Aerogel is a material that puzzled the science community due to its impressive physical and chemical properties. Aerogel is a solid material that possesses unique characteristics compared to other solids.
This is the part that induces curiosity in anyone interested in Aerogels. The lightest solid to be ever created on the earth is Aerogel.
It comprised of 97% air while maintaining the structural properties of a solid.
Where did it get the name Aerogel?
The term Aerogel comes from two words – Air and Gel. And there is history to that name!
Aerogel was invented by Samuel Stephens Kistler. Samuel was fascinated by jelly because of its dual nature to act as a solid as well as a liquid.
The reason why jelly has properties of liquid and solid is that it is a combination of both. A porous gelatin structure holds the water within it, creating a pseudo substance.
Samuel wondered what would happen if he replaced the water content with air. However, if the gel was dried simply, it would contract the solid structure, leading to cracks.
He understood that highly microporous structure of the gel collapses due to the high surface tension forces exerted by the liquid. So, he looked into alternative ways to remove liquid without hurting the solid structure.
And, he came up with the idea of replacing water with alcohol.
When alcohol gets converted to a supercritical state, it becomes in a state between gas and liquid, and it will not have surface tension. The solid microporous structure was made using Silica.
Once the alcohol evaporated away, the first Aerogel was formed. In the simplest of terms, Aerogel is made from removing water or solvent from a gelatinous structure.
Physical properties of Aerogel
The reason why Aerogel looks translucent is because of the fact that much of the material is just air. This also explains its very low density.
They are the lightest solids on earth and even a six-foot man-sized block of Aerogel will only weigh about one pound. The Guinness World Record for the lightest 3D printed material is a graphene Aerogel printed by Dong Lin.
Aerogel has other unique physical properties, and one among them is the incredible insulation against heat (0.023 W/mK at 100˚C).
Aerogel also has excellent acoustic properties, boasting 10 to 1000 times better sound insulation than polyurethane forms.
Since the structure consists of just 3% solid, Aerogel is very fragile. The two main solid material used for the preparation of Aerogel is silica and carbon.
How is Aerogel made?
Like we discussed, Aerogel is made by removing water content/solvent from a gel and replacing it with air. The modern method of Aerogel manufacturing uses a process called sol-gel.
The new manufacturing process was developed in 1983 by Arlon Hunt and the Microstructured Materials Group. They used a TEOS or Tetraethylorthosilicate in the production of Aerogel, which is much safer than the TMOS method that was used until then.
Another development was the use of liquid carbon dioxide which replaced the use of alcohol as the base solvent. The use of TMOS and alcohol in Aerogel product made it a very hazardous process.
We have a clear example of their devastating nature in the form of the explosion that destroyed an Aerogel production plant in Sweden.
The new manufacturing process produces the same yield that of TMOS without its dangers.
What are the applications of Aerogel?
The physical characteristics of Aerogel have made it one of the most studied man-made materials. Nowadays, you can find Aerogel in cosmetics, paints, wetsuits, etc.
However, their use in the aerospace industry has only widened ever since their invention. Aerogel was even used to catch comet and interstellar dust in NASA’s Stardust mission.
This unique material was used as the insulating material that kept the Mars Exploration Rover warm during its mission.
One among the modern applications of Aerogel includes using it as an insulating material for buildings.
Aerogel windows is a new technology that sandwiches aerogel between two sheets of glass. They are lighter than triple-layer glass windows and have much better insulation properties.
A new invention called the cotton Aerogel is now making waves in several industries. The cotton Aerogel can be used as an insulating material which can replace conventional bulky jackets.
A surprising application is the use of cotton Aerogel as a hemorrhage control device. The material can be injected into a bleeding wound and it will expand, applying pressure on the wound, stopping it from bleeding.
The Cotton Aerogel bleed controllers were developed by the researchers at NUS.
Why is Aerogel a good insulator?
From its applications, you must have noticed that industries use Aerogel for its insulation property. How does aerogel become such a good insulator?
Aerogel consists of two parts – Silica and Air. The silica solids are not good conductors of heat and they only comprise 3% of the overall material. The rest is air.
When you review the properties of air, it is clear that air has very low thermal conductivity. Such factors make Aerogel very light, making mass conduction impossible.
Secondly, Aerogel has extremely tiny pores, typically between 2-50 nm in diameter. These pores are so small that it is difficult for the air to diffuse through the material and transfer the convective heat.
This phenomenon is known as the 'Knudsen effect', and it separates aerogels from other types of foams.
However, it is important to note that aerogels are not necessarily effective insulators when it comes to radiative heat. It is possible to transfer heat through aerogels at high temperatures through infrared energy.
To counter this, many commercial aerogel insulation products have additional materials. These are known as IR opacifiers to reflect or absorb infrared radiations.
As for electricity, Aerogel can be conductive or nonconductive based on the solids used. Aerogels made with poly (3,4-theylenedioxythiophene): poly(4-styrenesulfonate) (PEDOT:PSS) are generally conductive.
Aerogel solid infused with carbon nanotubes and some other additives have proven to outperform conventional sound insulation by a significant margin.
Is Aerogel waterproof?
Again, such characteristics depend on the solids used in the Aerogel. By changing the solid structures and additives, it is possible to alter the properties of the aerogel. For example, industrial silica aerogel materials are specifically formulated to be hydrophobic (water-repellent).
Oxide-based aerogels are not waterproof. However, they can be easily modified to make them water-resistant using additives.
Why isn’t the Aerogel industry booming?
We have discussed at length about the amazing properties of Aerogel and how it can be of benefit to us in more ways than one. Son why isn’t the technology widespread yet?
There are more than one reasons for that. The first one being the fact that Aerogel is very hard to manufacture, even with the advancements that we have had in term of its production.
The largest Aerogel panels the industry managed to produce was a 90x90 cm panel. And this size is only possible through highly advanced machines.
If you were to search for aerogels to buy, the highest specification that you can find is 30x30cm. Special orders must be placed if you need higher sizes.
The price is another factor that prevents many from using or experimenting with Aerogel. The costly manufacturing process results in that cost being transferred to the buyers.
The result is that a silica Aerogel measuring 2.5 cm x 2.5 cm x 1.0 cm costs upwards of $50.
One of the major challenges faced by the Aerogel industry is the brittle nature of the solid. Make no mistake, the material is strong and can hold many times its weight.
However, the material does not hold up well under tension.
Advancements are happening towards simplifying the manufacturing process of Aerogel and improving its structural integrity. Once these limitations are addressed, Aerogel will get to more people and products.
Lack of industries vested in Aerogel production is also another reason why Aerogels aren’t that popular.
Aerogel is undoubtedly one among the miracle material we have invented. The material has immense potential in its many forms and combinations.
We can expect the limitations associated with Aerogels to lift soon. This will lower the cost of this unique material and improve the production rates.
As the scope of Aerogel applications continues to rise, more companies are likely to invest in Aerogel production. This will eventually improve the tech and help the material reach to the masses.