Silica-coated balls mimicking the structure of duck feathers display a range of bright hues across the visible spectrum and could potentially replace toxic metal oxides and other pigments used to create colour, a new study reports.
What’s more, researchers note the method used to fabricate these self-assembling “supraballs” is simple, fast, and easily scalable.
Colours are produced through absorption of light by molecules (pigmentary colors) or scattering of light by nanostructures (structural colors). Structural colors are superior in many ways due to their ability to be fine-tuned, resistance to bleaching, and reduced dependence on toxic materials.
However, structural colouring faces significant challenges; several traditional structural colors are iridescent and not useful for wide-angle displays, and there is a demand for a scalable mass production process.
Drawing inspiration from nature’s many examples of structural colours, Ming Xiao at the University of Akron and colleagues examined the structures of a duck wing feather and an iridescent turkey wing feather to create an optical model without iridescence. They designed nanoparticles with melanin cores and silica shells. Serving an analogous role to keratin in duck feathers, the silica shell of the supraball helped to control the spacing between melanin nanoparticles. Interestingly, overall supraball size had no obvious influence on colour, the scientists found, but adjusting the materials’ thickness tweaked how they scattered light.
The researchers examined how light entered the materials (via refractive indexes), observing that high refractive index cores and low refractive index shells increased reflectance to produce brighter colours. The authors say the supraballs could be directly added to paints, plastics and coatings or used as UV-resistant inks or cosmetics.