A glimpse into the future

You may not know it, but we are in the middle of a revolution of epic proportions on a minute scale. Nanotechnology is a long established, yet still rapidly growing area of chemistry that has the potential to revolutionise the way we live. Officially defined as any applied science that operates on a scale of less than 100 nanometres (a ten millionth of a metre), nanotechnology can be found in many every day household items: from titanium oxide in sunscreen to calcium peroxides in toothpastes. Although many of these products are new on the market, research into this area of science first began 150 years ago when Michael Faraday investigated colloidal gold solutions: suspending tiny particles of the precious metal in water to give a deep red liquid. Technology has naturally moved on and now the future is focused on tiny cylinders of carbon, the same atom that makes up diamond and coal. Today it is single walled carbon nanotubes that are at the forefront of nanotechnology and, if a few technological challenges can be overcome, we could soon be living in a very different world. The Boar investigated to see just how long we will have to wait.

#### Why are Carbon Nanotubes special?

A carbon nanotube is essentially a single layer of carbon atoms that has been rolled into a cylinder, which gives the molecule very interesting electrical, mechanical and thermal properties that vary according to how the sheet was folded. The sheets that are used for nanotubes are smooth, which means the nanotubes are all surface with no bulk material or scattering points for electrons. As such, carbon nanotubes are incredible electrical conductors and can handle the transference of high levels of charge over long distances with very little resistance.

Whilst the electrical and thermal characteristics are undoubtedly impressive, it is the tensile strength of carbon nanotubes that makes the material so extraordinary. Indeed with a breaking strength of 63 Giga-pascals, carbon nanotubes are amongst the strongest materials in the world. To put this in perspective, a one millimetre diameter carbon nanotube cable would be capable of suspending a large male elephant. Of course such a cable would require a significant number of nanotubes, which is where the first technical hitch becomes apparent.

#### Growing Carbon Nanotubes

To get a better understanding of how carbon nanotubes are produced, the Boar interviewed Professor Julie Macpherson at Warwick. One of Macpherson’s current investigations is focused on using nanostructures to study molecular interactions on an atomic scale

Naturally occurring carbon nanotubes are produced as a by-product of normal flames, however, for high purity and uniform length nanotubes a process called Chemical Vapour Disposition is used. This method involves scattering catalyst nanoparticles over a semiconductor substrate (usually silicon) and heating it to 900 Celsius with an atmosphere of carbon monoxide or methane. At this temperature the gas breaks down and the carbon atoms dissolve into the partially melted substrate until the substance is supersaturated. The material is allowed to cool, which reduces the carbon capacity of the silicon and causes the carbon, in cylindrical form, to crop out of the substrate. The carbon nanotubes are literally ‘grown’. By altering the size of the metal catalyst, which is usually iron, cobalt or nickel, the diameter of the nanotube can be altered.

#### Uses of Carbon Nanotubes

Given the strength, durability and lightness of carbon nanotubes it is perhaps inevitable that this material will find its way into the consumer market in the form of high performance goods. Already carbon nanotube composites have been suggested for ultramodern tennis rackets, bike frames, bullet proof jackets and even space elevators to name a few.

Equally exciting is the possibility of carbon nanotubes being used to store Hydrogen gas for use in fuel cells. Currently the gas needs to be stored at very high pressures, which is greatly hindering the progress of developing Hydrogen as an alternative fuel. However Dutch scientists are designing a material that may be able to contain the gas much more safely. Best described as a ‘Layer cake’, the substance consists of sheets of carbon (i.e. graphene) that are separated by balls of carbon atoms known as buckminsterfullerene. The scientists have predicted the material can hold 6 percent of its weight in hydrogen (current hydrogen stores can only hold 2 percent) and believe that, if carbon nanotubes replace the buckminsterfullerene, even more gas could be contained.

#### So what is stopping us?

The difficulty in turning carbon nanotubes into transistors, bikes and tennis rackets lies in the cost effective assembly of the molecules into useful fibres and films. For example to be used in sporting equipment a method of acquiring bulk quantities must be found before this potential is realised as the nanotubes would need to be mixed into a composite (with current technology a carbon nanotube tennis racquet would cost £1.3 million!).

In addition to this health and safety aspects are being called into question as carbon nanotubes are increasingly likened to the infamous asbestos due to their similar long and thin structures.

The cost of producing these carbon nanotubes is high – in 2003 a gram of carbon nanotubes cost around £1000. However, given the superb qualities and huge potential this material has, it is likely that carbon nanotubes will find their way into everyday life regardless of the cost.


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