If you’ve ever rebuilt a room in your home and gone to the hardware store to choose fresh paint, you know there are lot of different shades of white on the market. It seems that there is a new shade of white in the city – and this can have quite cold climate implications (literally).
In a study published Thursday in the ACS Applied Materials & Interfaces, researchers at Purdue University say they have now made the whitest paint on the planet. In creating the whitest paint ever, which researchers say reflects up to 98.1% of light, Purdue researchers are breaking their own record set last fall when they developed a paint that reflects 95.5% of sunlight.
It might seem pointless to run to get to the whitest paint of all with just a few percentage points, when many of us can’t tell the difference between most white chips at Home Depot. However, when it comes to the cooling effects of white paints, these small percentages matter.
Anyone who went out on a hot summer day knows how to wear white clothes; white reflects light, while black absorbs. But white paints that are currently on the market with labels such as “ultra-reflective” or “high reflectivity” reflect only about 80 percent to 90 percent of the light, said Xiulin Ruan, lead author of the study. This may be enough to make your kitchen look sparkling clean every day – but if we talk about cooling properties, it is less efficient.
“We think 90% to 98% are not very different, but we need to think about sun absorption,” Ruan said. “Our paint absorbs 1.9% of sunlight, but those commercial paints, even with reflective substances, absorb 10% of sunlight – five times more than our paint absorbs. They look white, they are quite white, but they are not white enough – they are not able to cool beyond the ambient temperature ”.
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Ruan said efforts to develop the whitest paint possible, which could also act as coolants, date back to the 1970s. Only Ruan’s team has been working for about seven years to obtain whiter and whiter paints, using methods. adding reflective materials to the paint to help repel the sun. This white paint successfully incorporates high concentrations of barium sulfate – a chemical compound that is used to produce white cosmetics and photo paper – with particles of different sizes scattered in the paint.
“Sunlight has different colors because it has different wavelengths,” Ruan explained. “We need different particle sizes to scatter each wavelength.”
The development of this type of ultra-reflective paint could change the game for the way we design buildings as our world gets hotter and hotter. There is a lot of work growing in terms of how urban design choices – changing super-hot and super-absorbent asphalt roofs for reflective surfaces, for example, or building in parks or other green spots in cities to literally cool the area – it can help us overcome the heat in cities and other built spaces without using more energy to power air conditioners.
Ruan and his team have great visions of the potential of paint; they estimate that the widespread use of super-reflective white paint in cities such as Reno or Phoenix could save up to 80% on air conditioning costs. “If you have very hot days, our paint alone might not do the job, but on other days it may prevent you from turning on the air conditioner,” he said.
These types of climate hacks sound like the solution to all our problems – but there are still many real world considerations to consider when we think of designing cities to set fire. “To make cities more reflective, you have to be very, very, very practical,” said Hashem Akbari, a professor of civil, environmental and environmental engineering at Concordia University.
Akbari pointed out that regular wear and tear on roofs or reflective walls can affect the percentages of reflectivity measured in a laboratory setting. “Soot and dust tend to decrease the reflectivity of the surface,” he said. “If they start with a super-dope reflectivity of 95%, air pollutants, drops, soot can accumulate on the surface and the reflectors decrease.”
However, Akbari said that starting with the regular replacement of roofs, which require updates every few decades or so, with more reflective materials – regardless of the white of the paint you use or the percentage it actually reflects. – would be a great start for most cities.
“If every roof that needed to be replaced could be replaced with a highly reflective roof, in a period of 10 to 30 years all roofs will be very reflective. You don’t have to push a certain technology, like a coating, “he said.” We should encourage the marketing and insulation of reflective materials as the roofs are changed. “