This thesis presents work done to improve the switching speed and contrast performance of electrochromic devices. Layer-by-Layer (LbL) assembly was used to deposit thin electrochromic films of materials ranging from organic, inorganic, conducting polymers, etc. The focus was on developing new materials with high contrast and long lifecycles. A detailed switching-speed study of solid-state EC devices of already-developed (PEDOT (Poly(3,4-ethylenedioxythiophene)), polyviologen, inorganic) materials and some new materials (Prodot-Sultone) was performed. Work was done to achieve the optimum thickness and number of bilayers in LbL films resulting in high-contrast and fast switching. Device sizes were varied for comparison of the performance of the lab-made prototype device with the commercially available "small pixel" size displays. Symmetrical EC devices were fabricated and tested whenever conducting polymers are used as an EC material. This symmetrical configuration utilizes conducting polymers as an electroactive layer on each of two ITO-coated substrates; potential is applied to the two layers of similar conducting polymers and the device changes color from one redox state to another. This method, along with LbL film assembly, are the main factors in the improvement of switching speed results over already-published work in the literature. PEDOT results show that EC devices fabricated by LbL assembly with a switching speed of less than 30 ms make EC flat-panel displays possible by adjusting film thickness, device size, and type of material. The high contrast value (84%) for RuP suggests that its LbL films can be used for low-power consumption displays where contrast, not fastest switching, is the prime importance. In addition to the electrochromic work, this thesis also includes a section on the application of LbL assembly in fabricating electromechanical bending actuators. For bending actuators based on ionic polymer metal composites (IPMCs), a new class of conductive composite network (CNC) electrode was investigated, based on LbL self-assembled multilayers of conductive gold (Au) nanoparticles. The CNC of an electromechanical actuator fabricated with 100 bilayers of polyallylamine hydrochloride (PAH)/Au NPs exhibits high strain value of 6.8% with an actuation speed of 0.18 seconds for a 26 µm thick IPMC with 0.4 µm thick LbL CNCs under 4 volts. / Ph. D.

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

Ionic polymer-metal composites (IPMCs) are widely studied for their potential as electromechanical sensors and actuators. Bending of the IMPC depends on internal ion motion under an electric potential, and the addition of an ionic liquid and ionic self-assembled multilayer (ISAM) conductive network composite (CNC) strongly enhances bending and improves lifetime. Ion conducting polyelectrolytes poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) and Nafion® were incorporated into an ISAM CNC film with poly(allylamine hydrochloride) (PAH) and anionic gold nanoparticles actuators to further improve bending. CNC films were optimized for bending through pH adjustments in PAH and adding NaCl to the PAMPS and Nafion® solutions. PAMPS-containing actuators showed larger and faster bending than those containing Nafion® in the CNC. The IPMC actuator was also evaluated for its potential as a humidity sensor based on its relative humidity (RH) dependent steady-state current. The detection range is at least 10-80%RH, with 5%RH increment differentiation and likely better resolution. Effects of CNC presence and thickness were studied, in conjunction with ionic liquid at a range of RH values. A thin CNC (pH 4 PAH) produced the greatest current differentiation between RH values. The current's response speed to a large RH decrease was approximately 4 times faster than that of a fast commercial digital hygrometer. Additionally, the presence of a CNC and ionic liquid improved the current response time. These results indicate that an IPMC based humidity sensor using a CNC and ionic liquid is very promising and merits further study. / Master of Science

The overall goal of this investigation was to elucidate specific structure-property relationships in perfluorosulfonate ionomers (PFSIs)-related materials. The project can be broken into two primary foci. First, we explored the current state of understanding related to morphology-property relationships in PFSIs with specific attention to the nano-scale organization of the ionic and crystalline domains. Specifically, the effect of uniaxial orientation on the structure and transport properties of Nafion® membranes was examined. Small angle X-ray scattering (SAXS) experiments on dry membranes that were uniaxially elongated showed a strong anisotropic morphology which was shown to persist over the swelling process without a significant relaxation. Herman's order parameters for the ionomer peak were strongly influenced by uniaxial deformation, which supports the presence of cylindrical rather than spherical morphology for ionic domains. Comparison of the water diffusion coefficients between unoriented and oriented samples revealed that uniaxial deformation of Nafion® membranes essentially enhances transport ability in one direction (i.e., the parallel to draw direction) and suppresses in the other two directions (i.e., two orthogonal directions relative to the stretching direction). Based on 1-dimensional analyses of oriented SAXS patterns at the azimuthal angle 90o, three recent models (lamellar model, semicrystalline rod-like model and fringed-micelle model) for the morphology of PFSIs were critically evaluated. The loss of meridional scattering, different orientation behavior of the crystalline and ionic domains, and inherent chain stiffness precludes the possibility of a chain-folded lamellar morphology. While the inter-aggregate dimensions remain constant at high draw ratios, the inter-crystalline spacings decrease significantly. Coupled with the distinctly different orientation behavior, these observations preclude the existence of crystallites solely within rod-like aggregates. While the worm-like ionic channel model was able to explain the behavior of SAXS and wide angle X-ray scattering (WAXS) relatively well, this model also had limitations such as (1) crystalline domains directly linked to the ionic domain (and thus a lack of amorphous domains) and (2) a presence of only a single ionic channel between two neighboring crystallites. Second, electroactive materials, specifically ionic polymer-metal composites (IPMCs) that undergo bending motions with the stimulus of a relatively weak electric field were fabricated. To understand the role of the nanoscale morphology of the membrane matrix in affecting the actuation behavior of IPMC systems, we evaluated actuation performance of IPMCs subjected to uniaxial orientation. The PFSI nanostructure altered by uniaxial orientation mimicked the fibrillar structure of biological muscle tissue and yielded a new anisotropic actuation response. It was evident that IPMCs cut from films oriented perpendicular to the draw direction yielded displacement values that were significantly greater than that of unoriented IPMCs. In contrast, IPMCs cut from films oriented parallel to the draw direction appeared to resist bending and yield displacement values that were much less than that of the unoriented IPMC. This anisotropic actuation behavior was attributed to the contribution of the nanoscale morphology to the bulk bending modulus. Overall, this study clearly demonstrated, for the first time, the importance of the nanoscale morphology in affecting/controlling the actuation behavior in IPMC systems. / Ph. D.

Foi estudada a enxertia de estireno induzida por radiação gama em filmes de poli(fluoreto de vinilideno) (PVDF) com espessura de 0,125 mm com doses entre 1 e 100 kGy em presença de soluções de estireno/N,Ndimetilformamida (DMF) (1:1, v/v) e estireno/tolueno (1:1, v/v) com taxa de dose de 5 kGy.h-1 por meio do método simultâneo de irradiação sob atmosfera de nitrogênio e em temperatura ambiente, usando raios gama de uma fonte de Co- 60. Depois de enxertados, os polímeros foram sulfonados em soluções de ácido clorossulfônico/1,2-dicloroetano (2 e 10 %). Os filmes foram caracterizados antes e depois de cada modificação com o cálculo do Grau de enxertia, (DOG), espectrometria no infravermelho (FT-IR), microscopia eletrônica de varredura (MEV), calorimetria exploratória diferencial (DSC) e termogravimetria (TG/DTG). Os resultados do grau de enxertia mostraram que a enxertia aumenta com o aumento da dose e varia enormemente de acordo com o solvente utilizado, com enxertias cerca de 20 vezes maiores quando do uso da DMF em relação ao do tolueno. Foi possível confirmar a enxertia do estireno por FT-IR graças ao aparecimento de novos picos característicos e por TG/DTG e DSC por meio das alterações do comportamento térmico dos materiais enxertados/sulfonados. Os materiais sulfonados ainda foram caracterizados por suas capacidades de troca iônica (IEC), que mostraram que tanto os aumentos do grau de enxertia quanto os da concentração do ácido clorossulfônico aumentam o IEC. Os resultados mostraram que é possível obter materiais com capacidades de troca iônica com possibilidade de aplicação como compósitos ionoméricos de metal-polímero. / Gamma-radiation-induced grafting of styrene into poly(vinylidene fluoride) (PVDF) films with 0.125 mm thickness at doses from 1 to 100 kGy in the presence of a styrene/N,N- dimethylformamide (DMF) solution (1:1, v/v) and styrene/toluene (1:1, v/v) at dose rate of 5 kGy h-1 was carried out by simultaneous method under nitrogen atmosphere at room temperature, using gamma rays from a Co-60. After grafting reactions, the polymer was then sulfonated in chlorosulfonic acid/1,2-dichloroethane (2 and 10%) for 3 hours. The films were characterized before and after modification by calculating the degree of grafting (DOG), infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetry (TG/DTG). DOG results show that grafting increases with dose, and varies enormously depending on the solvent used, with DOGs about 20 times greater in DMF than in toluene. It was possible to confirm the grafting of styrene by FT-IR due to the appearance of the new characteristic peaks and by the TG and DSC which exhibited changes in the thermal behavior of the grafted/sulfonated material. Sulfonated material was also characterized by ion exchange capacity (IEC) showed that both DOG and sulfonic acid concentration increase IEC values. Results showed that it is possible to obtain materials with ion exchange capacity of possible application as ionic polymer-metal composites.

