Configurations of adsorbed hard spheres after diffusion in a gravitational field

The deposition and adhesion of particles on a solid surface are governed by a great number of interplaying forces. In this paper we analyze, by means of computer simulations, the influence of (i) the short-range repulsive forces, modeled by hard sphere interactions, (ii) the gravitational forces, and (iii) the diffusion process of the particles in the fluid on the structure of the surface covered by the particles. In particular, the evolution of the limiting coverage, Θ∞ (where Θ is the reduced relative surface coverage), and the radial distribution, g(r), at the jamming limit, are determined as a function of the gravitational forces. These forces play an important role in many experiments performed on latex beads. Our results should stimulate new experiments in this field and, thus, be directly experimentally tested. It is shown, for example, that for polystyrene particles Θ∞ is constant and equal to the random sequential adsorption jamming limit value for radii R not larger than 1 μm. It increases for 1 ≤ R ≤ 3 μm and tends, for higher R, to a plateau, whose value is approximately equal to 0.61. The tendency to a closer packing when R is large, and thus large gravitational forces, is confirmed by the shape of the radial distribution function. This phenomenon occurs not only for jammed surfaces but also for unsaturated surfaces.