Stretchable circuitry could be used, for example, to create tactile, strain and motion sensors in wearable or conformable applications.
Dr Yong Zhu, an assistant professor of mechanical and aerospace engineering at NC State, and Feng Xu, a PhD student in Zhu’s lab have developed elastic conductors using silver nanowires. Silver has very high electric conductivity. The technique developed at NC State embeds 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.
Silver nanowires are placed on a silicon plate and a liquid polymer is poured over the silicon substrate, which flows around the silver nanowires. High heat turns the polymer from a liquid into an elastic solid, trapping the nanowires in the polymer. The polymer is peeled off the silicon plate.
Zhu says the elastic conductor technology could be commercially viable within five years. Fabrication is simple and is compatible with printing and patterning techniques, including screen and inkjet. Zhu’s team has made some prototypes, filed for patents and discussions about next steps towards commercialisation are taking place. When the polymer is stretched and relaxed, the surface containing nanowires buckles, creating a composite that is wavy on the side that contains silver nanowires and flat on the other.
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 silver nanowires, because the buckled shape of the material allows the nanowires to stay in a fixed position in relation to each other, as the polymer is being stretched.
The research was supported by the National Science Foundation.