Measurement of the wave-vector dependent diffusion coefficient in concentrated particle dispersions

Measurements are reported of the wave-vector dependent diffusion coefficient D(q) in the region of the first two peaks in the static structure factor for concentrated nonaqueous dispersions of polymethylmethacrylate spheres (diam≂0.4 μm). The particle volume fractions are taken up to the point of spontaneous crystallization. In order to minimize the effects of multiple scattering in these dynamic light scattering experiments, the particles are dispersed in solvent mixtures having refractive indexes close to those of the particles. The measured data for D(q) are compared with the results of two recent theoretical predictions, viz. the approach of Beenakker and Mazur based on a partial resummation of many-particle interactions, and the empirical effective two-particle mobility method of Snook et al.