4.8 Article

Achieving Flat-on Primary Crystals by Nanoconfined Crystallization in High-Temperature Polycarbonate/Poly(vinylidene fluoride) Multilayer Films and Its Effect on Dielectric Insulation

Journal

ACS APPLIED MATERIALS & INTERFACES
Volume 12, Issue 40, Pages 44892-44901

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/acsami.0c15457

Keywords

multilayer films; dielectric insulation; polycarbonate; poly(vinylidene fluoride); flat-on crystals

Funding

  1. Office of Naval Research [N00014-19-1-2032]
  2. U.S. Department of Energy User Facility [DESC0012704]

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To meet the stringent requirements of next generation film capacitors for power electronics, multilayer films (MLFs) are fabricated with the advantage of achieving high emperature rating, high energy density, and reasonably low loss simultaneously. In this study, a high permittivity polar polymer, poly(vinylidene fluoride) (PVDF), is Inultilayered with a linear, low loss dielectric polymer such as high-temperature polycarbonate (HTPC). However, the dielectric loss of these MLFs was still high as compared with current state-of-the-art biaxially oriented polypropylene (BOPP) films. The goal of this work is to decrease the dielectric loss and enhance dielectric insulation by achieving flat-on primary PVDF crystals in MLFs via rranocorrfined meltrecr-ystallization. Based on simultaneous small- and wide-angle X-ray scattering experiments, edge-on lamellar crystals were observed or all as-extruded MLFs, regardless of difTererrt PVDF layer thicknesses. However, after melting at 180 degrees C follorved by ecrystallization, flat-on primary crystals were successfully achieved when the PVDF layer thickness was below 39 nm. Above 78 nm for the PVDF layer, major edge-on primary crystals with minor flat-on secondary ct-ystals were observed. From leakage current, breakdown, lifetime, and electric displacement-electric field loop studies, MLFs with the flat-on primary crystals exhibited reduced loss and enhanced dielectric insulation as compared to as-extruded MLFs and those with edge-on primary/flat-on secondary crystals. This was attributed to the effective blockage of charge carriers by the flat-on PVDF primary crystals and their reduced ferroelectric switching.

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