The evolution of nature led to the introduction of highly effective and power efficient biological mechanisms. Imitating these mechanisms offers enormous potentials for the improvement of our life and the tools we use. Humans have always made efforts to imitate nature and we are increasingly reaching levels of advancement that it becomes significantly easier to imitate, copy, and adapt biological methods, processes and systems. Advances in science and technology are leading to knowledge and capabilities that are multiplying every year. This brought us to act beyond the simple mimicking of nature. Having better tools to understand and to implement nature’s principles we are now equipped like never before to be inspired by nature and to employ our tools in far superior ways. Effectively, by bio-inspiration we can have a better view and value of nature capability while studying its models to learn what can be extracted, copied or adapted. EAP as artificial muscles are adding an important element in the development of biologically inspired technologies. This paper reviews the various aspects of the field of biomimetics and the role that EAP play and the outlook for its evolution.

Device designers are continually confronted with the challenge of selecting the best actuator for a task and developers of new actuators are seeking applications for which their technologies are suitable. A web-based interface is presented that enables designers to input basic needs (force, displacement, frequency, cycle life, dimensions, voltage and power available) and retrieve an initial evaluation of the suitability of the various actuator technologies in the database. The prototype contains data for a number of emerging technologies including conducting polymers, dielectric elastomers, ferroelectric polymers, thermal and magnetic shape memory alloys, carbon nanotube actuators, liquid crystal elastomers, ionic polymer metal composites and mammalian skeletal muscle. The system is very early in the development process, and it is hoped that feedback from the EAP community will help guide the growth of and establish the need for this tool.

The Ionic Polymer-Metal Composite (IPMC) for flexible hydrodynamic propulsor blades can provide many new opportunities in the naval platforms, especially in developing robotic unmanned vehicles for both surveillance and combat. IPMC materials are quietly operational since they have no vibration causing components, i.e. gears, motors, shafts, and etc. For small Autonomous Underwater Vehicles (AUV), these features are truly attractive due to limited space. Also, IPMCs are friendly to solid-state electronics with digital programming capabilities. Active control is thus possible. Another advantage of these materials should be recognized from the fact that they can be operational in a self-oscillatory manner. There are several issues that still need to be addressed such as propulsor design, testing, robotic control as well as theoretical modeling of the appropriate design. In this effort, IPMC is investigated for propulsor blades applications in NaCl solution and a propulsor model with a robust control scheme is explored. An analytical model of a segmented IPMC propulsor was formulated to be used as a building block for furthering the model to adequately accommodate the relaxation behavior of IPMCs and for describing the dynamics of the flexible IPMC bending actuator.

In this paper, we present a fascinating new feature of Ionic Polymer-Metal Composite (IPMC), "self-oscillation." In the presence of Small Organic Molecules (SOMs) in an aqueous medium, the self-oscillatory and periodic deformation of IPMCs was evident. The oscillations are caused by the potential periodicity in the Pt anode where the activation-overpotential is altered by complex surface reactions under an applied DC current. Such a self-oscillatory behavior of IPMC was highly conceivable and repeatable when it was properly prepared. The importance of surface reactions can be acknowledged when the potential intermediates, such as PtOH, PtO, and PtCO are believed to exist. The oscillatory potential was obtained by properly alternating the presence and the absence of CO molecules on the anode at a constant current.

Ionic Polymer Metal Composites or IPMCs are emerging materials belonging to EAP class. They are of increasing interest in innovative applications due to several advantages respect to competing technologies (SMA, piezoelectric, etc.), such as the possibility to be used both as moving actuators and sensors, their lightness and the low actuation voltage. On the other hand their behaviour is not fully known and it is still subjected to deep investigations. In this perspective the development of a complete model, able to fully describe the electromechanical properties of the IPMC materials, is the aim of many research groups. To that purpose this work focuses on designing and realising a system to determine the frequency domain behaviour of an IPMC strip as actuator in order to collect information useful to model it. Here the IPMC deformation, caused by applying a voltage input signal across its thickness, is detected by using an infrared transmitter-receiver couple. This methodology is largely diffused and it is based on the acquisition of the intensity of the emitted ray after being reflected by the moving target, moreover it constitutes a low cost solution. Also a transducer is used to acquire information about the current absorbed by the device under test. For the specific application a conditioning circuitry and the software for signal processing has been designed and realised. Preliminary results show that the proposed system allows to infer a number of interesting properties of IPMC based actuators.

Recent advances in ionic polymer conductor composites (IPCC) and ionic polymer metal composites (IPMC) as biomimetic distributed nanosensors, nanoactuators, nanotransducers and artificial muscles are briefly discussed in this paper. These advances include brief reproduction of some of these advances that appeared in a new book and a recent set of 4 review articles published in the International Journal of Smart Materials and Structures, advances in manufacturing, force optimization, modeling and simulation and new products developed by Environmental Robots Incorporated, as well as numerous potential applications using Ionic Polymer-Metal Composites (IPMC's) as distributed nanosensors, nanotransducers, nanoactuators and artificial muscles. It is certainly clear that the extent of applications of IPCC's and IPMC's go beyond the scope of this paper or the space allocated to this paper. However, this paper will present the breadth and the depth of all such applications of IPCC's and IPMC's as biomimetic robotic distributed nanosensors, nanoactuators, nanotransducers and artificial/synthetic muscles.

Electromechanical devices made of dielectric elastomers represent today one of the most attractive and performing technologies within the field of electromechanical polymer actuation. We describe here a new configuration designed for monolithic dielectric elastomer actuators capable to show electrically activated linear contractions. Two helical electrodes integrated within the wall of an elastomeric hollow cylinder represent the core of the device, enabling the generation of active axial contractions and radial expansions. Detailed architecture, principle of operation and preliminary data on the performances of the new device are presented.

