Visible Photonic Bandgap Configured by Non‐Affine Block Copolymer Gyroid

Abstract Despite extensive efforts to self‐assemble block copolymers (BCPs) into gyroid photonic crystals, achieving a photonic bandgap (PBG) in the visible regime still remains unreachable due to the difficulty in accessing magnificent lattice sizes. Here, giant BCP gyroids with the largest lateral unit‐cell size reported to date (335.7 nm) are successfully assembled and their non‐affine lattice structures along with the corresponding photonic band structures are theoretically unveiled. The key to realizing this visible PBG is the precise control of non‐affine distortion within the largest gyroid lattices, which effectively transforms their morphology toward a high symmetry state. Particularly, high‐molecular‐weight polystyrene‐ b ‐poly(methyl methacrylate) (PS‐ b ‐PMMA) films are utilized as templates to construct the giant gyroid. The PMMA‐removed, PS gyroid films are treated with cosolvent mixtures of tetrahydrofuran and acetic acid to induce a directional contraction along the z ‐direction, thereby leading to precise fine‐tuning of non‐affine distortion. Numerical reconstructions of the resulting gyroid lattices revealed that increasing symmetry through non‐affine transformation is critical for opening and widening the PBG in the visible regime. By integrating theoretical modeling with experimental validation of a distinct visible PBG, this study fully uncovers the atlas of giant BCP gyroid structures and their PBG characteristics, which had previously remained elusive.