Molecular Dynamics-Based Calibrated Micromechanics Model for Elastic Properties of Fullerene-PMMA Nanocomposites Incorporating Interface Stress

Fullerene-based polymer nanocomposites are promising candidates for micro- and nano-electromechanical systems (MEMSs/NEMSs) due to their tunable mechanical performance and high surface-to-volume ratios. At the nanoscale, interfacial stresses strongly influence the effective elastic response, yet quantitative interface parameters are rarely available for continuum modeling. In the current investigation, a molecular dynamics (MD)-based calibrated micromechanics framework is developed to predict the bulk modulus of fullerene-poly(methyl methacrylate) (PMMA) nanocomposites that incorporate interface stress effects. Atomistic representative volume elements (RVEs) containing individual fullerene nanoparticles embedded in a polymer matrix are generated using controlled molecular packing and systematically equilibrated. The bulk moduli of both isolated fullerenes and fullerene-PMMA RVEs are extracted from energy-volume relationships using a Birch-Murnaghan equation of state. These MD results are used to calibrate a size-dependent micromechanics model and to extract the surface Lamé modulus of the polymer-fullerene interface directly. The extracted surface Lamé modulus remains nearly constant (approximately 19 N/m) across all investigated fullerene sizes. In contrast, the interfacial contribution to the effective bulk modulus increases significantly for smaller nanoparticles due to their higher surface to volume ratios. The calibrated model accurately reproduces MD predictions and provides a physically grounded multiscale link between atomistic interfacial behavior and continuum elastic properties. The proposed framework offers a predictive tool for the rational design of surface-dominated nanocomposites in MEMS/NEMS applications.