Interphase engineering in carbon black–reinforced piezoelectric nanocomposites: A combined experimental and micromechanical modeling study

Piezoelectric polymer–ceramic composites are promising for sensors, energy-harvesting, and flexible electronics. However, their performance is often limited by weak filler–matrix coupling. To address this challenge, carbon black (CB) nanoparticles with controlled surface modification were introduced to engineer the interphase in KNN–epoxy composites. A physics-based micromechanical model was developed to systematically investigate the role of interphase characteristics on the electro-mechanical response. The model captures the coupled effects of filler dispersion, interphase properties, and conductive network formation, and successfully reproduces the experimentally observed non-monotonic dependence of piezoelectric performance on CB content. Experimentally, three CB types—untreated (CB0), mildly oxidized (CB1), and heavily oxidized (CB2)—were evaluated. CB1-based composites achieved the best balance of mechanical, dielectric, and piezoelectric properties, showing improved dispersion, adhesion, and polarization. By integrating experimental results with predictive modeling, this study reveals that interphase engineering governs charge transport and polarization behavior, and establishes a design framework for optimizing piezoelectric performance in multi-scale hybrid nanocomposites.