The Density and Surface Tension of Aqueous Solutions of Propionate Ionic Liquids - [C4mim][Pro] and [C6mim][Pro] at Different Temperatures

The propionate acid ionic liquids, 1-alkyl-3-methylimidazolium propionate [C4mim][Pro] and [C6mim][Pro] were prepared by the neutralization method and characterized by 1H NMR spectroscopy and differential scanning calorimetry. The values of density and surface tension of aqueous [C4mim][Pro] and [C6mim][Pro] with various molalities were determined at different temperatures, and the coefficient of thermal expansion, the apparent molar volume and the parachor for these solutions were calculated. The values of the apparent molar expansibility of the solute obtained from data of the apparent molar volume are in good agreement with the values calculated by the Harned–Owen equation. An empirical equation for prediction of surface tension for aqueous [C4mim][Pro] and [C6mim][Pro] was put forward and the values of the surface tension predicted by the empirical equation are very similar and highly correlated with the corresponding experimental values and the results predicted by the parachor semi-empirical method for solutions.