The effect of colloidal forces on the self-diffusion coefficients in strongly interacting dispersions

The effects of colloidal forces on the self-diffusion coefficients in dispersions of uniform spherical particles have been examined. The short-time coefficients (for times smaller than the structural relaxation time) are computed using the equilibrium mobility-averaging procedure. The long-time values are based on the solution of the two-particle Smoluchowski equation (with proper ‘‘zero-flux’’ boundary condition at contact). Results are presented for hard-sphere dispersions as well as for dilute-gas dispersions (the latter being applicable in the semidilute regime). The dilute-gas results are presented for Yukawa potentials with repulsive and attractive tails so that the individual roles of repulsion and attraction and their interplay with hydrodynamic interactions can be demonstrated. In addition to the above limiting cases, both short-time and long-time coefficients are presented for a sample case of a repulsive Yukawa dispersion with strong positional correlations (e.g., charged micelles or macroions), for which the potential of mean force can be obtained through the mean spherical or the rescaled mean spherical approximation.