The thermodynamic parameters of adsorption of surface-active substances at air/solution and metal/solution interfaces

Equations relating the Gibbs energy of adsorption to the activity coefficients of surface-active substances were obtained. A decrease in the Gibbs energy of adsorption caused by an increase in the number of carbon atoms in a molecule (the Traube rule) was shown to be related to an increase in the activity coefficients of surfactants in their homologous series. The number of water molecules displaced from the surface layer in the adsorption of well-soluble aliphatic alcohols and acids was determined taking into account the activity coefficients of the surfactants. The standard Gibbs energies of adsorption of several surfactants at air/solution and metal/solution interfaces, which correspond to symmetrically selected standard states, were calculated. Precisely these parameters were shown to characterize the structure of the surface layer at interphase boundaries.