Electro-Active Paper (EAPap) is attractive as an EAP actuator material due to its merits in terms of lightweight, dry condition, large displacement output, low actuation voltage and low power consumption. This paper presents the fabrication and performance test of EAPap actuators. EAPap material has been made from cellulose materials. Cellulose fiber is dissolved into a solution and made into a sheet by using a spin coater. Thin electrodes are deposited on the cellophane sheet to comprise an EAPap. Next the EAPap is made into plate or beam specimens cut along a specific orientation to enhance the actuator performance. The EAPap is clamped on electric power connector and placed in an environmental chamber and the tip displacement of EAPap is measured with laser sensor. Also the blocking force of EAPap sample is measured. The measured force is compared with a theoretical beam model. These measurements are performed under a variety of environmental and input factors including frequency, actuation voltage, temperature and humidity. Characteristics of EAPap in terms of fibrous nature, their crystallinity, and mechanical, physical and electrochemical characteristics are presented.

A non-linear viscoelastic model for finite deformations of dielectric elastomer membranes using Christensen's theory of viscoelasticity is developed. For a time efficient numerical solution, the constitutive integral equations with a time dependent kernel (relaxation modulus) are reformulated into a recurrence form using Feng's recurrence formula and solution for the principal stretches are obtained. Uniaxial constant load tensile tests are conducted and compared with theoretical predictions. The model is also valid for small linear deformations.

As previously reported, a NASA Langley-developed electroactive polymer-ceramic hybrid system (HYBAS) has demonstrated significant enhancement in actuating displacement. The displacement of the system is derived from both the electrostrictive polymer and from single crystal elements. The electroactive elements are driven by a single power source. Recently, a modification of HYBAS has been made to increase the capability of air driving for synthetic jet devices (SJ) used in aerodynamic control technologies. The dependence of the air driving capability of the modified HYBAS on the configuration of the actuating device has been investigated. For this particular application, the modified HYBAS demonstrated a 50% increase in the volume change in the synthetic jet air chamber, as compared with that of the HYBAS without the modification.

Many different actuator configurations based on SRI International’s dielectric elastomer (DE) type of electroactive polymer (EAP) have been developed for a variety of applications. These actuators have shown excellent actuation properties including maximum actuation strains of up to 380% and energy densities of up to 3.4 J/g, using the planar mode of actuation. Recently, SRI has investigated different configurations of DE actuators that allow complex changes in surface shape and thus the creation of active surface texture. In this configuration, the “active” polymer film is bonded or coated with a thicker passive layer, such that changes in the polymer thickness during actuation of the DE device are at least partially transferred to (and often amplified by) the passive layer. Although the device gives out-of-plane motion, it can nonetheless be fabricated using two-dimensional patterning. The result is a rugged, flexible, and conformal skin that can be spatially actuated by subjecting patterned electrodes on a polymer substrate to an electric field. Using thickness-mode DE, we have demonstrated thickness changes of the order of 0.5 - 2 mm by laminating a passive elastomeric layer to a DE polymer that is only 60 μm in thickness. Such thickness changes would otherwise require a very large number of stacked layers of the DE film to produce comparable surface deformations. Preliminary pressures of 4.2 kPa (0.6 psi) in a direction normal to the plane of the DE film have been measured. However, theoretical calculations indicate that pressures of the order of 100 kPa are feasible using a single layer of DE film. Stacking multiple layers of DE film can lead to a further increase in achievable actuation pressures. Even with current levels of thickness change and actuation pressures, potential applications of such surface texture change are numerous. A thin, compliant pad made from these actuators can have a massaging or sensory augmentation function, and can be incorporated into garments if desired. The bumps and troughs could act as valves or pumping elements in a fluidic or microfluidic system. Such a device could also be the basis of a smart skin that controls boundary-layer flow properties in a boat or airplane so as to reduce overall drag. The DE elements of the pad can also be used as sensors to make a touch-sensitive skin for recording human interaction with the environment. By driving a thin, compliant vibrating layer at resonant frequencies, one can also configure these devices as solid or fluidic conveyors that transport material on a macroscopic or microscopic scale.

Solid state actuators provide deformation and actuation forces mainly excited by electric fields. Piezoelectric actuators are well established providing high forces at low strain due to their material characteristic. Electrostatic solid-state actuators consist of elastic dielectric layers between compliant electrodes. Applying electric fields of up to 100 V/μm at the electrodes the dielectric contracts due to electrostatic forces and expands in orthogonal direction. We use high elastic silicone elastomers with thin graphite powder electrodes. In order to increase the absolute strain values at limited voltage, we have developed a novel multilayer process technology to fabricate elastomer stack actuators with up to 100 layers. The electromechanical properties of the actuators have been evaluated theoretically and characterised experimentally. Maximum strain values up to 20% for prestressed multilayer films have been achieved. The novel multilayer fabrication technology provides multilayer stack actuators with various electrode patterns like universal linear actuators or matrix arrays for a wide range of applications as tactile displays for telemanipulation or Braille displays. The strain in vertical direction versus driving voltage shows a hysteresis due to viscous friction in the elastomer layers. These measurements correspond to a viscoelastic theoretical model. The mechanical stress versus strain characteristic shows a strong nonlinearity for strains > 30%. The dynamic characteristic has been evaluated by measuring the mechanical impedance in the frequency range of 2 to 1000 Hz.

Dielectric elastomers are known to produce large transverse strains in response to electrically induced Maxwell stresses and thus provide a useful form of electromechanical actuation. The transverse strain response of silicone (Dow Corning HS III RTV) based Maxwell stress actuators have been measured earlier as a function of driving electric field, frequency and pre-load. Experimental results show that a pre-load initially causes an increase in the strain. However, this increase appears to be a function of the relative geometries of the electroded area and of the specimen itself. The transverse strains in these materials decrease when larger values of pre-load are applied. Models of hyperelasticity that are capable of describing the large deformation of polymer materials have been used to interpret our results. Numerical finite element simulations of the material’s behavior using a hyperelastic model provides good agreement with most of our observations on the electric field and pre-strain dependencies of the transverse strain.

Interpenetrating polymer networks (IPN), as polymer hydrogels, exhibiting high electrical sensitivity were prepared. The swelling behavior of the IPN was studied by immersing the gel in various concentrations of aqueous NaCl solutions and various pH buffer solutions. The response of the IPN to electric fields was investigated. When a swollen IPN was placed between a pair of electrodes and an external DC electric field applied, the IPN exhibited a bending behavior. The IPN also displayed a step-wise bending behavior, that depended on the magnitude of the applied electric field, In addition, some IPN hydrogels underwent a change in volume on application of electrical stimulus. Switching the electrical stimulus led to a reversible volume change in the hydrogels. One electrode induced a contractile response, while the other electrode induced an expansion in the IPN. The behavior of the hydrogels arises from the movement of counterions in the solution, which is induced by the applied voltage. This movement allowed for a rapid contraction and expansion behavior with repeated voltage changes. The rate of change of the volume of the hydrogels was related to the magnitude of the applied voltage. This behavior suggests that the hydrogels studied are suitable candidates for a wide range of applications, including drug delivery systems, in robotics, as soft linear actuators, as sensors, and as biomimetic energy transducers.

