2. Thermodynamics of adsorption of surfactants at the fluid interfaces

Abstract

This chapter discusses the thermodynamics of the adsorption of surfactants at the fluid interface. The thermodynamic analysis of adsorption layers at liquid/fluid interfaces can provide the equation of state that expresses the surface pressure as the function of surface layer composition, and the adsorption isotherm, which determines the dependence of the adsorption of each dissolved component on their bulk concentrations. From these equations, the surface tension (pressure) isotherm can also be calculated and compared with experimental data. This chapter presents some general principles used to derive equations of state and adsorption isotherms for surface active molecules at liquid/fluid interfaces. It is shown that the majority of all known equations can be derived through a two-dimensional solution theory applying Butler's equations for the chemical potentials in a Gibbs dividing surface. Some new equations of state and adsorption isotherms are presented in this chapter that describe mixed surface layers of surfactants possessing different molar areas, or which comprise surfactants and proteins able to change orientation or conformation.