Nature-inspired surface for self-cleaning glass

A new multifunctional glass that allows water droplets to bounce of its surface like tiny rubber balls has been developed by scientists in America.

The surface, inspired by Nature’s textured surfaces, is also anti-fogging, self-cleaning and free of glare and could find uses in smartphone screens, cameras and photovoltaic cells.

Researchers from Massachusetts Institute of Technology (MIT) developed a new fabrication method using coating and etching techniques adapted from the semiconductor industry. The resulting surface pattern is an array of nanoscale cones that are five times as tall as their base width of 200nm.

The glass is coated with several thin layers – including a photoresist layer – which is then illuminated with a grid pattern and etched away. The resulting conical shapes give the material its unique characteristics.

“Precise geometric control of the conical shape and slenderness of the features as well as periodicity at the nanoscale are all keys to optimising the multifunctionality of the textured surface,” the researchers said in their paper published in ACS Nano.

The researchers say their fabricated nanostructures demonstrate structural superhydrophilicity and, in combination with a chemical coating, robust superhydrophobicity. The nanocones appear fragile when viewed microscopically, but the researchers say their calculations show they will be resistant to a wide range of forces including torrential rain, wind-driven pollen and poking with a finger.

Although more testing is needed to see how well the glass will hold up over time in practical applications, researchers believe it could be useful in photovoltaic cells. The new multifunctional surface has been shown to repel water more effectively than other panels treated with hydrophobic coatings, meaning the panels will be kept cleaner for longer.

The new coating is also able to prevent reflective losses – another problem suffered by photovoltaic panels – as the axial gradient in the effective refractive index minimises reflection through adiabatic index-matching between air and the substrate.

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