed

Jung, Hee Joon; Huh, June; Park, Cheolmin

2012-10-21

This feature article describes a new and facile process to fabricate a variety of thin films of non-volatile binary solute mixtures suitable for high performance organic electronic devices via electro-hydrodynamic flow of conventional corona discharge. Both Corona Discharge Coating (CDC) and a modified version of CDC, Scanning Corona Discharge Coating (SCDC), are based on utilizing directional electric flow, known as corona wind, of the charged uni-polar particles generated by corona discharge between a metallic needle and a bottom plate under a high electric field (5-10 kV cm(-1)). The electric flow rapidly spreads out the binary mixture solution on the bottom plate and subsequently forms a smooth and flat thin film in a large area within a few seconds. In the case of SCDC, the static movement of the bottom electrode on which a binary mixture solution is placed provides further control of thin film formation, giving rise to a film highly uniform over a large area. Interesting phase separation behaviors were observed including nanometer scale phase separation of a polymer-polymer binary mixture and vertical phase separation of a polymer-organic semiconductor mixture. Core-shell type phase separation of either polymer-polymer or polymer-colloidal nanoparticle binary mixtures was also developed with a periodically patterned microstructure when the relative location of the corona wind was controlled to a binary solution droplet on a substrate. We also demonstrate potential applications of thin functional films with controlled microstructures by corona coating to various organic electronic devices such as electroluminescent diodes, field effect transistors and non-volatile polymer memories.

Kinetically driven self-assembly of a binary solute mixture with controlled phase separation via electro-hydrodynamic flow of corona discharge

NASA Astrophysics Data System (ADS)

Jung, Hee Joon; Huh, June; Park, Cheolmin

2012-09-01

This feature article describes a new and facile process to fabricate a variety of thin films of non-volatile binary solute mixtures suitable for high performance organic electronic devices via electro-hydrodynamic flow of conventional corona discharge. Both Corona Discharge Coating (CDC) and a modified version of CDC, Scanning Corona Discharge Coating (SCDC), are based on utilizing directional electric flow, known as corona wind, of the charged uni-polar particles generated by corona discharge between a metallic needle and a bottom plate under a high electric field (5-10 kV cm-1). The electric flow rapidly spreads out the binary mixture solution on the bottom plate and subsequently forms a smooth and flat thin film in a large area within a few seconds. In the case of SCDC, the static movement of the bottom electrode on which a binary mixture solution is placed provides further control of thin film formation, giving rise to a film highly uniform over a large area. Interesting phase separation behaviors were observed including nanometer scale phase separation of a polymer-polymer binary mixture and vertical phase separation of a polymer-organic semiconductor mixture. Core-shell type phase separation of either polymer-polymer or polymer-colloidal nanoparticle binary mixtures was also developed with a periodically patterned microstructure when the relative location of the corona wind was controlled to a binary solution droplet on a substrate. We also demonstrate potential applications of thin functional films with controlled microstructures by corona coating to various organic electronic devices such as electroluminescent diodes, field effect transistors and non-volatile polymer memories.

A complementary switching mechanism for organic memory devices to regulate the conductance of binary states

NASA Astrophysics Data System (ADS)

Vyas, Giriraj; Dagar, Parveen; Sahu, Satyajit

2016-06-01

We have fabricated an organic non-volatile memory device wherein the ON/OFF current ratio has been controlled by varying the concentration of a small organic molecule, 2,3-Dichloro-5,6-dicyano-p-benzoquinone (DDQ), in an insulating matrix of a polymer Poly(4-vinylphenol) (PVP). A maximum ON-OFF ratio of 106 is obtained when the concentration of DDQ is half or 10 wt. % of PVP. In this process, the switching direction for the devices has also been altered, indicating the disparity in conduction mechanism. Conduction due to metal filament formation through the active material and the voltage dependent conformational change of the organic molecule seem to be the motivation behind the gradual change in the switching direction.

Application of the Cluster Expansion to a Mathematical Model of the Long Memory Phenomenon in a Financial Market

NASA Astrophysics Data System (ADS)

Kuroda, Koji; Maskawa, Jun-ichi; Murai, Joshin

2013-08-01

Empirical studies of the high frequency data in stock markets show that the time series of trade signs or signed volumes has a long memory property. In this paper, we present a discrete time stochastic process for polymer model which describes trader's trading strategy, and show that a scale limit of the process converges to superposition of fractional Brownian motions with Hurst exponents and Brownian motion, provided that the index γ of the time scale about the trader's investment strategy coincides with the index δ of the interaction range in the discrete time process. The main tool for the investigation is the method of cluster expansion developed in the mathematical study of statistical mechanics.

