Gibbs absorption equation

Using the Gibbs absorption equation and assuming Henry s law (eq. 3.42)... 

Figure D3.5.5 Equilibrium surface tension of sodium dodecyl sulfate (SDS) at the air-water interface as a function of surfactant concentration. The corresponding surface coverage was calculated using the Gibbs absorption equation (Eq. D3.5.26).

The expression for the excess Gibbs energy is built up from the usual NRTL equation normalized by infinite dilution activity coefficients, the Pitzer-Debye-Hiickel expression and the Born equation. The first expression is used to represent the local interactions, whereas the second describes the contribution of the long-range ion-ion interactions. The Bom equation accounts for the Gibbs energy of the transfer of ionic species from the infinite dilution state in a mixed-solvent to a similar state in the aqueous phase [38, 39], In order to become applicable to reactive absorption, the Electrolyte NRTL model must be extended to multicomponent systems. The model parameters include pure component dielectric constants of non-aqueous solvents, Born radii of ionic species and NRTL interaction parameters (molecule-molecule, molecule-electrolyte and electrolyte-electrolyte pairs). 

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