61–70 of 73 posts
How does this new paint compare to the contents of a spray paint can from Home Depot? Having a hard time searching the web for this one, the first few pages of hits are all about this new 98.1% paint.
You’re looking for something called “light reflectance value” or LRV. You can get 90-94% in wall paints; not sure about spray paints. https://www.kylieminteriors.ca/paint-colour-review-the-5-whi...
Earlier quoted context omitted.
It won't shine any brighter than the light that's hitting it.
Like... the sun?
If you mixed it with Vantablack, would you get the greyest possible paint? /s
You could try buying some and find out! https://culturehustle.com/products/black-v1-0-beta-the-world... You could also mix it with the 'whitest white' https://culturehustle.com/products/white-20
Vanta black is a whole different beast, but it also isn’t paint so I feel it’s cheating that particular race :)
Couldn’t this be revolutionary for spacecraft? Also would it make a better solar sail?
Colour me stupid, but in a simple white vs. black comparison, wouldn't a VantaBlack-clad solar sail absorb more energy, so be more useful? - ed I'm misunderestimating 'equal and opposite' photon reflections here, aren't I?
If you’re harvesting the momentum from a photon into momentum for your spaceship, you’re better off with white. A photon being reflected gives you its momentum twice. It’s first (briefly) caught like the black sail, imparting its momentum, but then it’s re emitted and hurled away, like a cannon, giving even more reactive momentum to the sail
Are airplanes more in need of cooling or heating? The outside temperature at cruising altitude is around -50° (roughly where the Celsius and Fahrenheit scales meet, btw), is the insulation good enough to just keep the inside at acceptable temperatures for humans?
It does not matter for airplanes. Both cooling and heating are in ample supply on an airplane.
Hence why the majority of airline fleets have white-painted upper fuselages.
I know nothing about this sort of stuff, but if this were applied to cars, would there be an increased risk of temporarily blinding other drivers on a sunny day?
It reflects something like 98% of light instead of 90%, so the actual increase in reflected light isn't that big. Flat scattering surfaces are never blinding. The problem is with specular reflections off of shiny surfaces. Even though a shiny surface may only reflect a small fraction of incident light, it's all pointing in one direction which can dazzle observers.
For its intended application, reflecting 98% instead of 90% means absorbing 5 times less heat when under Sun light.
That is a very large difference. A white paint with only 90% reflectance might cause negligible cooling, while one with 98% reflectance may cool a painted object to have a temperature less by more than 6 Celsius degrees in comparison with the air temperature.
The cooling depends on the ratio between how much solar light is absorbed and how much far infrared light is emitted.
So a cooling paint must be very white over the near infrared, visible and ultraviolet spectrum, but it must be black for the far infrared light which is emitted by the bodies at ambient temperature.
That method is described in the reference #17 from the bibliography of this paper.
There are 2 methods that can be used to make a white paint.
The first is to use a polymer as a binder and incorporate in it very small particles with high refractive index, i.e. a white pigment powder.
The second method is to make a polymer that solidifies as a foam. In this case, the polymer contains voids filled with air having low refractive index, instead of pigment particles, but the effect of the optical non-homogeneity is the same, so both foams and powders are white, when they do not absorb light.
The reference #17 describes such a method of making a polymeric foam, which can be used as a paint.
According to the table from this paper about boron nitride, the previous best combination of total solar reflectance and layer thickness and layer density was for that polymeric foam, which had a 96% total solar reflectance and a 300 micron thickness, outperforming all the previous paints based on white pigments.
While that foam had a slightly lower total solar reflectance, it had a better far infrared emittance, so the cooling performance was similar, i.e. of about 6 Celsius degrees below the air temperature.
Because the methods that use foams do not need pigments, they have the potential to be cheaper than the methods with pigments, which need both a polymer as binder and a mineral pigment.
Moreover, methods to make foams can be adapted to many different kinds of polymers, so there are chances that other polymers with even better performances or even lower cost can be found, perhaps a silicone polymer in foam form (silicones can have perfect resistance to solar light in outdoor conditions).