Using liquid metal to create ultra-stretchable wires

How many times you wished that your headphones had extra length or you ended up with tangled elastic electrical cord? North Carolina State University researchers are close to a great solution to these problems, since they managed to create conductive wires that won’t tangle and can function after being stretched up to eight times of their original length. Once perfected, these wires could find many uses, ranging from headphones and phone chargers, to electronic textiles and robotics.

To make the wires, researchers start with a thin tube made of an extremely elastic polymer composed of a triblock copolymer, poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) resin. The tube is filled a liquid metal alloy of eutectic gallium indium (EGaIn), which is an efficient conductor of electricity.

“Previous efforts to create stretchable wires focus on embedding metals or other electrical conductors in elastic polymers, but that creates a trade-off”, says Dr. Michael Dickey, an assistant professor of chemical and biomolecular engineering at NC State. “Increasing the amount of metal improves the conductivity of the composite, but diminishes its elasticity.”

NC State researchers took a different approach by keeping the materials separate, thus maintaining the maximum conductivity without impairing elasticity. The ability of the liquid metal to flow during the elongation of the fibers results in electrical continuity up to 1000% strain and metallic conductivity up to 700% strain.

The hollow fibers are easy to mass-produce with controlled size by using commercially available melt processing methods. While the manufacturing of the new wires is relatively straightforward, Dickey notes that one challenge needs to be addressed before the wires can be considered for popular products: how to minimize leakage of the metal if the wires are severed.

For more information, read the paper published in the journal Advanced Functional Materials: “Ultrastretchable Fibers with Metallic Conductivity Using a Liquid Metal Alloy Core”.