All‐polymer electromechanical systems consisting of electrostrictive poly(vinylidene fluoride‐trifluoroethylene) and conductive polyaniline

The low elastic modulus and the ability to withstand high strain without failure make the conducting polymer attractive for a wide range of acoustic applications based on high‐strain electroactive polymers. In this article, we examine the electric and electromechanical performance of all‐polymer electromechanical systems, fabricated by painting conductive polyaniline (PANI) doped with camphor sulfonic acid (HCSA) on both sides of electrostrictive Poly(vinylidene fluoride‐trifluoroethylene) (P(VDF‐TrFE)) copolymer films, and compare them with those from the same copolymers with gold electrodes. The all‐polymer composite films are flexible, with strong coherent interfaces between the electrostrictive polymer layer and the conductive polymer layer. The electric performance such as dielectric properties and polarization hysteresis loops from P(VDF‐TrFE)/PANI film is nearly identical to those of P(VDF‐TrFE)/gold films in a wide temperature (from −50 to 120°C), and frequency range (from 1 Hz to 1 MHz). The all‐polymer systems also show a similar or even larger electric field induced strain response than that of films with electrodes under identical measurement conditions. The results demonstrate that the polyaniline/HCSA is good candidate material as the electrodes for electroactive polymers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 945–951, 2000     

Enhancement of dielectric and energy density properties in the PVDF‐based copolymer/terpolymer blends

We investigated the high dielectric constant and energy storage density for the blends of P(VDF‐TrFE) copolymer and P(VDF‐TrFE‐CFE) terpolymer. The degradation of coercive field (E_c) and remnant polarization (P_r) of the copolymer under an electric field of 125 MV/m was observed and the copolymer changed into a typical relaxor ferroelectric with doping of terpolymer. The dielectric constant of P(VDF‐TrFE) was found to be ～11, but was enhanced to ～55 by blending with P(VDF‐TrFE‐CFE) at 60 wt%. Consequently, a higher energy density of about 4.2 J/cm³ was obtained in these blends in contrast to about 3.6 J/cm³ in the terpolymer at the very low applied electric field of 125 MV/m. These results demonstrate the promise of blend approaches for tailoring and enhancing the dielectric properties of ferroelectric polymers. POLYM. ENG. SCI., 55:1396–1402, 2015. © 2015 Society of Plastics Engineers     

Evolution of morphology,ferroelectric, and mechanical properties in poly(vinylidene fluoride)–poly(vinylidene fluoride‐trifluoroethylene) blends

Considering the complementary properties of poly(vinylidene fluoride) (PVDF) and poly(vinylidene fluoride‐trifluoroethylene) [P(VDF‐TrFE)], it appears that their blends have the potential to be promising candidates for device applications. We report the evolution of morphology, ferroelectric, and mechanical properties (modulus and hardness) and their dependence on preparation temperature for PVDF–P(VDF‐TrFE) blends. From ferroelectric hysteresis measurements it was found that P(VDF‐TrFE) rich blends treated at higher temperature show significant values of remanent polarization. Remanent polarization values show a fourfold increase in these P(VDF‐TrFE) rich blends treated at higher temperature. Interestingly, blends prepared from high temperature showed greater value of remanent polarization even though they were found to consist of smaller amount of electroactive phase as compared to their low temperature treated counterpart. Nanoindentation experiments revealed that high temperature treatment improves the modulus of blends by at least 100%. This report attempts to tie these findings to the morphology and crystallinity of these blends. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45955.     

Electrical energy discharging performance of poly(vinylidene fluoride‐co‐trifluoroethylene) by tuning its ferroelectric relaxation with polymethyl methacrylate

