Study On Electrical Conductivity Of Ionic Liquid And Molecular Liquid Mixtures

Ionic liquids(ILs)are novel green solvents with outstanding physicochemical properties,such as low vapor pressure,wide liquid range,good thermal stability,good chemical stability,high electrical conductivity and wide electrochemical window.They have been widely used in catalysis,separation,analysis and electrochemistry.However,the high viscosity of ILs limits their application in electrochemistry.Mixing ionic liquid with molecular liquid can overcome this drawback.If IL-ML mixtures are used as electrolyte,electrical conductivity is one of the most important factors influencing the electrochemical performance.In this paper,the electrical conductivities of 1-ethyl-3-methylimidazolium dicyanamid([EMIM][DCA])in propylene carbonate(PC)and ?-butyroladone(GBL)were studied,respectively.Electrical conductivities of [EMIM][DCA]-PC and [EMIM][DCA]-GBL mixtures were measured and correlated.The effects of temperature and IL concentration on the electrical conductivity were investigated comprehensively.The electrical conductivity of mixtures increases with increasing temperature.When the mole fraction of IL in mixture increases from 0 to 1,electrical conductivity increases to a maximum value,and then decreases with IL mole fraction.Besides,the maximum point moves to high IL concentration as temperature increasing.The electrical conductivity's dependence on temperature was described by Vogel-Tamman-Fulcher(VTF)equation and Arrhenius equation.VTF law showed high precision,but failed to include the effects of both temperature and IL concentration.In Arrhenius equation,the relationship between parameters(activation energy Ea and pre-exponential factor A)and the mole fraction of IL were obtained,but the accuracy of Arrhenius equation was modest.Taking advantages of both Arrhenius equation and VTF equation,some revisions of items in Arrhenius equation were made,then an improved four-parameter equation(quasi-Arrhenius equation)was proposed to correlate the electrical conductivity,in which the dependence of temperature and IL concentration were included,and the correlation results agreed well with experimental data.The electrical conductivities of [EMIM][DCA],[EMIM][DCA]-PC and [EMIM][DCA]-GBL were calculated by molecular dynamics simulation(MDS).The MDS of [EMIM][DCA] was conducted from 293.15 K to 353.15 K,and the electrical conductivity increases with increasing temperature.The MDS of [EMIM][DCA]-PC and [EMIM][DCA]-GBL covered the whole IL mole fraction,and the electrical conductivities of binary mixtures increase to a maximum value,then decrease with the IL concentration.However,the corresponding IL concentrations of the maximum electrical conductivities are different from the experimental data.Additionally,the calculated electrical conductivities are larger than experimental values by 1 or 2 orders of magnitudes.The deviations between the calculated data and experimental data might be mainly caused by the short molecular dynamics calculation time.