The rehabilitation community is at the threshold of a new age in which orthotic and prosthetic devices will no longer be separate, lifeless mechanisms, but intimate extensions of the human body-structurally, neurologically, and dynamically. In this paper we discuss scientific and technological advances that promise to accelerate the merging of body and machine, including the development of actuator technologies that behave like muscle and control methodologies that exploit principles of biological movement. We present a state-of-the-art device for leg rehabilitation: a powered ankle-foot orthosis for stroke, cerebral palsy, or multiple sclerosis patients. The device employs a forcecontrollable actuator and a biomimetic control scheme that automatically modulates ankle impedance and motive torque to satisfy patient-specific gait requirements. Although the device has some clinical benefits, problems still remain. The force-controllable actuator comprises an electric motor and a mechanical transmission, resulting in a heavy, bulky, and noisy mechanism. As a resolution of this difficulty, we argue that electroactive polymer-based artificial muscle technologies may offer considerable advantages to the physically challenged, allowing for joint impedance and motive force controllability, noise-free operation, and anthropomorphic device morphologies.

During the last decade and a half new polymers have emerged that respond to electrical stimulation with a significant shape or size change. This capability of electroactive polymer (EAP) materials is attracting the attention of engineers and scientists from many different disciplines. Practitioners in biomimetics are particularly excited about these materials since the artificial muscle aspect of EAPs can be applied to mimic the movements of animals and insects. In the foreseeable future, robotic mechanisms actuated by EAP will enable engineers to create devices previously imaginable only in science fiction. Last year, significant accomplishments were reported including the emergence of the first commercial product and the possibility that an arm can be made with EAP actuators having the potential of winning a wrestling match with a human. As such major accomplishments continue to be reported it is interesting to review the progress and provide a prospective regarding the development since the first EAPAD conference in 1999. This manuscript covers the progress in the field of EAP and the challenges that are being addressed.

The characteristics of Electro-actuated polymers (EAP) are typically considered inadequate for applications in robotics. But in recent years, there has been both dramatic increases in EAP technological capbilities and reductions in power requirements for actuating bio-inspired robotics. As the two trends continue to converge, one may anticipate that dramatic breakthroughs in biologically inspired robotic actuation will result due to the marraige of these technologies. This talk will provide a snapshot of how EAP actuator scientists and roboticists may work together on a common platform to accelerate the growth of both technologies. To demonstrate this concept of a platform to accelerate this convergence, the authors will discuss their work in the niche application of robotic facial expression. In particular, expressive robots appear to be within the range of EAP actuation, thanks to their low force requirements. Several robots will be shown that demonstrate realistic expressions with dramatically decreased force requirements. Also, detailed descriptions will be given of the engineering innovations that have enabled these robotics advancements-most notably, Structured-Porosity Elastomer Materials (SPEMs). SPEM manufacturing techniques create delicate cell-structures in a variety of elastomers that maintain the high elongation characteristics of the mother material, but because of the porisity, behave as sponge-materials, thus lower the force required to emulate facial expressions to levels output by several extant EAP actuators.

Electroelastomers (electroactive elastomers, a.k.a. dielectric elastomers) such as those based on acrylic elastomer films with compliant electrodes, when highly prestrained, exhibited up to 380% electromechanical strain in area expansion at 5 to 6 kV. By rolling highly prestrained acrylic films around a compression spring, multifunctional electroelastomer rolls (MERs, or spring rolls) were obtained that combined load bearing, actuation, and sensing functions. The design was extended to two-degree-of-freedom (2-DOF) and 3-DOF spring rolls by patterning the electrodes along the circumferential spans of the rolls. Multiple-DOF spring rolls retained the linear actuation of 1-DOF spring rolls with additional bending actuation. New electroelastomers were developed that preserved the high strain and energy capability of the acrylic films but could respond one order of magnitude faster. One-DOF spring rolls using this new material exhibited response speeds up to 100 Hz, and power densities as high as 400 W/kg of actuator mass and 2000 W/kg of electroelastomer mass based on maximum force, stroke, and frequency. Further, new electroelastomers were prepared that exhibited 200% strain without the need for prestrain. These materials may enable new actuators containing no prestrain-supporting structures that are even lighter, more compact, and compliant. The new actuators would have a higher percentage of active mass and higher energy and power densities than those based on the prestrained acrylic films matching the characteristics of animals. A roll actuator containing no supporting structure was fabricated to output 33% strain. Preliminary lifetime measurements confirmed the potentially long lifetime of the electroelastomers. Improvements in MER design and materials have enabled a new generation of small walking robots, MERbot, with a multi-DOF spring roll as each of its six legs, as well as a new type of robot that can be quickly fabricated from a single flat multifunctional actuator structure. Such small flat robots can hop or jump two to three times their height and have been able to quickly clear obstacles equal to the robots' height.

Dielectric elastomer actuators rely on the compressive force generated by the electrostatic attraction of a pair of electrodes across a low-modulus polymer.This in turn induces the deformation of the elastomer in the plane normal to the force. It has been shown that the response of such a device is proportional to the permittivity of the core elastomer layer. Here we report our progress in increasing the permittivity of a polyurethane elastomer through the addition of a conductive filler, graphite. At loadings near the percolation threshold, the actuation stress increases by a factor of over 500, and relative permittivity beyond 4000 is reported.

Previous research has demonstrated promise for the use of dielectric elastomer (DE) films in diaphragm pump applications. Because the films tend to be quite thin, single layers operate at very low pressures. To make this technology suitable for practical applications, the films may be organized into laminates which will operate at increased pressures. Radially stretched circular diaphragms of two materials were tested: 3M VHB 4905 polyacrylate and spin-cast Nusil CF19-2186 silicone. The diaphragms were stacked, each layer sharing an electrode with the adjacent layer. The stack was mounted on a sealed chamber and energized at varied electric fields while regulated pressure was applied to the interior chamber, displacing the diaphragm. The pressure-volume properties of the stacks were recorded for each activation state.

Dielectric elastomer actuators consist of an elastomer film sandwiched between compliant electrodes. They work as electrostatic actuators: when a large electric field is applied over the electrodes, the rubber is compressed and the elastomer film elongates in the film plane. The performance of dielectric elastomer actuators (DEA), when a constant potential is applied, is expressed in a universal equation where a combination of the elastomers materials properties enters through a single parameter - a figure of merit. The expansion of the actuator is related to the applied potential for a particular actuator geometry: an actuator that expands under constant width. The derivation takes finite elasticity of the elastomers into account. The figure of merit can be used as guide to optimizing elastomer properties for dielectric elastomer actuators. For very highly pre-strained elastomers, the equations no longer hold. Elastomers with optimal properties are not commercially available. Typical elastomers for electric applications, encapsulation of electronics take an example, show at least one materials property that diminish their performance in DEA. Elastomers are mapped in a diagram expressing the property space for DEA. Dynamical properties of dielectric elastomer actuators depend upon both electric and mechanical properties of the elastomer. The viscoelastic mechanical properties are intimately connected to network structure of the elastomer. The connection between network structure and the various relaxation times for the rubber that determines its viscoelastic properties are described.

