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 resona nce 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 285-34 0 K. For higher concentrations the system exhibited a rather complex s tructure, having both isotropic and anisotropic components. The nemati c nature of the anisotropic fraction was demonstrated by F-19 NMR stud ies. The F-19 NMR and EPR of nitroxides (TempTMA+, 5- and 16-DXSA) ins erted as paramagnetic probes into the concentrated NH4-PFO-water syste ms allowed us to establish that the lamellar phase could be mechanical ly oriented between quartz slides. The EPR investigation also gave det ails concerning the dynamics of both the oriented and non-oriented str uctures.