Use of surfactants is an effective way for dispersing CNTs [39]. Reports show
that the outer most nanotubes in a bundle are treated more than the innermost tubes
and the nanotube remains predominantly bundled even after surfactant treatment.
But mechanical methods like ultrasonication can debundle the nanotubes by steric
or electrostatic repulsions [40]. On sonication the high local shear will unravel the
outer carbon nanotubes in a bundle and expose other sites for additional surfactant
adsorption, thus the surfactant molecules gradually exfoliate the bundle in an
“unzippering” mechanism [41]. Some of the common surfactants used for the
dispersion of carbon nanotubes are sodium dodecyl benzene sulfonate (SDBS)
[42], dodecyl trimethyl ammonium bromide (DTAB) [43], hexadecyl trimethyl
ammonium bromide (CTAB) [44], octylphenol ethoxylate (Triton X-100) [45]
and sodium dodecyl sulfate (SDS) [46]. Covalent modification is another way to
solubilize the CNTs in different solvents and to improve the interaction with the
matrix in composites [47].
2.2.2 Carbon Nanofiber
After the discovery of carbon nanofiber (CNF), most of the works are focused on
the use of CNF as thermal, electrical and mechanical reinforcing filler to improve
the polymer characteristics [48, 49]. A significant amount of work has been
conducted by using the one dimensional carbon fillers like CNT and CNF. The
one dimensional filler may connect more polymer chains and afford more effective
load transfer, leading to an improvement of mechanical properties [50]. One
dimensional fillers can easily transfer the loads or reduce it than spherical fillers.
Well dispersed polymer composites filled with CNT or CNF can be achieved by
using the fine twin-screw extrusion, surfactant, oxidation of fillers and incorporation of functional groups on the surface of the fillers. The transmission electron
microscopy (TEM) images of the fillers are shown in Fig. 4.
Fig. 3 Rolling of graphene sheets to form different types of nanotubes [34]
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that the outer most nanotubes in a bundle are treated more than the innermost tubes
and the nanotube remains predominantly bundled even after surfactant treatment.
But mechanical methods like ultrasonication can debundle the nanotubes by steric
or electrostatic repulsions [40]. On sonication the high local shear will unravel the
outer carbon nanotubes in a bundle and expose other sites for additional surfactant
adsorption, thus the surfactant molecules gradually exfoliate the bundle in an
“unzippering” mechanism [41]. Some of the common surfactants used for the
dispersion of carbon nanotubes are sodium dodecyl benzene sulfonate (SDBS)
[42], dodecyl trimethyl ammonium bromide (DTAB) [43], hexadecyl trimethyl
ammonium bromide (CTAB) [44], octylphenol ethoxylate (Triton X-100) [45]
and sodium dodecyl sulfate (SDS) [46]. Covalent modification is another way to
solubilize the CNTs in different solvents and to improve the interaction with the
matrix in composites [47].
2.2.2 Carbon Nanofiber
After the discovery of carbon nanofiber (CNF), most of the works are focused on
the use of CNF as thermal, electrical and mechanical reinforcing filler to improve
the polymer characteristics [48, 49]. A significant amount of work has been
conducted by using the one dimensional carbon fillers like CNT and CNF. The
one dimensional filler may connect more polymer chains and afford more effective
load transfer, leading to an improvement of mechanical properties [50]. One
dimensional fillers can easily transfer the loads or reduce it than spherical fillers.
Well dispersed polymer composites filled with CNT or CNF can be achieved by
using the fine twin-screw extrusion, surfactant, oxidation of fillers and incorporation of functional groups on the surface of the fillers. The transmission electron
microscopy (TEM) images of the fillers are shown in Fig. 4.
Fig. 3 Rolling of graphene sheets to form different types of nanotubes [34]
94
A.B. Nair et al.