Silicone and acrylic elastomers have received increased attention as dielectric electroactive polymer (EAP) materials for actuator technology. The goal of this work was to develop and characterize a new class of silicones (DC3481) and to compare it with acrylic elastomers. The influence of various types of hardeners, hardener concentration, prestrain and high dielectric organic fillers was studied by mechanical, electrical and electromechanical experiments. Furthermore the temperature dependence and the viscoelastic properties were investigated. The results show that by changing type and concentration of hardener, the Young's modulus can be varied. In order to increase the dielectric constant, the silicone was blended with organic materials. Compared to acrylic elastomers, this new class of silicone elastomers has the advantage of a constant stiffness over a wide range of temperature and a lower viscosity that results in a higher response speed of the actuator.

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.

In this paper, we report a new electroactive polymer system, blends of P(VDF-TrFE) and P(VDF-CTFE). The thermal transition behavior and crystalline structure of the polymer blends were studied using the DSC and X-ray diffraction. The optimized thermal treating condition and composition for the blends were identified to have homogeneous materials. In order to find blends with high electromechanical performance, the maximum polarization level and the ratio of maximum polarization to remnant polarization are employed as key parameters to optimize the composition and process. Uniaxially stretching technique was employed to modify the morphology of the polymer blends and to enhance the electromechanical performance. The phase transition behavior can be significantly modified using thermal treating condition. In a stretched polymer blend, a polarization level about 60 mC/m2 at external electric field of 150 V/μm was obtained with a small remnant polarization, less than 10 mC/m2. This is very attractive for electromechanical applications.

When using polymeric networks to EAP material, certain requirements need to be fulfilled or at least partly fulfilled. The networks need to be strong since the driving voltage goes as the thickness of the film to the second power, but on the other hand the networks need to be soft and flexible in order to provide sufficiently motion. Several network parameters can be altered in order to alter the network properties but it turns out that the most obvious parameter - the chain length of the network reactants - has moderately influence at molecular lengths above the entanglement length only. The inter-chains entanglements dominate the properties rather than the actual crosslinks. Since chain lengths below the entanglement length result in hard networks, the chain length alone does not constitute a tunable parameter. Therefore, it is obvious to focus on controlling the entanglements. One way to do this is to make the network in solution and afterwards remove the solvent. This way the entanglement contribution is lowered because network chains will be surrounded by solvent molecules and therefore the number of trapped entanglements between network chains will be lowered. The chain length can then be used as an easily tunable parameter.

In this paper, we discuss the electrostriction enhancement mechanisms for ferroelectric polymers, including field enhancement mechanism in ferroelectric-dielectric composites, polarization enhancement mechanism and exchange coupling in ferroelectric nanocomposites, and percolation mechanism in ferroelectric-conductor composites.

A dielectric elastomer diaphragm is to be designed for potential use in a prosthetic blood pump. Application of an electric field deforms the membrane such that it moves from an initially flat configuration to an inflated state. This motion creates positive displacement of blood from the cardiac chambers thus mimicking the pump-like behavior of the natural heart. A comprehensive large deformation model accounting for the combined dielectric and elastic effect has been formulated. This paper presents recent developments in the model to further incorporate the entire nonlinear range of material elastic behavior and to more accurately represent the applied electric field by keeping the voltage constant as the membrane thickness decreases. The updated model is used to calculate the effects of varying system parameters such as pressure, voltage, prestretch, material constants, and membrane geometry. Analytical results are obtained for biaxially stretched 3M VHB 4905 polyacrylate films.

A modified two-dimensional computational model is developed to calculate the electromechanical properties of the electrostrictive graft elastomer. The electrostrictive graft elastomer, recently developed by NASA, is a type of electro-active polymer. In a previous paper, the authors calculated electrostrictive graft elastomer electromechanical properties using a 2-D atomic force field. For this 2-D polymer structure, a much higher electric field was required to produce strain compared with that required in experiments. Two reasons could explain the higher electric field strength: (1) Polymer chain movement is restricted to a 2-D plane rather than to a 3-D plane. Out-plane dihedral torsional angle change would thus not be modeled. For this reason, 2-D polymer chains are less flexible than actual 3-D polymer chains. (2) Boundary effect of the computational model. In the original model, a unit cell consisting of a single graft unit was developed to simulate the deformation of the electrostrictive graft elastomer. The boundary of the unit cell would restrict the rotation of the graft unit. In this paper, a modified 2-D computational model is established to overcome the above problems. Firstly, three-dimensional deformations, induced by both bending angle and dihedral torsional angle changes, are projected onto a two-dimensional plane. Using both theoretical and numerical analyses, the projected 2-D equilibrium bending angle is shown to have the same value as the 3-D equilibrium bending angle. The 2-D equivalent bending stiffness is derived using a series model based upon the fact that both bending and dihedral torsion produce configuration change. The equivalent stiffness is justified by the characteristics of the polymer chain and end-to-end distance. Secondly, a self-consistent scheme is developed to eliminate the boundary effect. Eight images of the unit cell are created peripherally, with the original unit cell in the center. Thus the boundary can only affect the rotation of the eight images, not the central unit cell. The modified 2-D computational model is employed to determine the electromechanical properties of the electrostrictive graft elastomer. Relations between electric field induced strain and electric field strength is calculated. The effect of molecular scale factors, such as free volume fraction, graft weight percentage, and graft orientation are also discussed. The results should enable molecular scale design of the electrostrictive graft elastomer.

Electron transport and ion transport are two critical processes taking place during electrochemical oxidation/reduction of conjugated polymers. Because they accompany and depend on each other, research on the individual processes is difficult. We present a device that allows us to measure ion transport directly and independently from electron transport in conjugated polymers. The device geometry makes the ion path much longer than the electron path, ensuring that ion transport is the rate-limiting step. Ion transport is also visualized directly through the color change of the film (electrochromism) as the electrochemical reaction proceeds, allowing one to precisely and quantitatively track the ion velocity. During reduction at sufficiently negative potentials, a phase front between the oxidized and reduced states was observed to travel into the film, the speed of which was proportional to the applied voltage, demonstrating that migration (rather than diffusion) is the key driving force. At less negative reducing potentials, the film gradually and more uniformly changed color, indicating that diffusion plays a large role. A simple first-cut model with drift and diffusion terms is presented. The simulated ion concentration profile matched the experimentally measured intensity profile strikingly well.

Ionic Polymer-metal Composites (IPMCs) are soft actuators and sensors. They generally consist of a thin perfluorinated ionomer membrane, metal electrodes plated on both faces, and are neutralized with certain counter cations, balancing the charge of the anions covalently fixed to the membrane. Under a suddenly applied step function (1 to 3 V), the IPMC in alkali-metal cation forms exhibits a fast bending motion towards the anode, followed by a slow relaxation. For Nafion-based IPMCs, this slow relaxation is towards the cathode, whereas for Flemion-based IPMCs, the slow relaxation continues the initial fast motion towards the anode. IPMC samples in sulfonic forms having sodium as cations are prepared, their electromechanical properties are characterized, and their actuation responses to various electric stimuli are investigated. Results show that for Nafion-based IPMCs, initial motion towards the anode can be ultimately eliminated by applying a slowly increasing potential, due to very slow charge accumulation and extensive cation redistribution within a boundary layer near the cathode electrode.

