US researchers have developed a new way of making windows that can switch from transparent to opaque to block sunlight on hot days. The new method has advantages over existing systems as it offers rapid response times and has low energy needs, says the research team from Massachusetts Institute of Technology (MIT).
Once glass is switched from clear to dark, or vice versa, the new system requires little or no power to maintain its new state; unlike other materials, it only needs electricity when it’s time to switch back again. The method relies on electrochromic materials, which change colour and transparency in response to an applied voltage. These are currently used to darken some aircraft windows but can take minutes to change colour and can then only turn to dark green, rather than black. The MIT team has come up with a means of speeding up the process, and has also produced a coating that can change from clear to black, by combining two chemical compounds, an organic material and a metal salt.
MIT professor of chemistry Mircea Dinca said, “It’s this combination of these two, of a relatively fast switching time and a nearly black colour, that has really got people excited.”
He added, “You could just flip a switch when the sun shines through the window, and turn it dark”.
The results of the research are reported in the online journal Chem, and the approach will now undergo further testing.