Capillary condensation in the two-dimensional lattice gas: A Monte Carlo test of fluctuation corrections to the Kelvin equation

Abstract

A two-dimensional lattice gas model with nearest-neighbour attractive interaction confined in a strip of width L between two parallel boundaries at which an attractive short-range force acts is studied by Monte Carlo simulations, for cases where the system is in the wet phase near the critical wetting transition line for . We study the shift of the chemical potential of the transition in the strip as a function of L by thermodynamic integration methods, , and also obtain the thickness of the wetting film at the chemical potential at which capillary condensation occurs. In the range the data are consistent with a variation according to the Kelvin equation, , as well as with a shifted Kelvin equation, , with a constant . Thus, we find no evidence for the fluctuation correction predicted by Parry and Evans. This failure is traced back to the fact that in this range of linear dimensions there are not yet any well developed wetting layers at coexistence, and the prediction from the theory of complete wetting does not hold in this range either. Instead we empirically find a relation over the whole range of system sizes we studied.