Matsumoto Ray, Thompson Matthew W, Cummings Peter T
Department of Chemical and Biomolecular Engineering , Vanderbilt University , Nashville , Tennessee 37235 , United States.
Multiscale Modeling and Simulation Center , Vanderbilt University , Nashville , Tennessee 37235 , United States.
J Phys Chem B. 2019 Nov 21;123(46):9944-9955. doi: 10.1021/acs.jpcb.9b08509. Epub 2019 Nov 12.
The dissolution of room temperature ionic liquids (RTILs) in organic solvents has been shown to enhance ion dynamics. We previously used molecular dynamics (MD) simulations to study the ionic liquid ([BMIM][TfN]) in 22 unique solvents over a wide range of concentrations. By screening over a large parameter space, we reached several conclusions: (1) ion diffusivity increases monotonically as a function of increasing ionic liquid composition, (2) pure solvent diffusivity strongly correlates with ion diffusivity, and (3) conductivity predicted by the Nernst-Einstein (NE) equation has a maximum at intermediate compositions of ionic liquid. Building off this work, we now utilize the same parameter space to study the structure of ([BMIM][TfN]) solvated in organic solvents. We explore ion correlations through a number of structural and thermodynamic properties, including liquid densities, pair correlation functions, ion pairing and ion caging lifetimes, and free energy calculations. Through these analyses, we find that some solvents are much more effective at screening ion-ion interactions than others and that these differences impact the ion dynamics in these mixtures. In general, the strong pairing of ionic liquids negatively impacts transport properties, but some solvents can robustly screen these interactions, resulting in greatly enhanced ion dynamics. These results uncover trends connecting ionic liquid structure to transport, which can help in the design of new electrolytes for energy storage devices, such as electrical double layer capacitors and batteries.
室温离子液体（RTILs）在有机溶剂中的溶解已被证明可增强离子动力学。我们之前使用分子动力学（MD）模拟研究了离子液体（[BMIM][TfN]）在22种独特溶剂中不同浓度下的情况。通过在一个大参数空间内进行筛选，我们得出了几个结论：（1）离子扩散率随离子液体组成的增加而单调增加；（2）纯溶剂扩散率与离子扩散率密切相关；（3）由能斯特 - 爱因斯坦（NE）方程预测的电导率在离子液体的中间组成处有最大值。基于这项工作，我们现在利用相同的参数空间来研究溶解在有机溶剂中的（[BMIM][TfN]）的结构。我们通过许多结构和热力学性质来探索离子相关性，包括液体密度、对关联函数、离子配对和离子笼寿命以及自由能计算。通过这些分析，我们发现一些溶剂在屏蔽离子 - 离子相互作用方面比其他溶剂更有效，并且这些差异会影响这些混合物中的离子动力学。一般来说，离子液体的强配对会对传输性质产生负面影响，但一些溶剂可以有效地屏蔽这些相互作用，从而大大增强离子动力学。这些结果揭示了将离子液体结构与传输联系起来的趋势，这有助于设计用于储能设备（如双电层电容器和电池）的新型电解质。
