Understanding Phase Separation of Water/O-alkylated Ionic Liquid Mixtures through Molecular Dynamics Simulation

Abstract

In this study, the phase separation between water and hydrophobic ionic liquids (ILs) composed of amide-based O-alkylated cations (i.e. O-ethyl-dimethylacetamidium (EDEA), O-methyl-dimethylacetamidium (MDEA), O-methyl-dimethylformamidium (MDMF) and O-methyl-1-ethylpyrrolidinonium (MEPyr)) and trifluoromethanesulfonate (TfO) anion was investigated via molecular dynamics simulations. We found that pcff force field, along with the scaled AM1-BCC charge model, can properly describe the behavior of the ionic liquid, which was validated by the calculated density of each ionic liquid. Phase separation of randomly mixed water-IL systems were observed within dozens of nanoseconds. In order to quantify the miscibility between water and hydrophobic ILs, relative concentration profiles of water-IL mixtures and interaction energies of water-ion were investigated for all water-IL systems. This theoretical information about the phase separation could serve as a cornerstone for the extraction of metal ions using ILs.