What are Carbon Nanotubes?
Carbon Nanotubes (CNTs) are tubes of Carbon measured, by diameter, in nanometers. Here, Carbon atoms which are covalently bonded in a hexagonal network come together in a hollow cylindrical or tubular shape.
Carbon Nanotubes often refer to Single-Wall Carbon Nanotubes (SWCNTs), but also refers to Multi-Wall Carbon Nanotubes (MWCNTs) which consist of multiple Single-Wall Carbon Nanotubes nested within each other in a concentric manner. Their diameters can reach more than 100nm.
Carbon Nanotubes can have different structures atoms, lengths, thicknesses and number of layers. The direction and angle that the sheets of Carbon atoms are rolled in is known as the chiral angle and, depending on the chiral angle of a nanotube as it was grown during synthesis, the CNT may act as either a semiconducting or metallic material and its electronic characteristics can vary.
The History of CNTs
The discovery of CNTs is widely credited to Sumio Iijima, a Japanese physicist and inventor who, in 1991, published a ground-breaking paper reporting the discovery of Multi-Walled Carbon Nanotubes. Although Carbon Nanotubes had been observed prior to his invention, many believe that the origin of CNTs may even be pre-historic in nature. Iijima’s work generated unprecedented interest in Carbon Nano-structures. Since the discovery of carbon nanotubes (CNTs) in 1991, an entirely new discipline in materials science has developed, Nanoscience.
Properties and physical forms of CNTs
They have excellent electrical and thermal conductivity, exceptional tensile strength owed to their nanostructure and strength of bonds between their Carbon atoms. Individual Carbon Nanotubes also naturally align themselves into “ropes”, called as “forests” or “carpets”, which are held together by relatively weak van der Waals forces. CNTs can have a mechanical tensile strength that is 400 times stronger than steel at one-sixth of the weight, as well as a very large aspect ratio. The combination of these features provides an opportunity to use CNTs as mechanical property enhancing filler material and to develop ultra-high strength, low-weight materials which have highly conductive electrical and thermal properties.
Carbon Nanotubes can theoretically conduct heat and electricity similarly to Copper, but without oxidative concerns, provided they are well dispersed. They are highly chemically stable and extremely resistant to corrosion.
CNTs are available for industrial applications in large quantities. Several CNTs manufacturers have a production capacity of >100 ton per year for Multi Walled Nanotubes. Among the physical forms that CNTs are available in, there is also a regular powder form, a “chunky” powder which is safer and easily dispersed into a polymer matrix, vertically aligned MWCNTs arrays. These are called “carpets” – both of which are exclusive to Goodfellow. The “carpets” or “forests” can be used as free-standing membranes and filters, and thermal interface materials among other applications.
Applications of Carbon Nanotubes
Due to their unique characteristics, inherited from Graphene, CNTs can be used for virtually any application that requires high strength, durability, corrosion-resistance, electrical conductivity, thermal conductivity and high strength-to-weight properties.
One of the largest uses of CNTs at present is as an additive to synthetic materials. When added to composites, the material can improve the thermal, mechanical and electrical properties and offer additional benefits such as strong flame retardancy, process-ability and UV resistance. Industries where these attributes and composites are especially sought after include automotive design, aerospace, electronics, energy, oil and gas, coatings and sporting goods.
The valuable electrical and thermal properties of CNTs are beneficial for use in electronic devices, Lithium-ion batteries, chemical/electrochemical and biosensors, transistors, electron field emitters, white light sources, Hydrogen storage cells, cathode ray tubes (CRTs) and electrical-shielding applications.
CNTs are also being used for filtration, to create high-flow membranes for energy-efficient water purification.
Carbon Nanotubes in Art and Design
In art and design applications, CNTs combination with natural yarns and fibers is of interest. Scientists have coated silk fibers with carbon nanotubes to create a tough and conductive wools and yarn, which can be woven or knit into wearable sensors. These sensors can be used in health and medical monitoring applications, while the yarn itself is washable, and water repellent. Yarns fibres embedded with CNTs are also being tested for power-producing applications, where the yarn can harvest power from a wearer’s breathing.