So in fluid mechanics we were learning about carbon nanotubes. These tiny cylinders (about 10E-09 m in diameter, hence the name) are likely to revolutionize many sectors of industry. They are made out of carbon, with a unique chemical structure making them extremely strong. Like diamonds, they are made of carbon, and their bond structure makes them even stronger than diamonds, depending on which way you try and break them. They tend to aggregate into ropes, and you can fuse them together, creating the possibility of making them into extremely strong wires. They are also good at conducting heat.

So. How does this have to do with a pair of water scissors?

Well, given that carbon nanotubes are so strong, they are exceedly difficult to cut. Engineers would like to cut them to whatever length they desire for their projects, but now they have to deal with the fact that they're going to be whatever length they grow to be (perhaps a couple microns). Thus the problem was put to researchers: How can we cut a micron-scale nanotube accurately when its bonds are stronger than a diamond's? We must make a pair of nanoscissors!

One group tried to do it chemically, sort of how some people cut DNA. But they had to use extremely strong chemicals, and they always ended up destroying the carbon nanotubes instead of cutting them.

Another laboratory decided to cut them physically by mixing them with extremely tiny bits of zircon (a very hard and resilient mineral), and then shaking the container. Unfortunately, this method also usually reduced the carbon nanotubes to bits or damaging them instead of cutting them.

Enter the group at Brown. Fluid mechanicians, they decide to cut the carbon nanotubes using water. How? Cavitation, of course!

Cavitation is a process by which turbulence or disturbences (pressure waves, what have you) in a liquid cause tiny areas where the pressure is low enough for the liquid to turn into a gas. This is kind like boiling, except boiling is usually accompanied by temperature rising enough to turn the liquid to a gas, because the state of a material is dependent on both temperature and pressure. But even when boiling, the first bubbles usually nucleate on contaminating particles or along the wall of the container, where local pressure is slightly lower.
After these bubbles form, they almost immediately collapse after the pressure goes back to normal. They collapse at super-sonic speed, and because the process is adiabatic, as the volume shrinks, the temperature goes way up-- to the tune of some 5000 degrees C. The energy produced very locally by this process is so high that the popping bubbles often give off sparks as they collapse, as well as pressure waves that can be heard as very loud sounds.

This aspect of cavitation makes it a huge engineering concern, and a big concern for secret spy nuclear submarines (see: Hunt for the Red October, "We're cavitating!!!") Cavitating makes a huge number of extremely loud pops, which can be easily picked up by the sonar on other vessels (i.e., Commies!!). The skins of submarines are optimized to reduce cavitation as much as possible, but it depends on what maneuvers you are doing. Cavitation can also happen in pistons and pipes and near the propellors of ships. The energy from the popping bubbles wears huge pits into the metal in these systems, incurring a large cost and necessitating the replacement of parts well before they should be worn out.

Cavitation is also a concern when using ultrasound on the body, because pressure waves like those used in ultrasound, if it's turned up too high, can induce cavitation in your blood, wreaking havoc on the nanostructures in your vessels. (Don't worry, they never turn it up that high!)

Cognizant of the effect of cavitation on nanostructures, the people at Brown decided to see how carbon nanotubes reacted to cavitation. As it turns out, if you put a lot of carbon nanotubes into water, when the bubbles form, the nanotubes are attracted to the low pressure region and in a sense adhere to the surface of the bubble. When it collapses, the surface area over which the nanotubes are spread decreases drastically, and the nanotubes buckle... along eigenmodes!

If you imagine pushing a rug from either side, the rug will buckle in a series of folds that are usually evenly spaced. These are the eigenmodes of the rugs, and the spacing between them would be the eigenspacing, as eigen just means "characteristic" in german. But you can change the eigenspacing of your rug by pushing it together with different energies. (It will also have different eigenspacing depending on how stiff a rug it is. You can imagine that a doormat might have only one eigenmode, while a blanket would have a lot.)

So, by controlling the size of the bubbles that form (by controlling the kind of sonic waves that initiate the cavitation), you can cut the carbon nanotubes to pretty much any length you want!

Using scissors.... MADE OF WATER!!!

Anyway, that was a really cool class.

Speaking of diamonds,
have you seen... Diamonds in the microwave?
» ikimashokie on 2008-02-16 01:52:40

Add that to random's list of ways to die.
Death by cativation of the blood. Ew. Did you know that the pistol shrimp uses the same phenomenon to stun or kill prey?

Of course you did.
» middaymoon on 2008-02-16 02:25:27

The chemical properties of carbon nanotubes (and other carbon nanostructures like fullerenes) are interesting as well. While carbon is normally thought to act more like an insulator than a conductor, carbon nanotubes have pi bond delocalization along their surfaces, making them great conductors. Altering the arrangement of pi bonds over the surface through chemical means can also transform carbon nanotubes into semiconductors. There's a lot of research going into using carbon nanotubes in circuits and other electrical applications.

Carbon chemistry is so awesome. All hail the tetravalent element--the basis of all life as we know it (or rather, as we have confirmed exists)!
» ranor on 2008-02-16 02:55:29

Oh, and by the way.
I've read that microtubials in brain cells give our brains their ability to tap into quantum fluctuations that are too small to normally make any chemical differences. How neat is that?
» middaymoon on 2008-02-16 05:59:53

Re:middaymoon
That's hotly debated. The idea of quantum consciousness/quantum mind is a fringe theory in modern neuroscience and physics. I think the idea itself is very cool, but we are a LONG way away from a paradigm shift in the direction of quantum consciousness.
» ranor on 2008-02-16 10:19:05

Name.

URL.

[to enter your email, use "mailto:youremail@domain.com"]
Subject.

Comment.

Word verification.

Copy the first 4 characters only.

If you are a member, try logging in again or accessing this page here.