Nematic liquid crystal viscosity: inadequacies of microscopic theories

Abstract

Recently Janik et al. reported measurements of the Miesowicz viscosity coefficients of the nematic liquid crystal and confronted them with the results of the available theoretical models. They found that none of them can be successfully applied for the purpose of the Miesowicz-type experiment. In this paper I present an explanation why the microscopic theories seem inadequate. In particular, I analyze the applicability and conclusions of the Osipov-Terentjev model, whose final predictions are highlighted to be the same as those of the Kuzuu-Doi theory. It has been shown that the microscopic theories can perfectly explain the behavior of the Miesowicz coefficients difference eta(3)-eta(2) but are inadequate to study their ratio eta(3)/eta(2), which is contributed by the Leslie coefficient alpha(4). A disagreement between experimental data and the theoretical results for alpha(4) is attributed to the fact that the isotropic contribution to alpha(4) in the nematic phase is beyond the scope of the theories that are based on the anisotropic orientational distributions.