Polymer conformations and dynamics in polymer nanoparticle composite with high nanoparticle loading

Polymer nanoparticle composites (PNC) with high loadings of nanoparticles (>50%) are an interesting class of material for a wide range of applications. Recent experiments have shown that these highly loaded PNC exhibit simultaneously improved strength and stiffness without compromising, sometimes even improving, the toughness compared to neat systems. These PNCs also show a large increase in the polymer glass transition temperature and viscosity, suggesting a slowdown in both segmental and chain-scale dynamics due to confinement. The goal of this work is to understand how confining polymers to the cavities of a random close packed nanoparticle solid affects polymer conformations and dynamics from the segmental to the chain scale. We performed molecular dynamics simulation of both entangled and unentangled coarse-grained polymer equilibrated in the voids of a nanoparticle packing. We varied the polymer fill fraction and compared the dynamics of the polymer in PNC to the pure polymer system, finding that the changes in the dynamics depend on the number of nanoparticles in contact with a polymer. Finally, we deformed the PNC uniaxially to track rearrangement behavior of nanoparticles and polymer segments to provide a molecular view of the toughening mechanism in these materials.