Paramagnetic probes for the investigation of ordered and disordered perfluorosurfactants, perfluoropolyethers and perfluorinated ionomers

In this review we describe the use of transition metal ions (Cu2+, Ti3+, VO2+, Mn2+) and stable nitroxide radicals with different shape, size and charge as paramagnetic probes for the study of perfluorinated compounds in the presence of solvents by electron spin resonance (ESR, ESE, ENDOR) spectroscopy. The physical state of the swelling solvents in perfluorinated ionomers (Nafion and perfluoropolyethers) is deduced by the analysis of the ESR spectral parameters and linewidths as a function of the operating frequency and temperature. The formation of metal aggregates in aqueous and nonaqueous solvents is discussed. The spectral characteristics and relaxation behavior of nitroxides is particularly informative when aggregates such as micelles, lamellar phases and other ordered systems, are formed in solution.