Molecular Dynamics Simulation Conductive Network Of Hybrid Nanoparticles With Different Sizes And Shapes In Polymer Nanocomposites

Polymer nanocomposites(PNCs)play an important role in the material field.They not only have superior mechanical properties than traditional polymer materials,but also have excellent electrical conductivity by constructing conductive network of nanoparticles.The dispersion and aggregation states of nanoparticles in the composites directly affect the formation of conductive network,and ultimately affect the conductivity of the composites.But it is difficult to directly characterize the microstructure of polymer nanocomposites from the molecular angle and quickly establish the relationship between the structure and electrical conductivity by using traditional polymer methods.Therefore,molecular dynamics simulation was used to study the influence of nanoparticles' size and shape on the formation of conductive network and electrical conductivity of polymer nanocomposites,the main research contents are as follows:(1)Influence of nanoparticles size on conductive network of polymer nanocomposites.The size of real nanoparticles(NPs)is polydisperse which is often omitted in the simulations.By adding spherical nanoparticles(NPs)with different sizes into the polymer materials,we study the effects of sizes,volume fraction,polydispersity and shear field on the conductive network of the polymer nanocomposites.In the quiesent state,the big NPs are adverse for the formation of the conductive network compared with the small NPs.As the concentration ratio of big NPs to the whole NPs increases from 0 to 1,the percolation threshold rises from 5.04%to 27.27%;To better understand it,the dispersion state,the largest cluster size and the number of clusters are employed to characterize the conductive network,which is consistent with the percolation threshold;Small and big NPs exhibit a weak antagonistic effect if their total concentration is fixed,the percolation threshold of monodisperse system is lower than that of polydisperse system;The shear field is beneficial to aggregating to a certain extent,forming the direct contact structure,and improving the electrical conductivity of the composites.When the shear rate increases from 0 to 0.5,the percolation threshold of the system with mixed nanoparticles ?=0.75 decreases from 13.0%to 11.3%.(2)Influence of nanoparticles shape on conductive network of polymer nanocomposites.The conductive nanoparticles(nanorods and nanosheets)can be properly dispersed in the polymer matrix for a certain proportion to form a good conductive network.We studied the influence of the volume fraction,shape of nanoparticles and shear field on electrical conductivity of polymer nanocomposites.In the PNCs system filled with mixed nanoparticles,nanorods are more conducive to the formation of conductive network compared with nanosheets;As the concentration ratio of nanorods to the whole NPs increases from 0 to 1,the percolation threshold of the composites varies from 6.45%to 4.06%.By calculating the structural parameters such as the nanoparticles distribution probability and the largest cluster size,we found that the nanorods contributes greatly to the conductive network.In the shear field,both the nanorods and nanosheets are oriented,the orientation of nanoparticles leads to the destruction of the conductive network and the decrease of the conductivity of the composites;However,the shear field has serious damage to the conductive network formed by nanorods,but small effect on nanosheets;Specially,there is no synergistic effect between nanorods and nanosheets in the quiescent state,but there is weak synergistic effect between the nanonarticles in the shear field.