Surpassing Cyphochilus scales in optical scattering strength by well-controlled electrospun nanostructures

Abstract

Scales of Cyphochilus white beetles present one of the strongest optical scattering materials in nature. However, the intricate optical fibrillar network nanostructure inside the scales has been difficult to mimic. Here, characteristic structural parameters inside Cyphochilus scales – mean fiber diameter, diameter distribution, filling fraction, and structural anisotropy – are replicated in synthetic nanofibrous materials to functionally mimic the biological material. To fabricate the synthetic nanostructure, electrospinning is chosen because this conventional technique is amenable to nanomanufacturing. The optimized parameters in electrospun structures are found to be only slightly different from those in Cyphochilus scales. At the optimum, electrospun structures exhibit even stronger optical scattering than Cyphochilus scales. An electrospun film with the similar characteristic structural parameters as those in Cyphochilus scales gives two resonance peaks in visible reflectance spectrum in the limit of a uniform fiber diameter, giving a purple structural color. As the distribution of diameter increases appreciably to experimentally achievable degrees, the resonance peaks broaden and the reflectance spectrum becomes relatively flat, resulting in disappearance of the structural color. These results support that controllable fibrous nanostructures that exceed the exceptionally strong broadband optical scattering found among living organisms can be volume-produced.