Multi-scale modeling of gas solubility in semi-crystalline polymers: bridging Molecular Dynamics with Lattice Fluid Theory

The prediction of the solubility of gasses in semi-crystalline polymers is still a challenging task due to the dif-ficulty in providing a comprehensive description of the morphological and mechanical perturbation felt by the amorphous phase intercalated with the impermeable crystal domains. Among the different modeling techniques, a frequently adopted strategy models the reduced solubility experienced by the confined amorphous phase via an additional pressure to the external gas pressure acting on the latter, the so-called constraint pressure 'pc'. The work presented here is dedicated to a newly developed multi-scale modeling strategy, belonging to the afore-mentioned category, that innovatively couples Molecular Dynamics simulations with Lattice Fluid theory. The model was applied to carbon dioxide, ethylene, and propane solubility isotherms in High-Density Polyethylene, and validated against experimental literature data, confirming its ability to model the solubility in semi -crystalline polymers. In addition, it showed good accordance with a fully macroscopic model already present in the literature. The successful multi-scale coupling presented here paves the way for the development of a fully predictive modeling strategy.