Scientists from Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have discovered a new technology that can change the opacity of windows with the flick of a switch.
Previous techniques of tunable windows relied upon electrochemical reactions that are quite expensive. The new technique uses geometry to adjust the transparency of the window which can eventually turn to cloudy, clear, somewhere in between or completely opaque.
The tunable window consists of a sheet made from glass or plastic, sandwiched between soft and transparent elastomers sprayed with a coat of silver nanowires. These nanowires are so small that they cannot scatter light on their own.
The nanowires of the glass can be energized with an applied voltage. The wires move towards one another squeezing and deforming the soft elastomer. The elastomer deforms unevenly as the nanowires too are distributed unevenly across the surface. The resultant toughness causes scattering of light, making the glass opaque. The change happens in an instant.
Postdoctoral fellow, Samuel Shian and David Clarke, Extended Tarr Family Professor of Materials at Harvard, discovered that the roughness of the elastomer surface depended mainly on the voltage. So if a person wants a window slightly clouded they need to apply less voltage than what is necessary for a completely opaque window.
Standard chemical-based controllable windows use vacuum deposition for coating the glass, a process that can deposit layers of a material molecule by molecule. In the new method, the nanowire layer can be sprayed or peeled onto the elastomer, making the technology scalable for large architectural projects.
“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.
The researchers will work on incorporating thinner elastomers that require lower voltages that are suitable for normal electronic supplies.
Image courtesy of David Clarke/Harvard SEAS