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Making Whiter Whites, with Less Work

Monday, August 18, 2014

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So you think you know white?

Mother Nature suggests otherwise, turning researchers on to a Southeast Asian beetle that effortlessly out-whites today's whitest white.

The light-scattering secrets of the Cyphochilus and L. Stigma beetles may hold the key to tomorrow's ultra-white paints, plastics and paper, while consuming less material than their dimmer current hues, say scientists at the University of Cambridge and the European Laboratory for non-Linear Spectroscopy in Italy.

'Maximum White'

“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’s Cavendish Laboratory, who led the research, published Friday (Aug. 15) in the journal Scientific Reports.

Cyphochilus beetle
Cambridge University

The Cyphochilus beetle is showing European researchers how to make whiter coatings and other products with less material.

In a research announcement inevitably titled "The Beetle's White Album," the researchers explain how Cyphochilus has optimized its internal structure to produce "maximum white with minimum material, like a painter who needs to whiten a wall with a very small quantity of paint."

The research could have major implications for paints, coatings and the myriad of other products worldwide that now rely on titanium dioxide pigment for whitening. Prices for the common pigment have been soaring worldwide as supplies diminish, leaving paint and coating makers scrambling for new sources and alternative materials.

What the Beetle Knows

Cyphochilus has developed its white veneer to hide among the white mushrooms of Southeast Asia.

Unlike bright colors, which are usually produced using pigments that absorb certain wavelengths of light and reflect others, white tissue needs to reflect all wavelengths of light with the same efficiency.

DrSilviaVignolini
eattheweeds.com

“Current technology is not able to produce a coating as white as these beetles can in such a thin layer,” said Dr. Silvia Vignolini.

The ultra-white Cyphochilus and L. Stigma beetles produce this coloration by exploiting the geometry of a dense complex network of chitin—a polysaccharide found in the outer skeleton of insects, crabs, shrimps, and lobsters and in the internal structures of other invertebrates, researchers explain.

Chitin filaments are just a few billionths of a meter thick and are not very reflective on their own.

Over millions of years, however, the beetles have developed a compressed network of chitin filaments that allows "high intensities of reflected light for all colors at the same time, resulting in a very intense white with very little material," Cambridge reports.

Structural Secrets

Said Vignolini: “In order to survive, these beetles need to optimize 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.”

The secret appears to be in the structure of the filaments.

Beetles
Scientific Reports

Scanning electron micrograph images (SEM) show the cross-section of the dense scales of the Cyphochilus (a) and Lepidiota stigma (c) beetles.

“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 co-author Dr. Matteo Burresi, of the Italian National Institute of Optics in Florence.

Lessons Learned

The beetle has taught the researchers two lessons, Vignolini said. Both may inform the future of coatings and many other applications.

“On one hand, we now know how to look to improve scattering strength of a given structure by varying its geometry," she said.

"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.”

“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’s Cavendish Laboratory, who led the research. - See more at: http://www.cam.ac.uk/research/news/the-beetles-white-album#sthash.uAiLLgw4.dpuf

   

Tagged categories: Architectural coatings; Color; Pigments; Research; Titanium dioxide

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