Molecular Dynamics Simulation Studies On The Ordered Orientation Of Polymer Chains At Nanocomposites Surface

The filler in polymer nanocomposites is one of the important factors can influence theaggregation states of polymers, and the aggregation structures of polymers can determineproperties of composites. The morphology of polymer and the filler content are alwaysinvestigated by experimental. However, there is lack of the mechanism of polymers aboutaggregations in those studies. Therefore, we studied the ordered orientation of polymer chainsat nanocomposites surface using molecular dynamics (MD) simulations to understand theinteractions between the polymers and fillers. Moreover, we can realize how crystal faces anddimention of surfaces affected the orderd behavior of polyethylene (PE) through investigatingthe effect of silica surfaces and Au surfaces on the ordered oritentation of PE, which canprobably provide theory basis for designing and preparing PE/SiO2and PE/Au composites.First, based on the geometries from molecular dynamics simulations and a packagecompiled by ourselves, the interactions between graphene nanosheet (GNS) and nine types offlexible polymers have been investigated with force field. Both the van der Waals (vdW)interaction and the electrostatic interaction (EI) for two same polymer chains and between apolymer and a GNS were calculated and compared. It is found that the vdW energies betweentwo same chains of polymer are smaller than the energies between the corresponding chainand GNS, which implies that the polymers are easily adsorbed by the GNS when theyapproach to GNS. Moreover, the N and O atoms in the polymers will strengthen theinteractions. The effect of cut-off distance was explored. It was found that the cut-off distanceplays a significant role in EI energy, but a less important role in vdW energy when the cut-offdistance is over9.5.Then, the structural and dynamical properties of PE adsorbed on (111),(220) and (331)surfaces of SiO2are studied by MD simulations. As described in the previous chapter, theinteraction between PE and GNS is weakest and PE is easyly to crystallize. Accoding to theliteratures, GNS which consists of carbon atoms can induce PE crystallization. Hence, westudied the structural and dynamical behaviors of PE adsorbed on SiO2surfaces which has Oand Si atoms. We analyzed the radial distribution, the order parameter and the diffusioncoefficient, and the results show that these surfaces of SiO2can induce ordered orientation ofPE although the induction effects of the surfaces are obviously different. Last, the aggregation structure of PE adsorbed on (100),(110) and (111) surfaces of Auare investigated by MD simulations. As described in the previous chapter, different structuresof surfaces of SiO2will result into different ordered behaviors. The results of in this captureare agrrement with previous capture although the inducing effects of the surfaces change toone-dimensional. In other words, the PE formed the ordered structure along the Au, but theinduction ability of Au with (100),(110) and (111) indexes are different.