Photonic spheres by microgel templating

We report on fabricating photonic spheres by combining submicron-sized microgels
and silica nanoparticles. By emulsifying the mixture and removing water through solvent drying,
we achieve spheres of packed microgels measuring from a few micrometers to tens of micrometers
in size. As the microgels de-swell, they exert pressure on the surrounding silica nanoparticles,
forming a foam-like network within the droplet. The polymer microgels are then removed by
calcination, leaving behind a silica foam. These photonic spheres exhibit structural colors in the
visible spectral range, including challenging shades like red. The versatile approach we present here can pave the way for designing photonic pigments and be a step forward in understanding
inverse structures with spherical morphology.