Carbon Nanotubes And Its Important Properties
The way carbon atoms are bonded to each other in carbon nanotubes, it gives rise to certain properties of carbon nanotubes, which are very unique to them. You can break the carbon nanotubes properties into the following:
- Carbon Nanotubes have high electrical conductivity
- Carbon Nanotubes have high thermal conductivity
- Carbon Nanotubes have a low thermal expansion co-efficient
- Carbon Nanotubes have high tensile strength
- Carbon Nanotubes are highly flexible with the ability to bend without damage
- Carbon Nanotubes are super elastic with18% elongation to failure
Let's get more into the details of some of these carbon nanotube properties.
Varying electrical conductivity
The conductivity of carbon nanotubes is a function of their chirality and their diameter. When it comes to their electrical behaviour, carbon nanotubes can be either semiconducting or metallic in nature. Although there is no change in the current observed in different parts of the metallic single walled nanotubes, electrical conductivity in case of multi walled nanotubes is a little complex in nature owing to the structural differences between their types. Theoretically speaking, metallic nanotubes are capable of carrying an electrical current density of 4 * 109A/cm2, over 1000 times greater compared to the metals like copper.
High thermal conductivity
Generally all carbon nanotubes have a very high thermal conductivity along the tube, reflective of a property referred to as ballistic connection. However, they're good insulators laterally to the nanotube's axis.
Low thermal expansion coefficient
Single walled carbon nanotubes have an almost '0' in-plane thermal expansion, but have a large inter-plane expansion, suggesting solid in-plane coupling, and high flexibility against the non-axial strains.
Good electron field emitters
Among various carbon nanotubes' properties is the one about their ability to function as field emitters. Field emission happens as a result of the electrons' tunneling from a metal tip, into a vacuum, when subjected to a strong electric field. The high aspect ratio and small diameter of the carbon nanotubes is ideal for such field emissions.
Some notable physical properties of carbon nanotubes
Majority of physical properties of carbon nanotubes are derived from graphene, in which the carbon atoms are densely organised in regular SP2 bonded atomic-scale hexagonal (or honeycomb) pattern. The same pattern also forms the basic structure of the other SP2 carbon bonded allotropes like carbon nanotubes and fullerenes. Following are some interesting physical properties of carbon nanotubes that you should be aware of:
Extremely high strength
Carbon nanotubes are considered the stiffest and strongest fibres when it comes to their tensile strength and elastic modulus respectively, owing to the strong chemical bonds existing between the carbon atoms, in their unique hexagonal structure. Single walled nanotubes are even stronger than steel, exhibiting extreme resistance to the physical forces.
High flexibility and elasticity
These Nanotubes are highly elastic and flexible too. Pressing on their tip may cause them to bend, but without causing any damage to the tip. The tip would normally return back to its original state upon release in the force. This property of carbon nanotubes makes them highly useful in the form of probe tips in high-resolution scanning probe microscopy.
High aspect ratio
Carbon nanotubes have a very high aspect ratio (around 1000:1), making them an excellent conductive additive for the plastics of all kinds. Such good aspect ratio means that a lower concentration of loading of nanotubes is required compared to the other conductive additives like stainless steel fibre, chopped carbon fibre or carbon black, for achieving the same extent of electrical conductivity.