As materials science continues to advance, the definition of what is a solid becomes increasingly hard to pin down. Super-light aerogels have been a target of research for decades, getting less dense as new variants are developed. Now a team of researchers from China’s Zhejiang University in the Department of Polymer Science and Engineering have broken the record for the lowest density solid to date with a new type of aerogel, and they owe it to our old friend graphene.
Aerogel is usually composed of silica or carbon compounds and is highly-prized for its durability and thermal insulation properties. This family of substances is sometimes called “frozen smoke” due to its hazy appearance. In 2012 a type of aerogel composed of graphite (dubbed Aerographite) took the crown as the least dense solid at 0.18 mg/cm3. The Zhejiang University graphene aerogel edges that out with a density of just 0.16 mg/cm3.
To put those numbers in perspective, the new aerogel has a lower density than helium and only twice as much as hydrogen. Regular air, like you’re breathing right now, has a density of about 1.2 mg/cm3. That’s 7.5 times heavier than graphene aerogel. Yes, it’s less dense than air, but this near-magical substance is still a solid. A sample of graphene aerogel a few centimeters across is so light that it can be supported by delicate plants as seen above.
The Zhejiang University lab, led by Professor Gao Chao, created this material by expanding on techniques previously used to make two-dimensional graphene films. This is the key to the incredible lightness of the materials. Graphene is composed of a single layer of carbon atoms, and researchers found they could simply use a freeze drying process to stack them in three-dimensions.
Solutions of carbon nanotubes are used in the drying process, eliminating the need for a template, as with most aerogels. The size of the gel is dependent on the size of the container it is made in,according to Gao. He believes the technique could be used to make aerogels thousands of cubic centimeters in size. The nanotubes act as a stabilizing structure holding the layers of graphene together allowing for easier production.
Graphene aerogel has some incredible properties that could see it used in many industries. For example, it’s incredibly elastic, returning to its original shape after being compressed. It’s super-low density also makes it highly absorbent. One gram of aerogel can absorb up to 900 times its own weight in organics like oil. There may come a day when environmental cleanup consists of spreading bits of graphene aerogel around to be scooped up later.
Beyond the environmental aspects, this material could have applications in energy storage and transfer. Graphene itself has been studied extensively for its high conductivity. It’s pretty amazing stuff.