Understanding the effect of nanoscale roughness on the wetting behavior of fluids using molecular simulation
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This work focuses on understanding the wetting behavior of fluids using molecular simulations. We introduce efficient Monte Carlo simulation techniques which enable us to compute important interfacial properties over a wide range of conditions. We first look at the effect of geometrical roughness on the wetting behavior of fluids. Results are presented in the form of wetting diagrams which indicates the Cassie, Wenzel, and impregnation regimes, a drop adopts on a rough surface. We examine the extent to which macroscopic models such as Cassie and Wenzel remain valid as the periodicity of the surface heterogeneities drops down to few molecular diameters. We also study the evolution of wetting diagrams with temperature. We notice that the macroscopic relations become unreliable in the Wenzel and impregnation regimes, as the length scale of features drops down to ten fluid diameters. Temperature is found to have a similar effect to that of decreasing the periodicities of heterogeneities. In the next step, we utilize the techniques developed in this work to understand the wetting behavior of water near flat non-polar surfaces. Interestingly, we observe interfacial properties such as cosθ and γ lv cosθ become independent of temperature at a particular surface strength. We also examine the extent to which substrate structure influences contact angle. We compare our results for the three model surfaces and notice contact angle to be relatively insensitive to the structure of the wall. We also study the evolution of wetting properties with temperature. Results indicate that energetic and entropic components of the work of adhesion can serve as important indicators of the degree of hydrophobicity of a surface. In the next step we introduce several simulation methodologies which allow us to understand wetting behavior of binary fluid mixtures. We study the effect of composition on important interfacial properties such as spreading, drying coefficient, contact angle and liquid vapor surface tension. We also introduce efficient simulation techniques which enables us to study the wetting behavior of liquid-liquid systems near a solid surface. This scheme allows us to track the evolution of important interfacial properties such as liquid-liquid surface tension and contact angle with pressure, temperature and surface strength.