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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 7 SURFACE ENGINEERING NEW ANTIREFLECTION COATING FOR PLASTIC Researchers at Penn State, State College, have developed an antire- flection (AR) coating that improves on existing coatings to make transparent plastics such as Plexiglas virtually in- visible. AR coatings on plastics have many practical applications, including glare reduction on eyeglasses, comput- er monitors, and smartphone displays when outdoors. The researchers discovered their new coating while trying to develop higher-efficiency solar panels. They needed an AR coating that worked well over the entire solar spectrum and at multiple angles as the sun crossed the sky, and one that could withstand var- ied weather over long periods of time outdoors. Because the technology is compatible with current manufacturing techniques, the team believes the coat- ing technology is scalable and widely applicable. In addition, the coating is antifogging. The AR coating could greatly improve plastic Fresnel lenses, a critical part of concentrating photovol- taic products. psu.edu . SELF-HEALING MATERIAL INSPIRED BY FLUID Localized corrosion found in tiny cracks has the potential to dismantle huge metal structures. This hard-to- detect corrosion in little scratches, dents, and cracks can cause pipelines to rupture and fuselages to detach from airplanes among other extremely dangerous events. Now, a team from Northwestern University, Evanston, Ill., has developed a new coating strategy for metal that self-heals within seconds when scratched, scraped, or cracked. The novel material could prevent these small defects from turning into local- ized corrosion and causing catastro- phic failure. When damaged by scratches and cracks, the team’s patent-pending sys- tem readily flows and reconnects to rapidly heal. The material can heal re- peatedly—even after scratching the ex- act same spot nearly 200 times in a row. While a few self-healing coatings already exist, those systems typically work for nanometer to micron-sized damages. To develop a coating that could heal larger scratches in the millimeter-scale, the researchers looked to fluid. “When a boat cuts through water, the water goes right back together,” ex- plains lead researcher Jiaxing Huang. “The ‘cut’ quickly heals because water flows readily. We were inspired to real- ize that fluids, such as oils, are the ulti- mate self-healing system.” But common oils flow too readily, Huang says. So he and his team needed to develop a system with contradict- ing properties—fluidic enough to flow automatically, but not so fluidic that it drips off the metal’s surface. The team met the challenge by creating a net- work of lightweight particles—in this case, graphene capsules—to thicken the oil. The network fixes the oil coating to prevent dripping. But when the net- work is damaged by a crack or scratch, it releases the oil to flow readily and re- connect. Huang says the material can be made with any hollow lightweight particle, not just graphene. The coating not only sticks, but sticks well—even underwater and in harsh chemical environments, such as acid baths. Huang imagines that it could be painted onto bridges and boats that are naturally submerged underwater as well as metal structures near leaked or spilled highly corrosive fluids. When brushed onto a surface from underwa- ter, the coating goes on evenly without trapping tiny bubbles of air or moisture that often lead to pin holes and corro- sion. northwestern.edu. BRIEF AZZ Inc., Fort Worth, Texas, will acquire Tennessee Galvanizing Inc., Jasper, Tenn., a metal coatings company with four galvanizing lines, including centrifuge, rod, conveyer, and a 42-ft structural kettle. azz.com. Plastic dome coated with a new AR coating (right), and uncoated dome (left). Courtesy of Giebink Lab/Penn State. A new coating for metals quickly heals scratches to prevent corrosion.