Shear-induced formation of multilamellar vesicles ("onions") in block copolymers

The use of shear to control the microstructure in the lyotropic lamellar re gion of a ternary isothermal poly(ethylene oxide)-b-poly(propylene oxide)-b -poly(ethylene oxide) (Pluronic P123)/ water/butanol system was investigate d by means of small angle neutron and light scattering (SANS, SALS), birefr ingence, and rheology. A transition from parallel to perpendicular alignmen t of lamellae, with a corresponding decrease in the viscosity, was found wi th increasing shear rate at high block copolymer concentrations. At low pol ymer content, however, the samples were shear thickening, and a shear-induc ed formation of multilamellar vesicles ("onions") was observed for the firs t time in block copolymer systems.