Molecular dynamics simulation study of the fracture property of the polymer nanocomposites filled with grafted nanoparticles
By employing a coarse-grained molecular dynamics simulation, we have investigated the fracture behavior of the polymer nanocomposites (PNCs) filled with the polymer-grafted nanoparticles (NPs) in details by particularly regulating the grafting density and the length of the grafted chain. By calculating the fracture energy, we observed that the rupture property first increases and then decreases with the increase of the grafting density or the length of grafted chains. The bond orientation degree and the van der Waals energy change are characterized to understand the fracture behavior. To further explain it, we analyzed the contribution of matrix chains, grafted chains, and NPs to the total stress. It is interesting to find that the stress borne by one bead of matrix chains or NPs gradually increases with the grafting density, while the stress borne by grafted chains first increases and then decreases. In addition, the stress borne by one bead of matrix chains or grafted chains gradually increases with the length of grafted chains, while the stress borne by NPs is nearly unchanged. As a result of these contributions, the optimal fracture property appears at the mediate grafting density or the length of grafted chain. Then, the number of voids is quantified, which first increases and then decreases with the strain because of the coalescence of small void into large ones. Accompanied by it, the maximum void size rises significantly. Furthermore, the maximum number of voids increases with the grafting density, while it is nearly independent of the length of the grafted chain. In particular, the voids prefer to generate at the end beads of chains or at the surface of NPs. In summary, this work could provide some further understanding how grafted chains affect the fracture properties of PNCs.