Oxidation Control of Bottlebrush Molecular Conformation for Producing Libraries of Photonic Structures

Self-assembly is important for creating photonic structures and structural color is typically tunable by varying the size of building blocks, which are themselves obtained after time-consuming chemical syntheses. The molecular conformation of bottlebrush block copolymers (BBCPs) in solution can be manipulated to create libraries of photonic structures. Amphiphilic BBCPs bearing oxidation-responsive ferrocene groups on the hydrophilic block are used to fabricate porous particles via evaporation-induced self-assembly of water-in-oil-in-water (W/O/W) double emulsions stabilized by the BBCP surfactant. In situ oxidation of the ferrocene groups by hydrogen peroxide at the W/O interface leads to enhanced hydrophilicity, more hydration, and chain extension of the hydrophilic block. Consequently, larger internal water droplets are spontaneously formed, yielding larger pores within the microparticles. The pore diameter is readily tunable from 144 to 301 nm with a single BBCP, thereby generating full-spectrum structural colors. This work provides a straightforward method for fabrication of libraries of photonic pigments in an easy and scalable manner.