Controllable fabrication of noniridescent microshaped photonic crystal assemblies by dynamic three-phase contact line behaviors on superhydrophobic substrates

Enormous research efforts have been made to self-assemble monodisperse colloidal spheres into special microscopic shapes (e.g., superbeads, superballs, or doughnuts), due to their widespread applications in sensors, displays, separation processes, catalysis, etc. But realization of photonic crystal (PC) assemblies with both facile microshape control and a noniridescent property is still a tough task. Herein, we demonstrate the controllable fabrication of noniridescent microshaped PC assemblies by evaporation-induced self-assembly inside aqueous colloidal dispersion droplet templates on superhydrophobic substrates. The microshapes of the PC assemblies could be tuned from microbeads to microwells to microellipsoids by manipulating the dynamic behaviors of the three-phase contact line of the colloidal droplets during the evaporating process. Structure characterization shows that the PC assemblies are crack-free, consisting of an ordered periodic arrangement of colloidal spheres in the surface layers and amorphous inner layers. The incorporation of black Fe₃O₄ nanoparticles into the PC assembly lattice is demonstrated to endow the PC assemblies with enhanced noniridescent structural colors with wide-viewing angles and a superparamagnetic property. The crack-free noniridescent PC assemblies with controlled microshapes have promising applications in the fields of nontoxic, nonbleaching pigments and energy-efficient full-color display pixels, and their facile fabrication procedure may provide guidance for creating new types of substructured colloidal particles.