In Situ-Carbonized ZnS Spheres with Bright Structural Color for Durable Colorful Polymer Films

The application of conventional structural color materials based on photonic crystals is limited due to the requirement of a long-range ordered structure. Although the structure colors based on Mie scattering break the bottleneck of long-range ordered structure, black backgrounds or black additives are needed. Here, by post-treating ZnS polycrystalline spheres synthesized with PVP as additives, in situ-carbonized ZnS spheres were obtained, displaying bright structural color. Specifically, we developed a facile calcination strategy in N₂ atmosphere to partially convert the PVP in ZnS spheres into carbon, thereby tuning the light absorption ability. Excitingly, the in situ-formed carbon indeed provides the ZnS spheres with bright color. The resulting ZnS spheres exhibit tunable color saturation from 24.1% to 80.4% with increasing calcination temperature from 400 to 800 °C. When the obtained spheres were incorporated into waterborne polyurethane (WPU) films at only 1 wt % loading, the spheres generated vivid, angle-independent structural colors with excellent processability on diverse substrates (PET, rubber, wood, glass). The composite films demonstrate exceptional durability against acid, alkali, abrasion, heat (100 °C, 1 h), and UV exposure (6 h), offering a robust and scalable route to high-performance structural color coatings for diverse applications.