Possible Replacement For Conventional Cooling Methods.
from Columbia University have created a high-performance, passive daytime radioactive cooling (PDRC) polymer coating with nano-to-microscale air voids that act as a spontaneous air cooler and can be fabricated, dyed or painted on rooftops, buildings, water tanks and vehicles to cool them down. The air voids, cools down the surface by reflecting sunlight and radiating heat to the colder atmosphere.
This new design is an extension of previous research, where the group found that simple plastics and polymers like acrylic, silicone and PET are good heat radiators that could be used for PDRCs. To overcome the difficulty of the usage of silver mirrors as reflectors in normal transparent polymers, the researchers used a solution-based phase-inversion technique to give the polymer a porous foam-like structure, allowing the air voids to scatter and reflect sunlight because of the difference in the refractive index between the air voids and the surrounding polymer. The polymer then turns white to avoid solar heating while its intrinsic emittance causes it to efficiently lose heat to the sky.
The researchers found that the polymer coatings had a solar reflectance (R) above 96 percent and a thermal emittance at about 97 percent, which kept the surface significantly cooler than its environment under different conditions. The polymer was six degrees Celsius cooler in the desert of Arizona and three degrees CCelsius cooler in the tropical climate of Bangladesh.
This can also be a replacement for conventional coolining methods like air conditioning which can be expenssive, require substantial amount of energy and have a strong green house effect. The researchers are now refining the design so it can be better applied, while also exploring other possibilities like the use of completely biocompatible polymers and solvents.