Monte Carlo simulation strategies to compute interfacial and bulk properties of binary fluid mixtures

We introduce Monte Carlo simulation methods for determining interfacial properties of binary fluid mixtures. The interface potential approach, in which the interfacial properties of a system are related to the surface excess free energy of a thin fluid film in contact with a surface, is utilized to deduce the wetting characteristics of a fluid mixture. The strategy described here provides an effective means to obtain the evolution of interfacial properties with the chemical composition of the fluid. This task is accomplished by implementing an activity fraction expanded ensemble technique, which allows one to obtain elements of the interface potential as a function of composition. We also show how this technique can be utilized to calculate bulk coexistence properties of fluid mixtures in an efficient manner. The computational strategies introduced here are applied to three model systems. One includes an argon-methane fluid mixture that is known to display simple behavior in the bulk. The second fluid model contains a size asymmetric mixture that exhibits azeotropy. The third model fluid is the well-studied size symmetric mixture that displays liquid-liquid-vapor phase coexistence. The techniques outlined here are used to compile the composition dependence of spreading and drying coefficients, liquid-vapor surface tension, and contact angle for these systems. We also compare our surface tension results with values estimated from predictive-style models that provide the surface tension of a fluid mixture in terms of pure component properties. Overall, we find that the general approach pursued here provides an efficient and precise means to calculate the bulk and wetting properties of fluid mixtures.