Engineers from Columbia University made white paint even whiter by removing white pigment and add a polymer coating that acts as a spontaneous air cooler.

With temperatures rising across the world, cooling solutions, preferably ones that don’t consume energy like air conditioners, are more important than ever, especially in urban environments. Los Angeles painted their black asphalt roads white to keep the city cool earlier this year, since the colour white reflects light, rather than absorb it like black does, hence cooling down. This phenomenon is known as passive daytime radiative cooling (PDRC).

By turning paint whiter than white, the engineers found a way to make it even cooler. They removed the white pigment and replaced it with a polymer coating with nano-to-microscale air voids. Because of this, the paint acts as a spontaneous air cooler. It can be fabricated, dyed and applied like paint on rooftops, buildings, water tanks, vehicles and even space crafts.

The researchers used a solution-based phase inversion technique, which gives the polymer a porous, foam-like structure. The air voids scatter and reflect sunlight, thus avoiding solar heating. The material reflects sunlight with up to 96 per cent and thermal emittance by 97 per cent. It stays significantly cooler than its environment, both in desert and tropical climates, without any thermal protection or shielding.

Aside from white paint, the engineers also created coloured polymer coatings by adding dyes.

Photos: Columbia University