Elongated aggregates formed by cationic gemini surfactants

The phase behavior of aqueous solutions of several dissymmetric gemini surf actants (with two hydrophobic chains of different lengths) was studied. Fro m rheological and X-ray scattering studies as well as from freeze fracture imaging, some general patterns of the phase behavior were observed which ar e remarkably different from those observed for monomeric surfactants. The s equence of phases observed with increasing surfactant concentration was an isotropic wormlike micellar phase, multilayered structures which are first isotropic and then organized with orientational ordering, and an inverted h exagonal phase. The multilayered phase showed a scattering peak correspondi ng to a periodicity of 40 Angstrom indicating the presence of stacks of bil ayers without a water layer in between. For some of the samples, cryo-TEM s howed that wormlike micelles (WLM) evolve into a ribbonlike structure (elon gated bilayer). Upon further increase in concentration, the ribbons transfo rm into multilayered structures with a well-defined width.