Biomedical Engineering Reference
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9.2 
Properties of Carbon Nanotubes
The basic structure of various CNTs is shown on Fig. 9.1. An SWCNT
can be thought as a rolled-up graphene sheet into a tube. Nanotubes
are considered one-dimensional structures according to their high
length-to-diameter ratio (aspect ratio). An SWCNT is considered as
a cylinder with only one wrapped graphene sheet. Several tubes of
different diameter can be fitted into each other to make a MWCNT.
MWCNTs are similar to a collection of concentric SWCNTs, and if two
graphene sheets are wrapped then double-walled carbon nanotubes
(DWCNTs) are fabricated. In the case of more SWCNTs and/or
MWCNTs are mixed in a mat, a bundle of CNTs can be released as
well. Furthermore, graphite consists of strongly bonded sheets of
sp
2
carbon atoms in a hexagonal arrangement, with a weaker van
der Waals bonding between the sheets that are separated by 3.4
Å
.
Figure 9.1
Structure of (a) single-walled carbon nanotube, (b) double-
walled carbon nanotube, (c) multi-walled carbon nanotube,
and (d) bundle of carbon nanotubes.
, called chiral vector or
chirality. Two atoms in a planar graphene sheet are chosen and one
is used as origin. The chiral vector
CNTs are described by a single vector
C
is pointed from the first atom
toward the second one (Fig. 9.2) and is defined as follows [41-44]:
C
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