Between CNT and polymer matrix

CNT can markedly reinforce polystyrene rod and epoxy thin film by forming CNT/polystyrene (PS) and CNT/epoxy composites (Wong et al., 2003). Molecular mechanics simulations and elasticity calculations clearly showed that, in the absence of chemical bonding between CNT and the matrix, the non-covalent bond interactions including electrostatic and van der Waals forces result in CNT-polymer interfacial shear stress (at OK) of about 138 and 186MPa, respectively, for CNT/ epoxy and CNT/PS, which are about an order of magnitude higher than microfiber-reinforced composites, the reason should attribute to intimate contact between the two solid phases at the molecular scale. Local non-uniformity of CNTs and mismatch of the coefficients of thermal expansions between CNT and polymer matrix may also promote the stress transfer between CNTs and polymer matrix. 

The chapter focuses on the studies that have been carried out on the processing and properties of CNT-PMMA composites. The various composite fabrication methods used by different researchers have been described followed by a discussion of the mechanical, electrical and thermal properties of CNT-PMMA composites. The key issues of CNT dispersion and interfacial adhesion between CNT and polymer matrix that are essential to develop these advanced composites have also been discussed. Some new ideas in this direction have also been proposed. 

CNT sidewall consists of hexagonal rings which are seamlessly arranged, and so it is rather inert in chemistry. This stable chemical characteristic of CNTs makes it difficult to achieve strong interfacial bonding between CNTs and polymer matrix. That is, in order to achieve high tensile strength and tensile modulus, structure modification is desired to improve the reactivity. 

For CNTs not well bonded to polymers, Jiang et al. [137] established a cohesive law for CNT/polymer interfaces. The cohesive law and its properties (e g. cohesive strength and cohesive energy) are obtained directly fiom the Lennard-Jones potential from the vdW interactions. Such a cohesive law is incorporated in the micromechanics model to study the mechanical behavior of CNT-reinforced composite materials. CNTs indeed improves the mechanical behavior of composite at the small strain. However, such improvement disappears at relatively large strain because the completely debonded nanotubes behave like voids in the matrix and may even weaken the composite. The increase of interface adhesion between CNTs and polymer matrix may significantly improve the composite behavior at the large strain [138]. 

Numerous studies have indicated that CNTs can nucleate PSCs, and it was suggested that both isothermal and nonisothermal crystallization behavior can be used as a bellwether of CNT/polymer soft epitaxial matching for templated crystallinity. With the addition of CNT fillers into polymer matrices, some new properties (electrical conductivity, flame resistance) can be imparted, while others (mechanical strength, thermal conductivity) can be enhanced. Again, these properties are dependent on the interplay between CNT and polymer matrix, as well as the organization of the two. 

A good interfacial adhesion between the matrix and the nanotubes is another effective parameter of CNT-polymer composites. There are some possible adhesions between CNT and polymer matrix, including physical, chemical and/or mechanical. It is known that diffusive and electrostatic adhesions... 

As already mentioned, CNT dispersion and stress transfer must all be optimized to reach maximum mechanical properties. One of the most challenging issues in polymer nanocomposites is the determination of the stress transfer efficiency through the interface between CNTs and polymer matrix. This is a prerequisite to take advantage of the extremely high modulus and strength of CNTs. In addition, the high aspect ratio of CNTs necessitates huge interfacial areas available for stress transfer compared to traditional micrometer-size fiber composites. 

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