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 (Δ E ) 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)/SiO 2 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.