Morphology of polysorbate 80 (Tween 80) micelles in aqueous 1,4-dioxane solutions

The structures of micelles of the surfactant polysorbate 80 (Tween 80) in 0-50% aqueous 1,4-dioxane solutions (pH 7.2, ionic strength 2.44 mM) were investigated by means of small-angle X-ray scattering. At 1,4-dioxane concentrations of 0-20%, core-shell cylindrical micelles formed because the crown-shaped polysorbate 80 molecules aggregated into a cylindrical layer of four chains entangled with one another through intra- and intermolecular interactions. At 30-40% 1,4-dioxane, core-shell discus micelles formed, and at 50% 1,4-dioxane, core-shell elliptic discus micelles formed by the same mechanism. By changing the 1,4-dioxane solvent concentration and increasing the solvent hydrophobicity, the micelles first change from core-shell cylindrical to core-shell discus and then from core-shell discus to core-shell elliptic discus micelles.