By Josh Perry, Editor
Typically, polymers are used as thermal insulators, but researchers from the Massachusetts Institute of Technology (MIT) in Cambridge, Mass. created new, thin polymer films (thinner than plastic wrap) that conduct heat better than ceramics and better than many metals.
By mixing polymer powder in solution to generate a film that they then stretched, MIT researchers have changed polyethylene’s microstructure, allowing heat to conduct through the polymer. (MIT)
According to a report from the school, this study could lead to more polymers that are used as thermal conductors in electronics cooling applications. For instance, one researcher suggested using polymers rather than metal to create lightweight heat exchangers.
Initially, in 2010, the research team created thin fibers of polyethylene that were 300 times more conductive than normal polyethylene but were in a form-factor that made it impractical for commercial applications.
“The researchers not only had to come up with a way to fabricate heat-conducting sheets of polymer, but they also had to custom-build an apparatus to test the material’s heat conduction, as well as develop computer codes to analyze images of the material’s microscopic structures,” the article described.
In the end, the researchers started with polyethylene powder and dissolved it in a solution that untangled the polymer’s normal mass of molecular chains that usually block the flow of heat and make polymers good insulators. The solution was placed on a nitrogen-cooled plate and formed a thick film before being put into a roll-to-roll drawing machine and stretched.
Polymers usually conduct heat at 0.1-0.5 W/mK but the films were conducting heat at 60 W/mK, twice as much as standard ceramics and four times the conductivity of steel.
“By imaging the ultrathin films, the researchers observed that the films exhibiting better heat conduction consisted of nanofibers with less randomly coiled chains, versus those in common polymers, which resemble tangled spaghetti,” the article explained. “Their observations could help researchers engineer polymer microstructures to efficiently conduct heat.”
The research was recently published in Nature Communications. The abstract read:
“Due to their unique properties, polymers – typically thermal insulators – can open up opportunities for advanced thermal management when they are transformed into thermal conductors. Recent studies have shown polymers can achieve high thermal conductivity, but the transport mechanisms have yet to be elucidated.
“Here we report polyethylene films with a high thermal conductivity of 62 Wm−1 K−1, over two orders-of-magnitude greater than that of typical polymers (~0.1 Wm−1 K−1) and exceeding that of many metals and ceramics. Structural studies and thermal modeling reveal that the film consists of nanofibers with crystalline and amorphous regions, and the amorphous region has a remarkably high thermal conductivity, over ~16 Wm−1 K−1.
“This work lays the foundation for rational design and synthesis of thermally conductive polymers for thermal management, particularly when flexible, lightweight, chemically inert, and electrically insulating thermal conductors are required.”