Structure and Entanglement Network of Model Polymer-Grafted Nanoparticle Monolayers

Ultrathin films containing polymer-grafted nanoparticles (PGNs) show promise for use in hybrid electronics and high energy density materials. In this work, we use a coarse-grained model to simulate a hexagonally packed monolayer of PGNs adsorbed on a smooth surface that is attractive to both nanoparticles and polymer chains. We find that decreasing graft density at the same graft length increases interpenetration of the polymer-grafted layers, as expected. We quantify both overall and interparticle entanglements (between polymers grafted to different PGNs). While the higher graft density particles have a higher overall number of entanglements per chain, the lower graft density particles have higher interparticle entanglements per chain due to their increased chain interpenetration. Finally, we apply uniaxial tensile deformation to the monolayers; the peak stress occurs at lower strain values for higher graft density particles, which is attributed to the relatively lower number of interparticle entanglements. Our analysis provides a molecular picture of how decreasing graft density leads to better interpenetration, increased interparticle entanglements, and increased toughness of PGN monolayers, though it can lead to slightly less uniformly spaced monolayers, in agreement with previous experimental observations. These tradeoffs are crucial to understand for the design of robust, well-ordered inorganic organic hybrid films.