Ionic electroactive actuators have received considerable attention in the past ten years. Ionic electroactive polymers, sometimes referred to as artificial muscles, have the ability to generate large bending strain and moderate stress at low applied voltages. Typical types of ionic electroactive polymer transducers include ionic polymers, conducting polymers, and carbon nanotubes. Preliminary research combining multiple types of materials proved to enhance certain transduction properties such as speed of response, maximum strain, or quasi-static actuation. Recently it was demonstrated that ionomer-ionic liquid transducers can operate in air for long periods of time (>250,000 cycles) and showed potential to reduce or eliminate the back-relaxation issue associated with ionomeric polymers. In addition, ionic liquids have higher electrical stability window than those operated with water as the solvent thereby increasing the maximum strain that the actuator can produce. In this work, a new technique developed for plating metal particulates on the surface of ionomeric materials is applied to the development of hybrid transducers that incorporate carbon nanotubes and conducting polymers as electrode materials. The new plating technique, named the direct assembly process, consists of mixing a conducting powder with an ionomer solution. This technique has demonstrated improved response time and strain output as compared to previous methods. Furthermore, the direct assembly process is less costly to implement than traditional impregnation-reduction methods due to less dependence on reducing agents, it requires less time, and is easier to implement than other processes. Electrodes applied using this new technique of mixing RuO₂ (surface area 45~65m²/g) particles and Nafion dispersion provided 5x the displacement and 10x the force compared to a transducer made with conventional methods. Furthermore, the study illustrated that the response speed of the transducer is optimized by varying the vol% of metal in the electrode. For RuO₂, the optimal loading was approximately 45%. This study shows that carbon nanotubes electrodes have an optimal performance at loadings around 30 vol%, while PANI electrodes are optimized at 95 vol%. Due to low percolation threshold, carbon nanotubes actuators perform better at lower loading than other conducting powders. The addition of nanotubes to the electrode tends to increase both the strain rate and the maximum strain of the hybrid actuator. SWNT/RuO₂ hybrid transducer has a strain rate of 2.5%/sec, and a maximum attainable peak-to-peak strain of 9.38% (+/- 2V). SWNT/PANI hybrid also increased both strain and strain rate but not as significant as with RuO₂. PANI/RuO₂ actuator had an overwhelming back relaxation.

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. Glycerol has a viscosity of about 1000 times that of water at room temperature, and has a greater molecular weight. 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-based IPMCs with glycerol as the solvent, and compare these with the results obtained using water. We also present the response of Nafion-based IPMCs with various cation forms treated with glycerol stimulated with suddenly applied and then sustained (DC) electric potentials in open air. IPMCs with glycerol 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. They may be good actuators when high-speed actuation is not necessary.

A computational model of transport and electromechanical transduction is developed for ionomeric polymer transducers. The transport model is based upon a coupled chemo-electrical multi-field formulation and computes the spatio-temporal charge density profile to an applied potential at the boundaries. The current induced in the polymer is computed using the isothermal transient ionic current associated with surface charge accumulation at the electrodes induced by non-zero charge density within the polymer. The bending moment induced in the polymer is assumed to be a summation of linear and quadratic functions of the charge density. Euler-Bernoulli beam mechanics are used to compute the bending deflection of the transducer to an applied potential. Comparisons with experimental data demonstrate that this model accurately predicts the transition in the electrical current response from primarily capacitive at low frequencies to primarily resistive at high frequencies. Furthermore, the model exhibits good qualitative agreement with measured strain response of the transducer as a function of frequency. The electromechanical coupling model accurately reflects the nonlinear behavior of the material at low-frequency excitation and the relative decrease in the nonlinear response as the excitation frequency is increased. These phenomena are directly related to the asymmetric charge density distribution that develops in the polymer due to anion immobility.

Reliable models are required for the design and optimization of dielectric elastomer actuators. Thereby knowledge of the constitutive behavior of the elastomer is of crucial importance. In this work a pre-strained circular actuator made of a dielectric elastomer is investigated: constitutive models based on uniaxial data are verified by comparing calculation results with experimental observations. An analytical model is derived for the instantaneous response to an activation voltage in the pre-strained circular actuator and a finite element (FE) model is used to simulate the time dependent behavior. Hyperelastic models are used and three strain energy formulations (Yeoh, Ogden and Mooney-Rivlin) are compared in their predictive capabilities. The results of the calculations with the three strain energy forms differ significantly, although all forms were successfully fitted to the same uniaxial data set. Predictions of the actuator behavior based on the Yeoh form agree to a great extent with measurements of the response at different pre-strain levels and activation voltages.

Biomimetic actuators that can produce soft-actuation but large force generation capability are of interest. Nafion, an effective ionomeric material from DuPont, has been shown to produce large deformation under low electric fields (<10V/mm). It is now generally accepted that such a response is caused by a direct electro-osmotic effect due to the existence and mobility of cations and subsequent swelling and de-swelling of the material. In this effort, multi-walled carbon nano-tube (MWNT)/Nafion nano-composites were prepared by casting in order to investigate the effect of MWNT loading in the range of 0 to 7 wt% on electromechanical properties of the MWNT/Nafion nano-composites. The measured elastic modulus and actuation force of the MWNT/Nafion nano-composites are drastically different, showing larger elastic modulus and improved electromechanical coupling, from the one without MWNT, implying that the effective MWNT loading is crucial in developing of high-performance biomimetic actuators. In this work, we also attempted to incorporate an equivalent circuit analysis to address the effect of capacitance and resistance of such MWNT/Nafion nanocomposites that would differ from conventional IPMCs.

