Enhanced dielectric performance and energy storage of PVDF-HFP-based composites induced by surface charged Al ₂ O ₃

In order to enhance dielectric properties and energy storage density of poly(vinylidene fluoride-hexafluoro propylene) (PVDF-HFP), surface charged gas-phase Al ₂ O ₃ nanoparticles (GP-Al ₂ O ₃ , with positive surface charges, ε’ ≈ 10) are selected as fillers to fabricate PVDF-HFP-based composites via simple physical blending and hot-molding techniques. The results show that GP-Al ₂ O ₃ are dispersed homogeneously in the PVDF-HFP matrix and the existence of nanoscale interface layer (matrix-filler) is investigated by SAXS. The dielectric constant of the composites filled with 10 wt % GP-Al ₂ O ₃ is 100.5 at 1 Hz, which is 5.6 times higher than that of pure PVDF-HFP. The maximum energy storage density of the composite is 4.06 J cm ⁻³ at an electrical field of 900 kV mm ⁻¹ with GP-Al ₂ O ₃ content of 1 wt %. Experimental results show that GP-Al ₂ O ₃ could induce uniform fillers’ distribution and increase the concentration of electroactive β-phase as well as enhance interfacial polarization in the matrix, which resulted in enhancements of dielectric constant and energy storage density of the PVDF-HFP composites. This work demonstrates that surface charged inorganic-oxide nanoparticles exhibit promising potential in fabricating ferroelectric polymer composites with relatively high dielectric constant and energy storage.