In the last ten years, new EAP materials have emerged that exhibit large displacement in response to electrical stimulation enabling great potential for the field. To develop efficient and robust EAP material for practical applications efforts are underway to understand the behavior of EAP materials and improved characterization techniques. Further, to enhance the actuation force the basic principles are being studied using comprehensive material science, electro-mechanics analytical tools and improved material processing techniques to gain better understanding of the parameters that control the EAP electro-activation force and deformation. The processes of synthesizing, fabricating, electroding, shaping and handling are being refined to maximize the EAP materials actuation capability and robustness. Methods of reliably characterizing the response of these materials are required to establish database with documented material properties in order to support design engineers considering use of these materials and towards making EAP as actuators of choice. Various configurations of EAP actuators and sensors need to be studied and modeled to produce an arsenal of effective smart EAP driven system. The development of the infrastructure is a multidisciplinary task involving materials science, chemistry, electro-mechanics, computers, electronics, and others. This paper will be a review of the status of the EAP field and the challenges to practical application of EAP materials as actuators.

The mechanisms underpinning the basis of electrochemical actuators utilizing inherently conducting polymers (ICPs) are briefly reviewed. Based on the fact that these actuators are simple electrochemical cells the parameters impacting on performance are discussed. Of particular interest here is the mode of electrical connection, the auxiliary electrode composition and the supporting electrolyte used. All are shown to have a dramatic effect on performance.

Among many kinds of polymer materials, electronic conductive material, that is polypyrrole, shows potential possibility for bio-relate actuator materials. However, it may be an impediment for practical use in polypyrrole actuator that polypyrrole usually requires electrolyte solution for actuation. Our first research theme is focused on this problem solving. We have investigated many kinds of solid polymer electrolyes for the substitution of electrolyte solution. Our goals are to find the stable solid electrolyte in the air, to establish the reliable fabrication process of it and to apply it for micropump application. Besides actuators, the reduction and oxidation property of polypyrrole can be exploited for active drug delivery systems by the control of structural deformation of it. We have investigated this kind of new and bio-related possibility of polypyrrole. Shape memory alloy has another possibility in the biomedical field. Due to its inherent excellent advantages as actuator materials, it can be used for micro active intravascular catheter. We have developed thin tube type bending actuator using shape memory alloy and characterized its performance by in-vivo test.

Ionic polymer-metal composites (IPMCs) consist of a polyelectrolyte membrane (usually, Nafion or Flemion) plated on both faces by a noble metal, and is neutralized with certain counterions that balance the electrical charge of the anions covalently fixed to the backbone membrane. In the hydrated state, a cantilevered strip of this composite performs bending vibration when subjected to an AC potential across its faces, and it produces millivolt potential when suddenly bent. Thus the composite is a soft actuator and sensor. Its coupled electrical-chemical-mechanical response depends on the chemical composition and structure of the backbone ionic polymer; the morphology of the metal electrodes; the nature of the cations; and the level of hydration. A systematic experimental evaluation of the mechanical response of both metal-plated and bare Nafion in various cation forms and various water saturation levels has been performed at UCSD. By examining the measured stiffness of the Nafion-based composites and the corresponding bare Nafion, under a variety of conditions, I have develop relations between internal forces and the resulting stiffness and deformation of this class of IPMCs. Based on these and through a comparative study of the effects of various cations on the material's stiffness and response, I have sought to identify potential micro-mechanisms responsible for the observed electro-mechanical behavior of these materials, model them, and compare the model results with experimental data. A summary of some of these developments is given in the present work.

The applicability of the concept of ionic reservoir for the description of hydrogel behavior was demonstrated by potentiometric titration of poly(N-isopropylacrylamide-co-1- vinylimidazole) hydrogel suspension. Four different regions of pH-changes of the microgel suspensions were identified on the titration curve in comparison with pure water. Particularly, at 10.5>pH>6.5 a hydrogel accumulates or releases H⁺ and Cl^- ions without significant swelling/deswelling whereas at 6.5>pH>4 the storage of the ions occurs both due to their binding with ionizable groups on polymer network and due to strong swelling. The mechanical response of hydrogel (swelling/deswelling) is assumed to be a faster process than the electrochemical response (equilibration of ion concentrations interior and exterior to the hydrogel). The size of hydrogel spheres should be diminished to fasten an ionic reservoir response of the hydrogel. A novel protocol for preparation of polymer hydrogel spherical particles on a nanometer scale (nanogels) has been developed. Temperature- and pH-sensitive nanogels were detected and characterized by the dynamic light scattering technique and atomic force microscopy. Ptoentiometric titration of the obtained nanogels shows that the decrease in the ionic reservoir size gains the efficiency and, presumably, the rate of the electrochemical response. These findings indicate the necessity of time-resolved pH-measurements of the hydrogel suspensions for the characterization of the rate of the solute diffusion through the gel/water surface.

Mechanical actuators that simultaneously provide high power densities and large force generation capacities are of great scientific and technological interest. Recently single wall carbon nanotube (SWNT) sheets (bucky papers) were shown to possess significant promise as electrochemical actuators. Embedding polyelectrolytes, like Nafion, within the nanotube matrix has the potential to address the limitations of SWNT bundling and tube slippage thus increasing force generation. In this paper two types of Nafion/SWNT composite actuators have been investigated depending on the method of fabrication. In the first case, infiltration of Nafion within SWNT sheet matrix was followed by annealing at 150 degree(s)C to invert Nafion's micellar structure and render it insoluble. This has resulted in a substantially exfoliated layer morphology that causes a reduction in both conductivity and actuation strain (c.a. 0.03%). In the second case, slow casting of a methanolic suspension of Nafion and SWNT soot, followed by annealing at 150 degree(s)C, resulted in a more homogeneous structure. This composite, upon electrochemical cycling between -1 and +1 V in aqueous electrolytes, exhibited actuation strains (as high as 0.43%). However, these higher strains are accompanied by an order of magnitude reduction in modulus largely due to Nafion swelling.

