Influence of crosslink density on the interfacial characteristics of epoxy nanocomposites

- Thermomechanical properties of epoxy/silica nanocomposites are examined.
- Nanoparticle size effect is significantly influenced by crosslink conversions.
- Interfacial adhesion of epoxy to silica decreases with increasing conversion ratio.
- Effective interphase explains the change of interfacial characteristics.

The thermo-mechanical characteristics of thermoset epoxy based nanocomposites are investigated with molecular dynamics (MD) simulations. For establishing molecular models, spherical silica (SiO2) nanoparticles and crosslinked epoxy structures (EPON 862®-TETA) are considered as a filler and matrix phase material, respectively. The reinforcing effect of stiffness and thermal stability by addressing the spherical silica nanofillers is clearly observed: increase in elastic modulus and decrease in thermal expansion coefficient. Meanwhile, the degree of enhancement decreases with increasing crosslink density. This phenomenon is attributed to the reduction of interfacial interactions between the filler and epoxy matrix with the valence changes of atoms which involve crosslinking reactions. To investigate the interphase property, a multiscale bridging method, combined with the multi-inclusion model and MD simulation, is introduced. Furthermore, the effective interphase concept is addressed to account for the inherent interfacial characteristics with the formation of crosslinks.