Surface Polyfluorinated Micelles

Abstract

Three novel polyfluorinated cationic surfactants and the corresponding three hydrocarbon analogues were synthesized. All of the surfactants formed globular micelles in water. The micellar formation was monitored by five independent methods. The results of the NMR measurements and the other four methods using the anionic dye Rose Bengal (RB) and anilinonaphthalenesulfonic acid as probe molecules agreed well with each other. The polyfluorinated micelles had rather low cmc values, on the order of 10-5 M. All of the micelles had similar aggregation numbers around 50−60. Using a detailed NMR relaxation study following addition of paramagnetic Mn2+ ions to the bulk water phase, the polyfluorinated micelles were shown to have a very unique microstructure with the perfluoroalkyl chain extending straightforwardly to the bulk water phase. The micropolarity around the ammonium group and the microviscosity in the core of the micelles were estimated using the probe molecules RB and perylene. The local oxygen concentration in the micelles was estimated from the NMR longitudinal relaxation time T1. The microstructure of water distributed within the micelles is discussed with relation to the observed local oxygen concentration. The rigidity of the micelle is also discussed using the mobility of each nuclei estimated from the T1 data. The unique protecting effect of the micelles against attack by hydroxide radicals generated in the bulk water phase using Fenton's method was examined using a bleaching reaction of RB as a probe molecule. The surface polyfluorinated micelles exhibited a greater protective effect than either CTAB or the hydrocarbon analogue surfactant micelles. This protective effect is discussed in relation to the unique microstructure of the surface polyfluorinated micelles.