International News
WHAT MAKES THE WHITEST PAINT SO WHITE ? 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 .
“ We looked at various commercial products , basically anything that ’ s white ,” said Xiangyu Li , a postdoctoral researcher at the Massachusetts Institute of Technology , who worked on this project as a Purdue Ph . D . student in Ruan ’ s lab . “ 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 .
“ A high concentration of particles that are also different sizes , gives the paint the broadest spectral scattering , which contributes to the highest reflectance ,” said Joseph Peoples , a Purdue Ph . D . student in mechanical engineering .
There is a little bit of room to make the paint whiter , but not much without compromising the paint . “ 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 ,” Li said .
HOW THE WHITEST PAINT IS ALSO THE COOLEST The paint ’ s whiteness also means that the paint is the coolest on record . Using high-accuracy temperature reading equipment called thermocouples , the researchers demonstrated outdoors that the paint can keep surfaces 19 degrees Fahrenheit cooler than their ambient surroundings at night . It can also cool surfaces 8 degrees Fahrenheit below their surroundings under strong sunlight during noon hours .
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 43 degrees Fahrenheit , the paint still managed to lower the sample temperature by 18 degrees Fahrenheit . This white 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 . Ruan ’ s lab had considered over 100 different materials , narrowed them down to 10 and tested about 50 different formulations for each material . Their previous ultra-white paint was a formulation made of calcium carbonate , an earthabundant compound commonly found in rocks and seashells .
The researchers showed in their study that like commercial paint , their barium sulphate-based paint can potentially handle
Purdue University / Jared Pike Purdue University | Joseph Peoples
outdoor conditions . The technique that the researchers used to create the paint is also compatible with the commercial paint fabrication process .
Patent applications for this paint formulation have been filed through the Purdue Research Foundation Office of Technology Commercialisation . This research was supported by the Cooling Technologies Research Center at Purdue
University and the Air Force Office of Scientific Research through the Defense University Research Instrumentation Programme . The research was performed at Purdue ’ s FLEX Lab and Ray W . Herrick Laboratories and the Birck Nanotechnology Center of Purdue ’ s Discovery Park . RACA
Source : Pardue University
Xiulin Ruan , a Purdue University professor of mechanical engineering , holds up his lab ’ s sample of the whitest paint on record .
An infrared camera shows how a sample of the whitest white paint ( the dark purple square in the middle ) actually cools the board below ambient temperature , something that not even commercial ‘ heat rejecting ’ paints do .
www . hvacronline . co . za RACA Journal I June 2021 7