| In the field of polymer physics,polymer crystallization is one of the most important branches.This is because the crystal structure can impart more excellent mechanical properties,solvent resistance,and heat resistance to polymer materials.Therefore,research on polymer crystallization is still closely concerned in academics and industry.In the research direction of polymer crystallization,the crystallization behavior of polymer nanocomposites has also received close attention.By filling polymer matrix with nanofillers,the crystallization process of the polymer can be significantly changed,including its crystal orientation and morphology,crystallization rate,crystallization mode,etc.These changes in crystallization behaviors will obviously further affect macroscopic physical properties of polymer materials.In order to elucidate the control mechanism of crystal orientation in polymer nanocomposites from the microscopic scale,the effect of nanofiller dimension on crystallization behavior of polymers and the effect of nanofillers on the behavior of stereocomplex crystallization in polymer blends,the dynamic Monte Carlo simulation method was used to study these contents.It includes the following aspects:1.Uniform orientation of polymer crystals was achieved in polymer filled with two-dimensional nanofillers by dynamic Monte Carlo simulation method.Generally speaking,polymer crystals induced by two-dimensional nanofillers always exhibit random orientation,which limits the improvement of physical properties of polymer nanocomposites to some extent.By dynamic Monte Carlo simulation method,heterogeneous nucleation of deformed polymer loops grafted on two-dimensional nanofillers can induce the appearance of a special nanohybrid shish-kebab(NHSK)structure exhibiting uniform crystal orientation.The grafted deformed polymer chains are first heterogeneously nucleated on filler surface,and then free chains around them participate in crystallization,resulting in the formation of the NHSK structure.2.The dimension of nanofillers has a great influence on crystallization behaviors of polymers.Dynamic Monte Carlo simulation was used to study the effects of the zero-dimensional nanoparticle,one-dimensional nanowire and two-dimensional nanosheet on crystallization behaviors of polymers.The results show that one-dimensional nanoparticle has strongest ability to induce polymer crystallization,and can induce the formation of crystals with uniform orientation.The system filled with two-dimensional nanoparticle has the stronger crystallizability than that filled with zero-dimensional nanoparticle.Two factors,surface area and segmental orientation in interfacial regions will directly affect the crystallization process of polymers.Further simulations revealed that more surface area can result in more interfacial oriented segments.In addition,the decrease of the length of one-dimensional nanoparticle causes the decrease of polymer crystallization rate and number of crystal lamellae.The decrease of the length of one-dimensional nanoparticle also leads to the drop of the degree of segmental orientation in interfacial regions,and thus crystal orientation is disrupted.3.The experiments results show that the presence of graphene oxide can promote the formation of stereocomplex crystals(SCs)in filled polylactides,but the related microcosmic mechanism has not been fully elucidated.Dynamic Monte Carlo simulation reveals the mechanism of the effect of two-dimensional nanoparticle on the formation of SCs in polymer blends.It was observed from the results that the nanofillers can lead to heterogeneous nucleation of mixed polymer chains.On the one hand,due to attractively interactions between polymer and nanofillers,the miscibility of mixed polymers can be improved in interfacial regions,.On the other hand,for the heterogeneous nucleation process,polymer chains prefer to crystallize by means of intermolecular packing alignments.Both of the above phenomena contribute to the formation of SCs. |
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