Forced rayleigh scattering in mixtures of colloidal particles

In this work, forced Rayleigh scattering is combined with a new deionization technique to measure the self-diffusion coefficient of strongly interacting charged polystyrene particles. For each measurement the, actually continuous, deionization process is stopped, allowing the suspension to relax from a sheared state to an equilibrium state. Conductivity and diffusion coefficient are monitored, both during this relaxation to equilibrium, and in dependence of the total deionization time. Relaxational behavior in the diffusion coefficient is observed in samples of both fluid and crystalline equilibrium state, while the conductivity remains unchanged. With increasing total deionization time the conductivity reaches a minimum and rises again to a stable plateau. The self-diffusion coefficient in equilibrium (i.e., at rest) also drops with increasing deionization time for monodisperse samples to unmeasurably low values. On the other hand, a finite, but small diffusion coefficient is found for the charge bidisperse sample.