Molecular Dynamics Simulation Of Tensile Properties Of Rubber Materials

Since the advent of computers,with the rapid development of computing technology and the continuous improvement of computer performance,molecular dynamics simulation technology has been widely used.People can already use the data obtained from traditional experiments to research physical and chemical properties through computer simulation techniques.Up to now,a lot of work has been done on experimental research on the mechanical properties of rubber materials,and many achievements have been made.However,there is still little research on the microscopic analysis of the structure of rubber materials.The research on the relationship between the microstructure and macroscopic mechanical properties of rubber materials currently lacks fundamental quantitative analysis and in-depth theoretical research.In this paper,the numerical simulation method is used to study the tensile behavior of rubber from a microscopic point of view.Quantitative analysis of the results from the atomic scale,to explore the microscopic factors affecting the physical and mechanical properties of rubber materials,to do some guidance for the future research of rubber materials.The objects studied in this paper are natural rubber,butadiene rubber,and gutta percha,which are commonly used rubber materials,and their microscopic ideal models are constructed using molecular dynamics methods.The focus of the study is as follows:1.The study of the minimum degree of polymerization.Through the analysis of solubility parameters under different degree of molecular chain polymerization,it was determined that the degree of polymerization of natural rubber moleculars that can be used for simulation can be determined.The results show that when the degree of polymerization increases to 20,the solubility parameter value does not fluctuate too much and is stable between 16.6 and 16.9?J/cm³?^1/2.This value is consistent with the experimental value.The results of the radial distribution function show that the constructed model reaches a completely amorphous and disordered structure and reflects the uniformity of the model performance.2.The influence of degree of polymerization on the tensile behavior of natural rubber.The ideal model of natural rubber was constructed using the degree of polymerization of 20,50,100,and 200 molecular chains,through the stress-strain curve,mean square displacement?MSD?,mean square radius of gyration?Rg²?,and the potential energy of van der Waals non-bonding bond,the potential energy of bond stretching,the potential energy of bond angle bending and the potential energy of dihedral angle twisting characterization analysis of rubber tensile behavior.The results show that within the scope of this article,the natural rubber has a greater stress response during the stretching process as the degree of polymerization increases;energy analysis of different potential energies shows that the potential energy of van der Waals non-bonding bond,the potential energy of bond stretching and he potential energy of dihedral angle twisting play a major role in the mechanical properties of natural rubber,the degree of polymerization has a certain influence on the change of the potential energy of van der Waals non-bonding bond,the potential energy of bond stretching and the potential energy of dihedral angle twisting,but it has no effect on the potential energy of bond angle bending;In the tensile process simulation,as the degree of polymerization increases,the MSD and Rg² change more and more,this is due to the fact that the increase in the length of the molecular chain increases the flexibility of the chain,making it more likely that the molecular chains become tangled and so on..3.Study on tensile behavior of different rubber species.Based on the foregoing studies,the same tensile model,the same degree of polymerization?100?,and the same temperature and pressure conditions were used to study the microscopic tensile behavior of natural rubber,eucommia rubber,and butadiene rubber ideal models.The results showed that the tensile properties of the cis-1,4-polyisoprene molecular model and the trans-1,4-polyisoprene molecular model are basically the same,while the cis-1,4-polyisoprene model shows a greater stress response than the previous two.Through the analysis of the mean square displacement,it was found that the tensile properties of the rubber material have a great correlation with the mobility of atoms in the material.In addition,through the analysis of the mean square radius of gyration we know that the size relationship between the three molecular chains in the flexibility is cis 1,4 polybutadiene molecules>cis 1,4 polyisoprene molecules>trans1,4 polyisoprene molecule.