Rotational viscosity coefficients of nematic and smecticC liquid crystals: Statistical theory

Summary The rotational diffusion of a rodlike molecule in a nematic and smecticC liquid crystal is considered in the molecular-field approximation. The microscopic friction constant, which determines the molecular rotation drag, possesses an exponential temperature dependence with the activation energy determined by the isotropic part of the intermolecular interaction energy. The rotational viscous coefficients,γ ₁ andγ _⊥ are obtained by averaging of the corresponding microscopic stress tensor with the nonequilibrium distribution function. The additional activation energy, proportional to the corresponding order parameter, appears in the expressions for the rotational viscosity coefficients both in nematics andC smectics. Work presented at the second USSR-Italy Bilateral Meeting on Liquid Crystals held in Moscow, September 15–21, 1988.