International. Researchers at Columbia Engineering have developed porous polymer (PPC) coatings that enable inexpensive and scalable ways to control light and heat in buildings.
They took advantage of the optical switching capability of PPCs at solar wavelengths to regulate solar heating and daylight, and extended the concept to thermal infrared wavelengths to modulate the heat radiated by objects.
The team began their work to optically change ppCs by chance, when Mandal noticed that a few drops of alcohol spilled over a white PPC fluoropolymer that made it transparent. "What we saw was the same mechanism that causes paper to become translucent when wet, but at an almost optimal level," Mandal says. "The physics of this have been explored previously, but the drastic change we saw led us to explore this particular case and how it can be used."
"Our work shows that by moistening PPCs with common liquids such as alcohols or water, we can reversibly change their optical transmittance at solar and thermal wavelengths," says Jyotirmoy Mandal, senior author of the study and a former doctoral student in the lab of Yuan Yang, an assistant professor of materials science and engineering. "By putting such PPCs on hollow plastic or glass panels, we can make building wraps that can regulate temperature and interior light."
Porous polymer coatings, which change from white to transparent when moistened, can be placed in plastic enclosures to make panels that control the light and temperature of buildings.
The design is similar to smart windows, but with greater optical switching capacity, and is built with simpler, cheaper materials that could make it deployable on a large scale. It builds on previous work that demonstrated a paint-like fluoropolymer coating with microscale nano air gaps that can cool buildings. However, that coating was static. "In places like New York, which sees warm summers and harsh winters, designs that can switch between heating and cooling modes can be more useful," Yang says.
The researchers also looked at how optical switching could be used for thermoregulation. "We imagine roofs that are white during the summer to keep buildings cool, and turn black during the winter to heat them," Yang says, "This can greatly reduce the air conditioning and heating costs of buildings."
Source: Columbia Engineering.