Poly(methyl methacrylate) (PMMA) was introduced into ferroelectric Poly(vinylidene fluoride‐co‐trifluoroethylene) P(VDF‐co‐TrFE) via a simple solution blending process and a series of P(VDF‐co‐TrFE)/PMMA blends with varied PMMA content was obtained in an effort to investigate the confinement effect of PMMA on the crystalline, dielectric, and electric energy storage properties of P(VDF‐co‐TrFE). PMMA addition could reduce the crystallinity dramatically as well as the crystal size due to its dilution effect and impediment effect on the crystallization of P(VDF‐co‐TrFE). PMMA introduction is also responsible for the phase transition of P(VDF‐co‐TrFE) from α phase into γ phase. As expected, both the dielectric constant and loss of the blends are reduced as PMMA addition increases for the dilute, decoupling, and confinement effect of PMMA on the relaxation behavior of crystal phases of P(VDF‐co‐TrFE) under external electric field. As a result, both the maximum and remnant polarization of the blends are significantly depressed. The irreversible polarization of P(VDF‐co‐TrFE) is effectively restricted by the addition of PMMA due to its impeding effect on the crystallization of P(VDF‐co‐TrFE) and restricting effect on the switch of the polar crystal domains. Therefore, the energy loss induced by the ferroelectric relaxation of P(VDF‐co‐TrFE) is significantly reduced to less than 25% at an electric field of 450 MV/m while the energy storage density is well maintained at about 10 J/cm^?3 in the blend with 30 wt % PMMA. The results may help to understand how the ferroelectric relaxation affects the energy loss of ferroelectrics fundamentally and design more desirable materials for high energy storage capacitors. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40114.     

Effect of water absorption on the mechanical properties of poly(vinylidene fluoride‐trifluoroethylene) copolymer films

Electroactive polymers are smart materials that respond to electrical stimulation by changing their shape and size. The objective of this study is to investigate the applicability of the poly(vinylidene fluoride‐trifluoroethylene) (P(VDF‐TrFE)) copolymer in sensors or actuators in an in vivo environment. The basic mechanical properties of P(VDF‐TrFE) thin films were estimated by carrying out tensile and creep tests using specimens submerged in water at 30°C for a few weeks. Furthermore, X‐ray diffraction analysis was employed to observe the micro‐structural changes in the P(VDF‐TrFE) films due to water absorption wherein water intercalated in the interstitial sites between the chains of the P(VDF‐TrFE) films. Consequently, the mechanical properties of the P(VDF‐TrFE) films were enhanced due to water absorption. POLYM. ENG. SCI., 54:2654–2659, 2014. © 2013 Society of Plastics Engineers     

Pyroelectric and dielectric properties of spin‐coated thin films of vinylidene fluoride–trifluoroethylene copolymers

This work emphasizes the use of vinylidene fluoride and trifluoroethylene copolymer P(VDF‐TrFE) as a pyroelectric sensor. The pyroelectric and dielectric properties of the copolymer have been investigated in the temperature interval 150–350 K. The samples were prepared by using a spin‐coating technique with 70/30 mol% VDF/TrFE copolymer. The final film thickness of the samples, which is mainly determined by the concentration of the copolymer, spinning rate and spin time, was measured with a surface profiler. The samples were annealed at 150 °C for 10 min to improve the crystallinity of the copolymer. The crystallinity of the annealed and non‐annealed samples was compared by IR spectroscopy. The most effective process by which to improve the pyroelectric response of the material is to pole the sample with huge poling field‐strengths at elevated temperatures. Both pyroelectric and dielectric activities of the samples were measured after each successful poling process. It was observed that while the pyroelectric activity of the material increases, the dielectric activity decreases, so the figure‐of‐merit of the material, which shows the sensor capability of the material, was increased by a significant amount. It was found that the pyroelectric coefficient of VDF/TrFE (70/30 mol%) copolymer is 68.7 µC m^?2 K^?1 at 300 K. © 2001 Society of Chemical Industry     

Strengthening of electromechanical properties for poly(vinylidene fluoride‐trifluoroethylene) films under tailored electric cycling

