How To Make Infrared Cooling Paint (Electricity Free Air Conditioning)

hi everyone in this video we'll be exploring a few potential methods to make paint that is capable of sub ambient radiant cooling basically this paint could provide passive electricity free air conditioning by sucking heat from its surroundings and hurling it into space as infrared radiation as unbelievable as that sounds there's a stack of published research documenting radiant paints that can reach temperatures as much as 10 degrees celsius lower than the surrounding air temperature there are a few different ways these paints have been made in the lab and having gleaned what i can from half a dozen different papers i think i've learned enough to make my own we'll make two or three varieties in this video and test the cooling capability as compared to off-the-shelf white paint the first thing to consider is how this paint is meant to work its first attribute is to have extremely high reflectance of light in the visible spectrum a useful radiant paint should be able to maintain sub-ambient temperatures even in direct sunlight and that becomes more difficult for every bit of sunlight that the paint fails to reflect as the remainder is absorbed as heat reflectance alone isn't adequate to provide cooling but it gives us a good starting point the real magic of radiative cooling is in the particular wavelength of infrared light that the paint emits all objects emit their energy as infrared light but for the most part that light is scattered around in the atmosphere absorbed by atmospheric gases and re-emitted such that much of it returns back to earth to be reabsorbed it so happens that just a small sliver of the infrared spectrum passes clean through the atmosphere with little to no scattering this is called the atmospheric infrared window if we can engineer the composition of our paint to release its thermal energy as infrared light at just the right wavelength it will blow right through the atmosphere and off into the coldness of space by combining this emission of light with a strong rejection of incoming light in other spectrums the overall effect is that the paint experiences a net loss of energy it gets cold the pigment in ordinary white paint that you can buy at a hardware store is usually titanium or zinc oxide these have great reflectance but they lack overlap in their emission spectrum with the atmospheric window so far the best results in making sub-ambient cooling paint have come from using one of two pigments calcium carbonate or barium sulfate both of these are bright white with good reflectance and most importantly the infrared emission is right where we want it here in this container is a little bit of diluted sulfuric acid and in this other one is barium nitrate dissolved in water mixing these two will form our pigment barium sulfate which is so insoluble it should immediately fall out of solution it's actually a very pretty reaction now soluble barium compounds like the barium nitrate that i started with in this container are actually fairly toxic so i made sure there was more than enough sulfuric acid to react with all of it and that takes care of the toxicity the reaction is what's called a double displacement where the sulfuric part of the acid switches places with the nitrate part of the barium nitrate in the end we get a mix of barium sulfate the insoluble pigment that we're looking for and nitric acid in this beaker i want to get rid of the acidity so i'll add some concentrated ammonia and this converts the nitric acid to ammonium nitrate now the waste from this experiment will be a nice fertilizer for my trees instead of a dangerous acidic mess the barium sulfate formed by this reaction is really hard to collect with filtering because the particles are so fine they pass right through it's better to let them settle out and then pour the water off the top the last little bit of water can be removed by pouring the remainder onto a sheet of printer paper with paper towel underneath to gently suck the water through with capillary action the paper contaminates the product slightly but the result is good enough for our purposes and here is our result barium sulfate powder that we can mix with an acrylic base to form our paint well right away i've noticed a problem this is a sample of sixty percent transparent acrylic base to forty percent barium sulfate pigment measured by weight let's brush this onto an object do you see the problem there's a lot of transparency in this paint for some reason the barium sulfate becomes very transparent when mixed with a liquid i can see now why this is not used as a standard white pigment in any case i'll try applying multiple coats and see how close to pure white we can get a little setup i've put together to test the light rejection of our paint samples i have a light meter that is sealed to an outlet port on this circular chamber and there's a focused beam of light coming in through another port and exiting through a slot in the side once i close off this open face anything i put in front of the slot will reflect light back into the chamber and give us a brightness reading that is dependent on the total reflectance of the sample i have a slide here that's been painted with off-the-shelf white paint and using the reflectance of the light from this flashlight we'll compare the reading with my homemade pigment so there is our reading with standard ultra white paint and switching in the barium sulfate sample we get a lower reading which is bad news this means the light rejection is not as good for the homemade sample and therefore even with the infrared emission it likely will not be able to cool objects in direct sunlight well after a few