For centuries, biology has provided fertile ground for hypothesis, discovery, and inspiration. Time-tested methods used in nature are being used as a basis for several research studies conducted at the NASA Langley Research Center as a part of Morphing Project, which develops and assesses breakthrough vehicle technologies. These studies range from low drag airfoil design guided by marine and avian morphologies to soaring techniques inspired by birds and the study of small flexible wing vehicles. Biology often suggests unconventional yet effective approaches such as non-planar wings, dynamic soaring, exploiting aeroelastic effects, collaborative control, flapping, and fibrous active materials. These approaches and other novel technologies for future flight vehicles are being studied in NASA's Morphing Project. This paper will discuss recent findings in the aeronautics-based, biologically-inspired research in the project.

Humans throughout history have always sought to mimic the appearance, mobility, functionality, intelligent operation, and thinking process of biological creatures. This field of biologically inspired technology, having the moniker biomimetics, has evolved from making static copies of human and animals in the form of statues to the emergence of robots that operate with realistic behavior. Imagine a person walking towards you where suddenly you notice something weird about him--he is not real but rather he is a robot. Your reaction would probably be "I can't believe it but this robot looks very real" just as you would react to an artificial flower that is a good imitation. You may even proceed and touch the robot to check if your assessment is correct but, as oppose to the flower case, the robot may be programmed to respond physical and verbally. This science fiction scenario could become a reality as the current trend continues in developing biologically inspired technologies. Technology evolution led to such fields as artificial muscles, artificial intelligence, and artificial vision as well as biomimetic capabilities in materials science, mechanics, electronics, computing science, information technology and many others. This paper will review the state of the art and challenges to biologically-inspired technologies and the role that EAP is expected to play as the technology evolves.

Designing and building devices that utilize electroactive polymer actuators brings into sharp focus the performance required of these materials. Using the example of a "rehabilitation glove", it is shown that the performance of polypyrrole actuators fall short of that required. In particular, the need to simultaneously produce 5% actuator strain at a 5 MPa isotonic stress cannot be achieved with the actuators investigated in our laboratories to date. However, significant improvements in the performance under load have been achieved with the use of ionic liquid electrolytes. The use of new materials such as composites of conducting polymers and carbon nanotubes offers the possibility of further improvements in actuator performance. Finally, redesigning the glove actuator offers a compromise solution that allows existing actuators to be used in a prototype device.

This paper examines methods of developing electroactive polymer (EAP) actuators for actuating human-like facial expressions in sociable robots. EAP actuators could improve such robots in several ways - they could reduce the mechanical complexity of the robots and the robots' weight and power requirements, potentially leading to robots that are more robust, more easily manufactured and ideal for autonomous mobility. After a discussion of the state of the technique in UTD's face-based communication robots (the Identity Emulation robots project), this paper considers various EAP actuation technologies, and ways of adapting them towards use in these robots. Applications of this class of human-robot interface devices will rise in relevance as humans and robots begin to have more sociable encounters in the coming years. Key to success in this undertaking is the multi-modal integration of mechanics, sociable intelligence, and design aesthestics and dynamic stable mobility, and the innovation of skin materials that are lighter in weight and deformed with less force. Recent innovations in urethane polymers, described in this paper, have resulted in a humanoid facial skin that is actuated by considerably reduced force (16 to 20 oz.), relative to previously available skin polymers. These actuation requirements may put this facial expression technology within the capabilities of existing EAP actuation technologies.

A new class of molecular actuators where bulk actuation mechanisms such as ion intercalation are enhanced by controllable single molecule conformational rearrangements offers great promise to exhibit large active strains at moderate stresses. Initial activation of poly(quarterthiophene) based molecular muscles, for example, show active strains in the order of 20%. Molecular rearrangements in these conjugated polymers are believed to be driven by the formation of pi-dimers (e.g. the tendency of pi orbitals to align due to Pauli’s exclusion principle) upon oxidation of the material creating thermodynamically stable molecular aggregates. Such thiophene based polymers, however, suffer from being brittle and difficult to handle. Polymer composites of the active polymer with a sulfated polymeric anion were therefore created and studied to increase the mechanical robustness of the films. This additional polyelectrolyte is a Sulfated Poly-Beta-Hydroxy Ether (S-PHE) designed to form a supporting elastic matrix for the new contractile compounds. Co-deposition of the polyanion with the conducting polymer material provides an elastic mechanical support to the relatively stiff conjugated polymer molecules, thus reducing film brittleness. The active properties of such poly(quarterthiophene)/S-PHE polymer actuator composites based on intrinsic molecular contractile units are presented and discussed.

Several examples of sensors and actuators inherent in biological species are reviewed with emphasis on their mechanisms for a given set of stimuli. Examples include, action plants (Venus flytrap, Cucumber tendrils) and bamboo, and algae. Based on these examples and their mechanisms, we designed artificial actuators, FGM piezo actuators and electroactive polymer actuators.

ER fluid devices range from high-power actuators generating kilo-Newton forces, to small-scale applications, such as a tactile graphics tablet. Each application presents different performance requirements for an ER fluid with respect to yield stress, current consumption, zero-field viscosity, and temperature response. This paper discusses the technological advantages that these devices can offer, together with their limitations. The focus will be on how the properties of the ER fluid can be tailored for suitability to a particular application. A case study of a large array of mini-actuators, for use as a graphics tablet for the visually impaired, is presented to illustrate design principles for ER valves.

Poly(3-thiophene acetic acid), PTAA, was synthesized via an oxidative polymerization and doped with perchloric acid to control its conductivity. Rheological properties of the HClO₄ doped PTAA/silicone oil suspensions were measured in the oscillatory shear mode to investigate the effects of electric field strength, particle concentration, and particle conductivity on ER characteristics. The PTAA based ER fluids exhibited a viscoelastic behavior under an applied electric field and the ER response enhanced with increasing electric field strength. The dynamic moduli, G’ and G”, dramatically increased by 10 orders of magnitude when the electric field strength was increased to 2 kV/mm. Effect of particle concentration and particle conductivity were apparent at moderate electric field strengths and the suspensions show saturated ER properties at electric field strength of 1 kV/mm. Moreover, the suspensions exhibited transition from fluid-like to solid-like behavior as electric field strength increased. Higher particle concentration and higher particle conductivity induced a lower transition electric field.

