Viscoelastic Properties of Liquid Crystal Polymers and Polymer Networks in Nematic Solvents

Case Western Reserve University, Cleveland OH

Investigators

Abstract

This project explores the effect of macromolecular structure on the viscoelastic behavior of liquid polymers (LCPs) and LCP networks in low molar mass nematic solvents. Previous research on the properties of dilute nematic solutions of LCPs of varying architectures uncovered a variety of novel viscometric phenomena, such as LCP-induced transitions between flow-aligning and flow-tumbling states. To explain these observations quantitatively, it is necessary to introduce a new viscous dissipation mechanism, not present in isotropic solutions, which derives from a mechanical coupling between director rotation and LCP backbone configuration. First, further studies of side-chain LCPs in nematic solution, including conoscopic optical analysis of the rate of director rotation, as well as direct determinations of chain dimensions and the relaxation molecular theory. Second, we seek to confirm the theoretical expectation that, for LCP networks swollen by a nematic solvent, there is a mechanical coupling between the distortional elasticity of the solvent, and the entropic elasticity of the LCP network. Third, new dynamical phenomena at higher LCP concentrations will be explored: e.g. the onset of chain entanglement elasticity and the coupling of the flow to the order parameters of LCP and solvent may lead to field- or stress-induced structural transitions. %%% These studies will explore new phenomena in the viscoelastic behavior of nematic materials containing polymers, and will generate information pertinent to the design of novel materials for device applications, based on solutions or gels of LCPs in nematic solvents.