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 (epsilon) BaTiO3 and ZrO2 core-shell nanoparticles having variable Al2O3 shell thicknesses were prepared via a layer-by-layer methylaluminoxane coating process. Subsequent chemisorptive activation of the single-site metallocene catalyst [rac-ethylene-bisindenyl]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 epsilon 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 (nu(f)) of nanoparticles below 0.06. The nanocomposites have leakage current densities of similar to 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 Al2O3 shell thickness dramatically suppresses the leakage current and high field dielectric loss in these nanocomposites.