The predictive behavior of the phase transition temperatures of imidazolium based ionic liquids

The applicability of ionic liquids in synthetic or separation science highly depends on the temperature range within they are really liquid. Therefore, the phase transitions are the most important property of these materials. Accordingly, the solid-solid and solid-liquid phase transitions of 1-methyl-3-tetradecylimidazolium. hexafluorophosphate ([C(14)mim](+)[PF6](-)) ionic liquid was studied by density functional calculations and semiempirical AMI molecular dynamic analysis. Our results show that the recently discovered anomalous structural change observed experimentally during crystalline to crystalline phase transition can be explained at molecular level with a conversion of two stable conformation of the [C(14)mim](+)[PF6](-) pair. The solid-liquid phase transition temperature of the imidazolium, cation-based ionic liquids was found to be affected by the length of alkyl side chain of the imidazol ring. In our present work a close relationship was found between the melting point of imidazolium cation-related ionic liquids and the dynamics of atomic vibrations in the side alkyl chain of different length of the cation.