Tracer diffusion in perfectly aligned liquid crystalline phases Kinetic theory and molecular dynamics simulations

Abstract

Solute diffusion in nematic liquid crystalline fluids has been studied using Enskog kinetic theory and molecular dynamics simulation. The liquid crystalline solvent is modelled by perfectly aligned hard ellipsoids of revolution, and the solute is either a spherical or ellipsoidal particle. The diffusion coefficient is calculated for a range of solvent densities and solute and solvent aspect ratios and sizes. The kinetic 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. The main focus of the study is the anisotropy of diffusion, defined as the ratio of diffusivity in directions parallel and perpendicular, respectively, 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 collision frequency, and depends only on size and shape of colliding particles. This result is confirmed by the simulations.