Mechanisms of Alignment of Lamellar-Forming Block Copolymers under Shear Flow

The potential applications of block copolymer thin films, which exploit their self-assembly capabilities, are greatly enhanced by achieving long-range order. In this study, we perform large-scale computer simulations to investigate the alignment of lamellae under shear flow. We elucidate the experimentally observed alignment behavior and classify the underlying mechanisms based on shear rate and degree of segregation. Our results reveal striking similarities to systems subjected to electric fields, suggesting a common pathway governing lamellar orientations. However, the presence of thin-film surfaces introduces distinct features in the alignment under shear compared to that under electric fields. We observe the emergence of three-dimensional rotational modes alongside the conventional two-dimensional rotation. Furthermore, a transient regime is identified within the melting mechanism, confirming the existence of the checkerboard pattern proposed earlier.