Tuning Windows for Privacy Using NanowiresRiia O’Donnell | March 27, 2016
Researchers at Harvard University are working on tunable privacy windows that go from clear to cloudy with a touch of a switch.
The concept isn’t new, but the team says their method is. Previous versions of the window glass relied on electrochemical reactions to get to the opaque state – vacuum deposition to coat glass with a layer of material on the molecular level. The process can be expensive and challenging.
The new technique, developed at the John A. Paulson School of Engineering and Applied Sciences at Harvard, uses geometry to adjust the level of transparency in window displays.
The window is a sandwich of glass or plastic with soft transparent elastomers that have been sprayed with a coating of silver nanowires. The wires are too small to scatter light independently. But when an electric voltage is applied, the nanowires move toward each other, clumping and squeezing. As a result, they deform the elastomer layer. Because the nanowires move randomly throughout the surface, the elastomer deforms unevenly: that rough deformation allows light to scatter through the glass layers, turning them to an opaque state. What’s more, the nanowire layer may be easier to apply, the researchers say: it can be sprayed or peeled onto the elastomer. The ability to scale the layer would make it a candidate for large-scale architectural applications.
The opacity change occurs in less than one second. Depending on the level of voltage applied, the glass can be tuned from partially to fully opaque, all within the control of the user. The team is working to incorporate even thinner elastomers, which would use less voltage to achieve privacy levels.