By Josh Perry, Editor
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In an effort to save on energy costs from air conditioning in office and residential buildings, researchers at the Massachusetts Institute of Technology (MIT) in Cambridge, Mass. have developed a transparent film that could be applied to windows and reject as much as 70 percent of incoming solar heat.

MIT researchers have developed a coating for windows that rejects up to 70 percent of incoming solar heat. (MIT)

A report from the school explained that the film remains see-through below 32°C and above that temperature turns translucent, or “frosted,” to block incoming solar thermal energy. MIT researchers claim that using this film on exterior-facing windows could save up to 10 percent on energy costs.

The secret to the film is the use of thermochromic materials, which change color in response to temperature and are frequently used in thermal imaging applications. The researchers used poly (N-isopropylacrylamide)-2-Aminoethylmethacrylate hydrochloride microparticles that are spheres filled with water. At certain temperatures, the spheres contract and squeeze out the water, turning into bundles of fibers that reflect light differently.

Previous efforts to use these materials were not successful because the microparticles contracted to a dimeter of only 100 nanometers. MIT researchers created microparticles that shrink to 500 nanometers, which is large enough to block the infrared spectrum.

“The researchers created a solution of the heat-shielding microparticles, which they applied between two sheets of 12-by-12-inch glass to create a film-coated window,” the report continued. “They shone light from a solar simulator onto the window to mimic incoming sunlight and found that the film turned frosty in response to the heat. When they measured the solar irradiance transmitted through the other side of the window, the researchers found the film was able to reject 70 percent of the heat produced by the lamp.”

A quick measurement of temperature showed a nine-degree drop from using the film.