Manipulating the Void Nucleation and Propagation in Silica Nanoparticle/Polyisoprene Nanocomposites via Grafted Chains: A Multiscale Simulation

The mechanical properties of silica nanoparticle (NP)/polyisoprene (PI) nanocomposites can be drastically manipulated by modifying the NPs with grafted chains. To reveal the mechanism, a multiscale model of NP/PI nanocomposites is first developed in which the potential functions are obtained by adopting the inverse Boltzmann iteration method. Then, the triaxial deformation simulation shows that the grafted silica NPs can enhance the mechanical properties by analyzing the rupture toughness. It is found that the increase in the entanglement number between grafted chains or between matrix chains and grafted chains can make up the decrease in that between matrix chains, which thus reduces the decreasing rate of the total entanglement number with the strain. This can be further proved by quantifying the contributed stress by matrix chains, grafted chains, and silica NPs, respectively. In addition, the nucleation and propagation of voids are explored by calculating the Voronoi volume of PI beads and NPs, respectively. The competition between the obstacle effect of silica NPs and the grafting effect on the total entanglement number and nucleation and propagation of voids are quantified. Finally, voids preferably nucleate at the PI-NP interface by characterizing the distribution of the local elastic modulus, which has a low elastic modulus. Moreover, grafted chains can inhibit the premature appearance of voids and reduce the emergence of voids, which thus improves the rupture toughness of nanocomposites. In summary, this work provides a clear and novel understanding of how grafted chains manipulate the rupture toughness of the silica NP/PI nanocomposites at the molecular scale.