Advances in electrochromatic dynamic window
(sustainabilityenvironment.com) – It comes from the United States and more precisely from North Carolina State University a new material for a dynamic window that can allow users to selectively block the entry of light or heat. An innovation that could open the door to the next generation of smart windows.
Chromogenic glasses – devices capable of changing their optical characteristics under certain conditions – are nothing new. For some time now we have been working on smart windows that change their transparency in a reversible way in response to external factors, such as temperature (thermochromic), light (photochromic) or an electrical signal (electrochromic).
But what these applications had failed to do so far was to independently modulate visible and near-infrared light through a single material. A feat that has succeeded the team of engineers of North Carolina State University, creators of a new dynamic window electrochromic equipped with three optical modes. In detail, the glass of the group can go from a normal state, that is, completely transparent, to one able to block the infrared rays and then the external heat, to one completely dark to keep out even the visible light.
New dynamic window, the makeup of tungsten oxide hydrate
The key to this is a well-known material on “traditional” electrochromic windows. Let’s talk about tungsten oxide or tungstic anhydride, a compound of cathodic staining that becomes darker in response to the application of a voltage. The US team found that turning it into hydrated tungsten oxide by adding water, could give the material an additional setting.
In detail, when lithium ions and electrons are injected into the hydrated tungsten oxide, we first move on to a phase of “heat blocking”, allowing the passage of visible wavelengths of light, but blocking infrared light. As ions and electrons increase, the material then goes into a dark phase, blocking both light and heat.
“The presence of water in the crystal structure makes the structure less dense, therefore more resistant to deformation when lithium and electron ions are injected into the material,” says Jenelle Fortunato, first author of the article and researcher at the university. “Our assumption is that because tungsten hydrate oxide can accommodate more lithium ions than normal tungsten oxide before deformation, two modes are achieved. There is a ‘cold’ mode – when the injection of lithium-ion and electrons affects the optical properties, but the structural change has not yet occurred – which absorbs infrared light. And then, after the structural change has occurred, there is a ‘dark’ mode that blocks both visible and infrared light”.
The research on the new dynamic window was published in the journal ACS Photonics.