Excess molar volume and excess Gibbs energy of activation for viscous flow for the binary mixtures of N-ethylpyridinium dicyanamide [C2py][DCA] with alcohols

Abstract

The density and viscosity of multicomponent solutions play an important role in industrial areas concerning mass and heat transfer, as well as fluid flow. To expand the potential application of ILs, it is important to know the physicochemical properties of ILs with solvents for ILs’ widely used. The density and viscosity for binary mixtures of ionic liquid (IL) [C2py][DCA] with ethanol, 1-propanol and 2-propanol were measured across the entire range of mole fraction (x1=0.0000–1.0000) at T=(288.15–318.15) K. The excess molar volumes, VE, were calculated and well fitted by Redlich–Kister equation. The obtained VE are negative values over the whole composition range and it means that there is greater interaction between the ions and the alcohol molecules. The values of Δη have been applied to description of the viscosity deviation of the mixtures from the ideal one, but the equation of excess Gibbs energy of activation for viscous flow, ΔG≠E, for mixture cannot be derived from Δη. And more serious is that an incorrect equation of ΔG≠E is widely used in the literature. In view of this situation, we put forward a new concept – the relative viscosity of mixture, ηr. On a basis of the new concept, a correct equation of ΔG≠E is obtained. The values of ηr and ΔG≠E of mixtures [C2py][DCA]+alcohol over the whole composition range were calculated. The values of ηr are less than one and ΔG≠E are negative so that this result means that the interaction among ions becomes weaker due to ion solvation. The ΔG≠E values of the mixtures [C2py][DCA]+alcohol were well fitted by the Redlich–Kister equation. Using the Redlich–Kister’s parameters, the values of viscosity for mixtures [C2py][DCA]+alcohols were estimated and the estimated η(est.) is in good agreement with the experimental η. In order to test the reliability of the method proposed in this work, we also deal with the data of mixtures for [HDBU]IM+H2O, [BDBU]IM+H2O and [Mim]Ac+Alcohols in the literatures. The results also prove that this method is reasonable.