In this paper we present experimental measurements as well as a theoretical model for the chemo-electro-mechanical behavior of multi walled (MWNT) carbon nanotubes sheet actuators. Investigations of MWNT paper as an actuator and the analysis of the experimental and theoretical characteristics are special features of the presented work. The influencing parameters of the actuation behavior such as thickness of sheet materials and electrolyte concentration have been investigated. We report the experimentally measured active displacement varying quadratically with the applied electric field and non-linearly with the electrolyte concentration. In the theoretical part, we present a macroscopic actuation model for the global displacement behavior of MWNT materials. Finally, a comparison between the theoretical and the experimental investigations has been conducted.

This work is part of a research project aimed at realising conducting polymer matrices for interfacing with cultured neurons. The polymer matrix has a dual function, one as a medium for recording electrical activity; the other is chemical stimulation through the release of bioactive molecules. In this work we use poly-3-hexylthiophene as a conducting polymer matrix. To test the polymer’s ability to release molecules upon the application of a potential it was doped with glutamate (GA). GA is an important neurotransmitter, and its controlled release can be important in several medical and tissue engineering applications. Diffusional and controlled release of GA from the polymer were assessed. Biocompatibility of the samples was evaluated at each stage using neuroblastoma cell cultures.

A number of architectures have been employed to realize the linear contraction desired of a large scale conducting polymer artificial muscle, with each having merits and problems. Bulk polymer actuators with no supporting electrode structure, coil- or spring-type designs, and thin linear actuators with pliant metal or semi-metallic surface electrodes have all found moderate success. For the purpose of scalable, highly reactive artificial muscles, it is proposed that a design of several thin, well coupled and highly conductive linear actuators will allow rapid charging, ion transport, and actuation. Here we present a novel electrode design utilizing conducting polymers, incorporating recent work on electrode materials, solvents, and electrolyte. The soft supporting electrode is a highly flexible design made from metal foil patterned by lithographic techniques to allow a wide range of deformations and no hindrance to linear motion by the supporting metal electrode. The design is such that the electrode metal maintains excellent electrical coupling with the actuator material throughout the range of motions. The actuator is based on the well-characterized conducting polymer polypyrrole. Other merits of this actuator lie in the inexpensive material design, ease of manufacture, and modular potential to create multi-actuator devices for high stress applications. In order to overcome adhesion and conduction problems exhibited by the low-cost materials, several surface treatments were evaluated. In the course of development, stainless steel samples coated with platinum and titanium oxide were evaluated with an adhesion test. In an attempt to improve overall actuator performance, films were grown on steel and glassy carbon substrates in organic and ionic liquid solvents and actuated in organic and ionic liquid based solutions.

We present the use of electroactive polymer actuators as components of a biolab-on-a-chip, which has potential applications in cell-based sensing. This technology takes full advantage of the properties of polypyrrole actuators as well as the wide range of CMOS sensors that can be created. System integration becomes an important issue when developing real applications of EAP technologies. The requirements of the application and the constraints imposed by the various components must be considered in the context of the whole system, along with any opportunities that present themselves. In this paper, we discuss some of these challenges, including actuator design, the use of complementary actuation techniques, miniaturization, and packaging.

A miniature controllable drug delivery device in which drug release is achieved by actuating polymeric valves is introduced. The valves made in flap configuration are bilayer structures which were fabricated as a thin gold film and an electrochemically deposited polypyrrole (PPy) layer. A drug simulate was stored in a reservoir and the drug release process was accomplished by bending the bilayer flaps with a small electrical potential bias in solution. The detailed fabrication procedures of this controllable drug delivery device are presented.

This paper describes the use of Metal Rubber, which is an electrically conductive, low modulus, and optically transparent free-standing nanocomposite, as an electrode for active polymer devices. With its controllable and tailorable properties [such as modulus (from ~ 1 MPa to 100 MPa), electrical conductivity, sensitivity to flex and strain, thickness, transmission, glass transition, and more], Metal Rubber exhibits massive improvements over traditional stiff electrodes that physically constrain the actuator device motion and thus limit productivity. Metal Rubber shows exceptional potential for use as flexible electrodes for many active polymer applications.

The understanding of the electromechanical response in electroactive polymers (EAPs) will lead the development of new materials or the improvement of existing materials. The recent development of electrostriction based high performance EAPs, such as irradiated P(VDF-TrFE) and dielectric elastomers, makes it more interesting to understand the micro-mechanism that contribute the observed strain response. However, the current widely accepted mechanisms, such as electric field induced phase transition and the Maxwell effect, could not explain some of the observed phenomena. In this paper, the structure and property of recrystallized P(VDF-TrFE) 65/35 copolymer which was previously irradiated with high-energy electrons are reported. It is found that the interfacial layer existing between the crystalline regions and amorphous regions plays an important role. This concept is further extended to explain the pre-stress dependence of the electromechanical response observed in dielectric elastomers. That is, partially ordered regions are induced in the dielectric elastomer by the pre-stress. These partially ordered regions are the key to the observed high electromechanical performance dielectric elastomers.

The preparation and characterization of a type of ECD which was based on a cathodic EC polymer film, Poly [3, 3-dimethyl-3, 4-dihydro-2H-thieno [3, 4-b][1, 4] dioxepine] (PProDOT-Me₂) is reported. A typical device was constructed by sandwiching a gel electrolyte between a PProDOT-Me₂ EC film deposited on Indium Tin oxide (ITO) coated glass and a counter electrode which was also ITO glass coated by a Vanadium oxide (V₂O₅) thin film. The ECD has been characterized. Device contrast ratio, measured as Ε%T, was equal to 60%, and ranged from 2% to 62% between the colored and bleached state measured at 580 nm. A lifetime of over 100,000 cycles between the fully oxidized and fully reduced state has been achieved with only 6% change in the transmittance. The switching speed of a 2.5cm x 2.5cm ECD could be reached in 1 second between the bleached and colored state. The device also has a long open circuit memory. It can remain in the bleached or colored state without being energized for 30 days, and the change in transmittance is less than 6% in colored state. The cyclic voltammetry method was used to detect the moisture content in the gel electrolyte. ECDs of various dimensions were also prepared, 2.5cm x 2.5cm, 7.5cm x 7.5cm, 15cm x 15cm and 30cm x 30cm. The largest scale EC polymer device achieved is 30cm x 30cm. Low sheet resistance ITO glass and a thin-film silver deposition frame were applied to overcome the electric potential drop across the ITO glass surface.

