Tunable Photonic Paints via Block Copolymer Self-Assembly and Refractive Index Engineering

Structurally colored paints based on photonic microparticles offer an intriguing alternative to conventional pigment-based colorants but face persistent challenges related to limited color vibrancy and excessive light scattering. In this work, we present a scalable strategy to fabricate water-based photonic paints using poly-(2-vinylpyridine)-block-poly-(methyl methacrylate) (P2VP-b-PMMA) microparticles formed via confined self-assembly in emulsion droplets. These microparticles exhibit a concentric lamellar morphology, resulting in a photonic bandgap in the visible spectral region. Selective incorporation of 2,4,6-triiodophenol (TIPh) into the P2VP domains increases the refractive index contrast between microphase-separated domains, giving rise to tunable and more intense structural colors compared to additive-free microparticles. Detailed optical and structural characterization reveals a correlation among additive content, photonic bandgap position, and structural ordering. To reduce diffuse scattering and enhance color saturation, the broadband absorber Sudan Black B (C₂₉H₂₄N₆) is then coassembled within the microparticles. These photonic pigments are finally combined with a waterborne polyurethane binder to produce robust, vividly colored coatings. The binder improves film homogeneity, reduces interparticle scattering, and enhances mechanical integrity. This multicomponent approachintegrating refractive index engineering, pigment dispersion control, and optical absorptionenables the fabrication of structurally colored paints with improved vibrancy, uniformity, and tunability.