Smart Sunglasses

Have you ever wanted to make your sunglasses darker or lighter with the touch of a button?

Chemical engineer Chunye Xu and colleagues at the University of Washington, Seattle, have been working on "smart" sunglasses that can lighten or darken on command. Grad student Chao Ma presented their prototype sunglasses, which are made with a polymer that changes shade with some help from a watch battery, before the Division of Polymeric Materials: Science & Engineering at the ACS national meeting this week in Chicago.

Sunlight can vary considerably during outdoor activities such as motorcycling or skiing. Traditional sunglass lenses, created with tinted glass or polycarbonate materials, have a fixed color state. Lenses made with photochromic materials adjust to changing light, but rather slowly. The electrochromic polymer in Xu's prototype enables the lenses to lighten or darken in literally one second with just several milliwatts of power. The button that engages the battery is located on the sidearm of the eyewear.

The researchers tested the lenses against light in the visible spectrum. In the colored state, the lenses block up to 99% of a wavelength of yellow light that can particularly aggravate human eyes.

Electrochromic polymers are not new, but this application stands out, commented Guoqiang Li, an optics researcher at the University of Arizona. Other similar materials require significantly more voltage, respond more slowly, and cannot maintain the color change without additional power, and this prototype can, he added. "This is a great advantage."

But Claes-Gôran Granqvist, a physics professor at Uppsala University, in Sweden, who also works with Uppsala-based electrochromic technology firm ChromoGenics, cautioned that the prototype lenses would be heavy and cumbersome. Xu describes the prototype lenses as having several layers sandwiched between two pieces of indium tin oxide-coated glass. The cathodic, working layer is a polymer that turns blue when voltage is applied and is called 3,3-dimethyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine, or PProDOT-Me_2. A layer of vanadium oxide stores ions, and the transparent electrolytic gel layer facilitates ion transport.

The researchers have also created polymers that darken to red or green, but they have not yet made prototype sunglasses from these materials. Xu said her group is also refining the circuitry of the sunglasses to make it more compact, and they are working with a company to examine the possibility of incorporating vision correction to make the smart glasses even smarter.