Scientists at Purdue University Create the “Whitest White” Paint Ever Seen: It Reflects 98% of the Sun’s Light

Xiulin Ruan, a Pur­due Uni­ver­si­ty pro­fes­sor of mechan­i­cal engi­neer­ing, holds up his lab’s sam­ple of the whitest paint on record. Pur­due University/Jared Pike

Sure­ly, you’ve heard of Vantablack, the high-tech coat­ing invent­ed by UK com­pa­ny Sur­rey NanoSys­tems that absorbs over 99 per­cent of light and makes three-dimen­sion­al objects look like black holes? Aside from its con­tro­ver­sial­ly exclu­sive use by artist Anish Kapoor, the black­est of black paints has so far proven to be most effec­tive in space. “You can imag­ine up in space peo­ple think of it as being real­ly black and dark,” Sur­rey NanoSys­tems chief tech­ni­cal offi­cer Ben Jensen explains. “But actu­al­ly it’s incred­i­bly bright up there because the Sun’s like a huge arc lamp and you’ve got light reflect­ing off the Earth and moon.”

All that sun­light can make cer­tain parts of the world unbear­ably hot for humans, a rapid­ly wors­en­ing phe­nom­e­non thanks to cli­mate change, which has itself been wors­ened by cli­mate con­trol sys­tems used to cool homes, offices, stores, etc. Since the 1970s sci­en­tists have attempt­ed to break the vicious cycle with white paints that can cool build­ings by reflect­ing sun­light from their sur­faces. “Paint­ing build­ings white to reflect sun­light and make them cool­er is com­mon in Greece and oth­er coun­tries,” notes The Wash­ing­ton Post. “Cities like New and Chica­go have pro­grams to paint roofs white to com­bat urban heat.”

The prob­lem is “com­mer­cial white paint gets warmer rather than cool­er,” writes Pur­due Uni­ver­si­ty. “Paints on the mar­ket that are designed to reject heat reflect only 80%-90% of sun­light and can’t make sur­faces cool­er than their sur­round­ings,” since they absorb ultra­vi­o­let light. That may well change soon, with the inven­tion by a team of Pur­due engi­neers of an as-yet unnamed, patent-pend­ing ultra-white paint that has “pushed the lim­its on how white paint can be.” Those lim­its now fall just slight­ly short of Vantablack on the oth­er side of the spec­trum (or grayscale).

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. Pur­due University/Joseph Peo­ples

Pur­due describes the prop­er­ties of the rev­o­lu­tion­ary com­pound.

Two fea­tures give the paint its extreme white­ness. One is the paint’s very high con­cen­tra­tion of a chem­i­cal com­pound called bar­i­um sul­fate, which is also used to make pho­to paper and cos­met­ics white.

The sec­ond fea­ture is that the bar­i­um sul­fate 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.

This for­mu­la “reflects up to 98.1% of sun­light — com­pared with the 95.5%,” of light reflect­ed by a pre­vi­ous com­pound that used cal­ci­um car­bon­ate instead of bar­i­um sul­fite. The less than 3% dif­fer­ence is more sig­nif­i­cant than it might seem.

Xiulin Ruan, pro­fes­sor of mechan­i­cal engi­neer­ing, describes the poten­tial of the new reflec­tive coat­ing: “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… If you look at the ener­gy [sav­ings] and cool­ing pow­er this paint can pro­vide, it’s real­ly excit­ing.”

Will there be a pro­pri­etary war between major play­ers in the art world to con­trol it? “Ide­al­ly,” Kait Sanchez writes at The Verge, “any­thing that could be used to improve people’s lives while reduc­ing the ener­gy they use should be free and wide­ly avail­able.” Ide­al­ly.

Learn more about the whitest white paint here and, if you have access, at the researchers’ pub­li­ca­tion in the jour­nal ACS Applied Mate­ri­als & Inter­faces.

via Smith­son­ian

Relat­ed Con­tent: 

YIn­Mn Blue, the First Shade of Blue Dis­cov­ered in 200 Years, Is Now Avail­able for Artists

Dis­cov­er Harvard’s Col­lec­tion of 2,500 Pig­ments: Pre­serv­ing the World’s Rare, Won­der­ful Col­ors

A 3,000-Year-Old Painter’s Palette from Ancient Egypt, with Traces of the Orig­i­nal Col­ors Still In It

Josh Jones is a writer and musi­cian based in Durham, NC. Fol­low him at @jdmagness