United States. Researchers at the American Chemical Society (ACS) develop a cost-effective, energy-efficient coating by mimicking a desert-dwelling chameleon. The material could keep buildings cool in summer or warm in winter, without additional energy.
Traditional heating and cooling systems are energy-intensive and, as they typically run on fossil fuels, are not sustainable. Taking inspiration from the Namaqua chameleon, Fuqiang Wang and his colleagues wanted to create a coating that changes color and adapts to outside temperature fluctuations.
The group of researchers considered that many desert creatures have specialized adaptations that allow them to survive in harsh environments with large daily temperature changes.
One of them is the Namaqua chameleon from southwest Africa, which alters its color to regulate its body temperature as conditions change. The creatures appear light gray in warm temperatures to reflect sunlight and stay cool, then turn dark brown once cooled to absorb heat.
This unique capability is a natural example of passive temperature control, a phenomenon that could be adapted to create more energy-efficient buildings. But many systems, such as cooling paints or colored steel shingles, are only designed to keep buildings cool or warm and cannot switch between "modes."
To make the coating, the researchers mixed thermochromic microcapsules, specialized microparticles and binders to form a suspension, which they sprayed or brushed onto a metal surface.
When heated to 68 degrees Fahrenheit, the surface began to change from dark gray to light gray. Once it reached 86 degrees, the light-colored film reflected up to 93% of solar radiation.
Even when heated to more than 175 degrees for an entire day, the material showed no signs of damage. Next, the team tested it alongside three conventional coatings — normal white paint, a passive radiative cooling paint, and blue steel tiles — in outdoor tests on miniature doghouse-sized buildings during the four seasons.
In winter, the new coating was slightly warmer than the passive radiative cooling system, although both maintained similar temperatures in warmer conditions.
In summer, the new coating was much cooler than white paint and steel tiles.
During the spring and autumn, the new coating was the only system that was able to adapt to the fluctuating temperature changes, moving from heating to cooling throughout the day.
The researchers said this color-changing system could save a considerable amount of energy in regions experiencing multiple seasons, while still being inexpensive and easy to manufacture.