Chemical potentials and equation of state of surface layers for a model assuming two-dimensional compressibility of adsorbed molecules

Equations for the chemical potentials of surface layer components are derived by accounting for the two-dimensional compressibility ɛ of adsorbed molecules having a molecular area ω that depends linearly on the surface pressure Π. The modified equations for the chemical potentials representing a generalised Butler equation, are used to derive equations of state and adsorption isotherms of surface layers both in the framework of the real two-dimensional solution theory and in the framework of the Gibbs dividing surface model. Data of surface tension, adsorption and rheological characteristics of surface layers formed from solutions of C12DMPO agree well with the theoretical models based on the assumption of intrinsic compressibility of adsorbed molecules. A good description of experimental data by the theoretical models was achieved without the consideration of surface layer compressibility in the equations for the chemical potentials.