The Different Types of Carbon Nanotubes
It wouldn't be wise to delve into the different types of carbon nanotubes without throwing some light on the carbon nanotubes (CNTs) first. Carbon nanotubes are nanoparticles or molecules made entirely from carbon atoms.
Technically speaking, carbon nanotubes can be called an allotrope of carbon. They take the form of cylindrical carbon molecules. They are possessed with unique properties to make them potentially beneficial in a vast variety of applications in the field of electronics, nanotechnology, optics and other fields of materials science.
These nanotubes are in the shape of hexagonal carbon rings arranged on a flat sheet, with every carbon atom connected to three more carbon atoms via covalent bonds. Hence every carbon ring is attached to the other on the edges, giving carbon nanotubes the shape of a cylindrical tube.
Two major types of carbon nanotubes
Coming to the different types of carbon nanotubes, they can be broadly categorised into multi-walled nanotubes (MWNTs) and single walled nanotubes (SWNTs).
SWNTs - First of the two major types of carbon nanotubes
MWNTs - Second of the two major types of carbon nanotubes
Multi walled nanotubes are made up of one or more layers of the hexagonal carbon structures, giving them the appearance of concentric tubes of graphene. The structure of MWNTs can be described using two different models:
Regardless of the MWNT model, the distance between different layers of graphene is generally very small, just about the same as in case of the graphite layers in a pencil, approximately 3.4 A.
The Russian Matryoshka doll structure is more commonly observed in the MWNTs, and its individual SWNT layers can be semiconducting or metallic in nature.
Other mixed variants of MWNTs are possible too, for instance the DWNTs or double walled nanotubes. These mixed types of carbon nanotubes may comprise of two or more different types of concentric carbon nanotubes arranged in different orders, with either random or regular layering.