Carbon nanotubes and their otherworldy properties

Some of you may have wondered in the past as to what the strongest fibre in the world is, and the short answer is 'carbon nanotube' fibres. However when I had the same query I was amazed not only by the pure display of strength of these nanotubes, but at the sheer versatility of what the fibres could do and, in turn, what this spells for the future. For instance, researchers at the University of Texas have woven artificial muscles from CNT's and filled the structures with paraffin wax; these muscles have been shown to lift 100,000 times their weight and weights 200 times heavier than any natural muscle of the same size. That in and of itself is amazing, but couple that with the fact that it is also extremely light, and you have a winning combination.

Let's delve into the technical side of it all. What you see with CNT's is essentially what you get. They are phenomenally small tubes made from carbon atoms that are arranged in a hexagonal mesh that are all interconnected with each other to create a cylindrical tube. These tubes are 100 times stronger than steel and 10,000 times thinner than the width of a single hair; the tubes' mechanical strength is a result of the strong bonds between the carbon atoms. They are covalently bonded to 3 other carbon atoms meaning there are 2 single bonds and 1 double bond. With millions of these atoms bonded together in this uniform structure, it's not surprising they display as much strength as they do.

There are two main categories of CNT's that differ in properties as a result of the way in which they are rolled up. For instance, single-walled CNT's are CNT's with only one layer of carbon hexagonal mesh which exhibits emphasised conducting properties and so is used in electronics like computer chips and the like. Multi-walled CNT's on the other hand have up to 100, or more, layers of these tubes surrounding each other increasing diameters, and held slightly apart from the layer above and below via intermolecular forces. Imagine an archery target where each concentric line represents a nanotube.

In addition to synthesising artificial muscles, scientists have been able to use carbon nanotubes to target specific cancer cells and eliminate them. What they have done is, they have taken an antibody produced by chickens, with CNT's bound to them. Following the augmentation, the antibodies are attracted to a protein produced by a specific type of breast cancer. The antibodies attach themselves to the tumor, at which point an infrared laser is pointed to where the antibodies have attached themselves to. The radiation emitted by the laser is absorbed by the CNT's which incinerates them, but also incinerates the tumor in the process. Now, this has been tested in laboratory conditions so is a far cry from being a perfect model for the eradication of cancer cells in a human body, however this is a huge step in the right direction and could mean that in the future, we will have a reliable way of removing malign cancer growths in people and possibly be on the road to curing cancer altogether. But that technology is locked far away in the future and will likely not be ready to be utilized in any of our lifetimes.

Well, this is all well and good, but how do you make CNT's? There are several ways to synthesise them, but I'll focus on two particularly interesting methods: arc discharge and laser ablation. Both of these methods require a vacuum in order to be performed, and both involve heating a carbon rod until it vapourises and allowing the subsequent vapour to cool. Upon cooling, CNT's are formed. However, the difference between the two methods is how the carbon rod within the vacuum is heated. In arc discharge, you subject the rod to thousands of volts before rapidly discharging the voltage. This causes the rod to heat up exponentially to the point where it begins to give off carbon vapour. This method can turn approximately 30% of the original rod into CNT's. Laser ablation on the other hand, heats up the carbon rod with the radiation emitted via a precision laser. Because of the fact that a laser is easier to control more precisely than a discharge of voltage, scientists can manipulate the conditions more easily and so have a higher yield, being able to turn around 70% of the original rod into CNT's, both single-walled and multi-walled.

Everything mentioned here is beyond impressive, and I haven't even touched upon the engineering opportunities CNT's present. But, I'll leave that piece of curiosity for you to follow.

This has been Timothy K. Bosse, thank you for reading.

Citations:
http://www.understandingnano.com/nanotubes-carbon.html
http://www.nanoscience.com/applications/education/overview/cnt-technology-overview/cnt-synthesis/
http://www.nanoscience.com/applications/education/overview/cnt-technology-overview/

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