Page 9 - Carbon Nanotube Fibres and Yarns

2 Carbon Nanotube Fibers and Yarns

Fig. 1.1 Carbon nanotube structures. (A) A graphene sheet is “rolled up” to make a
nanotube. T denotes the tube axis, and a 1 and a 2 are the unit vectors of graphene in real
space. (B) Armchair (n, n). (C) Zigzag (n, 0). (D) Triple-walled armchair carbon nanotube.
(Courtesy of Wikipedia, https://en.wikipedia.org/wiki/Carbon_nanotube.)

CNTs are categorized as single-walled nanotubes (SWNTs),
double-walled nanotubes (DWNT), and multi-walled nanotubes (MWNTs).
The MWNTs consist of multiple rolled layers of graphene (concentric
tubes in Fig. 1.1D). The interlayer distance in MWNTs is close to the dis-
tance between graphene layers in graphite, approximately 3.4 Å (0.34 nm).
CNTs are the strongest and stiffest materials yet discovered in terms
of tensile strength and elastic modulus, respectively, owing to their co-
2
valent sp bonds between the individual carbon atoms. Mass-produced
CNTs contain defects and possess considerably lower strength than that
predicted from perfect graphene sheets, but still much higher than any
existing commercial material. The challenge is to organize these nano-
tubes into macroscale structures without introducing further structural
defects so that they can express similar properties as their constituent
nanotubes.