In Situ Catalytic Encapsulation of Core-Shell Nanoparticles Having Variable Shell Thickness: Dielectric and Energy Storage Properties of High-Permittivity Metal Oxide Nanocomposites

Abstract

Aluminum oxide encapsulated high-permittivity (ε) BaTiO 3 and ZrO 2 core-shell nanoparticles having variable Al 2 O 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 (EBIZrCl 2 ) on these Al 2 O 3 -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 ε 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/cm 2 at an electric field of 10 5 V/cm, and very low dielectric loss in the frequency range 100 Hz−1 MHz. Increasing the Al 2 O 3 shell thickness dramatically suppresses the leakage current and high field dielectric loss in these nanocomposites.