Page 30 - Polymer-based Nanocomposites for Energy and Environmental Applications

Introduction of polymer-based nanocomposites 9

Consequently, the macromolecules can get their initial status after removing of
deforming forces. On the other hand, due to long regular macromolecule chains with
no spatially oriented structural units of bulk substitute, rubbers act as movable
materials that are capable to rotate around simple chemical bonds even at low
temperatures [47].

1.3 Polymer nanocomposite systems

1.3.1 Polymer-nonmetallic nanocomposites
1.3.1.1 Polymer-carbon nanotubes
The introduction of carbon nanotube (CNT) is referred to 1991, while Iijima
introduced it as a new emerging material with remarkable mechanical and electric
characteristics. Generally, there are two types of carbon nanotubes including
single-walled nanotubes (SWNT) that have a single graphite sheet seamlessly
wrapped into a cylindrical tube and multiwalled nanotubes (MWNT) with an array
of nanotubes that are concentrically allocated similar to rings of a tree trunk
[48,49]. Polymer/CNT nanocomposite is one of the most charming applications of
CNTs. This doping ameliorates thermal, electric, and mechanical factors of polymer
matrices. As a distinct item, the mechanical properties of CNT, especially with high
tensile strength and stiffness, achieve more attraction in the production of PNCs.
Moreover, their high aspect ratio makes them enable to be aligned along one axis
and applicable in fabrication of the conductive polymers for achieving the required
electric properties [49].
CNTs that are well aligned and highly regular structures depict advanced
characteristics such as high crystalline orientation and low interface thermal resis-
tance. Therefore, they are effective thermal interface materials (TIMs) in thermal
management. However, their frangibility, air gaps, and other defects can obstruct
thermally conducting abilities [50]. As a common problem for PNCs, the dispersion
of CNTs can impact on their performance in PNCs [49]. Meanwhile, CNTs are
arranged into ropes and bundles via van der Waals force, maintained by several
π-π interactions, and also fixed with each other based on their high aspect ratio. Con-
sequently, in case each CNT cannot be separated from the bundles, their remarkable
characteristics cannot be acquired further [51]. Also, in developing of superior
conductive polymer composite, CNTs must be precisely controlled at the interface
of a cocontinuous polymer blend through a balance of π-π and dipole-dipole interac-
tions [52]. In addition, good interfacial bonding among the polymer/CNT
nanocomposite influences on load transfers across the CNT matrix as a crucial point
in enhancing the mechanical final factors. [49].
As an effective way, chemical functionalization of CNTs can be very helpful in
addressing some challenges regarding to CNT application such as the inert chemical
structures with low surface energy and the intrinsic metallic character. For example,
chemical oxidation is chiefly carried out for covalent modification of CNTs [53].
Hooshmand Zaferani [54] represented the application of silane pretreatment of CNTs