Charge transport and glassy dynamics in imidazole-based liquids

Broadband dielectric spectroscopy, differential scanning calorimetry, rheology, and pulsed field gradient-nuclear magnetic resonance (PFG NMR) are combined to study glassy dynamics and charge transport in a homologous series of imidazole-based liquids with systematic variation of the alkyl chain length. The dielectric spectra are interpreted in terms of dipolar relaxation and a conductivity contribution. By applying the Einstein, Einstein-Smoluchowski, and Stokes-Einstein relations, translational diffusion coefficients-in quantitative agreement with PFG NMR measurements-are obtained. With increasing alkyl chain length, it is observed that the viscosity increases, whereas the structural alpha-relaxation rate decreases, in accordance with Maxwell's relation. Between the rate omega(e) of electrical relaxation and the rate omega(alpha) of the structural alpha-relaxation, scaling is observed over more than six decades with a decoupling index of about 2.