Effects of Nanoparticles Motion on a Bound Layer in Strongly Attractive Polymer Nanocomposites

The attractive interactions between polymers and nanoparticles (NPs) in polymer composites can lead to the formation of a "bound" layer around the nanoparticle (NP) with very slow dynamics. Previous simulations show that this bound layer has a significantly larger relaxation time compared to polymer matrix. However, these studies have been done for a NP that is fixed at its initial position and does not move during simulation (infinitely massive NP). Here, we perform molecular dynamics simulations for polymer composites, where the NP can move in the polymer matrix. We explore the degree to which the NP diffusion affects nanocomposite dynamics. To explain the effects of NP diffusion, we study the dynamical properties of polymer composites, e.g., scattering function, relaxation time. We find that the motion of the NP reduces the bound layer relaxation time significantly. We show that the bound layer diffuses with NPs, and that results in shorter relaxation time. We also study the effects of NP motion on the glass transition temperature.