Polymer Chemistry

Biography

Biography: Richard J. Spontak

Abstract

Block ionomers are block copolymers possessing at least one charged block and are of growing interest in the "bottom-up" design of developing technologies such as fuel cells, water-filtration membranes and electro¬active media. In most cases involving triblock and higher-order linear multiblock copolymers, however, charged endblocks compromise the stability of network formation, which imparts elasticity and can be of paramount application importance. This study focuses on the morphological development of midblock-sulfonated multiblock ionomers wherein the endblocks self-assemble into glassy microdomains that remain completely unaffected by the presence of the charged midblock and thus stabilize the formation of a molecular network. We have already demonstrated that these unique materials are capable of serving as ionic polymer-metal composites (IPMCs), photovoltaic elastomer gels (PVEGs) and physically-crosslinked hydrogels (PCHs). The polarity of the casting solvent is found to have a profound effect on the observed morphology, as discerned by both transmission electron microscopy (TEM) and transmission electron microtomography (TEMT). Characteristics of these various morphologies, including dispersed ionic microdomains embedded in a nonpolar matrix, have been measured by synchrotron small-angle x-ray scattering (SAXS). Exposure of nonequilibrium morphologies to solvent vapor quickly promotes equilibration to the expected alternating lamellar morphology, whereas exposure of the discrete ionic microdomains to liquid water results in a morphological transition that serves to connect the ionic microdomains and permit flow. Real-time SAXS patterns follow these transitions and permit direct correlation with macroscopic observations.