Polymer Films Conduct Heat Instead of Trapping It

While polymer usually traps heat, MIT researchers have found a way to modify its structure to create polymer films that conduct heat even better than many metal sand ceramics.

Polymer materials typically are natural insulators, which makes them well-suited for applications that need to trap heat inside them, like sleeves for coffee cups or oven mitts.

However, polymers also are used in electronic devices, which can cause overheating and possible device failure if the heat isn’t somehow dissipated.

Heat Conducting Polymers

Researchers at MIT now have solved this problem by modifying the natural reaction of polymers and creating polymer films that conduct heat rather than trapping it, an ability normally associated with metals.

A team of engineering researchers built upon previous work to fabricate thin films of conducting polymer by untangling the usual mess of molecular polymer chains in the material, which typically makes it difficult for heat to flow through.

“Common polyethylene has randomly coiled and tangled chains,” Yanfei Xu, one of the researchers on the project and an assistant professor at the University of Massachusetts Amherst, told Design News. “These chains look like spaghetti tangled up on a plate. These entanglements and voids, etc., act as defects that scatter heat-carriers, and results in polyethylene as thermal insulators.”

In experiments, researchers found that the films they created—which are thinner than plastic wrap—conduct heat better than ceramics and many metals, including steel, they said.

Xu and her colleagues achieved these results by building on previous work from 2010, in which they fabricated thin fibers of polyethylene 300 times more thermally conductive than normal polyethylene, and about as conductive as most metals.

By mixing polymer powder in solution to generate a film that they then stretched, MIT researchers have changed polyethylene’s microstructure, from spaghetti-like clumps of molecular chains (left), to straighter strands (right), allowing heat to conduct through the polymer better than most metals. (Image source: MIT)

Heat-Conducting Films

However, the fibers alone wouldn’t be useful for applications such as electronics and computer core processors, the makers of which became interested in the work for this purpose. Researchers knew they would have to create polymer films of the fibers if the technology would be applicable, they said.

To fabricate the thin films of conducting polymer, researchers started with a commercial polyethylene powder and then set out to untangle the molecular chains. To do this, they dissolved polyethylene powder in a solution that prompted the coiled chains to expand and untangle.

Researchers then built a custom flow system to unwind the molecular chains further, and then spilled the solution onto a liquid-nitrogen-cooled plate to form a thick film. In a final step, researchers used a roll-to-roll drawing machine to heat and stretch the film until it was thinner than plastic wrap.

The result was an impressive heat-conducting thin-film material, Xu told us.

“Our engineered polyethylene film [conducted heat] around 62 watts per meter per kelvin, which is two orders of magnitude more thermally conductive than most polymers, and also more conductive than steel and ceramics.,” she said. “Ceramic measures about 30 watts per meter per kelvin, and steel, around 15.

Compared with [these] traditional heat conductors, our polymer films are lightweight, corrosion resistant, and easy to process.”

Applications for these films range from heat-dissipating materials in laptops and mobile devices, as well as cooling elements in cars and refrigerators, Xu added. The team published a paper on its work in the journal Nature Communications.

Researchers aim to continue their work to dissipate heat more effectively in any direction, as currently, the polyethylene film conducts heat only along the length of the fibers that make up the film, Xu told us. “So we’re looking into better heat conduction in all three dimensions,” she said.

Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 20 years. She has lived and worked as a professional journalist in Phoenix, San Francisco and New York City. In her free time she enjoys surfing, traveling, music, yoga and cooking. She currently resides in a village on the southwest coast of Portugal.

 

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