Copolymers of polyvinylidene fluoride and trifluorethylene [P(VDF‐TrFE)] have potential applications in wearable and implantable electromechanical devices since they are mechanically flexible, and biocompatible. A tailored electric cyclic process is employed to enhance both electrical and mechanical properties in P(VDF‐TrFE) 65/35 mol % copolymer films. The films are subjected to lower and higher field magnitude electric cycling successively. For electrical properties, enhancement in remnant polarization, dielectric and piezoelectric constants occurs. From mechanical point of view, strengthening in the fracture strength happens. Wide‐angle X‐ray diffraction techniques examine changes of the orientation of the molecular chains, grain size, and crystallinity after electric cycling for the copolymer films. Scanning electron microscopy reveals evolutions of the microstructure, including rod‐like textures and fractography of the films. The results indicate that electric cycling causes the molecular chains to orient gradually along the direction perpendicular to the applied electric field. Consequently, an enhancement of 12.2% and 45% is realized for the remnant polarization and fracture strength, respectively for P(VDF‐TrFE) 65/35 copolymer film. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45926.     

Effect of ultrasonication and other processing conditions on the morphology,thermomechanical, and piezoelectric properties of poly(vinylidene difluoride‐trifluoroethylene) copolymer films

This study is carried out on the effect of processing conditions including preparation methods, ultrasonication, film thickness, and thermal annealing on the thermal, mechanical, and piezoelectric properties of copolymer of poly(vinylidene difluoride‐trifluoroethylene) (P(VDF‐TrFE)). Free‐standing films and films on substrates are prepared by solvent casting and spin‐coating, respectively. The results obtained by differential scanning calorimetry show that the Curie transition of the copolymer films was influenced by the preparation methods, with very little difference in the melting transition. The difference was attributed to a less uniform distribution of TrFE comonomer units within the crystalline and amorphous regions of the spin‐coating films. However, no effect of the preparation methods on the piezoelectric properties of the films was observed. It is also found that the short ultrasonication, film thickness higher than critical value of crystallization of P(VDF‐TrFE) (about 100 nm), and drying before annealing did not have a significant effect on the properties of the films. Surprisingly, the ultrasonication had a clear impact on the relaxations at high temperature of the polymer chains. In addition, this study indicates that a short annealing by 10 min at 140°C was enough to obtain well‐crystallized films, which is interesting from the industrial point of view. POLYM. ENG. SCI., 54:1280–1288, 2014. © 2013 Society of Plastics Engineers     

High polarization levels in poly(vinylidene fluoride–trifluoroethylene) ferroelectric thin films doped with diethyl phthalate

With a spin‐coating technique, ferroelectric thin films of poly(vinylidene fluoride–trifluoroethylene) copolymer [P(VDF–TrFE; with a content (mol %) ratio of 68/32 vinylidene fluoride/trifluoroethylene] were fabricated on silicon wafers covered with platinum and were doped with a nucleation agent, diethyl phthalate (DEP). The remnant polarization of copolymer thin films increased 70% after doping with DEP, and the coercive field was reduced, which is highly desirable in bistable memory devices. The dielectric constant of thin films also increased after doping. However, the effect of doping on the ferroelectric response was not remarkable in freestanding copolymer films. The results demonstrated that the ferroelectric dipole orientation in P(VDF–TrFE) thin films was significantly enhanced by the presence of DEP because the crystallinity of thin films decreased after doping, as revealed by X‐ray results. The dopant DEP acted as both a nucleation agent during the crystallization process and a plasticizer in the noncrystalline regions, which greatly enhanced the dipole orientation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1416–1419, 2003     

Tailoring the structural properties of PVDF and P(VDF‐TrFE) by using natural polymers as additives

The poly(vinylidene fluoride), PVDF, and its copolymer poly(vinylidene fluoride‐trifluoroethylene), P(VDF‐TrFE), are of great scientific and technological interest due to their ferro, pyro, and piezelectrical properties besides chemical and thermal stability. Recently, their biocompatibility has been shown as well. Therefore, considering all this potentiality, self‐standing films of PVDF and P(VDF‐TrFE) containing corn starch and latex of natural rubber as additives were produced by compressing/annealing forming blends. This process allows one to discard the necessity of using solvents to dissolve either PVDF or P(VDF‐TrFE), which are toxic to human. The films were structurally characterized through Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X‐ray diffraction, density, melt flow index, hardness, and thermal conductivity. The results showed that the polymers do not interact chemically with the additives leading to the formation of blends as physical mixtures where the additives are well dispersed within the blends at micrometer level. However, it was observed that the adhesion of the starch is better in the case of blends with P(VDF‐TrFE). Besides, the crystalline structures of the α‐PVDF and ferroelectric P(VDF‐TrFE) are kept in the blends. The density, hardness, melt flow index, and thermal conductivity values of the blends followed what should be expected from physical mixtures. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Tailored ferroelectric responses and enhanced energy density in PVDF‐based homopolymer/terpolymer blends

