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 difficulty 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 ‘p_c’. The work presented here is dedicated to a newly developed multi-scale modeling strategy, belonging to the aforementioned 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.