100 Nano-Stories: Sol-Gel Chemistry!

Episode #86: Chemistry & Material Science (Sol-Gel)!

Carlos Manuel Jarquín Sánchez
4 min readMay 2, 2021

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Preface! ✨

It’s your favorite material science & nanotechnology enthusiast! Finally, time to introduce Sol-Gel Chemistry at the fundamental level!

There is no article to prepare you, reader! Let’s begin today’s topic! 😄

What’s Sol-Gel Chemistry & Processing? 💡

Definitions! 🔑

The definition is in the word “Sol-Gel”!

Sol comes from the word “Solution.”

Gel comes from the word “Gel.”

Sol-Gel Chemistry means a solution of either a metal or carbon-based precursor with ethers to form a polymer. this polymer will create a vast network of polymers bonded to each other, creating a gel!

Polymers are a chain of many repeating/identical large molecules that make up a material.

Precursors are chemical compounds that participate in a chemical reaction to produce a new compound/molecule.

The Process! 🔑

To create silica aerogels, the “sol” starts as a liquid solution of colloidal nanoparticles.

A colloid (colloidal) is a particle that is in the range of 1 nanometer to 100 nanometers in diameter/size. But because these small particles are in a liquid (suspension), we call this a colloidal suspension.

A suspension is a mixture where the composition isn't the same in every single place of the mixture (heterogeneous). In this heterogeneous mixture, there is a distributed solid in a liquid. The solid in this case are the particles (colloid).

The liquid in the gel makes sure that the solid network of particles doesn’t collapse, and the solid particles make sure the liquid doesn’t escape (more information in a new article later!) 😄

In most cases, the precursors (main chemical) to begin creating hydrophilic silica aerogel are either tetramethoxysilane (TMOS) or tetraethoxysilane (TEOS).

TMOS Precursor

The main precursor in creating hydrophobic silica aerogel is commonly known as methyltriethoxysilane (MTES).

MTES Precursor

However, the silica atom has a partial positive charge (or lack of negative charge due to loss of negative charge) (δ+) ≈ 0.32 in TEOS. This means that the silicon atom (Si) tends to lose its Valence Electrons (VE) in its outer shell to the oxygen atoms attached to the silicon atom.

Oxygen has 6 valence electrons, and it takes one electron from silicon and methylene (CH2), which makes 8 valence electrons and fills up its outer shell.

This means that the negative charge is shifting away from the silicon atom in TEOS Precursor.

Bonus:

CH2 has 6 valence electrons, and it “borrows” two valence electrons with a methyl group (CH3) and Oxygen, so both the Carbon atom and Hydrogen Atoms have their outer electron shells full.

CH3 has 7 valence electrons in its outer shells, so it “borrows” an electron with CH2 to fulfill the carbon and hydrogen outer electron shells.

Closing Thoughts! 💭

Having all this information in mind gives you a sneak peek into how we can change mitigate the partial positive charge in the silicon atom via a catalyst and hydrolysis!

See you soon to explain how hydrolysis and catalysts can help us in the gel processing of silica aerogels! ✌🏽

Vocabulary! 📓

Sol“Solution.”

Gel“Gel.”

Sol-Gel ChemistryA solution of either a metal or carbon-based precursor with ethers to form a polymer. this polymer will create a vast network of polymers bonded to each other, creating a gel!

PolymersA chain of many repeating/identical large molecules that make up a material.

Precursors Chemical compounds that participate in a chemical reaction to produce a new compound/molecule.

Colloid (Colloidal) A particle that is in the range of 1 nanometer to 100 nanometers in diameter/size.

SuspensionA mixture where the composition isn’t the same in every single place of the mixture (heterogeneous).

Catalyst → A chemical that speeds up a chemical reaction without being affected; and it lowers the activation energy of the reactants so the reaction between two compounds can occur and form the new compound.

Hydrolysis → The chemical breakdown of a compound/molecule due to a water reaction with the compound.

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© 2021 by Carlos Manuel Jarquin Sanchez. All Rights Reserved.

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