Evidence for Multilamellar Vesicles in the Lamellar Phase of an Electrostatic Lyotropic Ternary System. A Solid State ²H-NMR and Freeze Fracture Electron Microscopy Study

Abstract

Deuterium solid state NMR and freeze fracture electron microscopy experiments have been carried out in the lamellar Lα phase of the water−sodium dodecyl sulfate−octanol system. Within the lamellar phase two types of bilayer organizations have been found. At high surfactant and alcohol concentrations, the lamellar phase is made of a stack of flat parallel bilayers while in the dilute part, it consists of multilayered vesicles of large radius (ca. 10 000 Å). These latter structures, commonly called spherulites, which appear spontaneously at low octanol contents and/or for high water dilution, can be described as textural defects of the lamellar phase. The location of this onion-like structure region is discussed within the framework of the membrane elasticity theory. As a side result, the presence of 33% glycerol in some of the freezefracture experiments is shown to barely affect the bending modulus of the film but rather disorder the molecular packing of the bilayers.