Blend of polymers is an effective way to tailor the ferroelectric responses and improve the energy storage properties of polymers. In this work, the microstructure and dielectric responses of the blends of poly(vinylidene fluoride) (PVDF) and poly(vinylidene fluoride‐trifluoroethylene‐chlorofluoroethylene) [P(VDF‐TrFE‐CFE)] have been studied. It is found that the addition of PVDF disturbs the crystallization process of P(VDF‐TrFE‐CFE), leading to lower crystallinity and smaller crystalline size. The aforementioned microstructure changes result in tailored ferroelectric responses. Dielectric responses show that the blend with 10 wt % PVDF achieves larger polarization response under high electric field (above 300 MV/m) due to the interfacial polarization. Because of the tailoring effect and the interfacial polarization, the blend with 10 wt % PVDF exhibits higher energy density and efficiency. Moreover, the breakdown strength (E_b) is also improved by adding a small amount of PVDF into the terpolymer. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40994.     

Facile preparation of ferroelectric poly(vinylidene fluoride‐co‐trifluoroethylene) thick films by solution casting

We investigated the effects of annealing temperature and vacuum treatment on the crystallinity and ferroelectric properties of solution‐casted poly(vinylidenefluoride‐co‐trifluoroethylene), P(VDF‐TrFE), thick films. We varied the annealing temperature from 70°C to 150°C and achieved high‐quality ferroelectric thick films annealed at 130°C. Ferroelectric domains and their properties were confirmed using X‐ray diffraction, Fourier transform infrared spectroscopy with attenuated total reflection mode and ferroelectric/piezoelectric measurement systems. Drying and/or annealing in the vacuum allowed for the improvement of crystallinity and ferroelectric/piezoelectric properties. Importantly, the piezoelectric coefficient, d₃₃, of our optimal P(VDF‐TrFE) films after sufficient poling treatment was 36 pC/N and our P(VDF‐TrFE) power generator produced an output voltage of ～6 V under periodic bending and unbending motions. POLYM. ENG. SCI., 54:466–471, 2014. © 2013 Society of Plastics Engineers     

Ferroelectric polymers with large electrostriction; based on semicrystalline VDF/TrFE/CTFE terpolymers

This paper discusses a new ferroelectric polymer with large electrostrictive response (∼4%) at ambient temperature, which is based on a processable semicrystalline terpolymer comprising vinylidene difluoride (VDF), trifluoroethylene (TrFE), and chlorotrifluoroethylene (CTFE). This VDF/TrFE/CTFE terpolymer was prepared by a combination of bulk polymerization process and a borane/oxygen initiator at ambient temperature. The incorporated bulky CTFE units in the terpolymer seem to reduce the crystalline domain size and move the ferroelectric-paraelectric (F-P) phase transition to near ambient temperature with a very small energy barrier. Some terpolymers exhibited common ferroelectric relaxor behaviors with a broad dielectric peak that shifted toward higher temperatures as the frequency increased, and a slim polarization hysteresis loop at near the dielectric peak (around ambient temperature) that gradually evolved into a normal ferroelectric polarization hysteresis loop with reduced temperature.     

