What's the difference between SWCNT and MWCNT?

Single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) have some similarities and some key differences. Both materials are made from hexagonal lattices of carbon, specifically graphene sheets rolled up to form tubular structures. However, the nested structure of MWCNTs gives them distinct properties that differentiate them from SWCNTs.

The table below compares SWCNT vs MWCNT for a variety of features:

	SWCNT	MWCNT
Appearance	Single layer of graphene	Multiple concentric layers of graphene
Diameter	< 2 nm	> 2 nm
Synthesis Conditions	Bulk synthesis is difficult Catalyst required	Bulk synthesis is easy Can be produced without catalyst
Electrical Conductivity	106 S m−1	105 S m−1
Purity	Poor	High
Defects	Higher chance of defects during functionalization	Lower chance of defects Difficult to repair defects
Retention in body	Less accumulation	More accumulation
Characterization	Easy	Complex
Flexibility (Young's Modulus)	High (~ 1 TPa )	Poor (1.28 TPa )
Applications	Electronics and Semiconductors Sensors Transparent Electrodes Optoelectronics Biomedicine: Drug Delivery, Biosensors, Bio-imaging	Structural Composites Electrochemical Devices Conductive Materials Catalyst Support Water Purification and Filtration
Cost and Scalability	More expensive due to need for precise synthesis conditions	Cheaper Easier to produce large quantities

SWCNT vs MWCNT

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Single-walled carbon nanotubes have just one layer of graphene rolled up into a tube with nanoscale diameters of < 2 nm. This ultrathin 1D structure with a high aspect ratio shows good flexibility and is easy to characterize. SWCNTs can have extremely high electrical and thermal conductivity depending on chirality.

It is this need for control over chirality to access excellent conductivity that makes SWCNT production complicated and expensive. Batches of SWCNTs can often be less pure, with mixtures of chirality. The ultrathin nature also means there is a higher chance of defects during functionalization or treatments. For these reasons SWCNTs are more suited to applications like flexible electronics, sensors, and biomedical applications where their flexibility and nanoscale dimensions can be most exploited.

Multi-walled carbon nanotubes are made from nanotubes nestled within one another. These extra layers provide protection against compression as well as defect formation. Due to their lack of flexibility, MWCNTs are best suited to increasing the mechanical strength of a system. They are much cheaper and easier to synthesise on a large-scale. Characterizing MWCNT is much more complicated however.

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