Bio-inspired, ultra-thin, and highly scattering white polymer films

 
Some beetles and butterflies are well-known for their highly effective nanostructures producing non-bleaching structural colours. The white beetle Cyphochilus insulanus, for example, is well-known for its scales, which produce a nearly perfect whiteness in a very efficient way with an astonishing low amount of material. Inspired by this biological prototype, we developed highly scattering white polymer films by foaming with CO2 saturation. Optimising pore diameter and fraction in terms broad-band reflectance through saturation parameters, we obtained very thin films comparable to the biomimetic inspiration. Even 24 µm thick films reflect up to 85% of the incident light.