A linear constitutive model for ionic polymer benders is developed to model sensing and actuation properties of ionic polymer transducers. The model is based on a set of linear coupled equations that relate stress, strain, applied field, and electric displacement. The constitutive equations are integrated to obtain an impedance model that is a function of transducer geometry and three material parameters. The material parameters are the electric permittivity, elastic modulus, and electromechanical coupling coefficient. Experiments are performed to determine the three material parameters from measured data on cantilever transducers. Experiments demonstrate that the strain coefficient of an ionic polymer transducer is on the order of 20,000 to 30,000 pm/V. Ionic polymers have very low coupling coefficient due to the large compliance and excessively high permittivity and the low speed of sound (≈ 250 to 300 m/s) limits the actuation bandwidth of any device constructed from the material. Furthermore, ionic polymers exhibit dielectric relaxation at higher frequencies and the coupling coefficient exhibits a sharp decrease below approximately 0.1 Hz. These characteristics limit the low frequency actuation capability of the material.

The electrostrictive graft elastomer is a new type of electromechanically active polymer. Recently developed by NASA, it consists of flexible backbone chains, each with side chains, called grafts. Grafts from neighboring backbones physically cross-link and form crystal units. The flexible backbone chains and the crystal graft units are composed of polarized monomers, which contain atoms with electric partial charges, generating dipole moments. Polarized domains are created by dipole moments in the crystal units. When the elastomer is placed into an electric field, external rotating moments are applied to polarized domains. It stimulates the rotation of the polarized crystal graft units, which further induces deformation of the elastomer. In this paper, two-dimensional computational models are established to analyze the deformation mechanism of the graft elastomer.

Modeling ionic diffusion in electrolytes requires the simultaneous solution of the Nernst-Planck (electro-diffusion) equation and Gauss' law. Unfortunately, the Nernst-Planck equation is not applicable in the ionic double layer that forms at an electrode/electrolyte interface. Furthermore, the large gradients of the electric potential in the double layer can cause numerical instabilities. The double layer is usually modeled using the Gouy-Chapman theory, a steady state solution, which predicts an exponential decay of the electric potential and ion concentration in the direction normal to the electrode. In the present paper we present a novel theory in which the Gouy-Chapman equation, a three-dimensional theory, is replaced by an interface (2-D) theory of the double layer. The effects of the double layer are then modeled as boundary conditions applied to the Nernst-Planck equation and Gauss' law. Interfacial equations are derived for the species mass balances, the conservation of charge, Gauss's law, and the quasi-static form of Faraday's law. Each of these physical principles is derived for both a regular (or single) interface and a double interface representing an electric double layer. The standard interfacial variables are augmented with an electric charge, electric potential, electric field, electric polarization, and electric displacement, whereas conventional electrostatics includes only interfacial charge.

This paper presents the experimental method to evaluate the adhesion forces between micro-objects and IPMC, and describes methods to reduce them. Ionic Polymer Metal Composite (IPMC) can be a key material in low-mass, high-displacement, single-moving part actuators and shows great potential for micro-gripper applications. To design fingers for a micro-gripper using IPMC, the study of the adhesion force between IPMC and micro-objects is of critical importance. Glass micro-spheres of various sizes were attached to silicon nitride Atomic Force Microscope (AFM) tips, and the adhesion forces between the micro-spheres and the IPMC sample surface were found experimentally by an AFM. These experiments were performed in dry environment. Experiments were then performed under water to see the effect on reduction of adhesion forces. It was found that for a glass micro-sphere of size 32.43-μm the adhesion force decreases from 144 nN in air to 8.64 nN in water.

This paper reports two classes of electroactive polymers developed recently which exhibit very high strain and elastic energy density. In the first class of the electroactive polymer, i.e., the defects modified poly(vinylidene fluoridetrifluoroethylene)(P(VDF-TrFE)) polymers, an electrostrictive strain of more than 7% and an elastic energy density above 1 J/cm³ can be induced under a field of 150 MV/m. The large electrostrictive strain in this class of polymers originates from the local molecular conformation change between the trans-gauche bonds and all trans bonds, which accompanies the field induced transformation from the non-polar phase to the polar phase. The second class of the polymer is an all organic composite, which shows a very high dielectric constant (>400) and high strain induced with a low applied field (2% strain under 13 MV/m). The strain is proportional to the applied field and the composite has an elastic modulus near 1 GPa.

Space-based astronomy and remote sensing systems would benefit from extremely large aperture mirrors that can permit greater-resolution images. To be cost effective and practical, such optical systems must be lightweight and capable of deployment from highly compacted stowed configurations. Such gossamer mirror structures are likely to be very flexible and therefore present challenges in achieving and maintaining the required optically precise shape. Active control based on dielectric elastomers was evaluated in order to address these challenges. Dielectric elastomers offer potential advantages over other candidate actuation technologies including high elastic strain, low power dissipation, tolerance of the space environment, and ease of commercial fabrication into large sheets. The basic functional element of dielectric elastomer actuation is a thin polymer film coated on both sides by a compliant electrode material. When voltage is applied between electrodes, a compressive force squeezes the film, causing it to expand in area. We have explored both material survivability issues and candidate designs of adaptive structures that incorporate dielectric elastomer actuation. Experimental testing has shown the operation of silicone-based actuator layers over a temperature range of -100 °C to 260 °C, suitable for most earth orbits. Analytical (finite element) and experimental methods suggested that dielectric elastomers can produce the necessary shape change when laminated to the back of a flexible mirror or incorporated into an inflatable mirror. Interferometric measurements verified the ability to effect controllable shape changes less than the wavelength of light. In an alternative design, discrete polymer actuators were shown to be able to control the position of a rigid mirror segment with a sensitivity of 1800 nm/V, suggesting that sub-wavelength position control is feasible. While initial results are promising, numerous technical challenges remain to be addressed, including the development of shape control algorithms, the fabrication of optically smooth reflective coatings, consideration of dynamic effects such as vibration, methods of addressing large-numbers of active areas, and stowability and deployment schemes.

With the ultimate goal of constructing diaphragm-type pumps, we have measured pressure-volume characteristics of single-layer dielectric elastomers diaphragms. Circular dielectric elastomer diaphragms were prepared by biaxial stretching of 3M VHB 4905 polyacrylate, or spin casting and modest or no biaxial stretching of silicone rubber films, followed by mounting to a sealed chamber having a 3.8 cm diameter opening. Pressure-volume characteristics were measured at voltages that provided field strengths up to 80 MV/m in un-deformed VHB films and 50-75 MV/m in silicone films. The most highly pre-strained VHB diaphragms were found to have linear pressure-volume characteristics whose slopes (diaphragm compliance) depended sensitively upon applied field at higher field strengths. Compliance of unstretched silicone diaphragms was nearly independent of field strength at the fields tested, but pressure-volume characteristics shifted markedly. For both kinds of dielectric elastomers, pressure-volume work loops of significant size can be obtained for certain operating pressures. Each type of diaphragm may have advantages in certain applications.

