By computer simulation the anisotropic long-time translational self-diffusion coefficients are calculated in the nematic phase of colloidal hard spherocylinders exhibiting Brownian dynamics in a solvent. In particular, the two diffusion coefficients $D_L^{\parallel }$ and $D_L^{\perp },$ parallel and perpendicular to the nematic director, are obtained for aspect ratios between 4.8 and 16 and for arbitrary densities. Long-time diffusion along the nematic director is nonmonotonic in density: Upon increasing the density, it first increases due to stronger alignment and then decreases due to packing constraints. It is shown that the ratio $D_L^{\parallel }{/D}_L^{\perp }$ and the orientation flip rate essentially scale with the nematic order parameter. While the ratio $D_L^{\parallel }{/D}_L^{\perp }$ increases with density in the nematic phase, it decreases dramatically with increasing density in the smectic-A phase. The results are compared to recent experiments.

• Received 8 September 1998

DOI:https://doi.org/10.1103/PhysRevE.59.1989