Ionic polymer-metal composites (IPMCs) consist of a perfluorinated ionomer membrane (usually Nafion or Flemion). The ionomer is plated on both faces with a noble metal such as gold or platinum. It is neutralized with a certain amount of counterions that balance the electrical charge of anions covalently fixed to the backbone membrane. IPMCs are electroactive materials that can be used as actuators and sensors. Their electrical-chemical-mechanical response is highly dependent on the cations used, the nature and the amount of solvent uptake, the morphology of the electrodes, and other factors. When a cantilever strip of solvated Nafion-based IPMC sample is subjected to a suddenly applied and sustained (DC) electric potential of several volts (1-3 V) across its faces, it bends towards the anode. For Nafion-based IPMCs with alkali metals, actuation towards the anode is followed by a slow back relaxation towards the cathode. If the electric potential is removed and the two electrodes are shorted during this back relaxation, the sample displays a fast bending deformation towards the cathode and then slowly relaxes back towards the anode, attaining a new equilibrium position generally distinct from its initial state. One way to change various phases of IPMC actuation is achieved by changing input potential. The electric potential inputs may be used to control the actuation of IPMCs. We present the results of a series of tests on Nafion-based IPMCs with ethylene glycol as solvent, actuated under electric potential inputs other than DC electric potential. We present experimental results for increasing ramp and sinusoidal electric potential waveforms.

The Molecular Dynamics Simulation technique has been used to describe the behavior of the polypyrrole/water interface at two different oxidation states: neutral (or reduced) and charged (or oxidized) polypyrrole state. The system was modeled by two symmetric and amorphous polymer layers, each one containing 64 polypyrrole chains with 10 monomeric units per chain and 2677 water molecules. When the oxidized polypyrrole was modeled, 128 chloride ions used as counterions to balance the excess of charge of the oxidized polypyrrole. From the simulated trajectories, several properties with atomic detail have been evaluated such as volume changes during oxidation or reduction process, the atomic and charge distribution profile across the polypyrrole/water interface, and the transitional diffusion coefficient and dehydration of chlorine ions from bulk water to the interior of the polymer matrix. In this sense, a diminution of the hydration and translational diffusion coefficient was obtained for the chloride ions when they penetrated into the polymer matrix.

Micromechanical model has been developed on the electromechanical response of the ionic polymer metal composites (IPMC). The response function based on the physico-chemical properties of the polymer electrolytes and metals is developed and is applied to that under the control of the electric potential. In the model, the response is attributed to two main effects. One is the electrokinetic effect, that is, the dragged water associated with the flow of counter ion causes the stress in the polymer electrolyte gel. The other is the effect due to the interfacial stress between the polymer electrolyte gel and the electrode. The electromechanical experiments of the IPMC were carried out and their results were compared with the simulation results which were calculated from the response function. The theoretical model can successfully apply to the experimental results, especially to the dependence on the difference of various factors such as ionic change, ionic conductivity, electrode capacitance, dimension of the ionic polymer, etc.

Poly(3,4-ethylenedioxythiophene), or PEDOT, freestanding films were synthesized and characterized as conducting polymer linear actuators. Variations of solvent and electrolyte led to the observation of strains greater than 4% with maximum strain rates of 0.2%/s during electrochemical interrogation in an ionic liquid environment. The ionic liquid 1,3-butylmethylimidazolium hexafluorophosphate, BMIMPF6, enabled the largest strains to be observed repeatedly while the polymer was held at a stress of 1.0MPa over tens of cycles. The ionic liquid environment also produced a single polarity in the relationship between charge and strain. This single polarity suggested that only the imidazolium cation was actively intercalating into and out of the polymer film. The possible sources and consequences of such a mechanism as compared to actuation in conventional solvents and electrolytes which show dual polarity of charge and strain is discussed.

Dependencies of electrochemomechanical deformation (ECMD) of polyaniline films on pH and supporting electrolyte concentration have been investigated to improve the performance of ECMD. It has been found that the magnitude and electroactive pH range of ECMD increase with increasing the concentration of supporting electrolyte. The electroactive pH range is extended from pH2 to pH3 for the strain of 5.5% with increasing the Cl- concentration from 0. 05 M to 3.0 M. The maximum strain of ECMD is attained to 7% with shifting the pH. These results are consistent with the facts of increased conductivity and the development of absorption spectra at higher electrolyte concentrations, which can be explained in terms of the Donnan effect.

It has been observed that the Ionic Polymer-Metal Composite (IPMC) is both inherently resistive and capacitive. This allows for the material to be modeled using an equivalent RC circuit to describe the charging/discharging behavior associated with the IPMC. Typically, the model includes two resistors and two capacitors, which will primarily account for the effective electrodes on the surface of the IPMC (top and bottom). There will also be a resistor placed between the two RC circuits to account for material between the electrodes and the resistance due to ion migration through polymer matrix. In this paper we report our recent effort to extend such a model to accommodate a multi-layer IPMCs a swell as inter-digitated electrodes. As expected the observed electric characteristics of an IPMC subjected to an electric field is highly non-linear. This is believed to be due primarily to the particle electrodes on the IPMC surface, which is inherently both captive and resistive due to particle seperation and density. The advantage of using such a model is to realize the capacitive and resistive effect and use them for multi-layer configuration. We also present typical experimental data.

The use of ionic liquids as solvents for ionic polymer (specifically, Nafion) transducers is demonstrated. Ionic liquids are attractive for this application because of their high inherent stability. Ionic liquids are salts that exist as liquids at room temperature and have no measureable vapor pressure. Therefore, the use of ionic liquids as solvents for ionic polymer transducers can eliminate the traditional problem of water evaporation in these devices. Another benefit of the use of ionic liquids in this way is the reduction or elimination of the characteristic back-relaxation common in water-solvated ionic polymer actuators. The results demonstrate that the viscosity of the ionic liquid and the degree to which the ionic liquid swells the membrane are the important physical parameters to consider. Five ionic liquids were studied, based on substituted pyrrolidinium, phosphonium, or imidazolium cations and fluoroanions. Of these five ionic liquids, transduction is demonstrated in three of them and the best results are obtained with 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ionic liquid. This substance has an electrochemical stability window of 4.1 V, a melting point of -10 °C, and a viscosity of 35-45 cP [19]. Results demonstrate that platinum-plated Nafion transducers solvated with this ionic liquid exhibit sensing and actuation responses and that these transducers are stable in air. Endurance testing of this sample reveals a decrease in the free strain of only 25 % after 250,000 actuation cycles in air.

