Influence of Exchangeable Cations on the Surface Free Energy of Kaolinite as Determined from Contact Angles

The influence of adsorbed H + , Na + , K + , Ca 2+ , Mg 2+ , Ba 2+ , and Al 3+ ions on the wettability of a kaolinite surface was determined from contact angles, which were measured in kaolinite-water drop-air (saturated water vapor) and kaolinite-diiodomethane drop-air systems. From the results and using a modified Young equation, the dispersion and nondispersion components of the free energy of the kaolinite hydrated surface were determined. The dispersion component of all the tested samples was between 32.8 and 38.9 mJ/m 2 , but the nondispersion component changed almost linearly from 53 to 95.9 mJ/m 2 with the change of the entropy of hydration of the adsorbed ions, except for K + and Ba 2+ . The latter ions were exceptions, probably due to their large ionic radii.