Silver nanowire conductors could mean better stretchable electronics
Earlier this year, a team led by North Carolina State University’s Dr. Yong Zhu reported success in creating elastic conductors made from carbon nanotubes. Such conductors could be used in stretchable electronics, which could in turn find use in things like bendable displays, smart fabrics, or even touch-sensitive robot skin. Now, he has made some more elastic conductors, but this time using silver nanowires – according to Zhu, they offer some big advantages over carbon nanotubes.
“Ag [silver] nanowires (NWs) have higher conductivity that carbon nanotubes (CNTs) or other metal nanowires,” he told us. “As such, the conductivity of AgNW stretchable conductor in our case is higher than other CNT based stretchable conductors.”
Additionally, silver nanowires should lend themselves more towards mass production. “AgNWs are chemically synthesized in solution, which makes them easily compatible with existing parallel or serial fabrication/patterning techniques,” he said. “CNTs are grown on substrate by dry methods and extra steps are required to disperse them in solution for printing.”
Finally, he added, AgNWs are biocompatible. This means they could safely be used in stretchable biomedical electronic devices. By contrast, he stated that “unrefined CNTs possess some degree of toxicity.”
The silver nanowire-based conductors are fabricated using a fairly simple technique.
First, the nanowires are laid on a silicon plate. A liquid polymer is then poured over them and heated, which causes it to convert from a liquid to an elastic solid form. It is subsequently peeled off the silicon, with the nanowires now sealed inside of it – some previous attempts at stretchable electronics have involved the conductive material being deposited on the outside of the substrate, from which it could possibly delaminate over time.
When the polymer sheet is stretched for the first time, the surface of the side containing the wires relaxes back into a buckled, wavy form. Every time it’s stretched after that, it can be elongated by up to 50 percent without any detrimental effect on the nanowires’ conductivity. This is because the buckling allows the wires to stay in a fixed position relative to one another, regardless of whether the polymer is in a stretched or relaxed state.