Thermodynamic Properties and Predicting the Surface Tension of Pyridinium-Based Ionic Liquids of [C6py][DCA] Using a New Eotvos Equation

The pyridinium-based ionic liquids [C(6)py][DCA] (N-hexyl-pyridinium dicyanamide) was prepared and characterized using 1H and 13C nuclear magnetic responancec (NMR) spectroscopies, Fourier transform infrared (FT-IR) spectroscopy, and differential scanning calorimetry (DSC). The density (p), surface tension (y), and refractive indices (n(D)) were measured at the temperature range from 288.15 to 338.15 K. Molecular volume (V-m), energy of surface (E-a), molar polarization (R-m), and polarization coefficient of [C6py][DCA] (ar) were calculated from the experimental data. E-a, R-m and as were approximately temperature -independent. The concept of molar surface Gibbs free energy (g(s)) was conceived, for which a new Eotvos equation was derived. The gs, critical temperature (T-c), and Eotvos empirical parameter related to polarity (kE) were also obtained. The new EitvOs equation was used to predict the surface tension and the predicted values of [C(6)py][DCA] are in close agreement with the corresponding experimental ones.