Temperature Dependence of the Viscosity Coefficients of Liquid Crystals

Abstract

Based upon the thermodynamics of irreversible processes a set of phenomenological equations which explain the temperature dependence of Leslie's viscosity coefficients of liquid crystals are presented. The equations are of the form α 4 =2η 0 exp ( E / k T )+constant× S + O ( S 2 ), in which S is the orientational order parameter and E is the activation energy which can be determined by viscosity measurements in the isotropic phase. The equations apply to the nematic phase in the case of finite S as well as to the isotropic phase in the limit of S =0. A fairly good agreement is found between the proposed equations and the existing experimental data.