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     

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.     

Dielectric properties and ferroelectric behavior of poly(vinylidene fluoride‐trifluoroethylene) 50/50 copolymer ultrathin films

Ultrathin films of poly(vinylidene fluoride‐trifluoroethylene) copolymer [P(VDF‐TrFE), with a content (mol %) ratio of 50/50 VDF/TrFE] were fabricated on silicon wafers covered with platinum by a spin‐coating technique, ranging in thickness from 20 nm to 1 μm. The effect of thickness on dielectric properties and polarization behavior was investigated. A critical thickness was found to be about 0.1 μm. An abrupt drop of dielectric constant was observed, although there is no significant change in dielectric loss at this thickness. Square and symmetric hysteresis loops were obtained in films thicker than 0.1 μm. However, for films thinner than 0.1 μm, fewer square hysteresis loops were observed. SEM and X‐ray results demonstrate that the effect of thickness on dielectric and ferroelectric properties could be explained by the changes of crystal structure in these films. In addition, the effects of irradiation on dielectric property and polarization response for ultrathin P(VDF‐TrFE) films were also presented. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2259–2266, 2001     

Structural and ferroelectric response in vinylidene fluoride/trifluoroethylene/hexafluoropropylene terpolymers

Poly(vinylidene fluoride/trifluoroethylene/hexafluoropropylene) terpolymers were synthesized by bulk polymerization process at ambient temperature based on alkyl borane/oxygen initiator. The ferroelectric and dielectric properties were investigated and compared with those of poly(vinylidene fluoride/trifluoroethylene) copolymer. The DSC, X-ray and FT-IR results suggest that the third comonomer in the polymer chain breaks the large polar domains into smaller domain size and reduces the crystallinity of terpolymer. As a result, both the ferroelectric-paraelectric phase transition and melting process take place at lower temperature. The smaller domain makes the dipoles reversal at lower electric field and reduces the polarization hysteresis as well as polarization level. High electrostrictive strain (2.5%) was obtained at low electric field for terpolymer with small quantity of HFP. The polarization and dielectric behaviors imply that the terpolymer is a typical ferroelectric relaxor. The terpolymer also shows higher room temperature dielectric constant than that of copolymer due to the lower phase-transition temperature.     

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.     

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.     

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.     

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     

Annealing effect on poly(vinylidene fluoride/trifluoroethylene) (70/30) copolymer thin films above the melting point

To further understand crystallization behaviors above the melting temperature (T_m), the morphologies and structure of ferroelectric poly(vinylidene fluoride/trifluoroethylene) [P(VDF–TrFE); 70/30] copolymer films at different temperatures were studied by atomic force microscopy, differential scanning calorimetry, and X‐ray diffraction (XRD). We found that there was a structural change in the P(VDF–TrFE) copolymer film above T_m, which corresponded to the transition from tightly arrayed grains to fiberlike crystals. For the samples annealed above T_m, heat treatment reduced the density of gauche defects and caused a better arrangement of the crystalline phase. So those samples were in the ferroelectric phase without gauche defects, with one sharp diffraction peak reflected in the XRD curves. It was helpful to further make clear the thermal behaviors from the melts of the P(VDF–TrFE) copolymers and discuss their application under higher temperatures. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

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     

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     

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.     

