Insights into the solubility of H2 in various polyethylene matrices at high pressure: A coarse-grained MC/MD study

Abstract

After isothermal crystallisation with coarse-grained (CG) molecular dynamics simulations, the solubility of H2 molecules in different amorphous/semi-crystalline polyethylene(PE) systems was investigated by hybrid GCMC/MD simulations with explicit crystalline phase in high-pressure environment. The crystalline phase is successfully obtained by isothermal crystallisation for branch-free PE, while the existence of the branch hindered the formation of the crystalline phase in PE. In the amorphous phase, the density of end groups turns out to be a critical factor of H2 solubility. As the branch density increase the density of the end groups, the branch density, but not the branch length has a strong positive correlation with H2 solubility. While H2 is excluded from the crystalline phase and the majority of them dissolve within the amorphous region, H2 molecules were observed to dissolve in the crystalline-amorphous interface and directly neighbouring with the crystalline phase, with a preference for dissolving in the amorphous phase without being directly linked to crystalline phase via chemical bonds. Such behaviour could be explained by the rigidity of bonded crystalline-amorphous interface.