Rotational Viscosity Coefficients γ₁ for Mixtures of Nematic Liquid Crystals

Abstract

The rotational viscosity coefficients γ₁ for mixtures of nematic liquid crystals have been determined as a function of temperature and composition. Mixtures of two components with equal clearing temperatures but different molecular lengths, of two homologues, and of a mesogenic and a nonmesogenic compound, together with a system which exhibits an induced smectic phase have been studied. The dependence on composition is understood qualitatively. Far away from the clearing point, the dependence on composition is similar to that of the shear viscosity coefficients in isotropic liquids. At high temperatures, the concentration dependence of γ₁ is influenced by the order parameter which strongly depends on concentration in systems with different clearing temperatures.