Electrostriction refers to the strain induced in a dielectric by electric polarization, which is usually very small for practical applications. In this paper we present a micromechanical analysis on the effective electrostriction of a P(VDF-TrFE) polymer based composite, where the relationship between the effective electrostrictive coefficients of the composite and its microstructure is established. Enhanced electrostriction in the composite has been demonstrated, and optimal microstructure for electrostriction enhancement has been identified. Our analysis provides a mechanism for the electrostriction enhancement, where the electrostrictive strain several times higher can be obtained if the microstructure of the composites can be carefully tailored.

Electroactive polymer actuators that utilize the Maxwell stress effect have generated considerable interest in recent years for use in applications such as artificial muscles, sensors, and parasitic energy capture. In order to maximize performance, the dielectric layer in Maxwell stress actuators should ideally have a high dielectric constant and high dielectric breakdown strength. In this study, the effect of high dielectric constant fillers on the electrical and mechanical properties of thin elastomeric films was examined. The fillers studied included the inorganic compounds titanium dioxide (TiO₂), barium titanate (BaTiO₃), and lead magnesium niobate-lead titanate (Pb(Mg_1/3Nb_2/3)O₃-PbTiO). A high dielectric constant filler based on a polymeric conjugated ligand-metal complex, poly(copper phthalocyanine), was also synthesized and studied. Maxwell stress actuators fabricated with BaTiO₃ dispersed in a silicone elastomer matrix were evaluated and compared with unfilled systems. A model was presented which relates filler volume fraction to actuation stress, strain, and elastic energy density at fields below dielectric breakdown. The model and experimental results suggest that for the case of strong filler particle-elastomer matrix interaction, actuation strain decreases with increasing filler content.

The electrostrictive graft elastomer is a new type of electromechanically active polymer developed by NASA. The material has demonstrated promising electromechanical properties including large electrical field induced strain, high electromechanical output, and a relatively high mechanical modulus. As a two-component system, the elastomer contains flexible backbone chains and electro-responsive polar grafted crystal domains. The two-component material system enables optimization of the electrostriction by controlling the relative fraction of the two components and the molecular morphology. The present work is a systematic study on the effects of the relative fraction of the two components and morphology on the electrical field induced strain. The results show that the elastomer containing more polar grafted domains and higher crystallinity yields higher electric field-induced strains.

Various type of non-ionic soft polymer materials from polymer gel to elastomers were actuated in efficient and remarkable manners by applying an electric field. The polymer gel swollen with large amount of dielectric solvent showed not only remarkable contraction and relaxation in the direction of the field, but also huge bending deformation within dozens of milliseconds. Molecular orientation of solvent did not play a critical role in the bending deformation, but a solvent drag induced by the field was the origin of an asymmetric pressure distribution which bended the gel. In the case of plasticized polymer, the solvent (or plasticizer) drag was difficult and negligibly small. However, we found a reversible creep deformation of the plasticized polymer. The deformation only occurred on the electrode surface. The strain induced could have reached over 300%. The sample was stable over 2 years. This creep deformation was successfully applied in bending of 100 degree per 30 milli-second under the current of nano-ampere range. Non-ionic polyurethane elastomers, which contained neither solvents nor plasticizers, could also be electrically bended, and the deformation was controlled systematically by changing chemical structures. The bending deformation showed memory effect, and the direction of the bending was chemically controllable. It was suggested that an asymmetric space charge distribution in the polymer film plays a critical role in the bending deformation. The concept presented through these works will be a guide to a novel type of electrically active dielectric-soft-polymer actuator or a kind of artificial muscles.

In this paper, the authors present the contraction/elongation behavior of cation-modified Polyacrylonitrile (PAN) fibers, which identifies the fibers to be effectively used as biomimetic actuators and artifical muscles. The research was intiated by realizing that the contraction/elongation behavior of PAN is governed by the diffusional processes of ions/solvents interaction. The PAN fibers were suitably annealed, cross-linked and hydrolyzed to become "active". The cation-modified process was performed using KOH, NaOH, and LiOH, respectively, for the boiling and alkaline-soaking mediums. It was found that the PAN fibers, regardless of whether being activated in KOH, NaOH, or LiOH, increased from their initial length after being activated and soaked in distilled water. Lengths then decreased after the fibers were soaked in the bases. Fibers treated with LiOH had the largest increase in length following immersion in distilled water. Fibers soaked in any of the three mediums generally had the same decrease in length following immersion in the alkaline solutions, as also occurred following immersion in HCl. Especially noticeable with the fibers treated with LiOH was that greater displacement in the lengths occurred using the 2 N solutions. It is our general notion that the Osmotic pressure of free ions plays an import role on the properties of PAN. However, the observation that Li⁺ treated PAN fibers exhibit the largest contraction/expansion capability compared to Na⁺ or K⁺ treated PANs, can raise another important issue, i.e. "hydration". Realizing that the Osmotic pressure of electrolyte systems in weakly dependent upon the types of ions, it is highly likely that the "hydration" phenomena of free ions within the PAN network plays a key role on its deformation properties. It should be noted that PAN fibers have the capability of changing their effective longitudinal strain more than 100% and have comparable strength to human muscle.

Deformations of conducting polymer films, such as polyaniline, polypyrrole and polythiophene, induced by electrochemical oxidation and reduction are presented and discussed in terms of the mechanisms. Soft actuators with variety of motions such as bending stick, breathing ring and shouting lip utilizing polypyrrole films are demonstrated. A new operation method is proposed using electrodeposited polypyrrole films.

Ionic polymer-metal composites (IPMCs) consist of a perfluorinated ionomer membrane (usually Nafion or Flemion) plated on both faces with a noble metal such as gold or platinum and neutralized with a certain amount of counterions that balance the electrical charge of anions covalently fixed to the membrane backbone. 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 solvent, the amount of solvent uptake, the morphology of the electrodes, and other factors. With water as the solvent, the applied electric potential must be limited to less than 1.3V at room temperature, to avoid electrolysis. Moreover, water evaporation in open air presents additional problems. These and related factors limit the application of IPMCs with water as the solvent. Ethylene glycol has a viscosity of about 16 times that of water at room temperature, and has a greater molecular weight. It is used as an anti-freeze. Like water, it consists of polar molecules and thus can serve as a solvent for IPMCs. We present the results of a series of tests on both Nafion- and Flemion-based IPMCs with ethylene glycol as the solvent, and compare these with the results obtained using water. IPMCs with ethylene glycol as their solvent have greater solvent uptake, and can be subjected to relatively high voltages without electrolysis. They can be actuated in open air for rather long time periods, and at low temperatures. They may be good actuators when high-speed actuation is not necessary.

