The whitest color in the world reflects more than 98% of sunlight

Professor of Mechanical Engineering at Pearlin University, Shilin Rouan, keeping a sample of “the world’s whitest paint” – © Purdue University / Jared Pike

American researchers have developed an ultra-reflective white paint. Containing barium sulfate particles, it reflects almost all sunlight.

Rare whitewash

The materials used to cover our buildings can have a large impact on their ability to reflect heat from the sun and their overall energy efficiency. To keep living spaces cool and reduce our dependence on air conditioners and other energy-intensive cooling systems, improve white paint so that they reflect more solar radiation. It is also an area of ​​exploration by researchers.

As part of the work presented in the magazine ACS Implemented Materials and Interfaces, From engineersPurdue University Made a white paint that represented 98.1% of sunlight (compared to 80 to 90% for commercially sold thermo-reflective paints). According to their calculations, it has a higher cooling capacity than conventional air conditioners.

The new ultra-white paint is due to the excellent performance of a clever mixture of barium sulfate particles, white photographic paper, and the chemical compound used in cosmetics. If these particles can make the paint too white and too reflective, then there is a limit that should not be exceeded: too much concentration can actually cause paint detachment or fragmentation.

The infrared image shows how a sample of paint made by Purdue engineers can cool its substrate below room temperature – © Purdue University / Joseph Peoples

By varying the size of the particles, however, it is possible to modify the ability of each of them to diffuse light, a wider range of particle sizes resulting in a larger fraction of the light spectrum coming from a paint light Is capable. Sun. The team has now identified the correct dosage to produce white.

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Impressive results

When tested from the outside, the paint placed surfaces to which it was applied during the night at a temperature of 10.5 ° C lower than its ambient environment, and 4.5 ° C under the strong sunlight during the day. Tests conducted in the heart of winter with an ambient temperature of 6.1 ° C showed that the material allowed the surface temperature to drop below about 10 ° C.

« A high concentration of particles of various sizes gives the paint a wide spectral diffusion, contributing to its unmatched reflectivity. “, Cast light on Joseph peoples, Co-author of the study.

« If you were to use this paint to cover a roof area of ​​about 93 square meters, we estimate that you could get a cooling capacity equal to 10 kW. », For its part, underlines Shilin RuanProfessor of Mechanical Engineering Purdue. « This is more than the central air conditioner installed in most homes. »

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