Diffusion in binary suspensions of charged colloids

The dependence of diffusion coefficient in the binary suspension system of charged spherical colloidal particles on the colloid diameter and surface potential was investigated experimentally. A ratio of the diffusion coefficient in the binary system to that in free water was less than unity. This means that the diffusion of a charged colloidal particle is slowed down through the friction induced on the colloidal particle by the electrostatic interaction in the binary system. The ratio was calculated by generalized Langevin equation, and it was found that the calculated ratio agreed well with the experimental ratio. Diffusion behavior of a charged colloidal particle through quartz powder was also studied in the binary suspension system. A decrease in the effective diffusion coefficient, in comparison with that in monodispersed system, was observed.