Molecular Dynamics Exploration of the Effects of Dissolved Ionic Additives on Interfacial Region Structure and Heat and Mass Transfer in Thin Liquid Films

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Molecular Dynamics Exploration of the Effects of Dissolved Ionic Additives on Interfacial Region Structure and Heat and Mass Transfer in Thin Liquid Films Van P. CareyMechanical Engineering DepartmentUniversity of California, Berkeley, CA(NSF proposal 0456982)Project Abstract The proposed research will include development of two different types of molecular dynamics (MD) simulations that will be used to explore the effects of dissolved ionic species on the interfacial region structure and heat and mass transfer in thin liquid water films. We will use the two different types of simulations to explore the effects of ionic additives in two contexts: (1) in a free thin liquid film between bulk phases, and (2) in a thin liquid film on a solid surface. The proposed MD simulations will explore how the ions affect the interfacial region structure, the interfacial tension, and the stability of water films. They will also explore the previously observed variation of the directional mass diffusion coefficients and the directional thermal conductivities in the film. In these simulations, appropriate potential functions for each species will be used to model force interactions among water molecules, ions and wall atoms. MD simulations will be run with pure water and dilute solutions of water and NaCl, and water and KCl for conditions spanning wide ranges of solute mole fraction, film thickness and system pressure. The solution simulation results will be extensively analyzed to determine how variation of ion concentration affects interfacial region structure, near interface properties, and film stability. This research will advance the state of the art for MD simulation methods and it will provide a molecular level understanding of how ions affect bubble merging processes and near-interface transport and stability in liquid water films on solid surfaces. Because these phenomena play central roles in many common boiling and condensation processes, the results of these studies will contribute to technological advancements in water quenching of cast metal parts, microevaporator design, and a number of other applications in which thin film evaporation or condensation is important. The exploration of transport in the interfacial region will clarify the mechanism of the observed anisotropic mass diffusion and heat transfer. This feature of transport in the interfacial region may be critically important in the spread of surfactants over the interface during transient processes, and in molecular assembly schemes in which construction occurs at a liquid-vapor interface. The effects of ions on interfacial phenomena in water revealed by this investigation will also contribute to the understanding of biological and environmental processes at a liquid water interface. An undergraduate research component of this research will aim to encourage underrepresented undergraduate students to consider graduate studies in MD simulation methods, advanced computing or nanoengineering.