100 Nano-Stories: UV Rayleigh Scattering!

Episode #49: Transparent Aerogel!

Carlos Manuel Jarquín Sánchez
4 min readMar 22, 2021

Preface! ✨

It’s your favorite material science & nanotechnology enthusiast! Today, I want to share with you my idea on Aerogels to enhance them for real-world applications!

However, to do so, I will need to discuss one key feature in aerogels: Rayleigh Scattering!

Got you, reader! Let’s give you a brief understanding of what Rayleigh Scattering is!

Rayleigh Scattering Explained! 💡

Review! 🔑

When light from the cosmos enters the Earth’s atmosphere, it will confront dust particles and molecules that are abundant in the atmosphere (in the air, there is mostly nitrogen and oxygen). When this occurs, the light will bounce from one molecule to another, sort of like a bouncy ball hitting two walls. This type of bouncing of light being redirected is called scattering. However, some of the particles/molecules in the air have the same size as the wavelength of the blue light/color. The blue light wavelength is 450–485 nanometers.

The equation of Rayleigh Scattering is proportional to 1 divided by the wavelength raised to the 4th power. This means that if the wavelength of a certain ray of light is short, then the wavelength of light will scatter more than a ray of light where the wavelength is larger.

The same thing happens in aerogels! The nanoscale network of pores in the aerogel scatter the light that goes through it with the same intensity mentioned in the photo!

Well, that’s interesting, Carlos! But how do we get to Ultra-violet (UV) Scattering?

UV Scattering!

If you want to reach lower or higher intensity wavelengths of light, I want you to think of a sunset!

In this sunset, the sun is farther away from us than midday. That means the wavelengths of light have gotten longer, and if wavelengths of light get longer, the intensity of the light goes into the wavelengths of yellow, orange, and red.

But the other reason why this sunset looks deep red and bright is that there are enough particles that have the same wavelength as red (620–750 nanometers). But the brighter parts of the sunset don't have enough particles to make the rest of the sunset a darker shade of red!

So it’s about the number of particles that you have and the intensity of the light to render colors such as the ones we have in the sky/sunset!

Now, if we want to make an aerogel that scatters UV Light to make it transparent/“invisible” in visible light, we do NOT make the pores smaller!

We have to make the light that passes through the aerogel go directly through the aerogel! Sometimes, the light will get redirected because of the nanopores, and the light could get redirected or absorbed! Because the light is absorbed, it will also absorb the blue wavelength of light! That is one reason that aerogel will have the blue light!

So to have a transparent aerogel, we have to focus on the number of particles AND the pores that make the surface of the aerogel! The reason why is because the pores will allow light to come into the gel, but the particles can scatter the light around, which could potentially absorb the light! 🧠

Closing Thoughts! 💭

Well, now we know how to change the laws of light to our doing thanks to the number of particles and pores in an aerogel! 😈

🎉 See you in the next article for my idea on aerogels! 🎉

Vocabulary! 📓

Silyation → The integration of a silyl group known as R3-Si. The letter “R” in organic chemistry usually means a methyl group known as CH3.

Rayleigh Scattering → Light rays are being redirected in different directions on passing through particles/atoms/molecules that are comparable to the wavelength of the light.

Spatial Arrangement → The property is possessed by an array of things that have space between them.

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