Study On Physicochemical Properties Of Ionic Liquids [C_nmmim][NTf₂]（n=2,4）

Two bis(trifluoromethyl)imide ionic liquids [Cnmmim][NTf2](n=2,4){1-Alkyl-2,3-dimethylimdazolium-N,N-bis(trifluorosulfonyl)imide} were preparedand characterized by1H NMR spectroscopy and differential scanning calorimetry(DSC).Some physicochemical properties of [Cnmmim][NTf2](n=2,4), such asdensity, surface tension, refractive index, viscosity, and electrical conductivity arerecorded in varied temperature,(298.15~338.15±0.01) K. The variation tendency ofthese parameters with temperature can be observed clearly and directly by linearfitting treatment. Moreover, some related constants of ionic liquid can be calculatedfrom the fitting lines. According to the relationship between ionic liquid density andtemperature, we obtain the molar volume, molecule volume, thermal expansioncoefficient, standard entropy, lattice energy, and contribution of per molar methyleneto molecule volume and lattic energy of corresponding ionic liquid; Based on therelation of ionic liquid surface tension with temperature, we obtain surface entropyand surface energy of ionic liquid. We also can get ionic liquid vaporization enthalpyusing Rebelo, Kabo, and Verevkin calculation method. Regarding to the variation ofionic liquid refractive index to temperature, molar polarizability (Rm), polarization(αp), and their variation tendency to temperature are gained. Meanwhile, polarizationof ionic liquid is discussed under the calculation result of Kabo and Verevkin method,and the meaning of δμis expounded; According to the fitting results of ionic liquidviscosity to temperature, Arrhenius and VTF equation are employed to analyze therule of viscosity to temperature and calculate electroconductivity activation energyand flow activation energy. Based on Eyring theory, the Gibbs free energy (ΔG≠) andits variation tendency to temperature are presented. According to the result betweenionic liquid electrical conductivity and temperature, we get some constants, such asmolar electrical conductivity, electroconductivity activation energy, etc. Furthermore,diffusion coefficient of ionic liquid could be computed by Nernst-Einstein equation. Using the Walden product, the values of W of several ionic liquids wereestimated at298.15K, we can see that the value of different ionic liquid is differert,Thus our conclusion is that W is a parameter related to the structure of ILs.