Self-Assembly and Magnetic Alignment in Cetyltrimethylammonium Bromide/Sodium Perfluorooctanoate Surfactant Mixtures Investigated Using 2H Nuclear Magnetic Resonance Spectroscopy

Deuterium nuclear magnetic resonance (H-2 NMR) spectroscopy has been used to investigate the phase behavior for mixtures of the cationic surfactant cetyltrimethylammonium bromide (CTAB) and the anionic surfactant sodium perfluorooctanoate (FC7) for total surfactant concentrations ranging from I to 25 wt %. The deuterated methyl of the quaternary methyl-ammonia group in CTAB-gamma-d(3) gives rise to a superposition of spectral components in the H-2 NMR spectra allowing for the identification and quantification of the different phases present. The CTAB/FC7 mixture exhibits a coexisting two-phase region composed of an isotropic (Iso) micelle/vesicle phase along with a lamellar (L,,) phase for all of the composition ranges investigated. The variation of the phase composition as a function of sample temperature, total wt % surfactant, and surfactant molar ratio are presented. In addition, the H-2 NMR reveals that the L, phase spontaneously aligns in the magnetic field, with the extent and distribution of magnetic alignment being determined. The H-2 NMR results are discussed in light of previously reported surfactant-templated material synthesis involving the CTAB/FC7 mixture.