Evaporation and disjoining pressure of ultrathin film on substrate: a molecular dynamics study

Abstract

The equilibrium evaporation of the thin liquid film on a solid substrate is studied by performing molecular dynamics simulation (MD). The evaporation properties are obtained for a simple atomic system in three-phase coexistence and compared with those of the modeling methods based on the disjoining pressure. The thickness of the film is varied and goes down to as small as a few molecular diameters. The MD results show that the evaporation rate of the ultrathin film on a high-energy substrate is smaller than that of a macroscopic film because of the solid molecular potential effective over the film. The comparison with the mean field theory based on the kinetic theory of gases and the classical Hamaker theory of disjoining pressure shows a sizable discrepancy when the film thickness is comparable to the size of the interfacial region. The discrepancy mostly disappears when the disjoining pressure is derived by using the static properties from MD. This indicates that the evaporation modeling on ultrathin film of which the disjoining pressure is an integral part critically requires an accurate representation of the property.