Gold Particles Stretch Out Electronics

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To make really flexible electronics, you need something that keeps conducting even when it gets stretched. But metal wires don’t do that — at a certain point they just snap. Researchers have tried all kinds of solutions: wires shaped like springs, liquid metals or stiff ‘islands’ of electronic components. None of those techniques are as stretchy or as flexible as people would like.

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Now there’s another solution: tiny bits of gold embedded in polyurethane, which flexes and stretches. A team at the University of Michigan invented the idea.

The stretchable, flexible conductor could lead to truly “foldable” e-readers or medical devices that fit better with the body.

The researchers, in the lab of engineering professor Nicholas Kotov, put down layers of tiny gold particles only about 13 nanometers across between layers of polyurethane. Ordinarily the particles would be randomly distributed in the polymer, and when stretched, one would expect the distances between them to get larger.

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But that didn’t happen. As they stretched the polyurethane, the gold particles arranged themselves into chains, which allowed the electrons to move just as they would in a wire. The material stayed conductive even when it was stretched to nearly six times its original length. The particles reverted to a more random pattern when the stretching was relaxed.

A paper describing the new material appeared in the July 18 online edition of the journal Nature.

Credit: University of Michigan / Joseph Xu