Properties And Uses Of Vertically Aligned Carbon Nanotubes
Carbon nanotubes (CNTs) are tubular structures of carbon atoms that have extraordinary mechanical, optical, chemical, and thermal properties. These are allotropes of carbon with a cylindrical structure. The fullerene structural family houses nanotubes. Carbon nanotubes have long, hollow structures, with one-atom thick sheets of carbon, called graphene, forming the walls of the structure. Owing to the strong chemical bonds between the atoms, carbon nanotubes have extraordinary mechanical strength which is quite a number of times stronger than steel or other industrial fibres. CNTs are used as composites for structural materials, sports equipment, armour vests, aerospace components, flame retardant materials and in spark protection, etc.
Carbon nanotubes are vertically arranged to form vertically aligned carbon nanotubes or VA-CNTs. Inter-tube Van der Waal attraction forces hold neighbouring carbon nanotubes in bundles to form vertically aligned carbon nanotubes. Since they are made of carbon nanotubes, vertically aligned carbon nanotubes exhibit the same properties as that of CNTs.
How to prepare vertically aligned carbon nanotubes
The common and widely known method for the synthesis of VA-CNTs is the growth of carbon nanotubes on a substrate through thermal chemical vapour deposition (CVD). This method has two main stages:
The formation and de-oxidation of catalyst particles.
The nucleation and growth of the vertically aligned carbon nanotubes on catalyst particles.
In the above mentioned method to produce high-density, vertically aligned carbon nanotubes, the CNT arrays are prepared by chemical vapour deposition technique. After this preparation, the arrays are then made dense membranes by capillary forces due to solvent evaporation. Since Van der Waal forces hold the carbon nanotubes together, a crowding effect is produced when the carbon nanotubes are made to grow on a substrate. This causes vertically aligned carbon nanotubes to grow perpendicular to the substrate.
Uses of vertically aligned nanotubes of carbon
Vertically aligned carbon nanotubes are used to produce advanced composite materials in high volumes because of their ability to produce carbon nanotubes in large numbers. They help make CNT production commercial.
They are used as field emitters in applications such as scanning probes, displays, microwave amplifiers, and parallel EBL.
They are used as thermal interface materials. Vertically aligned carbon nanotubes are ideal for heat dissipation in electronic packaging due to their intrinsic thermal conductivity and good mechanical properties.
Micro-patterning of vertically aligned carbon nanotubes is used for the fabrication of MEMS devices like pressure sensor, thermometer, switches, etc.
They are used in Lithium-ion batteries due to their greater capacities than graphite in the common commercial Li-ion batteries. Carbon nanotubes could increase ion diffusivity, thereby improving bulk electron transfer properties, which in turn increases the rate capabilities.
Vertically aligned carbon nanotubes are excellent substitutes to be used as catalyst supporters in fuel cells because they have regular pore structures and conductive paths, which allow for faster rates of electron transfer.
They can be utilized as templates for the formation of various metal or metal oxide constituents due to their tubular shape.
The microporous structure of vertically aligned carbon nanotubes makes them useful to be used as a gas permeation or absorption membrane.
They have good electromagnetic properties which means that vertically aligned carbon nanotubes can be used for electromagnetic shielding or as an electromagnetic radiation absorber.
These and much more are the uses of VA-CNTs. They are fast advancing as a replacement to many industrial materials due to their excellent mechanical strength along with other extraordinary properties. The applications of carbon nanotubes only seem to be increasing with the advancement of technology.