Scientist create the whitest paint ever – and it could save the planet


Purdue University professor Xiulin Ruan holds up his lab’s sample of the whitest paint on record. (Credit: Purdue University/Jared Pike)

The whitest paint ever has been created.

And it’s also the coolest, literally, according to the scientists who made it.
They say the new paint formulation could help buildings rely less on air conditioning

In an effort to curb global warming, engineers at Purdue University in the US last year created the ultra-white paint that pushed the limits of how white paint can be.

Now they’ve even outdone that. The newer paint not only is whiter, but also can keep surfaces cooler than the formulation that the researchers had previously demonstrated.

Professor Xiulin Ruan said: ‘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.’

The researchers believe that this white may be the closest equivalent of the blackest black – know as “Vantablack” – which absorbs up to 99.9 per cent of visible light.

The new whitest paint formulation reflects up to 98.1 per cent of sunlight — compared with the 95.5 percent of sunlight reflected by the researchers’ previous ultra-white paint — and sends infrared heat away from a surface at the same time.

Typical commercial white paint gets warmer rather than cooler. Paints on the market that are designed to reject heat reflect only 80 to 90 percent of sunlight and can’t make surfaces cooler than their surroundings.

The team’s research explaining how the paint works was published in the journal ACS Applied Materials & Interfaces.

They said that two features give the paint its extreme whiteness: one is the paint’s very high concentration of a chemical compound called barium sulphate which is also used to make photo paper and cosmetics white.

Dr Xiangyu Li, who worked on this project as a PhD student in Prof Ruan’s lab, said: ‘We looked at various commercial products, basically anything that’s white.

‘We found that using barium sulphate, you can theoretically make things really, really reflective, which means that they’re really, really white.’

The second feature is that the barium sulphate particles are all different sizes in the paint.

How much each particle scatters light depends on its size, so a wider range of particle sizes allows the paint to scatter more of the light spectrum from the sun.

Joseph Peoples, a Purdue PhD student in mechanical engineering, said: ‘A high concentration of particles that are also different sizes gives the paint the broadest spectral scattering, which contributes to the highest reflectance.’

The researchers say there is still a ‘little bit’ of room to make the paint whiter, but not much without compromising the paint.

Dr Li added: ‘Although a higher particle concentration is better for making something white, you can’t increase the concentration too much.

‘The higher the concentration, the easier it is for the paint to break or peel off.’

An infrared camera shows how a sample of the whitest white paint (the dark purple square in the middle) actually cools the board below (Credit: Purdue University/Joseph Peoples)

The paint’s whiteness also means that it is the coolest paint on record.

Using high-accuracy temperature reading equipment called thermocouples, the researchers demonstrated outdoors that the paint can keep surfaces 19 degrees Fahrenheit (-7 degrees Celsius) cooler than their ambient surroundings at night.

It can also cool surfaces 8F (-13C) below their surroundings under strong sunlight during the afternoon.

The paint’s solar reflectance is so effective, it even worked in the middle of winter.
During an outdoor test with an ambient temperature of 43F (6.1C), the paint still managed to lower the sample temperature by 18 degrees Fahrenheit (8C).

Dr Ruan said the paint is the result of six years of research building on attempts going back to the 1970s to develop radiative cooling paint as a feasible alternative to traditional air conditioners.

His lab had considered more than 100 different materials, narrowed them down to 10 and tested about 50 different formulations for each material.

Their previous whitest paint was a formulation made of calcium carbonate, commonly found in rocks and seashells.

The researchers showed in their study that like commercial paint, their barium sulphate-based paint can potentially handle outdoor conditions.

The technique used to create the paint is also compatible with the commercial paint fabrication process, according to the researchers.


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