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Asked by anon-251974 on 29 Apr 2020.
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Christine Beavers answered on 29 Apr 2020:
To explain a carbon nanotube, we need to start with some definitions. You make have heard of graphite, which is pencil lead. Graphite is composed of sheets of carbons, each carbon bonded to three other carbons, making a repeating pattern of hexagons. These sheets are pretty flat. Another form of pure carbon is the fullerene. The most common fullerene is C60, which looks life a traditional football, if you imagine a carbon at every corner of a hexagon or a pentagon. Still all the carbons are bonded to three others, but the mixture of pentagons with hexagons allows curvature.
A carbon nanotube is a mix between a fullerene and a graphite sheet. The sheet rolls up into a tube, and the ends are capped with half-spheres pepered with pentagons. These tubes can have variable dimensions, and can contain other molecules, even fullerenes. People have examined carbon nanotubes for various purposes, to carry other molecules, and selectively hold on to some molecues in a mixture. Carbon nanotubes can also conduct electricity, and can be pretty strong in certain directions; these physical properties might be important in finding practical uses for them.
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Holly Campbell answered on 29 Apr 2020:
To explain this, I’ll start by talking about graphite. Graphite is a form of pure carbon, made up of single atom-thick layers of carbon atoms in a hexagonal honeycomb-shaped arrangement. The carbon atoms in the layers are held together by very strong covalent bonds. The layers of covalently-bound carbon atoms are held together by weak van der Waal’s forces between the layers. Because the layers are held together by very weak forces, they can be exfoliated into single layers, which are known as graphene.
Graphite is a 3-dimensional material, which has length, width and height. Graphene is known as a 2-dimensional material because it has length and width, but the height is so small that the height dimension is considered to have been removed. When a graphene sheet rolls up into a tube-shape, it is called a carbon nanotube. Carbon nanotubes are known as 1-dimensional materials with only length because now both the height and width dimensions are so small that they are considered to have been removed. Removal of dimensions is known as quantum confinement, and it affects electronic properties of materials such as electrical conductivity. In fact, by slightly changing the ‘rolling up’ arrangement, carbon nanotubes can be tuned to either conduct electricity well like a metal, or to behave as a semiconductor!
Carbon nanotubes are very strong, and as well as having tunable electronic properties, they have interesting optical properties. Carbon nanotubes have therefore been used in all sorts of technological applications; the most interesting one that stands out to me is in tissue engineering where carbon nanotubes can act as scaffolding for bone growth! Many research groups around the world are investigating the potential applications in the future for these astounding little tubes! -
Susan Cartwright answered on 29 Apr 2020:
I can’t really add anything to Christine’s and Holly’s answers: it’s not my field. But I will add that there is quite a good explanation, and some nice pictures, at https://www.nanowerk.com/nanotechnology/introduction/introduction_to_nanotechnology_22.php
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