TRACER DIFFUSION IN PERFECTLY ALIGNED LIQUID-CRYSTALLINE PHASES - KINETIC-THEORY AND MOLECULAR-DYNAMICS SIMULATIONS

Solute diffusion in nematic liquid crystalline fluids has been studied using Enskog kinetic theory and molecular dynamics simulation. The li quid crystalline solvent is modelled by perfectly aligned hard ellipso ids of revolution, and the solute is either a spherical or ellipsoidal particle. The diffusion coefficient is calculated for a range of solv ent densities and solute and solvent aspect ratios and sizes. The kine tic theory enables us to study various parameters easily compared with simulation or experiment. The validity of the kinetic theory, and its range of applicability is tested against the computer simulations. Th e main focus of the study is the anisotropy of diffusion, defined as t he ratio of diffusivity in directions parallel and perpendicular, resp ectively, to the solvent director. If the pair correlation function at contact surface is taken to be isotropic, Enskog kinetic theory finds that the anisotropy in diffusion is independent of density and collis ion frequency, and depends only on size and shape of colliding particl es. This result is confirmed by the simulations.