USA: Engineers at Purdue University have created a white paint that is said to be able to keep surfaces up to 18ºF (10ºC) cooler than ambient.
In a paper published in the journal Cell Reports Physical Science, the researchers show that compared with commercial white paint, the paint that they developed can maintain a lower temperature under direct sunlight and reflect more ultraviolet rays.
According to the researchers, commercial heat rejecting paints currently on the market reflect only 80%-90% of sunlight and cannot achieve temperatures below their surroundings. The white paint that Purdue researchers created is said to be able to reflect 95.5% sunlight and efficiently radiates infrared heat.
Developing this paint formulation wasn’t easy. The six-year study builds on attempts going back to the 1970s to develop radiative cooling paint as a feasible alternative to traditional air conditioners.
The researchers considered over 100 different material combinations, narrowed them down to 10 and tested about 50 different formulations for each material. They landed on a formulation made of calcium carbonate, an earth-abundant compound commonly found as chalk in rocks and seashells.
This compound, used as the paint’s filler, allowed the formulation to behave essentially the same as commercial white paint but with greatly enhanced cooling properties. These calcium carbonate fillers absorb almost no UV rays due to a so-called large “band gap,” a result of their atomic structure. They also have a high concentration of particles that are different sizes, allowing the paint to scatter a wider range of wavelengths.
According to the researchers’ cost estimates, this paint would be both cheaper to produce than its commercial alternative.
The researchers are working on developing other paint colours that could have cooling benefits. The team filed an international patent application on this paint formulation through the Purdue Research Foundation Office of Technology Commercialisation.
This study was supported by the Cooling Technologies Research Center at Purdue University and the Air Force Office of Scientific Research through the Defense University Research Instrumentation Programme.