An introduction to nanotubes
Harry Kroto and Rick Smalley, while studying interstellar dust, stumbled upon a new type of carbon, C60. Through experiments, they found that this new carbon wasn’t composed of flat sheets, like graphite, but, rather, had a more three dimensional shape. This new carbon was hard, not slippery, a feature of graphite. A few years later, Iijima Sumio would discover the tubular sheet structure of C60 and observe the multi-walled variety, christening this new discovery the carbon nanotube (CNT). The single walled carbon nanotube would not be seen until 1993.
It was found that these tiny graphene tubes (typically 3 to 30 nm in size) had amazing intrinsic properties. Their bonding structure is sp2, the strongest bond known in nature. In fact, its bond is stronger than that of diamonds. This characteristic makes the carbon nanotube five times stronger than steel, with its resistance to stretch fifty times that.
Carbon nanotubes also display a very low failure rate, due to their absence of molecular defects. With enough stress, steel will ultimately fail. CNTs rarely do.
The application of carbon nanotubes has much to do with their different possible structures. For example, single-walled carbon nanotubes (SWNTs) are a great conductor of electricity, whereas the multi-walled nanotubes (MWNT) are not. However, MWNTs have a high resistance to chemicals. Their structure is similar to a set of nesting dolls, what scientists call the “Russian Doll model”.
Also of consideration is the way the graphene sheet is rolled. In an “armchair” configuration, the CNT is a metal. The “zigzag” model is a semiconductor. These designations are indicative of SWNTs, as MWNT’s structures are much more complex. An MWNT’s many layers can reveal a slew of configurations.
Creating carbon nanotubes
Since the discovery of CNTs, many ways of synthesizing them have been discovered.
The arc method is the easiest way to produce CNTs, as well as one of the cheapest, as this method can be completed in any moderately equipped laboratory. The downside is that the CNT needs to be processed further in order to remove the detritus of the technique. The CNT is created through the vaporization of two carbon rods.
Ball milling is an uncomplicated way of making CNTs. Graphite is placed in a stainless steel container with four steel balls. Argon is then added. The milling takes place at room temperature for up to a week. Further processing is also required with this method.
Due to their tiny size, extreme strength and unbelievable durability the breadth of applications of nanotubes is amazing. A few examples:
With the nanotubes thermal conductive properties, they are ideal for use in computers, where metal would typically melt at the high temperatures needed. “Alloys” of nanotubes have also been successfully used in this capacity.
At the macroscopic level, nanotubes can be woven, just like thread, and used as body armor. Even cables could be made out of this “superfabric”.
With global warming and pollution a growing concern, the CNTs ability to block even the tiniest particles is an important development. Not only can they block materials, they can successfully kill bacteria. Very important in a world where the scarcity of clean water is becoming more and more apparent.
Perhaps most exciting is the medical uses of such technology. The point of a CNT can act much like a needle, delivering medicine on the cellular level to a patient being treated for cancer. Also, due to carbon’s presence in our bodies, it is non-toxic, making it likely that we can build stents and implants containing CNTs that our bodies would not reject.
The science of nanotechnology is very young. We’ve only begun to see all the useful applications of CNTs. Who knows, with the cost of making nanotubes decreasing, maybe we’ll see prosthetics constructed completely of nanotubes, or, since DNA can be bonded to it, perhaps the obliteration of gene-related disorders.
To underscore the importance of CNTs, two scientists, Andre Geim and Konstantin Novoselov recently won the Nobel Prize in Physics for the isolation of graphene.
O’Connell, MJ. Carbon Nanotubes: Properties and applications. CRC Press; 2006; 3-10.
Foley, M. Carbon Nanotubes 101. Nanotechnology Now website. www.nanotech-now.com/carbon-nanotubes-101.htm
Carbon nanotube science and technology. www.personal.reading.ac.uk/scsharip/tubes.
Wikipedia web page. Carbon nanotube. www.en.wikipedia.org/wiki/carbon_nanotube