Relationship between short-time self-diffusion and high-frequency viscosity in charge-stabilized dispersions

Experimental determination of both the short-time self-diffusion coefficient and the high-frequency viscosity are reported for model charge-stabilized dispersions. Despite the charged nature of the particles, we find that both quantities are insensitive to direct interparticle interactions. Quantitative agreement between the experimental data and micromechanical hard sphere theory is observed for a range of particle sizes and added salt content. However, while the reciprocal of the short-time self-diffusion coefficient shows a similar concentration dependence as the high-frequency viscosity, the two do not obey a generalized Stokes-Einstein relation. The violation is due to subtle differences in hydrodynamic interactions between the two particle motions, in agreement with theory and simulation.