Foi estudada a enxertia de estireno induzida por radiação gama em filmes de poli(fluoreto de vinilideno) (PVDF) com espessura de 0,125 mm com doses entre 1 e 100 kGy em presença de soluções de estireno/N,Ndimetilformamida (DMF) (1:1, v/v) e estireno/tolueno (1:1, v/v) com taxa de dose de 5 kGy.h-1 por meio do método simultâneo de irradiação sob atmosfera de nitrogênio e em temperatura ambiente, usando raios gama de uma fonte de Co- 60. Depois de enxertados, os polímeros foram sulfonados em soluções de ácido clorossulfônico/1,2-dicloroetano (2 e 10 %). Os filmes foram caracterizados antes e depois de cada modificação com o cálculo do Grau de enxertia, (DOG), espectrometria no infravermelho (FT-IR), microscopia eletrônica de varredura (MEV), calorimetria exploratória diferencial (DSC) e termogravimetria (TG/DTG). Os resultados do grau de enxertia mostraram que a enxertia aumenta com o aumento da dose e varia enormemente de acordo com o solvente utilizado, com enxertias cerca de 20 vezes maiores quando do uso da DMF em relação ao do tolueno. Foi possível confirmar a enxertia do estireno por FT-IR graças ao aparecimento de novos picos característicos e por TG/DTG e DSC por meio das alterações do comportamento térmico dos materiais enxertados/sulfonados. Os materiais sulfonados ainda foram caracterizados por suas capacidades de troca iônica (IEC), que mostraram que tanto os aumentos do grau de enxertia quanto os da concentração do ácido clorossulfônico aumentam o IEC. Os resultados mostraram que é possível obter materiais com capacidades de troca iônica com possibilidade de aplicação como compósitos ionoméricos de metal-polímero. / Gamma-radiation-induced grafting of styrene into poly(vinylidene fluoride) (PVDF) films with 0.125 mm thickness at doses from 1 to 100 kGy in the presence of a styrene/N,N- dimethylformamide (DMF) solution (1:1, v/v) and styrene/toluene (1:1, v/v) at dose rate of 5 kGy h-1 was carried out by simultaneous method under nitrogen atmosphere at room temperature, using gamma rays from a Co-60. After grafting reactions, the polymer was then sulfonated in chlorosulfonic acid/1,2-dichloroethane (2 and 10%) for 3 hours. The films were characterized before and after modification by calculating the degree of grafting (DOG), infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetry (TG/DTG). DOG results show that grafting increases with dose, and varies enormously depending on the solvent used, with DOGs about 20 times greater in DMF than in toluene. It was possible to confirm the grafting of styrene by FT-IR due to the appearance of the new characteristic peaks and by the TG and DSC which exhibited changes in the thermal behavior of the grafted/sulfonated material. Sulfonated material was also characterized by ion exchange capacity (IEC) showed that both DOG and sulfonic acid concentration increase IEC values. Results showed that it is possible to obtain materials with ion exchange capacity of possible application as ionic polymer-metal composites.

