Enhancing Dielectric Properties of Poly(ether imide) Composites through Vapor Phase Infiltration of PMMA/AlO_<i>x</i> Hybrid Fibers

Polymer dielectric composites have garnered significant research interest owing to their versatile applications and tunable filler configurations. In this study, vapor phase infiltration is employed to incorporate inorganic alumina (AlOx) into poly(methyl methacrylate) (PMMA) fibers, creating multi-interfaced organic–inorganic hybrid fibers. Precursor exposure time serves as a critical parameter for controlling the deposition behavior and spatial organization of inorganic components within the hybrid fibers. Prolonged exposure time enables deep infiltration and homogeneous dispersion of alumina throughout the polymer fiber matrix, while short exposure time leads to a characteristic surface-rich architecture. These multi-interface hybrid fibers demonstrate exceptional multifunctional properties, including enhanced mechanical strength and thermal stability, making them promising candidates as advanced fillers for dielectric composites. These specially designed fillers were incorporated into PEI/fiber composites, resulting in enhanced dielectric constant, energy storage density, and high breakdown strength (700 kV/mm) while maintaining a low loss tangent and high charge/discharge efficiency when measured using large electrodes while achieving an energy storage density of 8.9 J/cm3 favorable for capacitor applications. This hybrid fiber approach establishes a paradigm for the design and development of next-generation filler materials in dielectric applications.