SELF-DIFFUSION IN ISOTROPIC AND NEMATIC PHASES OF HIGHLY ELONGATED HARD PARTICLES

Velocity time correlation functions (tcfs) and self-diffusion coeffici ents have been derived by means of an Enskog kinetic theory for hard e llipsoids in isotropic and in nematic environments. The tcfs, calculat ed on the basis of kinetic theory, track those calculated by Allen by molecular dynamics simulations and show evidence of two exponential de cays which we attribute to the differing rates of diffusion parallel a nd perpendicular to the ellipsoid principle axes. D/D(E) the ratio of the molecular dynamics (MD) self-diffusion coefficient to our Enskog e stimate has a density dependence characteristic of hard sphere systems when diffusion is perpendicular to the macroscopic director; however, diffusion along the director axis is enhanced and this behavior has n o hard sphere analog. In the isotropic phase, D/D(E) follows the same trend as documented previously by Alder in hard sphere systems.