Kink Bands in a Lamellar Diblock Copolymer Induced by Large Amplitude Oscillatory Shear

Recent studies have induced a biaxial texture in lamellae-forming poly(styrene- b -ethylene propylene) diblock copolymers by applying large amplitude oscillatory shear. According to small-angle X-ray scattering, this biaxial texture consists of “parallel” lamellae (normal to lamellae aligned perpendicular to the shearing surfaces) and “transverse” lamellae (normal to lamellae aligned parallel to the shearing direction). This study determines the arrangement of these two populations of lamellae by using field emission scanning electron microscopy to examine the microstructure and superstructure. The transverse lamellae are separated from the parallel lamellae by sets of parallel wall defects which have two characteristic orientations. This parallel−transverse biaxial morphology shows an astonishing resemblance to that of kink bands. The formation of kink bands suggests that the transverse lamellae could be the result of buckling in the parallel lamellae. Relaxation of the kink band superstructure during quiescent annealing occurs primarily by lamellae tilting, rather than twisting, and produces a variety of defect structures.