There is currently a need for actuators that will operate in low temperature environments. Ideally, the Ionic Polymer-Metal Composite (IPMC) actuator should be able to operate in a temperature range of 0 to -50 degrees Celsius. IPMC can be a useful solution for cold temperature actuation because of its soft actuation with relatively low input voltages while the base polymeric material can undergo a multiple phase transition below 0 degree Celsius. Due to the complex nature of the material, the physics become increasingly difficult to predict in a low temperature environment on account of the IPMC/s dependency upon water and/or tightly bounded cations/water for effective actuation. In this paper, we provide experimental data and an apparatus that is constructed to obtain force feedback from an IPMC sample that is placed in a subzero chamber. The electric/thermal/mechanical data for this experiment is presented and assumptions are made and explained regarding the nature of the cold temperature actuation. Also, analytical tool used is DSC to reveal the true water structures in the IPMC. It should be noted that the use of IPMC in the temperature range of -50 to 0 degree Celsius is of importance for a number of engineering applications.

In this paper we present a packaged actuator to be applied for micro and macro robotic applications. The actuator is based on polymer dielectrics, and intrinsically has musclelike characteristics capable of performing motions such as forward/backward/controllable compliance. The actuator is featured in several aspects such as simplicity and lightness in weight, cost-effectiveness, multiple DOF-actuation, and digital interface. In this paper, its basic concepts are briefly introduced and the issues about design, fabrication and applications are discussed.

We have developed the wireless tadpole robot that has simple geometry, driven by low voltage and the undulatory fin-motion using IPMC(Ionic Polymer Metal Composite) actuator. Behavior of TadRob is tested under various frequencies(1~8Hz) to find the correlation between actuator frequency and velocity of the robot. In addition, the robot velocity according to undulation motion and oscillation motion of the fin is compared to find the proper fin-motion to increase the efficiency of the robot. Also, steering capability is tested under variation of duty ratio. Based on experimental results, we can confirm that the velocity of TadRob can be controlled by changing frequency of input voltage and the steering angle can be increased with increasing the duty ratio.

Dielectric elastomer artificial muscles (electroelastomers) have been shown to exhibit excellent performance in a variety of actuator configurations. By rolling highly prestrained electroelastomer films onto a central compression spring, we have demonstrated multifunctional electroelastomer rolls (MERs) that combine load bearing, actuation, and sensing functions. The rolls are compact, have a potentially high electroelastomer-to-structure weight ratio, and can be configured to actuate in several ways including axial extension and bending, and as multiple degree-of-freedom (DOF) actuators that combine both extension and bending. 1-DOF, 2-DOF, and 3-DOF MERs have all been demonstrated through suitable electrode patterning on a single monolithic substrate. The bending MER actuators can act as leg and knee joints to produce biomimetic walking that is adaptable to many environments. Results of animation and the fabrications of a robot model of a synthetic bug or animal based on the MERs are presented. A new concept for an antagonist actuator for more precise control is introduced.

It is usual to use sensors for controlling an electrostrictive polymer (EP) actuator system. However, it may make the whole actuator system larger and more complex. Thus, it is quite difficult to use some sensors for building a simple and small EP actuator system. In this paper, a technique based on neural networks is proposed to control a simple EP actuator without any sensor. First, a closed loop controller with a sensor is applied to control this EP actuator and its data are measured. Then these data and the characteristics of EP polymers are used to train a neural network offline. The resultant neural network is applied to control a simple EP actuator with no sensor. The experimental data under the proposed technique are compared with those under the closed loop controller and its result is discussed.

We are developing an artificial muscle linear actuator using ionic polymer-metal composites (IPMC) which is an electro-active polymer that bends in response to electric stimuli and the goal of our study is to apply the actuator to robotic applications especially to a biped walking robot. In this paper, we will describe the structure of the actuator and an empirical model of the actuator which has two inputs and one output, and whose parameters are identified from input-output data. Based on the empirical model, we demonstrate walking simulations of a small-sized biped walking robot. In the numerical simulation we assume that the developed actuators are connected both in series and in parallel to a joint of the walking robot so that the actuators supply enough torque to the robot and that they are stretched and compressed enough. It is shown throughout the simulation that the biped walking robot with the actuators can walk on a level ground with a period synchronized with a period of input signal.

The dynamic bending piezoelectric properties of polyvinylidene fluoride cantilevers in the millimeter size range is reported. These devices are being investigated with the intention of developing a piezoelectric device based inner ear cochlear implant. The size restrictions and fluid environment of the inner ear place special requirements on a piezoelectric device, and it is essential to perform basic studies on sensor materials, deformation modes and device configurations to develop a successful implant. Results from both basic vibration tests and underwater acoustic measurements are presented. Experimental modal analysis reveals that millimeter length cantilevers exhibit three bending resonances under 1 kHz. The modal frequencies are sensitive functions of the length and thickness of the film, and are also affected substantially by the width of the cantilever and the nature of the electrode material. Further, all bending piezoelectric modes display high piezoelectric coupling coefficients in the range 0.2 - 0.35, and damping of < 2%. Experimental results are compared with a theoretical model of unimorph piezoelectric cantilever beams. Underwater acoustic measurements also reveal that single-cantilever devices in the millimeter length display acoustic sensitivities in the -195 to -210 dB range, in the 2 - 10 kHz regime. These sensitivities are comparable to commercial devices of larger size and more complex design. The viability of use of the conducting polymer polypyrrole as the electrode material in polymer piezoelectric sensors is also investigated. Results show that devices with polypyrrole electrodes are at least as sensitive as devices with metal electrodes, and these type all-polymer devices thus have great promise. The results presented in this paper can be used to design an appropriate sensory implant, as well as in other audio frequency applications.

The electromechanical behavior of dielectric elastomers is to be exploited for medical application in artificial blood pumps. It is required that the pump diaphragm achieves a swept volume increase of 70 cc into a systolic pressure of 120 mmHg with the main design objective being volumetric efficiency. As such, a model that accommodates large deformation behavior is used. In order to design prosthetic blood pumps that closely mimic the natural pumping chambers of the heart, a dielectric elastomer diaphragm design is proposed. The elastomer's change in shape in response to the applied electric field will permit it to be the active element of the pump just as the ventricular walls are in the natural heart. A comprehensive analytical model that accounts for the combined elastic and dielectric behavior of the membrane is used to compute the stresses and deformations of the inflated membrane. Dielectric elastomers are often pre-strained in order to obtain optimal electromechanical performance. The resulting model incorporates pre-strain and shows how system parameters such as pre-strain, pressure, electric field, and edge constraints affect membrane deformation. The model predicts more than adequate volume displacement for moderate pre-strain of the elastomer.

