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New smart window cuts energy and wipes out cleaning

Moth eyes could hold the key to energy saving, self-cleaning, anti-glare smart windows.

A biomimetic smart window based on the eyes of moths could cut HVAC energy use by 40 per cent, slash cleaning costs and reduce glare in tall buildings, according to researchers from University College London.

The glass proposed for the windows features pyramid-like nanostructure engravings reminiscent of a moth’s eye. At 200 nanometres, these nanostructure are 100 times smaller than a human hair. Controlling the surface morphology at the nanoscale allows scientists to tailor how the glass interacts with liquids and light with high precision.

The UCL researchers said the prototype samples of the glass confirmed self-cleaning, energy saving and anti-glare properties.

Self-cleaning

Because of the pencil-like, conical design of nanostructures engraved onto the glass, rain forms into spherical droplets that roll over the surface taking dirt, dust and other contaminants away. With typical glass, more water would come in contact with the glass, clinging to the surface and sliding down more slowly, leaving marks behind.

“It’s currently estimated that, because of the obvious difficulties involved, the cost of cleaning a skyscraper’s windows in its first five years is the same as the original cost of installing them. Our glass could drastically cut this expenditure,” project leader Dr Ioannis Papakonstantinou of UCL said.

“As the trend in architecture continues towards the inclusion of more glass, it’s vital that windows are as low-maintenance as possible.”

Energy-saving

The glass is coated with a thin (5-10 nanometre) coating of vanadium dioxide, which when cold stops thermal radiation from escaping, preventing heat loss. And during hot periods it prevents infrared radiation from the sun entering the building.

Because vanadium dioxide is a cheap and abundant material, which can be applied more thinly than current silver, gold or other materials used in current smart windows, it offers cost and sustainability advantages.

The researchers anticipate the windows could cut heating bills by up to 40 per cent, depending on the latitude of the building. They also say they would be well-suited to high-rise towers.

Anti-glare

The design of the nanostructures gives the windows the same anti-reflective properties found in the eyes of moths and other creatures that have evolved to hide from predators.

With the smart window, the amount of light reflected internally is cut to less than five per cent, compare with the typical 20-30 per cent achieved by other vanadium dioxide-coated smart windows.

The researchers said this glare reduction could translate into improved occupant comfort and productivity.

A scanning electron miscroscope photograph shows the pyramid-like nanostructures engraved onto glass. Image:  Engineering and Physical Sciences Research Council

A scanning electron miscroscope photograph shows the pyramid-like nanostructures engraved onto glass. Image: Engineering and Physical Sciences Research Council

“This is the first time that a nanostructure has been combined with a thermochromic coating,” Dr Papakonstantinou said. “The bio-inspired nanostructure amplifies the thermochromics properties of the coating and the net result is a self-cleaning, highly performing smart window.”

He said discussions were underway with UK glass manufacturers to drive the process towards commercialisation, and that the glass could reach the market within 3-5 years.

“We also hope to develop a ‘smart’ film that incorporates our nanostructures and can easily be added to conventional domestic, office, factory and other windows on a DIY basis to deliver the triple benefit of lower energy use, less light reflection and self-cleaning, without significantly affecting aesthetics.”

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