(659c) Evaluation of the Interface Potential Via a Force-Based Virtual Box Approach within the Isothermal-Isobaric Ensemble

The wetting properties of fluids on solid surfaces play a significant role in industrial applications, such as material synthesis and design. We have pursued a so-called interface potential approach, wherein one considers the growth of a thin fluid film from a solid surface. Two versions of the approach are employed: spreading and drying. The spreading (drying) interface potential provides the surface excess free energy as a function of the thickness of a thin liquid (vapor) film adjacent to the solid surface and in a mother vapor (liquid) phase. These free energy curves provide insight into the qualitative aspects of the wetting behavior and quantitative measures of wetting properties. Our group previously developed a means to compute these interface potentials via Transition Matrix Monte Carlo (TMMC) simulation within the grand canonical ensemble. In this presentation, we describe a new means to compute the interface potentials within an isothermal-isobar ensemble. The approach employs a force-based strategy to compute the free energy. More specifically, the average force the fluid imparts on the surface is calculated at multiple film thicknesses, and these data are integrated to determine the interface potential. Within the spreading method, one samples configurations with a highly elongated simulation box. As such, we leverage a virtual box strategy in which one replaces the bulk-like interior of the pore with a virtual box that is handled analytically. A combined Molecular Dynamics and Monte Carlo simulation algorithm is used to improve sampling and accuracy. We present results for (1) a Lennard-Jones fluid at an atomistic FCC substrate at different temperatures and substrate strengths and (2) SPC/E water at a structureless 9-3 surface.