When it comes to eye-catching insects, it’s hard to beat the blue morpho butterfly. One of the largest butterflies in the world, this native of Central and South America sports bright blue iridescent wings. If you have colour envy, advancements in the field of nanotechnology may allow you to one day paint your nails, or even your whole house, the same iridescent blue as this butterfly.
Cypris Materials, a company in Berkeley, California, used the blue morpho butterfly for inspiration in the development of their colour coating technology. They say their technology is able to achieve all the colours of the rainbow without any toxic dyes or pigments.
Replicating the blue morpho butterfly’s spectacular wing colour involves a trick of the light. The top of the blue morpho’s wings are actually translucent. The bright blue colour is produced by tiny overlapping microscopic scales arranged across the surface of the wing that reflect light. This type of colour production is called structural colour.
Structural colours are found throughout nature, says Dr. Natalia Dushkina, a professor from the Department of Physics at Millersville University, Pennsylvania. They’re produced by biological species including butterflies, birds, beetles, and fish, as well as shells, pearls and minerals like labradorite. The colours are generated by light reflecting back from a microstructure. “Everytime you see such intense blue-green colours with metallic sheen and glossiness, those are structural colours,” says Dushkina.
“The most important characteristic of structural colours is that they vary with the viewing angle,” says Dushkina. Take the iridescent feathers of a wood duck for example. “The colour changes if the duck tilts the head, or if the sun rays go down. During lunchtime, you see beautiful blue colour, and then at sunset, you look at the same duck and it is purplish.”
Structural colours are different from chemical pigments and dyes, which produce colour through the absorption of light. “Practically all the colours that you find in plants, those are dye colours. A chemical substance. It’s very difficult to extract those, and extracting natural dyes is an extremely expensive process,” says Dushkina.
Scientists have been chasing after the structural colour of a blue morphos butterfly for years. Not only do structural colours promise a dazzling iridescent shimmer effect that can’t be reproduced with pigments, but structural colours eliminate the need for pigments and dyes.
Early successes in the development of artificial structural colour through nanotechnology came from Japan in the 1990s. In a chapter on structural colours from the 2013 book Engineered Biomimicry, Dushkina and co-author Lakhtakia write that the first purely physical color for cosmetics was developed by the Japanese cosmetics company Shiseido, and the first fiber and fabric (textile) using that fiber based on structural color was produced and demonstrated by Nissan Corporation.
Cypris Materials first looked to nature’s structural colours because the team was looking for a way to reflect heat away from the outer surfaces of buildings, says Dr. Ryan Pearson, co-founder and CEO of Cypris Materials. Using nanotechnology, the team developed self-assembling synthetic polymers that reflect coloured light like the scales of a butterfly wing does.
When picking ingredients for eco-friendly paint, less is more. Paints and inks are typically composed of four different components: a binder, solvent, additives, and colourants. “What we make is essentially a binder,” says Pearson. Because the binder itself produces the colour, there is no need to add pigments or dyes. “We take inherently safe materials, reshape them a bit through our polymer chemistry, and we’re able to make a simpler, safer paint.”
Currently Cypris Materials is focusing on consumer applications for their paint, including electronics, cosmetics, and food packaging. “We’re looking forward to getting some first products out at the end of 2021,” says Pearson.