Simulation Of Morphology And Electrical Properties Of Polyethylene/Silicon Dioxide Nano-composite

Due to its excellent electrical insulation performance,PE is widely used in insulation materials of power equipment.The long term high electric field will cause the insulation performance of PE to be reduced and even be broken down.Moreover,with the rapid development of modern electrical industry,the demand of insulating material is getting higher and higher.It was found that adding inorganic nanoparticles into PE could greatly improve the properties of the material.The modification and design of new material through experiments cannot fully explain the microscopic mechanism of the change in the properties of new material.Therefore,molecular simulation technology is used to study the properties of PE and PE/SiO₂ nano-composites from the microscopic perspective of molecules/atoms.In this thesis,themodels of amorphous PE,SiO₂ and PE/SiO₂ modified by methacryloxypropyl trimethoxysilane were built by Materials Studio software.Through molecule method,the model is optimized and the related potential energy parameters were obtained.By molecular dynamics simulation,the trajectory of model can be obtained.Analyzing the trajectory of models,some properties can be calculated such as structure,energy,intermolecular interaction force,Young's modulus,Poisson's ratio and polarization intensity and so on.Based on density functional theory,the electronic energy of PE and PE/SiO₂ are calculated.The breakdown field strength and trap depth of PE and PE/SiO₂modified by methacryloxypropyl trimethoxysilane can be calculated by analyzing the electronic energy data.The Forcite module and Dmol3 module are used to calculate the relevant properties of PE and PE/SiO₂ modelrespectivelyin the software.By analyzing the temperature and energy curve from result files,PE/SiO₂ nano-composites have lower energy and more stable structure than PE.Moreover PE/SiO₂ model reaches equilibrium faster than PE in the simulation process.Under the same electric field,the polarization intensity of PE and PE/SiO₂ increases when the temperature raises.The polarization intensity of PE/SiO₂ is higher than that of PE.Under the same temperature,Young's modulus and Poisson's ratio of PE and PE/SiO₂ increase when the temperature raises.Young's modulus and Poisson's ratio of PE and PE/SiO₂are higher than that of PE.The electron energy of the model of PE and PE/SiO₂ is calculated under different electric fields.With the increase of electric field,the trap depth in PE and PE/SiO₂ increases continuously and reaches the depth of 3eV which is difficult to be observed in experiment.When the trap depth becomes flat with the increase of electric field strength,the HOMO level bursts on PE and PE/SiO₂ nano-composite occur.Meanwhile the models of PE and PE/SiO₂ begin to break down.The breakdown field of PE/SiO₂is higher than that of PE.