Thermophysical Properties of 1-Ethyl-3-methylimidazolium Ethylsulfate and 1-Butyl-3-methylimidazolium Methylsulfate Ionic Liquids

Abstract

Heat capacity, glass-transition, crystallization, and melting temperatures of 1-ethyl-3-methylimidazolium ethylsulfate ([Emim][EtSO4]) and 1-butyl-3-methylimidazolium methylsulfate ([Bmim][MeSO4]) ionic liquids (ILs) have been determined by differential scanning calorimetry (DSC). Their thermal stabilities have been analyzed by thermogravimetric analysis (TGA). Given the effect of the heating rate over the decomposition temperatures, isothermal TGA experiments are proposed as a more appropriate method to evaluate the thermal stability of the ILs. Inside the working range (−150 °C to 30 °C), [Emim][EtSO4] and [Bmim][MeSO4] present a glass-transition temperature of −78.4 °C and −91.9 °C, respectively. [Bmim][MeSO4] has a melting temperature of −4.1 °C. The Cp was determined in a working range (10 °C to 100 °C) where its value increases lineally with temperature.