Diffusion of concentrated neutral hard-sphere colloidal suspensions

Abstract

We evaluate theoretical expressions for the long-time wave-number-dependent self-diffusion and collective diffusion coefficients ${D}_{S}^{L}(k,\ensuremath{\varphi})$ and ${D}^{L}(k,\ensuremath{\varphi}),$ respectively, as a function of volume fraction \ensuremath{\varphi} and wave vector k for neutral monodisperse hard-sphere colloidal suspensions over the entire fluid range. The theory is based on the Smoluchowski equation with mean-field-like hydrodynamic interactions, cage diffusion, and is free of adjustable parameters. The basic physical mechanisms underlying our formulas are discussed and the results are compared with recent experimental results by Segr\`e and Pusey [Phys. Rev. Lett. 77, 771 (1996)].