Ionic Conducting Polymer Film (ICPF) micro grippers with multi-finger configurations were developed using spin-on Nafion and photolithographic technology. A commercial solution from Dupont Co. (Nafion SE-5012) was used to prepare ~0.2 μm thick ionic conducting polymer film. Micro cantilever structures were fabricated which composed of Au/Nafion/Au film layers. Grippers with 2-finger and 4-finger configurations were successfully developed. We have proved that the 2-fingered grippers can be actuated in water at ~5V DC voltages. The smallest 4-fingered grippers fabricated were 30 μm wide, 300 μm long and 0.4 μm thick for each finger. In addition, another interesting actuation behavior of the micro actuator was observed during fabrication. The actuators would curl up whenever they came in contact with water during the sacrificial release process. The curling process reversed instantaneously when the actuators are immersed in acid. We suggest that this phenomenon is probably due to the different volume expansions of Nafion in different medium. Besides, the current-voltage property was measured. We are further studying the consistency of their behaviors to modify the design and fabrication process for potential use in biological manipulations.

A quantitative analysis of drug release characteristics of polypyrrole (PPy) was performed for its application to a drug delivery system (DDS). The incorporation of various chemical substances into the PPy and controlling its release with the externally applied voltage to the PPy are possible. A qualitative drug release characteristics of the PPy was first examined using an indicator, phenolred and then the quantitative analysis was performed using salicylate as a dopant. A drug release characteristics with time was thoroughly investigated while varying the electrode area, polymerization time, the applied voltage for drug release. Based on these quantitative results, a preliminary experiment was carried out to check the feasibility of the PPy applicable to the neuronal system. Experimental results show that a neurotransmitter was released from the PPy with the externally applied voltage and hence the PPy can be applicable in a neuronal system.

Freestanding films of poly(3,4-ethylenedioxythiopene), PEDOT, were synthesized electrochemically from a solution containing EDOT monomer, tetrabutylammonium hexafluorophosphate, and water in propylene carbonate. The films were tested mechanically under constant stresses ranging from 0.6 to 2.1 MPa and subjected to various electrochemical waveforms while immersed in a bath containing propylene carbonate and an electrolyte. The characterization resulted in observations of ultimate linear strains of 2%, strain rates of 0.003 Hz, and strain to charge densities of 4 x 10^-10 m³/C, comparable to the conventional conducting polymer polypyrrole. In addition to the quantitative analysis, evidence of both anionic and cationic intercalation into the polymer is presented with a discussion of prospective mechanisms and consequences.

Electro-Active Paper (EAPap) has been interested due to its possibility for developing a new EAP material that has merits in terms of lightweight, dry condition, large displacement output, low actuation voltage and low power consumption. The possibility of EAPap can be proved by investigating the operational principle more thoroughly and by demonstrating a niche application. So far the working principle is believed to be a migration effect of moistures and some chemical contents in the paper. However this is not completely understood yet. Therefore, this paper will present basic studies of paper fibers for EAPap in terms of fibrous nature, their crystallinity, and mechanical, physical and electrochemical characteristics. These results will be able to summarize the migration effect and the direction for improving the performance of EAPap will be shown. 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.

A microwave switch based on EAP presents several advantages. A switch based on Flemion is studied. Flemion a perfluorinated carboxylic acid membrane shows improved performance as actuator material compared with Nafion (perfluorinated sulfonic acid). Flemion has a higher ion exchange capacity and good mechanical strength. In order to get a good Flemion actuator, highly conductive soft gold electrodes with large fractal structure have to be deposited on the membrane. The impregnation reduction technique used for plating requires exchange of a gold complex and reduction by gradual sodium sulfite additions. K⁺ shows the highest exchange ratio with the gold complex and reducing bath temperatures around 60°C with enough reducing agent present are shown to promote the growth of a gold fractal structure. The resulting material shows an actuation displacement with no relaxation, a key feature for switch applications. A simple mechanical switch based on a flemion actuator is prepared and tested as a microwave switch.

There is a great need to develop a computer screen based on Braille technology that allows blind people to access computer-based information to the same extent as sighted people. The lack of a "graphical user interface" for the blind severely restricts employment, educational and recreational opportunities readily available to sighted people in the "internet age". Equally, the development of a refreshable 2-D Braille screen offers the EAP community a great opportunity to make a tremendous impact with new actuator technology. In this paper we review progress made in the development of a prototype multi-dot Braille cell using conducting polymer actuators. Two innovations (a helical wire interconnect and ionic liquid electrolytes) have provided significant performance advances in terms of strain rate and cycle lifetime, respectively. Despite these advances, some further challenges remain.

Thin-film mirrors are attractive for large aperture, lightweight optical system and microwave antennas operating in micro-gravity space. The surface shape of these deployable thin film structures requires control to a precision range that depends on the specific applications. For optical systems, such surfaces need to be deployed and refined in the range of submicrons. Electroactive polymers (EAP) are potential candidates for making such thin film materials. Generally, EAPs are produced in thin film form with electrodes on their major surfaces. Depending on the reflectivity of the electrodes and surface roughness of the polymer they can also be produced with mirror finishes. A controllable mirror made of single-layer EAP mirror is proposed in this paper. An analytical solution of required voltage/strain distribution for forming a parabolic mirror from a planar film is presented. Calculations show a single layer film made of currently available EAP has the capability to control the focus distance of a 2-m mirror from infinity to 1.25 m. The results are verified by FEM model.

As an option in the creation of a synthetic bio-optic lens, we propose that spatial modulation of refractive index can be realized in polymer composites containing a colloidal ionophoric phase. The variation of refractive index could result from electric field induced orientation or polarization of the dispersed phase. Devices are envisioned in which the refractive index gradient will be controlled by variation of the local applied field with matrix-addressed microelectrode arrays. Of particular utility in the demonstration of this phenomena are ionophoric and ionomeric block copolymers containing poly(ethylene oxide), PEO, poly(acrylic acid), PAA, and poly(methylmethacrylate), PMMA, chain segments. Systems that will be discussed relative to the provision of options in the creation of a synthetic biooptic lens are: (1) Electric field induced polarization of electrorefractive moieties localized in nanoscopic, salt-doped PEO domains of PS-b-PEO composites and (2.) localized deformation of salt-doped elastomeric PDMS-b-PEO composites.

