Single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) are similar in certain respects but they also have striking differences. SWNTs are an allotrope of sp2 hybridized carbon similar to fullerenes. The structure is a cylindrical tube including six-membered carbon rings similar to graphite.
There are a large number of present and evolving applications for MWNTs. These include:
Electrically Conductive Polymers: MWNTs are suitable for these applications especially due to its high conductivity and high aspect ratio. The needed conductivity level can be achieved with much lesser loadings than for conventional solutions such as metal particulates or carbon black. Applications include electrostatic discharge protection in wafer processing fabrication, antistatic elastomeric and plastic components for automobile fuel line components, plastics rendered conductive to enable electrostatic spray painting of automobile body parts, RFI shielding materials, and more.
Battery Cathodes: Novel MWNT materials from SouthWest NanoTechnologies (SWeNT®) have shown considerable improvement in when integrated into cathodes.
Improved Structural Composites: MWNTs in the form of non-woven or woven fabrics or resin infused buckypaper when saturated with thermoset resins have shown considerable increase in stiffness and strength of composite structures such as structural laminates and golf club shafts for aerospace application.
Water filtration membranes: High aspect ration, high mechanical strength and large specific surface enable very efficient filtration media.
Other development applications include spray-coatable heater elements; thermal interface and other heat conduction materials; enhanced carbon fiber and others. A new group of MWNTs were developed by SWeNT known as specialty multi-walled CNT (SMW), by which the number of walls is controlled to vary between three to eight walls while maintaining CNT lengths more than 3 µm , hence yielding an aspect ratio in the 350 – 550 range. The lesser number of walls will result in higher purity, lesser structural defects and lesser waste of carbon material, while longer and straighter tubes provide better overall CNT morphology.o
Certain features of the SMW product are:
The SMW product has a considerably higher aspect ratio (length/diameter) when compared to either of the other grades and an increased aspect ratio is needed in order to develop a conductive network in the polymer matrix at a low loading of additive.
The SMW tubes are straight, which is also beneficial in establishing a conducting network.
Competitive materials show defects and impurities. Tubes may fracture during dispersion at defect sites, bringing down the number of electrical pathways and the resulting conductivity.
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