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

摘要

Aluminum oxide encapsulated high-permittivity (ε) 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 s 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 (v_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 Al2O3 shell thickness dramatically suppresses the leakage current and high field dielectric loss in these nanocomposites.