Adsorption and Extraction Constants

This expression of the work of adsorption is close to the expression of surface activity proposed by Rehbinder [6, p. 158]  

The work of adsorption is determined from Eq. (1) by using the Hnear section of the surface pressure curve as a function of the bulk concentration of the surfactant (the surface pressure does not exceed 3mN/M). The values obtained for the work of adsorption are usually compared with the values obtained for certain fractional surface coverages. Thus, it becomes possible to estimate the change in the free energy as a function of the molecular interaction in the monolayer. (The relation between the values of the work of adsorption determined from different isotherms is discussed in Refs. [37-39]). The adsorption entropy and enthalpy are determined from the temperature dependence of the work of adsorption [36-39]. 

To determine the work of adsorption, Abramson used the equation  

The Gibbs equation serves as a basis for studying the adsorption thermodynamics [11, 24,44]. For the strongly adsorbed surfactants with a small molar fraction in the solution compared to the molar fraction of the solvent (the solvents are mutually insoluble) the Gibbs equation is written as [45]  

At low concentrations of a high-activity surfactant in the bulk phase, the surface excess is usually identified by the surface concentration. 

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