Silver nanowires can be printed to fabricate patterned stretchable conductors.

Researchers from North Carolina State University (Raleigh) have developed highly conductive and elastic conductors made from silver nanowires. The conductors can be used to develop stretchable electronic devices. Developed by Yong Zhu, an assistant professor of mechanical and aerospace engineering at NC State, and Feng Xu, a PhD student in Zhu’s lab, the conductors are elastic and able to effectively and reliably transmit electric signals, regardless of whether they are deformed.

Silver offers very high electric conductivity. The new technique embeds highly conductive silver nanowires in a polymer that can withstand significant stretching without adversely affecting the material’s conductivity. This makes it attractive as a component for use in stretchable electronic devices.

“This development is very exciting because it could be immediately applied to a broad range of applications,” Zhu remarks. “In addition, our work focuses on high and stable conductivity under a large degree of deformation, complementary to most other work using silver nanowires that are more concerned with flexibility and transparency.”

The fabrication approach is very simple, Xu says. Silver nanowires are placed on a silicon plate and a liquid polymer is poured over the silicon substrate. The polymer is then exposed to high heat, which turns it from a liquid into an elastic solid. Because the polymer flows around the silver nanowires when it is in liquid form, the nanowires are trapped in the polymer when it becomes solid. The polymer can then be peeled off the silicon plate.

“Also silver nanowires can be printed to fabricate patterned stretchable conductors,” Xu says. The fact that it is easy to make patterns using the silver nanowire conductors should facilitate the technique’s use in electronics manufacturing.

When the nanowire-embedded polymer is stretched and relaxed, the surface of the polymer-containing nanowires buckles. The end result is that the composite is flat on the side without nanowires but wavy on the side with nanowires.

After the nanowire-embedded surface has buckled, the material can be stretched up to 50% of its elongation, or tensile strain, without affecting the conductivity of the wires. The buckled shape of the material allows the nanowires to stay in a fixed position relative to each other, even as the polymer is being stretched.

“In addition to having high conductivity and a large stable strain range, the new stretchable conductors show excellent robustness under repeated mechanical loading,” Zhu comments. Other reported stretchable conductive materials are typically deposited on top of substrates and could delaminate under repeated mechanical stretching or surface rubbing.