Interphase/interface modification on the dielectric properties of polycarbonate/poly(vinylidene fluoride-co-hexafluoropropylene) multilayer films for high-energy density capacitors

Unique three-component multilayer films with ATBTATBTA configuration were fabricated using forced assembly multilayer coextrusion for novel dielectric systems. The dielectric breakdown strength, displacementelectric 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. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 978-991