If you have a mobile phone, laptop or large screen TV, you’ll understand how annoying it is when sunlight glare renders your screen unviewable. It can even cost you a ticket if that glare hits your dashboard and you can’t see how fast you're going. And for people who wear spectacles, glare off the lenses can be debilitating. But now scientists at the Fraunhofer Institute for Mechanics of Materials IWM in Freiburg, Germany, have developed a new nanocoating for use on displays and eyeglasses that is not only perfectly non-reflecting, but is also scratch-proof and easy to clean. And where did the inspiration come from… would you believe moths?
The insect world revolves around survival of the fittest. As moths search for food at dusk they have to hide from predators. In order to stay camouflaged, the moth’s facet eyes are perfectly non-reflective, while other insects’ eyes may shimmer and give them away.
The Fraunhofer scientists say tiny protuberances, smaller than the wavelength of light, form a periodic structure on the surface of the moth’s eyes. This nanostructure creates a gentle transition between the refractive indices of the air and the cornea. The result is much reduced reflection and a moth that lives to fight another day.
The process
Whereas conventional methods apply an anti-reflective coating in a separate step after production, the Fraunhofer scientists have modified conventional injection molding to impart the desired nanostructure onto the surface during the process, obviating the need for a separate process step. The researchers have developed a hard material coating that reproduces the optically-effective surface structure.
“We use this to coat the molding tools. When the viscous polymer melt is injected into the mold, the nanostructures are transferred directly to the component,” says Dr Frank Burmeister, project manager at the IWM. “Because no second process step is required, manufacturers achieve an enormous cost saving and also increase efficiency.
“Normally, the component would have to undergo an additional separate process to apply the anti-reflex coating,” says Burmeister.
Normal plexiglass and some anti-reflex coatings are particularly sensitive and scratch easily, but the scientists are producing wipe-resistant and scratch-proof surfaces. For this purpose the injection mold is additionally flooded with an ultra-thin organic polyurethane substance.
The substance fills every crevice and hardens, like a two-component adhesive, resulting in an extremely thin nanocoating of polyurethane on which the optically effective surface structures, which are just one ten-thousandth of a millimeter thick, are also reproduced.
The auto industry will be the next beneficiaries of this technology as the scientists aim to develop components that are not only attractive to look at but also hard-wearing and easy to clean.