Molecular Origin of the Reinforcement Effect and Its Strain-Rate Dependence in Polymer Nanocomposite Glass

We investigate the molecular origin of mechanical reinforcement in a polymer nanocomposite (PNC) under a glass state via molecular dynamics simulations. The strength of the PNC system is found to be reinforced mainly via reduced plastic deformations of the nanoparticle neighborhood (NN). Such a reinforcement effect is found to decay with an increase in the strain rate. The Arrhenius-Eyring relation is used to analyze its origin. The amplitude of the reinforcement is found to be determined by the difference between the energy barrier (ΔE) for the activation of NN and the work (W) done by the applied stress to conquer that barrier. A larger strain rate is found to result in a larger W and, hence, a weaker reinforcement effect. Such a strain-rate dependence is verified in the experimental tensile tests of a poly(vinyl alcohol)/SiO₂ composite system. These results not only provide a new understanding of the molecular origin of the reinforcement effect in the PNC system, but also pave the way for a better design of the PNC material properties.