Sometimes scientists end up achieving or discovering something that was not the aim of their research. Scientists from Purdue University were trying to develop the whitest paint they could reflect light and keep houses. However, the ultra-white paint that they created was not only cooling but also found its way into the Guinness World Records 2022 book as the Whitest paint in the world.

The paint is designed to reflect over 98 percent of the sunlight that hits a surface it is coated with, thereby, making it cooler than its surroundings. This can reduce dependence, or even eliminate, the need for artificial air conditioning "When we started this project about seven years ago, we had saving energy and fighting climate change in mind," said Dr. Xiulin Ruan lead researcher in a statement.

An Ultra-reflective Paint

White paint
Xiulin Ruan, a Purdue University professor of mechanical engineering, holds up his lab's sample of the whitest paint on recordPurdue University/Jared Pike

The paint is the result of collaboration between Dr. Ruan and his students. So what was the aim of making the paint? The team aimed at creating a paint that would be able to reflect sunlight away from a structure. However, the process of making the paint exceptionally reflective resulted in the paint becoming extremely white.

An amazing 98.1 percent of solar radiation is reflected by the paint formulation, and simultaneously emitting infrared heat. As the paint absorbs more heat from the sunlight that it emits, the temperature of any surface coated with it is reduced below that of its surroundings without actually consuming any power. In October, the same team had created an ultra-white paint that was 95.5 percent reflective.

Cooling A Painted Surface

Commercially available white paints get warmer instead of cooler. And commercial paints that are engineered to counter heat can reflect only 80 to 90 percent of sunlight. They cannot make the surfaces or buildings coated with them lesser/cooler than their surroundings.

White paint
White paint (Representational Picture)Flickr/ Marco Verch Professional Photographer

However, in the study describing the paint, the authors stated that the new paint can provide potential benefits of radiative cooling. "If you were to use this paint to cover a roof area of about 1,000 square feet, we estimate that you could get a cooling power of 10 kilowatts. That's more powerful than the central air conditioners used by most houses," highlighted Dr. Ruan.

Reflecting Wide Spectrum of Sunlight

The record-setting paint is an outcome of research utilizing attempts dating back to the 1970s that aimed at designing a radiative cooling paint as a viable substitute for traditional air conditioners. For its development, Dr. Ruan's reviewed more than 100 different materials. They finally shortlisted 10 materials and tested around 50 different combinations for each of the materials.

What makes this new paint ultra-white? It can be attributed to two characteristics. First, is the high concentration of a compound known as barium sulfate, which is also used in cosmetics and photo paper. Second, is the different sizes of particles of barium sulfate present in the paint. A particular wavelength of sunlight that a particle scatters is dependent on its size. Therefore, a broader range of particles permits the paint to dissipate more of the sunlight's spectrum.