more experiments and failures to improve my results i found an excellent paper describing a process to make barium sulfate microspheres the goal of the paper seemed to be creating highly reflective coatings for pharmaceutical products which i guess matters for some reason in any case this sounded promising for my purposes the previously used acid method of making barium sulfate is an extremely fast chemical reaction because the reaction happens so rapidly the end product takes the form of amorphous blobs and random crystal structures to form a particular particle shape like microspheres the reaction needs to take place in an orderly fashion with controlled nucleation points the way this is accomplished is by using another chemical in the solution that temporarily bonds with the dissolved barium ions so there's some hesitation before they react the delay is imperceptible to the eye but it's enough to allow the crystals to nucleate from a billion little points and then continue growing outward at a steady rate in all directions forming spheres the chemical used to inhibit the reaction is called edta which i mix into my soluble barium solution no measurements were given in the paper i was referencing for this process so i guess a molar equivalent with the barium should be about right i tried half a dozen times to make this reaction work with barium nitrate as my starting chemical because i have a lot of it and it's fairly inexpensive this however seemed to cause a weird side reaction with the edta forming a sticky substance which was completely inseparable from my barium sulfate end product you can see it caused a brown tint to the light that passes through a solution of the resulting microspheres and i could not get rid of it no matter how many times i washed the particles with water and every other solvent i could think to try i even bought a centrifuge to separate and wash the particles more easily because unlike the acid formed barium sulfate the microspheres never seemed to settle to the bottom when separated by a centrifuge the result was a gelatinous and still transparent pile of muck at the bottom of the tube retaining the brown tint of the nitrate side reaction my problems were eventually solved by exchanging the barium nitrate for barium chloride which left the edta in a soluble state instead of sulfuric acid this reaction uses sodium sulfate as the contributor of the sulfate ion when the sulfate and chloride swap places we end up with sodium chloride ordinary table salt in solution and barium sulfate hopefully in the form of microspheres constant stirring and slow combination of the two liquids is needed to form microspheres of a consistent size but in the case of paint the best reflectivity comes from a variety of particle sizes fortunately that's easy to accomplish no stirring and a quick addition without the nitrate to form a weird gel the spheres do eventually settle to the bottom of this container by gravity alone but much more slowly than the acid-made pigment my earlier centrifuge purchase still ended up being helpful for this purpose as i can reduce the settling time from a few hours to just a few minutes at 4000 rpm repeating this a few times each time pouring off the liquid and adding fresh distilled water leaves fairly pure barium sulfate hopefully now in a state that is much more reflective and less transparent than the earlier amorphous particles so here i have a sample slide of my microsphere paint and this is my earlier made amorphous barium sulfate paint and i have to say visibly the difference is not as dramatic as i had hoped although there is a difference this is brighter white i've let these dry so that we can now take a look under the light meter so the microsphere paint does read a little bit better but it still has some obvious transparency since multiple papers report using barium sulfate in these paints there must be some unmentioned secret sauce that's being used to reduce the transparency my initial thoughts are that perhaps the barium pigment is being mixed with a standard titanium or zinc based paint or perhaps the barium paint is only used as a top coat over a layer of opaque white paint beneath it both of these options seem less than ideal i think achieving the best result will require a new approach entirely one method to make ultra white coatings without the use of pigments is to replicate the same mechanism which is responsible for the highly reflective properties of snow snow is remarkable because while it's made of transparent ice it somehow manages to reject and reflect over 98 percent of incoming sunlight making it even more reflective than almost all white paint it does this with an enormous amount of small air pockets which cause any light that passes through to stand a pretty good chance of hitting mirror-like surfaces of the ice crystals any light that makes it through one air gap soon hits another and another and another until almost all of it ends up being reflected back where it came from this effect can be roughly imitated with any transparent solid for example table salt which on a close-up view is made up of transparent crystals but get a whole pile of them together with air gaps in between and the pile appears white to make use of this snow scattering effect in a way that's practical for a painted surface we're looking to achieve the maximum amount of air gaps in the thinnest layer possible one method i found described in yet another article uses a clever series of physical reactions first dissolving an exotic plastic in acetone then adding a small amount of water when this dissolved plastic mixture dries the acetone evaporates first leaving behind a layer of plastic which is completely permeated with