Gap-Dependence of the Viscosity of a Thermotropic Liquid Crystalline Copolymer

We have measured the shear and complex viscosities of a thermotropic liquid crystalline copolymer of p-hydroxybenzoic acid and 2,6-hydroxynaphthoic acid as a function of capillary diameter and parallel-plate gap spacing. In contrast to a study by Wissbrun, Kiss, and Cogswell, who reported that the viscosity increases significantly at small gaps, we find no dependence on the capillary diameter and a small decrease in complex viscosity with parallel-plate spacing. In an appendix we address an experimental artifact that can lead to an apparent decrease of the viscosity with gap spacing even for flexible polymers.