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

Abstract

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.

Nature of Viscoelasticity in Lamellar Block Copolymers: Contraction Correlated to Strain Localization

“…A preferred slip plane is found in all systems that exhibit kink band defects, including hexagonally packed crystalline metals, laminated rocks, layered composites, etc. Thus, the existence of a preferential slip plane parallel to the lamellae partially explains the occurrence of kink bands in block copolymers [8,11] and could also contribute to shear-induced lamellar rotation [7].…”

Orientation behaviour of AB and ABC block copolymers under large amplitude oscillatory shear flow in bulk and in concentrated solution

“…Besides orientation of block copolymers also morphological defects induced by shear have attracted interest [21,24,[59][60][61]. In the following, focus will be on works dealing with lamellar block copolymers.…”

Block Copolymers in External Fields: Rheology, Flow‐Induced Phenomena, and Applications

“…7.7a), has been reported. It generally occurs in combination with other orientations during transient states [118-120, 122, 123] and/or in the presence of specific defects like kink bands [124,125]. In one situation, where the chain dynamics was dominated by the presence of entanglements, pure transverse alignment has been reported [126].…”