Adventitious Water Sorption in a Hydrophilic and a Hydrophobic Ionic Liquid: Analysis and Implications

The sorption of water in ionic liquids (ILs) is nearly impossible to prevent, and its presence is known to have a significant effect on the resulting mixtures' bulk and interfacial properties. The so-called "saturation" water concentrations have been reported, but water sorption rates and mixing behaviors in ILs are often overlooked as variables that can significantly change the resulting mixtures' physical properties over experimental time frames of several minutes to hours. The purpose of this work is to establish a range of these effects over similar time frames for two model ILs, protic ethylammonium nitrate (EAN) and aprotic butyltrimethylammonium bis(trifluoromethylsulfonyl)imide (N1114 TFSI), as they are exposed to controlled dry and humid environments. We report the water sorption rates for these liquids (270 ± 30 ppm/min for EAN and 30 ± 3 ppm/min for N1114 TFSI), examine the accuracy and precision associated with common methods for reporting water content, and discuss implications of changing water concentrations on experimental data and results.