Spherical colloidal photonic crystals with selected lattice plane exposure and enhanced color saturation for dynamic optical displays

While structural color materials have non-fading properties and contribute significantly to the sustainable development of pigments or dyes, they are plagued by low color saturation and limited color tunability. Here, we describe a new type of spherical colloidal photonic crystals (CPCs) prepared by droplet-based microfluidic strategy, featuring enhanced color saturation and tunable structural colors. Methyl viologen (MV) functionalized SiO2 colloids were synthesized and used for the preparation of CPCs in microdroplets. Because of the absorption of incoherently scattered light by MV, the ratio of peak-to-background amplitude in the reflectance spectra of CPCs is increased, leading to brilliant structural color with enhanced saturation. The lattice plane exposure of spherical CPCs is depended on the refractive index between the interparticle voids and SiO2 building blocks, and this offers an alternative way to tune the structural color in a spherical CPC. Accordingly, a dynamic optical display was constru...