This paper summarizes some of the work done to investigate the environmental stability, optical properties and electroactive response of a polyethylene glycol diepoxypropyl ether (n9)(PEGDE) polymer, acrylic elastomer and polyurethane. The first one confirms piezoelectricity; however it is not suitable for optical applications due to color instability and loss of transparency with various environmental conditions; the second confirms electrostriction with good transparency, while the polyurethane behaves with smaller mixed piezoelectric-electrostrictive response. The acrylic elastomer has demonstrated chemical stability with good optical properties for various environmental conditions

A large contrast ratio and rapid switching EC polymer device which consists of a laminated two-layer structure between two electrodes was prepared. The new design consists of an ITO glass electrode, a cathodic EC polymer film, a gel electrolyte and a counter-electrode that replaces the anodic EC polymer and ITO electrode. Several types of EC polymers, such as, poly[3,3-dimethyl-3,4-dihydro-2H-thieno(3,4-b)(1,4)dioxepine] (PProDOT-(CH₃)₂) and poly[3,4-(2,2-dimethylpropylenedioxy)-pyrrole] (PProDOP-(CH₃)₂) were synthesized as cathodic EC polymers. A carbon-based counter-electrode was prepared for comparison with an Au-based counter-electrode. Screen-printing was utilized for the carbon-based counter-electrode. Lithography and sputtering were used for the Au patterned glass counter-electrodes. Several kinds of polymer gel electrolytes were prepared for solid-state applications. Color change of high contrast ratio of visible light transmittance (>ΔΤ55%)of the device is rapidly obtained (0.5-1s) when even less than 2.5V is applied. The repeatability of color changeable EC polymer windows was estimated by the method of electrochemistry and spectrophotometry. This "smart window" technology can be used in many applications where a rapid color change between transparent and color states is required.

This paper presents preliminary results on the characterisation of the actuating performances, never explored before, of an elastomeric material (Dr Scholl’s, Canada, Gelactiv tubing), to realise dielectric elastomer actuators. Strain and stress performances of this material were compared to those of the most currently used acrylic elastomer (3M, U.S.A., VHB 4910). Planar actuators were realised and tested, using films of the two materials, coated with compliant electrodes made of carbon grease. Following the application of a two-second high-voltage impulse, the isotonic transverse displacement and the isometric transverse force were separately measured along a prestrained direction. Actuators made of the new elastomer showed, respect to those made of the acrylic polymer, a lower dielectric strength, a transverse strain more than twice greater for the same applied electric field (e.g. 1.8 % against 0.7 % @ 27 V/μm) and a transverse stress less than twice smaller (e.g. 3.7 KPa against 5.3 KPa @ 24 V/μm).

Neurological tremor affecting limbs can be divided into at least 6 different types with frequencies ranging from 2 to about 20 Hz. In order to alleviate the symptoms by suppressing the tremor, sensing and actuation systems able to perform at these frequencies are needed. Electroactive polymers exemplify "soft actuator" technology that may be especially suitable for use in conjunction with human limbs. The electrochemical and mechanical properties of polypyrrole dodecyl benzene sulphonate actuator films have been studied with this application in mind. The results show that the time constants for the change of length and for the stiffness change are significantly different; the stiffness change being about 10 times faster. Both force measurements and Electrochemical Quartz Crystal Microbalance measurements indicate that the actuation process is complex and involves at least two different processes. The EQCM results make it possible to formulate a hypothesis for the two different time constants: Sodium ions enter the polymer correlated with a fast mass change that probably involves a few (~4) strongly bound water molecules as well. On further reduction, about 10 additional water molecules enter the polymer in a slower process driven by osmotic pressure. Earlier work has tended to focus on achieving the maximum length change, therefore taking the time needed to include all processes. However, since the slower process described above is associated with the lowest strength of the actuator, concentrating on the faster stiffness change results in only a small reduction in the work done by the actuator. This may make actuation at higher frequencies feasible.

Here, we report on devices based on patterned thin films of the conducting polymer system poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulphonic acid) (PEDOT:PSS) combined with patterns of solid electrolyte. The key device functionalities base on the updating of the RedOx state of PEDOT. This results in control of the electronic properties of this conjugated polymer, i.e. the conductivity and optical properties are updated. Based on this we have achieved electric current rectifiers, transistors and display cells. Also, matrix addressed displays will be presented. Electrochemical switching is taking place when the oxidation and reduction potentials are overcome respectively. Therefore, these devices operate at voltage levels less then 2 Volts. Low voltage operation is achieved in devices not requiring any extremely narrow dimensions, as is the case for field effect driven devices. All devices reported can or has been made using standard printing techniques on flexible carriers.

Conducting polymer actuators are employed to create actively shaped hydrodynamic foils. The active foils are designed to allow control over camber, much like the ailerons of an airplane wing. Control of camber promises to enable variable thrust in propellers and screws, increased maneuverability, and improved stealth. The design and fabrication of the active foils are presented, the forces are measured and operation is demonstrated both in still air and water. The foils have a "wing" span of 240 mm, and an average chord length (width) of 70 mm. The trailing 30 mm of the foil is composed of a thin polypyrrole actuator that curls chordwise to achieve variable camber. The actuator consists of two 30 μm thick sheets of hexafluorophosphate doped polypyrrole separated from each other by a gel electrolyte. A polymer layer encapsulates the entire structure. Potentials are applied between the polymer layers to induce reversible bending by approximately 35 degrees, and generating forces of 0.15 N. These forces and displacements are expected to enable operation in water at flow rates of > 1 m/s and ~ 30 m/s in air.

Contemporary applications could benefit from multifunctional materials having anisotropic optical, electrical, thermal or mechanical properties. These desirable features, but with locally-controlled distribution of directional response, would be even more attractive. Such materials are difficult to engineer by conventional methods. However, the field-aided technology presented herein is able to locally tailor electroactive composites. By applying an electric field to a polymer in its liquid state, we have developed ability to orient chain- or fiber-like inclusions or phases from what was originally an isotropic material. Such composites can be formed from liquid solutions, melts, or mixture of pre-polymer and cross-linking agent. Upon curing, a "created composite" results consisting of these "pseudo fibers" embedded in a matrix. One can also create orientated composites from embedded spheres, flakes or fiber-like shapes in a liquid plastic. Orientation of the externally applied electric field defines the orientation of field-aided self-assembled composites. The strength and exposure duration of the electric field control the degree of created anisotropy. Results of electromechanical testing of these modified materials relevant to sensing and actuation applications are presented. Material microstructure is analyzed using microscopy and X-ray diffraction. The performance of these novel materials having different composition and morphology is being investigated.

