Porous nanoparticles overcome the conventional stiffness-damping tradeoff in polymer nanocomposites.

Nanoparticle-reinforced polymer nanocomposites offer tunable mechanical properties, yet the impact of nanoparticle surface configurations on mechanical and viscoelastic properties remains underexplored. Using coarse-grained molecular dynamics simulations, we investigate how smooth, corrugated, and porous nanoparticles affect the molecular dynamic behaviors of polymer chains, as well as stiffness and damping properties of polymethyl methacrylate (PMMA) nanocomposites. Our results show that all nanoparticle-PMMA systems enhance Young's and shear moduli, with porous nanoparticles providing the greatest improvements. Stronger interfacial interactions further amplify these effects. A quasi-linear correlation is observed between shear modulus and Debye-Waller factor-based molecular stiffness, with porous nanoparticles exhibiting higher shear moduli due to their unique structural confinement effect. Local molecular stiffness analysis reveals pronounced dynamic heterogeneity, leading to heterogeneous strain distributions under shear deformation. Small amplitude oscillatory tests demonstrate simultaneous enhancements in stiffness and damping, overcoming the conventional tradeoff. These findings highlight the potential of tailoring nanoparticle surface configurations for designing polymer nanocomposites with superior mechanical performance.