Clustering in adsorbed films

Abstract

Recently, Dash has shown that adsorption isotherms can show distinct types of behavior. In class I the bulk vapor pressure is reached asymptotically for an infinite adsorbed amount; in class II it is reached for a finite amount; in class III no adsorption takes place at all. We show that these possibilities can also be derived by a simple discussion of the possible forms of the free energy as function of the thickness of the adsorbed film. The question of clustering, i.e., the formation of drops, is also discussed.