The helium gas permeability of polytetrafluoroethylene (PTFE)/graphene nanocomposites was studied as a function of surface treatment and filler loading of the graphene nanoplatelets. Graphene was incorporated into PTFE up to 7 vol% via a solvent-assisted blending method and the composites sintered. The surface modification of the graphene occurred by oxyfluorination in perfluoroheptane solvent. The surface characteristics of the graphene nanoplatelets were assessed by X-ray photoelectron, Raman and infrared spectroscopy techniques and discussed. The incorporation of the oxyfluorinated and commercial grade graphene into the PTFE reduced the helium gas permeability by 96% at 4 vol% and by 88% at 7 vol% nanofiller contents, respectively. Oxyfluorination of graphene resulted in better dispersion of the graphene nanoplatelets compared to the unmodified ones. This was evidenced by scanning electron microscopy and X-ray tomographic inspection. The helium gas permeability of the PTFE nanocomposites was modelled by applying certain tortuosity models. The Bharadwaj model proved to be the most appropriate to describe the measured barrier properties. The modified Bharadwaj model suggested that the actual aspect ratio of the oxyfluorinated graphene was higher than that of the unmodified graphene nanoplatelets in the PTFE matrix. Accordingly, oxyfluorination proved to be a useful method to support the graphene intercalation with PTFE molecules.
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