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A D V A N C E D M A T E R I A L S & P R O C E S S E S | M A Y / J U N E 2 0 1 9 6 OMG! OUTRAGEOUSMATERIALSGOODNESS ENERGY STORAGE DEVICE TOUGH AS NAILS Researchers at Washington Univer- sity inSt. Louis, Mo., built anenergy stor- age device that can withstand a ham- mer striking it more than 40 times. The shatterproof supercapacitor is also non- flammable, unlike lithium-ion batter- ies. By controlling the formation of rust in solution, researchers grew a µm-thick porous mat of conducting fibers affixed to a soft, pliable layer of organic plastic. “We carefully designed the nano- structure orientation so that a polymer film assembles parallel to a rusted sur- face. It produces an interwoven mat of polymer nanofibers with a textile-like structure that is flexible and ideal for storing energy in a supercapacitor,” explains assistant chemistry profes- sor Julio D’Arcy. The team bent their new material to different angles over and over again. They hammered it re- peatedly and also tested it against an impact equivalent to a car collision at 30 mph. The device held up well: After the first hammer strike, it retained 80% of its ability to store energy at peak ef- ficiencies; after 40 strikes, it was still at 74%. wustl.edu. POLYMER FILMS CONDUCT HEAT BETTER THAN METALS Engineers at Massachusetts Insti- tute of Technology, Cambridge, are fab- ricating thin po- lymer films that conduct heat. In experiments, they found the films, which are thinner than plastic wrap, conduct heat bet- ter than ceramics and many metals including steel. The team’s re- sults may spur development of polymer insulators as lightweight, flex- ible, and corrosion-resistant alterna- tives to traditional metal heat conduc- tors, for applications ranging from heat dissipating materials in laptops to cool- ing elements in cars and refrigerators. “We think this result is a step to stimu- late the field,” says Gang Chen, the Carl Richard Soderberg professor of power engineering. “These polymers can cre- ate new applications and perhaps new industries, and may replace metals as heat exchangers.” Going forward, the researchers are looking for ways to make even better polymer heat conductors, by adjusting the fabrication process and experimenting with different types of polymers. The team’s polyethylene film conducts heat only along the length of A newmaterial combines epoxy with a form of lignin that can self-heal if sliced and elongate up to 2000%. Courtesy of ORNL. By mixing polymer powder in solution to generate a stretchy film, researchers changed polyethylene’s microstructure from clumps of molecular chains (left) to straighter strands (right), allowing heat to conduct through the polymer. the fibers that make up the film. Such a unidirectional heat conductor could be useful in carrying heat away in a spec- ified direction, inside devices such as laptops and other electronics. But ide- ally, he says the film should dissipate heat more effectively in any direction. mit.edu . SELF-HEALING MATERIAL MIXES LIGNIN AND EPOXY Scientists at the DOE’s Oak Ridge National Laboratory (ORNL), Tenn., de- veloped a new and stretchy material that outperforms the adhesiveness of the natural chemical that helps mus- sels stick to ships. This bio-based mate- rial composed of lignin and epoxy can self-heal and elongate up to 2000%. Researchers developed a new energy storage device that can withstand a hammer striking it more than 40 times. Courtesy of D’Arcy Laboratory/Washington University. The team came up with a unique meth- od to extract a specific form of lignin, a byproduct of biofuels production. “We targeted a component of lignin that is naturally rich in hydroxyl groups,” says researcher Amit Naskar. “The molecular structure creates a super-sticky, highly elastic material that can heal quickly, where broken, through hydrogen bond- ing.” The extracted lignin holds prom- ise to replace dopamine for a range of industrial applications including coat- ings, glues, and hydrogels. ornl.gov.