Ionic polymers are a recently discovered class of active materials that exhibit bidirectional electromechanical coupling. They are `soft' transducers that perform best when the mechanical deformation involves bending of the transducer. Ionic polymers are low voltage actuators -- they only require inputs on the order of 1V and cannot tolerate voltages above approximately 10V. The mechanisms responsible for the electromechanical coupling are not yet fully understood, and reports of the capabilities and limitations of ionic polymer transducers vary widely. In addition, suitable engineering models have not been developed. This document presents a dynamic model for ionic polymer transducers that is based on a pair of symmetric, linearly coupled equations with frequency dependent coefficients. The model is presented in the form of an equivalent circuit, employing an ideal transformer with a frequency dependent turns ratio to represent the electromechanical coupling. The circuit elements have clear physical interpretations, and expressions relating them to transducer dimensions and material properties are derived herein. The material parameters required for the model: modulus, density, electrical properties, and electromechanical coupling term are determined experimentally. The model is then validated by comparing simulated and experimental responses, and the agreement is good. Further validation is presented in the form of extensive experiments that confirm the predicted changes in transducer performance as transducer dimensions are varied. In addition, reciprocity between mechanical and electrical domains is demonstrated. This reciprocity is predicted by the model, and is a direct result of the symmetry in the equations on which the model is based. The capabilities of ionic polymer sensors and actuators, when used in the cantilevered bender configuration, are discussed and compared to piezoceramic and piezo polymer cantilevered benders. The energy density of all three actuators are within an order of magnitude of one another, with peak values of approximately 10J/m^3 and 4mJ/kg for ionic polymer actuators actuated with a 1.2V signal. Ionic polymer sensors compare favorably to piezoelectric sensors. Their charge sensitivity is approximately 320E-6C/m for a 0.2 x 5 x 17mm cantilevered bender, two orders of magnitude greater than a piezo polymer sensor with identical dimensions. This work is concluded with a demonstration of feedback control of a device powered by ionic polymer actuators. An ionic polymer sensor was used to provide the displacement feedback signal. This experiment is the first demonstration of feedback control using an ionic polymer sensor. Compensator design was performed using the model developed in the first chapter of this document, and experiments confirmed that implementation of the control scheme improved, in a narrow frequency range, the system's ability to track sinusoidal inputs. / Ph. D.

Ionomeric polymer metal composites can be used as transducers characterized by high strain and low force. They are created by bonding a thin conductive electrode to the surfaces of an ionomeric polymer. Much of the work in the past has focused on using a voltage across the thickness of the polymer to produce mechanical motion. That work has often demonstrated that the mechanism of transduction within the polymer was associated with the accumulation of charge in the polymer. This thesis will discuss the use of current as a means to better control the accumulation of charge. Better control of the charge will provide more reliable control of the mechanical motion of the polymer. The data presented in this thesis demonstrates that the response of an ionomeric polymer to a current input is repeatable. The repeatability is a desirable result; however, using current to actuate the polymers also produces back relaxation in the response. Examination of the back relaxation reveals a low frequency non-linearity. The nonlinearity is quantified by the fact that the gain associated with the back relaxation does not increase linearly with an increase in input current. There is also a change in the response at certain voltage thresholds. For example, when the voltage across the polymer exceeds 3 V, the rate of back relaxation increases. The repeatability of the response will aid in implementing reliable control of the polymer, but the non-linearities in the back relaxation will provide a considerable challenge in developing a model to be used in control. / Master of Science

Ionic polymer transducers (IPTs) are soft sensors and actuators which operate through a coupling of micro-scale chemical, electrical, and mechanical mechanisms. The use of ionic liquid as solvent for an IPT has been shown to dramatically increase transducer lifetime in free-air use, while also allowing for higher applied voltages without electrolysis. This work aims to further the understanding of the dominant mechanisms of IPT actuation and how these are affected when an ionic liquid is used as solvent. A micromechanical model of IPT actuation is developed following a previous approach given by Nemat-Nasser, and the dominant relationships in actuation are demonstrated through an analysis of electrostatic cluster interactions. The elastic modulus of Nafion as a function of ionic liquid uptake is measured using uniaxial tension tests and modeled in a micromechanical framework, showing an excellent fit to the data. Charge transport is modeled by considering both the cation and anion of the ionic liquid as mobile charge carriers, a phenomenon which is unique to ionic liquid IPTs as compared to their water-based counterparts. Numerical simulations are performed using the finite element method, and a modified theory of ion transport is discussed which can be extended to accurately describe electrochemical migration of ionic liquid ions at higher applied voltages. The results presented here demonstrate the dominant mechanisms of IPT actuation and identify those unique to ionic liquid IPTs, giving directions for future research and transducer development. / Master of Science

