The mobile-layer model for adsorption

The adsorption isotherms for Kr monolayers on graphite measured by A. Thomy and X. Duval, J. chim. phys., 67, 1101 (1970) are transformed into the ‘spreading pressure’ as a function of the number density of adsorbed molecules and compared with the pressure of a two-dimensional Lennard-Jones fluid determined by the molecular dynamics technique. The comparison shows that the mobile-layer model for adsorption fails at low temperatures. The liquid-solid phase transitions in the adsorption monolayer appear at lower densities than in a two dimensional Lennard-Jones fluid and the adsorbed liquid layer is compressible in contrast to the two-dimensional Lennard-Jones liquid.