Sunday, March 22, 2009

You Show Your NanoTubes, I'll Show My BuckeyBalls

I read a fascinating little tidbit in The New York Times (RSS Feed) that concerned carbon nanotubes.  You remember the Nobel prize in 1996 going to two scientists who discovered spheres of carbon shaped like two geodesic hemispheres stuck together, don't you?  The lattice work that comprised the molecular frame work of the spheres (molecules, really) was entirely carbon. Arranged in hexagons (which by itself, with hydrogens all around, is benzene) A bit like a chain link fence, or a honey bees wax.  The spheres, I believe, were "discovered" in carbon black.  The black stuff that smokes off a candle flame.   One of the more disgusting jobs out of many that would easily be categorized as such in the industrial revolution, for children, was collecting carbon black from a flame for the manufacture of various things requiring the blackening, ink like material in their make up.    My point is that the scientists found in some of this carbon black little spheres that when put into a tunneling electron microscope revealed a structure that was not only (Gasp!) spherical, but also reminded the scientists of Buckminster Fuller, the wacky architect and futurist who's work inspired the strange hippie house domes, as well as many very important design considerations in various architectural installations less tacky then Spaceship Earth.  It's his picture at the top of this entry.  I could never figure out as a kid why more people didn't like those dome things.  But then... I was a virgin.  
So the scientists dusted off their bell bottoms and named their spherical little molecules, found in soot, "buckyballs".  They also named other iterations of the benzene ring latticework "fullerines"  So I guess Buckminster Fuller was covered more or less.

Initially the great excitement in 1996 was pretty straightforward:  the scientists knew the kind of bonds one would find in a molecule like a buckeyball were astonishingly strong, rather difficult to construct in a lab, for example.  And yet, here was evidence, of the self assembly of such bonds in carbon, at reasonably low temperatures in a lab:  at or below 1000 degrees centigrade.  Unfortunately Time magazine didn't think this arcane fact of at what temp the buckeyballs were conceived necessarily gave it a right to the molecule of the year.  So, in a fit of desperation, despite winning Nobel prizes for the actual, potential scientific value of what the science suggested about the generation of buckeyballs in a lab, ect.,  the journalists far and wide sold a story about buckeyballs being revolutionary for what they might do in pharmacolgy and chemistry by sticking stuff inside them.  I don't remember one mention of electronics, but there may have been a little noise as to potential there as well, but not much.
Flash ahead twelve years and what have buckeyballs done for pharmacology?  Nothing, basically.  I mean, what a perfect molecule for the next Viagra, just the name alone kind of has some suggestive potential, but no...  No buckeyball based medicine.  
However, a sort of stretched out buckeyball has been getting serious press in the last six years.  Oftentimes in hilarious ways.  If you took a buckeyball and dipped it in magic paint, then pulled the buckeyball in a line, depending on the property of the paint, it might make a three dimensional tube, of the paint, exactly as round as the buckeyball, whatever length you pulled it.  Aware of this lovely picture, but without my ecstatic imagination, scientists decided just to open up the latticework of the buckeyball and extend it into a tube of the chain link like carbon atoms instead.  "Magic paint, " they said to me, frowning, "we're real men in white jackets Andy!"  I didn't feel comfortable telling them there was no need to raise their voices.
So what do the scientists do?  Well.... things weren't going well for them.  Turns out sheets of carbon one nanometer thick and undoped by steroids, or what have you, are a bit difficult to find at the local apothecary.  So, what became the gold standard in 2006 for the achievment of nano thin films of graphite (for all practical purposes, pure carbon)?  At the time, the material that was the goal (thin film of graphite) was worth something like $2,500 a gram.  This made it damn near the most expensive substance on earth, retail.  A dollar bill weighs a gram.  I mean, if you could print this damn graphite paper stuff, you were for all practical purposes printing money, right?  What became the gold standard, was a white jacketed laboratory chief walking up to the laboratory "bench" and pulling from a long thin drawer the instrument called "Dollar General Transparent Tape".  Pulling a length of this tape, applying it to a slab of graphite and ripping like a brazillian wax job is what amounted to the gold standard at the time.  You'd be surprised, I'm sure, to hear that things have changed.  
I'm not kidding, ripping thin layers of graphite with tape was for a period one of the most popular methods.  It isn't that forms of nanotubes weren't available in nature, it's just that they were so short and small (would you believe it?) that they looked and acted like dust, which means they required a great deal of bravery to even approach and do something useful with. And given the brevity in length of these nanotubes, any application that required tubes even a millimeter long would have seemed laughable were one to stir the burned residue on a carbon anode of a recently highly charged experiment.  
All was not lost however, due to the apparatus known as "Dollar Store Transparent Tape".  Once you'd waxed the graphite, you see, you'd take the flat sheet of graphite off of the tape with a solvent, then after drying, roll the thin layer latticework like a scroll.  This is what all the fuss was about.  How Magic Tape became famous. One a thin layer was rolled up, and once scientists looked at it in their scanning microscope and tested its structural features with the proper instruments they were able to determine that this rolled up thin layer of carbon was a true nanotube.  Not the kind where the mesh, or latticework seamlessly reconnects 360 degrees all around, but due to the mechanically strong attraction of the carbon atoms to each other, the tube was found to be essentially a multiwall tube once constructed.  And it was certainly the longest one ever, even if it was a fur piece smaller than a piece of Scotch Tape.  It was way bigger than dust, for example.