A new actuator system has been developed. This actuator uses Nafion, a solid electrolyte, in combination with Platinum Copper (Pt-Cu) electrodes and mobile ions of Cu²⁺ to create much larger actuation displacement at smaller levels of applied voltage (1V or less). This actuator provides bending deformation. Large deformation is provided by electrode reaction of copper. Since this reaction is reversible, Cu electrode is not consumed by using polarity change of applied voltage. This actuation mechanism is different from others. Because the induction of the large deflection of Nafion, the large number of the mobile cations is essential. Although it is possible to induce a large deflection by applying a higher electric field as alternative way, this would introduce the electrolysis of water that is not desired unless the device is always submerged in water. To convert bending deformation to liner actuation, we designed a device using a pair of Nafion actuator, which is termed as loop actuator. This loop actuator can be designed into the device with large force by making parallel array. Solid polymer electrolyte-metal composite actuator contains water inside. Therefore coating that prevents water from evaporation is needed for its use in dry condition.

Numerous researchers have shown that ionic polymer-metal composite (IPMC) actuators are capable of large strains when subjected to relatively small electric fields. In this paper, we present data showing that, with some electrical inputs, a portion of the strain remains once the electric field is removed. The remaining strain is on the order of 0.1%, and its magnitude is correlated to the total charge delivered to the actuator. Several experiments were conducted to explore the relationship between the electrically induced permanent strain and input shape, actuator geometry, and boundary conditions. The permanent strain magnitude was found to increase with actuator length and with the magnitude of a pulse input. For 20 second pulse inputs applied to a 5mm x 29mm actuator, the ratio of the permanent strain to the total electric charge delivered per unit actuator length was approximately 10 %strain/(C/mm). This ratio dropped as pulse duration was increased. A comparison of strain energy associated with the permanent strain to the total electrical work done on the actuator yielded values on the order of 5(mu) J/J. Previous research has indicated that IPMCs are not suitable for DC actuation. However, the permanent strain phenomenon may provide a means by which IPMCs can be used as DC actuators.

To answer the need for a dense array of actuators, we tried to integrate several actuators in a single Nafion membrane by simply patterning the soft metal electrodes deposited on the membrane. We designed several independent octagonal electrodes on the same membrane. The experiments showed that we could actuate each cell independently. The use of gold electrodes and tetraethyl ammonium ion instead of platinum copper electrodes and copper ion improves the repeatability but at the cost of the large deformation. We studied the influence of the membrane thickness on actuation. Nafion 115 (125-micron thick) showed a similar behavior than the classic Nafion 117 (180-micron thick). We also investigated Nafion 112 (50-micron thick) as an actuator. We did 6 gold plating cycles to deposit the same amount of gold as on the other membranes. This membrane showed a unique actuation behavior, due its high flexibility. We prepared a 3x3 array of disk shaped actuators using Nafion 112. We used hydrophobic masks to create the patterning. Upon actuation the cell quickly reached a quite large deformation and relaxed to an equilibrium position. To get actuation between two stable positions we are currently trying to create symmetric equilibrium positions for the cell.

This paper reports a novel electric deformation memory effect in connection with ionic polymer conductor composites (IPCC) and, in particular, ionic polymer composites (IPMC). This deformation memory effect is neither thermal, as observed in shape memory alloys, nor magnetic, as observed in magnetic shape memory alloys. It is shown that an IPCC is capable of storing geometric shape and deformation information for a given step voltage or imposed electric field, even when the field is turned off. This electric deformation memory effect is more profound than the existing thermal or magnetic shape memory effects that basically have only one configuration per a given threshold magnetic field or temperature. In other words, IPMC's do not need to be trained for a given shape memory effect such as SMA's or ferromagnetic shape memory materials but rather, they have an infinite set of possibilities of deformation shapes versus voltage that can be memorized even when the electric field is removed. This creates for the first time potential for given voltage signal or electric field. The data presented here in this paper will establish that from a neutral position and charge free state, for any given voltage, a cantilever sample of IPMC bends to a shape, and if one removes the voltage, the shape will not change and the material remembers the shape permanently. The process is highly reversible. Any change in shape is due to environmental changes such as humidity or temperature, and in a controlled environment, we observe that after the voltage is removed, having allowed the sample to stabilize, the shape stays almost permanently. Upon shorting out the electrodes on the two sides of the sample, the sample moves back to its initial configuration before the application of the step voltage.

A new approach is proposed, namely the use of Interpenetrating Polymer Networks (IPNs) in order to solve the interface and adhesion problems in the design of classical conducting polymer based actuators. Semi IPN type materials are synthesized between poly(3,4-ethylenedioxythiophene) and a poly(ethyleneoxide) based network as the ionic conducting partner. The synthetic pathway which will be presented ensures a gradual dispersion of the electronic conducting polymer through the thickness of the material i.e. the content decreases from the outside towards the center of the film. The system is thus similar to a layered one with the advantage that the intimate combination of the two polymers needs no adhesive interface. The influence of the morphology and chemical composition of the matrix on the electronic conductivity of the material have been studied. The surface conductivity can reach 15 S/cm. Finally, this material is capable of a 45 degree(s) angular deflexion under a 0.5 V potential difference.

Recently a new class of electrostrictive polymers, called electrostrictive graft elastomers, was developed at NASA Langley Research Center. In this work, the output force of a bending actuator made from electrostrictive graft elastomer was measured and modeled to understand the dependence of performance on device configuration. This understanding should lead to better actuator design and fabrication. The prototype bending actuator is 47micrometers thick and 8 mm wide. The output bending force at the tip was measured as a function of applied voltage and the distance from the tip to the holding stage. The output force at 2.1 kV increases from 124(mu) N at a length of 33.5 mm to 662(mu) N at 7 mm. Accourding to a small displacement, 5-layer, a strength-of- materials model, the output bending force of the actuator varies inversely with its length and directly with the square of the applied voltage. Consequently, the output bending force can be about 5 mN when the length of the actuator is reduced to 1 mm for application to micro- electromechanical (MEMS) devices. The experimental results will be presented and a method for enhancing the performance will also be discussed.

