Thermodynamic properties of 1-ethyl-3-methylimidazolium methyl phosphonate and 1-ethyl-3-methylimidazolium ethyl phosphonate
The ionic liquids 1-ethyl-3-methylimidazolium methyl phosphonate([Emim][OMP])and 1-ethyl-3-methylimidazolium ethyl phosphonate([Emim][OMP])were synthesized and characterized by nuclear magnetic resonance and elemental analysis.The thermal stability,phase behavior,density and viscosity(293.15-353.15K),and conductivity and surface tension(293.15-343.15K)were measured at atmospheric pressure,and correlated with established empirical equations.Some thermophysical properties such as the isobaric thermal expansion coefficients,molecular volume,standard entropy and lattice potential energy were determined using the measured density data,while the surface excess energy and entropy were estimated using the measured surface tension data.The thermal gravimetric analysis showed that the thermal decomposition temperatures(Tonset)of[Emim][OMP]and[Emim][OMP]were 271.0℃ and 259.2℃,respectively.Differential scanning calorimetry results revealed that[Emim][OMP]and[Emim][OEP]had no melting or freezing points,but only glass-transition temperatures(Tg),and the Tg of[Emim][OMP]and[Emim][OEP]were-84.87℃ and-85.00℃,respectively.The Walden rule analysis demonstrated that[Emim][OMP]and[Emim][OEP]ionic liquids complied with the Walden rule well,and were classified as"good ionic liquids".
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