Effects of Film Confinement on Dielectric and Electrical Properties of Graphene Oxide and Reduced Graphene Oxide-Based Polymer Nanocomposites: Implications for Energy Storage

Abstract

2D nanofillers such as graphene oxide (GO) and reduced GO (rGO)-based polymer nanocomposites have emerged as crucial materials for various applications, from flexible solid-state capacitors to electromagnetic interference (EMI) shielding devices. Specifically, the dielectric breakdown strength (EBD) and dielectric constant of polymer nanocomposite capacitors determine their ability to store energy, whereas frequency-dependent loss is crucial for EMI shielding applications. The miniaturization of energy storage and electronic devices demands a detailed understanding of the behavior of these polymer nanocomposites in the thin-film regime (micron to sub-micron thicknesses). In this work, we demonstrate the effect of confinement on the dielectric, electrical, and capacitive energy storage properties of the polyvinylidene fluoride (PVDF)–GO and PVDF–rGO films. We show that the dielectric permittivity is significantly impacted by the nanofiller confinement in thin (≈1 μm) PVDF polymer films, which is comparable to the lateral dimension of these 2D nanofillers. In thin PVDF–GO films, the nanofillers (and associated surface dipoles) become oriented quasi-parallel to the film interfaces, affecting the relative projected area to the applied electric field. The conductivity and loss tangent values increased as a function of frequency with reduced film thickness, which is beneficial to EMI shielding application. The EBD of the confined GO-based films was found to be relatively independent of the filler fraction, whereas rGO-based films increased with the filler fraction after an initial decrease. These results provide fundamental insights into rational design principles for using ultrathin GO and rGO-based polymer nanocomposite films in next-generation flexible electronic and energy storage devices.