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),Me2Si( BuN)(η-C5Me4)TiCl2, and (η -C5Me5)TiCl3 immobilized onmethylaluminoxane (MAO)-treated BaTiO3, ZrO2, 3-mol%-yttria-stabilized zirconia, 8-mol%-yttria-stabilized zirconia, sphere-shapedTiO2 nanoparticles, and rod-shapedTiO2 nanoparticles. The resulting compositematerials are structurally characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), C 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 ∼10-10 A/cm; relative permittivities increase as the nanoparticle volume fraction increases, with measured values as high as 6.1. At the same volume fraction, rod-shaped TiO2 nanoparticle-isotactic polypropylene nanocomposites exhibit significantly greater permittivities than the corresponding sphere-shaped TiO2 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.