Energy storage study of ferroelectric poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) terpolymers

A series of P(VDF-TrFE-CTFE)s were synthesized via a well-controlled chemical route including VDF/CTFE copolymerization and dechlorination of P(VDF-CTFE)s to convert CTFE units into TrFE units. The microstructure and properties of the terpolymers were characterized and tested with differential scanning calorimeter (DSC), NMR, dielectric constant and electric displacement-electric field (D-E) hysteresis loop. Thanks to the clean reaction system and ambient reaction condition of VDF/CTFE copolymerization and the hydrogenation of P(VDF-CTFE)s, the terpolymers obtained with high purity and uniformity exhibit a high electric breakdown field of over 500 MV/m, as a result, the highest energy density is obtained as 10.3 J/cm³. Via comparing the structure and properties of terpolymers with different compositions and from different preparing processes side-by-side, the TrFE content and the method of TrFE introduced are found to strongly affect the microstructure of the materials and consequently the dielectric properties. The advantages including the lower cost of materials, convenience of the materials preparation and relatively lower energy loss make it possible to be employed as capacitor material.     

Imaging the effect of dielectric breakdown in a multilayered polymer film

The dielectric strength and energy storage capability of poly(vinylidene fluoride‐hexafluoropropylene) copolymer (P[VDF‐HFP]) films are enhanced by interleaving layers of PVDF copolymer with thin layers of polycarbonate (PC). To gain insight into the breakdown processes in such materials, focused ion beam (FIB) milling in conjunction with scanning electron microscopy (SEM) was used to study the effect of a breakdown on the film. FIB can sequentially mill cross sections that are each imaged by SEM. The technique can provide quasi‐3D images across the film and give a detailed view of the damage caused by an electrical breakdown. Here, breakdowns initiated using a needle‐plane electrode configuration were imaged. In homogeneous films, the damage was confined to the small volume at the pinhole site. In 32‐layer 50/50 PC/P[VDF‐HFP] multilayer films, damage extending laterally up to ～ 15 μm into the film along the layer interfaces was seen. In addition to the delamination, layer buckling and distortion were apparent. The damage varied with the sample orientation, but the images indicate that the interfaces play an important role in the breakdown. They suggest that modifying the interface properties can be a strategy to further improve the dielectric strength of multilayer polymer dielectric materials. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Crystal phase of poly(vinylidene fluoride‐co‐trifluoroethylene) synthesized via hydrogenation of poly(vinylidene fluoride‐co‐chlorotrifluoroethylene)

Trifluoroethylene addition and thermal treatment induced crystal phase transition in a series of poly(vinylidene fluoride‐co‐trifluoroethylene) [P(VDF‐co‐TrFE)] containing varied TrFE molar ratio (6, 9, 12, and 20 mol %) prepared from the hydrogenation of poly(vinylidene fluoride‐co‐chlorotrifluoroethylene have been investigated by means of Fourier transform infrared spectral (FTIR), X‐ray diffraction (XRD), and differential scanning calorimetry (DSC) analyses. The comprehensive applications of the three techniques could distinguish α, β and γ phase of P(VDF‐co‐TrFE) very well. The multipeak fitting technique of DSC is successfully applied to calculate the percentage of different phases in the samples, which allows us to investigate the phase transition process of P(VDF‐co‐TrFE) precisely. It is found that the crystal phase of P(VDF‐co‐TrFE) films is turned from α + γ phase (6 mol % TrFE) to α + γ + β phase (9 and 12 mol % TrFE) to β phase (20 mol % TrFE) at high temperature, and from α + γ phase (6 mol % TrFE) to γ + β phase (9 mol % TrFE) to β phase (>12 mol % TrFE) at low fabricated temperature. Both the fabrication conditions and TrFE addition are responsible for the crystal phase transition of the hydrogenised P(VDF‐co‐TrFE). © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Ferroelectric nanodot formation from spin‐coated poly(vinylidene fluoride‐co‐trifluoroethylene) films and their application to organic solar cells

We demonstrated a facile route to the preparation of self‐assembled poly(vinylidene fluoride‐co‐trifluoroethylene) [P(VDF‐TrFE)] nanodots from spin‐coated thin films. We found that the initial film thickness would play an important role in the formation of such P(VDF‐TrFE) nanodots. Interestingly, the electric dipoles of such nanodots were self‐aligned toward the bottom electrode and their ferroelectric properties were determined by using piezoresponse force microscopy. In addition, the self‐polarized ferroelectric nanostructures were introduced to small molecular organic photovoltaic devices and allowed for enhancing the short circuit current density (J_sc) from 9.4 mA/cm² to 10.2 mA/cm² and the power conversion efficiency from 2.37% to 2.65%. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41230.     

