Magnetic resonance study on lamellar phases of ammonium perfluorooctanoate

The aggregation properties of ammonium perfluorooctanoate (NH₄-PFO) in concentrated aqueous phases have been investigated by magnetic resonance techniques and have been compared with the aggregation properties in dilute solutions. Magnetic resonance methods indicated that NH₄-PFO—water systems with surfactant concentrations below 45% (w/w) behaved as isotropic purely micellar solutions in the temperature range 285–340 K. For higher concentrations the system exhibited a rather complex structure, having both isotropic and anisotropic components. The nematic nature of the anisotropic fraction was demonstrated by ¹⁹F NMR studies. The ¹⁹F NMR and EPR of nitroxides (TempTMA⁺, 5- and 16-DXSA) inserted as paramagnetic probes into the concentrated NH₄-PFO—water systems allowed us to establish that the lamellar phase could be mechanically oriented between quartz slides. The EPR investigation also gave details concerning the dynamics of both the oriented and non-oriented structures.