WATER ABSORPTION AND EFFECT OF WATER CONTENT ON VISCOSITY AND ELECTRICAL CONDUCTIVITY OF TWO DIETHYLMETHYLAMMONIUM IONIC LIQUIDS

Since 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) of two diethylmethylammonium ionic liquids was analyzed. The studied compounds are 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 of other ILs [1], being the methanesulfonate much more hygroscopic than the trifluoromethanesulfonate (28% and 6% in weight for [C₂C₂C₁N][MeSO₃] and [C₂C₂C₁N][OTf], respectively). As it was expected, water considerably increases the ionic conductivity; values were duplicated in case of [C₂C₂C₁N][OTf] and quadruplicated for [C₂C₂C₁N][MeSO₃]. Likewise, the viscosity decreases drastically with water incorporation in the IL; changes of 88 % and 66% for trifluoromethanesulfonate and methanesulfonate, respectively, were measured.

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. [2].