An artificial muscle composed of electroactive nanowires or nanofibers would compare favorably to its biological counterpart in terms of generated force and speed, while devices based on discrete nanoactuators could perform functions similar to those of motor proteins in biological cells. A template synthesis method for producing polypyrrole nanowires is examined. Conductivity and electrochemical properties of resulting nanowires are evaluated, showing promise for future use as nanoactuators. Template synthesis is then extended to allow fabrication of polypyrrole nanowires directly on a planar substrate such as semiconductor wafer, enabling potential integration with semiconductor or microfluidic devices.

An interpenetrating polymer network (IPN) hydrogels composed of polyacrylic acid-co-poly(vinyl sulfonic acid)/polyaniline(PAA-co-PVSA/PANi) was prepared and exhibited electrical sensitive behavior according to applied electric stimuli. It is studied that hydrogels caused reversible volume change due to the switched electric stimuli. The positive electrode showed contractile behavior and the negative electrode showed expansion. The behavior of the hydrogels induced by electric voltage and moving counterions in solution show rapidly increasing variation (contraction and expansion) with time. As of increasing voltage have been increased the variation velocity of the volume change of the hydrogels. The rate of change of the volume of the hydrogel is related to the applied voltage. The hydrogels showed the behavior with applied electric stimuli, which is very important behavior for application as an actuator.

Since the field of Electroactive Polymers (EAP) actuators is fairly new there are no standard testing processes for such intelligent materials. This drawback can seriously limit the scope of application of EAP actuators, since the targeted industrial sectors (aerospace, biomedical...) demand high reliability and product assurance. As a first iteration two elements are required to define a test standard for an EAP actuator: a Unit Tester, and a Component Specification. In this paper a EAP Unit Tester architecture is presented along with the required classification of measurements to be included in the EAP actuator Component Specification. The proposed EAP Unit Tester allows on-line monitoring and recording of the following properties of the specimen under test: large deformation, small tip displacement, temperature at the electrodes, weight of the specimen, voltage and current driven into the EAP, load being applied to the actuator, output voltage of the EAP in sensing operation and mode of operation (structure/sensor/actuator/smart). The measurements are taken simultaneously, in real-time. The EAP Unit Tester includes a friendly Graphical User Interface. It uses embedded Excel tools to visualize data. In addition, real-time connectivity with MATLAB allows an easy testing of control algorithms. A novel methodology to measure the properties of EAP specimens versus a variable load is also presented. To this purpose a force signals generator in the range of mN was developed. The device is based on a DC mini-motor. It generates an opposing force to the movement of the EAP actuator. Since the device constantly opposes the EAP actuator movement it has been named Digital Force Generator (DFG). The DFG design allows simultaneous length and velocity measuring versus different load signals. By including such a device in the EAP Unit Tester the most suitable application for the specimen under test can be easily identified (vibration damper, large deformation actuator, large force actuator, fast actuator...).

Among ElectroActive Polymers (EAPs) the dielectric elastomer actuator is regarded as one of the most practically applicable in the near future. So far, its effect on the actuation phenomena has not been discussed sufficiently, although its strong dependency on prestrain is a significant drawback as an actuator. Recent observations clarifies that prestrain has the following pros and cons: prestrain plays an important role in generating large strain, whereas it rather contributes to the reduction of the strain. Prestrain provides the advantages of improving the response speed, increase of the breakdown voltage, and removing the boundary constraint caused by the inactive actuation area of the actuator. On the contrary, the elastic forces by prestrain makes the deformation smaller and the induced stress relaxation is severely detrimental as an actuator. Also, the permittivity decreases as prestrain goes up, which adds an adverse effect because the strain is proportional to the permittivity. In the present work, a comprehensive study on the effects of prestrain is performed. The key parameters affecting the overall performances are extracted and it is experimentally validated how they work on the actuation performance.

Polypyrrole/gold bilayer microactuators are being developed in our laboratory for biomedical applications such as microvalves. To fully open and close the valves, the bilayer hinges must be able to rotate between 0° and 180° within a few seconds against external forces. The layer thicknesses and hinge lengths must therefore be properly designed for the application. However, existing models fail to predict the correct behavior of microfabricated PPy/Au bilayer microactuators. Therefore, additional experimental data are needed to correctly forecast their performance. Bilayer actuators were fabricated with ranges of PPy thicknesses and hinge lengths. Bending angles were recorded through a stereomicroscope in the fully oxidized and reduced states. Isometric forces exerted by the hinges were measured with a force transducer, the output of which was read by a potentiostat and correlated with the applied potentials.

This paper presents quasi-static and dynamic results for dielectric elastomer actuators subject to a uniform mechanical pressure and an applied voltage. The numerical quasi-static results are compared to experimental data for actuators made from 3M VHB material. It is shown that the theoretical model for the active inflation of hyperelastic membranes is sensitive to the explicit form of the assumed strain energy function. The optimal constants of 2-Term and 3-Term Ogden models are determined from uniaxial and biaxial stress experimental data. Using the best overall values for the material constants, the electro-elastic model is used to predict the voltage-dependent behavior for the inflation of dielectric elastomer actuators. The correlation between the numerical results and the experimental data is good. In previous work, inertial effects have been neglected and a quasi-static approach employed. The method is presently expanded to include the dynamic response of dielectric elastomer actuators. In this case inertial effects become increasingly important as different equilibria modes are obtained during dynamic operation. The results show the potential for voltage-controlled bifurcations during the inflation of spherical dielectric elastomer actuators.

Conducting polymer actuators are being investigated for a number of applications. Both linear contracting/expanding and bending type actuators can be constructed that utilise the redox-induced volume changes in the conducting polymer. Improved actuator performance has been demonstrated by modifications to our helix-tube design. The pitch of the helix and bundling the actuators have increased the strain and force generated. Short-term improvements to the strain were also generated using new dopants, but cycle life was poor in this case. Further studies on the mechanism of actuation have continued to focus attention on the influence of the elastic modulus on the actuation strain. Surprising results have been obtained from polythiophene actuators that show an increased strain and increased work-per-cycle with an increasing applied load in isotonic operation. The observations were explained by an increase in modulus during the contraction cycle of the actuation. Preliminary studies show how the change in modulus can be conveniently measured using an in situ mechanical technique.

