That Ultra-White Paint That Helps Cool Surfaces? Make Your Own!

July 22, 2023 by Donald Papp 50 Comments

It started with [KB9ENS] looking into paints or coatings for passive or radiative cooling, and in the process he decided to DIY his own. Not only is it perfectly accessible to a home experimenter, his initial results look like they have some promise, as well.

[KB9ENS] read about a type of ultra-white paint formulation that not only reflects heat, but is able to radiate it into space, cooling the painted surface to below ambient temperature. This is intriguing because while commercial paints can insulate and reflect heat, they cannot make a surface cooler than its surroundings.

Anecdotally speaking, this painted battery section of a solar recharger gets too hot to touch in full sunlight. But when painted over, it was merely warm.

What really got [KB9ENS] thinking was that at its core, the passively-cooling paint in the research is essentially a whole lot of different particle sizes of barium sulfate (BaSO₄) mixed into an acrylic binder. These two ingredients are remarkably accessible. A half-pound of BaSO₄ from a pottery supply shop was only a few dollars, and a plain acrylic base is easily obtained from almost any paint or art supplier.

[KB9ENS] decided to mix up a crude batch of BaSO₄ paint, apply it to some things, and see how well it compared to other paints and coatings. He wetted the BaSO₄ with some isopropyl alcohol to help it mix into the base, and made a few different concentrations. A 60% concentration by volume seemed to give the best overall results.

There’s no indication of whether any lower-than-ambient cooling is happening, but according to a non-contact thermometer even this homemade mixture does a better job of keeping sunlight from heating things up compared to similarly-applied commercial paints (although it fared only slightly better than titanium dioxide-based white paint in the initial test.)

[KB9ENS] also painted the battery section of a solar recharger with his homemade paint and noted that while under normal circumstances — that is to say, in full sunlight — that section becomes too hot to touch, with the paint coating it was merely warm.

Actual passive cooling can do more than just keep something less warm than it would be otherwise. We’ve seen it recently used to passively and continuously generate power thanks to its ability to create a constant temperature differential, day and night.

Responsive Paintings Do It With Heat And Light

July 13, 2021 by Kristina Panos 2 Comments

Art is a conversation, yes. But normally, it’s a short one: the artist makes a statement and the audience responds, each bringing their own interpretations. The hard thing about being an artist is that once you release a piece into the world, it’s sort of bound and gagged in that it can’t defend itself from comments and misinterpretation.

On the other hand, interactive art allows for a longer discussion. Pieces are responsive and no longer mute. But so much of the interactive art out there is purely digital, and lacks a certain analog warmth that comes from physicality. For this year’s Hackaday Prize, [Laura] sought to put a digital interface on an analog visual piece and make paintings that change based on data inputs.

For now, [Laura] is focusing on adding two dynamic elements to her paintings: shifting color and light patterns in response to a viewer’s presence and/or actions using an Arduino and TinyML. For the color changes, [Laura] ended up mixing thermochromic pigment powder with a transparent gel medium.

This was a bit of a journey, because the regular kind of transparent medium came out too runny, and mixing the pigments with white paint made the colors come out lighter than [Laura] wanted and left white behind when heated. But transparent gel medium was just right. You can see the difference in this picture — the colors come out darker with the gel medium, and disappear almost completely with heat.

[Laura] didn’t want to just poke LEDs through the canvas, which in this case is a 1/8″ birch panel. Instead, there’s an RGB matrix shining behind a pair of thin, diffused cutouts filled with thermoplastic.

Check out the video after the break of a painting sketch that uses both techniques. Keep your eye on the purple triangles on the right side, and watch them slowly turn blue in real time as light patterns dance behind the diffused cutouts. Stick around for the second brief video that shows an updated light animation.

We’ve seen many ways of making interactive art, like this Rube Goldberg fairy tale ball maze that you control with your phone.

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