Poly(vinylidene fluoride-co-tetrafluoroethylene) (PVDF-TFE) is confined between alternating layers of poly(ethylene terephthalate) (PET) utilizing a unique multilayer processing technology, in which PVDF-TFE and PET are melt-processed in a continuous fashion. Postprocessing techniques including biaxial orientation and melt recrystallization were used to tune the crystal orientation of the PVDF-TFE layers, as well as achieve crystallinity in the PET layers through strain-induced crystallization and thermal annealing during the melt recrystallization step. A volume additive model was used to extract the effect of crystal orientation within the PVDF-TFE layers and revealed a significant enhancement in the modulus from 730 MPa in the as-extruded state (isotropic) to 840 MPa in the biaxially oriented state (on-edge) to 2230 MPa in the melt-recrystallized state (in-plane). Subsequently, in situ wide-angle X-ray scattering was used to observe the crystal structure evolution during uniaxial deformation in both the as-extruded and melt-recrystallized states. It is observed that the low-temperature ferroelectric PVDF-TFE crystal phase in the as-extruded state exhibits equatorial sharpening of the 110 and 200 crystal peaks during deformation, quantified using the Hermans orientation function, while in the melt-recrystallized state, an overall increase in the crystallinity occurs during deformation. Thus, we correlated the mechanical response (strain hardening) of the films to these respective evolved crystal structures and highlighted the ability to tailor mechanical response. With a better understanding of the structural evolution during deformation, it is possible to more fully characterize the structural response to handling during use of the high-barrier PVDF-TFE/PET multilayer films as commercial dielectrics and packaging materials.

In this study, we report layer thickness effect on the electrical insulation property of polysulfone (PSF)/poly(vinylidene fluoride) (PVDF) multilayer films having a fixed composition of PSF/PVDF = 30/70 (vol./vol.). Breakdown strength, dielectric lifetime, and electrical conductivity were studied for 32- and 256-layer films having various total film thicknesses. Among these films, those having thinner PVDF and PSF layers exhibited lower breakdown strength, shorter lifetime, and higher electrical conductivity than those having thicker layers. These experimental results were explained by Maxwell-Wagner-Sillars interfacial polarization due to contrasts in dielectric constant and electronic conductivity for PVDF and PSF, respectively. When both PVDF and PSF layers were thick (ca. > 100-200 nm), more space charges were available in PVDF and no electronic conduction was allowed for PSF. These accumulated interfacial charges could serve as effective traps for injected electrons from metal electrodes under high electric fields. As a result, reduced electrical conductivity and enhanced breakdown strength/dielectric lifetime properties were obtained. When both layers were thin (ca. < 100 nm), fewer space charges were available in PVDF and significant electronic conduction through PSF resulted in low interfacial polarization. Consequently, higher electrical conductivity, lower breakdown strength, and shorter lifetime were observed. These results provide us insights into potential physics to enhance electrical insulation property of polymer films using a multilayered structure having large dielectric constant contrast. (C) 2013 Elsevier Ltd. All rights reserved.

Polymer films with enhanced dielectric and breakdown properties are essential for the production of high energy density polymer film capacitors. By capitalizing on the synergistic effects of forced assembly nanolayer coextrusion and biaxial orientation, polymer multilayer films using poly(ethylene terephthalate) (PET) and a poly(vinylidene fluoride‐co‐tetrafluoroethylene) [P(VDF‐TFE)] copolymer were produced. These films exhibited breakdown fields, under a divergent field using needle/plane electrodes, as high as 1000 kV mm−1. The energy densities of these same materials, under a uniform electric field measured using plane/plane electrodes, were as high as 16 J cm−3. The confined morphologies of both PET and P(VDF‐TFE) were correlated to the observed breakdown properties and damage zones. On‐edge P(VDF‐TFE) crystals induced from solid‐state biaxial stretching enhanced the effective P(VDF‐TFE) layer dielectric constant and therefore increased the dielectric contrast between the PET and P(VDF‐TFE) layers. This resulted in additional charge buildup at the layer interface producing larger tree diameters and branches and ultimately increasing the breakdown and energy storage properties. In addition to energy storage and breakdown properties, the hysteresis behavior of these materials was also evaluated. By varying the morphology of the P(VDF‐TFE) layer, the low‐field dielectric loss (or ion migration behavior) could be manipulated, which in turn also changed the observed hysteresis behavior. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 882–896

ABSTRACTUnique three‐component multilayer films with ATBTATBTA 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. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 978–991

