Bio-inspired, large scale, highlyscattering films for nanoparticlealternative white surfaces

Abstract

Inspired by the white beetle of the genus Cyphochilus, we fabricate ultra-thin, porous PMMA films by foaming with CO2 saturation. Optimising pore diameter and fraction in terms of broad-band reflectance results in very thin films with exceptional whiteness. Already films with 60 μm-thick scattering layer feature a whiteness with a reflectance of 90%. Even 9 μm thin scattering layers appear white with a reflectance above 57%. The transport mean free path in the artificial films is between 3.5 μm and 4 μm being close to the evolutionary optimised natural prototype. The bio-inspired white films do not lose their whiteness during further shaping, allowing for various applications.