Just Chillin’: New Polymer Paint Helps Keep Energy Costs Down

In a time when it’s getting hotter and hotter outside, how do you stay cool inside?

That’s a challenge all over the world, but especially in less developed areas, where air-conditioning is too expensive or uses too much electricity to be a good solution.

Now there’s an answer for all of us.  Paint.

Ok, not just any paint – a  new polymer-based paint-like coating.  Researchers at Columbia University came up with this new twist on a familiar idea.

If you’ve ever been outside in the sun, you already know the idea.  You’re a lot cooler in a white shirt than a black shirt.

When it comes to cooling a building though, things aren’t quite so black and white.

Did you know?

A word about how we get these miracle materials.  PET (polyethylene terephthalate) is made from xylene, and acrylic from propylene.  Xylene and propylene in turn, are chemicals made by breaking apart molecules of petroleum or natural gas, which is why they are called petrochemicals.

White paint IS good for reflecting light, but heat from the sun in other wavelengths – not so much.  Some petrochemical-derived polymers (plastics), like acrylic and PET (the stuff water bottles are made from), are excellent for radiating back heat.

But because those plastics are transparent, they won’t reflect light – and because they are plastics, aren’t as easy to turn into a coating, like paint.

So the Columbia magic, was to incorporate the polymers into the paint AND replace the white in the paint, with air bubbles, to make a sort of foam.  (The short explanation is that the combination of the air bubbles and the polymer turns white.  The long explanation is in the journal Science.)

And this is what happens when you slap a coat of the new polymer coating on a building:

(Illustration from Columbia University)

(“PRDC” stands for “passive daytime radiative cooling”, meaning in this case, a painted surface that cools itself.)

Or as one of the Columbia researchers put it, “This simple but fundamental modification yields exceptional reflectance and emittance that equal or surpass those of state-of-the-art PRDC designs, but with a convenience that is almost paint-like.”  Which is to say, it’s simple, and it works.

To give the new coating a good workout, by the way, the Columbia group tested it in the Arizona desert, and the tropics of Bangladesh.  And – success!  Which is good news in hot times.

So we’ll go out today with one of the all-time warming classics, Martha and the Vandellas singing – Heat Wave.  But you knew that was coming.

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