Percolation of polydisperse nanorods in polymer nanocomposites: Insights from molecular dynamics simulation

The aspect ratio of nanorods (NR) is polydisperse in the real application which is often omitted in the electrical conductivity. In this work, by adopting a coarse-grained molecular dynamics simulation, the effect of the polydispersity index (PDI) of NRs on the conductive probability of polymer nanocomposites has been investigated in details under the quiescent state and under the shear field which aims to uncover their relationship. By analyzing the conductive network, it is found that the percolation threshold is inversely proportion to the PDI under the quiescent state. On one hand, one long NR can connect more other NRs than one short NR. In addition, more long NRs participate in building the conductive network with the PDI than short NRs, which thus enhances the conductive probability. Compared with in the quiescent state, the percolation threshold is enhanced under the shear field. By characterizing the orientation degree and the connection mode of both long NRs and short NRs, the shear field significantly changes the original conductive network which rationalizes the conductive probability. Interestingly the percolation threshold first increases and then decreases with the shear rate which reaches the maximum value at the intermediate shear rate. At the low shear rate, the initial orientation of NRs induces the breakage of the conductive network perpendicular to the shear direction which improves the percolation threshold. In addition, more short NRs participate in building the conductive network than long NRs with the further increase of the shear rate. Meanwhile more direct contact aggregation structure of NRs appears which induces the recovery of the conductive network.