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# Preface! ✨

It’s your favorite material science & nanotechnology enthusiast! To finalize our rabbit hole on the optical properties of aerogels, I want to discuss how to change some of the optical properties of aerogels to get to 100% transparency.

Here is the overview of the article to prepare you for our mini-brain dump! The article is only a 5-minute read! 😄

## TL;DR → What’s Hemispherical Transmittance? 🔑

• Refractive IndexThe reduction of speed of the light and the bending of the light as it passes from one material to another.
• Hemispherical Transmittance Ratio → The sum of the direct and diffuse transmittance of light in the particle of an aerogel.
• The Refractive Index can tell us how much of the light will bend at the surface of the material and when it travels through the material, which can tell us a bit more about the direct and diffuse transmittance of light in the aerogel.
• The Direct-Hemispherical Transmittance Ratio can tell us a ratio/percentage of how much transmittance we can receive, which can tell us more about the transparency of the aerogel.

Author’s Note:

This was an overview of the concept, but if this summary doesn't suffice and you are still confused, please read the article above to grasp all the concepts in their entirety.

Now that we have given the overview, let’s begin today’s discussion on manipulating the optical properties of aerogel!

# Nano-Pulation! 💡

## Where Can We Change The Properties? 🔑

Where do you think the properties of aerogel can be manipulated? It’s not the light.

You can change the properties if you change the aerogel structure, specifically the bulk density and the pores of the aerogel.

The reason why the bulk density is important to take notice of is that it can help determine the refractive index, which is the bending of the light as it passes from one material to another.

To calculate bulk density, you divide the mass by the volume of the aerogel. (m/v)

The reason why the pores of the aerogel are important to transparency and manipulation of the optical properties is that the light will enter the pores on the surface of the aerogel and begin to transmit through the aerogel. The smaller the pores, the less amount of light enters the aerogel.

Okay, but where can we change the properties? 🤔

## Sol-Gel Chemistry! 🔑

The process where aerogel is made is called the “Sol-Gel Process.” This same process is where all the properties of aerogel can be manipulated to increase the transmittance of light through the aerogel and have maximum transparency!

However, there is a section in the Sol-Gel Process which determines what will happen with all the optical properties in the aerogel: “The Aging Process!”

In the aging process of aerogel, the silica gel network will have time to strengthen and allow for the pores to slowly decrease in size/diameter, along with the bulk density to around 0.1 g/cm³, which is really low. (Air’s density is 0.001225 g/cm³.)

The final step towards transparency is Supercritical Drying, which is where the pores can shrink even smaller, which allows the Refractive Index to get closer to 1, which I will discuss soon!

# Closing Thoughts! 💭

This was a good introduction to Sol-Gel Chemistry, but I will have to make a new article explaining the importance and definitions of Sol-Gel Chemistry!

The intention behind this article was to explain how optical properties are an outcome of chemistry!

All the optical, mechanical, and thermal properties are determined by the chemistry of the aerogel! 💥

See you tomorrow to Introduce Sol-Gel Chemistry! 👋🏽

# Vocabulary! 📓

Refractive IndexThe reduction of speed of the light and the bending of the light as it passes from one material to another.

Density Mass per unit volume of a material/substance. (m / v)

Mass How much an actual object weighs.

Volume The amount of space that a 3-dimensional object (like aerogel) takes up.

Hemispherical Transmittance Ratio → The sum of the direct and diffuse transmittance of light in the particle of an aerogel.