No description available.

Ionic polymer membranes are commonly used in fuel cell power generation, water electrolysis and desalinization, chlorine generation, and other niche applications. Since the early 1990s ionic polymer membranes have also shown promise as distributed electromechanical actuators and sensors. The cost of these materials is very high because of the expensive noble metals that are used as the electrodes in these applications, however. Currently, high cost of these devices has prevented them from experiencing widespread use. The goal of the current research project is to study new methods of plating metal electrodes onto ionic polymer membranes in order to reduce the cost of these materials and open the door for potential industrial, aerospace, and biomedical applications. At this time ionic polymer actuators are only made using gold or platinum as the electrode in a lengthy and labor-intensive process. The current research focuses on using less costly metals and revising the metal deposition process. Several new methods allowing for faster deposition of metals onto ionic polymer membranes are developed and evaluated including sputter-coating, electroless plating, and impregnation/reduction. Using these methods, metal electrodes have been plated onto ionic polymer membranes in processes resulting in a purely surface deposition and in processes resulting in interpenetration of the metal into the polymer. This work shows that electromechanical coupling is present with all of these processes, although results indicate that interpenetration of the electrode is important for good adhesion of the metal and good performance of the transducers. Also studied were different metals; X-ray photoelectron spectroscopy (XPS) testing shows that the use of non-noble metals as the electrodes results in oxidation of the metal and corresponding loss of performance in the actuator. Noble metals are found to not experience the oxidation problem. Further work shows that non-noble metals can be effectively employed as electrodes if alloyed with noble metals by using a co-reduction technique. Also studied is the use of protective coatings of noble metal to stabilize the non-noble metal electrodes. Using these approaches, a new plating method is developed and the stability of the electrodes made using this method is studied. These results indicate that samples made using this new process may be actauted continuously for over 150,000 cycles with very little degredation in their performance. Using this new plating method, ionic polymer membrane transducers can be made in less than five hours. Characterization of these new devices shows that they have a mass energy density of 4-20 mJ/kg in the cantilevered mode. This compares well with a baseline material, which is found to have a mass energy density of 3-12 mJ/kg. Composition and morphology of the electrodes made using the new method are investigated using scanning electron microscopy (SEM) and the density and tensile modulus are measured. The density of the new material is found to be approximately 2100 kg/m^3 as compared to about 3200 kg/m^3 for the baseline material. Also, the tensile elastic modulus of the new material is about 55 MPa, or roughly one fourth of the tensile modulus of the baseline material (about 190 MPa). These results indicate that the new materials contain much less noble metal in the electrodes than the baseline material. The sensitivity of these devices has also been quantified and compared to the baseline. Results indicate that the new materials have a sensitivity on the order of 0.1-0.3 uA/mm/s whereas similarly sized samples of the baseline material typically have sensitivities on the order of 0.2-0.8 uA/mm/s. The most important conclusion of this work is that ionic polymer membrane transducers can be made using much less noble metal in the electrode than previously believed without sacrificing the performance of these devices. / Master of Science

