Structure, Entanglements, and Mechanical Properties of Adsorbed Polymer-Grafted Nanoparticles from Molecular Dynamics Simulations

Inorganic nanoparticles with polymer chains grafted to their surface, or polymer-grafted nanoparticles (PGNs), have potential as a means to create functional materials with a controllable nanoscale structure. For instance, a thin film of PGNs deposited on a surface can self-assemble into a hexagonally packed structure with mechanically robust and precise spacing. We perform molecular dynamics (MD) simulations of neat PGNs adsorbed on a flat surface with various graft densities, graft lengths, and surface adsorption strengths, to show how these synthetically controllable parameters affect the structure and entanglements. Specifically, we model a PGN as a spherical nanoparticle to which graft chains are tethered at random points on the surface, and use a simple bead-spring model with finitely extensible bonds to allow us to capture polymer entanglements. We first consider two nearby PGNs adsorbed on a surface (isolated from other PGNs) and analyze their interparticle spacing and entanglements. We then simulate adsorbed hexagonally packed PGN monolayers and relate their stress-strain behavior to nanoparticle arrangement and interparticle entanglements.