MOLECULAR THEORY OF FLOW ALIGNMENT OF NEMATIC LIQUID CRYSTALS

A mechanism to explain flow alignment of nematic liquid crystals is proposed. It is based on the rodlike shape of the molecules of these substances. A model calculation is performed in which the molecules are assumed to be equally and rigidly oriented ellipsoids of revolution, colliding with each other like the molecules of a gas. The two coefficients governing the linear relationship between torque per unit volume and shear rate are derived. The theory is used to predict the degree of flow alignment (which is found to be incomplete and to be independent of the shear rate) and to establish a relationship between the viscosity and one of the shear-torque coefficients. Theory and experiment are compared for p-azoxyanisole, and good agreement is found.