WHY THIS MATTERS IN BRIEF

Being able to apply new properties to glass, such as liquid mirrors, could help companies reduce their air conditioning bill and help homeowners improve their privacy.

Researchers from Imperial College London in the UK have developed a new material that can turn a transparent surface into a reflective one when an electric current is applied. We’ve all seen, at least in movies, one way mirrors used in police stations and spooky houses, but this latest development takes that idea to new levels of complexity and sophistication.

In their experiment the team used gold nanoparticles, which are thousands of times smaller than the width of a single human hair, and placed them between two liquids which do not mix. When voltage is applied, the nanoparticles, which are similar to the ones used to fight cancer and help restore people’s vision, self-assemble into a new configuration closely together, making the surface reflective. Without the voltage, they are spaced apart, and the surface reverts to being transparent.

Now you see it… now you don’t

“This voltage drives nanoparticles to an interface, where they congregate and form a mirror. When we switch the system to a different voltage, the particles move away from the interface and the mirror disappears,” explains Anthony Kucernak, a professor in Imperial’s Department of Chemistry.

As a result of the new development we could soon see a new range of advanced window and mirror systems that could have applications in everything from helping homeowners increase their levels of privacy all the way through to helping building operators reduce the cost of heating or cooling a building by giving them a new way to control the amount of light and heat coming into, for example, an office tower.

The Imperial College team are now considering commercialising the technology but before they do they want to increase the speed of the particles’ response, and once they manage to do that they see a wide range of alternative use cases emerging too, including using the process to create tunable optical filters for telescopes that help us better understand the universe, as well as even finding new ways to help is increase the sensitivity of chemical sensors.