Influence of Shear on the Alignment of a Lamellae-Forming Pentablock Copolymer

We characterize shear-induced states of order and disorder in a symmetric lamellae forming poly(cyclohexylethylene) (C)−polyethylene (E) CECEC pentablock copolymer. When subjected to a large amplitude reciprocating shear strain (γ = ±600%) in the ordered lamellae state, the sample rapidly aligns in a perpendicular orientation with long-range order. The order−disorder transition temperature T ODT(γ̇) decreases with increasing shear rate γ̇, such that a shear rate of γ̇ = 7 ± 1 s-1 is sufficient to disorder the material nearly 30 °C below the quiescent T ODT. Small-angle neutron scattering (SANS) from the sheared disordered state displays a symmetry that suggests a fundamentally different influence of shear compared to earlier observations of shear-induced anisotropy in the disordered states of lamellae forming diblock and triblock copolymers. Abrupt cessation of shear leads to spontaneous lamellar ordering into a macroscopically well-aligned transverse orientationan arrangement that previously has been inaccessible via processing. In contrast to this behavior, the perpendicular alignment forms when cooling the sample from above the T ODT while applying low shear rates, similar to the response of di- and triblock copolymers. These findings shed fresh insight into the complex phenomena that govern flow- and deformation-induced alignment of block copolymer melts.