Do Ionic Liquids Slow Down in Stages?

High impact recent articles have reported on the existence of a liquid-liquid (L-L) phase transition as a function of both pressure and temperature in ionic liquids (ILs) containing the popular trihexyltetradecylphosphonium cation (P), sometimes referred to as the "universal liquifier". The work presented here reports on the structural-dynamic pathway from liquid to glass of the most well-studied IL comprising the P cation. We present experimental and computational evidence that, on cooling, the path from the room-temperature liquid to the glass state is one of separate structural-dynamic changes.