Nanotube

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Two Main types of Carbon Nanotubes

Single-walled Nanotubes

A single walled nanotube is a one atom thick layer of graphite or graphene formed into a seamless cylinder. They have a diameter of close to 1 nanometer and exhibit unique electrical properties. Because of their size, modified carbon nanotubes can enter cells and deliver drugs or knock out unwanted genes. Recently, in a cross-collaboration between researchers in France and England, Alberto Bianco and Kosta Kostarelos used modified nanotubes to control the damage created by a stroke.

Single-walled nanotubes can have a specific strength of up to 48,000 kN*m/kg because of their low density. What this means; is that they have an extremely high strength to weight ratio. Their hardness also exceeds that of a diamond crystal at 420 gigapascals. Because of these characteristics, Single-walled carbon nanotubes have been added to strengthen materials for sports equipment, body armor, vehicles, rockets, and building materials. These nanotubes create networks within composite material to bear the load of the weight and strain placed upon them.


Multi-walled Nanotubes

Multi-walled nanotubes are multiple concentric tubes that are precisely nested within one another, whereby an inner nanotube core may slide, almost without friction, past the outer nanotube creating a telescopic motion. Subsequently an atomically perfect linear or rotational bearing is created. This can be construed as one of the first true examples of molecular nanotechnology, which can be dubbed as the precise positioning of atoms to create useful machines. At present, this property has been utilized to create the world's smallest rotational motor. As devices continue to shrink further into the sub-100 nanometer range following the trend predicted by Moore's law, the topic of thermal properties and transport in such nano-scale (microscopic) devices becomes ever more important.

Multi-walled carbon nanotubes share most of the same properties as their singles-walled counterparts except for certain electrical properties. Multi-walled carbon nanotubes with interconnected inner shells display a property called superconductivity. It is this property that makes multi-walled nanotubes excellent choices for super-capacitors (electronic devices used to store electrical energy in circuits). Using multi-walled nanotubes as the electrodes in capacitors provides more current and better electrical and mechanical stability than any other leading materials. The surface area of the tubes also gives them a distinct advantage. This happens because the energy is stored anywhere and everywhere along the tube's axis, unlike a conventional capacitor that only stores the energy at its ends. Super-capacitors are currently being manufactured from this technology. Research labs have been working both in Stanford and MIT to create carbon nanotube ultra-capacitors that could replace battery technology in electric cars.