Fuente: Journal of applied polymer Lugar: RESEARCH ARTICLE Multiscale mechanism of the shoulder peak effect.


ABSTRACT
Conductive polymer composites (CPCs) are promising candidates for flexible electronics and structural health monitoring. However, their practical application is often hindered by the shoulder peak effect—a non-monotonic rebound in the resistance–strain curve during unloading that compromises sensing accuracy and signal stability. Although previous studies have mainly focused on experimental observations, the molecular-level origin of this phenomenon remains insufficiently understood. In this work, experimental characterization is combined with molecular dynamics (MD) simulations to elucidate the interfacial interactions in graphene (GR)/ethylene–propylene–diene monomer (EPDM) composites. The results reveal that the shoulder peak effect primarily arises from the mismatch between the viscoelastic hysteresis of the EPDM matrix and the reconstruction of the conductive network. Notably, the composite containing 4 wt% GR forms a more uniform and stable conductive network with the strongest interfacial adhesion, significantly suppressing the shoulder peak effect. MD simulations further confirm that this formulation exhibits the highest interfacial binding energy and the most compact structural configuration. Overall, this study provides mechanistic insight and practical guidelines for designing high-reliability flexible strain sensors based on CPCs.