Water Absorption and Effect of Water Content on Viscosity and Electrical Conductivity of Two Diethylmethylammonium Ionic Liquids ^†

The effect of environmental water on certain properties of ionic liquids (ILs) can be decisive when considering a possible industrial application. The effect of environmental water absorption on electrical conductivity (using a conductimeter Crison Basic 30) and viscosity (using a rheometer AR2000 TA Instruments) on two diethylmethylammonium ionic liquids was analyzed. The studied compounds were based on a cation (diethylmethylammonium) and two anions (methanesulfonate and trifluoromethanesulfonate). In both ionic liquids the water absorption corresponded to a Fickian behavior, agreeing with previous literature data on other ILs, being methanesulfonate much more hygroscopic than trifluoromethanesulfonate (28% and 6% in weight for [EEMAm][MeSO₃] and [EEMAm][OTf], respectively). As expected, water considerably increased the ionic conductivity; values were duplicated in the case of [EEMAm][OTf] and quadruplicated for [EEMAm][MeSO₃]. Similarly, the viscosity decreased drastically with water incorporation in the IL—showing changes of 88% and 66% for trifluoromethanesulfonate and methanesulfonate, respectively. Furthermore, in the case of diethylmethylammonium trifluoromethanesulfonate, the functional dependence of the viscosity with the molar fraction of water was studied. According to the observed behavior, the viscosity of the pure IL was estimated using the equation proposed by Seddon et al.