Having lots of glass surfaces can brighten up a room, but it also lets in too much heat as well as neighbors’ prying eyes. A new metamaterial is not only more transparent to light, but adds privacy, cools the room inside, and automatically cleans itself.
Known as a Polymer-based Micro-photonic Multi-functional Metamaterial (PMMM), the team’s creation takes the form of a thin film that can be stuck onto a pane of regular glass. It gets its special properties from the microscopic structure of its surface, which is etched with a pattern of pyramids each just 10 microns wide.
These mini-pyramids scatter 73% of the light that hits them, which gives the material that frosted look. But despite that, it’s surprisingly more transparent to light than regular glass – 95% transmittance compared to the usual 91% of most glass. The team says that makes for a more comfortable lighting not just for people, but plants as well.
“When the material is used in roofs and walls, it allows for bright yet glare-free and privacy-protected indoor spaces for work and living,” said Gan Huang, lead author of the study. “In greenhouses, the high light transmittance could increase yields because the photosynthesis efficiency is estimated to be 9% higher than in greenhouses with glass roofs.”
PMMM’s coolest trick (pun intended) is its ability to beam heat directly into outer space, thus cooling a room. It sounds like sci-fi stuff, but it’s a well-studied phenomenon called radiative cooling that takes advantage of the fact that the Earth’s atmosphere is transparent to infrared wavelengths. By using the universe as one colossal heat sink, tests showed that the material kept a room 6 °C (10.8 °F) cooler than the ambient air.
To cap it all off, the film is self-cleaning. The surface full of tiny pyramids keeps a layer of air underneath any water droplets, so they just roll right off, taking any dust or dirt with them. Technically, this makes it superhydrophobic, with a contact angle of 152 degrees.
“The material can simultaneously optimize the use of sunlight indoors, provide passive cooling, and reduce reliance on air conditioning,” said Huang. “The solution is scalable and can be seamlessly integrated into plans for environmentally friendly building construction and urban development.”
The research was published in the journal Nature Communications.