The morphologies of two crystalline polymers, polyethylene terephthalate (PET) and poly(vinylidene fluoride-co-tetrafluoroethylene) [P(VDF-TFE)], were probed under nanolayer confinerhent using forced assembly multilayer film coextrusion. This multilayer system was used as a platform to investigate the effect of nanolayer coextrusion, biaxial stretching, and isothermal melt recrystallization on the confined morphologies of both of these polymers. To determine the effect of each of these variables independently, three sets of PET/P(VDF-TFE) multilayer films were produced, each with comparable film thickness and layer thickness. The morphology and X-ray data of the extruded PET/P(VDF-TFE) multilayer films, which were taken directly from the coextrusion process, indicate that the morphologies of both PET and P(VDF-TFE) were relatively unaffected by nanolayer confinement, even in very thin 40 nm layers. Biaxial stretching of multilayer films, produced from stretching micron thick layers down to nanolayers, facilitated the development of an on-edge P(VDF-TFE) crystal orientation in addition to an oriented PET fibrillar crystal structure. Finally, an approach of isothermal melt recrystallization was conducted on the biaxially stretched samples which revealed the formation of high aspect ratio in-plane P(VDF-TFE) crystals under nanolayer confinement while also further crystallizing the PET fibril crystals. Therefore, in the same multilayer system, three P(VDF-TFE) crystal orientations were achieved by utilizing nanolayer confinement, biaxial stretching, and isothermal melt recrystallization. Oxygen permeability was used as an additional structural probe for these confined PET and P(VDF-TFE) layer morphologies. From the transport data, it was determined that the PET layers possessed similar oxygen transport characteristics to the bulk materials, which was in good agreement with the morphology data of the PET layers in the various PET/P(VDF-TFE) multilayer films. In contrast, the on-edge P(VDF-TFE) orientation induced from biaxially stretching and in-plane P(VDF-TFE) crystal orientation induced from isothermal melt recrystallization of confined P(VDF-TFE) nanolayers yielded substantial reductions in the effective oxygen permeability of the P(VDF-TFE) layers in comparison to the bulk P(VDF-TFE) control. The various confined P(VDF-TFE) crystal orientations and subsequent enhanced barrier properties are enabled by the hard confinement of the PET nanolayers during biaxial stretching at high draw ratios and isothermal melt recrystallization at high temperatures. Finally, the water vapor transport rate (WVTR) was evaluated for these confined systems which mimicked the trends observed for oxygen permeability. The confined nanolayer morphologies, specifically the in-plane P(VDF-TFE) crystals, substantially reduced the WVTR in multilayer films opening new applications for this technology. (C) 2013 Elsevier Ltd. All rights reserved.

Recent advances utilizing forced assembly multilayer coextrusion have led to the development of a new approach to study the structure–property relationships of confined polymer crystallization. Confinement of crystalline polymer materials in layer thicknesses ranging from hundreds to tens of nanometers thick, resulted in multilayer films possessing enhanced gas barrier properties. The enhanced gas barrier has been attributed to nanolayer confinement of the crystalline polymer resulting in a highly ordered intralayer lamellae orientation extending over micron or larger scale areas. Research into the confined crystallization mechanism of the multilayered polymer films has resulted in several material case studies as well as an understanding of the chemical and thermodynamic parameters that control the degree and rate of the confinement in multilayer polymer systems. This review highlights our recent studies on the confinement of poly(ethylene oxide), poly(ε-caprolactone), polypropylene, and poly(vinylidene fluoride) polymers in multilayered films.

The dielectric lifetime and corresponding damage morphology of polycarbonate/poly(vinylidene fluoride-co-hexafluoropropylene) (PC/P(VDF-HFP)) layered systems are studied under constant direct current (DC) field. Melt blends of the two polymers are also considered for comparison. The dielectric lifetimes of the latter are systematically much shorter than the layered systems. The interfaces between the polymers act as flaws that induce up to two orders of magnitude difference between the layered and blend systems. The capacitance values versus time during breakdown progression exhibit an inversed S-shape pattern. The three regimes in the S-shape pattern are consecutively attributed to randomly isolated breakdowns, interconnecting breakdowns, and wearing-out of the capacitor film. The film breakdown images during dielectric lifetime test confirmed the transition from randomly isolated breakdowns to interconnecting breakdowns. This transition was further evidenced by a bimodal distribution in the Weibull analysis. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

Multilayered films comprising alternating layers of polycarbonate (PC) and poly(vinylidene fluoride-hexafluoropropylene) (P[VDF-HFP]) show an enhanced dielectric strength (EB> 750 kV/mm) and an increased energy storage density (Ud ~ 13.5 J/cm3) compared to monolithic PC and P[VDF-HFP] films. Here the role of electromechanical effects in the breakdown of multilayer films is explored both by imaging the changes in the layer structure caused by electrical fields below the breakdown field and by a direct measurement of the strain in multilayer PC/ P[VDF-HFP] films subjected to similar fields. Focused Ion Beam (FIB)/ Scanning Electron Microscopy (SEM) images of the layer structure in films subjected to repeated cycles at near-breakdown fields showed local changes in the thickness of individual layers, suggesting that mechanical forces arising from field-induced compression may play a role in the steps preceding the breakdown. The directly measured field induced strain showed evidence for both an elastic and a flow component to the strain. The mechanical responses of films with ≤ 50 vol% P[VDF-HFP] were modeled as simply the sum of an elastic and viscous flow. The observed electromechanical properties vary with the layer structure. This suggests that multilayering polymers may provide a means to mitigate deleterious electromechanical effects in low modulus, high dielectric materials.

A platinum salt complex {(Pt(NH3)4)Cl2}(Aldrich) was used to make 2 mg Pt/ml solution. The H + form of oriented Nafion ® was allowed to soak up the platinum salt overnight. Then 5wt% aqueous solution of sodium borohydride (NaBH 99%, Sigma-Aldirch) was used as the reducing agent. It was repeated 2 more times after the first series of Pt salt absorption and reducing cycling. IPMC displacement testing. The samples of IPMC were 2.0 cm in length, 0.5 cm in width and from 0.2 to 0.23 cm in thickness. Displacement measurements under sweep voltage input were carried our using an Imaging Solutions Group camera (LightWise LW-1.3-R-1394) interfaced to Lab- view TM . Image analysis was done using Datapoint software (Xannah Applied