CONTROLLING KINK BAND MORPHOLOGY IN BLOCK-COPOLYMERS - THRESHOLD CRITERIA AND STABILITY

The initiation, structure, and dynamics of defects control both the st ructure and physical properties of materials. In this work, kink band defects are systematically introduced into a lamellar poly(styrene-b-e thylene propylene) diblock copolymer by applying various rates and tot al strains of steady shear. However, kink bands are only produced when the shear strain exceeds a critical value. The mere existence of kink bands implies the presence of a preferential slip plane parallel to t he lamellae, which we estimate exists within the polystyrene microdoma ins. Furthermore, our results regarding the dependence of kink band ge ometry on shear rate and strain suggest that these defects are formed by the rotation of lamellae. Based on a rotation mechanism, the charac teristic size of the kink bands and their spatial distribution, it app ears that preexisting defects initiate kink bands. Insights gained fro m steady-shear-induced kink bands are extended to oscillatory shear al ignment of this high molecular weight diblock copolymer, allowing us t o circumvent a previously reported shear-stabilized parallel-transvers e biaxial texture.