The molar surface Gibbs energy of the aqueous solution of the ionic liquid [C₆mim][OAc]

Graphical abstract: Fitting values of γ(Pre) predicted by the molar surface Gibbs energy model versus corresponding experimental one, γ(Exp), a good straight line was obtained and it can be seen that predicted surface tension and the corresponding experimental values are highly correlated (correlation coefficient squared, r² = 0.999, standard deviation, s = 0.112) and extremely similar (gradient = 0.999; intercept = 0.00592). - Highlights: • A semi-empirical model molar surface Gibbs energy model was put forward. • The predicted γ by the model and matching experimental ones are highly correlated. • By the concept of the molar Gibbs energy, a new Eötvös equation is obtained. - Abstract: The density and surface tension for the aqueous solution of the ionic liquid (IL) 1-hexyl-3-methylimidazolium acetate [C₆mim][OAc] with various molalities were measured at T = (288.15 to 318.15) K with an interval of T = 5 K. On the basis of Li's model, as a new concept, the molar surface Gibbs energy of the ionic liquid solution was put forward and it was used to predict surface tension of aqueous [C₆mim][OAc]. The predicted values of the surface tension are highly correlated and extremely similar to the corresponding experimental values. It is worth noting that the molar surface Gibbs energy can be connected with the volume, density and surface tension. Therefore, it can be developed as a semi-empirical method to predict physical properties of substances like the parachor. In terms of the molar surface Gibbs energy, a new linear Eötvös equation is obtained. Using this new equation, the values of the molar surface enthalpy for aqueous [C₆mim][OAc] and other aqueous ILs were calculated. The results show that in the solution of the given molality, the molar surface enthalpy is a temperature-independent constant.