Anomalous water diffusion in epoxy/carbon nanoparticle composites

Abstract

Water absorption-desorption-resorption and swelling were studied for a DGEBA-based amine-cured epoxy resin filled with four types of carbon nanoparticles: multiwall carbon nanotubes (MWCNT), graphite nano-platelets (GnP), expanded graphite platelets, and carbon black. Nanocomposites are characterised by lower diffusivity (down to 20% for epoxy/GnP) and increased water sorption capacity compared to the neat epoxy. Anomalous water absorption and swelling of nanocomposites is finely described by the diffusion-relaxation model. The relaxation times, considered as quantitative indicators of changes in segmental mobility of the polymer, increased with addition of nanoparticles and decreased with temperature. Epoxy/MWCNT composites are characterised by the longest relaxation times (twofold increase) and highest Deborah numbers compared to the neat epoxy and other nanocomposites. Hydrothermal ageing effects and efficiency of nanoparticles on thermal and thermomechanical properties of the epoxy were estimated. Water uptake in nanocomposites is accompanied by several competing processes: plasticization, after-cure, and physical ageing of the polymer matrix.