Thermodynamic Properties of Ionic Liquids

Abstract

Basic physicochemical properties were discussed at different temperatures for 18 hydrophobic ionic liquids (ILs) which containing imidazolium and pyridinium as cations, separately. The ILs include 1-ethyl-3-methylimizazolium tris(pentafluoroethyl)trifluorophosphate ([C2mim][PF3(CF2CF3)3]), 1-acetonitrile-3- ethylimimdazolium bis(trifluoromethylsulfonyl) imide ([MCNMIM][NTf2]), 1-(cyanopropyl)-3-methylimidazolium bis[(trifluoromethyl)sulfonyl] imide [PCNMIM][NTf2], 1-ethanol-3-ethylimimdazolium bis(trifluoromethylsulfonyl)imide ([EOHMIM][NTf2]), 1-butylamide-3-ethylimimdazolium bis(trifluoromethylsulfonyl)-imide ([CH2CONHBuEIM][NTf2]), N-alkylpyridinium bis(trifluoromethylsulfonyl)imide {[Cnpy] [NTf2] (n = 2, 3, 4, 5, 6)}, N-alkyl-3-methylpyridinium bis(trifluoromethyl-sulfonyl)imide {[Cn3Mpy][NTf2] (n = 3, 4, 6)}, and N-alkyl-4-methylpyridinium bis(trifluoromethylsulfonyl) imide {[Cn4Mpy][NTf2] (n = 2, 4, 6)}. The molar volume, standard molar entropy, and lattice energy were estimated by the empirical and semiempirical equations. The dependences of density, dynamic viscosity, and electrical conductivity on temperature are discussed in the measured temperature range. It is found that with the increasing temperature, the density and dynamic viscosity decreased, while the electrical conductivity increases. The influences of microstructures of ILs, such as the introduction of the methylene, methyl, and functional groups on cations, on their basic physicochemical properties are discussed.