Temperature Behavior of the Electrical Conductivity of Emim-Based Ionic Liquids in Liquid and Solid States

In this paper we present experimental measurements of the temperature dependence of the electrical conductivity, sigma, in four ionic liquid compounds (ILs) in both the liquid and solid states and at atmospheric pressure. The chemicals measured are composed by the 1-ethyl-3-methyl-imidazolium (EMIM+) cation, which has been combined with four different anions: Cl-, Br-, BF4- and ethyl sulfate (ES-). In the liquid state, the temperature dependence of sigma, for the four ILs follows the Vogel-Tamman-Fulcher (VTF) equation with high precision. Around the transition between the solid and liquid states, the electrical conductivity of the three ILs with lighter anions presents an hysteresis loop, that can be explained as the apparition of supercooled liquid. In contrast, the EMIM-ES presents a smooth transition, without any jump in the sigma, value or any hysteresis loop (probably because its melting point is reported to be below the minimum temperature measured by us). Finally, the jump in sigma, is not related with the glass transition because its temperature value is well below the minimum temperature measured, and at that glass transition temperature the sigma, value is below the resolution of our conductivity meter (2 nS/cm).