Stretchable electrical wires heal back together after being severed
By Ben Coxworth
January 23, 2013
Last month, we heard about how a team led by North Carolina State University’s Dr. Michael Dickey had created an electrical wire that could be stretched up to eight times its regular length ... and still carry a current. This was possible thanks to a conductive liquid metal alloy of gallium and indium, contained inside the wire’s elastic polymer outer housing. Now, Dickey's team has developed a new wire that not only can be stretched, but that will heal itself when severed.
The researchers started out with a cylindrical length of a commercially-available self-healing polymer, then used solid wire to bore tiny tunnels through its core, running from one end to the other. Those tunnels, known as microfluidic channels, were then filled with the same gallium/indium liquid metal used in the previous stretchy wire. Because the wire’s conductive core is a liquid, it stretches along with the elastic housing, keeping the electrical current constantly flowing.
Should the wire be cut in two, the exposed liquid metal at each of the cut ends will oxidize. This causes a thin film to form over the exposed metal, “sort of like the crust on crème brulee,” as Dickey explained to us. While that film is fairly fragile, it’s enough to keep the liquid from leaking out of the housing.
If someone were to then pick up the two pieces of wire and press the severed ends back together, the polymer faces would meld with one another on a molecular level, while the film on the metal would give way, allowing the liquid to flow along the length of the wire once again.
In other words, the wire would return to being one continuous length of material.
Although this latest wire isn’t as stretchable as the previous version due to the different polymer used, its self-healing qualities would obviously make it very easy to repair. This could make it ideal for use in high-stress environments. Additionally, circuits could be created or rewired using nothing more than a pair of scissors. It’s also been suggested that multiple pieces of the liquid metal-carrying polymer could be joined together end-to-end, to create three-dimensional conductive structures.
A paper on the research was recently published in the journal Advanced Materials. The wire’s self-healing capabilities can be seen in the video below.
Source: North Carolina State University