Multilayer adsorption on solid surfaces:: Calculation of layer thickness on the basis of the athermal parallel layer model

A method for calculating the dependence of equivalent layer thickness on bulk phase composition in athermal binary mixtures has been devised. The prerequisite to the procedure is knowledge of the adsorption excess isotherm and of the cross-sectional area of one component. After integration of the excess isotherm according to the Gibbs equation, the equations of the parallel layer model are used to calculate the composition of the monolayer in contact with the surface, which in turn is used to calculate the thickness of the adsorption layer. The proposed method was tested on a hypothetical experimental system with calculated excess isotherms and a known function of equivalent layer thickness. Reliable results were obtained, especially when adsorption was preferential, the surface was relatively homogeneous, and the ratio of the cross-sectional areas of the individual components was close to the ratio of molar fractions. (C) 2001 Academic Press.