title: Monte Carlo simulation strategies for computing the wetting properties of fluids at geometrically rough surfaces.
abstract: We introduce Monte Carlo simulation methods for determining the wetting properties of model systems at geometrically rough interfaces. The techniques described here enable one to calculate the macroscopic contact angle of a droplet that organizes in one of the three wetting states commonly observed for fluids at geometrically rough surfaces: the Cassie, Wenzel, and impregnation states. We adopt an interface potential approach in which the wetting properties of a system are related to the surface density dependence of the surface excess free energy of a thin liquid film in contact with the substrate. We first describe challenges and inefficiencies encountered when implementing a direct version of this approach to compute the properties of fluids at rough surfaces. Next, we detail a series of convenient thermodynamic paths that enable one to obtain free energy information at relevant surface densities over a wide range of temperatures and substrate strengths in an efficient manner. We then show how this information is assembled to construct complete wetting diagrams at a temperature of interest. The strategy pursued within this work is general and is expected to be applicable to a wide range of molecular systems. To demonstrate the utility of the approach, we present results for a Lennard-Jones fluid in contact with a substrate containing rectangular-shaped grooves characterized by feature sizes of order ten fluid diameters. For this particular fluid-substrate combination, we find that the macroscopic theories of Cassie and Wenzel provide a reasonable description of simulation data.
authors.affiliation: Department of Chemical and Biological Engineering, University at Buffalo, The State University of New York, Buffalo, New York 14260-4200, USA.
authors.forename: Vaibhaw
authors.initials: V
authors.lastname: Kumar
authors.forename: Shyam
authors.initials: S
authors.lastname: Sridhar
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Errington
mesh_terms: D003198:Computer Simulation; D009010:Monte Carlo Method; D013499:Surface Properties; D013816:Thermodynamics; D017155:Wettability