Anti-reflection taken to nano levels

Moth’s eyes are perfectly non-reflective, enabling them to remain hidden from predators as they hunt for food and this idea is the basis for a new nanocoating which can be used on displays and glasses.

A periodic structure is formed on the surface of moth’s eye by tiny protuberances smaller than the wavelength of light. This structure creates a transition between the refractive indices of air and the cornea and reduces reflection of light, ensuring the animal is undetected. Scientists from the Fraunhofer Institute for Mechanics of Materials have used this principle and adapted it to a range of different application, including glasses, mobile phone displays and panel covers.

They have created a hybrid coating which reproduces the optically effective surface, is scratch-proof and easy to clean, and can be applied during the manufacture of parts, rather than in a separate step afterwards.

 “We have modified conventional injection moulding in such a way that the desired nanostructure is imparted to the surface during the process,” said Dr Frank Burmeister, project manager.

The hard material coating is used to coat the moulding tools, and when the polymer melt is injected into the mould, the nanostructures are transferred directly to the component, Burmeister said. Because no additional coating step is required, there is an enormous cost saving and increase in efficiency.

The scientists are able to produce wipe-resistant and scratch-proof surfaces by flooding the injection mould with an ultra-thin organic substance made of polyurethane. “The substance runs into every crevice and hardens, like a two component adhesive,” Burmeister said. This results in a thin nanocoating of polyurethane on which the optically effective surface structures are also reproduced.

The scientists are working with industrial partners to develop attractive, hard-wearing and easy to clean components for the auto industry.