microscopic water droplets when the water dries we're left with millions of tiny regularly spaced cavities in the plastic while the paper describing this process used an exotic and expensive plastic i was able to replicate their results with ordinary transparent acrylic which dissolves in acetone after a few days now you can't just add water directly to this solution of dissolved acrylic because the water causes the plastic to crash out of solution instantly forming little plastic jellyfish blobs with the water sealed inside i found the best way to introduce water is to first mix it in a one to four ratio with acetone so 0.1 mil of water is added for every 0.5 mils of this solution so let's give this a try if i've added enough water the dissolved acrylic should go on clear and then turn white as it dries pretty neat stuff isn't it we can make really highly reflective surfaces this way with minimal effort and low cost however in terms of the infrared emission spectrum it's not suitable for cooling for sub-ambient temperatures we still need the barium sulfate or some other pigment that hits the infrared window my idea at this point is to combine the brightest of my barium pigments my sulfate microspheres with the acrylic acetone mix if all goes well the snow scattering effect of the acrylic will aid in light rejection and opacity where the barium sulfate falls short and the barium sulfate will contribute favorable emission first of all here is a test of various water ratios in the acrylic base i dissolved 10 grams of acrylic in a hundred ml of acetone so i know there's one gram of plastic for every 10 ml of this solution this allows me a controlled way to add incremental amounts of water and find out just how much should be added per gram of plastic for the best result between 0.5 and .6 mils of water per gram of plastic gave me good reflectance in this test with minor loss of adhesion and contraction later when i opened a brand new can of acetone i found that i had to double the amount of water added to achieve the same result so apparently my old can absorbed quite a lot of water from the air with age once i determined the best results without pigment i did a few tests with added barium sulfate 2 grams of sulfate for 1 gram dissolved acrylic so here is a test slide with the best result of my combinations and to my eyes this looks significantly brighter than off-the-shelf paint if the reflectance test agrees and if there's enough pigment for good infrared emission i think there's a good chance that this will work so let's give this a try that is looking significantly better than my earlier attempts the snow scattering effect seems to be really effective here's off the shelf paint and my paint this might be a big enough difference to offer some cooling in sunlight so here is my first full-size test sample with ordinary white paint as the background of the square and an x in the center which is my snow scattering paint the x was painted right onto the wooden subsurface with the off-the-shelf paint painted around it so that it would not be a double layer which might make an unfair test now i've made an awkward infrared camera rig with dual split lens filters on my camera so that i can get both close focus on the infrared camera and distant focus simultaneously hopefully i'll also not overexpose the bright daylight landscape using this let's take a look at my test sample after leaving it out in the sun for a few minutes and here we do have a successful result clearly my paint is substantially cooler than the surrounding ordinary paint but is it sub ambient not quite the air temperature was about 65 degrees at this time so we're close but direct sunlight is the most difficult scenario for radiant paint the best recorded results are only a few degrees cooler than ambient temperatures in direct sunlight so to even get close with my diy methods is satisfying i think it's safe to say this is better cooling than you can probably get with any other paint currently available for purchase even so sub ambient temperatures are important for this to be useful fortunately noonday sun is only around for a small sliver of the day let's try some tests with indirect sunlight and see if we can hit subambient numbers this next test brought some unexpected results my paint is currently a few degrees colder than air temperature here in the shade sub-ambient but so is the commercial paint my paint might be slightly colder but not substantially in direct sunlight it's obvious that my paint is significantly better than ordinary ultra white but i didn't expect the off-the-shelf paint to be so close in performance once direct light was gone despite not matching with the infrared window it seems normal titanium based paints can work pretty well for sub-ambient nighttime cooling still barium should be able to do much better so all i can think is that i've not added enough pigment i thought two grams of pigment for each gram of dissolved acrylic was pretty generous but apparently more is needed here i have a four to one mix and in this jar six grams of pigment to each gram of dissolved acrylic you would think that adding so much would get in the way of the snow scattering effect but both of these mixes seem to work just fine and actually read a fair bit more reflective than my original two to one mix in outdoor testing the four to one mixture proved to be significantly better at daylight cooling than the two to one mix and the six to one was even better still but just by a few fractions of a degree this could maybe use a little bit of fine-tuning to dial in on the perfect mixture but the four to one paint variation is what i used to make this sign the result of which i think speaks for itself