Diffusion of charged colloidal particles at low volume fraction: Theoretical model and light scattering experiments

Abstract

An appropriate mean force potential was utilized in Felderhof's Theory to derive simple analytical expressions for the concentration dependence of the collective and short time self diffusion coefficients, as well as for the sedimentation velocity of charged spherical particles. It is demonstrated theoretically that the osmotic virial and the Oseen hydrodynamic terms play a dominant role. To check the theoretical model, the dependence of the collective diffusion coefficient on the volume fraction of latex particles was experimentally studied. Dynamic light scattering was used at several different concentrations of electrolyte. It turns out that our experimental results, as well as the results of other authors, are in very good agreement with the proposed theoretical model. The results show that the increase of the electrolyte concentration leads to increase of the particle charge, but almost does not change the particle surface potential. A minimum in the dependence of the diffusion coefficient of a single particle on the ionic strength was also obtained.