Thin Film Morphology of Block Copolymer Blends with Tunable Supramolecular Interactions for Lithographic Applications.
A modular and hierarchical self-assembly strategy using block copolymer blends (AB/B'C) with tunable supramolecular interactions is reported. By combining supramolecular assembly of hydrogen-bonding units with controlled phase separation of diblock copolymers, highly ordered square arrays or hexagonal arrays of cylindrical domains were obtained for mixtures of poly(ethylene oxide)-b-poly(styrene-r-4-hydroxystyrene) (PEO-b-P(S-r-4HS)) and poly(styrene-r-4-vinylpyridine)-b-poly(methyl methacrylate) (P(S-r-4VP)-b-PMMA) diblock copolymers under solvent annealing with controlled high humidity. The fraction of the H-bonded phenolic and pyridyl units was shown to be critical for both the generation of long-range order and controlling the spatial arrangement of the cylindrical domains. Both low absolute numbers and a near-stoichiometric ratio of pyridyl-to-phenolic groups are needed to produce ordered square arrays with separated PEO and PMMA domains, whereas a low ratio of pyridyl-to-phenolic groups facilitated the formation of ordered hexagonal arrays with mixed PEO and PMMA domains. Self-consistent field theory simulations suggest that the effective Flory−Huggins parameters between the various blocks control the stability of the different packing structures in this system. The modularity and tunability of this supramolecular block copolymer blending approach is a unique and powerful strategy to fabricate diverse nanostructures for a variety of applications such as block copolymer lithography.