This presentation considers the electrostrictive response of an ideal polar rubber in which each random link carries a dipole constrained to remain perpendicular to the link but free to rotate about it In such materials, there is a possibility of a genuine interplay between mechanical deformation and the electrical permittivity since an applied strain can align the dipole rotation axes. This is a plausible mechanism of genuine electrostriction in polar rubbers but our quantitative analysis has shown that the effect should make only a small contribution to the observed deformation of actuators constructed from polar rubber films with compliant electrodes. This prediction has been confirmed by quantitative measurement of the thickness strain in polar films subjected to high electric fields, the deformation being measured by laser-Doppler vibrometry. Measurements made on Viton B, in particular, show the material to be viscoelastic with a significant phase lag between the applied electric field and the observed strain. This phase lag is shown to be due primarily to the mechanical phase lag at twice the frequency of the applied electric field.

Electro-active paper (EAPap) is a paper that produces large displacement with small force under an electrical excitation. EAPap is made with a chemically treated paper by constructing thin electrodes on both sides of the paper. When electrical voltage is applied on the electrodes the EAPap produces bending displacement. To improve the bending performance of EAPap, different paper fibers-softwood, hardwood, bacteria cellulose, cellophane, carbon mixture paper, electrolyte containing paper and Korean traditional paper, are tested. It was found that a cellophane paper exhibits a remarkable bending performance. When 2kV/mm of excitation voltage was applied, more than 3mm of tip displacement was observed out of the 30 mm long paper beam. Different thin electrodes were made by two methods-a sputtering technique and an evaporation technique. The evaporation technique is better than the sputtering technique since it can produce the electrodes at relatively low temperature, which does not change the material properties of papers significantly. The principle that dictates the actuation of EAPap seems to be more based on ionic migration effect associated with the reaction of the constituents of the paper. Details of the experiments and results are addressed.

To achieve desirable biomimetic motion, actuators must be able to reproduce the important features of natural muscle such as power, stress, strain, speed of response, efficiency, and controllability. It is a mistake, however, to consider muscle as only an energy output device. Muscle is multifunctional. In locomotion, muscle often acts as an energy absorber, variable-stiffness suspension element, or position sensor, for example. Electroactive polymer technologies based on the electric-field-induced deformation of polymer dielectrics with compliant electrodes are particularly promising because they have demonstrated high strains and energy densities. Testing with experimental biological techniques and apparatus has confirmed that these dielectric elastomer artificial muscles can indeed reproduce several of the important characteristics of natural muscle. Several different artificial muscle actuator configurations have been tested, including flat actuators and tubular rolls. Rolls have been shown to act as structural elements and to incorporate position sensing. Biomimetic robot applications have been explored that exploit the muscle-like capabilities of the dielectric elastomer actuators, including serpentine manipulators, insect-like flapping-wing mechanisms, and insect-like walking robots.

A new biomemetic actuator is proposed. The actuator realizes bidirectional actuation since it is with a stretched film antagonistically configured with compliant electrodes. Also, it is distinguished from existing actuators with respect to the controllability of its compliance. Bidirectional actuation and compliance controllability are important characteristics for the artificial muscle actuator and the proposed one accomplishes these requirements without any mechanical substitute or complicated algorithms. In this paper its basic concepts and working principles are introduced with static and dynamic analysis. Control strategies for displacement as well as stiffness are introduced, and experimental results are given to confirm the effectiveness of the proposed methods. In addition, an example of robotic actuating devices is given to confirm the usefulness of the proposed actuator.

Dielectric elastomer actuator technology is based on electric field induced deformation. From the viewpoint of materials technology, many points must be addressed, among which are material dielectric properties, breakdown voltage, viscoelastic losses and elastomer spring mechanical properties. From the viewpoint of actuator manufacturing, we will mention elastomer thin film and fiber processing as well as compliant electrode design. However, among all the previously mentioned key-points, compliant electrode design remains the major problem to solve, as electrodes required to distribute the electric field in the material need to be at least as compliant as the active elastomer material. In this paper, we present the analysis of dielectric elastomer-based actuators made with metallic compliant electrodes that show a relatively good overall mechanical performance. Large displacements, force densities and low creep, as well as fast response and million cycles are achieved using micro-structuring and thin-film techniques. We have succeeded in making smart anisotropic compliant metallic electrodes that can maintain conductivity up to 33% expansion before breaking and loosing electrical connectivity. Actuators are made with a silicone elastomer as the active material and silver as coating electrodes. The spring constant of a 3-layer actuator consisting of silver electrodes with a thickness up to 1100 A and elastomer film with a thickness up to 50 micrometers is typically 2 times larger than that of the elastomer film taken alone. Force-displacement and constant load measurements are used as a basis to analyze the mechanical properties of the artificial muscle. Capacity measurements at high frequency in the kilohertz range are carried out to study the built-in sensor properties for feedback control of the actuator.

Dielectric elastomer actuators performance depends on their construction and the way they are driven. We describe the governing equations for the dynamic performance of actuators and show examples of their use. Both the properties of the base elastomer material and the compliant electrodes influence the actuators performance. The mechanical and electrical properties of elastomers are discussed with a focus on an acrylate pressure sensitive adhesive from 3M, which is used by a number of groups. The influence of these properties on the actuator properties is analyzed.

The recent discovery of high electromechanical performance in high-energy electron irradiated P(VDF-TrFE) copolymers opens a new avenue for developing high performance electroactive polymers. From basic materials consideration, it is expected that one can achieve high electromechanical performance by means of nonirradiation approach, such as introducing ter-monomer to form PVDF based terpolymer. The basic requirement for the ter-monomer is discussed in order to achieve a high electromechanical performance in P(VDF-TrFE) based terpolymer. Based on the conclusion, P(VDF-TrFE-CFE) terpolymer has been synthesized and the experimental results indicate that the terpolymer exhibits better electromechanical performance compared with irradiated copolymers. For example, both the electric induced strain and Young's modulus in P(VDF-TrFE-CFE) terpolymer could be higher than that in irradiated copolymers. X-ray diffraction, DSC and FTIR were employed to determine the structure and molecule conformation. Furthermore, a serious theoretical simulation was carried out for P(VDF-TrFE) based terpolymers with different ter-monomers. The results show that indeed the terpolymer with CFE favors gauche conformation, consistent with the experimental results.

