Flexible dielectric and electronic materials with high dielectric constant (k) and low loss are constantly pursued. Encapsulation of conductive fillers with insulating shells represents a promising approach, and has attracted substantial research efforts. However, progress is greatly impeded due to the lack of a fundamental understanding of the polarization mechanism. In this work, a series of core–shell polymer composites is studied, and the correlation between macroscopic dielectric properties (across entire composites) and microscopic polarization (around single fillers) is investigated. It is revealed that the polarization in polymer conductor composites is determined by electron transport across multiple neighboring conductive fillers—a domain‐type polarization. The formation of a core–shell filler structure affects the dielectric properties of tpolymer composites by essentially modifying the filler‐cluster size. Based on this understanding, a novel percolative composite is prepared with higher‐than‐normal filler concentration and optimized shell's electrical resistivity. The developed composite shows both high‐k due to enlarged cluster size and low loss due to restrained charge transport simultaneously, which cannot be achieved in traditional percolative composites or via simple core–shell filler design. The revealed polarization mechanism and the optimization strategy for core–shell fillers provide critical guidance and a new paradigm, for developing advanced polymer dielectrics with promising property sets.

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Flaky Cu (f-Cu) particles coated with various thickness of silica (SiO 2) were incorporated into poly(vinylidene fluoride) (PVDF) to investigate the effects of SiO 2 coating layer and its thickness on dielectric properties of the composites. The morphological and dielectric properties of the composites were characterized. The results indicate that the SiO 2 coating layer significantly affects the electrical properties of f-Cu@SiO 2 and f-Cu@SiO 2 /PVDF, and that the PVDF composites with f-Cu@SiO 2 particles exhibit superior dielectric properties compared with raw f-Cu. Dissipation factors (tanδ) of the f-Cu@SiO 2 /PVDF are remarkably suppressed and reduced to rather low level owing to the presence of SiO 2 shell which serves as an interlayer between the f-Cu particles preventing them from contacting with each other. Furthermore, the effect of suppression on tanδ tends to be more prominent as the thickness of SiO 2 coating layer increases. The as-prepared composites possess high dielectric constant and low tanδ, making them promising for the industrial application as embedded capacitors.

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To suppress the high dielectric loss of graphene oxide (GO)/poly(vinylidene fluoride) (PVDF) while maintaining high dielectric constant (high- k) near the percolation threshold, in this study, GO nanosheets coated with polydopamine (PDA) were integrated into PVDF to investigate the effects of the PDA shell and its concentrations on the dielectric properties of the nanocomposites. The results indicate that the dissipation factor and conductivity of the GO@PDA/PVDF are significantly suppressed to very low values compared with the pristine GO/PVDF composites, attributable to the PDA interlayer between the GO nanosheets which prevents them from direct contact with each other and remarkably reduces the leakage loss. Furthermore, activation energies of the GO/PVDF and GO@PDA/PVDF composites were calculated as 1.247 and 0.884 eV, respectively, indicating that the presence of PDA interlayer reduces the relaxation activation energy and makes the relaxation occur at low temperature for the GO@PDA/PVDF. The prepared GO@PDA/PVDF nanocomposites with high- k but low loss have potential applications in microelectronic engineering.