Moisture absorption behavior in silicon nitride epoxy nanocomposites

The kinetics of moisture uptake was investigated for both unfilled and nanofilled epoxy networks. The results indicate that the addition of silicon nitride nanofiller, which is covered by amine groups, increases the equilibrium water uptake but does not change the diffusion coefficient, as was observed for a hardener (amine)-rich unfilled sample. This behavior was explained by impediment of water diffusion by the particles. Comparing the dielectric spectra of the dry and wet samples suggests that the absorbed water has no significant effect on the dielectric spectra at frequencies > 10 Hz. At lower frequencies, the water increases the DC conductivity and the imaginary part of the relative permittivity. It is though that the reaction between the amine groups on the surface of the particles and the epoxy groups redistributes the amine content and, consequently, the absorbed water to the whole matrix. This might prevent the water from accumulating around the nanoparticles and producing a mid/high-frequency relaxation as reported in similar systems.