Molecular Dynamics Simulation Of Microscopic Dynamic Properties Of Polymer

The behavior of chains in polymers is extremely complex and can span several orders of magnitude in space and time scales.It is of great significance to study the dynamic properties and conformational parameters of polymers.At present,the simulation time scale of all atom model for large systems is very short,and it is generally believed that glass transition belongs to dynamics,so it is difficult to reduce the temperature of polymer to a supercooled state close to the critical temperature of modal coupling.At the same time,the quantitative prediction of polymer entanglement dynamics based on molecular simulation is also a major challenge in contemporary computational materials science,Therefore,this paper studies the microscopic dynamics of coarse-grained polymer by molecular dynamics simulation technology to explore the changes of internal conformation and dynamic characteristics of polymer.The results of pair distribution function of polymer system show that the particles have the characteristics of short-range order and long-range disorder.Moreover,the peaks of the distribution function are split,indicating that the polymer particles are distributed into very complex clusters,and the lower the temperature is,the more correlated the particles are.The self-intermediate scattering function and root mean square displacement curve of polymer particles appear in the middle stage and the plateau duration becomes longer and longer with the decrease of temperature.The four-point correlation function shows that there are fewer particles in the high temperature region,and the number of particles in the cooperative motion becomes more and more with the decrease of temperature,which is manifested as dynamic inhomogeneity.The simulation results show that the low temperature will cause the kinetic retardation of polymer and lead to the glass transition.Aiming at the effect of density on the structural and kinetic properties of polymer,the microscopic kinetic properties of polymer with different densities were studied in this paper.The simulation results show that the short-range correlation of low-density polymer is more complex than that of high-density polymer.The self van hove function shows that an increase in density leads to a decrease in the fluidity of particles.The self-intermediate scattering function and root mean square displacement indicate that the temperature of glass transition of polymer increases with increasing density.To explore different chain length on the microscopic dynamic properties of the polymer,this paper studies the different chain length microscopic kinetics characteristics of polymers,the pair distribution function shows that different chain long polymers possess the characteristics of the short-range order,long-range disorder,and generate the complex structure of particle clusters.The results of static structure factor show that the transformation process of polymer particles with different chain lengths accelerates with the increase of temperature,indicating that different chain lengths have no significant effect on the static properties of polymer.The self van hove function curve shows that the kinetic capacity of polymer particles with different chain lengths decreases with the increase of time.The simulation results of root mean square displacement and self-intermediate scatter function show that the kinetic ability of polymer particles with different chain lengths decreases with the decrease of temperature.The above results indicate that the kinetic properties of polymer particles with different chain lengths have no significant difference.