Free-standing polypyrrole (ppy) films 10-20mm thick were obtained by electropolymerization on metals and subsequent peeling off. The free-standing film can be reduced in aqueous solution up to -3.0 V without any presence of hydrogen release or polymer degradation, keeping a conductivity high enough to allow their use as electrode for elecromehanical reactions. Voltammetric experiments inside the polymer oxidation/reduction potential range show that the involved charge increases for decreasing sweep rates. A deep reduction of the film requires polarization times longer than 300 s at -0.6V or more cathodic potentials. According with the voltammetric (dynamic) reduction. Around -1.0V the polymeric structure is closed when still a 35 to 60% (depending on the scan rate) of the material remains oxidized. The reduction then goes on by slow migration of the counterions through the increasingly compacted polymetric entanglement by stimulating confrontational relaxation movements of the ppy chains. The cathodic maximum, appearing on the voltammograms between -.7 and -0.9V, is related to slow kinetic and structural processes since the film reduction is completely by long polarization time at -0.6V. Three potential windows are distinguished for these films in a aqueous solutions: from potentials a low as -3.0 to -0.6V the free-standing film is a compacted semiconducting electrode; from -0.6 to +0.5 V is a stationary oxidation/reduction region; at stationary higher potentials than +0.6V a degradation of the electromechanical activity occurs.

We have tried to apply electroactive shape memory polymer to smart actuator. Electroactive shape memory can be achieved by applying an electric field to shape memory polymer without any thermal heating as conventional shape memory polymers. For it, electrically conducting shape memory composites were prepared by incorporating carbon nanotube into polymer matrix. A segmented polyurethane block copolymer composed of 4,4'-methylene bis (phenylisocyanate), polycaprolactone, and 1,4-butanediol was synthesized to be used as shape memory polymer, and carbon nanotube was used after surface-modification by an acid. It was found that nanotube-reinforced composites could show high electrical conductivity with increased modulus at only several weight percentages of nanotube, and electroactive shape recovery effect more than 80% could be obtained. Consequently, electric field-stimulated shape memory could be demonstrated through combined composites of polyurethane and nanotube.

Random copolymer hydrogel actuators, composed of poly(acrylic acid) and poly(vinyl sulfonic acid, sodium salt), were prepared. The swelling ratios at various temperatures and pHs, the deswelling water ratio and contraction/expansion behavior under an electric field for the hydrogel actuators were measured. The hydrogels exhibited very high swelling ratios, in the range of 8200 ~ 18000%, at 37 °C, and showed temperature/pH dependent swelling behavior. The deswelling water ratio of the CO1 hydrogel sample showed about an 80% weight reduction under a 5 V applied voltage. When the hydrogel actuator in various pH buffer solutions is subjected to an electric field, the hydrogel actuator was contracted. When the electric stimulus was removed, the hydrogel actuator was expanded on its original size. The hydrogel actuator also showed stepwise contraction/expansion behavior depending on the electric stimulus.

In this paper, we present a standard irreversible thermodynamic model to describe the working principle of electroactive cellophane bending actuators. Based upon the fact that cellophane possesses a number of important properties of interest including ion-exchange capability, high water absorptivity, and good permeability, under an imposed electric field across the bender the ions and conjugated solvent will create a redistribution of them within the cellophane matrix and lead to effective strain in the bender geometry. The results are compared against the available data in terms of tip displacement. Also, the effect of electrode-thickness is investigated. The present study focuses on a phenomenological description of cellulophane actuators although a piezoelectric model is not included. A study is currently under way to experimentally verify if the working principle of electroactive cellophane actuators is ionic or piezoelectric.

In this paper we present experimental measurements as well as a theoretical model for the electro-mechanical behavior of single walled carbon nanotube (SWNT) sheet actuators. The SWNT material exhibits elongation and contraction of the carbon bond length due to electro-chemically induced surface charge and works at a relatively low operating voltage. The use of carbon nanotube sheet material sandwich with porous ceramic is a special feature of the presented work. In the experiment, two layers of SWNT with a ceramic layer in between were placed between two working-electrodes in an electrolyte solution bath. The counter electrode has been placed within the solution away from the composite. The charge transfer takes place between the working and the counter electrodes. The displacement of the composite was measured in the thickness direction, i.e. between the fixed and the mobile working electrodes. Depending on the applied voltage, different displacement values up to 0.8% of its original thickness were obtained. As influencing factors, the parameters such as applied electric field, thickness of the composite, solvent and electrode type were investigated. A clear dependency of the actuation on the applied potential was observed within the electro-chemical window. It is remarkable that an applied electric voltage exceeding the window leads to a hydrolysis of the solvent, i.e. generation of gas bubbles. In the theoretical part, a macroscopic model for the actuation of the SWNT material has been developed. A mechanical field equation which uses the applied electric potential as input gives the elongation and contraction of the material. Depending on the parameters given above, the time-behavior of the actuator has been simulated. Thus, by various numerical simulations and experimental investigations, the actuator-characteristic can be optimized. In conclusion, a good correlation between the experimental and the numerical results has been determined.

This paper describes the fabrication and characteristics of an ionic polymer-metal composite (IPMC) membrane-shaped micro-actuator and its application to the fabrication of a micro-pump. After fabricating two 8mm×8mm IPMC membrane-shaped actuators using a Nafion film, their displacements were measured. The fabricated IPMC membrane-shaped micro-actuators showed displacement of 14~27μ at the applied voltage ranging from 4VP-P to 10VP-P at 0.5Hz. Displacement of the IPMC actuator fabricated with a commercially available Nafion is large enough to make the IPMC actuator a membrane-shaped micro-actuator for fabricating an IPMC micro-pump. IPMC micro-pump was fabricated by assembling IPMC membrane-shaped micro-actuator and PDMS(polydimethylsiloxane) micro-channel together. PDMS micro-channel was designed to have nozzle/diffuser structures which make the fluids flow from inlet to outlet when the IPMC membrane-shaped micro-actuator is deflected up and down by the applied voltages. The measured flow rate of the fabricated IPMC micro-pump was about 9.9μℓ/min at 0.5Hz when the input voltage and duty ratio were 8V P-P and 50%, respectively. The test results illustrate that the fabricated IPMC micro-pump is suitable for pumping fluid through micro-channel on a PDMS substrate. Mechanical performances of beam-shaped and bridge-shaped conductive polymer actuator in aqueous solution and in solid electrolyte have been measured and analyzed. The optimum thickness of polypyrrole for the best bending performance is about 17-19 μm which has been polymerized at the current density of 5.4 μA/mm2 for 120 minutes. For the application of conductive polymer actuator to a micropump, silicon bulk micromachining process has been combined.

Virtual Reality (VR) is gaining more importance in our society. For many years, VR has been limited to the entertainment applications. Today, practical applications such as training and prototyping find a promising future in VR. Therefore there is an increasing demand for low-cost, lightweight haptic devices in virtual reality (VR) environment. Electroactive polymers seem to be a potential actuation technology that could satisfy these requirements. Dielectric polymers developed the past few years have shown large displacements (more than 300%). This feature makes them quite interesting for integration in haptic devices due to their muscle-like behaviour. Polymer actuators are flexible and lightweight as compared to traditional actuators. Using stacks with several layers of elatomeric film increase the force without limiting the output displacement. The paper discusses some design methods for a linear dielectric polymer actuator for VR devices. Experimental results of the actuator performance is presented.

We report the development of low modulus, highly conducting thin film electrodes formed by molecular-level self-assembly processing methods. The electrodes may be used on sensor or actuator materials requiring large strain.

