Simulation of mechanical properties based on microstructure in polyethylene/montmorillonite nanocomposites

Abstract

In order to explore the microscopic mechanism of mechanical properties in polyethylene/montmorillonite (PE/MMT) nanocomposite material,the molecular model and the molecule structure are simulated by simulation software,and the mechanisms of various complex phenomena of mechanical properties in PE/MMT nanocomposite material can be understood more in depth in the paper.To achieve this,the molecular model is developed under 423 K based on the molecular dynamics method and using the modules of Amorphous Cell as well,Forcite Tools and Reflex in the simulation software material studio includes polyethylene model,montmorillonite models without organization,organic montmorillonite model,and PE/MMT nanocomposites model.Then,microstructure and mechanical properties of PE/MMT nanocomposite material are analyzed by X-ray diffraction,radial distribution function and interaction energy test under universal force field,respectively.Some important findings emerge from the simulation results.First,after the molecular dynamic process of canonical ensemble (NVT) and constant-pressure,constant-temperature ensemble (NPT),the fluctuations in temperature and energy of polyethylene,montmorillonite without organization,organic montmorillonite,and PE/MMT nanocomposite material are all less than 5%.This implies that the low energy state is occupied and steady structures are formed in PE/MMT nanocomposite material.Second,the inter-layer spacing of organic montmorillonite is expanded to 20 due to cations of 18 alkyl three methyl ammonium chloride,which is increased by 79% compared with that of montmorillonite without organization.Meantime,the expansibility of PE/MMT nanocomposite material is obvious,and the density and volume of PE/MMT nanocomposite material are improved by -32% and 393% respectively,compared with those of organic montmorillonite.Third,when the mass fraction of organic montmorillonite reaches 4.0 wt%,the hydrogen bonding interaction obviously exists in PE/MMT nanocomposite material,and the interaction energy between polyethylene and montmorillonite layers has a maximum value of up to -390 kcal/mol,which leads to the stable structure of PE/MMT nanocomposite material and the significant improvement of the interfacial bonding between montmorillonite and polyethylene.Fourth,mechanical properties are significantly improved compared with that of polyethylene under elastic deformation,which is 4.0 wt% organic montmorillonite in PE/MMT nanocomposite material.Young's modulus,bulk modulus and shear modulus are increased by 38%,21% and 40%,respectively.Finally,the simulation results are compared with actual observed ones.The consistency between simulation results and actually observed ones can prove that the method of modeling PE/MMT nanocomposite material is correct and effective.Furthermore,when polyethylene chains enter into the layers of organic montmorillonite,it is verified that the PE/MMT nanocomposites can be formed and that the reason for the improvement of mechanical properties in PE/MMT nanocomposite material is the emergence of hydrogen bond.