Self diffusion in mixtures of charged spheres

2014 We have used the Forced Rayleigh Scattering technique to measure the self diffusion constant of the two separate species of charged polystyrene spheres mixed in a strongly interacting suspension. For a few large spheres diffusing in a larger density of smaller spheres, we find that the diffusion constant is simply related by Stokes law to the total viscosity of the suspension. For the same relative number of spheres the small spheres see each other as discrete particles and do not follow Stokes law with the total viscosity. In the opposite limit of a few small spheres in a sea of large spheres, we find that the self diffusion of the two species are equal. This implies that the dynamics of the small spheres are governed by the motion of the large ones. J. Phys. France 49 (1988) 1043-1047 JUIN 1988,