NEMATIC AND DISRUPTED LAMELLAR PHASES IN CESIUM PENTADECAFLUOROOCTANOATE (H2O)-H-2 - A SMALL-ANGLE SCATTERING STUDY

The cesium pentadecafluorooctanoate (CsPFO/(H2O)-H-2 system has been studied by small angle X-ray and neutron scattering. The lamellar phase has previously been shown to consist of lamellae pierced by water-filled defects. sen: (Leaver, M. S.; Holmes, M. C. J Phys. II 1993, 3, 105. Holmes, M. C.; Smith, A. M.; Leaver, M. S. J. Phys. II 1993, 3, 1357.) Here we present further evidence for this structure together with experimental evidence that profound changes in structure take place in the nematic phase. In the isotropic micellar phase, the surfactant aggregates form disk-shaped micelles. As the nematic phase is crossed from the isotropic micellar phase to the lamellar phase, there is an increase in orientational and positional order of the aggregates. There is also evidence for a structural rearrangement from disk-shaped micelles to elongated, flattened micelles which act as the precursor to the defected lamellar structure. Addition of electrolyte or cosurfactant accentuates this process.