PHASE-BEHAVIOR AND VISCOELASTICITY OF AOT MICROEMULSIONS CONTAINING TRIBLOCK COPOLYMERS

Mixtures of AOT (sodium bis(2-ethylhexyl) sulfosuccinate)/water/decane microemulsions with polyethylene oxide/polyisoprene/polyethylene oxid e (PEO/PI/PEO) triblock copolymers form highly associated solutions wi th unusual phase behavior and concentration dependence of the viscoela stic moduli. A gas-liquid phase transition, reported here for the firs t time in these mixtures, is attributed to the entropic gain accompany ing the conversion of loops to bridges, in accord with theories for po lymer brushes. The homogeneous condensed phase is highly viscous and e lastic. The volume fraction dependence of the high-frequency modulus c onforms to expectations from theories for either reversible networks o r solutions of flowerlike micelles. The apparent low shear, or plateau , viscosity, on the other hand, exhibits a maximum at a volume fractio n roughly twice that at the phase boundary. This unusual behavior is p redicted qualitatively for solutions of flowerlike micelles, but the q uantitative aspects of the response are more difficult to rationalize.