Behavior of perfluorinated surfactants at the electrode/solution interface

The electrochemical behaviors of perfluorinated anionic (FSA and FC-99), cationic (FSD), and nonionic (FSN) surfactants at Hg and Pt electrodes were studied by using the interfacial capacitance measurement and cyclovoltammogram techniques. Their behaviors were also compared with that of the analogous hydrogenated surfactants. In the potential region near the potential of zero charge, both types of surfactants were found to be adsorbed at the Hg/solution interface with their hydrophobic segments oriented toward the electrode surface. However, the surface activity of the perfluorinated surfactants is in general weaker and the saturated adsorption layer is less compact than that of the hydrogenated surfactants at the weakly charged Hg/solution interface. On a more hydrophilic Pt electrode surface and on a strongly charged surface of Hg, both types of surfactants were found to be adsorbed at the electrode/solution interface with their hydrophilic end-groups or segments situated at the interface. On the basis of these results, basic principles for application of perfluorinated surfactants in electrochemical systems were postulated.