Liquid-mixing to make aerogels

Author

Neil Baugh
October 25, 2023

TLDR: Taking advantage of poor liquid mixing to design better nanopatterned aerogels

Big Takeaways

  1. Aerogels are extremely low density materials made mostly of air — think sponges on steroids.

  2. They’re great heat insulators, but are brittle and hard to design.

  3. Using the idea that some liquids don’t mix well, scientists created aerogel nanoparticles that improved the strength of the gels.

The Problem

Aerogels are solid material scaffolds made up mostly of air. Practically speaking, they’re empty scaffolds of material with interesting properties. Think of a wine cork or a sponge, but remove 99% of the solid material in them and make it air.

They’re lightweight, sound proof, resistant to heat, and look almost ghostly in the light. Place a flower on one and light a blowtorch beneath it: nothing happens.

Flower petal resting on an aerogel. Courtesy of Lawrence Berkeley National Lab.

But they’re historically hard to control. The large fraction of air makes them weak and hard to customize for specific applications. A common way of dealing with both those problems is to pattern the gels on the nanoscale.

This week’s paper introduces a new liquid-based 3D printing approach to make aerogels out of nanoparticles

The Solution

This week’s authors used one important concept to make their discovery; some liquids don’t mix. Water and oil for example.

By controlling how the incompatible liquids are put together, you can make nanoparticles of defined sizes where the two liquids meet. You can then physically squish these nanoparticles together and they’ll behave as one larger solid. However, when made of jammed nanoparticles instead of the normal material, the solid becomes stronger and more mechanically robust.

So, the authors did exactly this to make nanoparticle-based aerogels. Then, they 3D printed them to give even greater control over the properties.

Nanoparticle aerogels sitting on cactus hair (a), flowers (c), and conducting electricity (d). Credit: Seyyed Hashemi and Mohammad Arjmand, Adv. Mat. 2023.

They made their aerogels out of different materials with varied properties suited for different applications. These gels are so light they can sit ontop of thin cactus hairs or flowers without moving a petal out of place. I’m not sure why they decided to make them into the shape of a pile of spaghetti, but hey, science is a mystery.

The strength, electrical conductivity, and oil absorption could all be controlled by changing the composition of the gels and their manufacturing process. Importantly, they made their gels much stronger by using the liquid-formed nanoparticles.

Given their extremely low solid content, aerogels make for promising absorbers of liquid pollutants like oils. The oils can replace the air inside the gels, making them extremely efficient sponges.

In this work, the aerogels absorbed roughly 345x their own weight of diesel oil. They were equally effective for other oils and liquid pollutants.

Aerogels absorbing oils. Credit: Seyyed Hashemi and Mohammad Arjmand, Adv. Mat. 2023

Overall, this work gave a new approach to design and fabricate aerogels with a wide range of controllable properties (conductivity, strength, absorption, magnetism, etc).

See you next week for more science,

Neil

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