Thermotropic Phase Transitions in Butyltrimethylammonium Bis(trifluoromethylsulfonyl)imide Ionic Liquids are Dependent on Heat Flux.

Transmission infrared spectroscopy (IR) and differential scanning calorimetry are used to identify and characterize multiple phase transitions of butyltrimethylammonium bis(trifluoromethylsulfonyl)imide ([N1114] [TFSI]). Phase-dependent properties are analyzed using temperature-controlled transmission IR, in which we identify changes in the molecular arrangements at and around phase transition temperatures between -80 and 30 °C, which span crystallization and melting phase transitions. Our data report the dependence of phase transition behavior across multiple heat flow rates and the resulting molecular organizations that are formed. This is significant as temperature-specific organizations and properties of ionic liquids (ILs) contribute significantly to their application in separations and in devices. We also identify and discuss the relationship between phase transition temperatures and classes of those transitions when various temperature ramp rates are applied. Our analysis indicates that these relationships of IL thermochemistry could be developed as a diagnostic for assigning phase transition types.