Graphite intercalation compounds are a class of materials systems formed as ions diffuse into a host graphite structure. The volume expansion associated with this process has been shown to be capable of performing work up to 3.8 MJ/m³. To evaluate GICs for solid state actuation, this study explores some factors affecting the rate at which the volume expansion occurs. Given that diffusion length has an exponential effect on rate, we tested a graphite paper comprised of 7-micron diameter PAN fibers. We found that the paper had ultimate strain and loading properties comparable to HOPG. The paper was cycled under various loads and temperatures to examine the strain rate and repeatability of the material. Testing showed a strong correlation between rate and temperature, while pressure had relatively little effect.

Based on the concept of Mazzone et al., we have designed a novel system to be used simultaneously as an input and output device for designing, presenting, or recognizing objects in three-dimensional space. Unlike state of the art stereoscopic display technologies that generate a virtual image of a three-dimensional object, the proposed system, a “digital clay” like device, physically imitates the desired object. The object can not only be touched and explored intuitively but also deform itself physically. In order to succeed in developing such a deformable structure, self-actuating ionic polymer-metal composite (IPMC) materials are proposed. IPMC is a type of electro active polymer (EAP) and has recently been drawing much attention. It has high force to weight ratio and shape flexibility, making it ideal for robotic applications. This paper introduces the first steps and results in the attempt of developing such a structure. A strip consisting of four actuators arranged in line was fabricated and evaluated, showing promising capabilities in deforming two-dimensionally. A simple model to simulate the deformation of an IPMC actuator using finite element methods (FEM) is also proposed and compared with the experimental results. The model can easily be implemented into computer aided engineering (CAE) software. This will expand the application possibilities of IPMCs. Furthermore, a novel method for creating multiple actuators on one membrane with a laser machining tool is introduced.

The human attention system is based on the capability of the eye of focusing and tracking. These actions are performed by the eyeball muscle system, as a consequence of visual stimuli. The F.A.C.E. (Facial Automaton for Conveying Emotions) project at our lab concerns the development of an android face endowed with dynamic expressiveness and artificial vision. Aimed at realising an artificial attention system for such an automaton, we present here a study for the development of pseudo-muscular polymer actuators for its eyeballs. The system is based on the mimicry of the muscular architecture of the human eye. In particular, linear actuators made of dielectric elastomers have been designed to replicate actions exerted by the main ocular muscles.

Current EAP actuator sheets or fibers perform reasonable well in the centimeter and mN range, but are not practical for larger force and deformation requirements. In order to make EAP actuators technology scalable a design methodology for polymer actuators is required. Design variables, optimization formulas and a general architecture are required, as it is usual in electromagnetic or hydraulic actuator design. This will allow the development of large EAP actuators specifically designed for a particular application. It will also help to enhance the EAP material final performance. This approach is not new, it is found in Nature. Skeletal muscle architecture has a profound influence on muscle force-generating properties and functionality. Based on existing literature on skeletal muscle biomechanics, the Nature design philosophy is inferred. Formulas and curves employed by Nature in the design of muscles are presented. Design units such as fiber, tendon, aponeurosis, and motor unit are compared with the equivalent design units to be taken into account in the design of EAP actuators. Finally a complete design methodology for the design of actuators based on multiple EAP fiber is proposed. In addition, the procedure gives an idea of the required parameters that must be clearly modeled and characterized at EAP material level.

Inflatable membrane reflectors are attractive for deployable, large aperture, lightweight optical and microwave systems in micro-gravity space environment. However, any fabrication flaw or temperature variation may results in significant aberration of the surface. Even for a perfectly fabricated inflatable membrane mirror with uniform thickness, theory shows it will form a Hencky curve surface rather than the desired parabolic or spherical surface. Precision control of the surface shape of extremely flexible membrane structures is a critical challenge for the success of this technology. Wirelessly controllable inflated reflectors made of electroactive polymers (EAP) are proposed in this paper. A finite element model was configured to predict the behavior of the inflatable EAP membranes under pre-strains, pressures and distributed electric charges on the surface. To explore the controllability of the inflatable EAP reflectors, an iteration algorithm was developed to find the required applied electric field distribution for correcting the aberration of a Hencky curve to the desired parabolic curve. The correction capability of the reflectors with available EAP materials was explored numerically and is presented in this paper.

The combination of electrical and hygroscopic nature of conducting polymers provided an insight into the development of a new class of electro-driven actuators or artificial muscle systems that worked in ambient air. The electrochemically synthesized polypyrrole films underwent quick and intensive bending in air as a result of a dimensional change due to the sorption of water vapor from one side of the film. Furthermore, an application of electric field caused contraction of the film in air. The dimensional change of the polypyrrole film under the electric field was expressed by two processes: one was the contraction due to the desorption of water vapor and the other was the thermal expansion of polymer chains both caused by Joule heating. The degree of contraction attained 1.2% under 2 V, where the initial speeds of contraction and elongation of the film were 4.4 and 1.8%/min, respectively. Under loading conditions, the power density increased with increasing load and the value attained 0.78 W/kg (6 μW) under the load of 60 g (4 MPa). Under isometric conditions, when dc 2 V is applied to the film under the thermostatic conditions (25°C, 50% RH), the film generated contractile stress repeatedly in response to the applied voltage. The stress reached 6.1 MPa, which was 4 orders of magnitude larger than its own weight and nearly 20 times that of skeletal muscle in animals. The generated stress under 2 V increased to 8.9 MPa upon stretching the film by 1%, which could be associated with the Young's modulus of the film rose due to the desorption of water vapor that plasticized polymer chains. The work capacity of the film increased as the applied voltage became higher and reached 48.2 kJ/m³ at 3 V, while the energy efficiency, defined as the ratio of work capacity to the electric energy, was the order of 10^-3%.

