Wide Neutrality Windows for Block Copolymer Vertical Orientation Using Congruent and Incongruent Polymer Bushes

Distinctive polymer brushes play a crucial role in providing a neutral surface conducive to orientational control of block copolymers (BCPs). This bottom-up approach effectively aligns the formation of vertical lamellar and cylinder lattice structures from the BCP. In conventional BCP self-assembly techniques, random copolymer (RCP) brushes are commonly employed to achieve substrate neutrality. However, these methods face significant drawbacks, including batch variations, lack of ability to tune surface energy during grafting, and synthetic challenges for chemically incompatible monomers. Blending homopolymer brushes to achieve mixed chemistry have been demonstrated to be effective for creating neutral substrate but require narrow blend formulations due to macrophase segregation. To address these issues, various approaches have been proposed to mitigate inconsistencies and enhance tunability, albeit with associated costs. Our proposition involves a system of polymer brushes composed of mixed ratios and chain lengths. We demonstrate that managing incongruent blends significantly widens the neutrality window of a lamellar forming BCP. This was attributed to formation of a brush canopy layer that is responsive to its chemical environment. This system effectively controls surface chemistry by combining the effects of chemistry and macromolecular structure, which offers a straightforward, low-cost template to serve as a tunable neutral brush for BCP self-assembly.