Non-equilibrium protic and aprotic ionic liquids: Measuring the distance from the equilibrium state

The anomalous phase behaviors of ionic liquids (ILs) were examined under low temperature (LT) and high pressure (HP). Under LT condition, crystal polymorphs and multiple crystallization pathways could be found for protic IL ethylammonium nitrate ([EAN][NO3]). For 1-ethyl-3-methylimidazolium nitrate ([C(2)mim][NO3]), an aprotic IL, simple LT-crystallization behavior was observed. However, HP conditions produced complicated phase behaviors. The HP-inherent conformer of the C(2)mim(+) cation governed the crystallization pathways. In the liquid state, a variety of complicated phase transitions were influenced by multiple passible non-equilibrium degree factors: charge (scalar), dipole moment (vector), conformations (topology), and proton (transfer/network). The non-equilibrium degrees of protic and aprotic ILs were described by various solid phases both at LT and HP. (C) 2019 Elsevier B.V. All rights reserved.