Influence of interfacial layers upon the barrier properties of polymer nanocomposites

Recent experiments in the context of polymer nanocomposites (PNCs) have observed counter intuitive behavior in which the addition of impenetrable nanofillers into a rigid polymer matrix resulted in the enhancement of the composite membrane's permeability (and diffusivity) to gas penetrants. Existing theoretical models have rationalized these observations as arising from the presence of interfacial layers around the nanoparticles whose properties differ significantly from the bulk properties of the polymer. Similar influences of interfacial layers have also been noted in the context of other macroscopic properties of nanofiller-polymer mixtures. In this article, we present a numerical approach building upon such earlier theoretical ideas, which: (i) Uses a microscopically based polymer model to determine the penetrant diffusivity characteristics in interfacial layers; (ii) embeds the so-determined interfacial characteristics into a numerical homogenization procedure, which accounts for the overlap of interfacial layers (approximately) and multibody interactions (exactly). The numerical approach is used to elucidate the influence of polymer matrix stiffness, particle sizes and particle volume fractions upon the penetrant diffusivity properties of PNCs.