Understanding Solute Diffusion and Friction in Ionic Liquids

该项目由宾夕法尼亚州立大学的Mark Maroncelli教授领导，由化学部的化学结构动力学和机理(CSDM-A)计划资助，旨在发展对一种新兴液体介质中分子运动的基本了解，这种液体介质称为室温离子液体(也称为离子液体)，在许多具有重要技术意义的领域具有相当大的前景，例如润滑剂、电池中的电解液和合成高价值化学品的溶剂。今天常用的液体由中性分子组成，而离子液体只由带电物种组成，如钠和氯-，这些离子是普通食盐的组成成分。尽管这样的小离子之间的强烈吸引力使氯化钠成为固体，除非在非常高的温度下，但通过增加组成离子的大小和做其他事情来抑制凝固，人们可以创造出在室温下保持液体的纯离子材料。对如何预测离子液体在这些应用中重要的基本方面，如溶质分子在给定的离子液体中移动的速度等认识不足，阻碍了它们的应用。马龙塞利教授和他的团队使用实验和理论工具相结合的方法，通过研究离子液体的结构和动力学如何决定分子运动中的摩擦力来应对这一挑战。宾夕法尼亚州立大学的研究小组正在使用计算机模拟，并辅之以一些核磁共振实验，以构建对离子液体中分子传输和重定向动力学的预测性理解，特别是这些动力学如何依赖于给定液体的结构及其离子的化学组成。第一个项目需要分子动力学模拟与溶质扩散实验数据的统计分析相结合，以开发可用于预测潜在技术感兴趣的新的溶质-离子液体组合的行为的模型。第二个项目使用模拟和理论相结合的方法来解释最近正电子湮没谱(PALS)技术应用于离子液体时所获得的明显反常的结果。PALS是一种众所周知的测量聚合物材料中空隙的方法，但它最近在离子液体中的应用提供了似乎不切实际的结果。由于空穴结构是分子输运理论的核心，这个项目试图学习如何正确解释离子液体中的PALS数据。最后一个项目涉及溶质旋转的模拟和核磁共振实验，以探索空穴如何随时间变化以及这些空穴动力学如何影响化学反应。

This project, led by Professor Mark Maroncelli at Penn State and funded by the Chemical Structure Dynamics and Mechanism (CSDM-A) program of the Chemistry Division, seeks to develop a fundamental understanding of molecular motion in an emerging class of liquid media known as room temperature ionic liquids (also called ionic liquids), which hold considerable promise in a number of areas of technological importance, for example as lubricants, electrolytes in batteries, and solvents for synthesis of high-value chemicals. Whereas liquids in common use today consist of neutral molecules, ionic liquids are comprised of only charged species, ions like Na+ and Cl-, the constituents of common table salt. Although the strong attraction between such small ions renders NaCl, solid except at very high temperatures, by increasing the sizes of the component ions and doing other things to inhibit solidification, one can create purely ionic materials that remain liquid at room temperature. Insufficient understanding of how to predict the basic aspects of ionic liquids important in these applications, such as how quickly a solute molecule moves through a given ionic liquid, hampers their applications. Professor Maroncelli and his group use a combination of experimental and theoretical tools to address this challenge by studying how the structure and dynamics of ionic liquids determine the friction experienced in molecular movements. The Penn State research team is using computer simulations, supplemented by some NMR experiments, to construct a predictive understanding of molecular transport and re-orientional dynamics in ionic liquids, in particular how these dynamics depend upon the structure of a given liquid and the chemical makeup of its ions. The first project entails molecular dynamics simulations coupled to statistical analysis of experimental data on solute diffusion in order to develop models that can be used to predict the behavior new solute - ionic liquid combinations of potential technological interest. The second project uses a combination of simulation and theory to interpret apparently anomalous results obtained when the technique positron annihilation spectroscopy (PALS) was recently applied to ionic liquids. PALS is a well-known method for measuring voids in polymeric materials, but its recent use in ionic liquids provided seemingly unrealistic results. Because void structure is central to theories of molecular transport, this project seeks to learn how to correctly interpret PALS data in ionic liquids. The final project involves simulations and NMR experiments of solute rotations in order to explore how voids change over time and how these void dynamics may influence chemical reactions.