A multi-scale modeling approach for the prediction of hydrogen transport properties in semi-crystalline polymers

Abstract

A multiscale modelling platform was developed for the prediction of both hydrogen sorption and diffusion coefficients in HDPE; the permeability across the material was ultimately estimated according to the solution-diffusion model. Molecular Dynamics (MD) simulations of semi-crystalline HDPE structures having tailored fractions of intercrystalline connections (tie-chains), representative of different thermal histories, were carried out. The sorption coefficient was estimated by means of the Lattice Fluid Equation of State which was fully parametrized on the MD simulation results [1]. The diffusion coefficient was evaluated from the Mean Square Displacement (MSD) of hydrogen molecules within the structures during MD simulations and scaling the latter with the impermeable crystalline domains induced tortuosity which was reproduced using a Finite Volume model of the 3D spherulitic morphology. At experimental level, a time-lag equipment was used to determine diffusivity and permeability on the different polyethylene samples whose degree of crystallinity was determined through X-Ray analysis. The modelling strategy allowed to establish useful correlations between the polymer molecular structure and the barrier performance paving the way for an enhanced screening and optimization of hydrogen polymeric liners.