Semi-interpenetrating polymer network (semi-IPN) hydrogels composed of chitosan and polyaniline (PANi) were prepared and the effects of various pHs and temperatures, and the electrical responsiveness, were studied. The swelling ratio of semi-IPNs depended on pH and temperature. The stimulus responses of semi-IPNs in electric fields were also investigated. When swollen, semi-IPNs were placed between a pair of electrodes, and exhibited bending behavior upon the application of an electric field. The electroresponsive behavior of the semi-IPN was also affected by the electrolyte concentration of the external solution. The semi-IPN also showed various degrees of increase of bending behavior depending on the electrical stimulus.

Conventional tactile sensors can only detect simple physical values such as pressure, but can hardly measure multi-directional movements in touch with the surface of objects. We propose a soft tactile sensor using an Ionic Polymer-Metal Composite (IPMC or known as ICPF). IPMC is excellent in softness, durability, easy molding, and so on. Many applications have been developed using as IPMC actuators. IPMC can also utilized as a sensor, because a voltage on the both ends of the film changes by adding mechanical stimuli and bending the film. It is found experimentally that IPMC has the characteristics as a speed sensor because the output voltages were in proportion to the velocities of the end of films by making vibrational motions. A tactile speed sensor that can measure the velocity vectors in 3-dimenstional movements was developed. The sensor has centroclinal structure made of silicone gel capsule, and four IPMC sensor modules were combined with the capsule inside in cross shape. The silicon gel capsule also seal in water, which is necessary for IPMC devices. The output voltages of each sensor were calibrated into the same maximum outputs because IPMC sensors have response variation. The amount of the velocity was estimated by calculating four outputs of each sensor modules. The direction of the movement can also be estimated by them only when the amount of the velocity exceeds the sufficient level. Experimental results show the sensor could estimate the velocity vector in real-time.

A comparison of key parameters of seven different gel electrolytes for use in electrochromic devices (ECD) is reported. The ionic conductivity, transmittance, and stability of the gel electrolytes are important considerations for smart window applications. The gel electrolytes were prepared by combining polymethylmethacrylate (PMMA) with a salt and a solvent combination. Two different salts, lithium perchlorate (LiClO4) and trifluorosulfonimide (LiN(CF3SO2)2), and three solvent combinations, acetonitrile and propylene carbonate (ACN and PC), ethylene carbonate and propylene carbonate (EC and PC), and Gamma-butyrolactone and propylene carbonate (GBL and PC) were investigated. Results show that gel electrolytes composed of a LiClO4 and GBL+PC combination and a LiClO4 and EC+PC combination are the best candidates for a smart window device based on its high conductivity over time and various temperatures, as well as its electrochemical stability and high transmittance.

Ionic electroactive polymers have been developed as mechanical sensors or actuators, taking advantage of the electromechanical coupling of the materials. This research attempts to take advantage of the chemomechanical and chemoelectrical coupling by characterizing the transient response as the polymer undergoes an ion exchange, thus using the polymer for ionic sensing. Nafion is a biocompatible material, and an implantable polymeric ion sensor which has applications in the biomedical field for bone healing research. An ion sensor and a strain gauge could determine the effects of motion allowed at the fracture site, thus improving rehabilitation procedures for bone fractures. The charge sensitivity of the material and the capacitance of the material were analyzed to determine the transient response. Both measures indicate a change when immersed in ionic salt solutions. It is demonstrated that measuring the capacitance is the best indicator of an ion exchange. Relative to a flat response in deionized water (±2%), the capacitance of the polymer exhibits an exponential decay of ~25% of its peak when placed in a salt solution. A linear correlation between the time constant of the decay and the ionic size of the exchanging ion was developed that could reasonably predict a diffusing ion. Tests using an energy dispersive spectrometer (EDS) indicate that 90% of the exchange occurs in the first 20 minutes, shown by both capacitance decay and an atomic level scan. The diffusion rate time constant was found to within 0.3% of the capacitance time constant, confirming the ability of capacitance to measure ion exchange.

Design and development of electro-active polymeric devices for sensing and actuation requires accurate characterization of its nonlinear dynamic behavior and performance characteristics. Thin film cantilevers are being applied for numerous sensor and actuator applications. A nonlinear model of a piezoelectric thin plate cantilever is developed in this work using a two-mode approximation developed by Galerkin's method. This reduced order model is then studied using perturbation method for the nonlinear dynamic response due to a harmonic excitation. The results obtained demonstrate the nonlinear nature of the dynamic behavior of thin plates made of polymer polyvinylidene fluoride. The exhibited nonlinear behavior includes parameter dependent amplitude modulation, nonlinear jump and nonlinear dependence on excitation frequency and excitation amplitude. This study is a step forward in understanding the associated dynamics so as to utilize these geometries in various transducer applications.

Electro-active polymers reinforced with carbon nanotubes have attracted many researchers in the recent years. Recent activities in this area show that conducting polymers with carbon nanotubes in an electrolytic medium possess actuation and sensing properties due to the change in bond length in the carbon atoms. However, their applications are limited due to their operation in a wet medium. In this paper, we explore the feasibility of electro-active polymers with dispersed carbon nanotubes that can be used for actuation and sensing in a dry medium like air to make them viable. Different polymer composites are considered for mixing with single-walled and multi-walled carbon nanotubes manufactured by chemical vapor deposition technique. Various dispersing techniques for aligning the carbon nanotubes like smart blending and chaotic mixing are also explored. The feasibility of actuation and sensing of these composites are verified by experimentation on several macrosystems comprised of these functional nanostructures.

Electro-Active Paper (EAPap) is attractive for EAP actuator due to its merits in terms of lightweight, dryness,large displacement output, low actuation voltage and low power consumption. EAPap actuator has been developed based on cellulose material. Several kinds of cellulose are used for EAPap actuators and the performance of EAPaps is investigated in terms of displacement along with frequency, voltage, temperature and humidity. To investigate the actuation principle, electrical impedance measurement is conducted and results are compared with conducting polymer and piezoelectric ceramic materials. The principle that dictates the actuation of EAPap is discussed. Since the power requirement of EAPap is so small that it can be activated by remote microwave power, which is promising for making flying objects.

The construction of electromechanical actuator has been achieved by using the conducting polypyrrole films deposition onto a gold-coated cellophane paper. This is probably the first report of this type of paper actuator. The conducting polypyrrole was electro-generated using either galvanostatic or potentiostatic conditions at 0.5 mA/cm2 current density or 0.7 volts applied potential. The two types of actuators were constructed namely: 1.Ppy/Cellophane bilayer 2. Ppy/ Cellophane paper /Ppy trilayer using electrochemical technique. These actuators showed a reversible and reproducible displacement in acetonitrile solution containing LiClO4 (1M). The maximum displacement of 9.1 mm was recorded for tri-layer device and 3.5 mm for bi-layer device in 1M LiClO4 acetonitrile solutions. The prepared actuator devices were investigated for their mechanical actuation in air medium. The actuation in air is comparatively less than in solution actuation, but still it showed significant movement in air also. The results obtained in acetonitrile solution containing 1M LiClO4 shows that the actuator requires very low excitation voltages of 0.2 MV m-1 at 0.5 Hz frequencies. The effect of humidity on the actuation properties was addressed. The humidity measurement was carried out between 60% to 95% humidity with the help of humidity-temperature controlled chamber. The resonating frequency of 3 Hz at 6 volts had shown 1.8 mm displacement at 95% humidity for gold-coated cellophane sample without polypyrrole.

