Grumpy blue chameleon

Colour-changing electronic skin could make human chameleons a possibility

Image credit: Dreamstime

Researchers from Tsinghua University, China, have developed a new type of electronic skin (e-skin) capable of changing colour noticeably with a small amount of stretching. This could have applications in prosthetics, robotics and wearable electronics.

For many years, materials scientists and engineers have attempted to replicate the ability of squid, octopodes, chameleons and other animals to change their skin colour at will. The artificial colour-changing materials produced, however, tend to require an impractical amount of strain to change colour to any noticeable degree.

A team of researchers from Tsinghua University in Beijing may have come the closest ever to replicating the abilities of these animals. Their new e-skin is able to respond to moderate mechanical strain with colour changes perceptible to the human eye.

The scientists used flexible electronics made from graphene, in the form of a sensitive strain sensor, and combined this with a stretchy electrochromic material: a material which reversibly changes colour in response to electric charge.

“We explored the substrate (underlying) effect on the electromechanical behaviour of graphene,” said Dr Tingting Yang, a materials scientist at Tsinghua University. “To obtain good performance with a simple process and reduced cost, we designed a modulus-gradient structure to use graphene as both the highly sensitive strain-sensing element and the insensitive stretchable electrode of the ECD layer.”

The researchers found that the strain sensor was sensitive enough to response to subtle strain of between zero and 10 per cent. This caused a visible colour change, with the colour representing the extent of the strain.

“It’s important to note that the capability we found for interactive colour changes with such small strain range has been rarely reported before,” she added.

According to Professor Hongwei Zhu, a senior author of the ‘2D Materials’ report on the new material, while graphene’s remarkable properties make it an attractive material in flexible electronics, the Tsinghua team’s results demonstrate the possibilities of the substrate in this field.

“The mechanical property of the substrate was strongly relevant to the performance of the strain sensing materials. This is something that has previously been somewhat overlooked, but that we believe should be closely considered in future studies of the electromechanical behaviour of certain functional materials,” he said.

According to the researchers, this more practical interactive e-skin could have applications in robotics, prosthetics and wearable technology. Various types of thin, flexible e-skins have emerged over previous years, with applications in healthcare monitoring and abilities such as touch sensitivity.

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