Introduction to Carbon Nanotube/Polymer Composites
Carbon nanotube/polymer composites are nanocomposites that contain carbon nanotubes (CNTs) paired with polymer matrix for huge improvements in mechanical, electrical and thermal properties. For their high surface area, high electrical conductivity, high thermal conductivity, high mechanical modulus and low density, carbon nanotubes are often used to improve polymer matrices.
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Performance of Carbon Nanotube-Polymer Composites
The carbon nanotubes are introduced and this really enhances the qualities of the composites. Carbon nanotubes, for instance, can improve the conductivity, mechanical and thermal properties of the composites.
Mechanical Properties
The addition of carbon nanotubes also gives polymer composites an excellent mechanical properties. For example, MWNTs/PMMA composites from in situ polymerisation exhibit notable increases in tensile strength, storage modulus, and glass transition temperature. Moreover, as long as the ratio of carbon nanotubes is set to some degree, the mechanical characteristics of the composite are at its best. For example, in some cases, the mechanical properties are best when the mass fraction of carbon nanotubes is 0.5%.
Electrical Properties
Carbon nanotubes have high electrical conductivity so the carbon nanotube/polymer composites are electrically good. They've even reported that at low levels, the composites have much higher electrical conductivity. The electrical percolation limit of SWCNTs/PVAc composite films, for instance, is very low. Moreover, the carbon nanotubes make the polymer even more conductive and hence suitable for antistatic applications.
Thermal Properties
Adding carbon nanotubes to polymer composites improves the thermal conductivity too. For instance, carbon nanotubes can slow the decomposition of polymers such as PMMA or PVA in terms of heat to make the composites thermally stable. The nanotubes can also mitigate the composite's CTE and stabilize it in humid and hot conditions.
Functional Properties
There are also some functional features in carbon nanotube/polymer composites — thermal conductivity, wave absorption, electrostatic dissipation. Carbon nanotube/cellulose paper, for instance, has 0.53 cm volume conductivity and is shielded to more than 20 dB between 15-40 GHz, and is a good wave-absorbing material.
Functionalization of Carbon Nanotubes
The dispersion issue is the first issue with using carbon nanotubes in high polymer composites. The surface has to be modified to enable better dispersion and stronger attachment between the carbon nanotubes and the polymer interface. The principal is to lower the surface energy, make it more compatible with organic phases, and more compatible with polymer composites. Common modification methods are mainly divided into chemical and physical methods.
Chemical Methods
These involve introducing specific functional groups on the surface of carbon nanotubes through chemical reactions or the application of external energy. The specific methods include:
Surface Treatment Modification: Using chemical treatments like acid treatment or sulfonation to treat carbon nanotubes and add functional groups to change their surface properties as per need (i.e., surface hydrophilicity, biocompatibility).
Outer Film Modification: Spreading a film of other materials uniformly on top of the carbon nanotubes, in order to alter the surface.
Local Activation Modification: Chemical reactions used to add different functional groups to the surface of carbon nanotubes, giving new purposes to the composite material as it is paired with the polymer. Carbon nanotube/amphiphilic polymer composites, for example, are more robust, which could be used in information technology, biomedicine and catalysis.
Physical Methods
This process causes mechanical stress (such as grinding or friction) to agitate the surface of carbon nanotubes by changing their physical and chemical makeup. This increases the internal energy of the carbon nanotubes and when pressure is applied, the activated surface of the carbon nanotubes reacts and binds to other materials, resulting in modification. This is usually done using ultrasonic dispersion or large shear forces on the carbon nanotubes to prevent aggregation and good dispersibility.
Fabrication Methods Involved in Carbon Nanotube Polymer Composites
There are generally two types of carbon nanotube/polymer composite synthesis.
In Situ Polymerization
In situ polymerization with carbon nanotubes is one way. This is by using the functional groups on the surface of carbon nanotubes to participate in polymerization or initiators to debond the carbon nanotubes so that they can polymerize and have good chemistry with the organic phase.
Physical Blending
The other method is physical blending, which can be divided into solution blending and melt blending. This approach depends on the affinity between functional groups on the carbon nanotubes and the organic phase, or the steric hindrance effect, to be good with the organic phase.
These two techniques have been applied to various polymer/CNT composites such as poly(methyl methacrylate)/CNTs (PMMA/CNTs), nylon-6 (PA6)/CNTs, poly(pyrrole) (PPY)/CNTs, PmPV/CNTs, PPV/CNTs and epoxy resin/CNTs composites.
It has been demonstrated that of all the carbon nanotube/polymer composites produced, the in situ polymerization composite is the least conducting, with a percolation limit of 0.06% mass. Solution-blended composites have percolation threshold of 0.05%–0.1% mass, and melt-blended composites have maximum percolation threshold of 0.1%–0.2% mass. The process used to make such composites must be formulated after taking into account all factors such as the polymer, the shape of the carbon nanotubes, the experimental setting, and the expected behavior of the composite material.
Uses and Potential Of Carbon Nanotube - Polymer Composites
Carbon nanotube-polymer composites (CNT-polymer composites) are particularly interesting in recent years in materials science for their special mechanical, thermal and electrical properties. Compounds made with CNTs embedded in a polymer matrix can improve the properties of the material and are therefore promising for a variety of applications in various domains.
Electronics: Due to carbon nanotubes' excellent electrical and thermal conductivity, CNT-polymer composites excel at electronic packaging and heat dissipation. For instance, they could be used as thermal interface materials in electronic devices for heat dissipation. Also, these composites are employed to produce field emission cathodes, and random-oriented CNT-polymer composites treated by solution processes can produce electron emitting with nanotube-inbound light.
Automotive and Aerospace: CNT-polymer composites have long been applied to automotive and aerospace applications due to their strength and lightweight. They can be used to make lighter and stronger building materials that will help save fuel and emit less.
Energy Storage: CNT-polymer composites are great for supercapacitors and batteries because they have large specific surface area and good electrical conductivity, they're great electrodes.
Filtration: Because of carbon nanotubes high porosity and chemical stability, CNT-polymer composites can also be used for water purification and air purification.
Sensors: These composites are electrically and mechanically excellent and are used in the construction of sensors like pressure sensors and chemical sensors.
Optoelectronic Applications: CNT-polymer composites are also applied to photovoltaic cells and other optoelectronic systems for the improved photoelectric conversion performance.
Sports Equipment: Carbon nanotube-reinforced polymer composites are used for high-performance sporting goods like golf clubs, tennis rackets, and bicycle frames as they are strong and lightweight.
Potential Uses: CNT-polymer composites showed considerable application potential in different areas, but it's still a long way to go. These concerns can range from carbon nanotube dispersion in the polymer matrix, interface interaction, to nanotube sphering and all can affect composite performance. This work will be further investigated by how to better make these composites for better performance and wider applications.
Finally, with their good properties, the carbon nanotube-polymer composites are a game changer in several domains. The more studies and technology are applied, the more these composites are likely to become ever more important, creating allied industries.
References
- Pal, G., and S. Kumar. "Modeling of carbon nanotubes and carbon nanotube–polymer composites." Progress in Aerospace Sciences 80 (2016): 33-58.
- Mohd N., et al. "Fabrication, functionalization, and application of carbon nanotube-reinforced polymer composite: An overview." Polymers 13.7 (2021): 1047.
