Supraparticles with Tailored Absorption and Their Optical Performance as Photonic Pigments in Sustainable Water-Based Paint

Many traditional pigments and dyes are toxic or have low photostability, causing environmental concerns. On the other hand, structural color photonic pigments, which derive their color from reflectance of light rather than absorption, can be made from sustainable, inexpensive materials and are nonfading. Supraparticles, which are spherical assemblies of colloidal particles, reflect light of a certain wavelength, depending on the particle size of the building blocks. In this work, we synthesized building blocks with an optimized scattering-to-absorption ratio by employing a polydopamine coating and created supraparticles via bulk emulsification and osmotic extraction. We evaluated the optical performance of water-based paint containing supraparticles of different sizes, polydispersities, structures, and degrees of absorption. We found that a larger size and higher polydispersity of the supraparticles led to paints with a wider reflection peak. The degree of crystallinity of the supraparticles, which decreased for polydopamine-coated compared to uncoated particles and was tuned via the osmotic pressure difference between droplets, had a comparatively smaller impact on the optical performance. Additionally, the scattering-to-absorption ratio of the building blocks allowed us to precisely tune the color in the paints. After these optimizations, the photonic supraparticle paints were used to paint several drawings to showcase their applicability, providing guidelines for high-quality photonic supraparticle pigments in water-based paints.