Aerogel: Hydrophobicity

Week #32: The Weak Link

Carlos Manuel Jarquín Sánchez
3 min readApr 23, 2023

Preface! ✨

Hello everyone!

My intentions for writing these articles are:

  • Explain technical information about aerogels in simple terms (to the public)
  • Store information and habits for my future self and others (in <7 minutes)

Coolio? Sweet. Enjoy the series :-)

The Catastrophe ⚛️

Most of the information is definitions of words used in aerogel textbooks. I simplified the words from their advanced bullshit for public readers to understand.

I’ve made a mistake…

A mistake that may cost me the aerogel itself.

I forgot about the hydrophobicity of the aerogel.

Alginate is a hydrophilic material; it loves water.


Because of its -OH groups (hydroxyls).

See the OH everywhere?

But to make the final aerogel, I need to make it hydrophobic.

It must repel water from making contact with the alginate.

So, now what do we use?

Polybutyl methacrylate.

Yeah, that’s a mouthful of a chemical.

So now what?

Let’s break it down.

Poly → Greek word for “many”


  • But → Four carbons in the primary molecule/compound chain.
  • yl → Bonded parts of molecules attached to a larger backbone; It is not part of the main carbon chain.

Meth → Not the okie coke. It’s one carbon atom.


Methacrylate is a monocarboxylic acid anion.

Mono → Greek word for “One, Only”

Anion → Negatively Charged

Carboxy → R−COOH group

“R” → CH3 group, methyl group

Acrylate Group

This is what polybutyl methacrylate looks like.


So how do we know it’s hydrophobic?

The methyl & methylene groups on the sides!

Anything molecule/compound made up of carbon & hydrogen only will have the ability to repel water. (also known as hydrocarbons)

Methyl Group → CH3

Methylene Group → CH2


Non-polarity & Electronegativity.

Each molecule has a charge. When you subtract all the different elements in a molecule, you’ll have three options:

  • Ionic Bonding - Electronegativity: > 1.7
  • Polar Covalent Bonding (Loves Water) - Electronegativity: 0.5 ≤ x ≤ 1.7
  • Non-Polar Covalent Bonding (Hates Water) - Electronegativity: < 0.5

Carbon has an electronegativity of 2.5

Hydrogen has an electronegativity of 2.1

Subtract bigger number minus smaller number.

2.5 - 2.1 = 0.4

That’s why hydrocarbons are hydrophobic.

But How Does It Bond In The Aerogel?

Polybutyl Methacrylate does what all other previous steps followed:


Sounds straightforward:

Polybutyl looks for a chemical, an atom, in the gel bead to bond to & create the hydrophobic groups to create the water-repelling aerogel.

It cross-links with the help of Calcium Chloride (CaCl2).


It’s not that simple.

You would need to add another element into polybutyl methacrylate.

We would need to add amine groups.

The final product would be an amide group + polybutyl methacrylate.

I talk more about this phenomenon in this article.

But either way, that’s it!

I’ll make an in-depth explanation of this in the upcoming 10 days.

I’ll be building some funds to make v1 of this filter.

After that, who knows where the shipping value will take me…

All for the vision of seeing the village thrive. 🏠

Connect →🔗



© 2023 by Carlos Manuel Jarquín Sánchez. All Rights Reserved.