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Dynamic windows switch seamlessly between opaque and transparent

Dynamic windows capable of switching from transparent to opaque and back again without degrading have been developed by Stanford University engineers.

The current prototypes undergo the transformation in less than a minute and are made from plates of conductive glass outlined with metal ions that spread out over the surface, blocking light, in response to electrical current.

The developers say that the windows have the potential to transform homes, businesses, cars and more and will reduce heating and cooling costs or the need for blinds.

Some smart windows are already being sold, such as those used on airlines, which are made of materials such as tungsten oxide that change colour when charged with electricity. However, these materials tend to be expensive, have a blue tint, can take over 20 minutes to dim and become less opaque over time.

“We did not tweak what was out there; we came up with a completely different solution,” said Stanford University’s Michael McGehee.

“We’ve had a lot of moments where we’ve thought, ‘how is it even possible that we’ve made something that works so well, so quickly,’ and we’re now running the technology by glass and other kinds of companies.”

McGehee and his group’s prototype blocks light through the movement of copper and another metal in a solution over a sheet of transparent indium tin oxide modified by platinum nanoparticles.

When transparent, the windows are clear and allow about 80 per cent of surrounding natural light through, and when dark, transmission drops to under five per cent.

The researchers switched the windows on and off at least 5,500 times and saw no change in the transmission of light, indicating that the design is durable.

There is still work to do before scaling up, however. McGehee says that there is currently a limit in how much area the prototypes can cover (the study looked at 25cm2 windows), but there are plans to address this problem.

The group also wants to iterate the metal electrodes with the goal to cut the cost of the prototype to at least half the cost of dynamic windows that are already on the market.

“We’re excited because dynamic window technology has the potential to optimise the lighting in rooms or vehicles, save about 20 per cent in heating and cooling costs and even change the way people wear sunglasses” McGehee said. “This is an important area that is barely being investigated at universities and there’s a lot of opportunity to keep us motivated.”

Last year, British researchers demonstrated self-cleaning smart glass that can also limit glare by utilising principles found in the eyes of moths. 

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