The Study Of Density And Surface Tension Of IL-Based Systems Containing TBP,DMC Or H₂O

Ionic liquid systems have shown great potential for industrial production.However,highly viscous nature of ILs often limits their application.The binary system composed of ionic liquid and organic solvent or the ternary system consisting of ionic liquid and water/organic solvent greatly reduce the viscosity of the ionic liquid.Thermodynamic properties of IL system are essential for the designing process and application.In this paper,the density and surface tension of ionic liquid binary and ternary systems were measured.The related thermodynamic functions were calculated and the effect of different anion and water on the density and surface tension were studied.The following research work has been investigated in this work:The density of pure substances and ionic liquid binary system were measured by vibrating tube densitometer at atmospheric pressure and in the temperature?293.15 to323.15?K range.Firstly,the density of 1-butyl-3-methylimidazolium tetrafluoroborate[Bmim][BF₄],1-butyl-3-methylimidazolium hexafluorophosphate?[Bmim][PF₆]?and1-butyl-3-methylimidazolium bis?trifluoromethylsulfonyl?imide?[Bmim][Tf₂N]?,tributyl phosphate?TBP?and dimethyl carbonate?DMC?were measured.The density data were compared with the literature data,the deviation was within 0.4%.From the results found that density of ionic liquid decreases with the decreasing anion volume.Then,the density of[Bmim][PF₆]-DMC,[Bmim][PF₆]-TBP,[Bmim][BF₄]-TBP and[Bmim][Tf₂N]-TBP were measured.The excess molar volume(?1_m^E?was calculated and successfully correlated with the Redlich-Kister equation,and the standard deviation was within 0.04.It was found that the excess molar volume of the binary systems[Bmim][PF₆]-DMC,[Bmim][PF₆]-TBP and[Bmim][BF₄]-TBP were all negative over the entire concentration range while the excess molar volume of the[Bmim][Tf₂N]-TBP system changing from negative to positive with the increasing of IL concentration.The variation of excess molar volume in different systems depend on the difference in shape and size of the unlike molecules as well as the dispersion type interactions over the specific interactions.The surface tension of three pure ionic liquids and ionic liquid binary system were measured by platinum plate method at atmospheric pressure and in the temperature?293.15to 323.15?K range.Comparison of the surface tension data for[Bmim][BF₄],[Bmim][PF₆]and[Bmim][Tf₂N],it was found that surface tension decreases with the increasing of anion volume.The surface tension of three systems[Bmim][PF₆]-TBP,[Bmim][BF₄]-TBP,and[Bmim][Tf₂N]-TBP were measured.The influence of different anion on the surface tension of ionic liquid system was studied.The results show that the surface tension of the ionic liquid binary system decreases with the increasing of anion volume.From the point of view of molecular interaction,when the anion size increasing,increasing of charge delocalization and weakening of hydrogen bond result in surface tension decreasing.In order to study the effect of water on the ionic liquid system,the density and surface tension of[Bmim][BF₄]-TBP-H₂O ternary system were measured at atmospheric pressure and in the temperature?293.15 to 323.15?K range.The excess molar volume was calculated by density data.It was found that the excess molar volume changing from negative to positive with the increasing of IL concentration.The main reason was that the water destroys the interaction between the anion and cation of ionic liquid,and water molecule forms hydrogen bond with anion and cation of ionic liquid.In the presence of a large amount of water,the surface tension rapidly increases,which indicates that the ionic liquid was equivalent to a surfactant in water.