Recently, poly(vinylidene fluoride) (PVDF)-based multilayer films have demonstrated enhanced dielectric properties, combining high energy density and high dielectric breakdown strength from the component polymers. In this work, further enhanced dielectric properties were achieved through interface/interphase modulation and biaxial orientation for the poly(ethylene terephthalate)/poly(methyl methacrylate)/poly(vinylidene fluoride-co-hexafluoropropylene) [PET/PMMA/P(VDF-HFP)] three-component multilayer films. Because PMMA is miscible with P(VDF-HFP) and compatible with PET, the interfacial adhesion between PET and P(VDF-HFP) layers should be improved. Biaxial stretching of the as-extruded multilayer films induced formation of highly oriented fibrillar crystals in both P(VDF-HFP) and PET, resulting in improved dielectric properties with respect to the unstretched films. First, the parallel orientation of PVDF crystals reduced the dielectric loss from the αc relaxation in α crystals. Second, biaxial stretching constrained the amorphous phase in P(VDF-HFP) and thus the migrational loss from impurity ions was reduced. Third, biaxial stretching induced a significant amount of rigid amorphous phase in PET, further enhancing the breakdown strength of multilayer films. Due to the synergistic effects of improved interfacial adhesion and biaxial orientation, the PET/PMMA/P(VDF-HFP) 65-layer films with 8 vol % PMMA exhibited optimal dielectric properties with an energy density of 17.4 J/cm(3) at breakdown and the lowest dielectric loss. These three-component multilayer films are promising for future high-energy-density film capacitor applications.

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Unique three-component multilayer films with ATB-TATBTA configuration were fabricated using forced assembly multilayer coextrusion for novel dielectric systems. The dielectric breakdown strength, displacement-electric field hysteresis, and dielectric spectroscopy of 65-layer polycarbonate (PC)/tie/ poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) were investigated with various tie materials. Three different tie materials, poly(methyl methacrylate) (PMMA), styrene-co-acrylonitrile copolymer with 30% acrylonitrile content (SAN30), and poly(ethylene terephthalate-co-1,4-cycohexanedimethylene terephthalate) (PETG) were chosen owing to their various degrees of interaction with either P(VDF-HFP) or PC. The 65-layer PC/ PMMA/P(VDF-HFP) films exhibited a 25% enhancement in breakdown properties, 50% higher energy density, 40% smaller hysteresis loop areas, and orders of magnitude slower ion migration relative to the 33-layer PC/P(VDF-HFP) control. These property improvements are mainly attributed to the localized interactions at PMMA/P(VDF-HFP) and PMMA/PC interfaces, forming interphase regions. The modified PMMA/P(VDF-HFP) interphase region can effectively hinder the migration of impurity ions in P(VDF-HFP), reducing their mobility within the layer. Additionally, a small fraction of PMMA can lead to slightly increased dielectric constant of the composite films owing to strong interaction between PMMA and P(VDF-HFP). The other two systems with PETG and SAN30 as tie layers exhibited marginal improvements in dielectric properties owing to their weaker interactions with the P(VDF-HFP) layers. V C 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 978-991

Current development of advanced power electronics for electric vehicles demands high temperature, high energy density, and low loss polymer dielectrics. Multilayer films (MLFs), which are comprised of alternating high temperature/low loss linear dielectric polymer such as polysulfone (PSF) and high energy density polymer such as poly(vinylidene fluoride) (PVDF), are promising for this application, because high temperature tolerance, high energy density, and low loss can be achieved simultaneously. This study explored the reduction of impurity ion conduction loss in PSF/ PVDF MLFs (e.g., the dissipation factor is as low as 0.003 at 1 Hz and 100 °C) without sacrificing high dielectric constant and high energy density. Various electric poling processes were explored at a temperature slightly below the glass transition temperature (T g ∼ 185 °C) of PSF. Compared with pure alternating current (AC) and pure direct current (DC) poling methods, unipolar (DC + AC) poling was found to be the most effective in polarizing impurity ions from the PVDF layers into the PSF layers. Because of the low segmental mobility below T g , impurity ions were largely "locked" in PSF. The immobilization of impurity ions was thermally stable up to 120 °C. Because DC-link capacitors work with unipolar charge and discharge processes, these PSF/PVDF MLFs with low dielectric losses are promising for the application of advanced power electronics for the automobile industry.