Finite Element Analysis of Adaptive-Stiffening and Shape-Control SMA Hybrid Composites

NASA Technical Reports Server (NTRS)

Gao, Xiujie; Burton, Deborah; Turner, Travis L.; Brinson, Catherine

2005-01-01

Shape memory alloy hybrid composites with adaptive-stiffening or morphing functions are simulated using finite element analysis. The composite structure is a laminated fiber-polymer composite beam with embedded SMA ribbons at various positions with respect to the neutral axis of the beam. Adaptive stiffening or morphing is activated via selective resistance heating of the SMA ribbons or uniform thermal loads on the beam. The thermomechanical behavior of these composites was simulated in ABAQUS using user-defined SMA elements. The examples demonstrate the usefulness of the methods for the design and simulation of SMA hybrid composites. Keywords: shape memory alloys, Nitinol, ABAQUS, finite element analysis, post-buckling control, shape control, deflection control, adaptive stiffening, morphing, constitutive modeling, user element

Holographic recording materials development. [development of cis-trans isomerization for holographic memory

NASA Technical Reports Server (NTRS)

1974-01-01

Developments in the area of organic cis-trans isomerization systems for holographic memory applications are reported. The chemical research effort consisted of photochemical studies leading to the selection of a stilbene derivative and a polymer matrix system which have greatly improved refractive index differences between the cis and trans isomers as well as demonstrated efficiency of the photoisomerization process. In work on lithium niobate effects of sample stoichiometry and of read and write beam polarizations on recording efficiency were investigated. LiNbO3 was used for a study of angular sensitivity and of capability for simultaneous recording of extended objects without interference. The current status of LiNbO3 as a holographic recording material is summarized.

Piezoelectric micromachined ultrasonic transducers and micropumps: from design to optomicrofluidic applications

NASA Astrophysics Data System (ADS)

Khazaaleh, Shadi; Saeed, Numan; Taha, Inas; Madzik, Mateusz T.; Viegas, Jaime

2017-02-01

In this work, we present the experimental results of a new wafer-level production platform for aluminum nitride based piezoelectric micromachined ultrasonic transducers (PMUTs), operated by lower than 10 V peak-to-peak signals, and covering ultrasonic frequency ranges from 200 kHz up to 10 MHz, with measured axial displacements ranging from a few nanometers up to 600 nm. The fabricated devices have a low footprint of (130x130) μm2. The experimental results are in excellent agreement with finite-element method simulations. The small footprint and driving voltages of these piezo-microactuators are well suited for the development of micropump and micromixer designs for portable microfluidics applications.

Shape Memory Polymer Self-Deploying Membrane Reflectors

DTIC Science & Technology

2007-01-30

stability relative to their [Candidate A] counterparts and very low moisture uptake. Initial attempts to incorporate [this particular constituent] were...specimen (Figure 19). The sample was then reheated and "deployed" (Figure 20) while being held with the bend axis oriented vertically such that gravity...addressed as a separate task for the purposes of describing Statement of Work content, material process development was conducted in parallel with and

High Performance Polymer Memory and Its Formation

DTIC Science & Technology

2007-04-26

the retention time of the device was performed to estimate the barrier height of the charge trap . The activation energy was approximated to be about...characteristics and presented a model to explain the mechanism of electrical switching in the device. By exploiting an electric-field induced charge transfer...electrical current in the high conductivity state would be due to some temperature-independent charge tunneling processes. The IV curves could be

Polylactide-based polyurethane shape memory nanocomposites (Fe3O4/PLAUs) with fast magnetic responsiveness

NASA Astrophysics Data System (ADS)

Gu, Shu-Ying; Jin, Sheng-Peng; Gao, Xie-Feng; Mu, Jian

2016-05-01

Polylactide-based polyurethane shape memory nanocomposites (Fe3O4/PLAUs) with fast magnetic responsiveness are presented. For the purpose of fast response and homogeneous dispersion of magnetic nanoparticles, oleic acid was used to improve the dispersibility of Fe3O4 nanoparticles in a polymer matrix. A homogeneous distribution of Fe3O4 nanoparticles in the polymer matrix was obtained for nanocomposites with low Fe3O4 loading content. A small agglomeration was observed for nanocomposites with 6 wt% and 9 wt% loading content, leading to a small decline in the mechanical properties. PLAU and its nanocomposites have glass transition around 52 °C, which can be used as the triggering temperature. PLAU and its nanocomposites have shape fixity ratios above 99%, shape recovery ratios above 82% for the first cycle and shape recovery ratios above 91% for the second cycle. PLAU and its nanocomposites also exhibit a fast water bath or magnetic responsiveness. The magnetic recovery time decreases with an increase in the loading content of Fe3O4 nanoparticles due to an improvement in heating performance for increased weight percentage of fillers. The nanocomposites have fast responses in an alternating magnetic field and have potential application in biomedical areas such as intravascular stent.

Thermomechanical properties of polyurethane shape memory polymer-experiment and modelling

NASA Astrophysics Data System (ADS)

Pieczyska, E. A.; Maj, M.; Kowalczyk-Gajewska, K.; Staszczak, M.; Gradys, A.; Majewski, M.; Cristea, M.; Tobushi, H.; Hayashi, S.

