Model for anomalous moisture diffusion through a polymer–clay nanocomposite

Abstract

Experimental data are reported on moisture diffusion and the elastoplastic response of an intercalated nanocomposite with vinyl ester resin matrix and montmorillonite clay filler at room temperature. Observations in diffusion tests show that water transport in the neat resin is Fickian, whereas it becomes anomalous (non-Fickian) with the growth of the clay content. This transition is attributed to immobilization of penetrant molecules on the surfaces of hydrophilic clay layers. Observations in uniaxial tensile tests demonstrate that the response of vinyl ester resin is strongly elastoplastic, whereas an increase in the clay content results in a severe decrease of plastic strains observed as a noticeable reduction of curvatures of the stress-strain diagrams. This is explained by slowing down of molecular mobility in the host matrix driven by confinement of chains in galleries between platelets. Constitutive equations are developed for the anomalous moisture diffusion through and the elastoplastic behavior of a nanocomposite. Adjustable parameters in these relations are found by fitting the experimental data. Fair agreement is demonstrated between the observations and the results of numerical simulation. A striking similarity is revealed between changes in diffusivity, ultimate water uptake and the rate of plastic flow with an increase in the clay content.

A review of the water barrier properties of polymer/clay and polymer/graphene nanocomposites

“…The formation of clusters during the penetration of water has been observed in many polymer systems [4,12,41,52,53,62,68,113,114]. The presence of water clusters often causes a reduction in water diffusivity.…”

“…In relation to polymer/clay nanocomposites, Drozdov et al [114] found that water transport in the neat resin was Fickian but became non-Fickian with increasing clay content. This was attributed to a water clustering effect.…”

Evaluation of interfacial relaxation due to water absorption in fiber–polymer composites

“…Two phases might also be appropriate in situations for which moisture exists in free and bound states. Drozdov et al [34] simplified modeling by assuming that penetrant molecules cannot leave the binding sites, thus substantially reducing the number of adjustable parameters involved.…”

Influence of multi-walled carbon nanotubes on the β form crystallization of syndiotactic polystyrene at low temperature

“…The shift of the glass transition temperature at lower temperatures is also worth noting in all the composite samples. Probably, as observed in other polymer nanocomposites systems, the presence of CNT in the matrix induces an increase of free volume, and consequently an increase in the molecular mobility at lower temperature [24,25].…”