Does anyone else remember the Muppet Show skit called “PIGS IN SPACE“?  Actually, it was called “PIIIIIIIIIIIIIIIIIGSSSS IIIIINNNNNNN SPAAAAAAAAAAAAACE,” mainly because in outer space distances are vast and despite the fact that sound doesn’t travel through a vacuum, all announcements about astronaut pigs really should be made with excessive reverb.  I don’t really have any more time to go on about the pigs but I bring them up because they are hilarious and because they were the first thing I thought of when I heard about Cellulose Aerogel, which is the material I’m about to describe in excruciating detail over the course of this post.

Image courtesy madsilence.wordpress.com

Three score and ten years ago, a bunch of scientists invented aerogel, a material so air-entrained that it makes angel food cake seem as dense as a lead ingot.  As an insulator, aerogel is “four times more efficient than fiberglass or foam … according to Dr. Peter Tsou of NASA’s Jet Propulsion Laboratory, ‘you could take a two- or three-bedroom house, insulate it with aerogel, and you could heat the house with a candle. But eventually the house would become too hot'” (Fox).  Aerogel is lightweight, efficient, flameproof, vapor-permeable, and more plastic than fiberglass or foam insulation.  And, until recently it has been prohibitively expensive.

Image courtesy Aspen Aerogel

You make aerogel by first constructing a conventional gel, and then replacing the entrained liquid though supercritical drying.  If you’re thinking supercritical drying involves some pretty harsh language and a lot of gelatinous tears, think again.  The process is “accomplished by increasing the temperature and pressure of the solvent phase inside of the gel structure beyond its critical point. This ‘supercritical’ extraction condition lowers the surface tension between the liquid and the solid pore surfaces so that depressurization of the system at temperatures above the critical temperature leaves the pore structure filled with gas. The resultant material is 90 percent air, but retains the structure and rigidity of the non-liquid gel components” (Source: Aspen Aerogel). 

Image courtesy Aspen Aerogel

I’m thinking of this kind of like a salad dressing where you mix oil and vinegar together vigorously, so that tiny droplets of vinegar are suspended in the oil.  The supercritical part is that you basically zap the vinegar out and suddenly the oil has tiny pores in it where the acid used to be … only the salad dressing is more solid than oil, really it’s kind of like swiss cheese…. Hmmm maybe the culinary metaphor was the wrong way to go. 

Anyway, you might want to grab a chair at this point because you’re not going to believe this next part and you might fall down if you’re standing up because I mean really, who comes up with this stuff???

Researchers (I know not where) decided to soak some cellulose, which is the structural component of plant cells from which we make paper and cardboard, in a solution of metallic nanoparticles (like ya do).  In case you’re taking notes, the solution was comprised of iron sulfate and cobalt chloride, so the cellulose fibers took on the properties of metal and became magnetic.  Next, in order to turn this crazy wood-metal cocktail into an aerogel the researchers freeze-dried the nanoparticle-infused cellulose, leaving behind a lightweight, moisture-free, porous mesh of solid fibers.  This resulted in “a flexible, lightweight, super-absorbent sponge that can also be crushed down into a flat piece of magnetic “nanopaper” capable of supporting 400,000 pounds per square inch” (Dillow).  Or to put it another way, it can support the weight of approximately 33 adult male elephants per square inch.

Image courtesy www.popsci.com (The Aerogel is supporting a brick).

The resulting material can be flexed and folded, and it’s highly absorbent.  If you hammer the air out of it, you are essentially left with a piece of magnetic paper that can support the weight of the aforementioned elephants.  Applications for a “super-strong, flexible, absorbent, magnetic sponge” abound in materials science: for example, it could easily find a home in “microfluidic devices like fuel cells or used to make small actuators” (Dillow).  I could also see how it might be incorporated as a filter or used to insulate submarines.

WU XING:

Filing under wood and metal – this was a no-brainer.

Cited:

Dillow, Clay. “New Flexible Cellulose Aerogel is both a Magnetic Sponge and a Flexible Nanopaper” Popsci.com 08/09/10.  Accessed 10/26/10.  URL.

Fox, Stuart. “Superinsulating Aerogels Arrive on Home Insulation Market at Last” Popsci.com 02/04/10. Acessed 10/26/10. URL.