Nanoparticle, Size, Shape, and Interfacial Effects on Leakage Current Density, Permittivity, and Breakdown Strength of Metal Oxide-Polyolefin Nanocomposites: Experiment and Theory

A series of 0-3 metal oxide-polyolefin nanocomposites are synthesized via in situ olefin polymerization, using the following single-site metallocene catalysts: C2-symmetric dichloro[rac-ethylenebisindenyl]-zirconium(IV),Me ₂Si( ^tBuN)(η ⁵-C ₅Me ₄)TiCl ₂, and(η ⁵-C ₅Me ₅)TiCl ₃ immobilized onmethylaluminoxane (MAO)-treated BaTiO ₃, ZrO ₂, 3-mol %-yttria-stabilized zirconia, 8-mol%-yttria-stabilized zirconia, sphere-shaped TiO2 nanoparticles, and rod-shaped TiO ₂ nanoparticles. The resulting compositematerials are structurally characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), ¹³C nuclear magnetic resonance (NMR) spectroscopy, and differential scanning calorimetry (DSC). TEM analysis shows that the nanoparticles are well-dispersed in the polymer matrix, with each individual nanoparticle surrounded by polymer. Electrical measurements reveal that most of these nanocomposites have leakage current densities of ∼10 ^-6-10 ^-8 A/cm ²; relative permittivities increase as the nanoparticle volume fraction increases, withmeasured values as high as 6.1. At the same volume fraction, rod-shaped TiO ₂ nanoparticle-isotactic polypropylene nanocomposites exhibit significantly greater permittivities than the corresponding sphere-shaped TiO ₂ nanoparticleisotactic polypropylene nanocomposites. Effective medium theories fail to give a quantitative description of the capacitance behavior, but do aid substantially in interpreting the trends qualitatively. The energy storage densities of these nanocomposites are estimated to be as high as 9.4 J/cm ³.