MONOLAYER ADSORPTION OF AR AND KR ON GRAPHITE - THEORETICAL ISOTHERMSAND SPREADING PRESSURES

The validity of analytical equations for two-dimensional fluids in the prediction of monolayer adsorption isotherms and spreading pressures of rare gases on graphite is analyzed. The statistical mechanical theo ry of Steele is used to relate the properties of the adsorbed and two- dimensional fluids. In such theory the model of graphite is a perfectl y flat surface, which means that only the first order contribution of the fluid-solid interactions are taken into account. Two analytical eq uations for two-dimensional Lennard-Jones fluids are used: one propose d by Reddy-O'Shea, based in the fit on pressure and potential energy c omputer simulated results, and other proposed by Cuadros-Mulero, based in the fit of the Helmholtz free energy calculated from computer simu lated results of the radial distribution function. The theoretical res ults are compared with experimental results of Constabaris et al. (J. Chem. Phys. 37, 915 (1962)) for Ar and of Putnam and Fort (J. Phys. Ch em. 79, 459 (1975)) for Kr. Good agreement is found using both equatio ns in both cases. (C) 1997 Academic Press