Ionic liquids for liquid-in-glass thermometers

Abstract

The varied portfolio of applications of ionic liquids (ILs) is broadened in this work by presenting the possibility of their use as thermometric fluids in liquid-in-glass thermometers. Two ILs, namely tris(2-hydroxyethyl)methylammonium methylsulfate ([TEMA][MeSO₄]) and trihexyl(tetradecyl)phosphonium bis{(trifluoromethyl)sulfonyl}amide ([P₆₆₆₁₄][NTf₂]), have been selected for the construction of thermometers with ranges of operation tuned to general and speciality applications. The regular expansion of the IL volume with changes in temperature has been tested, and successful prototypes have been built, consisting of liquid-in-glass devices with an approximately spherical reservoir and a capillary tube attached. These devices have the advantage of operating with a fluid of ionic nature and a practically negligible vapor pressure. In addition, the inherent tunability of IL properties is a powerful tool in the possible design of speciality thermometers.