BROWNIAN-MOTION OF COLLOIDAL PARTICLES IN A MODEL POROUS-MEDIUM

The motion of interacting colloidal particles diffusing in a model por ous medium is studied by means of computer simulations using a Brownia n dynamics algorithm. The particles are assumed to interact through a repulsive Yukawa pair potential. The porous medium is formed by a frac tion of the colloidal particles whose positions are frozen in a given spatial configuration. Varying the molar fraction of the mobile partic les, keeping constant the total particle concentration, and/or varying the parameters of the pair potential; we vary the effective porous me dium in which the mobile particles diffuse. Here we report results for the mean squared displacement of the mobile particles for different v alues of their molar fraction and of the Yukawa amplitude. We compare our results with theoretical calculations from two independent approac hes to the description of tracer diffusion in colloidal mixtures, by c onsidering the case in both theories, in which a fraction of the parti cles has vanishing free-diffusion coefficient. We find that both theor ies predict the same basic qualitative trends for the mean squared dis placement obtained from the Brownian dynamics experiments. For complet eness, we also present the static structure of the colloidal suspensio n permeating our model porous medium.