  Photonic materials with angular independent structural colour 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. In this article, 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 emulsified toluene-in-water
droplets. By restricting water permeation through the droplet interface, the
size of the pores can be precisely addressed, resulting in structurally
coloured pigments. Furthermore, the reflected colour can be tuned to reflect
across the full visible spectrum using only a single polymer (Mn = 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 colour
purity without the need for either refractive index matching or the inclusion
of a broadband absorber.

Soft Condensed Matter;Optics