Thermodynamics of fluids in random microporous materials from scaled particle theory

The thermodynamic properties of fluids confined to disordered porous solids are studied using a scaled particle theory approach. For simple hard sphere fluids in matrices of hard spheres, this method is of comparable accuracy to those previously introduced. In past studies of such systems, a strong thermodynamic similarity between the partly quenched and fully annealed cases has been evident; an exception to this behavior occurs when the diameters are nonadditive. For adsorbed polymeric molecules, on the other hand, the scaled particle theory introduced in this paper is the only route to the thermodynamics yet presented. The partition coefficients for polymers at infinite dilution in matrices of various porosities agree well with simulation over many orders of magnitude. For bulk polymers, the scaled polymer predictions are in much closer agreement with simulation than those of the traditional pressure and compressibility equations.