Flying colours: Butterflies are inspiring an entirely new approach to paint - Hindustan Times
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Flying colours: Butterflies are inspiring an entirely new approach to paint

ByNatasha Rego
Feb 16, 2024 07:30 PM IST

After years of studying how colourless scales on their wings cause iridescence, researchers have made a paint of clear nanoparticles that scatter,diffract light

Chemistry and physics are all very well, but the future of paint could well be geometric. And our guides in this field, are butterflies.

Butterfly installations coated with the structural paint. The challenge was finding a structure that would reflect light in a fixed way, without the shade changing as the viewer moved. This was cracked by researchers at the University of Central Florida. (Courtesy Debashis Chanda / UCF) PREMIUM
Butterfly installations coated with the structural paint. The challenge was finding a structure that would reflect light in a fixed way, without the shade changing as the viewer moved. This was cracked by researchers at the University of Central Florida. (Courtesy Debashis Chanda / UCF)

The lessons aren’t coming from their powdery pigments, but from their iridescence, which is the result of an intricate network of scales on their wings.

These scales have no inherent colour. They are, instead, layered and separated by pockets of air. This scatters and diffracts light, often several times across the tiny span, causing the flashes of vivid colour we see as certain butterflies flit past.

After decades of trying, scientists were finally able to replicate this effect in a lab, in 2023.

“The entire structural colour community has been working on this for many years,” says Debashis Chanda, a professor of physics at the University of Central Florida’s NanoScience Technology Center. His team figured it out.

“It’s not that we didn’t know how to make structural colour. But because of the nature of reflectance, structural colour has always been angle-dependent, ie, it changes or fades depending on how near or far you are from the surface,” he says.

Drawing inspiration from the butterfly, and from certain other animals such as peacocks and beetles, Chanda and his team got around this by building a symmetric five-layer architecture that uses colourless aluminium nanoparticles and insulating aluminium oxide layers.

By changing the dimensions of these layers, the researchers showed, in a paper published in Science Advances, one can produce a specific structural colour that is no longer angle-dependent. For instance, make the nanoparticles smaller and they absorb blue-green light and emit only yellow. Increase the size of the nanoparticles and the hue tends towards the blues of the spectrum.

“We were looking for an arrangement that would allow us to produce any colour from a single material, unlike pigments, where different minerals produce different colours,” says Chanda. “This is an important find because it has the potential to replace pigmented and artificially synthesised colours that are full of heavy metals like cadmium and cobalt and fossil fuels.”

The structural colour is produced in the form of nanoflakes, and combined with a commercial-grade binder to make paint. But two hues have so far remained elusive. “For black, you have to absorb the whole visible spectrum,” says Chanda. “At the moment, we still cannot foresee how to create black.”

The structural colour is produced in the form of nanoflakes and combined with a commercial-grade binder to make paint. (Courtesy Debashis Chanda / UCF)
The structural colour is produced in the form of nanoflakes and combined with a commercial-grade binder to make paint. (Courtesy Debashis Chanda / UCF)

The other colour is a specific deep red. “For this, we have to further optimise our parameters to suppress all blues and greens so that only light at 633 nanometres is reflected back. We still have to work that out, but we’ll get there eventually,” Chanda says

The paint has other interesting properties. The particles are 1,000 times wider than they are thick. As a result, this paint achieves full opaque coverage at a thickness of 150 nanometres, making it thousands of times lighter than the current lightest paints in the world.

It is also has the potential to act as an energy-saving device. “Because the multilayer stack is designed to resonate only with the spectrum of light visible to humans, it completely reflects every other wavelength of light that it is not interacting with, including infrared light – which is notorious for heating the earth – and thus helps keep a surface cool,” Chanda says.

The next step will be to work towards commercial viability. “It’s all very exciting,” says Chanda. “The possibility of a widely available, non-toxic, ultralightweight, cooling paint could change up the industry for the better.”

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