The Role of Surface Tension in Multilayer Gas Adsorption

Abstract

The assumptions of the BET theory of multilayer gas adsorption are examined with regard to the possibility of taking account of the effect of surface tension. The surface energy of the adsorbed phase is calculated by the use of a Fourier analysis of the surface configuration. This energy is then used in the calculation of the corresponding factor in the partition function, leading ultimately to an isotherm equation which includes the surface tension effect. This isotherm is compared with experiment, with the result that the surface tension effect alone is found to overcorrect the BET theory. When compared with the result of recent theoretical treatments of the extension of the attractive forces into the adsorbed phase, our expression is shown to have the same dependence on layer thickness, but to be a relatively unimportant correction under usual conditions.