Self Diffusion Constant and Viscosity of Charged Polystyrene Colloids

Abstract

We have used the “Forced Rayleigh scattering” technique with spiropyran dyed polystyrene spheres in aqueous suspension, to measure the self diffusion as a function of the strength of interaction between the particles. The latter quantity was modified both by adding electrolyte and by changing the particle concentration, as well as by using spheres with different diameters and charges. We find that the diffusion constant decreases monotonically from the Stokes value as the repulsive interaction is increased, until the interactions are sufficiently strong to form a colloidal crystal. At this point there is a first order transition indicated by the decrease of the diffusion constant by ~ four orders of magnitude and the presence of Bragg reflections. These measurements are compared with viscosity measurements done in the liquid and solid states, with quasielastic light scattering measurements and with models for diffusion and viscosity in interacting systems.