An Analysis of the Thermal Transition Behavior of P666,14 NTF2 Around the Liquid-liquid Transition

Recent research has suggested that various ionic liquids (ILs) may exhibit signs of liquid-liquid transitions (LLT) at temperatures around the glass transition. Because the presence of an LLT in any liquid would have large implications on our understanding of the potential behavior of all liquids, overwhelming evidence is needed to support such a claim.

Herein, we conducted experiments on ILs based on the P666,14 cation (Trihexyltetradecylphosphonium bis (trifluoromethylsulfonyl)amide), with an emphasis on the compounds containing an NTF2 anion. The results show evidence of a transition occurring that could likely be an LLT; however, additional unexplained features were found to be present as well. Calorimetry and X-ray diffraction experiments were performed on these samples to elucidate the thermodynamic signatures of such transitions, and we have arrived at conclusions that provide likely origins for each thermal event, and additional support for the conclusion that an LLT occurs in these liquids.