Diffusion in concentrated hard sphere dispersions: Effective two particle mobility tensors

In view of the practical difficulties already encountered plus those anticipated in the implementation of many-body hydrodynamic interactions, we examine a number of empirically screened two particle mobility tensors. The empirical screening constant(s), which depend on the dispersion concentration, are adjusted to give the best agreement with available experimental mutual and local self-diffusion constants for concentrated hard sphere dispersions. These diffusion constants are obtained experimentally from the first cumulant of the coherent intermediate scattering function in the small and large wave vector limits. We find that the experimental data can only be satisfactorily reproduced by employing a pair mobility tensor containing two adjustable screening terms. The predictions of the final mobility tensor at intermediate wave vectors are also qualitatively consistent with experiments.