100 Nano-Stories: Supercritical vs. Subcritical Fluid! 💧

Episode #25: What’s The Difference Between The Two States?

Preface! → ✨

Sure, Carlos! But can you explain it in under 5 minutes? I’m tired from doing homework, so please make it quick!

Hahaha, got you, reader! I’ll make sure to do so! In the meantime, Patrick, you can kick off “Supercritical vs. Subcritical Fluids!”

Photo by KnowYourMeme.com!

What’s A Supercritical Fluid? → ❗

Thanks for the explanation, Carlos, but can you demonstrate how the supercritical state would look like?

Tell you what, reader. I’ll explain the supercritical fluid & the critical point using Supercritical CO2! We will use Supercritical CO2 (SC-CO2) because it is the fluid that will turn the gel into aerogel (replacing the methanol in the gel)!

Photo by Wikipedia!

Now, this may look like a bunch of gibberish, but watch how we decipher the Supercritical CO2 Diagram!

The Critical Temperature of CO2 is 31°C or about 300 Kelvin. That is the temperature required for CO2 to reach the critical temperature.

But Carlos, you forgot the pressure! Remember what you said?

The Critical Pressure of CO2 is 74 bar (Pascals), which is our unit of pressure! We need to reach this specific pressure for CO2 to reach the critical pressure.

But because of the pressure and the temperature, you can pressurize CO2 (74–100 bars) while maintaining low temperatures (40–60°C) to reach CO2’s Supercritical Point! This is what is known as Low-Temperature Supercritical Drying (LTSCD)!

Photo by Aerogel.org!

Cool, Carlos! But if that’s supercritical drying, what’s subcritical drying?

What’s A Subcritical Fluid? → ❗

The Critical Temperature for CO2 is 31°C, and The Critical Pressure for CO2 is 74 bar.

To reach the subcritical fluid of CO2, all you have to do is lower the temperature below 31°C, and the SC-CO2 will go below The Critical Point, returning to a liquid state.

Wait, what? That was it? 🤯

Yup! Subcritical actually means to be below a certain requirement/threshold, and lowering the temperature puts us below the threshold, therefore, we are in a subcritical state.

See what I did there, reader?

Photo by KnowYourMeme.com

Closing Thoughts! → 💭

And I explained the difference between the two states in under 5 minutes!

Hahaha, good job, Carlos! What’s for the next article? After all, you are 1/4 of the way with “100 Nano-Stories”!

Photo by Pinterest!

Vocabulary →📓

Pascal → The SI Unit of Pressure, and is equal to one kilogram per meter per second squared.

Critical Point → The pressure-temperature curve designates conditions under which a liquid and its vapor allow for properties of both liquid and gas to coexist.

CO2 → Carbon Dioxide.

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.

Subcritical Drying → The temperature is below the supercritical temperature of a substance.

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

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