Conducting polymer actuators were first proposed more than ten years ago. Reported performance has improved dramatically, particularly in the past few years, due to changes in synthesis methods, better characterization and an understanding of the underlying mechanisms. These actuators are able to displace large loads (up to 100x greater than mammalian skeletal muscle), with moderate displacements (typically 2 %), and with power to mass ratios similar to that of muscle, while powered using potentials of no more than a few volts. Unlike electric motors and muscle, these actuators exhibit a catch state, enabling them to maintain force without consuming energy. Despite the impressive performance, commercial applications are at an early stage. One reason is the need to carefully consider the details of the actuator construction, including the thickness and surface area of the polymer, the electrolyte conductivity and geometry, the counter electrode spacing, the shape of the input voltage and the means of electrical contact to the polymer, in designing effective actuators. A set of design guidelines is presented that assist the device designer in determining the optimum actuator configuration. These are derived from extensive characterization and modeling of hexafluorophosphate-doped polypyrrole actuators. The set of design tools helps transform conducting polymer actuators into engineering materials that can be selected and designed for particular applications based on rational criteria. Most of the underlying physical principles used in determining these rules also underlie other conducting polymer actuators, polymer devices such as electrochromic displays, supercapacitors and batteries, carbon nanotube actuators, and electrochemically driven devices that involve volumetric charge storage.

This paper studies the state of the water and the ionic conductivity of solid polymer electrolyte membranes (SPM) in relation to polymer actuators. The ionic conductivity was evaluated by impedance measurements and the specification of water in the SPM, such as total water, freezable water, non- freezable water, was carried out by DSC measurements. Dependency on the type of fixed charge of perfluorinated polymers and the couter ion was studied. The effect of the heat-treatment of the SPM was also studied. These properties were discussed in relation to the performance of the actuation of the composite composed of the SPM and gold on the basis of the proposed response model and the microscopic structure of the SPM.

A composite actuator based on a polymer electrolyte and metal electrodes is described. Electrode deposition is described qualitatively with corresponding experimental results. A general continuum model describing the transport and deformation of solid polymer electrolyte processes is developed. The formulation is based on global integral postulates for the conservation of mass, momentum, energy, charge, and the second law of thermodynamics. The global equations are then localized in the volume and on the material surfaces bounding the polymer. The model is simplified to a three component system of a fixed negatively charged polymeric matrix, diffusing hydroxonium ions, and free water within the polymer matrix. Contrary to the existing electrostatic models, the deformation is attributed to water induced swelling. The proposed internal pressure based model includes the stress relaxation phenomenon due to water redistribution governed by Darcy's law.

This paper presents a detailed description of various techniques and experimental procedures in manufacturing Ionic Polymeric-Metal Composites (IPMCs) that, if fully developed, can be used as effective biomemetic sensors, actuators, and artificial muscles as well as fully electroded with embedded electrodes for fuel cell. The performance of those IPMCs manufactured by different manufacturing techniques are presented and compared. In particular, a number of issues such as force optimization using the Taguchi design of experiment technique, effects of different cations on the electromechanical performance of IPMCs, electrode and particle size distribution control, manufacturing cost minimization approaches, scaling and 3D muscle production issues and heterogeneous composites by physical loading techniques are also reviewed and discussed.

Ionomeric Polymer-Metal Composites (IPMC) are attractive type of electroactive polymer actuation materials because of their characteristics of large electrically induced bending, mechanical flexibility, low excitation voltage, low density, and ease of fabrication. The diffusion of ions between the electrodes causes the material to bend. The unique features of the IPMC materials and their need for special operating environment require new approaches to measuring their characteristics. A macro model that relates the electric input and mechanical output is required for the material characterization and application. This paper addresses the macro models for the electric inputs and electromechanical actuation of IPMC. A distributed RC line model is developed to describe the varying capacitance of the electric input behavior and a four-parameter model to express the relaxation phenomena. The power capacities of the IPMCs are estimated according to the established models and the measured results. Results for several types of IPMCs, which present different behaviors, are presented.

A series of experiments are performed to quantify the stress induced in ionic polymer actuators by electrical stimulation. The test fixture is validated by measuring the modulus of hydrated samples comparing the measurements to previous results in the open literature. A series of dynamic tests demonstrates that the modulus of the material can be varied up to approximately 30% through the application of a DC electric field to the polymer. Dynamic tests indicate that the peak in-plane stress is on the order of 10-100 kPa for 1 V step changes in the applied potential. The magnitude of the in-plane stress drops approximately 10 dB per decade as a function of frequency for short duration sinusoidal excitations. Experimental results reveal that out-of-plane bending contributes substantially to the in-plane stress induced in the polymer. Constraining the out-of-plane motion reduces the induced stress by a factor of 4 to 5. Long duration sinusoidal excitation induces a controllable relaxation within the polymer and a dehydration in which the rate of stress is controlled by the amplitude of the excitation. The magnitude of the induced stress is much larger during relaxation or dehydration as compared to the stress induced by electrical stimulation. Stresses on the order of 100 kPa to 1 Mpa are measured.

Measurement represents one of the oldest methods used by human beings to better understand and control the world. Many measurement systems are primarily physical sensors, which measure time, temperature, weight, distance, and various other physical parameters. The need for cheaper, faster, and more accurate meansurements has been a driving force for the development of new systems and technologies for measurements of materials, both chemical and biological. In fact, chemical and biological sensors (or biosensors) are the evolved products of physical measurement technologies. Chemical sensors are measurement devices that convert a chemical or physical change of a specific analyte into a measurable signal, whose magnitude is normally proportional to the concentration of the analyte. On the other hand, biosensors are a subset of chemical sensors that employ a biological sensing element connected to a transducer to recognize the physiochemical change and to produce the measurable signal from particular analytes, which are not necessary to be biological materials themselves, although sometimes they are. Depending on the basis of the transduction principle, chemical and biological sensors can be classified into three major classes with different transducers: sensors with electrical transducers, sensors with optical transducers, and sensors with other transducers (e.g. mass change). The unique properties of carbon nanotubes have led to their use in areas as diverse as sensors, actuators, field-emitting flat panel displays, energy and gas storages (Dai and Mau, 2001). As we shall see below, the principles for carbon nanotube sensors to detect the nature of gases and to determine their concentrations are based on change in electrical properties induced by charge transfer with the gas molecules (e.g. O₂, H₂, CO₂) or in mass due to physical adsorption. This article provides a status report on the research and development of carbon nanotube sensors.

