Improved dielectric and energy storage properties of poly(vinyl alcohol) nanocomposites by strengthening interfacial hydrogen-bonding interaction

Dielectric capacitor has drawn much attention recently both in academia and in industry because of its high power density and excellent cycle performances. In order to meet the demand for high energy density, high-e (dielectric permittivity) nanoparticles are dispersed into polymer matrices to form nanocomposites with both high epsilon and high E-b (breakdown strength). Polymer-nanoparticle interface has great influence on energy storage properties. In order to find out whether we can prepare well-dispersed nanocomposites by forming a thin coating layer (less than 2 nm) on the surface of nanoparticles with strengthened interfacial interaction, such as hydrogen-bonding interaction, a specific coating molecule, i.e., 3,4,5-trihydrobenzoic acid (or Gallic Acid, GA), was selected for surface modification of BaTiO3 (BT) in this research. A coating layer of only 1.6 nm in thickness formed by the reaction between phenolic hydroxyl groups in GA and surface hydroxyl groups on BT to produce modified BT@GA nanoparticles. Hydrogen-bonding interaction did form between GA and the hydroxyl groups in PVA matrix. This ensured fine dispersion, higher epsilon, higher E-b and higher energy storage density for PVA + BT@GA nanocomposites. For PVA + 40% BT@GA, e reached 51 at 1 kHz, while Eb was 144 MV/m, which is twice as that of PVA + 40% BT. The discharging energy density of PVA + 40% BT@GA reaches 0.554 J/cm(3) at 50 MV/m, about fourth times as that of pristine PVA.