The surface tension and interfacial composition of water/ethanol mixture

• A new model is developed to fit the water/ethanol surface tension. • The model fits for entire composition range very well, with two parameters. • The model complements Van Der Waals interfacial theory and describe the water/ethanol surface as a real fluid interface. This study develops a model to fit the surface tension of the water/ethanol mixture for the complete composition range from 0 to 1. The theoretical framework complements Van Der Waals theory on the density gradient. The modelling results overcome the limitation of Gibbs adsorption isotherm, which completely ignores the composition of the interfacial layer. Furthermore, the model presents a new method to correctly calculate the composition of the interfacial layer for binary liquid mixture and surfactant solutions.