Kinetic Competition of Gases during Mixture Adsorption on Planar Surfaces

We present results of a Kinetic Monte Carlo investigation of the adsorption dynamics of a binary mixture of gases on a planar surface, with a focus on the role that molecular interactions play during uptake equilibration. We show how increasing the strength of molecular interactions enhances the temporary coverage overshoot of the weaker binding species, a phenomenon driven by its faster adsorption rate. Snapshots of the adsorbed mixture configurations as a function of time allow us to follow in detail the evolution of the adsorbed mixture toward equilibrium. Clustering effects, due to both molecular interactions and differences in the adsorption/desorption rates, determine how the competition between the species on the surface takes place, leading to the final equilibrium composition. Our results are in overall agreement with recent experimental measurements of the adsorption kinetics of Ar-CH₄ mixtures on graphite.