Molecular theory of adsorption in pore spaces. Part 2.—Thermodynamic and molecular lattice model descriptions of capillary condensation

Abstract

A new thermodynamic analysis, which avoids some of the limitations of previous treatments, is made of the process of adsorption and filling in cylinders. Expressions for the surface tension are derived for a molecular lattice model and relationships with the Gibbs and Frenkel, Halsey, Hill equation examined. The special nature of the latter equation is discussed and compared with the lattice model. Results for a nitrogen-like system at 77.4 K are compared with predictions from various thermodynamic equations. It is found that an adsorption correction to the Cohan equation is necessary for the best agreement but that none of the thermodynamic expressions tested were able to predict the molecular results.