The Future is a Porous Solid

Article by Astoria Jellett

It’s called aerogel, and it is the future.

Actually, it’s already eighty years old. Like many a great invention, aerogel purportedly resulted from a competition between a couple of dweeby guys, this time to see if they could replace the liquid of a jelly with a gas, without causing the structure to shrink. Chemistry professor Samuel Kistler published his victorious findings in a 1931 issue of Nature.

Kistler’s original process involved replacing the liquid of a jelly with more and different, miscible liquid, placing it in a closed autoclave, then raising its temperature while maintaining pressure, so that the liquid transforms into a gas without evaporating, and with no disturbance to the gel structure.

“The jelly has had no way of‘knowing’ that the liquid within its meshes hasbecome a gas,” Kistler wrote. “All that remains is to allow the gasto escape, and there is left behind a coherent aerogelof unchanged volume.” It’s basically like a tiny beehive, a porous network that can be made with a variety of materials. “So far, we have prepared silica, alumina, nickeltartarate, stannic oxide, tungstic oxide, gelatine,agar, nitrocellulose, cellulose, and egg albumin aerogelsand see no reason why this list may not be extendedindefinitely. Apart from the scientific significanceof these observations, the new physical propertiesdeveloped in the materials are of unusual interest.”

Unusual interest indeed. Aerogel is one of the lightest materials in the world, with an extremely low density and low thermoconductivity. That makes it an excellent insulator – NASA has already used it in space suits and the Mars Rover, and the Georgia Institute of Technology used it in its 2007 Solar Decathlon house project as part of the skylight. That’s the other thing – it looks like frozen smoke, because its nano-sized dendritic structure scatters light the same way our atmosphere does, appearing blue against dark backgrounds (re: the sky) and yellow against bright ones (re: the sun).

It is extremely strong, able to hold up to 4,000 times its weight. However, it does not behave like a gel at all – extremely brittle, it shatters like glass. A chemical treatment can also make aerogel water-repellant and therefore less degradable.

Four years after publishing his findings, Kistler signed a contract with Monsanto (of “March Against Monsanto” fame) to produce a line of silica aerogel products, mostly flattening agents for paint. (It can also thicken cosmetics.) But Kistler’s method was rather costly and time-consuming, and the line was discontinued in 1970. But it wasn’t long before aerogel experienced a rebirth in popularity, when researchers developed a faster production method using supercritical drying.

Now, we can use aerogel in just about anything.

Combined with fibrous material, we can make blankets. (Weaving it with fiber solves the brittle problem.) It can clean up chemical spills and purify water through adhesion. In addition to insulation, NASA also uses aerogel to trap stardust. It makes a great electromagnetic shield, drug delivery system (Did I mention it’s biocompatible?), and it’s already in Dunlop tennis racquets and our batteries. Aerogel can be spun to cover aircraft wings to prevent ice from forming and Chevrolet put it in their new C7 Corvette to contain the heat of the transmission tunnel. Most recently, Google used it in their Nexus 7 tablet.

And to top it all off, you can even make aerogel at home.