Stress-Driven Nanostructural Evolution and Its Impact on Hydrogen Diffusion in PE and PA6

Polyethylene (PE) and polyamide 6 (PA6) are critical liner materials for high-pressure hydrogen storage, yet the coupling between triaxial stress and hydrogen (H 2 ) diffusion and permeability remains poorly quantified. Using molecular dynamics simulations, we investigate microstructural evolution and H 2 transport kinetics of amorphous PE and PA6 under anisotropic triaxial loading. Our results reveal a fundamental divergence in material response: under applied stress, PE develops strongly aligned-chain domains, characterized by pronounced backbone orientation and local densification. In contrast, the rigid H-bonding network of PA6 suppresses chain reorganization, maintaining a stable amorphous state. We find that H 2 diffusion in PE is inversely correlated with the degree of chain alignment, with highly aligned-chain domains acting as effective barriers that substantially reduce the diffusion coefficient. The primary contribution of this work is the identification of a dynamic tortuous path inhibition, where local phase transitions under service-level stresses actively modulate H 2 permeability. These findings provide a theoretical framework for designing smart polymer liners that utilize operational mechanical loads to enhance their own barrier performance.