Bio-Inspired Self-Cleaning Window Is Developed

University College London (UCL) researchers have developed a bio-inspired "smart window" that could cut window-cleaning costs in tall buildings while reducing heating bills. The window uses nanostructures that amplify the thermochromic properties of a coating applied to the glass to cut glare, save energy and enable self-cleaning.

“This is the first time that a nanostructure has been combined with a thermochromic coating," says Ioannis Papakonstantinou, senior lecturer in electronic and electrical engineering and project leader.

The technology relies on a pencil-like, conical design of nanostructures engraved onto the glass that traps air and ensures that only a small amount of water comes into contact with the surface. This makes the window resistant to water, so rain hitting the outside forms spherical droplets that roll over the surface, and picks up dirt, dust and other contaminants.

According to Papakonstantinou, the cost of cleaning a skyscraper’s windows in its first five years is equal to the original cost of installing them. "Our glass could drastically cut this expenditure," he says.

The glass is coated with a 5- to 10-nanometer film of vanadium dioxide that, during cold periods, stops thermal radiation escaping and so prevents heat loss. During hot periods, it prevents the sun's infrared radiation from entering a building. Vanadium dioxide is a relatively inexpensive cheap and abundant material, combining with the thinness of the coating to offer cost and sustainability advantages over silver/gold-based and other coatings used by current energy-saving windows.

The nanostructures’ design also gives the windows the same anti-reflective properties found in the eyes of moths and other creatures that have evolved to hide from predators. It cuts the amount of light reflected internally in a room (glare) to less than 5 percent—compared with the 20-30 percent achieved by other prototype vanadium dioxide-coated energy-saving windows.