Nanostructure-free crescent-shaped microparticles as full-color reflective pigments

Structural colors arise from nanostructures or special microgeometries. Here, the authors report on crescent-shaped microparticles as full-color reflective pigments that show brilliant colors in directional light and are transparent in ambient light. Structural colors provide a promising visualization with high color saturation, iridescent characteristics, and fade resistance. However, pragmatic uses are frequently impeded by complex manufacturing processes for sophisticated nanostructures. Here, we report a facile emulsion-templating strategy to produce crescent-shaped microparticles as structural color pigments. The micro-crescents exhibit brilliant colors under directional light originating from total internal reflections and optical interferences in the absence of periodic nanostructures while being transparent under ambient light. The colors are finely tunable by adjusting the size of the micro-crescents, which can be further mixed to enrich the variety. Importantly, the pre-defined convex surface secures high stability of colors and enables structural coloration on target surfaces through direct deposition as inks. We anticipate this class of nanostructure-free structural colorants is pragmatic as invisible inks in particular for anti-counterfeiting patches and color cosmetics with distinctive impressions due to low-cost, scalable manufacturing, unique optical properties, and versatility.

Automated summary

This article introduces a new type of structural color, crescent-shaped microparticles, which exhibit brilliant colors under directional light and are transparent under ambient light. By adjusting the size of the microparticles, the colors can be finely tuned. These nanostructure-free colorants can be used as invisible inks for anti-counterfeiting patches and color cosmetics, due to their low-cost, scalable manufacturing, unique optical properties, and versatility.