By utilizing strain gage technology it is possible to directly and continuously measure the electrochemically induced strain response of EAP actuators. Strain sensitive actuators were constructed by directly vapor depositing gold (EvAu) on polyimide strain gages which are capable of measuring strain with an accuracy of +/- 1(mu) (epsilon) . Strain sensitive actuators were used to evaluate the strain response of polypyrrole (PPy), poly(3,4-ethylenedioxypyrrole) (PEDOP) and poly(3,6-bis(2-(3,4-ethylenedioxy)thienyl)-N-carbazole) (PBEDOT-Cz). PPy was shown to produce significantly higher strain when compared to PEDOP and PBEDOT-Cz. The resulting overall strain for the materials was: 236, 33, and 35 (mu) (epsilon) respectively. From the initial investigation, adhesion of the EAP to the EvAu layer was identified as a major factor in the resulting lifetime and strain response of these actuators. Therefore an electrochemically deposited Au layer (EcAu) was deposited on top of the EvAu layer to improve the adhesion of the EAP to the working electrode. By changing the surface roughness from requals3.43 (EvAu) to requals8.26 and 18.00 (EcAu) the normalized strain response after 2000 cycles increases from 45% to 60% and 68% respectively. Also by changing the surface roughness from 5 to 23, the resulting strain response increases from ~100 (mu) (epsilon) to 600-800 (mu) (epsilon) for Ppy.

Conducting polymers are new materials that were developed in the late 1970s as intrinsically electronic conductors at the molecular level. The presence of polymer, solvent, and ionic components reminds one of the composition of the materials chosen by nature to produce muscles, neurons, and skin in living creatures. The ability to transform electrical energy into mechanical energy through an electrochemical reaction, promoting film swelling and shrinking during oxidation or reduction, respectively, produces a macroscopic change in its volume. On specially designed bi-layer polymeric stripes this conformational change gives rise to stripe curl and bending, where the position or angle of the free end of the polymeric stripe is directly related to the degree of oxidation, or charged consumed. Study of these curvature variations has been currently performed only in a manual basis. In this paper we propose a preliminary study of the polymeric muscle electromechanical properties by using a computer vision system. The vision system required is simple: it is composed of cameras for tracking the muscle from different angles and special algorithms, based on active contours, to analyse the deformable motion. Graphical results support the validity of this approach, which opens the way for performing automatic testing on artificial muscles with commercial purposes.

IPMC is an electroactive polymer (EAP) that has been the subject of research and development since 1992. The advantages of IPMC in requiring low activation voltage and the induced large bending strain led to its consideration for various potential applications. However, before the benefits of IPMC can be effectively exploited for practical use, the electromechanical behavior of this group of EAP materials must be properly understood and quantified. An experimental setup was developed for data acquisition from IPMC strips that are subjected to various tip mass load levels. This data acquisition setup was used to measure the displacement and curvature of IPMC as a function of the input signal. Sample strips were immersed in water to minimize the effect of moisture content. In order to avoid electrolysis, the samples were subjected to 1-V square wave with either positive or negative polarity. Experiments have shown that IPMC has history dependence and the characteristics response is dominated by the backbone (e.g., Nafion, Flemion, etc.) and ionic content (e.g., Na+, Li+, etc.).

A direct method for determining the dynamic stiffness properties of electroviscoelastic materials is described. Electroviscoelastic materials (EVEMs) are characterized as having stiffness and damping properties that vary with frequency, temperature, and applied voltage. The test system described allows the direct measurement of the complex stiffness (shear modulus, loss factor) of EVEMs at varying voltages and temperatures. Design of the test apparatus incorporates a double-lap shear type refrigerated test fixture utilizing a laser vibrometer to measure the dynamic response of the moving mass subjected to a periodic chirp excitation. A refrigeration system controls the temperature of the moving mass, stationary masses, and test specimens in order to study the effect of temperature on dynamic material property behavior. The test system is first validated by measuring the dynamic properties of a known viscoelastic damping material as function of frequency and temperature. Second the material properties of an EVEM are studied as a function of frequency only. The EVEM consists of poly (p-phenylenes) particles doped with FeCl3 suspended in a blended silicone gel, which reacts to an electric field. Techniques addressing data reduction, mechanical compliance, and electrical insulation are discussed.

In this paper a variety of techniques to characterize the mechanical properties of polymers in the MHz frequency range based on the impedance analysis of thickness and thickness shear composite resonators will be presented. The analysis is based on inverting the impedance data of the composite resonator to find the best fit using the material coefficients of the piezoelectric resonator and attached polymer layer. Mason's equivalent circuit is used along with standard acoustic circuit elements to generate the impedance of the composite resonators and interpret the experimental data. Inversion techniques will be presented which allow for the direct determination of the acoustic load if the material properties of the resonator are known before being joined to the polymer. A specific example of this technique, the quartz crystal microbalance will be presented and it will be shown how the model can be extended to include all the acoustic elements of the experimental setup including the acoustic load of the solution. In the model all elements are treated as complex to account for loss mechanisms (viscous effects, electric dissipation etc.). If the free resonator is modeled prior to deposition a transform is presented that allows for the determination of the acoustic load directly. The advantage being that one no longer has to assume a functional form of the acoustic load (eg. mass damping) since it can be measured directly and compared to the various models. In addition the transform allows for an easy determination of the mass sensitivity and bandwidth for the system. The theory can be extended to account for electrode mass changes (adsorption/condensation and desertion/evaporation) or for use in chemical monitoring by the addition of a chemically sensitive layer (artificial noses and tongues). The technique has also applications for the direct determination of the elastic coefficients of polymer materials.

In this paper we present an extended summary of the fundamental properties and characteristics of Ionic Polymeric-Metal Composites (IPMCs) as biomemetic sensors, actuators, and artificial muscles. Als, the phenomenological modeling of the underlying sensing and actuation mechanisms in IPMCs is presented based on linear irreversible thermodynamics with two driving forces; an electric field and a solvent pressure gradient and two fluxes, electric current and solvent flux. The importance of capacitors which arise from nanoparticles residing at the surface/subsurface of IPMCs is also discussed. We also present some quantitative experimental results on the Onsager coefficients.

