Harvard’s tunable window can make the transition in less than a second. The window is made of a sheet of glass or plastic surrounded on either side by soft elastomers. Each elastomer layer is coated with nanowires, so that when left untouched they don’t interrupt light. All it takes is an electric charge for the nanowires to move towards each other in response to the applied energy. As the nanowires move across the surface of the elastomer, they are no longer spread evenly, so they disrupt and scatter light enough to make the glass opaque.
Samuel Shian, a postdoctoral fellow on the Harvard research team, describes the process like a lake or a pond that freezes over in the winter: “If the frozen pond is smooth, you can see through the ice. But if the ice is heavily scratched, you can’t see through.” When the nanowires move together in response to an electric charge, they make the surface of the elastomer rough and unpredictable, clouding visibility.
Because Harvard’s tunable window technique relies on a physical process with accessible materials, it is expected to be much more affordable than the electrochemical reaction required for past solutions. Those chemical solutions also take time, so they are impractical compared with the one-second switch of Harvard’s window. The researchers are now working to develop thinner elastomers for the window material itself, lowering the voltage required to activate nanowires so that the window can be even more affordable and accessible. Harvard has also filed a patent application on the technology, so we may see collaborations with glass manufacturers and window products in the relatively near future.
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