What if engineers could replace heat-dispersing metal with a lightweight, flexible, and corrosion resistant polymer to cool electronic devices like smartphones, laptops, refrigerators, and even motor vehicles?
MIT engineers have developed an ultrathin polymer that can do exactly that.
Researcher Yanfei Xu, (lead author) along with senior co-author Gang Chen, the Carl Richard Soderberg Professor of Power Engineering at MIT, as well as Daniel Kraemer, Bai Song, Jiawei Zhou, James Loomis, Jianjian Wang, Migda Li, Hadi Ghasemi, Xiaopeng Huang, and Xiaobo Li from MIT, and Zhang Jiang of Argonne National Laboratory has been working on transforming the insulating properties of a polymer so that the same material could actually conduct heat.
In 2010, the team reported success in fabricating thin fibers of polyethylene that were 300 times more thermally conductive than normal polyethylene, and about as conductive as most metals. But for polymer conductors to work in modern technology applications, the materials would have to be scaled up from ultrathin fibers to more manageable films.
Just recently, the team succeeded in fabricating 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 doesn’t flow easily through this jumbled mess, which crates polymer’s intrinsic insulating properties.
Xu and her colleagues looked for ways to untangle polyethylene’s molecular knots, forming parallel chains that conduct heat. They dissolved polyethylene powder in a solution that prompted the coiled chains to expand and untangle. A custom-built flow system further untangled the molecular chains and spit 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.
The team then built an apparatus to test the film’s heat conduction. While most polymers conduct heat at around 0.1 to 0.5 watts per meter per kelvin, Xu found the new polyethylene film measured around 60 watts per meter per kelvin. The team’s film is two orders of magnitude more thermally conductive than most polymers, and also more conductive than steel and ceramics.