The imidazole ring offers great potential for a variety of applications including gene delivery vectors, ionic liquids, electromechanical actuators, and novel monomers and polymers. The imidazole ring provides a unique building block for these applications due to its thermal stability, aromatic nature, ability to form ionic salts, and ease of functionalization. Free radical polymerization of 1-vinylimidazole (1-VIm) and free radical copolymerizations with methyl methacrylate (MMA) and n-butyl acrylate (nBA) afforded homopolymers and copolymers with tunable solution and thermal properties. Aqueous SEC provided reproducible and reliable molecular weights for poly(1-VIm) in the absence of polymer aggregates. Analysis of the thermal properties revealed ideal random copolymers with MMA and non-ideal copolymers with nBA. Small angle X-ray scattering determined that the spacing between ionic groups remained constant with increased nonionic comonomer incorporation while the spacing between adjacent polymer backbones increased. Functionalization of 1-VIm with varying length alkyl halides and polymerization prepared a series of imidazolium homopolymers. Anion exchange reactions controlled the thermal and solution properties, and the bromide counteranion quantitatively exchanged to tetrafluoroborate (BF4), trifluoromethanesulfonate (TfO), and bis(trifluoromethanesulfonyl)imide (Tf2N). Thermogravimetric analysis revealed that thermal stability increased with decreased alkyl substituent length and larger counteranion size, and differential scanning calorimetry determined that glass transition temperature (Tg) decreased with increased alkyl substituent length and larger counteranion size. Electrochemical impedance spectroscopy determined the ionic conductivities of the imidazolium homopolymers, and analysis using the Vogel-Fulcher-Tammann equation revealed that the activation energy of ion conduction increased as alkyl substituent length increased. Polymer morphology determined using X-ray scattering also influenced the ionic conductivity. As the alkyl substituent length increased, the spacing between adjacent polymer backbones increased, which decreased the ionic conductivity due to the ion-hopping mechanism of ion conduction. Unsuccessful attempts to control the radical polymerization of 1-VIm led to the investigation of 1-(4-vinylbenzyl)imidazole (VBIm), which is a styrenic-based monomer with excellent propagating radical stability. Triblock copolymers incorporating VBIm monomer into a soft random copolymer center block and reinforcing, hard segment outer blocks provided a template for tuning the properties of the ionomer membranes for electroactive devices. Analysis of the morphology and mechanical properties using small angle X-ray scattering and dynamic mechanical analysis determined microphase separation and optimal mechanical properties for electromechanical transducer fabrication. Testing electromechanical transducers revealed superior performance relative to the benchmark Nafion®. Optimization of triblock copolymer design criteria through varying the comonomer ratio of VBIm and nBA in the soft center block, quaternization reactions, and ionic liquid introduction influenced mechanical properties and ionic conductivity. Higher percentages of VBIm and quaternization of VBIm in the random central block increased Tg and ionic conductivity. IL selectively incorporated into the imidazole-containing phases with no leakage observed for ionic systems, reduced the center block Tg, and increased ionic conductivity. Controlling charge density along poly(1-VIm) through well-defined alkylation reactions with 1-bromobutane provided a potential vector for nonviral gene delivery and polyanion binding. Analysis of DNA and heparin binding using gel electrophoresis revealed a decrease in N/P ratio with increased alkylation percentage. Dynamic light scattering indicated an increase in zeta potential with increasing alkylation percentages, and relatively uniform polyplex sizes in aqueous media. The MTT assay developed cytotoxicity profiles with little toxicity prior to 83% alkylation. Finally, the luciferase expression assay revealed inefficient nucleic acid delivery to multiple cell types. Synthesis of poly(1-VIm) vectors with glutathione conjugates provided an avenue for simultaneous therapeutic gene and anti-oxidant delivery in vitro. Cytotoxicity assays of cells pretreated with glutathione-conjugated poly(1-VIm) prior to oxidative stress showed that higher glutathione conjugation levels improved cell viability. / Ph. D.

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.

No description available.

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.

No description available.