| dc.description.abstract | A catanionic surfactant system is an aqueous mixture of cationic and anionic surfactants. This type of systems display rich self-assembling behavior when the surface charge density （i.e., the molar ratio of the constituent surfactants） and water content are varied, with the spontaneous formation of the pharmaceutically important structure, unilamellar vesicle, being a particularly encouraging observation for the systems. While considerable efforts have been dedicated to the catanionic systems constituted by conventional surfactants, researches on the systems composed of cationic and anionic gemini surfactants are rare, if any. Gemini surfactants are a family of novel surfactants which distinguished themselves from conventional surfactants with their spacer-linked dimeric molecular configuration; the additional degrees of freedom afforded by the presence of the spacer often make the phase behavior of the gemini surfactants even richer. Given the lack of the relevant researches, this present study aspires to investigate the physicochemical properties and self-assembling behavior of the unexplored gemini catanionic systems. We exploit visual inspection, polarized microscopy, dynamic light scattering, small angle X-ray scattering and rheology to study the influences of the surface charge density and spacer length on the phase behavior and rheological properties of a gemini catanionic system. It is found that the vesicles were spontaneously formed in a wide composition range for the gemini catanionic systems; and the phase behavior of the systems is highly dependent on the surface charge density. The larger the surface charge density is, the stronger the intermolecular repulsions and the higher the tendency of forming highly curved structures （e.g., micelles）are; on the contrary, approaching to electric neutrality for the surface results in weakened electrostatic repulsions between molecules and in enhanced propensity of forming structures with low surface curvatures （e.g., lamellar structures）, which is accompanied by the occurrence of phase separation arising from the discrepancy in the ionization of the gemini surfactants. Nevertheless, the mechanism of how the spacer length affects the phase behavior of the catanionic systems is not clear even though this influence is indeed present. | en_US |