Making Highly Reflective Paint

To cool your roof or car or boat, you can paint it with special paint that will become highly reflective, so that the Sun is not able to warm it anymore. If you watch the video below from minute 13 you will see how it is done. In the first part he shows how to make a reflective paint but with risky material and waay more complicated.

The maker of the video above uses Acetone, which you should not handle without gloves! I may have given him this idea through a comment with links and am very happy he picked it up! 😉

How to make it:

  • Prepare Aceton and pieces of acrylic plastic
  • Put pieces of clear acrylic plastic in the aceton
  • Wait untill the acrylic is dissolved
  • Add a bit of aceton to a seringe, mixed with a bit of water 1 (water) to 4 (Acetone)
  • Add the water acetone mixture to the acetone with dissolved acrylic (amount depends on the dryness of the acetone)
  • Now you can apply it as a paint but wear gloves and do it outside close the bottle

The cooling effect in the video above has three causes

  1. Light reflection
  2. Emission by a material
  3. Thermal radiation

Reflection

When light is reflected it just bounces off the electrons, that absorb the energy of a photon and then throw out the same photon. This is why metals are reflective : Lots of electrons, and silver being the most conductive is also the most reflective.

What goes on in the bubble paint is that light bounces off spherical voids in the material multiple times until it leaves the material again.

Emission

Now every material has an absorbtion spectrum, meaning it will absorb light energy of certain frequencies and not of others well. This is because the energy of light in certain bands will push the electrons to another band, one it is used to occupying, and when the electron falls back the light is emitted again. This is what makes some materials emit light in certain frequency bands. The maker says that calcium emits in the infra red region that means the material can cool to outer space. This makes one paint cooler during the day than another, and this is what makes the paint he creates special.

Calcium has some emission bands in the IR, barium has less

Thermal radiation

The idea of radiation is based on temperature. It is based on the energy in the material that can cause photons to be emitted. Because of quantum dynamic principles the light can not contain more energy than is available, which then determines its color. This is why for example LED lamps have a ‘color temperature’ of say 2700 for sunlight and 4000 for bleuish (more higher frequencies). All materials radiate photons, and warm materials radiate infra red photons (we call it heat).

The neat thing about the paints is that thermal radiation happens no matter what, a black material radiates as much as a white material. This is why there is no difference between the paints at night : Its all just thermal radiation. The cool thing is (literally) that if the paint is on a heat conductive material it can suck heat from below and radiate it to the sky all night, but then during the day it will not allow it to heat up.