Non-canonical self-assembly of surfactant/cosurfactant mixtures detected by combining the power of SANS and cryo-TEM

We found that the initially present small Tw20 micelles become somewhat larger and more oblate with increasing EHG concentration. However, they do not form wormlike micelles, but instead these small oblate micelles arrange themselves into wormlike aggregates of individual micelles, which only show low viscosity. For higher EHG concentration, a two-phase region is found, above which still such wormlike aggregates of small micelles are still observed, which are in equilibrium with bilayer structures. Only at much higher EHG concentrations pure bilayer structures are formed. The latter effect is ascribed to the intrinsic molecular polydispersity of the surfactant head group. However, the overall assembly behaviour arises from having a surfactant that favours to have a highly curved interface, while the cosurfactant favours a rather flat structure.