Elongated aggregates formed by cationic gemini surfactants

The phase behavior of aqueous solutions of several dissymmetric gemini surfactants (with two hydrophobic chains of different lengths) was studied. From rheological and X-ray scattering studies as well as from freeze fracture imaging, some general patterns of the phase behavior were observed which are remarkably different from those observed for monomeric surfactants. The sequence 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 hexagonal phase. The multilayered phase showed a scattering peak corresponding to a periodicity of 40 Angstrom indicating the presence of stacks of bilayers without a water layer in between. For some of the samples, cryo-TEM showed that wormlike micelles (WLM) evolve into a ribbonlike structure (elongated bilayer). Upon further increase in concentration, the ribbons transform into multilayered structures with a well-defined width.