Coupled effects of nanoparticle surface roughness and grafting architecture on mechanical reinforcement in polymer nanocomposites.

Polymer nanocomposites derive their mechanical performance from nanoscale interfacial mechanisms that govern stress transfer, nanoconfinement, and deformation resistance. Among these mechanisms, nanoparticle surface geometry, interfacial interactions, and grafting architecture are particularly important, yet their coupled effects on reinforcement remain insufficiently understood. Here, coarse-grained molecular dynamics simulations are used to investigate polymer nanocomposites containing a rigid spherical nanoparticle with either smooth or sinusoidally rough surface geometry. Non-grafted and grafted systems with different grafting architectures are compared under weak and strong interfacial interactions. Under weak interfacial interactions, changes in surface roughness and grafting produce only modest differences in the tensile response. In contrast, under strong interactions, higher-amplitude roughness produces higher elastic moduli than the smooth case, consistent with more restricted interfacial polymer mobility and more effective load transfer. Grafting further amplifies reinforcement by creating permanent nanoparticle-polymer connectivity and increasing the mean number of topological constraints. Primitive-path analysis shows that grafting produces a larger topological shift than surface roughness. Beyond uniform grafting, the spatial organization of grafting sites provides additional tunability. Clustered grafting induces directional mechanical response, while targeted placement of grafting sites at surface apexes of surface-roughened nanoparticle more effectively couples tethered polymer chains to surface roughness features. These findings demonstrate that nanocomposite reinforcement arises from a cooperative interplay among surface roughness, interfacial interaction, and grafting architecture. The results provide molecular-level design principles for engineering polymer nanocomposites with improved interfacial load transfer, stiffness, and tailored mechanical performance.