Computer simulation of carbon nanotube pull-out from polymer by the molecular dynamics method

The influence of the polymer matrix density, chemical cross-links in the interface, and geometrical defect in the carbon nanotubes (CNTs) on the CNT pull-out from polymer has been analyzed by the molecular dynamics simulation. The interfacial shear strength (ISS) has also been estimated with the change of total potential energy. In the simulation, the crystalline polyethylene matrix is set up in a hexagonal array with the polymer chains parallel to the CNT axis. First, we investigate the effect of the polymer matrix density on the ISS by changing the distance between the chains. Simulated results show that the ISS increases with the increase of matrix density. Next, we examine the cross-link effect on the ISS by adding polyethylene cross-links in the interface. Here, an energy based switching criterion addressing cross-links traveling on the CNT has been proposed. It is found that the presence of cross-links and the cross-link positions affect the ISS. Finally, pentagon-heptagon defect, which reduces the tensile strength of the CNT and has been experimentally observed by Hashimoto et al. [Hashimoto A, Suenaga K, Gloter A, Urita K, Iijima S. Direct evidence for atomic defects in graphene layers. Nature 2004;430:870-3], has been addressed as a geometrical defect in the CNT. When cross-links are present between the CNT and the polymer, this defect reduces the ISS due to the improper connections of cross-links around this defective region.