Influence of crosslink ratio on the thermomechanical properties of polymer nanocomposites and interphase: a molecular dynamics simulation

Abstract

The effect of different crosslink ratios on the thermal and mechanical properties of thermoset epoxy-based nanocomposites are investigated by molecular dynamics (MD) simulations and a sequential scale bridging method. For establishing molecular models crosslinked epoxy structures composed of epoxy resin EPON 862 and curing agent TETA with a wide range of crosslink ratios are considered. Silica (SiO2) nanoparticles having different radii are introduced as a filler material in order to analyze the characteristics of interphase regions regarding the particle size effect. The elastic modulus and thermal expansion coefficient of various unit cells with different crosslink ratios and particle sizes are investigated using MD simulations. The results illustrate that the degree of bulk property changes of nanocomposites with respect to crosslink ratios is lower than the cases of pure epoxy structures. For the quantification of the properties of interphase regions, the interaction energy densities are investigated and a sequential scale bridging method is applied. The interaction between the particle and matrix is weakened as the crosslink ratio increases. Moreover, the elastic modulus of interphase is reduced and the size effects on thermal expansion of interphase are hindered with the presence of more crosslinked networks. The results indicate that the interphase behaviors are significantly diminished as crosslink ratio increases.