Bright Silver Brilliancy from Irregular Microstructures in Butterfly Curetis acuta Moore

Abstract

AbstractStructural whiteness in nature is one of the useful optical phenomena contributed by refined microstructures and serves important biological functions. However, whiteness residing in wings, antennae, and bodies of butterflies often draws less attention, with undetected physical mechanisms and applications. Here, it is discovered that bright silver scales on the ventral side of butterfly Curetis acuta Moore have enhanced broadband reflection with particular angle dependency, which is dominated by the irregularity of scales. The broadband reflection is the result of color mixing effect caused by laminated scales with irregular layer space and thickness. The special angle dependency suggests that the reflection intensity changes with azimuth angles but remains unvaried at different viewing angles along given direction. This is the consequence of diffraction caused by ridges and irregular holes on the scales, which generates the shining effect and extends the viewing angle of broadband reflection. The characteristic reflection property is speculated to be used for intraspecific communication. Furthermore, it is found that the broadband reflection property of the silver scales is helpful to lower the body temperature under direct sunshine. These findings for light and thermo controlling would offer a potential strategy to design bioinspired advanced materials for low‐energy, reflectance‐based applications.