| Since the discovery of carbon nanotubes (CNTs) by Iijima in 1991, CNTs have attracted great research interest due to their unique properties such as high electrical and thermal conductivity, excellent stiffness against bending, and high tensile strength. Using CNTs as nanofibers to enhance the mechanical, electrical, thermal, and optical properties of composite materials has been pursued extensively both in experimental and theoretical studies. Recently, experiments have shown remarkable enhancements in elastic modulus and strength of polymer composites with an addition of small amounts of CNTs. It is well established, from the research on microfiber-reinforced composites over the past few decades, that the structure and properties of the fiber-matrix interface play a major role in determining mechanical performance and structural integrity of composite materials. However, due to difficulties in devising experiments to study the CNT-polymer interface, molecular mechanics (MM) and molecular dynamics (MD) simulations have become increasingly popular in the investigations of reinforcement mechanisms in CNT-polymer composite systems. This dissertation is dedicated to conduct theoretical study on the interfacial characteristics of CNT reinforced polymer composites.Firstly, force-field-based MD simulations are performed to study the interaction between polymers and SWNTs. The"wrapping"of nanotubes by polymer chains was computed. The influence of temperature, nanotube radius and chirality on polymer adhesion was investigated. Furthermore, the"filling"of nanotubes by polymer chains was examined. The results show that the interaction between the SWNT and the polymer is strongly influenced by the specific monomer structure such as aromatic rings, which affect polymers'affinities for SWNTs significantly. The attractive interaction between the simulated polymers and the SWNTs monotonically increases when the SWNT radius is increased. The temperature influence is neglectable for Polyethylene (PE) and Polypropylene (PP) but strong for Polystyrene (PS) and Polyaniline (PANI). Also, our simulations indicate that the adhesion energy between the SWNT and the polymer strongly depends on the chirality. For SWNTs with similar molecular weights, diameters and lengths, the armchair nanotube may be the best nanotube type for reinforcement. The simulations of filling reveal that molecules of PE, PP and PS can fill into a (10, 10) SWNT cavity due to the attractive van der Waals interactions. The possible extension of polymers into SWNT cavities can be used to structurally bridge the SWNTs and polymers to significantly improve the load transfer between them when SWNTs are used to produce nanocomposites.Also, the influence of chemical functionalization on the interfacial bonding characteristics of single-walled nanotubes (SWNTs) reinforced polymer composites was investigated using molecular mechanics and molecular dynamics simulations. The simulations show that functionalization of nanotubes at low densities of functionalized carbon atoms drastically increase their interfacial bonding and shear stress between the nanotubes and the polymer matrix, where chemisorption to as little as 5.0% of the nanotube carbon atoms increases the shear stress by about 1000%. This indicates that increasing the load transfer between SWNTs and a polymer matrix in a composite via chemisorption may be an effective way and chemical attachment of nanotubes during processing may be in part responsible for the enhanced stress transfer observed in some systems of the nanotube-polymer composites. Furthermore, this suggests the possibility to use functionalized nanotubes to effectively reinforce other kinds of polymer-based materials as well.The simulation resutes and the conclusions, which could decrease the research time and the cost, would be of important in the production of CNTs reinforced polymer composites.
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