Study on thermophysical properties for aqueous solutions of ionic liquid N-ethyl-pyridine dicyanamide [C2py][DCA]

The IL (ionic liquid) [C(2)py]IDCA] (N-ethyl-pyridine dicyanamide) was prepared and confirmed by H-1 NMR (H-1 nuclear magnetic resonance) spectroscopy, C-13 NMR (C-13 nuclear magnetic resonance) spectroscopy. The values of density and surface tension of the IL [C(2)py][ DCA] and its aqueous solutions with various molalities were determined at T= (288.15 to 318.15) K. The values of the molar volume for aqueous solutions of [C(2)py][DCA], V, were calculated and increase with the increase of temperature and molarity. On the basis of thermodynamics, a semi empirical model-molar surface Gibbs free energy model of the ionic liquid solution was put forward. It can be used to predict the surface tension and the predicted values of the surface tension for aqueous [C(2)py]IDCA] are all most the same with the corresponding experimental ones. In terms of the concept of the molar surface Gibbs free energy, a new Efitvos equation is obtained. Each parameter of the new equation has a clear physical meaning, energy dimension and is more convenient to use. (C) 2016 Elsevier B.V. All rights reserved.