Page 85 - Carbon Nanotube Fibres and Yarns

78 Carbon Nanotube Fibers and Yarns

contributions from the interphases and the CNTs. Mathematic models of
polymer nanocomposites must incorporate the interphase and its properties
to provide realistic predictions [34].
The structures of interphase for CNT-reinforced PAN-based carbon fibers
have been found to be distinctly different from the bulk phases of carbonized
PAN fiber [35]. Fig. 5.4A1 shows HR-TEM images of the cross- sections of
carbonized PAN/DWNT composite fibers. Clearly the addition of DWNT
leads to a much more ordered graphitic structure in the vicinity of the DWNTs
along the radial direction. In our previous review [36], we proposed that the
reinforcement of CNT on polymer fibers came from both the CNT itself
and the interphase polymer. As the interphase regions grow, they would come
to contact with each other and merge into a wholly integrated interphase
polymer fiber (Fig. 5.4B). The interesting question is whether there is a clear
boundary when two interphase regions contact and merge together. Fig. 5.4B
shows how two interphase regions interfere and form an integrated structure.
Similar to the interference of ripples on the surface of water, the CNTs in
PAN act as ripple centers and the interphase structures propagate radially like
ripple waves. The influence of the CNT on the interphase structure weakens
as the radial distance increases, just like the spreading of ripples on water sur-
face. Two or more interphase regions interfere in a similar way to the interfer-
ences of ripple waves. In order to form a wholly integrated interphase polymer
fibers, there must be sufficient uniformly distributed ripple centers and the

Fig. 5.4 (A) HR-TEM images of the cross-sections carbonized PAN/DWNT fibers [35b]; (B)
scheme of the interference of interphase structures [36]. (Source of (A): B.A. Newcomb,
L.A. Giannuzzi, K.M. Lyons, P.V. Gulgunje, K. Gupta, Y. Liu, M. Kamath, K. McDonald, J. Moon,
B. Feng, High resolution transmission electron microscopy study on polyacrylonitrile/carbon
nanotube based carbon fibers and the effect of structure develop ment on the thermal and
electrical conductivities, Carbon 93 (2015) 502–514. Source of (B): Y. Liu, S. Kumar, Polymer/
carbon nanotube nano composite fibers—a review, ACS Appl. Mater. Interfaces 6 (9) (2014)
6069–6087.)