Engineers in the US claim to have created “the whitest color yet” – which they believe will help fight global warming.
The ultra white coating developed at Purdue University in Indiana reflects up to 98.1 percent of the sunlight and emits infrared heat in the process.
Currently, colors on the market that are designed to give off heat only reflect between 80 and 90 percent of sunlight.
Buildings in hot climates coated with the new paint would stay cool more efficiently. Reduction of the need for air conditioning.
Paints could provide an environmentally friendly way to reduce the power required to keep them running all the time in mild weather.
Xiulin Ruan, professor of mechanical engineering at Purdue University, holds up his laboratory’s sample of the “whitest color ever recorded.”
NEW COLOR CAN MAKE SURFACES COOLER THAN THE SURROUNDINGS
Using high-precision temperature measuring devices, so-called thermocouples, the researchers showed that the paint can keep surfaces 19 ° F cooler than their surroundings at night.
It can also cool surfaces under strong environment 8 ° F below their environment during midday hours.
The color’s solar reflectivity is so effective that it works even in the middle of winter.
During an outdoor test with an ambient temperature of 43 ° F, the paint still managed to lower the sample temperature by 18 ° F.
The Purdue University team last October revealed a white color that reflects 95.5 percent of sunlight. At 98.1 percent, however, this new version is even more effective.
Last year’s “whitest color” was a formulation made from calcium carbonate, an earth-rich compound often found in rocks and seashells.
However, this new version uses a chemical compound called barium sulfate.
“If you were to use this paint to cover a roof area of about 1,000 square feet, you could get 10 kilowatts of cooling,” said Xiulin Ruan, professor of mechanical engineering at Purdue University.
“It’s more powerful than the central air conditioning that most homes use.”
The new record of Purdue’s white color, published in ACS Applied Materials & Interfaces magazine, is the result of six years of research.
The project builds on attempts that go back to the 1970s to develop radiant cooling paint as a possible alternative to conventional air conditioning systems.
Ruan’s lab had looked at over 100 different materials, narrowed them down to 10, and tested about 50 different formulations for each material.
The researchers showed in their study that their barium sulfate-based paint, like commercial paints, can potentially deal with outside conditions.
Two characteristics give the varnish its extreme whiteness – one is the very high concentration of barium sulfate, which is also used to whiten photo paper and cosmetics.
“We looked at a variety of commercial products, basically anything that was white,” said Xiangyu Li, a postdoctoral fellow at the Massachusetts Institute of Technology (MIT) who also worked on the project.
“We found that with barium sulfate, in theory, you can really, really reflect things, which means they are really, really white.”
The second characteristic is that the barium sulfate particles are all different sizes in color.
Barium sulfate is the inorganic compound with the chemical formula BaSO4. It is also used to whiten photo paper and cosmetics (archive image)
An infrared camera shows how a sample of the whitest white color (the dark purple square in the middle right) actually cools the plate below ambient temperature, which is not even the case with commercially available “heat rejecting” paints.
How strongly each particle scatters light depends on its size. A wider range of particle sizes allows the color to scatter more spectrum of light from the sun.
“A high concentration of particles of different sizes gives the color the broadest spectral spread, which contributes to the highest reflectivity,” said Joseph Peoples, also at Purdue University.
The technique the researchers used to create the paint is also compatible with the commercial paint manufacturing process.
With a reflectivity of 98.1 percent, there is little room to whiter the color, according to researchers, but not much without affecting the end product.
“While a higher concentration of particles is better for making something white, you can’t increase the concentration too much,” Li said.
“The higher the concentration, the easier it is for the paint to break off or peel off.”
“No More Black”: Researchers at the Massachusetts Institute of Technology (MIT) covered a £ 1.6 million diamond (pictured before and after) with the substance to prove its blackness
The researchers believe that this white could be the closest equivalent to some of the blackest blacks ever developed.
A product developed by Surrey NanoSystems called Vantablack absorbs up to 99.965 percent of visible light.
However, in 2019, Vantablack was upgraded by a team at MIT who increased the absorption rate to 99.995 percent.
MIT covered a £ 1.6 million diamond with the substance worthy of the spinal tap to prove its blackness – and it seemed to disappear instantly.
The MIT material was made from vertically aligned carbon nanotubes – microscopic carbon filaments – grown on a surface of chlorine-etched aluminum foil.
BLACK ABSORBS AND WHITE REFLECTIONS
Heat and light are different types of energy. Light energy can be converted into thermal energy.
A black object absorbs all wavelengths of light and converts them into heat so that the object becomes warm.
A white object reflects all wavelengths of light, so the light is not converted into heat and the temperature of the object does not increase noticeably.
Different wavelengths (colors) of light have different amounts of energy. Violet light has more energy than red light.
If we compare an object that absorbs purple light to an object that absorbs the same number of photons (light particles) from red light, the object that absorbs purple light absorbs more heat than the object that absorbs red light.
The amount of heat absorbed is also affected by how light or dark an object is.
A dark object of a certain color absorbs more photons than a light object of the same color, so it absorbs more heat and becomes warmer.
Source: UC Santa Barbara