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

薄膜中溶解离子添加剂对界面区结构和热质传递影响的分子动力学探索Van P.Carey机械工程系加州大学伯克利分校(NSF Proposal 0456982)项目摘要拟议的研究将包括发展两种不同类型的分子动力学(MD)模拟，用于探索溶解离子物种对薄液膜中界面区结构和热质传递的影响。我们将使用两种不同类型的模拟来探索离子添加剂在两种情况下的效果：(1)在体相之间的自由薄液膜中，(2)在固体表面的薄液膜中。分子动力学模拟将探索离子如何影响界面区域结构、界面张力和水膜的稳定性。他们还将探索先前观察到的薄膜中定向质量扩散系数和定向导热系数的变化。在这些模拟中，将使用每个物种的适当势函数来模拟水分子、离子和壁原子之间的力相互作用。MD模拟将在纯水和水和氯化钠的稀溶液以及水和氯化钾的稀溶液中进行，条件跨越溶质摩尔分数、膜厚和系统压力的广泛范围。将对溶液模拟结果进行广泛的分析，以确定离子浓度的变化如何影响界面区结构、界面附近的性质和膜的稳定性。这项研究将促进分子动力学模拟方法的发展，并将从分子水平上理解离子如何影响气泡合并过程以及固体表面液膜中的近界面输运和稳定性。由于这些现象在许多常见的沸腾和冷凝过程中起着核心作用，这些研究的结果将有助于在铸造金属部件的水淬火、微蒸发器设计以及其他一些薄膜蒸发或冷凝非常重要的应用方面的技术进步。界面区输运的探索将阐明所观察到的各向异性质量扩散和热传递的机制。界面区域的这一传输特征在过渡过程中表面活性剂在界面上的扩散以及在气液界面发生结构的分子组装方案中可能是至关重要的。本研究揭示的离子对水中界面现象的影响也将有助于理解液水界面的生物和环境过程。这项研究的一个本科生研究部分旨在鼓励未被充分代表的本科生考虑攻读MD模拟方法、先进计算或纳米工程方面的研究生课程。

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.