Development and Application of Molecular Simulation Methods to Compute Bulk and Interfacial Properties of Ionic Liquids

计算离子液体体积和界面性质的分子模拟方法的开发和应用

• 批准号: 1362572
• 负责人: Jeffrey Errington
• 金额: $ 40.5万
• 依托单位: SUNY at Buffalo
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-06-15 至 2018-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1362572&HistoricalAwards=false
• 关键词: Development; Application; Molecular; Simulation; Methods

Jeffrey Errington of the State University of New York at Buffalo is supported by an award from the Chemical Theory, Models and Computational Methods program in the Chemistry Division to carry out the development and application of molecular simulation methods to compute properties of ionic fluids at interfaces, e.g., where another fluid or the walls of a container is encountered. These places are particularly difficult for accurate computations compared to others away from interfaces. Numerous current and emerging technologies such as supercapacitors (which store energy in small areas) and solar cells (which convert sunlight to electricity) contain ionic fluids, e.g., salts in which the ions move as liquids at room temperature. In many cases, how well such devices perform their work depends on properties of the fluid in more than one place, i.e., both close to and far from containing walls. Development of a deeper fundamental understanding of the behavior of ionic fluids in the presence of surfaces would have a profound influence on the ability of scientists and engineers to improve device performance, design novel technologies, and harness the unique features of natural systems. For example, information of this type may provide insight into how the chemistry of an ionic liquid or surface could be tuned to optimize the performance of a supercapacitor in energy storage, improve a coating placed on various materials, or facilitate development of a lens whose focus and other properties can be changed at will. Both graduate and undergraduate students are being trained in the areas of surface thermodynamics, statistical mechanics, and computer simulation. The principal investigator also participates in outreach at a local middle school.The group studies two fundamental issues: (1) the temperature dependence of the interfacial properties (e.g., contact angle) of ionic fluids such as room temperature ionic liquids (RTILs), molten salts and charged colloids, and (2) the impact of small molecules, such as water and carbon dioxide, on the interfacial properties of RTILs. The temperature dependence of interfacial properties has received relatively little attention. Recent simulation results for model ionic fluids suggest that these fluids exhibit highly tunable temperature dependence, which could be exploited in the design of technological devices. Experiments provide contradictory views regarding how water impacts the surface tension of RTILs. In the present work, molecular simulation is used to resolve these discrepancies and provide a better understanding of the link between macroscopic interfacial properties and the manner in which molecules partition within these inhomogeneous systems. To facilitate the investigation of these issues, the group pursues two methodological advances: (1) an isothermal-isobaric version of the interface potential approach and (2) strategies for sampling mixtures of ionic liquids. The interface potential approach focuses on the surface excess free energy of a thin fluid film in contact with a substrate. The investigator's group has employed a grand canonical version of this approach for several years with success. However, application of this technique to complex systems is hindered by molecule transfers required within a grand canonical ensemble. The research team addresses this limitation via development of a version of the method that is implemented within the isothermal-isobaric ensemble. This advance allows one to both address complex systems and leverage popular molecular dynamics software to complete calculations.

布法罗的纽约州立大学的Jeffrey Errington获得了化学系化学理论、模型和计算方法项目的奖项支持，进行分子模拟方法的开发和应用，以计算界面处离子流体的性质，例如，其中遇到另一种流体或容器壁。与远离接口的其他地方相比，这些地方特别难以进行精确计算。 许多当前和新兴的技术，如超级电容器（其在小区域中存储能量）和太阳能电池（其将阳光转化为电力）包含离子流体，例如，离子在室温下以液体形式运动的盐。 在许多情况下，这种装置如何良好地执行其工作取决于在多于一个地方的流体的性质，即，无论是靠近还是远离容器壁。对离子流体在表面存在下的行为的更深入的基本理解的发展将对科学家和工程师提高设备性能，设计新技术和利用自然系统的独特功能的能力产生深远的影响。 例如，这种类型的信息可以提供对如何调节离子液体或表面的化学性质以优化超级电容器在能量存储中的性能、改善置于各种材料上的涂层或促进其焦点和其他性质可以随意改变的透镜的开发的洞察。研究生和本科生都在表面热力学，统计力学和计算机模拟领域接受培训。主要研究者还参加了当地一所中学的外展活动。该小组研究了两个基本问题：（1）界面性质的温度依赖性（例如，接触角），和（2）小分子，如水和二氧化碳，对RTIL界面性质的影响。界面性质的温度依赖性受到的关注相对较少。最近的模拟结果表明，这些流体具有高度可调的温度依赖性，这可以利用在技术设备的设计。关于水如何影响RTIL的表面张力，实验提供了相互矛盾的观点。在目前的工作中，分子模拟是用来解决这些差异，并提供了一个更好的理解宏观的界面性质和分子在这些不均匀的系统内分区的方式之间的联系。为了促进这些问题的调查，该小组寻求两种方法上的进步：（1）界面势方法的等温等压版本和（2）离子液体混合物的采样策略。界面势法着重于与基底接触的薄流体膜的表面过剩自由能。研究者的小组已经成功地使用了这种方法的一个大规范版本好几年了。然而，这一技术的复杂系统的应用受到阻碍的分子转移内所需的巨正则系综。研究小组通过开发在等温等压系综内实施的方法版本来解决这一限制。这一进步使人们既可以处理复杂的系统，又可以利用流行的分子动力学软件来完成计算。