Monte Carlo simulation methods for computing the wetting and drying properties of model systems

Abstract

We introduce general Monte Carlo simulation methods for determining the wetting and drying properties of model systems. We employ an interface-potential-based 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. Two versions of this approach are explored: a "spreading" method focused on the growth of a thin liquid film from a surface in a mother vapor and a "drying" method focused on the growth of a thin vapor film from a surface in a mother liquid. The former provides a direct measure of the spreading coefficient while the latter provides an analogous drying coefficient. When coupled with an independent measure of the liquid-vapor surface tension, these coefficients enable one to compute the contact angle. We also show how one can combine information gathered from application of the spreading and drying methods at a common state point to obtain direct measures of the contact angle and liquid-vapor surface tension. The computational strategies introduced here are applied to two model systems. One includes a monatomic Lennard-Jones fluid that interacts with a structureless substrate via a long-ranged substrate potential. The second model contains a monatomic Lennard-Jones fluid that interacts with an atomistically detailed substrate via a short-ranged potential. Expanded ensemble techniques are coupled with the interface potential approach to compile the temperature- and substrate strength-dependence of various interfacial properties for these systems. Overall, we find that the approach pursued here provides an efficient and precise means to calculate the wetting and drying properties of model systems.

Liquid drops on a surface: Using density functional theory to calculate the binding potential and drop profiles and comparing with results from mesoscopic modelling

“…This prevents a quantitative comparison between our results with existing simulation results for continuum models, such as those in Refs. [16][17][18][19][20][21][22][23]. However, since we do find good qualitative agreement, we are currently applying the method using continuum (FMT) DFT.…”

Understanding the influence of Coulomb and dispersion interactions on the wetting behavior of ionic liquids

“…5,19,20 The scaling approach adopted here allows us to readily compare the wetting properties of ionic liquids with those of the base Lennard-Jones fluid (α = 0), which have been thoroughly investigated in earlier works. 1,2,21 We note that the potential examined in this study differs from the one used by Leroy and Weiss 5 in another important aspect. In their study, a parameter λ was used to modulate the dispersion interactions without affecting the repulsive part.…”

“…The interface-potential-based approach employed here allows us to calculate surface tensions of fluids over a wide range of temperature. 2 In this work, we provide results for surface tensions of various ionic liquids and discuss their compliance with Guggenheim's corresponding states theory.…”

“…2 This method enables us to obtain precise values of surface tensions in a computationally efficient manner. In Figure 2, we plot the surface tensions as a function of temperature for all fluids.…”

“…We note that the potential associated with the control wall does not affect the solid-fluid interfacial properties at the substrate of interest. 2 We now briefly explain the procedure used to compute wetting properties. A detailed description of the approach is provided in recent articles from our group.…”