Uniform Block Copolymer Photonic Microspheres with Tunable Structural Colors across Full Visible Spectrum Enabled by Quaternizing Additives

Block copolymer (BCP) photonic microspheres have attracted significant interest for applications in inks, sensors, and displays. However, their fabrication typically requires bottlebrush BCPs with high molecular weights to attain domain sizes sufficient for visible structural color. In this study, we report a straightforward and effective strategy for producing uniform-sized photonic microspheres through the confined assembly of lamellae-forming poly(styrene-block-2-vinylpyridine) (PS-b-P2VP) diblock copolymers and quaternizing additives within emulsion droplets. This approach allows for tunable structural color across the entire visible spectrum. A series of bromine-functionalized additives are synthesized and employed to increase BCP domain sizes. Among these, 8-bromooctylbenzene (BOB) is identified as the most effective additive due to its exceptional reactivity toward P2VP chains, enabling efficient quaternization of the BCPs. The incorporation of BOB induces a significant increase of domain spacing from 147 to 212 nm while maintaining well-ordered, onion-like lamellae in BCP microspheres. This method enables precise control over the structural colors of BCP photonic microspheres across the whole visible range by simply adjusting the molar ratio of BOB to BCP. Furthermore, the BCP photonic microspheres exhibit reversible structural color transitions in response to pH variations, highlighting their potential for advanced sensing applications.