Disordered packings of core-shell particles with angle-independent structural colors

Abstract

Making materials that display angle-independent structural color requires control over both scattering and short-range correlations in the refractive index. We demonstrate a simple way to make such materials by packing core-shell colloidal particles consisting of high-refractive-index cores and soft, transparent shells. The core-shell structure allows us to control the scattering cross-section of the particles independently of the interparticle distance, which sets the resonance condition. At the same time, the softness of the shells makes it easy to assemble disordered structures through centrifugation. We show that packings of these particles display angle-independent structural colors that can be tuned by changing the shell diameter, either by using different particles or simply by varying the concentration of the suspension. The transparency of the suspensions can be tuned independently of the color by changing the core diameter. These materials might be useful for electronic displays, cosmetics, or long-lasting dyes.