Coupled Effects of Filler Aspect Ratio and Interfacial Characteristics on the Mechanical/Thermal/Electrical Properties of Graphene Nanocomposites

Owing to interfacial defects and filler‐size effects, mechanical/thermal/electrical experimental performances of graphene‐reinforced polymer nanocomposites frequently deviate greatly from theoretical predictions. This study develops a cross‐scale multi‐physics effective medium theory (EMT) model for graphene/epoxy nanocomposites, integrating aspect‐ratio‐dependent interfacial degradation. Validated against multiple experimental datasets, the model yields prediction errors below 10%, surpassing traditional homogenization approaches. A competitive size‐dependent effect is uncovered: increasing graphene aspect ratio linearly boosts interfacial modulus ( E int = 5434 α + 3.722 MPa) yet reduces composite Young's modulus by up to 55%. Larger aspect ratios induce exponential decay of interfacial thermal and electrical conductivity and break internal transport networks. At 0.5 vol% loading, low‐aspect‐ratio graphene ( α < 8 × 10 −3 ) increases Young's modulus by 42%, thermal conductivity by 117%, and electrical conductivity by over four orders of magnitude versus neat epoxy. This work provides quantitative insights for designing high‐performance graphene‐polymer nanocomposites.