Ionic Polymer-Metal Composites (IPMCs) are soft actuators, generally referred to as "artificial muscles" which are made out of high polymer gel films of perfluorosulfonic acid chemically plated with gold. These composites bend by applying a low voltage between electrodes on both sides. The actuator is soft and works in water. It bends silently, responds quickly and has a long life. In our previous work, snake-like swimming robots and a 3DOF 2-D manipulator have been developed. In this research we have investigated the bending response of an IPMC artificial muscle in high-pressure water environments, with future applications in deep-sea actuators and robots. The artificial muscles have an advantage over electric motors because they do not need sealing from water, which is difficult in high-pressure water environments. Bending responses of artificial muscles were measured at three different pressure levels, 30MPa, 70MPa and 100MPa. The maximum pressure, 100MPa is the same pressure as the deepest ocean on earth, (10,000m.) From experiments, there was found to be almost no difference with that at normal water pressure of 1Pa. We present detailed results of responses of these artificial muscles including current responses and videos of bending motion with respect to combinations of several different input voltages, frequencies and wave patterns.

The transport of charged species, including both polarons/bipolarons and charge-compensating ions, occurs when conjugated polymers switch between oxidized and reduced states. However, physics-based models of the charge transport processes have not yet been developed. Previously, we presented an electrochromic device that made the path for ion transport much longer than that for electrons, ensuring that ion transport was the rate-limiting step so that the constitutive equation for ion transport could be formulated. Ion concentration profiles and velocities could be tracked by color changes. In this paper, we present the correlation between ion transport and volume change, measured in this device using a mechanical profilometer to scan height profiles during electrochemical reduction. In addition, the effects of electrolyte concentration, electrolyte temperature, film thickness, and ion barrier stiffness on ion transport velocities are explored.

This paper presents the application of polypyrrole(PPy) as a medium material for the release and the detection of a neurotransmitter, i.e. epinephrine, using its electrically stimulated ion exchange property. Neuron signals are transmitted in a synapse, which is composed of releasing and detecting parts of neurotransmitters. PPy was electrochemically polymerized with NaDBS as dopants on Au electrode and then was incorporated with epinephrine by cation exchange process. The incorporated epinephrine was released by applying a controlled voltage and the released amount of epinephrine was determined using an ultraviolet (UV) spectrometry. Experimental results of the releasing part show that the released amount of epinephrine depended not only on the thickness and the size of PPy film but also on the releasing time. Spontaneously diffused epinephrine amount was measured to be only 18% of the voltage driven release amount. The absorbance change of epinephrine due to the applied potential during releasing process is negligible compared with that of the released epinephrine. Overoxidized PPy(OxPPy) for the detecting part shows a good cation permselectivity for the detection of epinephrine and the current is also higher than that at the Au electrode in the same concentration of the epinephrine. The current level is different with dopants with which the OxPPy film is polymerized and the sensitivity of the OxPPy electrode depends on the thickness of PPy film.

The electromechanical behavior of ionic polymer-metal composite (IPMC) based on a chitosan/polyaniline (CP) interpenetrating polymer network (IPN) is influenced by the internal structure of the CP ion exchange membrane. The freeze-drying method was found to be successful in improving the IPMC electromechanical properties. The effect of various pH (1, 4, 7, 10) on the equilibrium water content (EWC) and electromechanical response were investigated. From swelling ratio and differential scanning calorimetry (DSC) measurements, the freeze-dried membranes exhibited a higher swelling ratio and increased free water content. Electron beam lithography (EBL) was used to manufacture the IPMC metal electrodes. Experiments on the bending of IPMC samples in a direct current electric field showed that the freeze-dried samples had a faster and larger bending motion than non-freeze-dried samples.

In the present investigations, we have fabricated the electromechanical actuators using conducting Polyaniline and Cellophane paper. The actuation behaviour of two types of paper actuators namely bi-layer and tri-layer in air medium are presented in this paper. The electro generation of polyaniline was carried out in propylene carbonate medium in the presence of dichloro acetic acid (DCA). The displacement in tri-layer devices, are more than that of bi-layer counter parts. The explanation towards this type of actuation behavior is given. Actuation behavioral studies were mainly focused on the effect of various dopant ions namely Cl^-, ClO₄^-, BF₄^- and PF₆^-. The effect of varying film thickness and change in relative humidity are also addressed in this communication. The possible working mechanism has been discussed.

This paper presents the design and analysis of an IPMC (Ionic Polymer-Metal Composite) driven micropump. It should be noted that IPMC is a promising material candidate for micropump applications since it can be operated with low input voltages and can produce large stroke volumes along with controllable flow rates. Moreover, the micropump manufacturing process with IPMC is convenient. It is anticipated that the manufacturing cost of the IPMC micropump is competitive when compared to other competing technologies. In order to design an effective IPMC diaphragm that functions as an actuating motor for a micropump, a finite element analysis was utilized to optimize the shape of IPMC diaphragm and estimate stroke volume through several parametric studies. In addition, effect of the pump chamber's pressure on the stroke volume was numerically investigated. Appropriate inlet and outlet nozzle/diffusers for the micropump were also chosen. Based on the selected geometry of nozzle/diffusers and the estimated stroke volume, flow rate of the IPMC micropump was predicted.

Conjugated polymers are nowadays used in two different types of device. On the one hand, they act as electronically active semiconducting/conducting materials in organic electronic devices. On the other hand, one exploits them as electromechanically active materials since it has been observed that they can experience huge macroscopic strains upon electrochemical doping. We investigated the combination of these two effects by measuring the electromechanical behavior of typical polymeric electronic devices like rectifying (and/or light emitting) diodes. In the case of a poly(para phenylene vinylene) (MDMO-PPV) based diodes, we observed two types of electromechanical actuation. In the forward direction, a significant current (up to several mA/cm²) is flowing. Joule heating induces a thermo-electrostrictive bending of the device substrate. In the reverse direction, the diode behaves like a capacitor. Therefore the strains are induced by Maxwell forces. For poly(3-hexyl-thiophene) (P3HT) based diodes, displacement versus voltage in the reverse direction revealed a power law with an exponent of 1.5. This surprising result can be modeled by Coulombic attraction of the doped impurities present in the depletion zone and the charges present in the metal at the interface.

The aim of the presentation is to propose an alternative model of mammalian skeletal muscle function, which reflects the simplicity of nature and can be applied in engineering. Van der Waals attractive and repulsive electrostatic forces are assumed to control the design of internal structures and functions of contractile units of the muscles - sarcomere. The role of myosin heads is crucial for the higher order formation. The model of the myosin head lattice is the working model for the sarcomere contraction interpretation. The contraction is interpreted as a calcium induced phase transition of the lattice, which results in relative actin-myosin sliding and/or force generation. The model should provide the engineering science with a simple analogy to technical actuators of high performance.

