ON THE THEORY OF CONCENTRATED HARD-SPHERE SUSPENSIONS

A systematic theory for the dynamics of hard-sphere suspensions of int eracting Brownian particles with both hydrodynamic and direct interact ions is presented. A generalized diffusion equation is derived for con centrated suspensions. The volume fraction (phi) dependence of the sho rt- and long-time self-diffusion coefficients are thus explored from a unifying point of view. The long-range hydrodynamic interactions due to the Oseen tenser are shown to play a crucial role in both coefficie nts, while the short-range hydrodynamic interactions just lead to corr ections. The importance of the correlation effects between particles d ue to the long-range hydrodynamic interactions is also stressed. The n onlocal correlation effect is an important factor, leading to the beha vior of the long-time self-diffusion coefficient (D-S(L)) as D-S(L) si milar to (l - phi/phi(0))(2) near the volume fraction of phi(0) = 0.57 18. The direct interactions are also found to be drastically reduced b y the short-range hydrodynamic interactions.