Polymers are commonly used for thermal insulation as they are excellent at trapping heat. Thin polymer films were developed that conduct heat — an ability normally associated with metals. The films, which are thinner than plastic wrap, conduct heat better than many metals including steel and ceramic.
Researchers fabricated thin fibers of polyethylene that were 300 times more thermally conductive than normal polyethylene and about as conductive as most metals; however, in order for polymer conductors to work, they would have to be scaled up from ultrathin fibers (a single fiber measured 1/100 of the diameter of a human hair) to more manageable films.
The researchers developed a means to fabricate heat-conducting sheets of polymer and also custom-built an apparatus to test the material's heat conduction. Computer codes were designed to analyze images of the material's microscopic structures. The result was the fabrication of thin films of conducting polymer, starting with a commercial polyethylene powder. Normally, the microscopic structure of polyethylene and most polymers resembles a spaghetti-like tangle of molecular chains. Heat has a difficult time flowing through this, which explains a polymer's intrinsic insulating properties.
To untangle polyethylene's molecular knots to form parallel chains along which heat can better conduct, polyethylene powder was dissolved in a solution that prompted the coiled chains to expand and untangle. A custom-built flow system further untangled the molecular chains and spit out the solution onto a liquid-nitrogen-cooled plate to form a thick film, which was then placed on a roll-to-roll drawing machine that heated and stretched the film until it was thinner than plastic wrap.
While most polymers conduct heat at around 0.1 to 0.5 watts per meter per kelvin, the new polyethylene film measured around 60 watts per meter per kelvin. (Diamond, the best heat-conducting material, comes in at around 2,000 watts per meter per kelvin, while ceramic measures about 30 and steel, around 15.) The film is two orders of magnitude more thermally conductive than most polymers and also more conductive than steel and ceramics.
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