MICROSCOPY, X-RAY-DIFFRACTION, AND NMR-STUDIES OF LYOTROPIC LIQUID-CRYSTAL PHASES IN THE C22EO6/WATER SYSTEM - A NEW INTERMEDIATE PHASE

Mixtures of the nonionic surfactant hexaethylene glycol cis-13-docosenyl ether (C22EO6) With water (H2O)-H-2 were studied by optical microscopy, small-angle X-ray scattering, and H-2 NMR spectroscopy. A schematic phase diagram has been obtained, which shows two high-temperature bicontinuous cubic phases (V2) and a low-temperature fluid intermediate phase (Fl) in addition to the usual hexagonal (H-1) and lamellar (L(alpha)) phases. Although thermodynamically stable and separated from the L(alpha) phase by a first-order transition, the Fl phase bas a lamellar structure. It differs from the L(alpha) phase structure in that the lamellae are broken by water-filled defects, which exhibit no correlation in position between layers. Possible structures for the defects are examined. The occurrence of this phase rather than a V1 cubic phase is attributed to decreased alkyl chain flexibility.