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Artificial chameleon skin instantly changes color to match background

Flexible camouflage technology could be used for soldier stealth and displays

by Prachi Patel, special to C&EN
August 10, 2021

Credit: Seung Hwan Ko et al.
A thermochromic material changes color to match the surface below it. Video is 2x normal speed.

A chameleon-like artificial skin can sense its local background and instantly change color in complex patterns to match and blend in (Nat. Commun. 2021, DOI: 10.1038/s41467-021-24916-w). While others have made active camouflage systems before, the new technology is simple and cost-effective for large areas, says its developer Seung Hwan Ko, a mechanical engineer at Seoul National University.

The integration of a color-sensing and a color-changing mechanism makes this artificial chameleon the first of its kind, says Albert Schenning, a chemist at Eindhoven University of Technology who was not involved in the work. The resulting high-resolution, adaptive camouflage could be used for camouflage suits or vehicle coatings for the military, or for next-generation flexible displays. Ko also imagines uses in color-changing art, building facades, and clothing.

Chameleons conceal themselves in their surroundings by altering the spacing between guanine nanocrystals in their skin, which changes the wavelength of light their skin reflects. Researchers have tried to mimic this prowess by approaches like changing the distance between nanostructures or using light-reflecting nanoparticles. But most approaches have required complex, expensive fabrication processes and had slow color-changing times.

A series of photographs shows a robot chameleon having different colors when crawling across a surface of different colors.
Credit: Seung Hwan Ko
A soft, 30 cm long robot with a temperature-based color-changing skin instantaneously takes on the color of the background it is crawling on.

Ko and his colleagues use a mechanism that relies on temperature-induced color change. The surface of their thin, flexible color-changing skin is coated with ink made of thermochromic liquid crystals, materials that take on different shades of red, green, and blue at specific temperatures. Below that is a stack of heating layers, each a transparent polyimide film coated with silver nanowires in different patterns including waves and stripes. The nanowires heat up when an electric current passes through them.

The team connects this artificial camouflage skin to a commercially available color sensor and a microcontroller chip. The sensor relays background color data to the microcontroller, which electrically heats up the nanowires in the three layers to various temperatures. The temperature patterns trigger the desired patches of color in the liquid crystals.

The active electronic control gives an almost instantaneous color change. The researchers demonstrated this by attaching the camouflage skin to a lizard-like robot that changes color across its body in real-time as it walks on a background with varying colors.

Because the device is made by spray-coating inks of the silver nanowires and liquid crystals in an ambient environment, it could easily be mass-produced using roll-to-roll processing, Ko says. The team plans to create more high-resolution color patterns for complex backgrounds and speed up the color change even more.


The caption on the video accompanying this story was updated to include that the video was sped up twofold.



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