Following the biological paradigm, artificial polymeric systems considered as candidates for actuation applied to biomedical devices and systems were tested taking into account longitudinal strain as a result of energy conversion from external sources. Among them, dielectric elastomers show good mechanical performances, but they require very high voltages for the driving, on the order of kilovolts, which are not suitable for devices that are in contact with biological systems. Conducting polymers work in a voltage range much more reasonable, but they show only few percents of longitudinal strain. On the other hand, it is known that, for instance, in a planar configuration of DBS-doped polypyrrole, the longest dimension undergoes a dimensional change of 0.5% up to 4% while the shortest one has a strain of roughly 35%. In this work, we discuss the latest advances concerning conducting polymer based devices and assess the worth of exploiting the interesting properties characterizing the radial strain of conducting polymer fibers rather than the axial strain. We also describe a possible method able to convert radial to longitudinal strain via a braided mesh acting as a merely mechanical transducer or even as a strain amplifier. The described technical improvements and observations, together with a voltage drop range acceptable for biomedical applications, give conducting polymers a new appeal for this kind of utilization and promise new interesting applications.

An ionic polymer-metal composite (IPMC) consisting of a thin perfluorinated ionomer (usually, Nafion® or Flemion®) strip, platinum and/or gold plated on both faces, undergoes large bending motion when a small electric field is applied across its thickness. When the same membrane is suddenly bent, a small electric potential of the order of millivolts is produced across its surfaces. This actuation and sensing response depends on the structure of the ionomer, the morphology of the metal electrodes, the nature of cations, and the level of hydration. IPMCs in alkali-metal cation form under direct current (DC) show a fast 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. In contrast, the actuation of both Nafion- and Flemion-based IPMCs in tetrabutylammonium (TBA⁺) cation form consists of a continuous slow motion towards the anode. We have discovered that when an IPMC is neutralized by combined Na⁺ and TBA⁺ cations to produce a suitable Na-TBA-form membrane, different actuation behavior results. The proportion of the cations can be tailored to obtain a desired actuation response, e.g., to control the duration, speed, and the maximum amplitude of the initial motion towards the anode, or the magnitude and the speed of the subsequent relaxation. A series of cation combination tests on both Nafion- and Flemion-based IPMCs are carried out. Various essential physical properties of the IPMCs in various cation compositions are measured and compared. A summary of these results is presented.

Dielectric elastomer actuators offer unprecedented opportunities for actuation in a wide range of applications. To make appealing large scale and efficient systems, new electronic devices combining high voltage and flexibility need to be designed. In this paper we report the first mechatronic system, made of an array of electro-active polymer based actuators integrated with thin film photoconductive high voltage switches fabricated on a plastic film substrate. The actuator is an acrylic elastomer diaphragm that expands under electrical stimulation. Each actuator is connected to the high voltage power supply through a photoconductive switch, which is addressed and closed by illumination. The amorphous silicon switches are made on flexible and transparent polyimide (Kapton E®) substrates. Individual switches were tested up to 8 kV and a nine-element array was successfully working at 5 kV.

Two liquid crystal elastomers (LCEs) were synthesized based on those reported by Finkelmann and coworkers. The elastomers were mechanically aligned in the SmA phase. One of the elastomers was prepared with a chiral mesogen with the aim of producing a SmA* phase. Both these elastomers were studied mechanically under the influence of a uniaxial force; also their response to thermally and electrically induced dimensional changes was measured. Dimensional changes were measured using a Dynamic Mechanical Analyzer (DMA). Crosslinking liquid crystal polymers increases the materials’ Young’s modulus and gives it the ability to retain its original shape upon removal of external forces. This characteristic makes LCEs highly suitable as actuator devices. Electromechanical studies performed on these samples indicate a need to improve material composition.

This paper presents a strategy of design, realization and control of pseudomuscular actuator controllable in position and compliance. The actuator was designed as a bundle of electromechanical actuating elements, made by dielectric elastomers. The control strategy was inspired to the Feldman's biological muscle model. Presented simulations show that opportune recruitments of the bundle active units enable a satisfying approximation of the quadratic length-force characteristic of the biological muscle.

We will present organic electrochemical transistors that show both bi-stable and dynamic current modulation. In electrochemical devices, both ions and electrons are used as charge carriers. The device is all-organic and has been realized using common printing techniques, such as screen-printing. As the substrate, both cellulose-based paper and polyester foil have been used. PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrene sulphonic acid)) is used as the conducting and electrochemical active material. PEDOT:PSS is switched between different redox states, corresponding to semi-conducting and conducting states. Operating voltages is below 2V and on/off ratios up to 105 have been reached (typical value is 5000). The operation of these devices does not depend on any critical dimensions; typical dimensions used are around 200 microns. With a certain geometrical design the dynamic transistor can be employed for frequency doubling. For the bi-stable transistor the modulation of the current is done by direct electronic contact, compared to the dynamic transistor that is modulated by induction of electrochemistry. The electrolyte in these devices can either be solidified or a liquid. The bi-stable device in combination with a layer of Nafion as electrolyte demonstrates humidity sensor functionality. Since substrates based on paper and common printing techniques can be used for fabrication, this give rise to an environmental friendly and non-expensive device setup.

Ionic polymer metal composites have been demonstrated to offer great potential as versatile actuators. However, the low force output of these actuators continues to be an inhibiting factor in their development. Researchers have begun to investigate thicker ionic polymer metal composite actuators that offer greater force output. An alternative approach is to use multiple strips of actuator in parallel to increase the force output. In this paper the development of such an actuator is detailed. Issues of parallel or series electrical connection are discussed. Experimental results from the actuator are presented showing the unblocked position response and blocked force response. Losses within the system are considered for various numbers of strips. Finally PID control is applied to the actuator to demonstrate the controlled actuator performance.

