A shear stabilized biaxial texture in a lamellar block copolymer

Abstract

Block copolymers spontaneously self-assemble into a variety of morphologies. Recent studies have produced a biaxial texture in poly(styrene-b-ethylene propylene), SEP, diblock copolymers by applying oscillatory shear. This biaxial texture consists of “parallel” lamellae (normal to lamellae aligned perpendicular to shearing surfaces) and “transverse” lamellae (normal to lamellae aligned parallel to shearing direction) according to small-angle X-ray scattering, SAXS. The present study has determined how these two populations of lamellae are arranged and how they relax upon quiescent annealing by examining the superstructure via FE-SEM.Sample preparation for the JEOL 6300 FE-SEM was designed to preserve a sample's orientation with respect to the shearing direction and provide a large viewing area (.1 - .3 mm2) relative to what is typical with cryo-ultramicrotomed sections for TEM. Bulk samples were cut and mounted on a specimen stub with one of the 3 orthogonal directions of the shearing geometry oriented perpendicular to the stub surface.