Thermodynamics of Mixed Monolayers

From the identity of the chemical potential of each component, including the solvent, in the bulk and the surface phase, the Gibbs equation is deduced. Relations are obtained between surface pressure, adsorptions and molar fractions in the bulk phase. The equations hold both for adsorbed and for spread films. A penetrated film is also considered. The relation between molar fraction and surface pressure was tested for the system Na-laurate and sapoalbin, having very different saturation adsorption values. Agreement between theory and experiment is satisfactory.