Courtesy Imperial College London

By modifying the distance between a single layer of gold nanaoparticles, a team of researchers from Imperial College London have developed a filter that can transition between a mirrored and transparent surface.

In order to achieve this, the team positioned the nanoparticles at the intersection of two liquids with different densities, so that they would not mix. They then ran an electrical current to modify the spacing of the nanoparticles to alter the material's optical properties. "At one extreme, all the wavelengths are reflected, and the layer acts as a mirror," writes Hayley Dunning in a news article for Imperial College London. "At the other extreme, where the nanoparticles are dispersed, all wavelengths are permitted through the interface and it acts as a window."

“Putting theory into practice can be difficult," said professor Anthony Kucernak, co-author of the published study. "As one always has to be aware of material stability limits, so finding the correct electrochemical conditions under which the effect could occur was challenging.”

Early this week, "Electrotuneable Nanoplasmonic Liquid Mirror" was published in the Nature Materials journal.