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，由化学部门的化学结构动力学和机制（CSDM-A）项目资助，旨在发展对一种新兴液体介质的分子运动的基本理解，这种液体介质被称为室温离子液体（也称为离子液体），它在许多重要的技术领域具有相当大的前景，例如润滑剂，电池中的电解质，以及用于合成高价值化学品的溶剂。今天常用的液体是由中性分子组成的，而离子液体只由带电的离子组成，比如Na+和Cl-，它们是普通食盐的成分。尽管这些小离子之间的强烈吸引力使得NaCl在高温下是固体，但通过增加组成离子的大小和做其他事情来抑制凝固，人们可以制造出在室温下保持液体的纯离子材料。对于如何预测在这些应用中重要的离子液体的基本方面，如溶质分子通过给定离子液体的速度有多快，了解不足阻碍了它们的应用。Maroncelli教授和他的团队通过研究离子液体的结构和动力学如何决定分子运动中所经历的摩擦，使用实验和理论相结合的工具来解决这一挑战。宾夕法尼亚州立大学的研究小组正在使用计算机模拟，辅以一些核磁共振实验，来构建离子液体中分子传输和再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，以开发可用于预测行为的模型，新的溶质-离子液体组合的潜在技术兴趣。第二个项目采用模拟和理论相结合的方法来解释正电子湮灭光谱（PALS）技术最近应用于离子液体时获得的明显异常结果。PALS是一种众所周知的测量聚合物材料空隙的方法，但它最近在离子液体中的应用提供了看似不切实际的结果。由于空洞结构是分子输运理论的核心，该项目旨在学习如何正确解释离子液体中的PALS数据。最终项目涉及溶质旋转的模拟和核磁共振实验，以探索孔隙如何随时间变化以及这些孔隙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.