Researchers in China have drawn on the world’s strongest material to create new-generation ‘E-skin’ with multiple potential applications across numerous industries.
Whether for camouflage, temperature regulation or communication purposes, many animals have a colour-changing ability. Chameleons might be the natural world’s best-known chromatic shifters but there’s also the likes of squid, octopus and a host more varieties.
Artificial colour-changing skin isn’t new but has tended to be technologically limited in the past. A Chinese engineering team’s recent breakthrough could now change the playing field for all.
The researchers, based at Beijing’s Tsinghua University, have managed to develop electronic skin that interacts with its wearer. When this skin changes colour, minimal mechanical strain is involved and the shift requires no special equipment to observe with the human eye. Neither of these scenarios was previously possible.
The new ‘E-Skin’ features flexible electronics manufactured from graphene. No material is stronger, thinner or more conductive than graphene. It’s these qualities that are behind the one atom-thick, pure carbon product’s ‘wonder material’ tag.
The strain factor associated with historic colour-changing skin has been up to 500 per cent. The new electronic skin, however, produces a visible colour changing effect at sub-10 per cent strain. The colour-change occurs when an electrical current is applied to the skin’s ECD (electrochromic device) component. The ECD is one of two graphene layers present – the other is its strain sensor.
“We explored the underlying effect on the electromechanical behaviour of graphene”, explains head researcher Dr Tingting Yang. “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.
'We found subtle strain - between zero and 10 per cent - was enough to cause an obvious colour change, and the RGB [Red, Green, Blue] value of the colour quantified the magnitude of the applied strain.”
This new Chinese electrochromic technology is still being evolved but multiple future uses are already envisaged for it. These include potential robotic, prosthetic and battlefield applications, to name but three.
“Graphene, with its high transparency, rapid carrier transport, flexibility and large specific surface area, shows application potential for flexible electronics, including stretchable electrodes, supercapacitor, sensors, and optical devices”, adds Yang’s colleague, Professor Hongwei Zhu. “However, our results also show that the mechanical property 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.”