Harvard’s take on smart windows: just add silver


Smart windows are one of the technologies that has become a given when it comes to the future of home design. The idea is that instead of adding curtains or blinds to windows for privacy and light control, the windows themselves could be programmed to go from clear to more opaque depending on the time of day or as the homeowner sees fit.

The benefit of smart windows is that the amount of light and heat entering the home could be precisely controlled. In warmer months, the windows could block more light and heat from entering to keep cooling needs down and vice versa during colder months. The windows could also let more or less light in during different parts of the day to regulate temperatures and lighting needs.

Many of the examples we’ve seen so far have involved an electrochemical process to cause the transition from clear to translucent or opaque. This method would be expensive to manufacture, not to mention the use of possibly toxic chemicals.

A team at Harvard’s John A. Paulson School of Engineering and Applied Sciences has come up with their own approach to smart windows that is completely different and potentially much cheaper. Instead of an electrochemical reaction, a physical reaction causes a change in opacity with just a flick of a switch and a touch of silver.

The window consists of a sheet of glass or plastic sandwiched between two transparent elastomer sheets sprayed with silver nanowires. The nanowires are too small to scatter light on their own so the window is clear, but apply an electric voltage and that’s when the magic happens.

According to the university, “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 uneven roughness causes light to scatter, turning the glass opaque.”

The opacity of the window can be controlled by the amount of voltage applied. A lower voltage creates a small amount of roughness to the elastomer meaning the window would just be a little cloudy, but a much higher voltage would increase the roughness enough to create an opaque window.

The research team is now focusing on making the elastomer coating even thinner so that lower voltages could create the same changes, making the technology better suited for standard homes and businesses.

The new technology would allow precise control over the transparency of windows and how much light is let in.

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