Platinum has been used as an effective electrode material for Ionic Polymer-Metal Composites (IPMCs) actuators. Realizing that platinum is a strong catalyst for many electrochemical reactions, the platinum surface allows many components to be adsorbed. Therefore, under imposed electrical potentials, platinum electrodes used for IPMCs introduce complex electrochemical phenomena on the platinum/electrolyte interface. This study points out that the electrochemistry of platinum is important in understanding the fundamental actuation mechanism of IPMCs. Electrochemical analyses, including voltammetry, AC impedance, and capacitance measurements, on IPMC samples were carried out in aqueous solutions. The experiments revealed the complex electrochemical behavior of IPMCs, including inductive behavior in higher frequencies than had originally been expected. The Mott-Schottky experiment was also performed to investigate the charge transfer and the possible adsorption mechanism associated with IPMCs. Seemingly, the equivalent circuit of IPMC follows a RLC circuit.

Inkjet printing of conductive polymers has been successfully done before, but never before has the process been used to electrode piezoelectric polymers as we have done. Piezoelectric polymers such as poly(vinylidene fluoride) (PVDF) rely on high electric fields to take advantage of their mechanical output. The electrodes need to be securely attached to the PVDF and are traditionally made of metal. The rigidity of metal significantly reduces the performance of devices made with PVDF. We have applied much more flexible conductive polymer PEDOT/PSS (3,4-polyethylenedioxythiophene-polystyrenesulfonate) electrodes on PVDF using an HP 5850 inkjet printer. The inkjet printing method is simple and cost effective. It deposits the PEDOT/PSS in uniform coatings and allows for the creation of any desired patterns on the surface of the PVDF. We have also constructed bimorphs and actuators using PVDF with the new electrodes.

Piezoelectric polymer sheets are presently supplied with metallic electrodes that have thickness comparable to the polymer sheet, so the electrode stiffness considerably degrades the performance of actuators make of such sheets. Conducting polymers, such as PEDOT/PSS, may be a good substitute for metal as an electroding material given the high flexibility of polymers. The lower conductivity of polymers, though, forces consideration of the voltage distribution in the electrodes, which will not be uniform due to amplitude decay and phase lag. We have developed a simple analytical solution for the voltage distribution, and have found an excellent agreement with experimental measurements from piezoelectric bimorphs that have been constructed in our laboratory.

This paper focuses on the mechanical and electrical characteristics of electro-active paper (EAPap) as a bio-inspired actuator and the potential use of these actuators in some specific applications. EAPap can undergo a large bending displacement at a relatively low voltage under low power consumption in dry conditions. EAPap samples as tested are made from chemically treated cellulose paper. When an electrical field is applied to the electrodes, a “bending displacement” is produced as the material tends to deform into a constant curvature coil. However, the EAPap is a complex anisotropic material, which has not been extensively characterized and additional basic and design testing is required before developing application devices from EAPap. Mechanical properties of selected EAPap materials along three material axes are addressed. EAPap material exhibits two distinct elastic constants connected by a bifurcation point along the stress strain diagram. The initial Young’s modulus of EAPap is in the range of 5-8GPa, -- quite high compared to other polymer materials. The thermo-mechanical analysis of EAPap is investigated to determine such factors as the degree of dimensional change due to dehydration and the maximum use temperature. Fatigue test identifies critical properties of this under-analyzed class of materials to provide a measure of its fatigue capabilities. The Electrical impedance analysis and dielectric property measurement with frequency are also important information that allows us to characterize the electrical behavior of EAPap. The performance of Eapap is measured in terms of tip displacement, blocking force and electrical power consumption. Through this series of tests, better understanding of the EAPap materials is obtained to researchers and designers interested in smart materials and EAP areas.

The essential motion of the ionic polymer-metal composite (IPMC) is bending, therefore some mechanisms are expected to transform from the bending to other required motions. Motivated by the motion of a spiral spring, we discovered that the bending of the ionic polymer could be directly transformed to the limited angle rotation. We introduce the model of the rotary actuator, which consists of mechanical, electrical and electromechanical dynamics. The motion of the rotary actuator is demonstrated in the experiment. The stationary properties are measured and the parameters of the dynamical model are identified, which are also validated by experiments.

On purpose to overcome the limit of conventional ionic polymer-metal composites (IPMC) using the commercial ionic membranes, novel IPMCs with radiation-grafted ion-exchange membranes were prepared. Poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-co-HFP) and poly(ethylene-co-tetrafluoroethylene) (ETFE) were radiation-grafted with styrene, and then sulfonated. The properties of the membranes were modulated by controlling the amount of polystyrene sulfonic acid (PSSA) groups in the membranes. The amount of PSSA groups were tuned by controlling the total absorbed dose of γ-ray. The membranes were characterized by measuring the water-uptake, the ion-exchange capacity, and the ion conductivity. The performance of the IPMCs using these membranes were analyzed with laser displacement meter. They exhibited much larger bending displacement in comparison with Nafion-based IPMC. With increasing the amount of PSSA groups, the maximum displacement and the bending speed were remarkably increased. The results made sure that the property of ion-exchange membrane was the key element affecting the actuation performance of IPMC.

Improving the lifetime of conjugated polymer-based devices that undergo repeated cyclic electrical stimulation, such as actuators, is important for commercialization. In general, conjugated polymers are contacted by metal electrodes; strain from volume change can cause the polymers to delaminate, which slowly deteriorates performance or results in sudden device failure. In this paper, we used polypyrrole on gold to investigate methods for improving adhesion. Gold electrode surfaces were roughened through electroplating, and the adhesion of polypyrrole deposited on these surfaces was tested upon extended electrochemical cycling. Delamination was quantified using a tape test and followed versus cycle number until the polypyrrole was removed or was no longer electroactive. Untreated control surfaces were also monitored. The most effective method for improving adhesion was a 1 μm thick layer of electroplated Au, which extending the lifetime of the interface beyond the 50,000 cycle lifetime of PPy in aqueous solutions.