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Abstract. A nanolayered polymer films approach to designing and fabricating gradient refractive index (GRIN) lenses with designer refractive index distribution profiles and an independently prescribed lens surface geometry have been demonstrated to produce a new class of optics. This approach utilized nanolayered polymer materials, constructed with polymethylmethacrylate and a styrene-co-acrylonitrile copolymer with a tailorable refractive index intermediate to bulk materials, to fabricate discrete GRIN profile materials. A process to fabricate nanolayered polymer GRIN optics from these materials through thermoforming and finishing steps is reviewed. A collection of technology-demonstrating previously reported nanolayered GRIN case studies is presented that include:(1) the optical performance of a f/# 2.25 spherical GRIN plano-convex singlet with one quarter (2) the weight of a similar BK7 lens and a bio-inspired aspheric human eye GRIN lens. Original research on the fabrication and characterization of a Luneburg inspired GRIN ball lens is presented as a developing application of the nanolayered polymer technology. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Advanced film capacitors require polymers with high thermal stability, high breakdown strength, and low loss for high temperature dielectric applications. To fulfill such requirements, two polymer multilayer film systems were coextruded via the forced assembly technique. High glass transition temperature (T g ) polycarbonate (HTPC, T g = 165 C) and polysulfone (PSF, T g = 185 C) were multilayered with a high dielectric constant polymer, poly(vinylidene fluoride) (PVDF), respectively. The PSF/PVDF system was more thermally stable than the HTPC/PVDF system because of the higher T g for PSF. At temperatures lower than 170 C, the HTPC/PVDF system exhibited comparable breakdown strength and hysteresis loss as the PSF/PVDF system. While at temperatures above 170 C, the PSF/PVDF system exhibited a higher breakdown strength because of the higher T g of PSF. The electric displacement-electric field (D-E) loop behavior of the PSF/PVDF system was studied as a function of temperature. Moreover, a melt-recrystallization process could further decrease the hysteresis loss for the PSF/PVDF system due to better edge-on crystal orientation. These results demonstrate that PSF/PVDF and HTPC/PVDF systems are applicable for high temperature film capacitors.

The long-term dielectric lifetime properties of multilayered polycarbonate/poly(vinylidene fluoride-co-hexafluoropropylene) [PC/P(VDF-HFP)] films were measured as a function of the layer thickness. An optimum layer thickness of 160 nm was determined with the longest dielectric lifetime. The morphology of the damaged sites after dielectric breakdown was examined using scanning electron microscope. Acoustic emission detection system was coupled with the dielectric setup to correlate fracture events and dielectric breakdown to thereby elucidate the mechanisms of the enhancements in dielectric lifetime properties. Two types of acoustic signals were always observed during the breakdown process for multilayered films. The high-amplitude signals were attributed to the formation of breakdown pinholes caused by the primary discharge from top to bottom electrode. The subsequent lowamplitude signals were attributed to internal discharges that could further damage the film. The total number of acoustic hits, in particular, low-amplitude hits, increased with decreasing layer thickness, indicating more internal discharges occurred along the layered interface. It was concluded that the breakdown event initiated at a defect initiated "hotspot" formed because of internal pressure buildup. The film was punctured when the pressure buildup inside the film overcame the mechanical strength of the film. More number of PC layers and layer interfaces were desirable to slow down and divert the damage propagation through the film thickness direction. The crazes in P(VDF-HFP) can, however, easily propagate across PC layers with less than 160 nm layer thickness.Recent studies on the layered polymer capacitor films have focused on dielectric properties, including dielectric lifetime, 3 breakdown strength, 1,2 and hysteresis. 14 Significant enhancements were observed for dielectric lifetime and breakdown strength, and hysteresis was reduced by decreasing poly(vinylidene fluoride)(PVDF) layer thickness. Wolak 15 and Mackey 2