INFLUENCE OF BULK DIFFUSION ON THE ADSORPTION OF HARD-SPHERES ON A FLAT SURFACE

Irreversible adsorption of hard spheres onto a solid surface is analyzed by using a generalization of the "random sequential adsorption" (RSA) model: "diffusion random sequential adsorption" (DRSA). In addition to the irreversible nature of the adsorption process and exclusion effects of the adsorbed configurations of hard spheres, the new model also considers the interactions between adsorbed particles and particles from the bulk, diffusing toward the surface. It is shown, in particular, that this affects the structure of adsorbed configurations for coverages different from the jamming limit coverage theta(infinity). Surprisingly, theta(infinity) appears to be identical for configurations generated by RSA and DRSA algorithms. Moreover, the structures of the configurations, as characterized by the radial distribution function g(r), are also identical at the jamming limit, whereas they differ for lower coverages. The coupling between the bulk diffusion process and the "adsorption process" is also analyzed as a function of the coverage. New approximate boundary conditions at the interface for the adsorption-diffusion equations are derived and the adsorption rate is calculated for a particular example.