| Above the critical micelle concentration (cmc), surfactants or their mixtures can self-assemble into a variety of aggregates such as micelles, vesicle-phase and lamellar phase etc. Among them, vesicle-phase is highlighted theoretically and experimentally due to its implication as models for biological membranes or as drug delivery systems. In this paper, we study the structure, property and phase behavior of vesicle-phase from three points as follows:1. A surfactant mixture (MHPEPE) including two components, one is single-tailed and the other double-tailed, is synthesized. The phase behavior of MHPEPE in aqueous solution is studied and the regions of uni and multilamellar vesicle-phase are determined respectively. The results of Freezing-Fracture Transmission Electron Microscopy (FF-TEM), Negative-Staining TEM (NS-TEM) and Polarizing Optical Microscopy (POM) show that the additions of acid and salt may induce phase transitions from the single unilamellar vesicle-phase to two-phase, at the bottom of which multilamellar vesicle-phase is formed. Moreover, the addition of alkali and change of temperature can also induce phase transitions.2. In order to study the issue about vesicle formation spontaneously, in situ chemical kinetic routes are developed to build up catanionic surfactant systems without introduction of shear forces. FF-TEM, Dynamic Light Scattering (DLS) measurement and Small-angle Neutron Scattering (SANS) experiment are used to demonstrate that vesicles do spontaneously form in extremely dilute catanionic surfactant systems when one of the components is produced by the chemical reaction, which settles a present controversial physical-chemical problem together with the previously published studies about concentrated systems in which lamella were produced spontaneously without shear forces. |
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