Preparation and characterization of anionic collagen: P(VDF/TrFE) composites

Anionic collagen:P(VDF/TrFE) (75/25) membrane composites were prepared by mixing anionic collagen and P(VDF/TrFE) in aqueous concentrated acetic acid:dimethylsulfoxide solutions and characterized by infrared, electron scanning microscopy, thermal analysis and dielectric properties. The results show that under the appropriate conditions anionic collagen:P(VDF/TrFE) composites, with ratios in the range from 4:1 to 1:4 may be conveniently prepared in the form of membranes, without the loss of tropocollagen secondary structure. As suggested by infrared spectroscopy and thermal analysis, mixing is accompanied by macromolecular interaction conditions anionic collagen and P(VDF/TrFE). Although preliminary, the determined pyroelectric coefficient for the 1:1 composite of 1.89 × 10^?4Cm^?2K^?1, is higher than those determined under the same conditions for native, anionic collagen and P(VDF/TrFE) and of respectively 0.37 × 10^?4Cm^?2K^?1, 1.16 × 10^?4Cm^?2 K^?1 and 17 × 10^?6 Cm^?2K^?1, but comparable to that for PZT (4.2 × 10^?4Cm^?2K^?1) at the same temperature. This increase in pyroelectric coefficient for the 1:1 composite, in respect to anionic collagen membranes, may be a result of a anionic collagen: P(VDF/TrFE) interaction. A model based on hydrogen bonding formation between acidic and alcoholic hydroxyl groups of anionic collagen and the flurine atoms of P(VDF/TrFE) is proposed.     

A study on thermal behavior of a poly(VDF‐CTFE) copolymers binder for high energy materials

This article describes a study on thermal behavior of poly(vinylidene fluoride‐chlorotrifluoroetheylene) [poly(VDF‐CTFE)] copolymers as polymeric binders of specific interest for high energy materials (HEMs) composites by thermal analytical techniques. The non‐isothermal thermogravimetry (TG) for poly (VDF‐CTFE) copolymers was recorded in air and N₂ atmospheres. The results of TG thermograms show that poly(VDF‐CTFE) copolymers get degrade at lower temperature when in air than in N₂ atmosphere. In the derivative curve, there was single maximum degradation peak (T_max) indicating one‐stage degradation of poly(VDF‐CTFE) copolymers for all the samples. The other thermal properties such as glass transition temperature (T_g) and degradation temperature (T_d) for poly(VDF‐CTFE) copolymers were measured by employing differential scanning calorimeter (DSC) technique. The kinetic parameters related to thermal degradation of poly(VDF‐CTFE) copolymers were investigated through non‐isothermal Kissinger kinetic method using DSC method. The activation energies for thermal degradation of poly(VDF‐CTFE) copolymers were found in a range of 218–278 kJ/mol. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Tunable Mechanical and Electrical Properties of Coaxial Electrospun Composite Nanofibers of P(VDF-TrFE) and P(VDF-TrFE-CTFE)

The coaxial core/shell composite electrospun nanofibers consisting of relaxor ferroelectric P(VDF-TrFE-CTFE) and ferroelectric P(VDF-TrFE) polymers are successfully tailored towards superior structural, mechanical, and electrical properties over the individual polymers. The core/shell-TrFE/CTFE membrane discloses a more prominent mechanical anisotropy between the revolving direction (RD) and cross direction (CD) associated with a higher tensile modulus of 26.9 MPa and good strength-ductility balance, beneficial from a better degree of nanofiber alignment, the increased density, and C-F bonding. The interfacial coupling between the terpolymer P(VDF-TrFE-CTFE) and copolymer P(VDF-TrFE) is responsible for comparable full-frequency dielectric responses between the core/shell-TrFE/CTFE and pristine terpolymer. Moreover, an impressive piezoelectric coefficient up to 50.5 pm/V is achieved in the core/shell-TrFE/CTFE composite structure. Our findings corroborate the promising approach of coaxial electrospinning in efficiently tuning mechanical and electrical performances of the electrospun core/shell composite nanofiber membranes-based electroactive polymers (EAPs) actuators as artificial muscle implants.     

Influence of polarization,reorientation, and coupling of dipole on electrocaloric effect in ferroelectrics

Electrocaloric effects due to entropy change and dipole coupling upon electric field in second-order phase transition (tetragonal-cubic) ferroelectrics are investigated by a three-dimensional Devonshire's theory and statistic method. In diabatic condition, increase in vibration entropy to heat the ferroelectric is due to decreases in polarization entropy and configuration entropy of dipole reorientation in the specific directions. Coupling effect originated from the reorientation of dipoles accompany with electric hysteresis loop happens in the nearest neighbor dipoles parallel to electric field direction. Numerical simulations exhibit that polarization effect causes electrocaloric peak at the Curie's temperature independent of electric field, reorientation effect of dipole causes a shift of electrocaloric peak to high temperature with electric field, and coupling effect between dipoles gives rise to increase in electrocaloric effect with decreasing temperature. A method to predetermine the excellent electrocaloric effect of ferroelectrics from dielectric and/or polarization experimental results is proposed.     

