Molecular Dynamics Simulation Of Ionic Liquid-water Systems

Ionic liquids(ILs)have been widely applied in various industrial fields as a new type of green environment-friendly materials,but it's inevitable to incorporate small molecules in the process of ILs production.And ILs are often hygroscopic,even those hydrophobic ILs can absorb a certain amount of water from air under normal conditions.It leads to the change of micro-structure and dynamics properties greatly.In this paper,Mixtures of ILs and water were studied by the molecular dynamics simulation.Summary of main research contents and conclusions are:Firstly,effects of water on the viscosity properties and microstructure of 1-butyl-3-methylimidazole acetate([Bmim][Ac])were studied by molecular dynamics simulation.The results showed that the viscosity of[Bmim][Ac]increases firstly and then decreases with the increase of water content,which was same to the experimental phenomenon.The chainlike structure of anions and water phases were observed in the mixtures.The water content increases the chainlike structure until the water content was saturated.The formation of the chainlike structure reduces the diffusivity of systems and increases viscosities,and then water acts as diluent in the system which lead to the decrease of viscositiesSecondly,anions of tetrafluoroborate([BF4]-),bis[(trifluoromethyl)sul-fonyl]imide([Tf2N]-),propionate([C3COO]-)with[Bmim]+ and 1-butylpyridine acetate([Bpy][Ac])with water were used to study the effect of anions and cations on the viscosity of the system.The results showed that the viscosity of[Bmim][BF4]and[Bmim][Tf2N]decrease monotonically with the increase of water content.The viscosity of the system containing carboxylic acid anions increase firstly and then decrease with the increase of water content,and chainlike structure were observed in the mixtures too,which is same to the systems of[Bmim][Ac].Finally,the cluster behavior of[Cnmim][Cl](n=4,6,8,10,12)aqueous solution was studied.The results showed that the cluster increases with the increase of ILs concentration and the increase of imidazole cation side chain length.