Mass and charge transport in 1-alkyl-3-methylimidazolium triflate ionic liquids.

Abstract

Temperature-dependent transport properties in ionic liquids, such as the ionic conductivity and fluidity, are often characterized empirically through equations that require multiple adjustable fitting parameters in order to adequately describe the data. These fitting parameters offer no insight into the molecular-level mechanism of transport. Here the temperature dependence of these transport properties in 1-alkyl-3-methylimidazolium triflate ionic liquids is explained using the compensated Arrhenius formalism (CAF), where the conductivity or fluidity assumes an Arrhenius-like form that also contains a dipole density dependence in the exponential prefactor. The resulting CAF activation energies for conductivity and fluidity are much higher than those obtained from polar organic liquids and electrolytes. The CAF very accurately describes the temperature dependence of both conductivity and fluidity using only system properties (i.e., density and activation energy). These results imply that the transport mechanism in molten salts is very similar to that in polar organic liquids and electrolytes.