Mechanical properties of glassy polymer nanocomposites via atomistic and continuum models: The role of Interphases*

We propose a novel hierarchical computational approach to predict the distribution of mechanical properties of polymer nanocomposites (PNCs), based on homogenization approaches and atomistic molecular dynamics (MD) simulations. The homogenization methodology follows a systematic nano/micro/macro coupling between detailed atomistic non-equilibrium MD simulations and a variational approach based on the Hill–Mandel lemma. We apply the proposed scheme in model glassy polybutadiene/silica PNCs for different nanoparticle (NP) volume fractions. Using MD simulations, we directly probe the polymer/NP interphases under non-equilibrium conditions (tensile deformation), and compute the density, stress and strain distributions. A detailed analysis reveal the role of different chain conformations (train, loops, bridges) to the mechanical properties at the interphase. The effective Young modulus and Poisson ratio of the organic/inorganic interphases are directly calculated from the local stress and strain data. Interphases are shown to exhibit higher rigidity compared to the bulk material. The distribution of mechanical properties across the atomistic model PNCs is used together with the homogenization approach to develop a continuum model for predicting the mechanical properties of the PNCs.