Using ions to probe ionic liquids

Scientists at the U.S. Department of Energy’s Brookhaven National Laboratory are using a very small and light ion, the electron, to study the structure and dynamics of ionic liquids and how those properties influence chemical reactivity.

Ionic liquids are made of positive and negative ions that pack so poorly together that they are liquids near room temperature. They offer extremely low volatility, non-flammability, new reactivity patterns, and the formation of separate phases that allow the easy separation of products — properties that make them safer to work with, easier to recycle, and less likely to pollute the atmosphere than traditional solvents.

Brookhaven chemist James Wishart and postdoctoral research associate Alison Funston use pulsed electron beams to initiate chemical reactions in ionic liquids, causing some of the ions to give up one of their own electrons. The isolated electrons can exist for hundreds of nanoseconds surrounded by solvent. Systematic variation of ionic liquid composition shows that solvated electron absorption spectra depend strongly on the structure of the ionic liquid and on the presence of functional groups such as hydroxyl groups.

While it takes only a few nanoseconds for electrons to become fully equilibrated (solvated) in ionic liquids, that is one thousand times slower than in most conventional solvents. During that time, the pre-solvated electrons are highly susceptible to capture by low concentrations of dissolved compounds. This can result in unanticipated reactivity patterns that have profound implications for uses of ionic liquids in radiation-filled environments such as the nuclear fuel cycle.

Wishart and Funston use electron scavengers to probe this reactivity and they measure ionic liquid solvation dynamics by following the laser-induced fluorescence of dye molecules that are sensitive to their surroundings. Viscosity is a key factor in all this work, and they have designed new, lower-viscosity ionic liquids to aid these studies.

To learn more, see Funston’s poster on Wednesday, Sept. 10, 2003, at 7:30 p.m. (PHYS 372), or hear her talk during the “Ionic Liquids: Progress and Prospects” session on Thursday, Sept. 11, at 2:50 p.m. (IEC 196), both at the Jacob Javits Convention Center. This work was funded by the Division of Chemical Sciences, Office of Basic Energy Sciences at DOE’s Office of Science, and by Brookhaven’s Laboratory Directed Research and Development Program.