Ionic polymer gels, consisting of a polymer network with ionizable groups and a liquid phase with mobile ions, exhibit very good actuatoric capabilities due to their large swelling ratios. In this paper we investigate gels immersed in salt solution at different positions - in direct contact with the anode, the cathode or in the middle of the electric field. The concentrations of anions and cations in these gels as well as the electric potential inside and outside the gel are calculated for a given number of anionic groups fixed to the polymer. The applied chemo-electric formulation consists of a convection-diffusion equation for the chemical field and a Laplace equation for the electric field. The numerical simulation of the coupled formulation has been performed by using unconditionally stable space-time finite elements. Based on the results of the numerical simulation we compare the concentrations inside and outside the gel for the different test cases in order to optimize the position of the gel film. The highest swelling ratio of the gel has been taken as criterium for the optimization. The optimal condition is characterized by a maximum value of the concentration differences and of the Donnan potential.

New actuator technologies are moving closer towards the creation of artificial muscles. For these muscles to behave in synergy with natural human muscle then they must be controlled in a similar manner. It has been postulated that the control of human motion is achieved through a force and position control strategy termed impedance control. An impedance controller has been developed for implementation on an ionic polymer-metal composite (IPMC) actuator. The basis for this controller is a PID position controller that is demonstrated to accurately control the position response of the IPMC actuator. This position controller is extended to form an impedance controller with a force control loop and impedance filter. Inspite of identified non-linearities in the polymer force output during motion, the impedance controller has been successfully implemented demonstrating the controller design process and good performance of the control strategy.

The development of a sensory subsystem for use in the position control of a dielectric elastomer transducer (DET) is reported. In this study, the dielectric elastomer serves as both a source of sensory feedback and as the primary actuator. Specifically, stretched film DETs are considered to test the sensory subsystem. The capacitance of the film is measured in real-time using a low-voltage carrier signal that is superimposed on the control signal for actuation of the film. The relationship between the capacitance of the DET and applied voltage is presented for operating conditions outside of the elastic-buckling mode. The inference of strain made by the sensory subsystem is compared to that measured from digital images of the DET taken during operation and close correlation between the two measurements is confirmed. The capacitance measured during operation within the elastic-buckling mode shows a surprising drop under conditions of low frequency excitation and aged carbon grease electrodes. The measured capacitance in the elastic-buckling mode shows a dramatic increase during high-frequency excitation and with newly fabricated carbon grease electrodes.

An effort to model the dynamic motion of an ionic-polymer metal composite elestic beam was undertaken. Development of the static portion of the model was begun by assuming the beam behaves in accordance with the nonlinear equation used to describe large-angle deflection of elastic cantilever beams. A Simulink simulation was developed to estimate the final deflection of a beam due to a constant moment. The dynamic portion of the model was developed by assuming that each segment of the beam could be represented as a simple second-order system. Future efforts to more accurately model beam motion - by modifying the method used to model the forcing moment, by expanding the model to predict the performance of beams of all dimensions, and by validating model performance against actual beam motion - were recommended.

In this multi-institutional effort, polyacrylonitrile- nanofibers (PAN-N) have been fabricated by the electro- spinning method. Realizing that the response time of PAN is governed by the diffusional processes of ions/solvents interaction, the use of sucn PAN-N are promising for fabricating fast response PAN artificial muscles. PAN-N fibers were suitably annealed, cross-linked and hydrolyzed to become active. It should be noted that activated PAN fibers have their capability of changing effective longitudinal strain more than 100%, and their comparable strength to human muscle. Therefore, such high strength of the PAN fibers is a dfinite advantage over other types of ionic gels that are usually very weak. A key molecular structure of PAN, hydrogen bonding between hydrogen and the neighboring nitrogen of the nitrile group, exhibiting insolubility, thermal stability, and resistance to swelling in most organic solvents, is thought to be due to its cross-linked polymer structure. In this paper, the authors present the analytic results of such PAN fibers, including micrographs and solid-states NMR. These results provide a great potential in developing fast activating PAN-N muscles and linear actuators, as well as integrated pairs of antagonistic muscles and muscle sarcomere and myosin/actin- like assembly.

Electroviscoelastic materials (EVEMs) are polymeric materials that exhibit changes in structural properties when a voltage is applied across it. In the current study, an EVEM is developed that produce large changes in stiffness and damping materials with applied voltage. The resulting material exhibits many of the same properties as an electrorheological (ER) material, except the current material is self-supporting and thus can be used to applications where viscoelastic materials are used. The EVEM is composed of three components: 20% (by mass) of poly (p-phenylene) (PPP) particles doped with CuCl₂ or FeCl₃, 64% of Dow Sylgard 527 silicone gel, and 16% Dow Corning Sylgard 182 silicone elastomer, where the elastomer is added to for stiffening. Experimental harmonic tests using a double-lap shear test and a 0.025 thick specimens between 1 and 150 Hz reveal a factor six increase in stiffening and a factor of three decrease in damping with applied voltage (1500v).

Although conducting polymer (CP) actuators can operate with just a few volts and generate much higher forces than natural muscle, their poor dynamic performance limits their applications. A control system scheme to increase their dynamic performance is presented in this paper, based on the analysis of CP actuator models. By using a closed-loop control system, the potential abilities of CP actuators are exploited more fully. Experimental results show that, for a CP actuator fabricated from a commercially available polyaniline fiber PANIONT and an aqueous HCl electrolyte, use of a control system in the oxidization process, decreased settling time (transient time) by 87.4%; in the reduction process, settling time decreased more than 94.2%. The performance improvements from using control systems depend on the maximum signal the CP actuator can be burdened with, not simply on the performance of the CP actuators themselves. The possibilities and limitations of actuator control systems may determine the CP actuators that can eventually be incorporated into practical devices.

Polyelectrolyte gels are distinguished by enormous swelling capabilities under the influence of external physical or chemical stimuli. No other kind of material attains similar volume expansiveness. These properties make them most attractive candidates for a new generation of pseudomuscular actuators. In contrast to chemical stimulations which are able to trigger large in-toto deformations, weak electric fields can only induce considerable bending strains in ionic polymer gels when confined to direct electrical effects. This, of course, restricts their potential for technical applications. To characterize their chemo-mechanical and electrical behavior and the underlying physico-chemical processes, experimental and theoretical findings are presented. Measurements of basic mechanical and electrical parameters on polyelectrolyte gels allow quantification of their electroactive responses, especially with respect to the direct effects of external electric fields on the Donnan potential inside the gels. Model calculations on the basis of a coupled chemo-electro-mechanical multi- field formulation are in good agreement with the experimental results. Although the emphasis of this study is given to various anionic and cationic gels of the polyacrylamide family, a new class of hydrogels based on the biopolymer chitosan is included. These natural polymers have excellent properties such as biocompatibility, biodegradability, non-toxicity etc. making them predestinate to biomedical applications.

