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 <0.45. For large spheres (diameter 2R>2m), [H(q)]H() and thus, we measure the short-time self-diffusion coefficient Ds==D0H() where D0 is the free-particle diffusion coefficient. We find that H()=1-1.77(±0.07) for 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.
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics