Reduction of Dielectric Hysteresis in Multilayered Films via Nanoconfinement

Abstract

Micro/nanolayer coextrusion was used to fabricate polycarbonate (PC)/poly(vinylidene fluoride) (PVDF) layered films with significantly reduced dielectric losses while maintaining high energy density. The high-field polarization hysteresis was characterized for layered films as a function of PVDF layer thickness (6000 to 10 nm) and composition (10 to 70 vol % PVDF), and was found to decrease with decreasing layer thickness and PVDF content. To gain a mechanistic understanding of the layer thickness (or nanoconfinement) effect, wide-angle X-ray diffraction, polarized Fourier transform infrared spectroscopy, and broadband dielectric spectroscopy were employed. The results revealed that charge migration, instead of dipole flipping, was responsible for the hysteresis in multilayered films. The absence of PVDF dipoleflipping was attributed to the nonuniform electric field distribution in the layered structure, where the field in PVDF layers were calculated to be significantly lower than that in PC layers due to large contrast in dielectric constant (∼3 for PC versus ∼12 for PVDF). The charges were likely to be impurity ions in the form of catalyst residue or surfactants from suspension polymerization. The characteristics of the dielectric spectroscopy relaxation indicated that ions mostly existed in the PVDF layers, and PC/PVDF interfaces prevented them from entering adjacent layers. Therefore, as the layer thickness decreases to nanometer scales, the amount of ion movement, dielectric loss, and hysteresis were decreased. This study provides clear evidence of the nanoconfinement effect in multilayered films, which advantageously decreases the hysteresis loss.

Semicrystalline Structure–Dielectric Property Relationship and Electrical Conduction in a Biaxially Oriented Poly(vinylidene fluoride) Film under High Electric Fields and High Temperatures

“…Al electrodes appeared to be more resistant to the electrochemical reaction than Ag electrodes. To prevent direct electrochemical reactions between PVDF and the metal electrodes, we propose to carry out future research to sandwich PVDF with thin layers of a stable dielectric polymer such as PC (e.g., in multilayer films 13,56 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 …”

“…Considering Au is too expensive to be used as metal electrodes for practical applications, we propose to end-cap PVDF with a dielectric polymer (e.g., polycarbonate, PC) in a sandwich geometry or in multilayer films 13,56 to prevent direct contact of PVDF with metal electrodes. This research currently is under investigation and will be reported in the future.…”

Polymer-Based Dielectrics with High Energy Storage Density

“…Both mechanisms can be realized if the film contains a very large number of individual layers (and hence many interfaces). Recently, Baer and colleagues (35,36) demonstrated nanomultilayers consisting of alternating PC and PVDF (or PVDF-based copolymer) layers. PC is a low-permittivity (K = 3), low-loss polymer, whereas PVDF-based polymers have higher permittivity (K = 10-15) and higher loss.…”

“…Moreover, by combining VDF-based ferroelectric polymers (high polarization and large hysteresis loss) and low-K, low-loss materials with the nanoconfinement effect offered by the large number of interfaces, this approach also leads to a significant reduction in energy loss. For instance, the loss in a PC-PVDF multilayer with <100-nm individual layers and 30-70% volume fraction of PC can be reduced by nearly one order of magnitude compared with the loss in pure PVDF (35). A similar multilayer approach has been adopted in other polymer-inorganic (41) and self-assembled all-organic (42) systems.…”

Enhanced electric breakdown strength and high energy density of barium titanate filled polymer nanocomposites

“…5(c)), reducing the generation of charge carriers which may results in ionic or dc conduction and decreases electric breakdown strength, via decreasing the concentration of ionizable hydroxyl groups and ion migration on the surface of BT nanoparticles. 31,32 Furthermore, due to the well dispersion of surface modified BT nanoparticles, more interfaces play as active roles to the enhanced electric breakdown properties (Fig. 5(d)), having positive influences on interfacial charge around the surface of BT nanoparticles and charge concentration associated with the diffuse double layers between BT nanoparticles and PVDF matrix.…”