New York Researchers from Harvard University have developed a technique that can quickly change the opacity of a window, turning it cloudy, clear or somewhere in between with the flick of a switch. Previous technologies used in "tunable" windows relied on electrochemical reactions and were very expensive. "However, the new technology uses geometry to adjust the transparency of a window which is a much cheaper option," said David Clarke from Harvard's John A. Paulson School of Engineering and Applied Sciences. The "tunable" window is comprised of a sheet of glass or plastic, sandwiched between transparent, soft elastomers sprayed with a coating of silver nanowires, too small to scatter light on their own. With an applied voltage, the nanowires on either side of the glass are energised to move toward each other, squeezing and deforming the soft elastomer. Since the nanowires are distributed unevenly across the surface, the elastomer deforms unevenly. The resulting roughness causes light to scatter, turning the glass opaque in less than a second. "It's like a frozen pond. If the frozen pond is smooth, you can see through the ice. But if the ice is heavily scratched, you can't see through," added postdoctoral fellow Samuel Shian in a paper that appeared in the journal Optics Letters. "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," Clarke noted.
The team is now working on incorporating thinner elastomers, which would require lower voltages, more suited for standard electrical supplies.