DISJOINING PRESSURE OF THIN INTERLAYERS OF A 2-DIMENSIONAL LATTICE FLUID

The thermodynamic properties of a fluid whose molecules occupy the poi nts of a plane hexagonal lattice are studied by the Monte Carlo method in a large canonical ensemble. Calculations are performed for two val ues of the energy of pairwise molecular interaction epsilon = - 0.7 an d - 0.4 kT. These values correspond to a dense two-dimensional gas at temperatures above the critical temperature. The distribution is obtai ned for local density in interlayers of different widths L bounded by lyophobic walls. Results are obtained to express the effect of L on th e mean values of density, potential energy, coordination number, adsor ption, and free energy. It is shown that overlapping of the boundary l ayers of a fluid with reduced density gives rise to lyophobic forces o f attraction and a negative disjoining pressure PI = -K(s)exp(-L/lambd a), where lambda is on the order of the correlation length xi in the b ulk fluid. The values of lambda and xi increase as the critical temper ature is approached. A statistical analysis is made of the distributio n of clusters with respect to size, as well as the shape of the cluste rs in relation to the width of the interlayers. A decrease in L is acc ompanied by a decrease in the fraction of monomers in the interlayers and elongation of the clusters in the direction of the interlayer axis .