Competitive Adsorption of Perfluorohydrocarbon and Hydrocarbon Surfactants from Their Micellar Solution at the Air-Water Interface

Abstract

The mixed adsorption of perfluorohydrocarbon, C₈F₁₇SO₃Li, (LiFOS), and hydrocarbon, C₁₄H₂₉SO₄Li, (LTS), surfactants at the air-water interface was studied in orde r to clarify the compositions of an adsorbed film and a micelle. The LTS in an adsorbed film was measured at 30°C by radiotracer method using ³H-labeled compounds. The adsorbed amount of LiFOS was estimated by the Gibbs adsorption isotherms applied to both single and micellar solutions. The micelle compositions at the CMC were computed by the Shinoda's theory for a mixing micelle. It has been concluded that at the CMC the fraction of the hydrocarbon surfactant in the micelle is higher than that in the adsorbed film. Also, the radiotracer study indicates that the adsorbed amount of LTS decreases with increasing bulk concentration beyond the CMC, whereas the adsorbed amount of LiFOS increases. The results can be interpreted by the fact that the concentration change based on the single species of LiFOS takes place with increasing bulk concentration of the mixed solutions, though the micellar compositions are not varied.