Researchers use liquid metal to create wires that stretch eight times their original length

Dec 18, 2012
The tube, filled with liquid metal, can be stretched many times its original length. Credit: Dr. Michael Dickey, North Carolina State University

(Phys.org)—Researchers from North Carolina State University have created conductive wires that can be stretched up to eight times their original length while still functioning. The wires can be used for everything from headphones to phone chargers, and hold potential for use in electronic textiles.

To make the wires, researchers start with a thin tube made of an extremely elastic polymer and then fill the tube with a liquid metal alloy of gallium and , which is an efficient conductor of electricity.

"Previous efforts to create stretchable wires focus on embedding metals or other in elastic polymers, but that creates a trade-off," says Dr. Michael Dickey, an assistant professor of chemical and biomolecular engineering at NC State and co-author of a paper on the research.

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Researchers from North Carolina State University have created conductive wires that can be stretched up to eight times their original length while still functioning. The wires can be used for everything from headphones to phone chargers, and hold potential for use in electronic textiles. The paper, Credit: Dr. Michael Dickey, North Carolina State University

"Increasing the amount of metal improves the conductivity of the composite, but diminishes its elasticity," Dickey says. "Our approach keeps the materials separate, so you have maximum conductivity without impairing elasticity. In short, our wires are orders of magnitude more stretchable than the most conductive wires, and at least an order of magnitude more conductive than the most stretchable wires currently in the literature."

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.

The paper, "Ultrastretchable Fibers with Metallic Conductivity Using a Alloy Core," is published online in .

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More information: "Ultrastretchable Fibers with Metallic Conductivity Using a Liquid Metal Alloy Core" Authors: Shu Zhu, Ju-Hee So, Robin Mays, Sharvil Desai, William R. Barnes, Behnam Pourdeyhimi, Michael D. Dickey. Published: online Dec. 13, Advanced Functional Materials.

Abstract
This paper describes the fabrication and characterization of fibers that are ultra-stretchable and have metallic electrical conductivity. The fibers consist of a liquid metal alloy, eutectic gallium indium (EGaIn), injected into the core of stretchable hollow fibers composed of a triblock copolymer, poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) resin. The hollow fibers are easy to mass-produce with controlled size by using commercially available melt processing methods. The fibers are similar to conventional metallic wires (metal core, surrounded by polymeric insulation), but can be stretched orders of magnitude further while retaining electrical conductivity. Mechanical measurements with and without the liquid metal inside the fibers show the liquid core has a negligible impact on the mechanical properties of the fibers, which is in contrast to most conductive composite fibers. The fibers also maintain the same tactile properties with and without the metal because the conductive elements are confined to the core of the fiber. As expected, electrical measurements show that the fibers increase resistance as the fiber elongates and the cross sectional area narrows. Fibers with large diameters (~600 [micrometers]) change from a triangular to a more circular cross-section during stretching, which has the appeal of lowering the resistance below that predicted by theory. 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 (~3×10-5 [Omega] cm) up to 700% strain. As a demonstration of their utility, the ultrastretchable fibers were used as the wires for stretchable earphones and a stretchable battery charger.

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User comments : 13

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baudrunner
2.8 / 5 (8) Dec 18, 2012
Would repeated stretching and relaxing not induce an electro-magnetic field which can be tapped for energy? That way, novelty t-shirts with flashing led's or that respond to or play music wouldn't need batteries, or at least require smaller batteries that would last a lot longer.
Noumenon
3.7 / 5 (18) Dec 18, 2012
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.


Perhaps they could compound the liquid metal alloy directly with the elastomer, using a High let-down-ratio (LDR), and then inject this resulting composite into the elastomer extrusion (tube)? The core will then be a "gel", which will not leak,.. while maintaining the physical properties of the tube.
iiibogdan
not rated yet Dec 18, 2012
"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"

maybe mix the liquid metal with something so it solidifies in contact with air
Lurker2358
3.4 / 5 (5) Dec 18, 2012
I'm guessing this could be useful in robotics by allowing wiring that flexes better.

Electronic biomimickry is a field where "synthetic muscles" and other robot structures are made to pattern animal behavior at the nano-scale to produce more flexibility. Having flexible and even extendable wiring could potentially solve lots of problems.

I could conceive of something like this for the power supply cables for actual skeletal muscles in a robot or a prosthetic device, although you'd want to coat it in a way that would be safe for the body in the case of implants.
Trenchant
5 / 5 (1) Dec 19, 2012
Great concept but mass producing products, like headphones, with rare earth metals may not be the best application. Robotics or specialized medical products may be the wiser route.
Eikka
3.7 / 5 (3) Dec 19, 2012
Since the resistance of the wire is dependent on the cross-section area and lenght, which changes when you pull on it, you can use it as an excellent sensor for stretching and strain over much greater distances than other strain gauges.

That's extremely useful, because you no longer need sliding contact potentiometers or elaborate digital encoders to detect e.g. the angle of a limb. You could incorporate the wire directly into an analog PID feedback loop and do away with a lot of processing.

baudrunner
2.3 / 5 (3) Dec 19, 2012
Nope, it wouldn't. Why the deform of metal should lead into electromagnetic field? Not quite accidentally, you were upvoted for it with three people already.
(wish I could flag you for bad English)

Why, indeed. First: this is not the place to instruct you in the basics of electromagnetic induction - that knowledge is assumed for anyone responding to the article, and is, incidentally, quite obviously not there in your case. Second: people "upvoted" me because I have given them ideas, and you can assume that they do actually know what I am talking about. But, why "quite accidentally"?
ValeriaT
1 / 5 (2) Dec 20, 2012
Because the PO is increasingly flooded with naive kids, who A) don't understand physics and B) who expect huge exploitation of every silly result of basic research regardless its actual price. Just such silly publics enables the lazy incompetent scientists to survive.
Q-Star
1.8 / 5 (5) Dec 20, 2012
Because the PO is increasingly flooded with naive kids, who A) don't understand physics and B) who expect huge exploitation of every silly result of basic research regardless its actual price. Just such silly publics enables the lazy incompetent scientists to survive.


Does that mean that the aether flat water wave model is no longer applicable to non moving electrons?
antialias_physorg
5 / 5 (3) Dec 22, 2012
But in this case he's correct. Simply waving a piece of metal about (or stretchig/compressing it or tying it in knots or whatever) doesn't induce anything....UNLESS you do it relative to a magnetic field which has at least some component at right angles to the (loop of) wire.

But if you're now thinking of using the Earth's magnetic field then that is so weak that the induced current is utterly negligible.
Grallen
5 / 5 (1) Dec 23, 2012
The rare metals are just being used in the lab because of how easy they are to work with. I am sure they will find liquid alloys for abundant metals in short order.
ValeriaT
2.3 / 5 (3) Dec 23, 2012
Yep, sodium/potassium alloy...
Eikka
1 / 5 (1) Jan 03, 2013
Simply waving a piece of metal about doesn't induce anything

But if you're now thinking of using the Earth's magnetic field...


Speaking of which, I understood that the earth's magnetic field is due to the motion of molten metal in the outer core. At sufficient speeds and configurations, bits of moving metals can and do become self-excited dynamos that amplify any existing magnetic field, however small.

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