Ionomeric polymer transducers (IPTs) are an exciting new class of smart materials that can serve a dual purpose in engineering or biomedical applications as sensors or actuators. Most commonly they are used for mechanical actuation, as they have the ability to generate large bending strains and moderate stress under low applied voltages. Although the actuation capabilities of IPTs have been extensively studied, the sensing capabilities of these transducers have yet to be fully explored. The work presented herein aims to investigate the fundamental sensing characteristics of these transducers and apply the acquired knowledge toward the development of an electronic stethoscope for digital auscultation. The sensors were characterized both geometrically and electrically to determine their effectiveness in resolving a signal from sub 1 Hz to 2 kHz. Impedance spectroscopy was used to interrogate the sensing mechanism. Following the characterization of the transducer, a bio–acoustic sensor was designed and fabricated. The bio–acoustic sensor was placed over the carotid artery to resolve the arterial pressure waveform in situ and on the thorax to measure the S1 and S2 sounds generated by the heart. The temporal response and spectral content was compared with previously known data and a commercially available electronic stethoscope to prove the acquisition of cardiovascular sounds. / Master of Science

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

Ionic polymer transducers comprise a class of active material that exhibit interesting chemoelectromechanical coupling capabilities. With the ability to convert energy between chemical, electrical and mechanical domains, these materials offer potential for use in numerous engineering applications. The research presented in this dissertation focuses primarily on the electromechanical coupling that exists within these ionic polymer materials. When plated with a conductive surface electrode, these ionomeric membranes function effectively as either sensors or actuators. Mechanically compliant, these transducers demonstrate large strain, but limited force, capabilites while operating at low excitation voltages. The objective of this research is to improve understanding of the transduction properties inherent in the ionic polymer. Most of the existing work in this area has focused on the actuation response, therefore the focus of this research is on providing a better understanding of the sensing and impedance responses of the ionic polymer transducer. Using transport theory as the basis, a set of analytical models are developed to characterize the charge motion that develops within an ionomer when subject to either mechanical or electrical loading. These models characterize the internal potential and charge density responses of the membrane, as well as the expected surface current that would be measured as the result of external loading. In addition to the analytical work, numerous experimental characterizations of the membrane are also presented. The ionic polymer's actuation, sensing and impedance responses are each considered as a function of the counterion and solvent type present within the ionic polymer. These studies demonstrate the importance of the ionomer's impedance response in understanding the electromechanical capabilites of an ionic polymer transducer. Most sample-to-sample variation can be attributed to the voltage to current conversion that occurs within the ionic polymer. By relating these experimental results to the analytical models, it is possible to characterize these changes in performance in terms of the effective diffusion and permittivity parameters of the transducer. A final series of experiments are also considered to determine the effectiveness of the model in predicting the impedance response as a function of temperature, solvent viscosity and preloading of the membrane. / Ph. D.