2015-04-01

In this paper extensive research on the polyurethane shape memory polymer (PU-SMP) is reported, including its structure analysis, our experimental investigation of its thermomechanical properties and its modelling. The influence of the effects of thermomechanical couplings on the SMP behaviour during tension at room temperature is studied using a fast and sensitive infrared camera. It is shown that the thermomechanical behaviour of the SMP significantly depends on the strain rate: at a higher strain rate higher stress and temperature values are obtained. This indicates that an increase of the strain rate leads to activation of different deformation mechanisms at the micro-scale, along with reorientation and alignment of the molecular chains. Furthermore, influence of temperature on the SMP’s mechanical behaviour is studied. It is observed during the loading in a thermal chamber that at the temperature 20 °C below the glass transition temperature (Tg) the PU-SMP strengthens about six times compared to the material above Tg but does not exhibit the shape recovery. A finite-strain constitutive model is formulated, where the SMP is described as a two-phase material composed of a hyperelastic rubbery phase and elastic-viscoplastic glassy phase. The volume content of phases is governed by the current temperature. Finally, model predictions are compared with the experimental results.

3D Printed Reversible Shape Changing Components with Stimuli Responsive Materials

PubMed Central

Mao, Yiqi; Ding, Zhen; Yuan, Chao; Ai, Shigang; Isakov, Michael; Wu, Jiangtao; Wang, Tiejun; Dunn, Martin L.; Qi, H. Jerry

2016-01-01

The creation of reversibly-actuating components that alter their shapes in a controllable manner in response to environmental stimuli is a grand challenge in active materials, structures, and robotics. Here we demonstrate a new reversible shape-changing component design concept enabled by 3D printing two stimuli responsive polymers—shape memory polymers and hydrogels—in prescribed 3D architectures. This approach uses the swelling of a hydrogel as the driving force for the shape change, and the temperature-dependent modulus of a shape memory polymer to regulate the time of such shape change. Controlling the temperature and aqueous environment allows switching between two stable configurations – the structures are relatively stiff and can carry load in each – without any mechanical loading and unloading. Specific shape changing scenarios, e.g., based on bending, or twisting in prescribed directions, are enabled via the controlled interplay between the active materials and the 3D printed architectures. The physical phenomena are complex and nonintuitive, and so to help understand the interplay of geometric, material, and environmental stimuli parameters we develop 3D nonlinear finite element models. Finally, we create several 2D and 3D shape changing components that demonstrate the role of key parameters and illustrate the broad application potential of the proposed approach. PMID:27109063

Shape Memory Polymers Containing Higher Acrylate Content Display Increased Endothelial Cell Attachment

PubMed Central

Govindarajan, Tina; Shandas, Robin

2018-01-01

Shape Memory Polymers (SMPs) are smart materials that can recall their shape upon the application of a stimulus, which makes them appealing materials for a variety of applications, especially in biomedical devices. Most prior SMP research has focused on tuning bulk properties; studying surface effects of SMPs may extend the use of these materials to blood-contacting applications, such as cardiovascular stents, where surfaces that support rapid endothelialization have been correlated to stent success. Here, we evaluate endothelial attachment onto the surfaces of a family of SMPs previously developed in our group that have shown promise for biomedical devices. Nine SMP formulations containing varying amounts of tert-Butyl acrylate (tBA) and Poly(ethylene glycol) dimethacrylate (PEGDMA) were analyzed for endothelial cell attachment. Dynamic mechanical analysis (DMA), contact angle studies, and atomic force microscopy (AFM) were used to verify bulk and surface properties of the SMPs. Human umbilical vein endothelial cell (HUVEC) attachment and viability was verified using fluorescent methods. Endothelial cells preferentially attached to SMPs with higher tBA content, which have rougher, more hydrophobic surfaces. HUVECs also displayed an increased metabolic activity on these high tBA SMPs over the course of the study. This class of SMPs may be promising candidates for next generation blood-contacting devices. PMID:29707382

The effect of moisture absorption on the physical properties of polyurethane shape memory polymer foams.

PubMed

Yu, Ya-Jen; Hearon, Keith; Wilson, Thomas S; Maitland, Duncan J

2011-08-01

The effect of moisture absorption on the glass transition temperature (T(g)) and stress/strain behavior of network polyurethane shape memory polymer (SMP) foams has been investigated. With our ultimate goal of engineering polyurethane SMP foams for use in blood contacting environments, we have investigated the effects of moisture exposure on the physical properties of polyurethane foams. To our best knowledge, this study is the first to investigate the effects of moisture absorption at varying humidity levels (non-immersion and immersion) on the physical properties of polyurethane SMP foams. The SMP foams were exposed to differing humidity levels for varying lengths of time, and they exhibited a maximum water uptake of 8.0% (by mass) after exposure to 100% relative humidity for 96 h. Differential scanning calorimetry results demonstrated that water absorption significantly decreased the T(g) of the foam, with a maximum water uptake shifting the T(g) from 67 °C to 5 °C. Samples that were immersed in water for 96 h and immediately subjected to tensile testing exhibited 100% increases in failure strains and 500% decreases in failure stresses; however, in all cases of time and humidity exposure, the plasticization effect was reversible upon placing moisture-saturated samples in 40% humidity environments for 24 h.