100 Nano-Stories: Intro To Aerogel And Xerogel!

Episode #10: Brief Intro To The Drying of Silica Gels!

Carlos Manuel Jarquín Sánchez
4 min readJan 7, 2021
Dried Silica Aerogel! Photo by Institute of Making.


Hey, hey, aerogel enthusiasts! Now that we talked about the mathematics of the aging of silica gels, it’s time we move on to the next stage of silica gel production: the drying of silica aerogels!

Uh, Carlos, I’m new here to your series on “100 Nano-Stories”, so can you please give me your previous article on silica gels?

Thank you, Carlos! You’re a real life-saver!

As a bonus, I will also be including vocabulary terms and extra resources at the end for anyone who got lost in the article or for anyone interested in diving more into the topic, reader!

Thanks, Carlos! But I was reading your subtitle, and I was wondering if I could ask you about the content of today’s article.

Go ahead, reader! What did you have in mind?

Instead of talking about the drying of aerogels, can you talk about what types of silica gels we can make out of the drying process instead? Pleaseee? 🤞🏽

Well… alright, then! I’ll talk about the types of silica gels we can produce and some quick facts about them! Then we can talk about the drying process in the next article! Deal?

It’s a deal, Carlos! 😁

Gel-Drying Process

The drying of the gels is where we can determine if we end up with aerogel, a xerogel, or a cryogel. There have been so many methods of drying, but the most common ones are:

  • Supercritical Drying
  • Evaporation
  • Subcritical Drying

So, which ones end up with Aerogel or Xerogel, Carlos?

Almost there, reader! Drying the gel allows for the pores to be free of the solid structure from the liquid in the lords, otherwise, this would cause capillary action, which is what would cause the structure to collapse, and we don’t end up with our precious silica aerogel! That’s no Bueno, reader!

Hmmm… now I see why you wanted to prepare us…but seriously, can you at least tell us what process gives yo what type of gel?

Yup! Supercritical & Subcritical Drying will result in Aerogels, and Evaporation/Thermal Drying will result in Xerogels!

An aerogel is kept/obtained when the liquid is successfully removed and replaced with gas, with either a minuscule shrinkage of the gel or no shrinkage of the gel. As previously mentioned, this can be obtained via supercritical drying or subcritical drying.

A xerogel is kept/obtained when the entire structure undergoes drying, but slowly at room temperature. Sometimes it can retain the structure, but the material will have so many cracks, and about 85–90% of the gel structure will shrink.

Finally, allow me to demonstrate how these two gels look like!

See the difference? Photo by Notice.

Woah! I am so excited about your next article, Carlos!

Thank you! See you tomorrow, reader! 👋🏽

Vocabulary 📓

Capillary Action - The ability of a liquid to flow against gravity in a narrow space such as our silica gel network. If unable to, the entire structure can collapse.

Aerogel - The world’s lightest solid that is produced by the removal of the liquid component from a conventional gel.

Xerogel - A very light solid (similar to aerogel) caused by drying/evaporating with rapid shrinkage of the gel.

Supercritical Drying - Liquid in a gel/substance is being transformed into a gas with the absence of the surface tension and the capillary stress of the gel. It’s what allows for a silica gel to transform into an aerogel.

Surface Tension - It’s what allows for the bulk of a liquid molecule to have less surface area. In elementary terms, a liquid surface will shrink to the minimum amount of surface area possible.

Capillary Stress - The pressure between two fluids that are unable to become a homogenous mixture, and this mixture is trapped in a thin tube. For aerogel, the inhomogeneous mixture has capillary stress, and this “thin tube” is our network of silica nanopores.

Homogenous - A mixture/structure where the composition is uniform in every location of the mixture/structure.

Resources 💻

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