Photonic Crystal Palette of Binary Block Copolymer Blends for Full Visible Structural Color Encryption

Abstract Structural color (SC) arising from a periodically ordered self‐assembled block copolymer (BCP) photonic crystal (PC) is useful for reflective‐mode sensing displays owing to its capability of stimuli‐responsive structure alteration. However, a set of PC inks, each providing a precisely addressable SC in the full visible range, has rarely been demonstrated. Here, a strategy for developing BCP PC inks with tunable structures is presented. This involves solution‐blending of two lamellar‐forming BCPs with different molecular weights. By controlling the mixing ratio of the two BCPs, a thin 1D BCP PC film is developed with alternating in‐plane lamellae whose periodicity varies linearly from ≈46 to ≈91 nm. Subsequent preferential swelling of one‐type lamellae with either solvent or non‐volatile ionic liquid causes the photonic band gap of the films to red‐shift, giving rise to full‐visible‐range SC correlated with the pristine nanostructures of the blended films in both liquid and solid states. The BCP PC palette of solution‐blended binary solutions is conveniently employed in various coating processes, allowing facile development of BCP SC on the targeted surface. Furthermore, full‐color SC paintings are realized with their transparent PC inks, facilitating low‐power pattern encryption.