Volumetric properties of binary mixtures of ionic liquid with tributyl phosphate and dimethyl carbonate

In this work, the densities (ρ) were investigated for binary mixtures of ionic liquids (ILs) with molecular solvents, namely tributyl phosphate (TBP) and dimethyl carbonate (DMC), covering the entire concentrations over the temperature range from T = (293.15 to 323.15) K at 0.1 MPa. The involved ILs are 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim]PF6), 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4) and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([Bmim]Tf2N). From the experimental density values, molar volume (Vm), the thermal expansion coefficient (αp) and excess molar volume (VE) for binary mixtures were calculated. The VE values ranging from (−2.1040 to 0.417) cm3·mol−1 were interpreted in terms of intermolecular interactions and structural characteristics in the binary mixtures. For {[Bmim]PF6 + DMC, [Bmim]PF6 + TBP and [Bmim]BF4 + TBP} mixtures, the VE values are negative due to the dominant electrostatic attraction between cation and anion in IL and hydrogen bonding between IL and TBP/DMC. While for the large molecular system, {[Bmim]Tf2N + TBP}, steric hindrance leads to VE values changing from negative to positive with the increasing of IL concentration. Additionally, the VE values were correlated with Redlich-Kister polynomial equation.