(734e) Entanglements and Toughness of Model Polymer-Grafted Nanoparticle Monolayers

Inorganic nanoparticles with polymer chains grafted to their surface, known as polymer-grafted nanoparticles (PGNs), can be used as building blocks for functional materials with a controllable nanoscale structure. We use coarse-grained molecular dynamics (MD) simulations to show how experimental parameters such as graft density and chain length control the structural, entanglement, and mechanical properties of neat PGNs in a hexagonally packed monolayer. Considering systems from a very high to moderate graft density which were stable as well-ordered monolayers, we find that the graft chains of nearby PGNs interpenetrate more in systems with lower (moderate rather than high) graft density. When chains are long enough to entangle, this also leads to an increased number of interparticle entanglements per chain for the lower graft density systems. In addition to studying mechanical properties of particles on surfaces in the melt state, we cooled the systems below the glass transition and removed the surface to study the glassy freestanding thin film. In either case, lower graft density led to improved toughness of the material. Finally, we found that the craze microstructure in the PGN films is significantly different than that of homopolymer films, with the PGN films having more regular perforations that appear primarily in interstitial areas of the particles, which is qualitatively in line with recent experimental findings.