In this paper, we present a novel actuation method employing dielectric elastomer and a micro--inchworm robot actuated by the proposed method. Different from the previous approaches adopting pretensions of dielectric elastomer, the method depends solely on the deformation caused by the Maxwell stress, and thus, their critical problem such as stress relaxation as time goes on is cleared, though the amount of deformation is largely reduced. In addition, the proposed actuation method provides advantageous features of reduction in size, speed of response, ruggedness in operation. Using the actuator, a three-degree-of-freedom actuator module is developed, which can provide up-down, and two rotational degree-of-freedom motion. In the application of the proposed actuation method, a micro-robot mimicking the motion of an inchworm is developed.

Tactile sensation is one of the most important sensory functions along with the auditory sensation for the visually impaired because it replaces the visual sensation of the persons with sight. In this paper, we present a tactile display device as a dynamic Braille display that is the unique tool for exchanging information among them. The proposed tactile cell of the Braille display is based on the dielectric elastomer and it has advantageous features over the existing ones with respect to intrinsic softness, ease of fabrication, cost effectiveness and miniaturization. We introduce a new idea for actuation and describe the actuating mechanism of the Braille pin in details capable of realizing the enhanced spatial density of the tactile cells. Finally, results of psychophysical experiments are given and its effectiveness is confirmed.

A typical limitation of polypyrrole based conducting polymer actuators is the low achievable active linear strains (2 % recoverable at 10 MPa, 7 % max) that these active materials exhibit when activated in a common propylene carbonate / tetraethylammonium hexafluorophosphate electrolyte. Mammalian skeletal muscle, on the other hand, exhibits large recoverable linear strains on the order of 20%. Such large linear strains are desirable for applications in life-like robotics, artificial prostheses or medical devices. We report herein the measurement of recoverable linear strains in excess of 14 % at 2.5 MPa (20 % max) for polypyrrole activated in the 1-butyl-3-methyl imidazolium tetrafluoroborate liquid salt electrolyte. This advancement in conducting polymer actuator technology will impact many engineering fields, where a lightweight, large displacement actuator is needed. Benefits and trade offs of utilizing ionic liquid electrolytes for higher performance polypyrrole actuation are discussed.

Electroactive polymers (EAP) are attractive actuation materials because of their large deformation, flexibility, and low density. The large deformation, especially in the bending mode, poses a challenge to the material and actuator characterization due to the geometric nonlinearity that is developed during the characterization. A CCD camera system was constructed to record the curved shapes of bending during the activation of EAP films and image-processing software was developed to digitize the bending curve s. A computer program was written to solve the inverse problem of cantilever EAP beams with a tip position limiter. Using the program and acquired curve images with and without a tip position limiter as well as the corresponding tip force, the performance of the beam under different applied voltages and tip force loads was determined. The experimental setup and the principles of the computer program are described and discussed in this paper.

Some electroactive polymers produce large electric-field-induced strains that can be used for electromechanical actuation. The measurement of the strain response, especially the dynamic response under high driving fields, is difficult. We have developed a transverse strain measurement system based on the Zygo laser Doppler interferometer. The system can measure transverse strain responses of polymer samples of different sizes over a wide displacement range and a frequency range from DC up to 100 Hz. We have used this interferometric system to investigate the strain response of Maxwell stress actuators fabricated from silicone (Dow Corning HS III RTV) and thermoplastic polyurethane (Dow Pellethane 2103) films. The static and dynamic strain responses of the materials to a variety of driving electric fields such as step fields, AC fields and DC bias fields have been measured as functions of amplitude and frequency. The strain response has a quadratic relationship with the driving field and shows a strong dependence on the frequency of the applied field. Of the two kinds of polymers investigated, HS III silicone polymer shows higher strain and breakdown fields. High transverse strains of 3.25 % (static) and 2.08 % (dynamic at 1 Hz) for HS III silicone polymers have been obtained. In addition, the effect of mechanical tensile load on the transverse strain has also been studied. The experimental data are interpreted in terms of measured material properties and small strain models for dielectric film actuators.

We report here the fabrication and characterization of solid-state conducting polymer actuators. The electrochemical activity of polyaniline (PANI) thin film coated with solid-state polyelectrolyte is very similar to the polyaniline thin film in an aqueous solution. The solid-state actuator is adhered to a lever arm of a force transducer and the force generation is measured in real time. The force generated by the actuator is found to be length dependent. However, the overall torque generated by the actuators with different lengths remains essentially the same. The effect of stimulation signals such as voltage, and current, on the bending angle and displacement is also studied using square wave potential.

Temperature- and pH-responsive semi-interpenetrating polymer network (SIPN) hydrogels, constructed with chitosan (CS) and poly(diallyldimethylammonium chloride) (PDADMAC), were studied. The characterizations of the IPN hydrogels were investigated by swelling tests and bending experiments, under various conditions. When the swollen IPN hydrogel was placed between a pair of electrodes it exhibited bending behavior on the application of an electric field, which showed stepwise bending behavior depending on the magnitude of the electrical stimulus. In order to clarify the relationship between the equilibrium swelling ratio and bending behavior of the SIPN hydrogels, the state of water in the SIPN hydrogel was also investigated using differential scanning calorimetry (DSC).

The formation of nuclei of oxidized and dark material on a film of reduced, compacted and clear material was followed from electrochromic films of different conducting polymers, providing that this type of nucleation is a general fact of those materials, as established by the Electrochemically Stimulated Conformational Relaxation model. When the nucleation is stopped at any intermediate state of the nuclei growth, by switching off the polarization, the reduced and clear regions are oxidized at expenses of the oxidized ones. Any intermediate and uniform colour is attained by switching off the polarization at different times, proving the non-stoichiometric nature of the oxidized material. That means that any intermediate composition can be attained and that infinitesimal changes of the composition are possible. Any property of the material linked to the composition also will change in a continuous and infinitesimal way. Those infinitesimal changes linked to the reverse electrochemical reactions are strongly influenced by any physical or chemical change: here we present a tactile sensing artificial muscle.

Poly(vinyl chloride) (PVC) plasticized with large amount of plasticizer has been investigated as a material for artificial muscle or actuator that can be actuated by applying an electric field. This material shows "creep deformation" on an electrode. The deformation looks like a pseudopodial deformation of amoeba. The deformation can be utilized for swift bending motility. In this paper, we investigated the mechanism of the creep deformation. Microscopic Raman spectroscopy revealed that the orientation of polymer network or plasticizer molecule was hardly detectable under the experimental conditions employed for the electrical actuation. Orientation of plasticizer was detected only slightly at higher field application. Small angle X-ray scattering analysis clarified that the PVC gel (plasticized PVC) sustains network structure even at the very high plasticizer content like 90wt%. With the increase of plasticizer content, space distance increased linearly, implying the network structure is sustained. This nature of the PVC gel plays a critical roll in the elastic creep deformation. The network structure of the gel depends on the chemical nature of the plasticizer itself. When the increase of plasticizer content caused serious deterioration of the physical network of PVC polymer chain, the PVC gel only deformed irreversibly by creep. The bending deformation also investigated from the viewpoint of electrode asymmetry. The results suggest effective charge injection and the charge concentration on the electrode is the controlling factor of this amoeba-like deformation.

