Moth eyes key to develop non-reflective windscreen

May 14-German scientists have studied the nano-structure of moth eyes to develop a new anti-reflecting polymer-based windscreen coating that lets the light through, and does not reflect it back. Happy motorists get no glare from lights and illuminated signs outside, making their journeys much safer.

It s tough being a moth. Searching for food as dusk, they are prey to greedy predators birds, frogs, lizards, cats So nature has designed their eyes to have tiny bumps so that they do not reflect light, giving away their position.

Now scientists at the Fraunhofer Institute for Mechanics of Materials IWM in Freiburg, Germany, have mapped these moth eye structures and incorporated them into windscreen coatings.

These protuberances, smaller than the wavelength of light, stipple the surface of these new coatings (as they do moth eyeballs), easing the path of lightwaves from the air outside, through the windscreen, to drivers eyes. They do this by changing the frequency at which lightwaves travel. These frequencies are different when light travels through the air and when light goes through the eye s cornea. The stippled windscreen changes that light frequency to one better suited to the eyes markedly improving visual clarity for drivers.

As well as this clever advance, Fraunhofer scientists have also reduced the cost of applying these coatings: normally windshields get a toughening film, which is then improved with an additional anti-reflective coating. The researchers, instead, have devised a process to create the moth-eye nano-dimples using a mould which incorporates these nano-structures.

We have modified conventional injection molding in such a way that the desired nanostructure is imparted to the surface during the process. When the viscous polymer melt is injected into the mold, the nanostructures are transferred directly to the component, said Dr Frank Burmeister, the project manager. Normally the component would have to undergo an additional separate process to apply the anti-reflex coating.

Also, because anti-reflection coatings can often be easily scratched, the German team have added an ultra-thin polyurethane organic substance to the mold, which coats the whole film, without filling in the gaps between the dimples and stipples, which are one ten-thousandth of a millimetre thick.

Burmeister said: The substance runs into every crevice and hardens, like a two-component adhesive. His team thinks this coating could be applied to other auto industry components, which would be hard-wearing and easy to clean. Dr Burmeister said his team was working with industrial partners to achieve this additional goal.