Specific ion adsorption at liquid | liquid interfaces: effect of the ionic charge

The effect of the charge of adsorbed ions on their surface concentration was examined for a series of negatively charged ions at the water | 1,2-dichloroethane (DCE) interface. Langmuir and Frumkin isotherms and Coulomb law were used to fit the experimental data. The limiting surface concentration Γs, as determined from the surface tension measurements, was found to be related to the charge number z of the adsorbed ions, in agreement with the derived formula Γs=1.42×10−6/z4/3 mol m−2. Application of this formula to the determination of the dissociation and equilibrium constants of surface reactions is demonstrated for slightly soluble calix[4]arene ligands.