Nanoasperity-driven reinforcement and viscoelastic modulation in polymer nanocomposites: A coarse-grained molecular dynamics study

Inorganic nanofillers in biological materials often possess irregular geometries and rough surfaces, commonly referred to as nanoasperities, that are thought to enhance reinforcement by increasing interfacial area, resisting interfacial slip, and confining surrounding polymer chains. However, how nanoasperity-driven mechanisms translate into tunable mechanical and viscoelastic responses in engineering polymer nanocomposites remains unclear. In this study, we employ coarse-grained molecular dynamics simulations to systematically investigate the coupled effects of nanofiller surface roughness and interfacial interaction strength on the mechanical behavior of polymethyl methacrylate (PMMA) nanocomposites. The results reveal that nanoasperities induce pronounced polymer confinement whose effectiveness depends critically on both nanoasperity configuration and interfacial interactions. Under strong interfacial interactions, deep nanoasperities enable synergistic mechanical interlocking and interfacial confinement, leading to markedly enhanced load transfer and increased elastic and shear moduli. In contrast, weak interfacial interactions permit interfacial slipping and limit chain confinement, suppressing reinforcement regardless of surface roughness. Viscoelastic analysis further shows that while increasing interfacial strength elevates both storage and loss moduli, the loss tangent is governed by the competition between interfacial confinement and heterogeneous chain dynamics away from the nanofiller surface. Overall, this study demonstrates that nanoasperity-induced reinforcement emerges from the coupled interplay of nanoasperity configuration, interfacial mechanics, and polymer chain dynamics, providing molecular-level design guidelines for designing polymer nanocomposites with tailored stiffness and damping.