A model for anomalous moisture diffusion through a polymer–clay nanocomposite

Experimental data are reported on moisture diffusion and the elastoplastic response in uniaxial tensile tests of an intercalated nanocomposite with vinyl ester resin matrix and montmorillonite clay filler at room temperature. Observations in diffusion tests show that the moisture transport in the neat resin is Fickian, whereas it becomes noticeably anomalous (non-Fickian) with the growth of the clay content. This transition is attributed to immobilization of water molecules on surfaces of hydrophilic clay layers. Experimental data in mechanical tests demonstrate that the response of vinyl ester resin is strongly elastoplastic, whereas an increase in the clay content reduces plastic strains. This result 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 anomalous moisture diffusion through a nanocomposite and for its elastoplastic behavior. 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. Key-words: Anomalous diffusion, Elastoplasticity, Nanocomposite ∗Present address: Triton Systems Inc., 200 Turnpike Road, Chelmsford, MA 01824, USA