Structure and properties of fluorinated polymer/poly(ethylene oxide) blends

BACKGROUND: In order to explore ways for improving the toughness of copolymers of vinylidene difluoride and chlorotrifluoroethylene (P(VDF‐CTFE)), polyethylene oxide (PEO) with ultrahigh molecular weight and good mechanical properties was applied for the first time to prepare P(VDF‐CTFE)/PEO blends for adhesives applications. RESULTS: The results show that with an increase of PEO content, the mechanical properties of the blends are improved markedly, and blends with high strength, modulus and toughness are obtained. The difference in the solubility parameters of P(VDF‐CTFE) and PEO is small, and only a single α‐relaxation peak is observed in the high‐temperature zone for the blends, indicating that the blend system is partially miscible. The experimental values for the glass transition temperature of the blend varying with PEO content are always higher than those predicted by the Fox equation, and a strong interaction is supposed to occur between the molecules of P(VDF‐CTFE) and PEO. The relative crystallinity of the blends increases with PEO content, and the PEO particles disperse homogeneously in the P(VDF‐CTFE) matrix, whose average size decreases with increasing PEO content. Phase‐inverted morphologies of the blends are observed above 60 wt% of PEO. CONCLUSION: The partial miscibility of P(VDF‐CTFE)/PEO blends leads to an improvement of the mechanical properties of the blends, which is an effective way to improve the toughness of fluorinated polymers. Copyright © 2009 Society of Chemical Industry     

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     

Fabrication and properties of solution processed all polymer thin‐film ferroelectric device

A ferroelectric device, making use of a flexible plastic, polyethylenterephtalate (PET), as a substrate was fabricated by all solution processes. PET was globally coated by a conducting polymer, poly(3,4‐ethylenedioxythiophene) poly(styrenesulfonate) acid (PEDOT/PSSH), which is used as bottom electrode. The ferroelectric copolymer, poly(vinylidenefluoride–trifluoroethylene) (PVDF–TrFE), thin film was deposited by spin‐coating process from solution. The top electrode, polyaniline, was coated by solution process as well. The ferroelectric properties were measured on this all solution processed all polymer ferroelectric thin‐film devices. A square and symmetric hysteresis loop was observed with high‐polarization level at 15‐V drive voltage on a all polymer device with 700 Å (PVDF–TrFE) film. The relatively inexpensive conducting polyaniline electrode is functional well and therefore is a good candidate as electrode material for ferroelectric polymer thin‐film device. The remnant polarization P_r was 8.5 μC/cm² before the fatigue. The ferroelectric degradation starts after 1 × 10³ times of switching and decreases to 4.9 μC/cm² after 1 × 10⁵ times of switching. The pulse polarization test shows switching take places as fast as a few micro seconds to reach 90% of the saturated polarization. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Low‐Temperature Phase Transition in AgNbO3

AgNbO₃ is a weak ferroelectric with antiferroelectricity due to Ag displacements at room temperature. A dielectric anomaly at 250 K, which has not been observed previously, reveals a transition between the weak ferroelectric phase (M1 phase) at the higher temperature and a new ferroelectric phase (M0 phase) at the lower temperature in AgNbO₃. This transition was further verified by the pyroelectric current and differential scanning calorimetry measurements. The spontaneous polarization value is found to be much larger in the M0 phase than that of the M1 phase. A well‐defined saturating ferroelectric hysteresis loop can also be observed at 77 K, showing a remnant polarization value of 2.4 μC/cm² and a coercive field of 25 kV/cm. All the above results indicate that the larger polarization of the M0 phase mainly comes from the alignment of the antiferroelectric displacements of the Ag atoms.