Copper shines as flexible conductor


Modern materials that are light, flexible and highly conductive have immense technological potential – it’s just a matter of finding concepts affordable enough for general use.

Copper shines as flexible conductor
Copper nanowires
Image credit: flickr user: Kelly Jiang

While previous successes in the field of ultra-lightweight “aerogel monoliths” have largely relied on the use of precious gold and silver nanowires, researchers  at Monash University and the Melbourne Centre for Nanofabrication have discovered a new way of working with copper nanowires and a PVA “nano glue”, which could prove to be a real game changer.

By turning to copper – both abundant and cheap – the researchers were able to develop a cost-effective way of making flexible conductors to open up the potential for commercial application in a range of new-generation concepts: from prosthetic skin to electronic paper, for implantable medical devices, and for flexible displays and touch screens.

“Aerogel monoliths are like kitchen sponges but ours are made of ultra-fine copper nanowires, using a fabrication process called freeze drying,” said lead researcher Associate Professor Wenlong Cheng, from Monash University’s Department of Chemical Engineering.

“The copper aerogel monoliths are conductive and could be further embedded into polymeric elastomers – extremely flexible, stretchable materials – to obtain conducting rubbers.”

Despite its conductivity, copper’s tendency to oxidation and the poor mechanical stability of copper nanowire aerogel monoliths mean its potential has been largely unexplored.

According to the press release by Monash University, the researchers found that adding a trace amount of poly(vinyl alcohol) (PVA) to their aerogels substantially improved their mechanical strength and robustness without impairing their conductivity.

What’s more, once the PVA was included, the aerogels could be used to make electrically conductive rubber materials without the need for any prewiring. Reshaping was also easy.

“The conducting rubbers could be shaped in arbitrary 1D, 2D and 3D shapes simply by cutting, while maintaining the conductivities. The conductivity can be tuned simply by adjusting the loading of copper nanowires,” said Mr Cheng.

“A low loading of nano wires would be appropriate for a pressure sensor whereas a high loading is suitable for a stretchable conductor.”

According to Mr Cheng, they can be used in rubber-like electronic devices that, unlike paper-like electronic devices, can stretch as well as bend. They can also be attached to topologically complex curved surfaces, serving as real skin-like sensing devices.

In their report, published recently in ACS Nano, the researchers noted that devices using their copper-based aerogels were not quite as sensitive as those using gold nanowires, but had many other advantages, most notably their low-cost materials, simpler and more affordable processing, and great versatility.