A SIMPLE STATISTICAL-MECHANICAL APPROACH FOR STUDYING MULTILAYER ADSORPTION - EXTENSIONS OF THE BET ADSORPTION-ISOTHERM

A new statistical mechanical approach for studying multilayer adsorpti on phenomena is presented. It is shown that a multilayer adsorbed film can be treated as a multicomponent monolayer, the equilibrium equatio ns of which are determined from the adsorption process and the process es which form the constituents of the monolayer. The derivation of the equilibrium equations is extremely simple and allows the extension of the BET isotherm to complicated systems. In this respect, the effect of the short-range lateral interactions on the properties of the BET i sotherm is examined. In addition, effects coming from multisite occupa ncy with or without lateral interactions and from the energetic hetero geneity of the adsorbent surface affecting only the first or the first and the second sublayer are also taken into account and discussed.