Mechanical Properties of Glassy Polymer Nanocomposites Via Atomistic and Continuum Models: the Role of Interphases

The mechanical properties of glassy polymer nanocomposites (PNCs) are investigated via a new hierarchical computational methodology, which combines atomistic molecular dynamics (MD) simulations and homogenization approaches. The homogenization methodology is based on a systematic nano/micro/macro coupling between detailed atomistic MD simulations and a variational approach through the Hill–Mandel lemma. The proposed methodology is applied in model glassy polybutadiene/silica nanocomposites for different nanoparticle (NP) volume fractions. Initially, using MD simulations, the polymer/NP interphase in PNCs is directly examined by probing the density distribution and the stress profile at equilibrium. By using a continuum mechanics based approach, we can compute effective deformation gradients for each atom, allowing us to probe the distribution of the (local) stress and strain fields in the atomistic model. With this new approach, the effective Young modulus and the Poisson ratio of the polymer/NP interphases are directly calculated, exhibiting a higher rigidity compared to the polymer matrix. In the last part of the proposed approach, the mechanical properties at the interphases and the polymer are used together with the homogenization approach to develop a continuum model for predicting the mechanical properties of the PNCs, which are found to be in very good agreement with the effective mechanical properties calculated through atomistic MD simulations.