Permeability in amorphous barrier membranes. Experiments and comparison with model predictions

Abstract

This work examines transport in amorphous polymer nanocomposites containing elongated fillers and analyzes how geometric and interfacial features emerging during nanocomposite production control effective barrier properties like diffusivity or permeability. Diffusion of water and heptadecanol was measured in polydimethylsiloxane- and epoxy-based matrices loaded with graphene or modified bentonite and interpreted through non-steady Fickean fits, finite-element simulations, and analytical models. Classical tortuosity descriptions fail to capture the experimental trends unless the aspect ratio and orientational disorder of the fillers are allowed to evolve with volume fraction, reflecting aggregation, partial fragmentation, or modest changes in angular distributions. Raman spectroscopy, X-ray diffraction, and optical microscopy support these effects,particularly the concentration-dependent reduction and increased dispersion of aspect ratios. In epoxy–graphene composites, diffusivity is enhanced rather than reduced; simulations incorporating a localized region of increased diffusivity around the platelets yield a quantitative correction factor that captures this behavior and shows that sufficiently high local mobility can overcome tortuosity. Overall, diffusivity/permeability emerges as a remarkably sensitive probe of micro- and nanoscale structural variations and, when interpreted through physically constrained refinements of existing models, provides insights into the effective architecture of real nanocomposites beyond what direct imaging alone can resolve.