Angular-Independent Photonic Pigments via the Controlled Micellization of Amphiphilic Bottlebrush Block Copolymers

Photonic materials with angular-independent structural color are highly desirable because they offer the broad viewing angles required for application as colorants in paints, cosmetics, textiles, or displays. However, they are challenging to fabricate as they require isotropic nanoscale architectures with only short-range correlation. Here, porous microparticles with such a structure are produced in a single, scalable step from an amphiphilic bottlebrush block copolymer. This is achieved by exploiting a novel "controlled micellization" self-assembly mechanism within an emulsified toluene-in-water droplet. By restricting water permeation through the droplet interface, the size of the pores can be precisely addressed, resulting in structurally colored pigments. Furthermore, the reflected color can be tuned to reflect across the full visible spectrum using only a single polymer (M_n  = 290 kDa) by altering the initial emulsification conditions. Such "photonic pigments" have several key advantages over their crystalline analogues, as they provide isotropic structural coloration that suppresses iridescence and improves color purity without the need for either refractive index matching or the inclusion of a broadband absorber.