Understanding Solute Diffusion and Friction in Ionic Liquids

Project: Research project

Project Details


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.

Effective start/end date8/15/177/31/21


  • National Science Foundation: $450,000.00


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