Deformation in polymer nanoparticle composites (PNC) at ultra high loading: interplay of jammed solids and glassy mechanics

Polymer nanoparticle composites (PNC) with ultra high loading of nanoparticles (NP) (>50%) have been shown to exhibit simultaneously improved strength and stiffness without compromising, and sometimes even improving, the toughness compared to the neat systems. As a result, these composites have become an interesting class of material for a variety of applications. Furthermore, when the particle volume fraction approaches random-close-pack, these composite systems become a combination of a jammed solid (the random-close-packed NPs) filled with a glass-forming polymer in its interstices. In our study, we aim to understand the origin of these performance enhancements by examining the dynamics of both polymer and NPs during active deformation. We performed molecular dynamics simulation of coarse-grained, glass forming polymers equilibrated in the voids of a random-close-packed NP packing and subsequently applied uniaxial tensile strain to the bulk system. We examined the mechanical characteristics of the PNC systems with different polymer fill fractions at temperatures below the glass transition temperature. We also compared the NP rearrangement behavior in the presence of polymer to the neat NP systems to provide a molecular view of the toughening mechanism in these materials.