Nanostructured Glass Is Based on Butterfly Wing

Glass for displays, tablets, laptops, smartphones, and solar cells needs to allow light to pass through, but could benefit from a surface that repels water, oil, and other liquids. Researchers from the University of Pittsburgh (Pitt) created a new type of glass that is clear across a range of wavelengths and angles as well as superomniphobic and antifogging. The design for the glass was inspired by the wings of the glasswing butterfly (Greta oto). Machine learning techniques were used to help streamline the development process.

A glasswing butterfly. Courtesy of minka2507 from Pixabay.

Inspired by the random nanostructures on the wings of the glasswing butterfly, which are smaller than the wavelengths of visible light, the Pitt team developed an approach to create self-healing, random reentrant, nanostructured glass with supertransmission properties (99.5% at 550 nm wavelength for double-sided glass) and superclarity (haze under 0.1%).

The Pitt researchers partnered with with SigOpt to use machine learning to develop the new glass more efficiently. “When you create something like this, you don’t start with a lot of data, and each trial takes a great deal of time,” professor Paul Leu said. “We used machine learning to suggest variables to change, and it took us fewer tries to create this material as a result.”

The researchers used a multiobjective learning and Bayesian optimization approach to guide their experiments of glass substrate fabrication. Michael McCourt, a research engineer at SigOpt, said that Bayesian optimization and active search were ideal tools to explore the balance between transparency and omniphobicity efficiently.

The glass exhibited resistance to condensation with an antifogging efficiency of more than 90% and demonstrated the departure of water droplets smaller than 2 μm. The surface demonstrated the ability to restore liquid repellency after physical damage through heating for 15 minutes.

“The glass is superomniphobic, meaning it repels a wide variety of liquids such as orange juice, coffee, water, blood, and milk,” researcher Sajad Haghanifar said. “The glass is also antifogging, as water condensation tends to easily roll off the surface, and the view through the glass remains unobstructed. Finally, the nanostructured glass is durable from abrasion due to its self-healing properties — abrading the surface with a rough sponge damages the coating, but heating it restores it to its original function.”

The glass is superomniphobic, meaning it repels a wide variety of liquids. Courtesy of professor Paul Leu/University of Pittsburgh.

The high transparency of this glass could reduce the brightness and power demands on displays, possibly extending their battery life. The glass is antireflective across higher angles, improving viewing angles. Its haze rate could improve the clarity of images and text.

Natural surfaces like moth eyes and butterfly wings display omniphobic properties that make them self-cleaning, bacteria resistant, and water repellent — adaptations for survival that researchers continue to seek to replicate and improve upon in synthetic materials. The Pitt team believes that its nanostructured glass could be useful in a variety of optical applications where self-cleaning, antifouling, and antifogging functionalities are important.

The research was published in Materials Horizons (https://pubs.rsc.org/en/content/articlelanding/2019/mh/c9mh00589g) and was presented at the International Conference on Machine Learning (ICML 2019), June 9-15, 2019, in Long Beach, Calif.