Influence of Shear on Solvated Amphiphilic Block Copolymers with Lamellar Morphology

Abstract

The effect of shear on lyotropic lamellar phases consisting of amphiphilic block copolymers was studied by in situ small-angle neutron scattering (SANS) and rheo-optics. Two different ternary systems containing a commercially available Pluronic type poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) block copolymer, P123 (EO20PO70EO20) or F127 (EO100PO70EO100), as well as water and butanol were investigated over a wide range of concentrations. Orientation diagrams were constructed for both ternary systems; both exhibited a parallel-to-perpendicular transition of planar lamellae and a shear-induced formation of multilamellar vesicles (also termed liposomes, onions, or spherulites). For both systems, the vesicle formation occurred at low polymer content close to the phase boundary of the lamellar region and was accompanied by shear thickening. In addition, the kinetics and temperature dependence of the parallel-to-perpendicular transition were studied.