Article Cite This: Macromolecules XXXX, XXX, XXX−XXX
Flat-On Secondary Crystals as Effective Blocks To Reduce Ionic Conduction Loss in Polysulfone/Poly(vinylidene fluoride) Multilayer Dielectric Films Huadong Huang,† Xinyue Chen,† Ruipeng Li,‡ Masafumi Fukuto,‡ Donald E. Schuele,† Michael Ponting,§ Deepak Langhe,*,§ Eric Baer,† and Lei Zhu*,†
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Center for Layered Polymeric Systems (CLiPS) and Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, Ohio 44106-7202, United States ‡ National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, New York 11973, United States § PolymerPlus, LLC, 7700 Hub Pkwy, Valley View, Ohio 44125, United States S Supporting Information *
ABSTRACT: Recently, poly(vinylidene fluoride) (PVDF)based multilayer films have demonstrated good potential as high energy density, high temperature, and low loss polymer dielectrics for advanced electrical and power applications. However, impurity ion conduction in the PVDF layers can cause significant dielectric loss at high temperatures. In this study, we discovered a facile melt-recrystallization method to suppress ionic conduction loss in polysulfone (PSF)/PVDF 50/50 (v/v) 33-layer films. By use of combined differential scanning calorimetry, broadband dielectric spectroscopy, and simultaneous small-angle X-ray scattering/wide-angle X-ray diffraction techniques, the underlying mechanism for the suppression of ionic conduction was unraveled. Basically, the growth and hierarchical organization of primary and secondary PVDF crystals confined in 400 nm layers played an important role. When the cooling rate during melt-recrystallization was high (e.g., ≥500 °C/min), small and poorly oriented secondary crystals between orderly stacked edge-on primary crystals allowed free transport of impurity ions in PVDF layers. At low to moderate cooling rates (i.e.,
