Molecular dynamics study of EPDM - Part I: modelling and validation

Abstract In recent years, molecular dynamics (MD) simulation has been gradually applied to the study of the Ethylene—propylene—diene monomer’s (EPDM) macroscopic properties. However, up to now, there is no unified standard for the modelling of EPDM. Through simulations of the cohesive energy density, dielectric constant, and thermal conductivity of EPDM cells, the optimal polymerization degree and crosslinking density for the simulation are determined in this manuscript to be 100 monomers and 6.88 × 10 −4 mol cm −3 , respectively, which ensures both simulation accuracy and simulation speed. The glass transition temperature, thermal expansion, mechanics, gas diffusion and solubility properties of EPDM rubber are investigated and compared with the experimental results reported in literature to verify the rationality of optimal parameters setting for polymerization degree and crosslinking density proposed in this manuscript. Subsequently, a standardized MD modelling process for EPDM is proposed. The simulation results indicate: (1) The thermal expansion and mechanical properties of EPDM are temperature dependent. (2) CO 2 is dominant in the competitive diffusion process among multiple gases. Unlike crosslinking methods used in references that directly used interatomic distance as a crosslinking criterion, a new method is proposed that allows the crosslinking agent dicumyl peroxide to truly participate in the reaction process through a self-built script. It is the first time that quantitative control of the model’s crosslinking density is achieved by changing the molar ratio of DCP to EPDM.