• micellar structure;
  • polysorbate 80;
  • solvent hydrophobicity;
  • 1,4-dioxane solvent

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.