ANOTHER APPROACH TO A SURFACE EQUATION OF STATE

A new approach for describing the adsorption isotherms of soluble amphiphiles at fluid interfaces is proposed. This approach assumes the adsorption to occur in two thermodynamically discriminable states in the surface layer for the same amphiphilic species such that the first one is realized at the lower and the second one at the higher bulk concentrations. There is an interval at medium concentrations, characterized by a gradually occurring transition from state I to state II. This transition is described by a polynomial. This approach succeeds in describing the entire adsorption isotherm of any amphiphile in terms of known thermodynamic assumptions with an accuracy unknown so far. This is demonstrated by using three different amphiphiles which cannot be described satisfactorily by known surface equations of state.