Meliorative dielectric properties in core@double-shell structured Al@Al2O3@PDA/PVDF nanocomposites via decoupling the intra-particle polarization and inter-particle polarization

Percolating polymeric composites present enormous potential owing to high dielectric constant (ε) which can be realized near the percolation threshold, but the accompanied large loss forbids their extensive use in practice. Great efforts have been devoted to coat conductive particles with an insulating shell for constrained dielectric loss, yet they markedly reduce ε. In this work, we explore poly(vinylidene fluoride) (PVDF) composites with a serial of core@double-shell Al@Al2O3@PDA (polydopamine) nanoparticles with various PDA shell thicknesses. It reveals that the high ε of the nanocomposites results from a fast intra-particle polarization and a slow inter-particle polarization. The formation of double-shell enables the independent control of the two polarizations always coupled in traditional percolating composites. Through facilitating intra-particle polarization and repressing inter-particle polarization, Al@Al2O3@PDA/PVDF can achieve a much higher ε and lower dielectric loss simultaneously, far exceeding the unmodified Al@Al2O3/PVDF. Moreover, the calculated activation energy of carrier migration in Al@Al2O3@PDA/PVDF is obviously higher than that in untreated nanocomposites, indicating enhanced charge-trapping capability in the core@double-shell nanofiller composites. This core@double-shell strategy offers a new paradigm for the design and preparation of percolating composites with desirable dielectric performances.