A number of polymer based actuator technologies have emerged over the past decade. How do these compare with traditional actuators and are there applications for which they are appropriate? Some of the answers to these questions are provided by outlining the rationale for employing an electroactive polymer to control hydrodynamic surfaces. The surfaces are sections of propeller blades whose trailing edges are deflected in order to change camber. The objective is to insert the actuators into the blades. High work per unit volume is required of the actuators. The ideal actuator technologies also feature relatively large strains in order to deflect the trailing edges with minimal mechanical amplification. It is argued that the high work densities, flexibility in shaping and the ability to hold a force without expending energy (catch state) provide electroactive polymers with advantages over electromagnetic actuators, which also lack the torque to directly drive the blade deflection. Candidate actuators are compared, including electroactive polymers, shape memory alloys, magnetostrictives and traditional piezoceramics. Selections are made on the bases of work density, strain, existence of a catch state, drive voltage and cost. It is suggested that conducting polymer actuators are best suited for the variable camber application. It is also argued that in general electroactive polymers are well-suited for applications in which actuator volume or mass are very limited, catch states are desired, cycle life is moderate to low, or noise cannot be tolerated. Some electroactive polymers also feature low voltage operation, and may be biocompatible.

This paper investigates various experimental techniques of improving the optical properties as well as the electro-active characteristics of polyurethane polymer films for smart lens applications. Two experimental methods are used for preparing the films, the first consists of molding the polymer under various pressure and temperature conditions while the second is based on producing films of various thicknesses by the solvent casting method using tetrahydrofuran (THF) as solvent followed by a 100°C annealing in vacuum for 30min. Testing samples of 50 mm diameter are rigidly attached to circular frames and tested under applied field in the range of 30-80 kV/mm. The first method produces thicker and stiffer films with deformation response in the order of 0.8 mm; however, they are translucent. The second method results in thinner films with lower flexibility and reasonable electro-active response in the order of 0.3 mm. The transparency of the latter samples is excellent and closes the gap to produce a smart lens.

The synthesis, characterization and polymerization of two new electrochromic (EC) monomers based on 3, 4-alkylenedioxythiophene are reported. One is 3, 4-bis-(2, 2, 2-trifluoro-ethoxy)-thiophene which contains electron withdrawing group. Another is 6, 6-dimethy-6, 7-dihydro-5H-4, 8-dioxa-2-thia-6-sila-azulene which contains an electron donating group. Primary experiment results show that the new monomers have potential to form EC materials with new colors after polymerization. Color mixing of two EC polymers with blue and red color was studied. The principle of subtractive color mixing for achieving new color EC materials is also demonstrated.

A hybrid actuation system (HYBAS) utilizing advantages of a combination of electromechanical responses of an electroative polymer (EAP), an electrostrictive copolymer, and an electroactive ceramic single crystal, PZN-PT single crystal, has been developed. The system employs the contribution of the actuation elements cooperatively and exhibits a significantly enhanced electromechanical performance compared to the performances of the device made of each constituting material, the electroactive polymer or the ceramic single crystal, individually. The theoretical modeling of the performances of the HYBAS is in good agreement with experimental observation. The consistence between the theoretical modeling and experimental test make the design concept an effective route for the development of high performance actuating devices for many applications. The theoretical modeling, fabrication of the HYBAS and the initial experimental results will be presented and discussed.

A controlled drug delivery system in which drug release is achieved by actuating an array of polymeric valves on a set of drug reservoirs is introduced. The valves are bilayer structures, with one layer a thin film of evaporated gold and the other electrochemically deposited polypyrrole. The valves are made in the shape of flaps fixed on one side to the valve seats. Drug reservoirs are covered by an array of such valves, and release of the drugs stored in the reservoirs is accomplished by bending the bilayer flaps back with a small applied bias. The fabrication procedures and proof-of-principle drug release experiments for this controlled drug delivery device are described. Energy consumption of this reversible valve design is compared with metal corrosion based valves developed earlier by other and our group.

The important characteristics of the activated Polyacrylonitrile (PAN) fibers are its ability to change in length more than 100% and its comparable strength to human muscle. As against to other reported works in which commercially available fibers with diameters in the range of 10s of micrometers were used, here we tried to study the phenomenon in a few hundred nanometer diameter fibers. These fibers are expected to have smaller response times and higher deformations than conventional micronsized fibers. These PAN fibers were made by electrospinning. The fibers are placed in a solution and the change in the shape of the fibers was observed with change in pH. The fibers contracted in acidic solution and expanded in basic solution similar to that reported in the literature. Here we measured the variation in the diameter of the fibers using E-SEM while the change in pH is taking place. It appears that a variation of more than 100% was observed similar to that observed with conventional fibers of diameter ranging from 10 to 50mm. These results provide a potential in developing fast actuating PAN muscles and linear acuators, and muscle structures similar to sarcomere/myosin/actin-like assembly. In addition, we were able to observe giant volume changes more than 1,000% with conventional PAN fibers.

An IMPC actuated flapping wing has been designed and demonstrated for mimicking flapping motion of a bird wing. The flapping wing can produce twist motion as well as flap up and down motions. For design of the wing, an equivalent beam model has been proposed based on the measured force-displacement data. The equivalent model is used to determine suitable IPMC actuator patterns that can create twist motion during up- and down-strokes of the wing. The IPMC actuator pattern is inserted in a wing-shaped plastic film to form a complete flapping wing. Experimental results show that the properly shaped IPMCs can create aniosotropic motion that is often required for producing effective thrust and lift forces in bird flight.

Recent advances in electroactive polymers including high field induced strain, high elastic energy density (~1 J/cm3), and relatively high energy conversion efficiency, approaching those of natural muscles, create new opportunities for many applications. Harvesting electric energy from mechanical sources such as a soldier during walking is one such example. Several electroactive polymers developed recently are briefly reviewed. The paper further presents analysis on the key steps in achieving energy harvesting effectively. It is shown that one may make use of smart electronics to modify the electric boundary conditions in the electroactive polymers during the energy harvesting cycle to realize higher energy conversion efficiency in the systems compared with the efficiency of the material itself. Due to the fact that the energy density of the electromagnetic based energy harvesting devices scales with the square root of the device volume, the paper shows that the electroactive polymers based energy harvesting devices exhibit higher energy density and therefore are more suitable for this application.

