Chemical speciation in ionic liquids and their mixtures with polar solvents using dielectric spectroscopy

Hefter, G., Buchner, R., Hunger, J. and Stoppa, A. (2009) Chemical speciation in ionic liquids and their mixtures with polar solvents using dielectric spectroscopy. In: Plechkova, N.V., Rogers, R.D. and Seddon, K.R., (eds.) Ionic Liquids: From Knowledge to Application. American Chemical Society, Washington, DC, pp. 61-74.

Abstract

Broadband dielectric relaxation spectroscopy (DRS) is a powerful tool for studying the nature and dynamics of room-temperature ionic liquids, as well as providing the only means to directly measure their dielectric constants. The DR spectra of neat ionic liquids exhibit many modes, especially at high frequencies, where they reflect 'intermolecular' vibrations and librations. Detailed investigations have also been made into mixtures of ionic liquids with molecular solvents of varying character. The spectra indicate that typical ionic liquids retain their chemical nature even after significant dilution by a molecular solvent such as dichloromethane. Contrary to popular belief, there is little evidence for the existence of discrete ion pairs in the neat ionic liquids; such species appear to exist only at high dilution (typically at xIL < 0.1) in molecular solvents.