Determination of the critical micellar concentration of perfluorinated surfactants by cyclic voltammetry at liquid/liquid interfaces

Abstract

Based on the hypothesis that cyclic voltammetry applied to the interface formed by two immiscible electrolyte solutions can be used for determining critical micellar concentrations (cmc) of charged surfactants provided they exhibit ion transfer currents, we have carried out the study of three perfluorinated acids (perfluoroctanoic acid, PFO, perfluorononanoic acid, PFN, and perfluorodecanoic acid, PFD), dissolved in the aqueous phase. Cyclic voltammetry at the water/1,2-dichloroethane interface as well as fluorescence and surface pressure measurements, have been employed for cmc determinations and comparison. From the variation of voltammetric parameters on surfactant concentration it was possible to determine the cmc for these surfactants, obtaining good agreements with other methodologies. Impedance spectroscopy experiments have been also carried out to characterize the properties of the interface, demonstrating that at high surfactant concentration values, a monolayer with different domains is formed.