Electro-Active Paper (EAPap) is attractive for EAP actuator due to its merits in terms of lightweight, dry condition, large displacement output, low actuation voltage and low power consumption. A promising EAPap actuator has been developed using cellulose paper. It is necessary to investigate the environmental factors for many applications. The performance variation along with the temperature and humidity is investigated. Tip displacement is measured by laser sensor and the power consumption of EAPap is investigated. When 0.3kV/mm of excitation voltage is applied, more than 4mm of tip displacement is obtained out of 40mm long EAPap sample. Since the power requirement of EAPap is so small(8.8mW/cm²), it can be activated by remote microwave power, which is promising for many applications

Electrorheological properties in steady shear of perchloric acid doped poly(3-thiophene acetic acid), PTAA, particles in silicone oil were investigated to determine the effects of field strength, particle concentration, doping degree (conductivity values), operating temperature, and nonionic surfactant. The PTAA/silicone oil suspensions show the typical ER response of Bingham flow behavior upon the application of electric field. The yield stress increases with electric field strength, E, and particle volume fraction, f, according to a scaling law of the form, τ_y∝Ε^αΦ^γ. The scaling exponent a approaches the value of 2, predicted by the polarization model, as the particle volume fraction decreases and when the doping level of the particles decreases. The scaling exponent g tends to unity, as predicted by the polarization model, when the electric field strength is low. The yield stress under electric field initially increases with temperature up to 25 °C, and then levels off. At electric fields above of 1.5 kV/mm, the yield stress increases significantly by up to 50% on addition of small amounts of a nonionic surfactant.

A study of recrystallization on high-energy electron irradiated poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer with composition 65/35 mol% is reported in this paper. Electron irradiated copolymer P(VDF-TrFE) exhibits a high electromechanical performance that is attractive for many applications. The structure and morphology of the recrystallized samples were determined using DSC, X-ray diffraction and FTIR. The polarization behavior of the recrystallized samples was also studied. The nonpolar phase content in the recrystallized samples was much lower than that in the irradiated samples. For irradiated samples that exhibited the best electromechanical performance, the corresponding recrystallized material had a high polar phase content, correspondingly a high remanent polarization was observed. For samples irradiated with higher doses, which have low polarization levels, after recrystallization the material exhibited a much higher polarization level with a very small remanent polarization, an attractive combination for many electromechanical applications.

In this paper a model is postulated to describe the optical response of an electroactive polymer hydrogel due to applied electrical fields. This model consists of a series of several modules: an electrical module that identifies the relationship between the applied voltage/current, electrode location and material and applied electrical field; a chemical module that correlates the percentage monomer in the gel, percentage cross linker, solvent ionic strength and pH; a mechanical module that employs the output of the chemical module to calculate deformation, taking into consideration experimentally measured elastic and viscoelastic characteristics; an optical module that will incorporate results from the previous modules to yield important optical characteristics (such as focal length and refractive index). It is anticipated that ultimately this model will set the required voltage to produce particular optical characteristics. Using an elastic modulus of 2160 Pa, a Poisson's ratio of 0.33 and experimentally measured gel response force of 0.1 N has resulted in a mechanical module which fully describes the gel motion. This result is promising; however, the mechanical module is currently using elastic properties, whereas viscoelastic properties are ideally needed.

In order to solve the interface and adhesion problems encountered with multilayered actuators, IPN based actuators are presented. The IPNs are synthesized between poly(ethylene oxide) and polybutadiene networks in which the conducting polymer (poly(3,4-ethylenedioxythiophene)), PEDOT, is gradually dispersed i.e. the content decreases from the outside towards the center of the film. The conducting IPN morphology was investigated by DMA and microscopy. The choice of the solid polymer electrolyte system is critical when operating in air. Aqueous solution or organic solvents containing electrolytes were first used, but drying failure could not be prevented. The most promising results are obtained with a room temperature ionic liquid, 1-ethyl-3-methylimidazolium bis-(trifluoromethylsulfonyl)imide (EMITFSI). During the redox reactions involving PEDOT in EMITFSI, a cation transfer mechanism occurred. Moreover, the bis-(trifluoromethylsulfonyl)imide anion behaves as a plasticizing agent for the IPN matrix. We observed that no degradation of the conducting polymer and no drying process occurred during period as long as 3 months. These actuators can achieve more than 7 E6 bendings from 1 to 18 Hz under applied potential from 2 to 5 V

Ionic polymer transducers are soft actuators that produce large bending deflections when a small voltage is applied across their thickness. The electromechanical coupling in ionomeric materials is due to the charge motion in the polymer backbone. Increasing the capacitance of the actuator increases the motion of the charges and the actuation performance of ionic polymer transducers has been shown to be strongly correlated with charge motion. Ionomers exhibit large capacitance due to the electric double layer formed on the polymer-electrode interface. Increasing the effective interfacial area results in the increase in the capacitance, and manipulating the electroding process of the ionic polymers has proved to have major effect on capacitance and therefore transduction. In this paper a novel electroding technique is developed and characterized. The method is composed of mixing an ionic polymer solution with a fine metal powder such as RuO_2, and attaching it to the membrane as an electrode. Scanning Electron Microscopy images are obtained for several plating processes, and relations between plating parameters and electrode morphology are established. The transducers are characterized as actuators by measuring their strain output, force output, and capacitance. Capacitance values of up to 45 mF/cm^2 are obtained using the novel electroding method, which is between five and ten times higher than that obtained with a standard impregnation-reduction process. The performance of the transducers fabricated with the novel electroding technique exceeds the performance of those fabricated with the impregnation-reduction method by a factor of between 2 and 5. Transducers fabricated with the impregnation-reduction method generally produce 200 to 500 microstrain/V while the ones fabricated with the new process exhibited free strain values of greater than 1550 microstrain/V at low frequencies.

In this paper a piezoelectric composite membranes were developed for charge generator to promoter bone regeneration on defects sites. Is known that the osteogenesis process is induced by interactions between biological mechanisms and electrical phenomena. The membranes were prepared by mixing Barium Titanate (BT) powders and PVDF-TrFE (PVDF:TrFE = 60:40 mol%) on dimethylformamide medium. This precursor solution was dried and crystallized at 100oC for 12 hours. Composites membranes were obtained by following methods: solvent casting (SC), spincoating (SP), solvent extraction by water addition (WS) and hot pressing (HP). The microstructural analysis performed by SEM showed connectivity type 3-0 and 3-1 with high homogeneity for samples of ceramic volume fraction major than 0.50. Powder agglomerates within the polymer matrix was evidenced were observed for composites with the BT volume fraction major than 40%. The composite of ceramic fraction of 0.55 presented the best values of remanent polarization (~33mC/cm2), but the flexibility of these composites with the larger ceramic fraction was significantly affected. For in vivo evaluation PVDF-TrFE/BT 90/10 membranes with 3cm larger were longitudinally implanted under tibiae of male rabbit. After 21 days the animals were sacrificed. By histological analyses were observed neo formed bone with a high mitotic activity. In the interface bone-membrane was evidenced a pronounced callus formation. These results encourage further applications of these membranes in bone-repair process.

Novel liquid crystalline elastomers with properties that mimic the action of a muscle have been developed. Uniaxial contraction of free standing film of the material can be achieved by heating the film through the nematic to isotropic phase transition. Thermoelastic response shows strain changes through the nematic-isotropic phase transition of about 30-35%. Retractive force of nearly 450 kPa was measured in the isotropic phase. Static workloop studies show that the visco-elastic losses in these materials to be very small.