Modelling Gas Transport in Multiphasic Materials: Application to Semicrystalline Membranes

The description of gas permeation across heterogeneous materials has been studied with many methods, mainly focusing on composites with high aspect ratios and low filler volume fractions. In the present work, the extension of these approaches to semicrystalline polymers is studied, considering a wide range of crystalline volume fractions to tackle applications ranging from membranes to barrier materials. A numerical approach focused on tortuosity effects related to the presence of impermeable crystalline domains was considered. Algorithms based on random sequential adsorption and Voronoi tessellation were used to reproduce the morphology of semicrystalline polymers. The flux reduction across the microstructures generated due to the presence of impermeable crystals was calculated by solving local mass balance through a finite volume method. Using this strategy, it was possible to investigate the effect of crystallites' arrangement, size distribution, orientation and shape on the relative permeability and the tortuosity of semicrystalline membranes. The results were analyzed considering existing macroscopic models and new analytical equations were proposed in order to account on such morphological effects for the prediction of the tortuosity in semicrystalline polymers.