Calculation of the thickness of solid-liquid multimolecular adsorption layers on the basis of the athermal parallel layer model

A method has been developed to calculate the equivalent layer thickness as a function of the bulk phase composition for athermal binary mixtures. It n eeds the knowledge of the adsorption excess isotherm and the cross sectiona l area of one of the two components. After integration of the Gibbs adsorpt ion isotherm equation, the composition of the monolayer, in direct contact with the solid surface, and the equivalent layer thickness can be calculate d. The procedure was tested by using both generated model excess isotherms, where the equivalent layer thickness functions were known, and selected ex perimental systems. These tests confirmed the applicability of the method. The results are especially reliable if the adsorption is preferential, the surface is relatively homogeneous, and the ratio of the cross sectional are as of the two components is not significantly different from that of the mo lar volumes.