(178ac) Molecular Dynamics Simulation Study of Tris(pentafluoroethyl)Trifluorophosphate-Based Ionic Liquid and Small Molecules Mixtures

As a new type of green solvents with many unique properties, ionic liquids have been paid much attention all over the world. Recently, tris(pentafluoroethyl)trifluorophosphate ([FEP])-based ionic liquids have been widely studied due to their excellent properties, such as hydrolytic stability, low viscosity, high electrochemical and thermal stability ^[1]. However, there is little report about the structure and properties of [FEP]-based ionic liquids from microcosmic view. To understand the properties of [FEP]-based ionic liquids, we studied the solvation properties of water (H₂O), methanol (CH₃OH) and dimethyl ether (CH₃OCH₃) in 1-hexyl-3-methylimidazolium ([hmim])[FEP] by molecular dynamics simulation.

Based on the simulation results, the excess molar volume (V^E) and excess molar enthalpy (H^E) were calculated for mixtures of H₂O- [hmim][FEP], CH₃OH-[hmim][FEP] and CH₃OCH₃-hmim][FEP]. The values of V^Eand H^E are negative for the three mixtures, and the negative values follow the order of CH₃OCH₃ > CH₃OH > H₂O. The radial distribution functions (RDF) of solute-solute of the three mixtures were investigated, which show that some H₂O/CH₃OH molecules aggregate in [hmim][FEP]. For comparison, the same RDFs for the three solutes in [hmim] hexafluorophosphate ([PF₆]) were also analyzed. It is found that [hmim][FEP] is much more hydrophobic than [hmim][PF₆], which is consistent with the experimental result in the literature ^[1].

Reference

[1].  NV. Ignat'ev, U. Welz-Biermann, A. Kucheryna, G. Bissky, H .Willner. New ionic liquids with tris(perfluoroalkyl)trifluorophosphate (FAP) anions. J Fluor Chem, 2005, 126: 1150-1159.

Acknowledgment

This work was supported by the National Natural Scientific Fund of China (21106146, 20976004, 20903098).