100 Nano-Stories: Silylation!
Episode #48: Hydrophilic Aerogel → Hydrophobic Aerogel (Part 3)!
Preface! ✨
It’s your favorite material science & nanotechnology enthusiast! Before we get into today’s topic, let’s discuss some brief concepts real quick!
The article below is a must-read to proceed to the following article! The article is only 7 minutes long! 😁
The essential points in the previous article are as follows:
- Essentially, any molecule that is composed of only oxygen and hydrogen (water) will have polar bonds. Therefore, the molecule will be polar.
- Essentially, any molecule that is composed of only carbon or hydrogen will have non-polar bonds. Therefore, the molecule/organic compound will be non-polar.
- Polar Molecules → Hydrophilic Aerogel.
- Non-polar Molecules → Hydrophobic Aerogel.
- Hydrophilic Aerogels will absorb water and destroy the aerogel.
- Hydrophobic Aerogels will repel water and bounce away from the aerogel.
If you want to know about the first & second way to turn a hydrophilic aerogel into a hydrophobic aerogel, I will add the article towards the end!
Now that we got all of the new readers caught up with the articles, let’s move on to how to convert a hydrophilic aerogel to a hydrophobic aerogel!
The Silylation Method! 💡
The Process! 🔑
In simple terms, silylation is the technique to change the surface chemistry of the wet gels before they undergo any kind of drying (supercritical, subcritical, ambient, etc.)
The wet gels are prepared with sol-gel applications & chemistry, and then proceed towards the solvent exchanges & reacting with a silylating agent to change the surface of the aerogel to have non-polar groups!
It means it’s cool, reader! 😅
But you’re right, let me explain the reaction to you! 😁
Sol-Gel Chemistry! 🔑
Sol-Gel is the process where solid materials from solid nanoparticles from small molecules. This means that these solid nanoparticles form together to create a network of nanoparticles that bundle up in a liquid (or in this case, a gel!).
A catalyst is a substance that can increase the rate of a chemical change without the substance undergoing any permanent chemical change. One example of a catalyst is an enzyme: it increases chemical changes in your body without the enzyme itself undergoing a chemical change!
Silyation is integrating a silyl group known as R3-Si. The letter “R” in organic chemistry usually means a methyl group known as CH3. R → CH3/Methyl Group. Si → Silicon.
Q & A! 🔑
But what silylating agents work for the aerogel to go from hydrophilic to hydrophobic?
Anything that contains the R3-Si molecule! This molecule will be the hydrophobe that can convert the surface chemistry of the aerogel from hydrophilic to hydrophilic aerogel.
But why does the R3-Si molecule work to make the surface of the aerogel non-polar, therefore, making the aerogel hydrophobic to water?
The electronegativity of a Carbon atom is 2.5. The electronegativity of a Hydrogen atom is 2.1. The overall difference in electronegativity is 0.4, which is less than the required 0.5 difference in electronegativity. The difference in electronegativity results in a non-polar/hydrophobic molecule.
Essentially, any molecule that is composed of only carbon or hydrogen will have non-polar bonds.
The silicon atom has an electronegativity of 1.9, which is higher than 0.5. However, because of the 3 methyl groups, the electronegativity of silicon “cancels” out, and it won’t be enough to make the molecule polar. So the aerogel stays hydrophobic.
Closing Thoughts! 💭
Ahh, how we love silylation! Now we understand how electronegativity made the difference in solving this problem!
Now you understand the interesting reaction, Jack Skellington! 😏
Ok. . . looks like you’re not amused, but if that doesn’t cheer you up, we are two articles away from reaching 50 Stories!
See you soon on Ultraviolet Rayleigh Scattering! ✌🏽
Vocabulary! 📓
Hydrophilic Aerogel → Polar molecules are attached to the surface of the aerogel. Hydrophilic Aerogels will absorb water.
Hydrophobic Aerogel → Non-Polar molecules are attached to the surface of the aerogel. Hydrophobic Aerogels will repel water.
Polar molecules → The electrical charges of the molecule are not evenly distributed. The OH group is a polar molecule commonly found on the surface of hydrophilic aerogels. Polar molecules are hydrophilic.
Non-Polar molecules → The electrical charges of the molecule are evenly distributed. No positive or negative charges are formed in the molecule. All alkanes, alkenes, and alkynes are non-polar molecules because they are composed of carbon and hydrogen.
Electronegativity → The chance that a pair of elections will be attached to a certain atom. If the difference between the electronegativity is greater or equal to 0.5, the molecule is polar. If the difference in electronegativity in the molecule is less than 0.5, the molecule is non-polar.
Sol-Gel Process → The process where solid materials from solid nanoparticles from small molecules. This means that these solid nanoparticles form together to create a network of nanoparticles that bundle up in a liquid (or in this case, a gel!).
Catalyst → A substance that can increase the rate of a chemical change without the substance undergoing any permanent chemical change. One example of a catalyst is an enzyme: it increases chemical changes in your body without the enzyme itself undergoing a chemical change!
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.
R → CH3/Methyl Group.
Si → Silicon.
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