As the most representative one-dimensional nanomaterial, single-walled carbon nanotubes（SWCNTs） have many excellent physical and chemical properties. With the continuous in-depth research on the basic and application of single-walled carbon nanotubes, they have shown broad application prospects in many fields, including nano electronic devices, composite material enhancers, energy storage media, catalysts and catalyst carriers, sensors, field emitters, conductive films, bio-nano materials, etc., some of which have already achieved industrial applications.
Mechanical properties of single-walled carbon nanotubes
The carbon atoms of single-walled carbon nanotubes are combined with very strong C-C covalent bonds. It is speculated from the structure that they have high axial strength, bremsstrahlung and elastic modulus. Researchers measured the vibration frequency of the free end of CNTs and found that the Young’s modulus of carbon nanotubes can reach 1Tpa, which is almost equal to the Young’s modulus of diamond, which is about 5 times that of steel. SWCNTs have extremely high axial strength, it’s about 100 times that of steel; the elastic strain of single-walled carbon nanotubes is 5%, up to 12%, which is about 60 times that of steel. CNT has excellent toughness and bendability.
Single-walled carbon nanotubes are excellent reinforcements for composite materials, which can impart their excellent mechanical properties to composite materials, so that composite materials show the strength, toughness, elasticity and fatigue resistance that they don’t originally possess. In terms of nanoprobes, carbon nanotubes can be used to make scanning probe tips with higher resolution and greater depth of detection.
Electrical properties of single-walled carbon nanotubes
The spiral tubular structure of single-walled carbon nanotubes determines its unique and excellent electrical properties. Theoretical studies have shown that due to the ballistic transportation of electrons in carbon nanotubes, the current-carrying capacity of them are as high as 109A/cm2, which is 1000 times higher than that of copper with good conductivity. The diameter of a single-walled carbon nanotube is about 2nm, and the movement of electrons in it has quantum behavior. Affected by quantum physics, as the diameter and spiral mode of SWCNT change, the energy gap of the valence band and the conduction band can be changed from nearly zero to 1eV, its conductivity can be metallic and semiconducting, so the conductivity of carbon nanotubes can be adjusted by changing the chirality angle and diameter. So far, no other substance has been found to be like single-walled carbon nanotubes can similarly adjust the energy gap by simply changing the arrangement of atoms.
Carbon nanotubes, like graphite and diamond, are excellent thermal conductors. Like their electrical conductivity, carbon nanotubes also have excellent axial thermal conductivity and are ideal thermal conductive materials. Theoretical calculations show that the carbon nanotube（CNT） heat conduction system has a large average free path of phonons, phonons can be smoothly transmitted along the pipe, and its axial thermal conductivity is about 6600W/m•K or more, which is similar to the thermal conductivity of single-layer graphene. The researchers measured that the room temperature thermal conductivity of single-walled carbon nanotube（SWCNT） is close to 3500W/m•K, which is much greater than that of diamond and graphite (~2000W/m•K). Although the heat exchange performance of carbon nanotubes in the axial direction is very high, their heat exchange performance in the vertical direction is relatively low, and carbon nanotubes are limited by their own geometric properties, and their expansion rate is almost zero, so even many carbon nanotubes bundled into a bundle, heat will not be transferred from one carbon nanotube to another.
The excellent thermal conductivity of single-walled carbon nanotubes(SWCNTs) are considered to be an excellent material for the contact surface of next-generation radiators, which can make them a thermal conductivity agent for computer CPU chip radiators in the future. The carbon nanotube CPU radiator, whose contact surface with the CPU is entirely made of carbon nanotubes, has a thermal conductivity 5 times that of commonly used copper materials. At the same time, single-walled carbon nanotubes have good application prospects in high thermal conductivity composite materials and can be used in various high-temperature components such as engines and rockets.
Optical properties of single-walled carbon nanotubes
The unique structure of single-walled carbon nanotubes has created its unique optical properties. Raman spectroscopy, fluorescence spectroscopy and ultraviolet-visible-near infrared spectroscopy have been widely used in the study of its optical properties. Raman spectroscopy is the most commonly used detection tool for single-walled carbon nanotubes. The characteristic vibration mode of single-walled carbon nanotubes ring breathing vibration mode (RBM) appears at about 200nm. RBM can be used to determine the microstructure of carbon nanotubes and determine whether the sample contains single-walled carbon nanotubes.
Magnetic properties of single-walled carbon nanotubes
Carbon nanotubes have unique magnetic properties, which are anisotropic and diamagnetic, and can be used as soft ferromagnetic materials. Some single-walled carbon nanotubes with specific structures also have superconductivity and can be used as superconducting wires.
Gas storage performance of single-walled carbon nanotubes
The one-dimensional tubular structure and large length-to-diameter ratio of single-walled carbon nanotubes make the hollow tube cavity have a strong capillary effect, so that it has unique adsorption, gas storage and infiltration characteristics. According to existing research reports, single-walled carbon nanotubes are the adsorption materials with the largest hydrogen storage capacity, far exceeding other traditional hydrogen storage materials, and will help promote the development of hydrogen fuel cells.
The catalytic activity of single-walled carbon nanotubes
Single-walled carbon nanotubes have excellent electronic conductivity, high chemical stability and large specific surface area(SSA). They can be used as catalysts or catalyst carriers, and have higher catalytic activity. No matter in traditional heterogeneous catalysis, or in electrocatalysis and photocatalysis, single-walled carbon nanotubes have shown great application potentials.
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