On Void Formation during the Simulated Tensile Testing of Polymer-Filler Particle Composites.

We simulate model polymer composites composed of linear polymer strands and spherical, monodisperse filler particles (FP). These molecular dynamics simulations implement a coarse-grained, bead-spring force field, and we vary several formulation parameters to study their influences on material properties. These parameters include FP radius, FP volume fraction, temperature, and the polymer-polymer, FP-FP, and polymer-FP interaction potentials. Uniaxial extension of the simulation cells allows direct comparison of the mechanical reinforcement (or weakening) provided by the FP. We focus on the formation of microscopic voids during simulated tensile testing of glassy polymer composites and quantify how the characteristic spatial and morphological arrangement of these voids varies as a function of the interaction potentials used in the simulations. We discuss the implications for polymer composite design and formulation, specifically observing that an interaction scenario with a repulsive polymer-FP cross-interaction produces additional mechanical reinforcement above the glass transition temperature (T g ) but is detrimental to performance below T g , at the FP sizes and volume fractions examined in this work.