the lettering is my homemade paint surrounded by off-the-shelf ultra white which clocks in at a full 20 degrees fahrenheit warmer after a few minutes in the sun that is an incredible difference in temperature for two paints of the same color my paint is still reading slightly above air temperature but just barely i think it would be sub-ambient if it were not fighting the heat conduction from the surrounding paint strangely even with this great daytime result i found that once the sun went down both the commercial paint and my own were still neck and neck for sub-ambient temperatures both paints in this shot were reading below 65 degrees while the air temperature was 85 this is a great result for both paints i have to say i did not expect ordinary white paint to perform so well it's terrible during daylight hours but it does have cooling potential at night now since i tested so many different paints i got tired of making my own barium sulfate and ended up just buying some theoretically microspheres should do even better than this store-bought amorphous powder but since the snow scattering acrylic mix is the primary reflecting agent of this paint added reflection from the pigment is just a bonus obviously the paint works even with this amorphous pigment which is great news for ease of manufacturing now at this point having so far only matched air temperature in direct sunlight i re-read some of the articles about how sub-ambient temperatures have been reached by others and realized most daylight cooling requires putting a film over the top of the paint to insulate it from the heat conduction of the wind a thin polyethylene film apparently works well and allows infrared light to pass through it i used this little tray to hold two samples of paint my paint and off the shelf paint with a thin film stretched over the top to insulate the samples with this finally we get some daylight cooling my first test in this tray gave us about two degrees fahrenheit below ambient this was in direct noon day sunlight so even though it's only a few degrees of cooling it's cooling that could be counted on even in very unfavorable conditions added to 20 plus degrees of cooling below air temperature at night it's not hard to think of ways that this could be used to keep something cold all day long for example by cooling a building to 20 degrees below air temperature at night so it lasts through the next day like a giant thermal battery by the time it approaches air temperature the sun is setting again and a new cooling cycle begins now the way that i have these samples set up in this tray is actually a close approximation to how radiative cooling is most likely to find practical use not by directly painting buildings because they would become too cold in winter but rather to make cooling panels that cycle water or air through them only when cooling is needed some companies have already developed cooling panels and even installed them in limited test cases but as far as i've found no one has yet made them available for normal purchase i would very much like to make and test my own panels that could potentially be recreated by anyone at home this paint is a really good start but i could easily double this video length just by discussing ideas to improve it no promises but i think we're looking at a series this video's sponsor is brilliant i am really selective about the companies that sponsor these videos but i keep going back to brilliant because i so appreciate the way that they approach education brilliant specializes in teaching stem topics through interactive and visually intuitive courses which really makes the information stick in your mind you can learn anything from basic math and logic to special relativity with everything in between when i work on projects like this one i use a lot of measurements in percentages and parts which is very important for being able to replicate the results consistently if you have trouble making sense of those things activate a free trial of brilliant and check out their new course on everyday math it starts with very simple visual problems that you can go through at your own pace their courses on logic and probability are some of my favorites as well there's tons of other courses for anyone who would like to learn something new to get started for free go to brilliant.org forward slash nighthawk or click the link in the video description below and the first 200 will get 20 percent off brilliant's annual premium subscription now i realize it has been a long time since my previous video i've had some minor but annoyingly long lasting health issues that slowed me down this last year thanks for sticking with me especially those of you who support these videos on patreon i'll probably be slow in posting new videos for a few months still but i am working on projects in the background there's lots i'm excited to show you i'm excited to keep improving on this radiant paint and i hope you've enjoyed this video thanks for watching i'll see you next time

Channel: NightHawkInLight

Views: 730,905

Keywords:

Id: N3bJnKmeNJY

Length: 25min 34sec (1534 seconds)

Published: Sat Jul 09 2022

Reddit Comments

[u/storyinmemo]

I watched this shortly after the burn this year and would interested n collaborating on experiments to see how effective this can be in both cost and performance for next year's burn.

[u/MiguelMenendez]

This guy looks like Ted Cruz’ smarter younger brother.

[u/grasshulaskirt]

Yessss

[u/james_casy]

Thanks for sharing. I’ve been interested in radiative cooling since seeing this Ted talk but this is the first diy project I’ve seen.

https://www.ted.com/talks/aaswath_raman_how_we_can_turn_the_cold_of_outer_space_into_a_renewable_resource