Electrolytic conductivity of four imidazolium-based ionic liquids

In this article, electrolytic (ionic) conductivity measurements of four ionic liquids (ILs), namely, 1-ethyl-3-methylimidazolium bis[(trifluoromethyl) sulfonyl] imide ([C₂2 mim][NTf₂ 2 ]), 1-ethyl-3- methylimidazolium trifluoromethanesulfonate ([C₂ 2 mim][OTf]), 1-hexyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([C₆ 6 mim][NTf₂ 2 ]), and 1-ethyl-3-methylimidazolium ethyl sulfate ([C₂ 2 mim][EtSO₄ 4 ]) (ECOENG212®), were performed in a temperature range of (288.15 to 333.15) K. [C₆ 6 mim][NTf ₂ 2 ] was chosen to be a reference ionic liquid for several properties, including the electrolytic conductivity by the IUPAC Project 2002-005-1-100. For that reason, the measurements performed with that ionic liquid primarily serve the purpose to validate the instrumentation and the experimental procedure used in this work. The measurements were carried out using a complex impedance method, applying a novel electronic device designed and constructed for this purpose. The complete setup includes a Schott Instruments LF 913 T, used as a four-electrode conductivity cell, and a lock-in amplifier. The cell was calibrated using standard reference KCl aqueous solutions. The measurements of the impedance of the conductivity cell were carried out along a range of frequencies from (0.2 to 30) kHz, and the results were extrapolated to infinite frequency, in order to determine the electrolytic conductivity of the liquid samples. The results obtained for the ionic liquid [C₆6 mim][NTf₂ 2 ] were compared to reference data, and it was estimated that the overall uncertainty of the present results is better than 2 %. All the data obtained were compared with available literature data, and were analyzed and discussed in respect to the effect of temperature, cation alkyl chain length, and anion.