Structural effects in partially-wetting thin evaporating liquid films near the contact line

Abstract

Evaporating thin liquid films at triple-phase lines play important roles in phase-change processes. Many researchers have tried to model a steady one on an isothermal surface using continuum mathematical models. Usually they choose to solve the profile from a nanoscale position where the film thickness is slightly larger than the adsorbed film. This position is vaguely defined and due to the lack of experimental information, assumptions have to be made about the initial film profile especially the slope and curvature. In the present work, we apply the boundary conditions at the microscale and solve the film profile back through the nanoscale. The vagueness and assumptions are therefore avoided. To achieve comprehensive description for the very thin part near the adsorbed film, the structural force component and the short-range Born repulsion component are included in the disjoining pressure expression besides the dispersion component. We try out five different forms of dispersion components and five different forms of structural components. It is found that only when dispersion component, short-range Born repulsion component, and one specific form of structural component are working together, a complete film profile from microscale to nanoscale can be obtained including the thin film beyond the apparent contact line, and the obtained profile is qualitatively consistent with the most recent experimental report. The results indicate that an oscillatory structural force of exponential decay dominates when the film thickness is between 2 and 25 molecular diameters.