SOLUTION STRUCTURE, RHEOLOGY, AND NANOCOMPOSITES OF A LIQUID CRYSTALLINE POLYELECTROLYTE

High-performance polymers, most notably all-aromatic polyamides (aramids), enable the convergence of the disparate material properties, such as low density, high strength, high stiffness, and thermal stability. Sulfonated derivatives of aramids (sulfo-aramids) represent a unique class of materials that are a nexus between stiff and strong engineering materials and soft and dynamic biological matter. Specifically, sulfo-aramids are water soluble and often self-assemble into rodlike supramolecular structures in solution, similar to rodlike viruses or polypeptide helical assemblies. Such rodlike systems undergo spontaneous self-organization into a liquid crystalline (nematic) phase above a critical concentration, resulting in a high degree of local orientational order. Application of an external field, such as shear flow, can either increase or decrease the global orientational order of the nematic phase. Thus, understanding the solution structure and rheology of such phases has important implications for the fabrication of high-performance, sulfo-aramid nanocomposites. In this Dissertation, we investigate aspects of the solution structure, rheology, and nanocomposites fabricated from helical, rodlike assemblies of the sulfo-aramid, poly(2,2’- benzidine-4,4’-disulfonyl terephthalamide) (PBDT). PBDT forms a fully nematic phase at low concentrations in water, evidencing its high aspect ratio, enabling environmentally-benign fabrication of advanced nanocomposites with liquid crystalline graphene oxide or ionic liquids. Moreover, the low concentrations required for formation of a fully nematic phase enables direct interrogation of the rheological responses of the liquid crystalline rodlike assemblies. In contrast, the rheology of previously studied model LCPs are dominated by the nematic defect texture. In addition, the dynamic self-assembled nature of PBDT rodlike assemblies result in an unusual rheological behavior, known as irreversible shear-activated gelation, at high concentrations. Overall, our new insights on the solution structure and rheology of sulfo-aramids not only inform the design of advanced nanocomposites, but also provide a new platform for elucidating the flow behavior of high-aspect-ratio, charged rods.