Influence of shear on the alignment of a lamellae-forming pentablock copolymer

We characterize shear-induced states of order and disorder in a symmetric l amellae forming poly(cyclohexylethylene) (C)-polyethylene (E) CECEC pentabl ock copolymer. When subjected to a large amplitude reciprocating shear stra in (gamma = +/-600) in the ordered lamellae state, the sample rapidly align s in a perpendicular orientation with long-range order. The order-disorder transition temperature T-ODT-(gamma )decreases with increasing shear rate g amma, such that a shear rate of gamma = 7 +/- 1 s(-1) is sufficient to diso rder the material nearly 30 degreesC below the quiescent T-ODT Small-angle neutron scattering (SANS) from the sheared disordered state displays a symm etry 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 sh ear leads to spontaneous lamellar ordering into a macroscopically well-alig ned transverse orientation-an arrangement that previously has been inaccess ible via processing. In contrast to this behavior, the perpendicular alignm ent forms when cooling the sample from above the T-ODT while applying low s hear rates, similar to the response of di- and triblock copolymers. These f indings shed fresh insight into the complex phenomena that govern flow- and deformation-induced alignment of block copolymer melts.