Gas transport in ethylene-propylene-diene (EPDM) elastomer: Molecular simulation and experimental study

Time lag permeation measurements with ethylene-propylene-diene (EPDM) elastomer have been undertaken in an effort to characterize the gas transport properties of this barrier material. The derived solubility and diffusivity of a series of probe gases including helium, hydrogen, neon, argon, krypton, oxygen, nitrogen, carbon dioxide and methane were measured and compared with molecular simulation predictions. Molecular Dynamics (MD) and Grand Canonical Monte Carlo (GCMC) calculations were performed to provide estimates for diffusivity and solubility, respectively. Agreement between the molecular simulations and experimental data is obtained for simple spherical monatomic probe gases, with greater deviation observed for non-spherical polyatomic gases. Additionally, agreement between semi-empirical correlations based on the effective cross-sectional area of the diffusing species and the effective Lennard-Jones interaction constant of the sorbed species is better than widely used correlations based on gas critical properties. Furthermore, the molecular simulations provide a meaningful representation for the elastomer studied and additionally appear to capture the fundamental principles of sorption and diffusion of the chosen probe gases.