ORIENTATIONAL RELAXATION IN A COLLOIDAL SUSPENSION OF SPHERES

We study orientational relaxation in a colloidal suspension of spheres on the basis of the gene Smoluchowski equation. The time dependence of the polarization correlation function is characterized by a wave-vector- and frequency-dependent rotational-diffusion tensor. In the absence of hydrodynamic interactions the short-time decay of the correlation function is governed by free translational and rotational diffusion. This observation leads to a simple expression for the high-frequency limit of the rotational-diffusion tensor. We also derive a concise and transparent expression for the wave-vector- and frequency-dependent rotational-diffusion tensor of a semidilute suspension.