Cambridge materials revelation looks all white
The physical properties of ultra-white scales on a South East Asia beetle could be utilised to make whiter paper, plastics and paints according to Cambridge UK researchers.
And the process could use far less material than required in current manufacturing methods, they believe.
“Current technology is not able to produce a coating as white as these beetles can in such a thin layer,” said Dr Silvia Vignolini of the University of Cambridge’s Cavendish Laboratory, who led the research.
Nature’s gamechanger is the Cyphochilus beetle, native to South-East Asia, is whiter than paper, thanks to ultra-thin scales which cover its body.
A new study of the optical properties of these scales has shown they are able to scatter light more efficiently than any other biological tissue known, which is how they are able to achieve such a bright whiteness. The findings are published today in the journal Scientific Reports.
Animals produce colours for several purposes, from camouflage to communication, to mating and thermoregulation. Bright colours are usually produced using pigments, which absorb certain wavelengths of light and reflect others, which our eyes then perceive as colour.
To appear as white, however, a tissue needs to reflect all wavelengths of light with the same efficiency. The ultra-white Cyphochilus and L. Stigma beetles produce this colouration by exploiting the geometry of a dense complex network of chitin – a molecule similar in structure to cellulose, which is found throughout nature, including in the shells of molluscs, the exoskeletons of insects and the cell walls of fungi. The chitin filaments are just a few billionths of a metre thick, and on their own are not particularly good at reflecting light.
The research, a collaboration between the University of Cambridge and the European Laboratory for non-Linear Spectroscopy in Italy has shown that the beetles have optimised their internal structure in order to produce maximum white with minimum material, like a painter who needs to whiten a wall with a very small quantity of paint. This efficiency is particularly important for insects that fly, as it makes them lighter.
Over millions of years of evolution the beetles have developed a compressed network of chitin filaments. This network is directionally-dependent, or anisotropic, which allows high intensities of reflected light for all colours at the same time, resulting in a very intense white with very little material.
Dr Vignolini said: “In order to survive, these beetles need to optimise their optical response but this comes with the strong constraint of using as little material as possible in order to save energy and to keep the scales light enough in order to fly. Curiously, these beetles succeed in this task using chitin, which has a relatively low refractive index.
Exactly how this could be possible remained unclear up to now. The researchers studied how light propagates in the white scales, quantitatively measuring their scattering strength for the first time and demonstrating that they scatter light more efficiently than any other low-refractive-index material yet known.
In recent years, many engineers having been looking to structures found in nature to inspire their designs. “The lessons we are learning from these beetles is two-fold,” said Dr Vignolini.
“On one hand, we now know how to look to improve scattering strength of a given structure by varying its geometry. On the other hand the use of strongly scattering materials, such as the particles commonly used for white paint, is not mandatory to achieve an ultra-white coating.”
The research was funded by the European Research Council and the Biotechnology and Biological Sciences Research Council.
• PHOTOGRAPH SHOWS: Cyphochilus beetle. Credit: Lorenzo Cortese and Silvia Vignolini