The popularity of minimally invasive surgical procedures over traditional open procedures motivates us to develop new instruments that address the limits of existing technology and enable more widespread use of minimally invasive approaches. Robotic surgical instruments have the potential to provide improved dexterity and range of motion within the confines of the human body when compared with manually actuated instruments. The high strain response and elastic energy density of electron-irradiated P(VDF-TrFE) make it a candidate actuator material for robotic instruments that provide electronic mediation and multiple degrees of freedom of tip movement. We are currently studying both active and passive properties of P(VDF-TrFE) with the goal of constructing a mathematical model of the material's behavior. Studies have been conducted on 15 micron thick film samples in rolled and rolled-flattened configurations. Passive properties can be represented by a 5 parameter viscoelastic model with two time constants on the order of ten and 200 seconds. Active responses were found to have strong dependence upon field and modest dependence upon load. We suggest means by which the active and passive responses can be combined in a model of steady-state response that would be of value in positioning tasks. The time course of the active response appears to contain components on two time scales, but further studies are required to characterized it in more detail.

Conducting polymer-based actuators undergo volumetric changes as they are oxidized or reduced, from which mechanical work can be obtained. Polypyrrole (Ppy)-based actuator devices have attracted recent interest because of their similarities with the natural muscles. However, the operation of these and others actuators has largely been constrained to microscopical world. Macroscopical operation is clearly desirable for many potential applications. We have fabricated a new macroscopical actuator device based on PPy acting in liquid media. Using trilayers (PPy film/adhesive polymer /PPy film), and rigid pieces articulate actuators of 9,5 cm in long have been developed. The position of the trilayers at the device and its design simulate the movement of a finger where the movements of each trilayer are as articulations. These materials present a high degree of mobility, a good energy density, a medium speed of response and low operation voltages; these features are desirable for robotic applications. A simple equation based on electrochemical characterization of trilayer can predict device performance from load conditions. A lineal join for a double articulated (finger-like) device using macroscopical trilayer actuator has been demonstrated.

Nanocomposites are a new class of composites which are typically nanoparticle-filled polymers. One promising kind of nanocomposite is clay-based and polymer-layered silicates nanocomposites because the starting clay materials are naturally abundant and, also, their intercalation chemistry is well understood at the present time. A certain clay, Montmorillonite (M_xAl_{4- x}Mg_x)Si₈O_20$(OH4 has two-dimensional layers of their crystal structure lattice where the layer thickness is around 1 nm with the lateral dimension of approximately 30 nm to a few microns. These layers organize themselves to form stacks, so-called the Gallery through a van der Walls gap in between them. In this work, Montmorillonite (MMT) was modified by a cationic surfactant so as to lower its surface energy significantly. Such a process gave rise to favorable intercalation of nanoparticles within the galleries. The obtained XRD patterns and TEM images indicate that the silicate layers are completely and uniformly dispersed (nearly exfoliated) in a continuous polymer matrix of Nafion that has been successfully used as a starting material of ionic polymer-metal composites (IPMC's).

The nonverbal expression of the emotions, especially in the human face, has rapidly become an area of intense interest in computer science and robotics. Exploring the emotions as a link between external events and behavioural responses, artificial intelligence designers and psychologists are approaching a theoretical understanding of foundational principles which will be key to the physical embodiment of artificial intelligence. In fact, it has been well demonstrated that many important aspects of intelligence are grounded in intimate communication with the physical world- so-called embodied intelligence . It follows naturally, then, that recent advances in emotive artificial intelligence show clear and undeniable broadening in the capacities of biologically-inspired robots to survive and thrive in a social environment. The means by which AI may express its foundling emotions are clearly integral to such capacities. In effect: powerful facial expressions are critical to the development of intelligent, sociable robots. Following discussion the importance of the nonverbal expression of emotions in humans and robots, this paper describes methods used in robotically emulating nonverbal expressions using human-like robotic faces. Furthermore, it describes the potentially revolutionary impact of electroactive polymer (EAP) actuators as artificial muscles for such robotic devices.

This paper reports on the development of a lightweight hyper-redundant manipulator driven by embedded dielectric polymer actuators. This manipulator uses binary actuation and belongs to a class of digital mechanisms that are able to perform precise discrete motions without the need for sensing and feedback control. The system is built from an assembly of modular parallel stages and has potential to be miniaturized for applications ranging from biomedical devices to space system components. The polymer actuators can make such devices feasible. This paper presents the design of a modular polymer actuator that can work under both tension and compression. The actuators achieve improved performance by incorporating an elastic passive element to maintain uniform force-displacement characteristic and bi-stable action. A flexible frame also insures nearly optimal pre-strain required by dielectric film based actuators.

Reported is the fabrication method and experimental results pertaining to a new class of liquid crystal elastometer- graphite (LCE-G) composites as electrically controllable biomimetic artificial muscles. These films (10mmx20mmx0.32mm) of monodomain nematic liquid side chain crystal elastomers graphite (LSCE-G) composites were transversely pressed between uniform layers of fine graphite powder of 2 microns average diameter under a stress of 100 kPa. The resulting composite expanded to (12 mmx24mmx0.33mm) and had about 53% by volume embedded graphite powder. The composite became a conductor and had an effective resistivity of about 2 ohms/square on its surface and about 1 ohmsquare across its thickness. Upon applying DC voltage of 0.5 to 5 volts to the samples for 4 seconds, under a stress if abiyt 10 kPa, the sample contracted quickly in about a second to about 18 mm lengthwise with an average linear strain of about 25%. The samples generally had negligible contractions in the thickness and transverse direction. The cooling was also quick and it took the sample about 4.4 seconds to revert back to its initial length.