Ionomeric polymer transducers consist of an ion-exchange membrane plated with conductive metal layers on its outer surfaces. Such materials are known to exhibit electromechanical coupling under the application of electric fields and imposed deformation (Oguro et al., 1992; Shahinpoor et al., 1998). Compared to other types of electromechanical transducers, such as piezoelectric materials, ionomeric transducers have the advantage of high-strain output (> 9% is possible), low-voltage operation (typically less than 5 V), and high sensitivity in the charge-sensing mode. A series of experiments on actuators with various ionic polymers such as Nafion and novel poly(Arylene ether disulphonate) systems (BPS and PATS) and electrode composition demonstrated the existence of a linear correlation between the strain response and the capacitance of the material. This correlation was shown to be independent of the polymer composition and the plating parameters. Due to the fact that the low-frequency capacitance of an ionomer is strongly related to charge accumulation at the electrodes, this correlation suggests a strong relationship between the surface charge accumulation and the mechanical deformation in ionomeric actuators. The strain response of water-hydrated transducers varies from 50 μstrain/V to 750 μstrain/V at 1Hz while the strain-to-charge response is between 9 ^μstrain_{^c_m²} and 15 ^μstrain_{^c_m²}. This contribution suggests a strong correlation between cationic motion and the strain in the polymer at the ionomer-conductor interface. A novel fabrication technique for ionic polymer transducers was developed for this dissertation for the purpose of quantifying the relationship between electrode composition and transducer performance. It consists of mixing an ionic polymer dispersion (or solution) with a fine conducting powder and attaching it to the membrane as an electrode. The Direct Assembly Process (DAP) allows the use of any type of ionomer, diluent, conducting powder, and counter ion in the transducer, and permits the exploration of any novel polymeric design. Several conducting powders have been incorporated in the electrode including single-walled carbon nanotubes (SWNT), polyaniline (PANI) powders, high surface area RuO2, and carbon black electrodes. The DAP provided the tool which enabled us to study the effect of electrode architecture on performance of ionic polymer transducers. The DAP allows the variation in the electrode architecture which enabled us to fabricate dry transducers with 50x better performance compared to transducers made using the state of the art impregnation-reduction technique. DAP fabricated transducers achieved a strain of 9.4% at a strain rate of 1%/s. Each electrode material had an optimal concentration in the electrode. For RuO2, the optimal loading was approximately 45% by volume. This study also demonstrated that carbon nanotubes electrodes have an optimal performance at loadings around 30 vol%, while PANI electrodes are optimized at 95 vol%. Extensional actuation in ionic polymer transducers was first reported and characterized in this dissertation. An electromechanical coupling model presented by Leo et al. (2005) defined the strain in the active areas as a function of the charge. This model assumed a linear and a quadratic term that produces a nonlinear response for a sine wave actuation input. The quadratic term in the strain generates a zero net bending moment for ionic polymer transducers with symmetric electrodes, while the linear term is canceled in extensional actuation for symmetric electrodes. Experimental results demonstrated strains on the order of 110 μstrain in the thickness direction compared to 1700 μstrain peak to peak on the external fibers for the same transducer, could be achieved when it is allowed to bend under +/-2V potential at 0.5 Hz. Extensional and bending actuation in ionic polymer transducers were explained using a bimorph active area model. Several experiments were performed to compare the bending actuation with the extensional actuation capability. The active area in the model was assumed to be the high surface area electrode. Electric double layer theory states that ions accumulate in a thin boundary layer close to the metal-polymer interface. Since the metal powders are evenly dispersed in the electrode area of the transducer, this area is expected to actuate evenly upon voltage application. This active area model emphasizes the importance the boundary layer on the conductor-ionomer interfacial area. Computing model parameters based on experimental results demonstrated that the active areas model collapses the bending data from a maximum variation of 200% for the strain per charge, to less than 68% for the model linear term. Furthermore, the model successfully predicted bending response from parameters computed using thickness experimental results. The prediction was particularly precise in estimating the trends of non-linearity as a function of the amount of asymmetry between the two electrodes. / Ph. D.

Ionic polymer transducers are a class of electroactive polymer materials that exhibit coupling between the electrical, chemical, and mechanical domains. With the ability for use as both sensors and actuators, these compliant, light weight, low voltage materials have the potential to benefit diverse application areas. Since the transduction properties of these materials were recently discovered, full understanding of their dynamic characteristics has not yet been achieved. This research has the goal of better understanding the actuation response of ionic polymers. A specific emphasis has been placed on investigating the observed nonlinear behavior because the existing proposed models do not account for these characteristics. Employing the Volterra representation, harmonic ratio analysis, and multisine excitations, characterization results for cantilever samples showed that the nonlinearity is dynamic and input-dependent, dominant at low frequencies, and that its influence varies depending on the solvent. It was determined that lower viscosity solvents trigger the nonlinear mechanisms at higher frequencies. Additionally, the primary components of the harmonic distortion appear to result from quadratic and cubic nonlinearities. Using knowledge gained from the characterization study, the utility of different candidate system structures was explored to model these nonlinear response characteristics. The ideal structure for modeling the current-controlled voltage and tip velocity was shown to consist of an underlying linear system with a dynamic input nonlinearity. The input nonlinearity is composed of a parallel connection of linear and nonlinear terms, where each nonlinear element has the form of a Hammerstein system. This system structure was validated against data from measured time and frequency responses. As a potential application, and consequently further validation of the chosen model structure, a square-plate polymer actuator was considered. In this study, the plate was clamped at the four corners where a uniform input was applied, measuring the center-point displacement. Characterization and modeling were performed on this system, with results similar to the cantilever sample. Applying output feedback control, in the form of proportional-integral compensation, showed that accurate tracking performance could be achieved in the presence of nonlinear distortions. Special attention was extended here to the potential application in deformable mirror systems. / Ph. D.