Frequency‐Dependent Viscoelasticity in Bidisperse Carbon Black‐Filled Natural Rubber Nanocomposites: The Critical Role of Heterosized Filler Pairs

ABSTRACT The frequency‐dependent viscoelasticity of bidisperse carbon black (CB)‐filled natural rubber (NR) nanocomposites is investigated using coarse‐grained molecular dynamics. The Payne effect becomes more pronounced with increasing frequency and strain amplitude. High frequencies cause extensive nanoparticle (NP) network disruption, reducing loss modulus. Low frequencies enable network reformation and chain friction, increasing loss modulus under large strains. The change in non‐bonded interaction energy is dominated by CBCB interactions, with negligible NRNR and CBNR contributions on the normalized per‐pair scale. A frequency‐driven transition in the dominant CB pair is identified: same‐sized pairs dominate at low frequencies, while heterosized pairs prevail at high frequencies. The frequency 2.5 × 10 −5 fs −1 marks a characteristic point where the NP network maximally constrains chain mobility. These findings establish that the Payne effect is primarily governed by NP network dynamics, with heterosized CB pairs playing a key role in modulating the frequency‐dependent energy dissipation.