An ionic polymer actuator consists of a thin Nafion-117 sheet plated with gold or platinum on both sides. An ionic polymer actuator undergoes large deformation in the presence of low applied voltage across its thickness and exhibits low impedance. They can also be used as large displacement sensors by bending them to induce stresses and generate a voltage response. They operate best in a humid environment. Ionic polymer actuators have been used for various practical applications such as bio-mimetic robotic propulsion, flexible low mass robotic arms, propellors for swimming robotic structures, linear and platform type robotic actuators and active catheter systems. One of the disadvantages of ionic polymer actuators is that their settling time to a unit step voltage is on the order of 5-20 seconds in a cantilever configuration. The slow time constant of an ionic polymer limits the actuation bandwidth. The characteristics of ionic polymer actuators, low force and large displacement (as compared to other actuator technologies such as PZT or PVDF), cannot be used in applications requiring a faster response time for a given actuation signal. Due to this limitation, many applications will not be able to make use of the large displacement effectively because of the limited bandwidth of the actuator. Another disadvantage of using an ionic polymer actuator is that the stiffness of the actuator is a function of the hydration of the polymer. Difficulties in controlling the hydration, which changes with respect to time, results in inconsistencies in the mechanical response exhibited by the polymers during continual usage. Several physical models of ionic polymer actuators have been proposed. The physical phenomenon responsible for the bending is not completely understood and no clear set of principles have been able to explain the motion of the polymers completely. Physical phenomena like ionic motion, back diffusion of water and electrostatic force have been used to explain these models. This research demonstrates the use of feedback control to overcome the limitation of slow settling time. First, an empirical model of the ionic polymers developed by Kanno was modified by studying the step response of these actuators. The empirical model is used to design a feedback compensator by state space modeling techniques. Since the ionic polymer actuator has a slow settling time in the open-loop, the design objectives are to minimize the settling time and constrain the control voltage to be less than a prescribed value. The controller is designed using Linear Quadratic Regulator (LQR) techniques which reduced the number of design parameters to one variable. Simulations are performed which show settling times of 0.03 seconds for closed-loop feedback control are possible as compared to the open-loop settling time of 16-18 seconds. The maximum control voltage varied from 1.2 Volts to 3.5 Volts depending on the LQR design parameter. The controller is implemented and results obtained are consistent with the simulations. Closed-loop settling time is observed to be 4-8 seconds and the ratio of the peak response to the steady-state response is reduced by an order of magnitude. Discrepancies between the experiment and the simulations are attributed to the inconsistencies in the resonant frequency of the actuator. Experiments demonstrate that changes in the surface hydration of the polymer result in 20\% variations in the actuator resonance. Variations in the actuator resonance require a more conservative compensator design, thus limiting the performance of the feedback control system. / Master of Science

Ionic polymer metal composites (IPMC) are a new class of smart materials that have attractive characteristics such as muscle like softness, low voltage and power consumption, and good performance in aqueous environments. Therefore, there is a significant motivation for research on design and development of IPMC based biomimetic propulsion systems for underwater vehicles. In aerospace, underwater vehicles finds application for forensic studies of spaceship wrecks, missile fragments and any airplane accidents in sea and ocean terrains. Such vehicles can also survey moons and planets that house water oceans. Among biomimetic swimming systems, fish inspired swimming has gained interest since fish like swimming provides high maneuverability, high cruising speed, noiseless propulsion and efficient stabilization compared to conventional propulsion systems. In this work, the paired pectoral fin based oscillatory propulsion using IPMC for aquatic propulsor applications is studied. Dynamic characteristics of IPMC fin are analyzed using numerical simulations and optimization is used to improve the fin design. A complex hydrodynamic function is used to describe the behavior of an active IPMC fin actuator in water. The structural model of the IPMC fin is obtained by modifying the classical dynamic equation for a slender beam to account for the electromechanical dynamics of the IPMC beam in water. A quasi-steady blade element model that accounts for unsteady phenomena such as added mass effects, dynamic stall, and the cumulative Wagner effect is used to estimate the hydrodynamic performance of the flapping fin. It is shown that the use of optimization methods can lead to significant improvement in performance of the IPMC fin. Further, three fish species with high performance flapping pectoral fin locomotion are chosen and performance analysis of each fin design is conducted to discover the better configurations for engineering applications. Dynamic characteristics of IPMC actuated flapping fins having the same size as the actual fins of three different fish species, Gomphosus varius, Scarus frenatus and Sthethojulis trilineata, are also analyzed. Finally, a comparative study is performed to analyze the performance of the three different biomimetic IPMC flapping pectoral fins.

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