Hydrodynamic interactions in hard-sphere suspensions

We study the effects of hydrodynamic interactions on the diffusion of hard spheres in concentrated suspensions. Using a multiple-light-scattering technique, we measure [H(q)], a weighted average of H(q), a function that characterizes the hydrodynamic interaction. By changing the size of the spheres we probe the particle size dependence of [H(q)] and find reasonable agreement with recent calculations for volume fractions φ2μm), [H(q)]→H(∞) and thus, we measure the short-time self-diffusion coefficient ${\mathit{D}}_{\mathit{s}}$==${\mathit{D}}_0$H(∞) where ${\mathit{D}}_0$ is the free-particle diffusion coefficient. We find that H(∞)=1-1.77(±0.07)φ for φ≤0.45. This agrees with the linear (low-concentration) term calculated for short-time self-diffusion. The short-time diffusion coefficient is also found to be continuous across the freezing transition.