European Coatings Show 2019

•••8••• Innovationen AZO GmbH + Co. KG www.azo.com Halle: 6 • Stand: 331 IST Pumpen und Dosiertechnik GmbH www.istpumpen.com Halle: 6 • Stand: 153 Messe- telegramm Anzeige Tagesseminar zur Plasmatechnologie Das Einsatzspektrum von Kunst- stoffen lässt sich durch die Modifi- zierung der Oberflächeneigen- schaften erweitern. Hierfür bietet die plasmagestützte Oberflächen- funktionalisierung eine umwelt- verträgliche und elegante Lösung. Zu diesem Thema bietet die RWTH Aachen am 28.11.2019 das Seminar „Plasmatechnik in der Praxis“ an. Um das Potenzial der Plasmatech- nologie in der Kunststoffverarbei- tung ausschöpfen zu können, ist die Kenntnis der Materialeigen- schaften, der Plasmaeigenschaf- ten sowie ein Verständnis der Präparations- und Verarbeitungs- prozesse hilfreich. Diese Kennt- nisse werden im Seminar vermit- telt. Darüber hinaus gelangen die Teilnehmer zu einem besseren Verständnis der Zusammenhän- ge zwischen Prozess, Plasma und Kunststoff, die die Prozessopti- mierung und Fehleranalyse er- leichtern. Mithilfe von Plasma lässt sich die Oberfläche von Kunststoff verän- dern. Foto: Roland Ulbricht / pixelio.de Plastic dome coated with a new antireflection coating (right), and uncoated dome (left) Photo: Giebink Lab / Penn State Improving light harvesting Researchers invent antireection coating that makes plastic invisible A ntireflection (AR) coatings on plastics have a multitude of practical applica- tions, including glare reduction on eye- glasses, computer monitors and the display on your smart-phone when outdoors. Now, researchers at Penn State have developed an AR coating that improves on existing coatings to the extent that it canmake trans- parent plastics, such as Plexiglas, virtually invisible. “This discovery came about as we were trying to make higher- efficiency solar panels,” said Chris Giebink, associate professor of electrical engineering, Penn State. “Our approach involved concen- trating light onto small, high-ef- ficiency solar cells using plastic lenses, and we needed to minimize their reflection loss.” They needed an antireflection coating that worked well over the entire solar spectrum and at multiple angles as the sun crossed the sky. They also needed a coating that could stand up to weath- er over long periods of time outdoors. “We would have liked to find an off-the- shelf solution, but there wasn’t one that met our performance requirements,” he said. “So, we started looking for our own solution.” AR coatings for solar cells That was a tall order. Although it is com- paratively easy to make a coating that will eliminate reflection at a particular wavelength or in a particular direction, one that could fit all their criteria did not exist. For instance, eyeglass AR coat- ings are targeted to the narrow visible portion of the spectrum. But the solar spectrum is about five times as broad as the visible spectrum, so such a coating would not perform well for a concen- trating solar cell system. Reflections occur when light travels from one medium, such as air, into a second medium, in this case plastic. If the difference in their refractive index, which specifies how fast light travels in a particular material, is large – air has a refractive index of 1.0 and plastic 1.5 – then there will be a lot of reflection. The lowest index for a natural coating mate- rial such as magnesium fluoride or Tef- lon is about 1.3. The refractive index can be graded – slowly varied – between 1.3 and 1.5 by blending different materials, but the gap between 1.3 and 1.0 remains. In a recent paper, Giebink and coauthors describe a new process to bridge the gap between Teflon and air. They used a sacrificial molecule to create nanoscale pores in evaporated Teflon, thereby cre- ating a graded index Teflon-air film that fools light into seeing a smooth transition from 1.0 to 1.5, eliminating essentially all reflections. “The interesting thing about Teflon, which is a polymer, is when you heat it up in a crucible, the large polymer chains cleave into smaller frag- ments that are small enough to volatize and send up a vapour flux. When these land on a substrate they can repolymerize and form Teflon,” Giebink said. Unmanned aerial vehicles When the sacrificial molecules are added to the flux, the Teflon will reform around the molecules. Dis- solving the sacrificial molecules out leaves a nanoporous film that can be graded by adding more pores. “We’ve been interacting with a number of companies that are looking for improved antireflec- tion coatings for plastic, and some of the applications have been surprising,” he said. “They range from eliminating glare from the plastic domes that protect security cameras to eliminating stray re- flections inside virtual/augmented-reality headsets.” One unexpected application is in high altitude UAVs, or unmanned aerial vehi- cles. These are planes with giant wing- spans that are coated with solar cells. Used primarily for reconnaissance, these planes rely on sunlight to stay in near perpetual flight and so a lot of the light they receive is at a glancing angle where reflections are highest. One of the com- panies that makes these solar cells is exploring the AR coating to see if it can improve the amount of light harvested by a UAV. Because the technology is compatible with current manufacturing techniques, Giebink believes the coating technology is widely applicable. Antireflection coatings on sunglasses Photo: Brooke Cagle on Unsplash