Protonation and weakening of an epoxy resin–SiO2 composite with silane coupling agents under moist conditions.

We modeled the degradation of a composite produced from an amine-cured epoxy resin and SiO₂ nanoparticles with a silane coupling agent (SCA) under wet conditions using electron-level simulations. For the epoxy region, the amine group is protonated depending on its location under neutral or acidic conditions. Protonation substantially weakens the amine C–N bond. For SCA-connected HO–SiO₂, terminal –OH of SiO₂ is deprotonated under neutral or alkaline conditions, and the energetic barrier to break the Si–O bond is < 1 eV when 50% of the terminal –OH is deprotonated. These findings support the experimental data on pH-dependent degradation. [ABSTRACT FROM AUTHOR]