Pulled Polyethylene Takes The Heat

Engineers at MIT have found a way to transform polyethylene into a material that conducts heat as well as most metals (Nat. Nanotechnol., DOI: 10.1038/nnano.2010.27). The discovery could lead to new types of inexpensive heat-transfer materials used to help cool solar collectors, heat exchangers, and electronics. Bulk polymers are generally regarded as thermal insulators, a property arising from the tangled web of polymer filaments that contains void spaces and impurities that impede the flow of heat. Typical methods to improve polymer thermal conductivity focus on composite materials in which metal nanoparticles, ceramics, or carbon nanotubes are embedded in a polymer matrix. MIT’s Sheng Shen, Gang Chen, and coworkers decided instead to improve on methods for straightening out polymer chains to eliminate defects. The team created crystalline polyethylene nanofibers having diameters of up to 500 nm and lengths of tens of millimeters by drawing out strands of polymer gel with a tungsten needle or the cantilever tip of an atomic force microscope. The stretched-out fibers with aligned polymer chains have a thermal conductivity 300 times greater than the bulk polymer and better than pure iron, platinum, and nickel. The researchers have produced individual fibers in the lab so far, Chen says, so the next step is to scale up the process to make polymer sheets.