So what? your thinking.  I don't blame you, that was basically my reaction to the Buckeyballs for pharmacology concept, yawn...  Turns out these nanotubes that were so hard to make before, are becoming quite a bit easier with the ripeness of time.  The military is pumping money into the subject.  And here's the reason:  for some reason (probably the energy crises and all around popularity of nanotechnology as a science subject or investing strategy) journalists decided that normal folks might understand crazy notions in the material science world like: strength, and hardness and conductivity.  Turns out that nanotubes, made of that thin film of carbon, has some very interesting qualities on all those accounts.  As you may recall from the periodic table on the dining room wall, next to the sexy poster of a waterfall, Carbon is not a metal.  However, as you may recall from superconductors, and ceramics research, ect. all that goes Zap isn't Gold.  Turns out that whether nanotubes have a particular variety of conductivity at room temperature, or not, has to do with how you roll them up.   It's easy to visualize.  If you lay out a tile floor in a room then you have a choice as to how the floor will look when you are done.  It can appear, based on its orientation, as a bunch of squares or diamonds.  turn the tile one way, it will lay out as squares.  Turn it an eighth turn, it will lay out like diamonds.  Squares on a point.  Mother nature loves this sort of thing a great deal.  Origami is based rather heavily on it.  And the yoke of geometry in the hands of men was, before the Calculus, a divided square.  I frequently wish that in the general imagination it remained that way.  Math is anything but abstract when you are laying out a tile floor, or folding a Swan for World Hiroshima day.  
So, how you orient your flat sheet of graphite, before you roll it, creates a different orientation to the bonds within the circle of the tube.  This difference of orientation has an impact on what the electrical qualities of the finished nanotube are.  For example, if the hexagons are oriented in one particular way when you roll it up then the finished tube acts, electrically, like metal.  If you orient the sheet a different way, then the nanotube will not be a metal.  The difference would hardly seem to matter since Quantum Mechanics matters so much more at this size that the inside of the tube has been rumored to be a Strange Place indeed, including such fun things as frictionless tube within a tube telescoping and lossless transmission of energy over distances.  Not that it matters for our purposes here, but this nanotube stuff, which incidentally has become a military technology and is a long, long way from Scotch Tape these days, is more conductive than copper by something like a factor of 50.  

The reason I mentioned the "is it, or isn't it a metal" distinction is pretty darn cool actually.  Outside of transmission of electricity inside a semiconductor, or in powerlines, nanotubes have some very fun properties.  They glow, for example, luminesece.  But only, due to the physics of the thing, where the nano tube does not act like a metal.  What's cool about all this is that you have so much control over the final product merely by making gross physical adjustments to its manufacture.  Nobody was talking about THIS when buckeyballs were the next drug D'jour.

Lastly, is probably one of nanotubes most astonishing, mind bending qualities.  Nanotubes structurally are the strongest material known.  By alot.  And when you consider man made materials, it is just a quantum leap from the next manipulatable material item in terms of hardness.
The primary reason are the SP2 bonds that describe the latticework of the carbon atoms.  These bonds are what are responsible for the measurement of hardness in the various allotropes of pure carbon (diamond, graphite, fullerines buckminster and otherwise)  Diamond's bonds are sp3 bonds, and sp3's are less strong than  sp2 bonds in nanotubes and their sibling, graphite.  
So, among other qualities in a huge range of fields, that is why scientists are going coco for nanotubes.  This is a material that will approach Moores law in terms of our ability to manufacture it industrially (incredible strides are being made in Florida State Univeristy, for example.  They are one of the biggest recipients from two branches of American defense).  It will have application in items as small as a few nanometers thick to as large as a skyscraper.  They were recently put together in a muscle made of the strands of tubes and found along one axis to be nearly as hard as diamond, but along another axis to be able to move like a muscle based on controllable conditions.  This blows my mind considerably.  As you can see, buckeyballs deserve their name, given the capacious gifts of their progeny. 

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