Conductivity of ionic liquids in mixtures

The conductivity of a number of mixtures formed between ionic liquids (IL) and molecular liquids (ML) were investigated at several temperatures with the use of impedance spectroscopy. The specific conductivity of IL+ML mixtures show a maximum on the sigma=f(x(IL)) curve. Ionic liquids such as 1-methyl-3-propylimidazolium bromide (MPImBr) or 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF(4)) and MLs such as water, propylene carbonate (PC), N-methylformamide (NMF) and 1-methylimidazole (MIm) were used. The conductivity maximum for IL+water is at a level of ca. 92-98 mS/cm at T=298 K, while in the case of non-aqueous MLs the maximum is at ca. 18-30 mS/cm. The conductivity of a mixture of two ionic liquids EMImBF(4)+EMImBr depends monotonically on the composition. The temperature dependence of the conductivity for both neat ionic liquids as well as the mixtures, in the temperature range of 288-368 K, obeys an Arrhenius law. The activation energy E-# for the mixtures IL+ML in all cases decreases linearly at increasing amount of the molecular liquid. (c) 2005 Elsevier B.V. All rights reserved.