Yanfei Xu, an assistant professor of mechanical and industrial engineering at the University of Massachusetts Amherst, is co-author of a study that shows how to build polymer films that conduct heat as well or better than some metals and ceramics. The researchers say they can transform polymers that usually function as thermal insulators, into highly efficient thermal conductors that can transfer heat four times higher than stainless steel. But these heat conducting polymers are still electrical insulating. The findings are published in the journal Nature Communications.
Strong, light polymers with high heat conductivity have many uses including as parts for cell phones, computers and other electronic devices where there is a need to transfer heat away from the internal processors and screens. They are lightweight, durable, flexible, corrosion resistant and easy to process. These polymer films are expected to offer unique advantages over traditional heat conductors, such as metals and ceramics.
This tangled mass includes coils, snarls and knots that prevent efficient heat transfer (figure a). When the researchers discovered how to engineer these tangled chains, and transform them into long aligned strands that are ordered (figure b), the conductivity increased sharply.
Xu says the key to changing the polyethylene from thermal insulators to conductors is straightening out the long chains of molecules that make up the polyethylene. She says the polymer’s natural state is one of disorder. If you look at the polymer, it is made of long chains of monomers, repeating molecular units, that are attached end-to-end, she says. “These long chains are tangled together like a plate of spaghetti,” Xu says.
This tangled mass includes coils, snarls and knots that prevent efficient heat transfer. When the researchers discovered how to engineer these tangled chains, and transform them into long aligned strands that are ordered, the conductivity increased sharply.
“In summary, we have developed a scalable manufacturing process for producing polymer films with metal-like thermal conductivity,” the researchers say
Xu conducted much of the research when she was a postdoctoral associate in Professor Gang Chen's group at the Massachusetts Institute of Technology before joining the faculty at UMass Amherst College of Engineering in early 2019. The other authors of the paper are Daniel Kraemer, Bai Song, Jiawei Zhou, James Loomis, Jianjian Wang, Mingda Li, Hadi Ghasemi, Xiaopeng Huang, Xiaobo Li and Gang Chen from MIT’s department of mechanical engineering, and Zhang Jiang from Advanced Photon Source, Argonne National Laboratory.
The past few years have witnessed a surge in the interest of using polymers for thermal management and energy conversion. The research team believes that the high thermal conductivity achieved in these polymer films, with their unique combination of characteristics – light weight, optical transparency and chemical stability – will play a key role in many existing and unforeseen applications. Of course, polyethylene itself has limitations in the temperature range it can cover.
Xu and the other researchers say they foresee that further improvement of the thermal conductivity of the persistent amorphous phase will be the key developing the next generation of heat-conducting polymers, in polyethylene and beyond. (May 2019)