Structural and macroscopic characterization of a gel phase of densely packed monodisperse, unilamellar vesicles

In the phase diagram of the surfactant system sodium oleate/octanol/water a very stiff gel phase has been found, which is usually not present in simil ar systems. The phases of this system have been characterized by electric c onductivity and rheological measurements. The structures present have been investigated by means of freeze-fracture electron microscopy and small-angl e neutron scattering (SANS). These experiments have shown that addition of octanol to the surfactant solution for concentrations higher than 130 mM Na oleate leads to the formation of small unilamellar vesicles. For sufficien tly high octanol content these vesicles are so monodisperse that they are a ble to form a densely packed system with long-range order and with a shear modulus that is about 100 times higher than normally found for vesicle syst ems. Upon dilution with water the vesicles swell while keeping the packing fraction constant until a maximum diameter of about 450 Angstrom is reached , beyond which no further growth of the vesicles can take place. This is th e first system of such type that forms a cubic-phase-like arrangement of mo nodisperse vesicles.