Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences have developed a technique for quickly changing the opacity of a window, turning it cloudy, clear or somewhere in between at the flick of a switch.
Tunable windows aren't new but most previous technologies have relied on electrochemical reactions achieved through expensive manufacturing. This novel technology, developed by David Clarke, professor of materials, and postdoctoral fellow Samuel Shian, uses geometry to adjust the transparency of a window. The research is described in a paper in Optics Letters.
Their novel tunable window is comprised of a sheet of glass or plastic sandwiched between soft, transparent elastomers sprayed with a coating of silver nanowires that are too small to scatter light on their own. But apply an electric voltage and things quickly change.
With an applied voltage, the nanowires on either side of the glass are energized to move toward each other, squeezing and deforming the soft elastomer. Because the nanowires are distributed unevenly across the surface, the elastomer deforms unevenly. The resulting roughness scatters incoming light, turning the glass opaque. This change happens in less than a second.
"Because this is a physical phenomenon rather than based on a chemical reaction, it is a simpler and potentially cheaper way to achieve commercial tunable windows."David Clarke, Harvard University
It's like a frozen pond, explained Shian: "If the frozen pond is smooth, you can see through the ice. But if the ice is heavily scratched, you can't see through." Clarke and Shian found that the roughness of the elastomer surface depended on the voltage, so if you wanted a window that is only lightly clouded, you would apply less voltage than if you wanted a totally opaque window.
"Because this is a physical phenomenon rather than based on a chemical reaction, it is a simpler and potentially cheaper way to achieve commercial tunable windows," said Clarke.
Current chemical-based controllable windows require vacuum deposition to coat the glass, an expensive and painstaking process that deposits layers of a material molecule by molecule. In Clarke and Shian's method, by contrast, the nanowire layer can simply be sprayed or peeled onto the elastomer, making the technology scalable for larger architectural projects.
The team is now working on making tunable windows with thinner elastomers, which would require lower voltages more suited for standard electrical supplies. Harvard's Office of Technology Development has filed a patent application on the technology and is already engaging with potential licensees in the glass manufacturing industry.
This story is adapted from material from the Harvard John A. Paulson School of Engineering and Applied Sciences, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.