Derivation of a new equation for prediction of the thin layer depth of the extended-Langmuir model for dilute binary mixtures

Extended Langmuir model is a model which correlates the surface tension data with bulk composition. One of main objectives of this model is considering the surface as a thin layer of finite depth. In the present work by combination of the Gibbs equation with extended Langmuir model and making some assumptions a new and simple equation was derived for estimating the depth of surface thin layer of dilute binary liquid mixtures. It was shown that the depth of surface layer decreases in a linear form with increasing of solute concentration in the dilute region.