Investigation On Interfacial Mechanical Behavior Of Carbon Nanotubes/Polyethylene Composites

Carbon nanotubes (CNTs) have been widely used in polymer composites as filler material due to the outstanding physical and mechanical properties. Semi-crystalline polymer products usually have a congregated structure, in which the crystalline phase will coexist with amorphous phase. Crystallization behavior, microcrystalline structure and the relationship between the interfacial phase and interfacial mechanics of CNT/Polyethylene (CNT/PE) composite have been studied by molecular dynamics simulation in this thesis.Firstly, the coarse grained model of PE was constructed based on Iterative Boltzmann Inversion method. The mechanism of microstructure evolution of PE crystallization process was analyzed by coarse-grained molecular dynamics (CGMD). The results showed that chain-folded lamellae come into being by means of folding, arrangement and packing of the random coil molecular chains.Secondly, the effect of 3% CNTs on PE crystallization behavior was investigated by MD simulations. The results suggested that CNTs can significantly improve the crystallinity, crystallization temperature and glass transition temperature of PE. Besides, CNTs can locally strengthen semi-crystalline polymer. PE molecules near CNTs will orient and form the interfacial crystallite structure. Interfacial structure and morphology are dependant the diameter of CNT. When CNT’s diameter is large, PE molecules follow the lattice matching effect strictly and wrap on the surface of CNT with helical conformation. When CNT’s diameter is small, the lattice matching effect of CNT and PE will become weak and the PE molecules will orient along the CNT axial direction.The pullout test of CNT from PE matrix was simulated by molecular dynamics. The effect of CNT’s length, molecular chain orientation and crystalline morphology on the interfacial mechanical behavior was investigated. The results suggested that the shear stress will increase with CNTs length and the helical conformation. Interface can improve the interfacial strength of CNT/PE interface composite.