Carbon Nanotubes were discoved by Sumio Iijima with the use of a transmission electron microscope. Their unique properties make them very intersting and give them a lot of potential directions to go with further research and new products.
Here is a brief explaination of how Carbon Nanotubes are made.
Nanomanufacturing
Carbon Nanotubes are essentially graphite that has been rolled up into a cylindrical manner. Each end of the cylinder contains a fullerene (seen above) which is essentially a closed cage molecule. The shape of nanotubes is based off the hexagonal lattice of Carbon atoms. The hexagonal lattice gives rise to three distinct conformational forms of the crystalline graphite nanotubes, the armchair, zigzag, and chiral positions.
There exists a simple equation so that one can tell what conformation the nanotube is. The Chiral Vector R = N(A1) + M(A2), where A1 and A2 are the unit vectors and N and M are integers. The Chiral Angle of the molecule is defined as the angle A1 and the Chiral Vector.
The Molecule will exhibit an Armchair conformation when N = M and the is 30 degrees. The Zigzag conformation is exhibited when M or N = 0 and the Chiral Vector 0 degrees. Any other set of parameters will yield a Chiral Conformation.
The chirality of the molecule gives it unique properties. For instance Carbon Nanotubes are either conductive or semi-conductive. When N - M =3x (where x is an integer) the Nanotube is conductive and in all other situations the material is semi-conductive. This information can also be determined by the conformation the Carbon Nanotube is in: for instance all armchair conformations are conductive in addition to 1/3 of zigzag conformations and the rest of semi-conductive. The Chirality also determines lattice, density and other properties of the molecule.
The Nanotubes are broken up into two catergories, single-wall nanotubes and multi-wall nanotubes. Single-wall nanotubes are just your basic cylinder comprised of Carbon atoms as described above, where the multi-wall nanotubes contain cyliners made of carbon within one another (seen below).
In 1996 a research group for an effective way to create single-wall carbon Nanotubes using laser vaporization. The laser hit select areas of Carbon under a 1200 degree C condition. To help initiate growth factors a cobalt-nickle catalyst is used to prevent the fullerent from being added to the opposite ends of the cylinder. These catalysts allow 70-90% of the targeted carbon to be converted into Carbon Nanotubes. These conditions can be maintained by firing the laser beams every 50ns. Multi-wall Carbon Nanotubes are grown in a similar fashion but without a catalyst. Though we can growth both Single/Multi-wall Carbon Nanotubes, the mechanisms for doing so are not all that well understood. Much effort is going to understanding these mechanisms because if we understand them better we will coorespondingly be able to grow them better and get a yield higher than 70-90% in a more cost efficient manner.
Carbon nanotubes have immense possibilities. Perhaps one of their greatest attributes is their electroconductivity. For example when the nanotubes are electrically injected with an electronic charge to alter their structure, it can make the sheet move. This property creates many applications in terms of biomedical engineering to create artificial muscles and limbs. Due to the strength and flexibility of carbon nanotubes it would be a perfect material to recreate muscles. Also when an electric current is ran through a nanotube sheet, it will light up due to incandescent heating, which offers many possibilities terms of creating a light source that doesn't use a filament. Also with this researchers are starting to try placing these sheets, which are virtually "see-through" into windows. Microwave radiation could be used to heat the sheets enabling heat within the windows as well as being able to light up when a current is run through them.
The demand for faster technologies especially in electrical devices has given rise to smaller more powerful processing chips. The smaller they are and the more transistors they have the better they perform, as there is less of a distance the information has to go. But at the same time these improved chips require more and more power which relates to the problem, where up to 90% of the power can be lost as heat. Heat is an enemy of most machines because it keeps them from operating under ideal conditions and causes extra stress to components. Because of the unique properties that Carbon Nanotubes exhibit, it would seem to me that Nanotechnology could be fairly significant in future products. At the start of J-term I first read an article about them and there thermal capacities. This was a strong interest of mine because heat is an enemy of many of the devices we use in our day-to-day activities. For instance for every 10 degree Celsius in operating temperature cuts the overall lifespan of the product in half. Therefore members of the scientific community are always trying to combat and dissapate heat through the use of fans and metal heat sinks.
To combat this at present chips use heat sinks which are finned conductive plates of aluminum or copper. Copper is the ideal heat sink because its a very good thermal conductor but its weight and rising costs are problems. These plates are placed onto of the Central Processing Unit (CPU) and absorb the thermal energy pulling it away from the CPU to keep it at an optimal temperature. There have been several movements towards creating chips with Carbon Nanotubes aligned in a specific manner on heat sinks and on the processor. Imperfection on the surface of the heat sink, leaves pockets where air gets trapped. These air pockets resist what would otherwise be a consistent directional movement of heat from the processor to heat sink, to the colder air inside the machine and then is blown out through vents via fans. The key factor to making Carbon Nanotubes reliable heat conductors is to make the flexible which means that Single-Walled Carbon Nanotubes are best fit for the job. It should also be noted that the conformation of the molecule is important because chiral Nanotubes dont absorb heat as well as the armchair and zigzag conformations.
The experimentors give the analogy of brushing your teeth: the more the Nanotubes are able to bend the more nooks and crannies (ie air pockets). The flexibility of the Carbon Nanotubes depended on the conductivity and defectiveness, the less conductive and more defective the more flexible they were. Using Nanotubes to fill air pocket has prooved to be more promising than the greases which are currently used to fill them because they are better able to fill the gaps and keep the processor cool. In one experiment they Carbon Nanotube aided chip was able to use 11% more of the power supplied and have its cooling performance improved by 19% compared to its non Nanotube counterpart. This area of technology looks especially promising in products that are too small to have fans built into them such as cell phones.
While I was reading over research about Carbon Nanotubes I stumbled over an article that talked about how water placed inside a Single Walled Carbon Nanotube doesn't freeze even when the temperature is near absolute zero. I thought this was rather interesting and a legitimate topic to do calculations for since we had already done some basic calculations for a water molecule/dimer. This new type of water dubbed nanotube water have the same molecular structure as water: two Hydrogen atoms bonded to an Oxygen atom.
As the temperature begins to drop into the freezing range the molecules of water form an icy inner layer inside the Single-Walled Nanotube which is essentialy like a tube of ice within the Nanotube. This change occurs somewhere around the realm of negative 445 degrees Fahrenheit. This ice tube is held together permanently by four hydrogen bonds to the closest available molecules.
The nature of the ice tube is more stable due to the amount of Hydrogen bonds each molecule possesses (4) compared to regular liquid H2O, which on average has approximately 3.8 Hydrogen bonds. The water within the ice tube is constantly creating and breaking Hydrogen bonds and therefore Nanotube water on average only exhibit about 1.86 Hydrogen Bonds. Because there are less bonds and they are kept in constant motion by the making and breaking of bonds between other molecules of Nanotube water and the inner wall of the ice tube pending on there proximity to one another and the number of bonds they already possess. This property of the Nanotube water is what allows it to keep from being turned into solid ice even and very frigid temperatures.
These finding were discovered by the Argonne National Labratory. To get the water inside Single-Walled Carbon Nanotubes they exposed the tubes to warm water vapor and then cooled it. This change in temperature induced the spontaneous formation of a chain of water molecules within. Because the water is forced into a one dimensional channel it exhibits different properties than normal water. This study was done in hopes of learning more about proton and water transport in plants and transmembrane proteins because they confine their contents to a size similar than nanotubes.