A transducer consisting of multiple layers of ionic polymer material is developed for applications in sensing, actuation, and control. The transducer consists of two to four individual layers each approximately 200 microns thick. The transducers are connected in parallel to minimize the electric field requirements for actuation. The tradeoff in deflection and force can be controlled by controlling the mechanical constraint at the interface. Packaging the transducer in an outer coating produces a hard constraint between layers and reduces the deflection with a force that increases linearly with the number of layers. This configuration also increases the bandwidth of the transducer. Removing the outer packaging produces an actuator that maintains the deflection of a single layer but has an increased force output. This is obtained by allowing the layers to slide relative to one another during bending. Experiments on transducers with one to three layers are performed and the results are compared to Newbury’s equivalent circuit model, which was modified to accommodate the multilayer polymers. The modification was performed on four different boundary conditions, two electrical the series and the parallel connection, and two mechanical the zero interfacial friction and the zero slip on the interface. Results demonstrate that the largest obstacle to obtaining good performance is water transport between the individual layers. Water crossover produces a near short circuit electrical condition and produces feedthrough between actuation layers and sensing layers. Electrical feedthrough due to water crossover eliminates the ability to produce a transducer that has combined sensing and actuation properties. Eliminating water crossover through good insulation enables the development of a small (5 mm x 30 mm) transducer that has sensing and actuation bandwidth on the order of 100 Hz.

IPMC (Ionic Polymer Metal Composite) is a promising candidate actuator for bio-related applications mainly due to its biocompatibility, soft properties and operation in wet condition. The widely used and commercialized ion-exchange polymer film has limitation in thicknesses, but more various film thicknesses are required for extensive applications. Especially for the enhanced force as an actuator, acquisition of thick film is essential. Various ion-exchange polymer films with thickness of 0.4-1.2 mm have been prepared by casting of liquid ion-exchange polymer. As well, IPMC actuators using cast ion-exchange polymer films have been fabricated and the basic mechanical characteristics such as stiffness, displacement and force were measured and analyzed. These results can be used for the optimized design of actuators for different applications.

The uniqueness of liquid crystals (LCs) lies in the large anisotropies in their properties, which can be utilized to generate high electromechanical responses. In a properly oriented liquid crystal polymer system, an external electric field can induce re-orientation of the mesogenic units possessing a dielectric anisotropy, which, when coupled with the shape anisotrophy of the mesogenic units, can in turn produce large mechanical strain. Anisotropic liquid crystal gels, which can be obtained by in situ photopolymerization of the reactive LC molecules in the presence of non-reactive LC molecules in an oriented state, are an example of such liquid crystal polymer systems. It has been shown that a homeotropically aligned liquid crystal gel in its nematic phase exhibits high electrically induced strain (>2%) with an elastic modulus of 100MPa and a high electromechanical conversion efficiency (75%) under an electric field of 25 MV/m. These anisotropic LC polymeric materials could provide a technologically compatible system for such applications as artificial muscles and as micro-electromechanical devices.

The primary purpose of this research is to create a flexible, self-sustaining gel with an optical transparency of over 70% for light in the range of 400 to 700 nanometers. Attention is focused on identifying and controlling the effect of crosslinker concentration and degree of neutralization on the polymer gel optical transparency, structural rigidity and electroactive response. Appropriate flexible and transparent electrodes suited for the present application are identified. Spectrophotometer tests indicate that there is a large gap between the spectra from crosslinker content of 175mg and 200mg (with an intensity difference of approximately 40% at 440nm).

An integrated oxygen control system has been explored by using bi-morph actuators based on polypyrrole conducting polymers (CP). The practical focus was control of a fruit storage atmosphere at 5% oxygen. An oxygen sensor and a simple actuator-valve assembly were integrated to limit the influx of atmospheric oxygen to a small chamber representing a fruit storage package. Electrochemical oxygen sensors such as zinc-air cells with output potentials up to one volt appear to be well suited for this task as they are able to drive trilayer strips based on CPs that actuate over a similar voltage range. The bimorph actuator used gave reliable and repeatable mechanical behaviour for about 50 hours. In one sensor-actuator system trialled the output from a lead-oxygen sensor was electronically augmented to drive the actuator-valve. A set oxygen concentration of 5% was readily maintained with response times of tens of seconds. In the other system the voltage output from a zinc-air cell was used directly to control a very light actuator-valve that limited the free diffusion of air into the test chamber. Control of the oxygen concentration was achieved but at lower rates of oxygen flux and with longer response times.

Temperature-, pH- and electrical-responsive semi-interpenetrating polymer network (semi-IPN) hydrogels constructed with chitosan and polyacrylonitrile (PAN) were studied. The swelling ratio of hydrogels depends on pH and temperature. The stimuli response of the semi-IPN hydrogel in electric fields was also investigated. When swollen, the semi-IPN was placed between a pair of electrodes, and it exhibited bending behavior upon the application of an electric field. The electro responsive behavior of the present 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.

A thin strip of thermoplastic polyurethane (PU) was found to bend to the cathode side under the application of a DC electric field. As the field was reversed, the bending went to the anode side at first and then switched back to the cathode side. The mechanism responsible for this bending and switching phenomena was investigated by means of monitoring the charging and discharging current during the application of electric field. It was found that the bending direction and magnitude can be correlated to the direction and magnitude of current flow. A detailed analysis of the current response shows that it is most likely a space charge limited current. A model based on a charge accumulation at the sample surface will also be presented in this paper. It can explain the bending as well as switching effect of the PU film. In order to visualize the charge contents in the PU film, we apply the thermally stimulated discharge current (TSDC) technique for the measurement. Our preliminary result has confirmed the existence of charged layers at the surfaces of the PU film.

The piezoelectric effect of electroactive cellulose has been studied. Hardwood and softwood papers were selected to estimate a bending actuation performance in connection with electromechanical coupling factors. The cantilever unimorph actuators are considered. The results show that the coupling is highly non-linear particularly at high k₃₁ for both papers but not at low k₃₁. The effect of the thickness ratio is a critical operating factor at lower k₃₁. In comparison of both appers, softwood paper showed larger coupling factors than that of hardwood paper due to lower Young's modulus affecting its stiffness as expected. The future study will center around the sensitivity analysis on the performance analysis of different types of electroactive cellulose actuators. Also, the temperature dependence of the coupling factors will be investigated due to the change of crystalline structure of cellulose in a form of paper.

Interpenetrating polymer networks (IPN) composed of poly(vinyl alcohol) (PVA) and hyaluronic acid (HA) were prepared and exhibited electrical sensitive behavior. The swelling behavior of the PVA/HA IPN was studied by immersion of the gel in aqueous NaCl solutions at various concentrations and pHs. Also, the stimuli response of the PVA/HA IPN in electric fields was investigated. When swollen IPN was placed between a pair of electrodes, the PVA/HA IPN exhibited bending behavior upon the application of an electric field. The PVA/HA IPN also showed stepwise bending behavior depending on the electric stimulus. Also, for using biomedical application, the bending behavior of PVA/HA IPN has been studied in hank’s solution at pH 7.4