Studies of Volumetric and Viscosity Properties in Aqueous Solutions of Imidazolium Based Ionic Liquids at Different Temperatures and at Ambient Pressure

Abstract

The ionic liquids (ILs) 1,3-dimethyl imidazolium methyl sulfate [MIm][MeSO4] and 1-ethyl-3-methyl imidazolium ethyl sulfate [EMIm][EtSO4] have been synthesized and characterized by 1H NMR, 13C NMR, mass spectrometry, TGA and DSC methods. The densities and viscosities of binary aqueous solutions of [MIm][MeSO4] (0.02458 to 0.18922 mol·kg−1) and [EMIm][EtSO4] (0.01044 to 0.21261 mol·kg−1) are reported at (293.15, 298.15 and 303.15) K and at ambient pressure. Apparent and partial molar volumes of the studied ILs are calculated at the studied concentrations. The limiting partial molar volumes of the studied ILs were obtained using an appropriate extrapolation method. The limiting apparent molar expansivity values at 298.15 K are also obtained. The relative viscosity data are analyzed by applying the Jones–Dole equation and Vand’s equations. Positive viscosity A and B coefficients were observed for both studied ILs, while the D coefficients were also found to be necessary, showing specific behavior depending upon the solute–solute interactions. Calculations of the B coefficients for anions are reported. The application of Vand’s equation to the viscosity data enabled us to calculate the Einstein–Simha factor (ν) and particle interaction coefficient ( $$Q$$ ) for the ion-pairs. The calculated ν values are found to be less than Einstein’s value of 2.5. The results are discussed from the points of view of the water structure making effect, solute–solvent hydrogen bond interaction and the presence of hydrophobic interaction.