LONDON Stretchable wiring that could be developed for use in a range of applications from headphones to phone chargers has been reported by researchers from North Carolina State University (Raleigh, North Carolina).
The wires which can stretch up to eight times their original length while maintaining electrical conductivity are composed of a tube of highly elastic polymer that is then filled with a liquid alloy of gallium and indium, which is an efficient conductor of electricity, according to authors of a paper recently published in Advanced Functional Materials.
The stretchable skin is made of a triblock copolymer, poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS)
resin. As expected, measurements show that the resistance increases as the wire elongates and the cross-sectional area reduces. Fibers with large
diameters of about 600-microns change from a triangular to a more circular
cross-section during stretching, the researchers reported.
Click on image to enlarge.
The polymer tube, filled with liquid metal, can be stretched to many times its original length. (Source: NCSU).
"Previous efforts to create stretchable wires focus on embedding metals or other electrical conductors in elastic polymers, but that creates a trade-off," said Michael Dickey, an assistant professor of chemical and biomolecular engineering at NC State and co-author of the research paper. "Increasing the amount of metal improves the conductivity of the composite, but diminishes its elasticity."
The NC State approach keeps the elastic stretchable polymer and the conductive medium separate and thereby maximizes 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," Dickey said, in a statement.
Some challenges remain before the wires can be considered for commercial production. One is the issue of the leakage of the indium-gallium metal if wires are broken.
The design, manufacture and implementation of flexible circuits is the subject of a session at DesignCon 2013, taking place Jan. 28 to 31, in Santa Clara, Calif. The session takes place at 2:00pm on Wednesday, Jan. 30 in Ballroom E and is scheduled to include speakers from DuPont, IBM and Molex. DesignCon
is organized by UBM Tech, the publisher of EE Times
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Ultrastretchable fibers with metallic conductivity using a liquid metal alloy core
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