Potts model of intermolecular interactions in 1-methyl-3-propylimidazolium chloride

Abstract

The intramolecular motions such as conformational transformations affect intermolecular interactions in an ionic liquid, because the so-called "ionic liquid" is a molecular liquid. Itoh et al. reported that modification of the side-chain in the 1-butyl-3-methylimidazolium salt could reduce the glass transition point and the viscosity coefficient, even though it approximately maintained the size of the imidazolium cation. This fact suggests that the intramolecular motions play an important role in the interaction between the imidazolium cations. We performed DFT calculations to study molecular structures of the imidazolium cations in ionic liquids, but the results on the one-body problem gave little information about macroscopic properties of ionic liquids. This fact suggests that there is no way to investigate the problem on ionic liquids without the viewpoint of the many-body problem. Now I employ the three-states Potts model to formulate intermolecular interactions between two ion-pairs with their conformations. The interaction energy between the Potts spins is estimated by DFT calculations of the ion-pair dimer in the imidazolium ionic liquids.