A Ferroconcrete‐Like All‐Organic Nanocomposite Exhibiting Improved Mechanical Property,High Breakdown Strength,and High Energy Efficiency

Polymer‐based nanocomposite dielectrics with high energy storage capacity are crucial enablers for numerous applications in modern electronic and electrical industries. The energy density of parallel plate capacitors is determined by breakdown strength and dielectric permittivity of the inner dielectrics. Poly(vinylidene fluoride‐trifluoroethylene‐chlorofluoroethylene) (P(VDF‐TrFE‐CFE)), with the highest permittivity among all the dielectric polymers, is a promising candidate for high energy density capacitors. However, its relatively low breakdown strength and energy efficiency restrict the applications. In this work, a new method combining combinatorial‐electrospinning and hot‐pressing is proposed to fabricate P(VDF‐TrFE‐CFE)‐based all‐organic dielectrics with ferroconcrete‐like structure. In this structure, continuous fibers of polysulfone (PSF) with high Young's modulus act as tough scaffold to improve the mechanical properties of nanocomposites, and an over 750% enhancement of Young's modulus is obtained. The enhanced mechanical properties bring about significant improvement in Weibull breakdown strength to 485 MV m^?1, more than 50% higher than neat terpolymer. Furthermore, the suppressed leakage current and conduction loss, and hence the improved discharge energy efficiency under moderate electric field, are achieved due to the high insulation of PSF and its interfacial restriction on space charge mobility.     

Thickness Dependence of Dielectric,Leakage, and Ferroelectric Properties of Bi6Fe2Ti3O18 Thin Films Derived by Chemical Solution Deposition

We prepared Bi₆Fe₂Ti₃O₁₈ thin films on Pt/Ti/SiO₂/Si substrates with thickness ranging from ～300 to ～900 nm by using a chemical solution deposition route and investigated the thickness effects on the microstructure, dielectric, leakage, and ferroelectric properties of Bi₆Fe₂Ti₃O₁₈ thin films. Increasing thickness improves the surface morphology, dielectric, and leakage properties of Bi₆Fe₂Ti₃O₁₈ thin films and a well‐defined ferroelectric hysteresis loops can form for the thin films with the thickness above 400 nm. Moreover, the thickness dependence of saturation polarization is insignificant, whereas the remnant polarization decreases slightly with increasing thickness and it possesses a maximal value of ～20 μC/cm² for the 500 nm‐thick thin films. The mechanisms of the thickness dependence of microstructure, dielectric, and ferroelectric properties are discussed in detail. The results will provide a guidance to optimize the ferroelectric properties in Bi₆Fe₂Ti₃O₁₈ thin films by chemical solution deposition, which is important to further explore single‐phase multiferroics in the n = 5 Aurivillius thin films.     

Dielectric,piezoelectric and ferroelectric properties of a poly (vinylidene fluoride-co-trifluoroethylene) synthesized via a hydrogenation process

The dielectric, piezoelectric and ferroelectric properties of a poly (vinylidene fluoride-co-trifluoroethylene) (P (VDF-co-TrFE)) copolymer synthesized via a novel hydrogenation process are presented in this work. Comparing with the direct copolymerized P(VDF-co-TrFE), the head-to-head (H–H) connection of vinylidene fluoride (VDF) and trifluoroethylene (TrFE) units in hydrogenized P(VDF-co-TrFE) results in the increasing crystal domains and the improvement of overall crystallinity and. Therefore, excellent electric properties, including dielectric constant of 11 at a frequency of 100 Hz, a piezoelectric value (d₃₃) of ?23 pC/N, a remnant polarization (P_r) of 7 μC/cm² and a maximum polarization (P_s) of 10 μC/cm² were observed in hydrogenized P(VDF-co-TrFE), which are rather close to that obtained in copolymerized copolymer. The results indicate that the improved condensed structures offer the low cost and convenient hydrogenized P(VDF-co-TrFE) broader application scenery in piezoelectric devices than the direct copolymer.