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.

纽约州立大学布法罗州立大学的Jeffrey Errington得到了化学理论，模型和计算方法计划的奖励，以开发和应用分子模拟方法来计算接口上离子流体的特性，例如，例如，在此处，在此处遇到了另一个容器或容器的壁。与其他距离界面相比，这些位置对于准确的计算特别困难。 许多当前和新兴技术，例如超级电容器（将能量存储在小区域）和太阳能电池（将阳光转化为电能）含有离子流体，例如，在室温下将离子作为液体移动的盐。 在许多情况下，此类设备的执行程度如何取决于多个地方的流体特性，即，既靠近墙壁，又远。在存在表面上对离子流体行为的更深入的理解发展将对科学家和工程师提高设备性能，设计新颖技术和利用自然系统的独特特征的能力产生深远的影响。 例如，这种类型的信息可以提供有关如何调整离子液体或表面的化学性能以优化超级电容器在能量存储中的性能，改善放置各种材料的涂层的性能的信息，或者促进可以随意更改其焦点和其他特性的镜头的涂层。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。首席研究者还在当地的一所中学参加宣传。该小组研究了两个基本问题：（1）离子流体的界面特性（例如接触角）的温度依赖性，例如室温离子液体（RTILS），熔融盐和电荷胶体，以及（2）小对象的影响（2） rtils。界面特性的温度依赖性几乎没有得到关注。模型离子流体的最新仿真结果表明，这些流体表现出高度可调的温度依赖性，可以在技术设备的设计中利用。实验提供了关于水如何影响RTIL的表面张力的矛盾观点。在目前的工作中，分子模拟用于解决这些差异，并更好地理解宏观界面特性与分子在这些不均匀系统中分区的方式之间的联系。为了促进对这些问题的调查，该小组追求了两个方法论进步：（1）界面潜在方法的等温静相版本以及（2）对离子液体采样混合物的策略。界面电势方法集中于与基材接触的薄流体膜的表面过剩能量。研究人员小组已成功使用了这种方法的宏伟规范版本，并取得了成功。但是，在宏伟的规范合奏中需要的分子传输阻碍了将该技术应用于复杂系统。研究团队通过开发在等温静音合奏中实现的方法来解决这一限制。这一进步使人们可以解决复杂的系统并利用流行的分子动力学软件来完成计算。