MICELLE TO VESICLE TRANSITION INDUCED BY COSURFACTANT - RHEOLOGICAL STUDY AND DIRECT OBSERVATIONS

We report a micelle-vesicle transition induced by the addition of a ne utral cosurfactant, hexanol, into a wormlike micellar solution of gemi ni cationic surfactant. This transition was investigated with rheology measurements as well as direct imaging techniques. It was observed by cryo transmission electron microscopy that micelles first become elon gated with an increase of hexanol, which increases the viscosity. As t he hexanol concentration is increased, another more fluid phase appear s, where micelles are highly branched and coexist with small vesicles. One can describe this transition as a decrease of the spontaneous cur vature caused by the cosurfactant molecule, which induces the elongati on, and then the branching of micelles as well as the formation of sma ll unilamellar vesicles. With a further increase of hexanol, these ves icles grow in size, which allows their observation by optical microsco py with differential interferential contrast. Some of these vesicles s how long tubule-like shape, typically a few micrometers thick and up t o several hundred micrometers long.