Ultra‐Bright Stimuli‐Responsive Photonic Crystals for High‐Performance Anticounterfeiting Coatings

Abstract Photonic crystals (PCs) with unique light manipulation capability have attracted widespread attentions. However, weak photonic bandgaps, poor structural color saturation, and tedious preparation process restrict their further development and practical application. Herein, an ultra‐bright stimuli‐responsive PC film with excellent optical performance is prepared by assembly of cadmium sulfide@polyacrylic acid (CdS@PAA) core–shell nanoparticles into PCs through molecule‐mediated shearing‐induced assembly technique (MSAT), this fabrication process is fast and facile, the solid periodic micro/nano‐structures can be formed within 10 s, and a wide selection range of structural color can be obtained. The high refractive index of CdS guarantees high brightness of the PC films. The prerequisite of using MSAT for preparation of large‐sized ultra‐bright PC film is that the CdS@PAA nanoparticles possess appropriate thickness of PAA shell. Compared with conventional PCs, the ultra‐bright PC films present strong photonic bandgaps and high structural color saturation, the relative reflectance is up to 130% compared with a standard aluminum mirror, which is more than four times reflectivity of PS@PAA microspheres. In addition, the PC paint is prepared by mashing the ultra‐bright PC film and blending it with transparent polydimethylsiloxane (PDMS) matrix, the PC coating prepared by alkali treated ultra‐bright PC pigments can achieve good water response ability and anticounterfeiting effect.