How Does Nanoscale Roughness Influence Wetting Behavior?
Eric M. Grzelak, Dept. of Chemical and Biological Engineering, University at Buffalo, 303 Furnas Hall, Buffalo, NY 14260 and Jeffrey R. Errington, Chemical and Biological Engineering, University at Buffalo, 303 Furnas Hall, Buffalo, NY 14260.
The way in which a fluid wets a surface it contacts depends greatly on the properties of that surface, including its roughness. This is evidenced by the successes and failures of things such as metal welded ceramics or water repellent fabrics. In this presentation we illustrate our recent computational work designed to better understand the effects on wetting of surface roughness ranging from molecular to nanoscopic length scales. Grand canonical transition matrix Monte Carlo simulations are used to determine the surface free energy of a fluid in contact with an atomistically described surface containing measureable roughness. The free energy is then used to calculate spreading coefficients and prewetting saturation points below and above the wetting temperature respectively. These data are then extrapolated to precisely determine the wetting temperature. In this study we use a Lennard-Jones fluid interacting with a substrate comprised of static particles. These particles are arranged in crystalline configurations and then etched to provide nanoscopic contours. The results of our simulations are compared to predictions from the Wenzel and Cassie wetting models. Lastly, finite-size influences on the technique are explored.