In situ catalytic encapsulation of core-shell nanoparticles having variable shell thickness: Dielectric and energy storage properties of high-permittivity metal oxide nanocomposites

Aluminum oxide encapsulated high-permittivity (-) BaTiO₃ and ZrO₂ core-shell nanoparticles having variable Al₂O ₃ shell thicknesses were prepared via a layer-by-layer methylaluminoxane coating process. Subsequent chemisorptive activation of the single-site metallocene catalyst [rac-ethylenebisindenyl]zirconium dichloride (EBIZrCl₂) on these Al₂O₃-encapsulated nanoparticles, followed by propylene addition, affords 0-3 metal oxide-isotactic polypropylene nanocomposites. Nanocomposite microstructure is analyzed by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, differential scanning calorimetry, atomic force microscopy, and Raman spectroscopy. The in situ polymerization process yields homogeneously dispersed nanoparticles in a polyolefin matrix. Electrical measurements indicate that as the concentration of the filler nanoparticles increases, the effective permittivity of the nanocomposites increases, affording - values as high as 6.2. The effective permittivites of such composites can be predicted by the Maxwell-Garnett formalism using the effective medium theory for volume fractions (ν_f) of nanoparticles below 0.06. The nanocomposites have leakage current densities of ∼10^-7-10^-9 A/cm² at an electric field of 10⁵ V/cm, and very low dielectric loss in the frequency range 100 Hz-1 MHz. Increasing the Al₂O₃ shell thickness dramatically suppresses the leakage current and high field dielectric loss in these nanocomposites.