A thermally driven liquid crystalline elastomer bending actuator was prepared with extended cycling capabilities. This device operated with strain rates of 1 Hz displacement and 0.13 Hz recovery starting from 25.1 degree(s)C to a maximum of 150 degree(s)C. The device is a bending actuator having a multilaminated material structure. Observed displacements were lower than previous freestanding liquid crystalline elastomer films due to the constraints imposed on the liquid crystalline elastomer by the device architecture. A device operated with low power of less than 2 W and cycled over a 1000 times successfully.

A large contrast ratio and rapid switching electrochromic(EC) polymer device which consists of laminated two-layer structure between two electrodes was proposed. The new design which only comprises an ITO coated glass electrode, a cathodic poly(3,4-propylenedioxythiophene) derivative (PProDOT-(CH_3$2) EC polymer film, a solid electrolyte and an Au-based counterelectrode which replaces anodic EC polymer and ITO electrode. Carbon-based counterelectrode was prepared for comparing with Au-based counterelectrode. Lithography and sputtering were used for Au patterning on glass substrate, while screen printing was used for carbon-based counterelectrode. Covering percentage of Au is less than 20%, in order to keep the electrode high transmittance. We also prepared a solid electrolyte, such as poly(methyl metracrylate)(PMMA) based containing LiClO₄ gel electrolyte for solid state applications. A special parafilm was utilized on sealing the assembly device. Color change of high contrast ratio of transmittance (>(Delta) 50% T) of the device is rapidly (0.5-1s) obtained upon applied 2.5V voltage and repeatable (10,000 times). The temperature range under which the switching is stable is wide, -40 degree(s)C ~ 100 degree(s)C. The repeatability of current of EC polymer devices while color change was estimated by electrochemistry.

The fabrication, testing and performance of a new device for the protection of optical sensors will be described. The device consists of a transparent substrate, a transparent conducting electrode, insulating polymers, and a reflective top electrode layer. Using standard fabrication techniques, arrays of apertures can be created with sizes ranging from micrometers to millimeters. A stress gradient resulting from different coefficients of thermal expansion between the top polymer layer and the reflective metal electrode, rolls back the composite thin film structure from the aperture area following the chemical removal of a release layer, thus forming the open condition. The application of a voltage between the transparent conducting and reflective metal electrodes creates an electrostatic force that unrolls the curled film, closing the artificial eyelid. Fabricated devices have been completed on glass substrates with indium tin oxide electrodes. The curled films have diameters of less than 100micrometers with the arrays having fill factor transparencies of over 70%. Greater transparencies are possible with optimized designs. The electrical and optical results from the testing of the artificial eyelid will be discussed.

Traditional conducting polymer actuators such as polypyrrole offer tremendous active stress at low actuation voltages but with moderate strain, strain-rate and efficiency. We report the synthesis of novel thiophene based conducting polymer molecular actuators, exhibiting electrically triggered molecular conformational transitions. In this new class of materials, actuation is the result of conformational rearrangement of the polymer backbone at the molecular level and is not simply due to ion intercalation in the bulk polymer chain upon electrochemical activation. Molecular actuation mechanisms results from (pi) $min(pi) stacking of thiophene oligomers upon oxidation, producing a reversible molecular displacement which is expected to lead to surprising material properties such as electrically controllable porosity and large strains. The hypothesis of active molecular conformational changes is supported by in situ electrochemical data. Single molecule techniques are considered for molecular actuator characterization. Mechanical properties of these new materials are currently being assessed.

This work presents the novel composite material based on a polymer (LDPE) and metal alloy, which have a close melting point. The process of blending the main components of the composite was developed using the extrusion mixing. The process of extrusion of composite films with a thickness 50- 300 micrometers was worked out using an extruder equipped with a cast film die. This process allowed production of the binary composite, with up to 15 wt. % of the alloy dispersed uniformly in the polymer matrix. It was shown that carbon black is highly compatible with the basic components and could be dispensed uniformly in the obtained films. The structure of the composite films was studied with a scanning electron microscope. Physical properties of the binary and ternary composites were investigated, including conductivity and temperature dependence of the thermal capacity. Non- ohmic behavior of the ternary composites was revealed. The IR spectra of the composites were studied using an FTIR spectrophotometer. It was shown that processing polyethylen in the presence of a low-melting-point alloy causes changes in the structure of polyethylene. The presence of alloy caused intensive oxidation of carbon black in the ternary composite as well.

The wave transmission and attenuation behaviors of electro-active polymer (EAP) are investigated. Nonionic EAP is made by PVA (Polyvinyl Alcohol) with DMSO (dimethyl sulfoxide), and aluminum electrodes are made on both sides of the EAP. Two types of wave transmission experiments are performed. Acoustic waves are normally impinged upon the EAP plate and the transmitted sound pressure level is measured using microphones. The EAP plate exhibits a good passive damping performance at mid frequency region. When an electric field is applied, the resonance of EAP plate is shifted down due to the change of the thickness of the plate. This tunable characteristic is applicable for escaping a certain noise frequency.

Two ionic electroactive polymer (EAP) gels, crosslinked partially sulfonated poly(styren-b-ethylene-co-butylene-b- styrene) (S-SEBS) and partially sulfonated crosslinked polystyrene (S-XL-PS), exhibit reversible bending in low DC electric fields when immersed in salt solutions. Both gels bent toward the cathode when pre-equilibrated in salt solutions. The steady-state bending angle increased as the size of the hydrated cation of the salt increased. The initial speed of bending increased as the mobility of the hydrated cation increased. Both the steady-state bending angle and initial speed of bending reached a maximum at an intermediate salt concentration, which varied little with the type of the salt. The time needed to reach the steady- state bending angle was associated with the time needed for the major hydrated cations to transport through the gel slabs. When the S-XL-PS gel ws pre-equilibrated in distilled water before the bending experiments, the gel first bent toward the anode before reversing toward the cathode in 0.065 - 0.08 M (C₄H₉)₄NHSO₄ (TBA) solutions. Such bending behavior did not occur in TBA at other concentrations (0.005 - 0.06 M), nor in other salt solutions Na₂SO₄, Cs₂SO₄, (CH₃)₄NHSO₄ (TMA) and the S-SEBS gel. Actuation performance of gels of the above polymers and their nanoparticle composites are compared and discussed.