| Polymer nanocomposites have better mechanical,optical and electrical properties than pure polymers,which haves attracted much attention in polymer physics and materials science.Generally,the macroscopic properties of a material are determined by its microscopic phase.The macroscopic properties of polymer nanocomposites are mainly determined by the dispersion of nanoparticles(NPs)in the polymer matrix.In order to effectively control the macroscopic properties of polymer nanocomposites,it is necessary to study the interaction mechanism between polymer and NPs,and to analysis the phase change of NPs in polymer nanocomposites.Since it is difficult to elucidate the interaction mechanism of each phase of polymer nanoparticle composites in experiments and theories,it is more convenient to study the polymer nanocomposites by the calculating and simulation method.Using Molecular Dynamics simulation,flattened polymer chain decorated crystals of NPs are observed for polymer–NP mixtures confined between two parallel substrates.In order to minimize the entropy loss,polymer chains instead of NPs aggregate at the substrate surfaces when the number of NPs is high enough to have the conformation of chains significantly disturbed.Increasing NP concentration to be much higher than that of polymer chains leads to an ordered arrangement of NPs in the central region,which are sandwiched between two thin layers of polymer chains.A scaling model regarding polymer chains consisting of packed correlation blobs is provided to clarify the physics mechanism behind the formation of thin polymer layer and the crystallization of NPs.The order structure of the crystallized NPs is shown to be switchable through an adjustment of the bulk concentrations of polymer chains and NPs.Using molecular dynamics simulations,we have also measured the indirect interacting force between surface-separated nanoparticles within athermal polymers.Our simulations confirm the existence of repulsion between NPs with separation beyond the range of attractive forces.Due to the entropy effect in the system,varying the polymer concentration,the length of polymer chains and the size of nanoparticles,we demonstrate that both attractive and repulsive forces are monotonically strengthened by increasing polymer concentration and/or enlarging the size of NPs.The indirect interacting force as function of separation between NPs has no dependence on polymer chain length for semi-dilute polymers.Finally,the existence of indirect forces was confirmed by calculating the radial distribution functions of monomers surrounding NPs.Through this study,we found that the flattened polymer chain decorated crystals of nanoparticles for polymer–NP mixtures confined between two parallel substrates.The interaction mechanism of each phase in the athermal system was analyzed by the calculation of the indirect force of the nanoparticle.The results of the dynamic simulation will also give us a more perfect understanding of the interaction mechanism and the corresponding phase behavior of the polymer nanocomposites. |
