Evaluation of Microscopic Gas Transport and Mechanical Properties of Flexible Sealing Layers for Lined Rock Cavern Compressed Air Energy Storage Under High‐Pressure Conditions

ABSTRACT Flexible sealing layers for lined rock caverns (LRCs) must provide both gas barrier capacity and deformation resistance under high‐pressure storage conditions. Although gas transport in polymers has been widely investigated, systematic comparisons of candidate cavern‐lining materials for different storage gases under identical conditions remain limited. Molecular dynamics (MD) simulations were performed for polyurethane (PU), butyl rubber (IIR), natural rubber (NR), and polyethylene (PE) in contact with air, H 2 , and CO 2 at 313 K and a nominal pressure of 20 MPa. Gas density distributions, radial distribution functions, mean squared displacements, cumulative penetration, and atomistic tensile responses were evaluated. Under the adopted conditions, gas mobility and penetration followed PE > NR > IIR > PU. PU exhibited the lowest through‐layer penetration, consistent with strong kinetic confinement of gas migration. IIR combined low gas uptake with restricted diffusion, consistent with local steric confinement associated with dense methyl substitution. PU and IIR also showed comparatively high stiffness and continuously increasing stress over the investigated strain range. These results identify PU and IIR as promising candidates for further experimental qualification and establish an LRC‐oriented framework for preliminary material screening.