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.

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.