Study On Mechanical Simulation And Properties Of PMMA/SiO₂ Composite Based On Molecular Dynamics

Polymeric Nano-Composites has the advantages of polymer and inorganic nanoparticles,and have excellent mechanical properties,optical properties,thermodynamic properties and other properties.The functionalization and customization of Polymeric Nano-Composites is the development trend of modern materials science,which makes the customizability and designability of composite materials become the hot research content.Polymethyl methacrylate(PMMA)is one of the most widely used materials in polymer.It has good transmittance,low density and other advantages,but its surface hardness is not enough,easy to scratch and other shortcomings also limit its application.In this paper,nano silica particles were added to PMMA to improve the poor mechanical properties of PMMA,and nano silica was modified to enhance the compatibility with polymer,so as to further improve the mechanical properties.With the continuous development of Computational Materials Science,the use of computer for molecular dynamics simulation has become an important way to explore composite design.In this paper,based on the method of molecular dynamics simulation,nano silica particles are used as the reinforcement of polymer,and the dynamics simulation and mechanical properties simulation of pure PMMA and PMMA/SiO2 composites are carried out.The research content includes the following four aspects:(1)According to the molecular structure of PMMA,its molecular chain model is established,and the pure PMMA dynamic simulation model is constructed.Using the NPT and NVT ensemble to relax the crystal cell,and then calculate the mechanical properties at different temperatures.The mechanical parameters such as modulus of elasticity,Poisson's ratio,shear modulus,bulk modulus and Cauchy pressure are obtained at room temperature,high and low temperature.Compared with the existing experimental data and results,the validity and rationality of the simulation method are effectively verified.(2)According to the crystal type of silica,the spherical nano silica particle model with different diameters is established,and the dynamics simulation is carried out by using NPT and NVT ensemble.The diffusion coefficient of different diameter spherical nano silicon dioxide particles is calculated by analyzing the mean square displacement in a specific time,and the diffusion coefficient at different temperatures is studied.The variation law of diffusion coefficient with temperature and particle size is summarized by using arenius theory.(3)For PMMA/SiO2 and PMMA/modified SiO2 composites,the same method was used for dynamic simulation.By comparing the cell density and side length of the composite before and after modification,the compatibility and binding degree of the polymer and nano particles were determined.Then the mechanical properties of the two composites at different temperatures were calculated,the results show that the mechanical properties of the composite are greatly improved compared with pure PMMA.With the increase of temperature,the Kirschner pressures of the two composite materials and pure PMMA show the same change trend.It is clarified that with the increase of temperature,the brittleness of the above materials decreases and the toughness increases.(4)Using experimental methods,nano silica particles were modified by KH-570.Moreover,PMMA/SiO2 and PMMA/modified SiO2 composites were prepared.And then the mechanical tensile tests of the above two composite materials and pure PMMA were carried out.The results showed that the tensile strength and elongation at break of the unmodified nanocomposites and the modified nanocomposites were increased compared with the pure PMMA.