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 (gamma = +/-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-(gamma )decreases with increasing shear rate gamma, such that a shear rate of gamma = 7 +/- 1 s(-1) is sufficient to disorder the material nearly 30 degreesC 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.
|Publication status||Published - 2001|