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

Abstract

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