Effective Morphology Control of Block Copolymers and Spreading Area-Dependent Phase Diagram at the Air/Water Interface.

Over the past several decades, tremendous efforts have been made to understand the fundamental physics of block copolymer (BCP) self-assembly in bulk or thin films, and this has led to the development of BCP-based bottom-up nanofabrication. BCPs also form periodic nanostructures at the air/water interface, which has potential application to ultrathin-film nanopatterning with molecular-level precision. Nonetheless, controlling the nanostructure formation at the air/water interface is restricted by the inherent parameters of BCPs; BCP morphology is determined by the hydrophilic-to-hydrophobic block ratio. Here we show that controlling the spreading area of BCPs at the air/water interface can tune the shape and size of BCP structures, suggesting a new phase diagram of BCP structures as a function of the relative block fraction and spreading area. A neat polystyrene-b-poly(2-vinylpyridine), known to form a dot morphology, instead forms a strand or planar morphology when the spreading area is varied with Langmuir-Blodgett technique.