Page 100 - Carbon Nanotube Fibres and Yarns

92 Carbon Nanotube Fibers and Yarns

10 3 3
Surface area (m 2 /g) 10 2 Surface area (m 2 /g) 10

1
10
10 2
10 0
0 10 20 30 40 0 200 400 600 800 1000
(A) CNT wall number (B) CNT number in a SWNT bundle

25
CNT bundle diameter (nm) 20

15

10
DMF
5 DMAc
0 1000 2000 3000
(C) CNT aspect ratio
Fig. 5.11 (A) CNT surface area as a function of wall number; (B) surface area as a function
of CNT number in a SWNT bundle; and (C) dispersed CNT bundles diameters in a solvent
as a function of CNT aspect ratio [85]. (Source: X. Yan, H. Dong, Y. Liu, B.A. Newcomb, H.G.
Chae, S. Kumar, Z. Xiao, T. Liu, Effect of processing conditions on the dispersion of carbon
nanotubes in polyacrylonitrile solutions, J. Appl. Polym. Sci. 132 (26) (2015) 42177.)

of CNTs in the bundle. Although CNTs have high surface areas up to
2
~1330 m /g (SWNT), the interfacial area between the CNTs and the
matrixes is dramatically reduced if the CNTs aggregate in bundles in-
stead of being exfoliated individual tubes. The interfacial area plays an
important role in stress transfer between the CNTs and the polymer
[10], which is critical for reinforcement of composites. Our studies found
that the dispersed CNT bundle diameter (bundle size) is dependent on
the aspect ratio of the CNT (Fig. 5.11C) [85]. The interactions among
CNTs, solvent molecules, and polymer chains can affect the dispersion
of CNTs [86]. Chemical modifications and surfactants have been used to
improve the dispersion of CNTs in solvents and polymer matrices, but
it is not clear how the grafting groups and surfactants affect interphase
development. Poor CNT dispersion is a detriment to the reinforcement
of polymer nanocomposites fibers.