Shear alignment of a swollen lamellar phase in a ternary polymer blend

Abstract

The shear-induced structural changes in the swollen lamellar phase of a ternary polymer blend are investigated, and comparisons are made with the bicontinuous microemulsion (BμE) phase. The BμE, having 10 vol % copolymer, exhibits flow-induced phase separation under steady shear, whereas the swollen lamellar phase, with only 20 vol % copolymer and 80% homopolymers, goes into a perpendicular orientation at all accessible shear rates. This unexpected behavior, seen with small angle neutron scattering, is further characterized by rheological measurements. Oscillatory shear with large amplitude, on the other hand, induces perpendicular alignments at low frequencies, and a flipping of orientation to parallel alignment at higher frequencies. The lamellar phase also exhibits a shear-induced isotropic-lamellar-isotropic transition just above the order-disorder transition. The rheological properties show marked changes as the copolymer concentration is systematically increased from the BμE into the swollen lamellar region of the phase diagram. The orientation patterns observed in the lamellar phase are explained on the basis of fluctuations.