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A scanning electron microscope image of the nanostructures engraved onto glass. Controlling the surface morphology at the nanoscale allows high precision tailoring of the glass's interaction with liquids and light. 

Nanotechnology may provide self-cleaning, energy-saving 'smart glass' for vehicles

Improving driver visibility is a major aspect of vehicle safety that is increasingly supported by stereo cameras, LiDAR, and infrared systems. But fundamental to visibility is being able to see clearly through clean glass windows, and front and rear windshields.

Now, researchers at a U.K. university have revealed a "smart" window solution for buildings that may also be applicable to vehicles. It uses nanotechnology to achieve not only self-cleaning but also delivers energy saving and anti-glare properties.

“This is the first time that a nanostructure has been combined with a thermochromic coating,” said Dr. Ioannis Papakonstantinou of the Department of Electronic and Electrical Engineering, University College London (UCL). “The bio-inspired nanostructure amplifies the thermochromic properties of the coating, and the net result is a self-cleaning, highly performing smart window.”

As project leader of a highly specialist team, Papakonstantinou said initial applications of nanostructures could be to skyscraper windows but at present he believes that in theory there was no reason why the system could not be extrapolated to road vehicles provided it met required safety standards and other legislation.

“It should, because it simply involves application of a coating of about one micron. But of course there would need to be a test program to establish—for example, how quickly water droplets would flow down automotive glass, particularly the windshield.”

The research work at UCL is being supported by the U.K.’s Engineering and Physical Sciences Research Council, and prototype examples of the technology are said to confirm that the three key benefits can be delivered.

The self-cleaning application sees rain hitting a glass surface to form spherical droplets that roll easily across that surface carrying away dust, dirt, and any other contaminants. Explained Papakonstantinou: “This is due to the pencil-like, conical design of nanostructures engraved onto the glass, trapping air and ensuring that only a tiny amount of water comes into contact with the surface.”

Regular glass typically sees raindrops clinging to the surface before sliding down, leaving marks.

To achieve energy saving, a glass surface is coated with a 5- to 10-nm (0.2- to 0.4-µin) film of vanadium dioxide (a cheap and abundant material), which prevents heat loss or, in hot climates, prevents solar IR entering the vehicle.

“The design of the nanostructures also gives the windows the same anti-reflective properties found in the eyes of moths and other creatures to hide them from predators!” noted Papakonstantinou. “It cuts the amount of light reflected internally in a room to less than 5% compared to 20-30% achieved by other prototype vanadium-dioxide-coated energy saving windows.”

He stressed that the UCL findings are the result of a research project and that the next big step would be to scale-up the nano manufacturing techniques and the vanadium-dioxide coating process used to create the prototypes. For this purpose, Papakonstantinou has secured a €1.8M grant from the European Research Council.

The UCL team also includes Prof. Ivan Parkin of the university’s Department of Chemistry, and researcher Alaric Taylor of the Department of Electronic and Electrical Engineering.

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