What's whiter than white? These Cyphochilus beetles from Southeast Asia. Their scales are whiter than paper, and no human technology can replicate their brilliance.
What is whiter than white? These beetles, apparently – because their scales make them whiter than paper. No human technology can match their brilliance using such thin material.
The scales of the Cyphochilus (pictured above) and Lepidiota stigma beetles, which are native to South-East Asia, contain tight, complex networks of chitin filaments (see image below). Chitin is a substance with a similar molecular structure to cellulose, and it builds the cell walls of fungi and the shells of crustaceans as well as insect exoskeletons.
On their own, the chitin filaments reflect light poorly. But researchers at the University of Cambridge and the European Laboratory for Non-linear Spectroscopy in Florence, Italy, have found that the geometry of a filament network makes the whole thing reflect light extremely efficiently. It reflects light of all colours anisotropically, meaning that it bounces the light in one direction only. That makes the beetles' scales appear bright white.
"These scales have a structure that is truly complex, since it gives rise to something that is more than the sum of its parts," said team member Matteo Burresi of the Italian National Institute of Optics in Florence. "A randomly packed collection of its constituent elements by itself is not sufficient to achieve the degree of brightness that we observe."
What sets the brilliant beetles apart from artificial reflectors, though, is that the scales are ultra-thin. Their individual chitin filaments are just a few thousandths of a millimetre thick, minimising weight and so reducing the energy the beetles need to fly. It may not be too long before these beetles are inspiring a host of new materials that will be whiter than white too.
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