Mechanical Properties and Crazing Behavior in Model Polymer-Grafted Nanoparticle Thin Films

Thin films comprised of inorganic-organic polymer-grafted nanoparticles (PGNs) show promise for use in flexible electronics and high energy density materials. Recently, there has been significant interest in tuning the properties of the polymer-grafted layers to optimize entanglement formation between neighboring PGNs and improve mechanical performance. In this work, we show how graft density and polymer length affect inter-PGN entanglements and mechanical properties using coarse-grained molecular dynamics (MD) simulations. Specifically, we simulate twelve PGNs organized in a hexagonal spacing on a smooth, attractive surface. We rigidly attach the first monomer of every chain to the surface of a nanoparticle (using rigid body constraints) and model the polymers as bead-spring chains. We first quantify the number of interparticle entanglements between PGNs and show that moderate graft density particles have increased interparticle entanglements per chain and better mechanical toughness compared to high graft density particles in the melt state. We then cool the monolayer below the glass transition and compare the crazing behavior of PGN thin films to their analogous homopolymer thin films.