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Meet the incredible shrinking material. Most things swell when they warm up, creating engineering headaches, but now a 3D-printed material has been configured to contract instead.
When two interlinked materials expand at different rates, they can warp or crack. It’s a problem in buildings, bridges, electronics and anything else that is exposed to a wide temperature swing. So forcing a material to shrink instead of swell is a much-prized goal.
Now Qiming Wang at the University of Southern California in Los Angeles and his colleagues have done just that. Using a 3D printer, they took two materials that naturally expand in the heat and rigged them so they do the opposite.
The trick is to arrange them in a loose matrix with the material that expands faster placed inside the one that expands slower. When this composite is blasted with heat, the inner material can only expand inwards, pulling the outer material with it. The entire thing shrinks.
The design can be used to take any two materials and tune them so they expand or shrink at any desired rate, says Jonathan Hopkins at the University of California in Los Angeles. Dental fillings, for example, feel sensitive because they don’t expand by the same amount as our teeth when we eat or drink something hot. Perfectly matching that change to the natural change in our teeth would eliminate that problem, says Wang.
Materials could also be designed to remain the same size under any heat changes – an effect that could create stable microchips, which currently crack when operated for too long, and satellites, which vibrate as they travel through the sun’s heat.
Another possibility is to make solar power more efficient, says Hopkins. If you put a solar panel on a series of pillars made of the shrinking material, the sun will heat one side of each pillar, leaving the other side cool. The side sitting in the sun will contract, causing the pillar to bend towards the sun.
“You don’t need to take any of the energy you’re getting from the sun to actually point it toward the sun,” Hopkins says. “You can actually just use the sun’s heat to passively follow the sun like a flower.”
Journal reference: Physical Review Letters, DOI: 10.1103/PhysRevLett.117.175901
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