Investigating Hydrogen Dynamics in EPDM Rubber with Evolving Fractional Free Volume

The advancement of hydrogen-based energy systems necessitates a comprehensive understanding of hydrogen interactions with polymeric materials, particularly in high-pressure applications. EPDM rubber is commonly utilized in components such as O-rings and hoses, where its performance under hydrogen exposure is critical to sealing applications. While polymers are chemically inert to hydrogen, the dynamics of hydrogen within these materials are unique compared to other diatomic gases and can significantly influence their mechanical performance and long-term integrity. In this study, we focus on the dynamics of hydrogen in EPDM rubber, hypothesizing that the diffusivity of hydrogen is intricately linked to the evolving fractional free volume (FFV) within the polymer matrix. Using molecular dynamics simulations, we specifically investigate how the size and shape of free volume pores affect the mobility of hydrogen by applying a range of nominal strain and compression values across various configurations, including isotropic and anisotropic conditions. We present detailed analyses of diffusion coefficients of hydrogen gas over the full pressure range relevant to hydrogen energy storage and emphasize the relationship between hydrogen mobility and FFV. Our findings provide critical insights for developing predictive models of hydrogen transport in polymers and inform experimental efforts aimed at understanding the structural changes induced by hydrogen exposure.