Thermochemical Properties of the 1-Ethyl-3-Methylimidazolium Bis(trifluoromethylsulfonyl)imide Ionic Liquid under Conditions of Equilibrium with Atmospheric Moisture

Abstract

Thermochemical properties of the 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ionic liquid [EMim]NTf₂ containing moisture absorbed from the atmosphere (0.242 wt %) are investigated. The phase behavior and thermal stability relative to salt dried in vacuum are studied by means of thermogravimetry and differential scanning calorimetry at different heating and cooling rates. The glass transition, crystallization, and melting temperatures, the enthalpies of phase transitions, and the changes in heat capacity during the formation of glass are determined. It is established that the absorbed water crystallizes at a temperature of around −40.6°C and has virtually no effect on the thermal stability and phase behavior of the salt. Rapid cooling results in the ionic liquid transitioning into the glass state at −91.7 °C and the formation of three mesophases with different melting temperatures; one crystalline modification that melts at a temperature of −19.3°C forms upon slow cooling.