Charge Transport and Dipolar Relaxations in Imidazolium-Based Ionic Liquids

Charge transport and dipolar relaxations in a series of imidazolium-based ionic liquids are studied by means of broadband dielectric spectroscopy. Despite the shift of more than 5 decades in the dielectric spectra upon systematic variation of the anion, scaling with respect to the dc conductivities and the characteristic rates yields a collapsing plot. The dielectric spectra are described at higher frequencies in terms of dipolar relaxations whereas hopping conduction in a random spatially varying energy landscape is quantitatively shown to dominate the spectra at lower frequencies. The beta-relaxations observed for both the precursor and the ionic liquids are assigned to librational motion of the imidazolium ring. The corresponding dielectric strength exhibits a strong dependence on the anion.