Ivan P. Parkin, a chemistry professor at University College London, and his colleague Troy D. Manning, currently working at the University of Liverpool, in England, have developed an intelligent window coating that allows visible light to pass through the glass but will reflect infrared radiation at temperatures above 29 °C [J. Mater. Chem., 14, 2554 (2004)].
The coating is made mostly of vanadium dioxide, a material that scientists knew could switch between absorbing and reflecting IR light, depending upon the electrons arrangement. Until now, however, this switch occurred around 70 °Ctoo high to be practical. By adding 1.9% tungsten to the vanadium dioxide coating, Parkin and Manning were able to make the thermochromic switch occur at just above room temperature. With more tungsten, they can reduce the switching temperature to as low as 10 °C.
To make the smart windows, the researchers deposit the film onto glass at atmospheric pressure during the standard float-glass manufacturing process. Because the film grows quickly and doesnt require high-cost vacuum systems, Parkin and Manning say the process is ideally suited to high-throughput manufacturing.
Before the material makes it to market though, the researchers will need to determine how durable the coating is, because they want to ensure that it will last as long as the windows do. Also, Parkin says that the coating turns the glass an unattractive greenish-yellow color, so the team is looking into ways to tone down the color.