Shear-Induced Formation of Multilamellar Vesicles (“Onions”) in Block Copolymers

The use of shear to control the microstructure in the lyotropic lamellar region of a ternary isothermal poly(ethylene oxide)- b -poly(propylene oxide)- b -poly(ethylene oxide) (Pluronic P123)/water/butanol system was investigated by means of small angle neutron and light scattering (SANS, SALS), birefringence, and rheology. A transition from parallel to perpendicular alignment of lamellae, with a corresponding decrease in the viscosity, was found with increasing shear rate at high block copolymer concentrations. At low polymer content, however, the samples were shear thickening, and a shear-induced formation of multilamellar vesicles (“onions”) was observed for the first time in block copolymer systems.