The desert-dwelling Namaqua chameleon has a pretty neat trick – it changes skin color to stay cool when outdoor temperatures rise, and stay warm when they drop. An experimental new coating could one day do the same thing for our homes.
Native to southwestern Africa, the chameleon takes on a light gray color in response to hot ambient temperatures. Doing so helps keep it from overheating, by reflecting the hot infrared wavelength of incoming sunlight. When temperatures drop, however, the reptile's skin takes on a dark brown heat-absorbing color.
Led by the Harbin Institute of Technology's Prof. Fuqiang Wang, an international team of scientists set out to replicate that functionality in a color-changing liquid coating that could be applied to the roofs and exterior walls of houses and other buildings.
The resulting "temperature-adaptive radiative cooling coating" (TARCC) contains microcapsules filled with polyvinylidene fluoride, which is a chemical that changes color in response to changes in temperature. In order to test the coating, the researchers applied it to aluminum-foil-covered polystyrene boxes, then allowed it to dry into a film.
When that film was heated to 68 ºF (20 ºC), it began to switch from a dark gray to light gray color. Upon reaching 86 ºF (30 ºC), it became so light that it reflected up to 93% of solar radiation.
In a subsequent experiment, the TARCC was applied to miniature house-like outdoor structures which were monitored throughout all four seasons. As a control, other identical structures were covered in regular white paint, a passive radiative cooling paint, and blue steel tiles.
Not only did the TARCC stay much cooler than the white paint and steel tiles in hot summer temperatures, it was also the only material that could switch between heating and cooling states as outdoor temperatures fluctuated throughout the day in spring and autumn.
A paper on the research was recently published in the journal Nano Letters.
And as an interesting side note, scientists at MIT previously developed chameleon-inspired Thermeleon roof tiles that switch between black and white coloration in response to temperature changes.
Source: American Chemical Society