Study On Crystallization Behavior Of Confined Polymer Systems By Dynamic Monte Carlo Simulation

With the rapid development of nanotechnology in the field of microelectronics,the condensed structure and dynamic behavior of polymer materials confined by nano scale have attracted widespread attention in the academic community.When the polymer is confined to the nanometer scale,its crystallization behavior will be significantly affected,which leads to great differences in the dynamics,thermodynamics and molecular structure form compared with that of the bulk polymers,and then leads to the change of physical properties of the confined polymer materials.However,due to the limitations of the experimental observation scale,it is impossible to fully reveal the microscopic mechanism of the crystallization growth and nucleation process of the confined polymers from the microscopic scale.So far,the physical root of the difference in the crystallization behavior of the confined polymer have not been clearly explained.Therefore,it is of great significance to further study the crystallization kinetics and final crystal morphology of the confined polymer from the microscopic perspective for the regulation of the crystallization behavior of confined polymer materials.In this paper,dynamic Monte Carlo simulations were performed to investigate the crystallization behavior of different confined polymer systems(including structure confined polymer systems,space confined polymer systems and structure and space dual confined polymer systems).The main research contents and conclusions are given as follows:1.Dynamic Monte Carlo simulation of the crystallization behavior of structure confined polymer systems grafted on one-dimensional nanofiller.Monte Carlo simulation is used to study the effects of grafting density and polymer-filler interaction on the crystallization behavior of grafted polymer systems.The results show that for the grafted polymer systems,with the increase of grafting density,the density of chain segments near the interface,the number of crystals and the degree of conformational extension of molecular chains increase,which is conducive to the improvement of the crystallization ability of the grafted confined polymer systems.In addition,the grafting density and the polymer-filler interaction have a great effect on the crystal morphology of the grafted polymer systems.For grafted polymer system with 52 molecular chains,when the polymer-filler interaction is-0.4,the nanohybrid shish-kebab structure will be formed.For grafted polymer system with 128 molecular chains,when the polymer-filler interaction is-1.0,the nanohybrid shish-kebab structure will be appeared.Because of the high grafting density and crowding effect of 252 molecular chains,the nanohybrid shish-kebab structure can not be formed when the polymer-filler interaction is enhanced.Therefore,the formation of nanohybrid shish-kebab structure requires appropriate grafting density and relatively high polymer-filler interaction.2.Dynamic Monte Carlo simulation of the crystallization behavior of one-dimensional confined polymer systems.Monte Carlo simulation is used to study the effects of film thickness,polymer-substrate interaction and molecular weight on the crystallization behavior of space confined polymers.The results show that in confined polymer systems with different film thicknesses,as the film thickness decreases,the interfacial effect and heterogeneous nucleation effect of the systems are enhanced,and the conformational entropy of the molecular chain is decreased,so that the crystallization rate of the confined polymers is significantly accelerated.In addition,the crystal orientation and morphology of the confined polymer also depend on the thickness of the film.In the thinner films,the crystals are lying on the substrate surface,while in the thicker film,some inclined orientation nuclei are generated.In the confined polymer systems with different polymer-substrate interactions,with the increase of the polymer-substrate interaction,the crystal morphology does not change,and the crystal morphology are mainly lying on the substrate surface,but the crystallization rate is accelerated first and then slowed down.When the polymer-substrate interaction is-3,an amorphous layer will be formed between the polymer and the substrate,which will restrict the movement of the chain segments and thus hinder the crystallization process.In the confined polymer systems with different chain lengths,with the increase of chain length,the crystal morphology does not change,and the crystal morphology are mainly lying on the substrate surface.However,the nucleation mechanism of the polymers changed from intermolecular nucleation to intramolecular nucleation,and the conformational extension degree of the molecular chains increased,and the crystallization rate gradually accelerated.3.Dynamic Monte Carlo simulation of the crystallization behavior of structure and space dual confined polymer systems.Monte Carlo simulation is used to study the effect of grafting density on the crystallization behavior of structure and space dual confined polymer systems and structure confined polymer systems.Then,the effects of polymer-substrate interaction on the crystallization behavior of structure and space dual confined polymer systems were investigated.The results show that in the structure confined polymer systems,with the increase of grafting density,the crystallization rate increases,the final crystallinity increases,and the crystal orientation changes from parallel to the substrate surface to perpendicular to the substrate surface.In the dual confined polymer systems,the crystal orientation is mainly parallel to the substrate surface.When the grafting density is lower,the crystallization rate is faster,the final crystallinity is higher,the crowding effect between molecular chains is weaker,and crystal nuclei are mainly formed by intramolecular nucleation.When the grafting density is higher,the crystallization ability is weakened,the crowding effect between molecular chains is enhanced,and crystal nuclei are mainly formed by intermolecular nucleation.In the confined polymer systems with low grafting density,the appropriate grafting density and polymer-substrate interaction have synergistic effect on the promotion of the nucleation process.With the increase of polymer-substrate interaction,the crystallization rate and final crystallinity show a trend of first increase and then decrease,but the crystal orientation and morphology did not change.In the confined polymer systems with medium grafting density,the grafting density plays a leading role in the crystallization kinetics of the confined polymer systems.With the increase of the polymer-substrate interaction,the crystallization rate and final crystallinity significantly decreased,and the crystal orientation changes from perpendicular to the substrate surface to lying on the substrate surface.In the confined polymer systems with high grafting density,homogeneous nucleation controls the whole crystallization process.With the increase of polymer-substrate interaction,the crystallization rate and final crystallinity do not change,and the crystal orientation changes from perpendicular to the substrate surface to lying on the substrate surface.The simulation results in this paper can help people understand the microscopic mechanism of the crystallization behavior of confined polymer systems,and provide reliable theoretical guidance for the experimental design of polymer nanocomposites with excellent physical properties.