Journal
JOURNAL OF CHEMICAL PHYSICS
Volume 135, Issue 18, Pages -Publisher
AMER INST PHYSICS
DOI: 10.1063/1.3655817
Keywords
contact angle; drops; free energy; interface phenomena; Lennard-Jones potential; liquid films; Monte Carlo methods; surface roughness; thin films; wetting
Funding
- National Science Foundation [CBET-0828979]
- Directorate For Engineering
- Div Of Chem, Bioeng, Env, & Transp Sys [0828979] Funding Source: National Science Foundation
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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. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3655817]
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