Research on dielectric property of polyethylene with defects based on molecular dynamics

Because of the good performance, polyethylene is widely used in the material industry. However, the chemical defects of the polyethylene have a badly influence in the dielectric properties of the polyethylene. Therefore, the study of dielectric properties of polyethylene with different chemical defects is essential. In this paper the polyethylene with defects is calculated by the molecular dynamics simulation. The amorphous cell is modeled by 60 chains of 13-tridecane containing chemical defect to simulate the amorphous polyethylene. After the molecular dynamics calculations, the thermodynamic properties including cell structure parameters and the kinetic properties including dipole moment autocorrelation function are got from the analysis of the simulation. Frequency spectrum and temperature spectrum of the complex dielectric constant can be obtained from the dipole moment autocorrelation function and the Kohlraush-Williams-Watts expression. From the calculation results, several conclusions can be obtained. The dielectric constant ε″ _max/Δε positively related to relaxation time τ(T), and dielectric constants of polyethylene Δε and ε″ _max increase with the growth of characteristic ratio which is the characterization of the chain flexibility. The calculation results of the dielectric properties and the trap depth calculated by the electron affinity shows that deeper traps lead to greater dielectric constants of polyethylene Δε and ε″_max.