The Effect of Resin/Hardener Stoichiometry on the Electrical Properties of Silicon Nitride/Epoxy Nanocomposites

The effect of resin/hardener stoichiometry was investigated for both unfilled epoxy and nanocomposite samples. The results indicate that incorporating silicon nitride nanofiller, which contains amine groups on its surface, has a significant influence on the resin/hardener reaction. At 2 wt.% of nanofiller, it was estimated that the powder contains amine groups equivalent to around 5 wt.% of the hardener mass, which results in the displacement of the optimum resin/hardener mass ratio by the same amount (∼5 wt.%). The dielectric spectra showed that the β relaxation is directly related to the hydroxyether groups that are generated by the reaction between the epoxy and the amine groups. Therefore, the relaxation strength is proportional to the crosslinking density and consequently related to the glass transition temperature. The DC conductivity increases considerably as a result of incorporating silicon nitride nanofiller when not compensating for its impact on the resin/hardener stoichiometry. This might be related to the increase in the amine content of the material caused by the amine groups existing on the surface of the nanoparticles. When the stoichiometry effect is taken into account, the DC conductivity decreased to a value that is comparable to that of the unfilled polymer.