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To improve the high‐temperature stability of poly(vinylidene fluoride hexafluoropropylene) P(VDF‐HFP)‐based composite film for its potential application in energy storage, the modified silicon nitride (mSi3N4) nanoparticles are fabricated using silane coupling agent (KH‐570) and introduced into P(VDF‐HFP). When the mass fraction of mSi3N4 is 7.5 wt%, the recoverable energy density (Wrec) of the mSi3N4/ P(VDF‐HFP) composite film reaches to 1.79 J/cm3 under a 125 MV/m electric field, which is 82.7% higher than pure P(VDF‐HFP). Interestingly, the dielectric properties of mSi3N4/P(VDF‐HFP) show a considerable thermal stability at a high‐frequency ranging from −20 to 160°C, providing an effective approach for preparing energy storage composites working for high‐temperature environments. [ABSTRACT FROM AUTHOR]

We present a molecular dynamics simulation method including x‐ray diffractometer pattern calculation, mean square displacement (MSD), and nonbonding energy distribution (NED) to disclose the dependencies of condensed structure on its crystalline process of the poly(vinylidene fluoride‐trifluoroethylene) (P(VDF‐TrFE)) films. For comparison, the P(VDF‐TrFE) solution is casted into the films, and followed that different thermal processes are performed to fabricate the crystalline states of the films. Simulation and experimental results have good consistency, indicating that high temperature annealing can effectively promote all‐trans β phase in the crystal region of P(VDF‐TrFE). As such, P(VDF‐TrFE) 80/20 mol% annealing at 140°C shows a higher MSD (~27.5 Å2) and a faster reducing rate of NED than that of other films, contributing to a large maximum polarization (Ps) of ~15.5 μC cm−2, high a remnant polarization (Pr) of ~11.8 μC cm−2, and an attractive piezoelectric strain coefficient (d33) of −27.1 pC N−1 under 200 MV m−1, respectively, and providing a reference for the applications of P(VDF‐TrFE) in flexible sensors, actuators, transducers, and so forth. [ABSTRACT FROM AUTHOR]

This study presents an advanced two‐step hot‐pressing process for fabricating the 1‐3 type Pb(ZrTi)O3/poly(vinylidene fluoride‐trifluoroethylene) (PZT/P(VDF‐TrFE)) piezoelectric composite sheets, demonstrating significant potential for nondestructive evaluation and information storage applications. The engineered columnar architecture within these composites induces a two‐phase clamping effect, which, upon polarization, facilitates the elongation of PZT and suppresses its lateral vibrations, thus enhancing the electromechanical coupling effect as verified by COMSOL simulations. A notable dielectric constant of 2200 at 100 Hz and a coupling coefficient of 0.725 was achieved with specific geometric modifications to the PZT/P(VDF‐TrFE) sheets. These findings suggest that P(VDF‐TrFE) as a polymer matrix exceeds the performance of conventional epoxy matrices, offering a novel approach to designing 1‐3 type piezoelectric composites. Highlights: P(VDF‐TrFE) effectively drives the elongation strain of internal PZT columns.COMSOL simulation clarifies the clamping effect of piezoelectric P(VDF‐TrFE).PZT/P(VDF‐TrFE) shows a higher kt of 0.725 than that of pure PZT samples. [ABSTRACT FROM AUTHOR]

Wearable electrochemical sensors, which can track various biomarkers in real‐time, is one of the most promising bioanalytical devices in the point of care testing and health management. Sample collection modules, as the important front‐end of the sensors, capture and transfer enough sample so as to achieve real‐time, precise and accurate detection. Noninvasive and minimally invasive techniques for sample collection are highly desired. However, it is still a key challenge to realize a reliable sample acquisition. Herein, we provide an overview on the progress in the sample collection methods for wearable electrochemical sensors. It covers the conventional and emerging methods/structures including reverse iontophoresis, microneedles, as well as microfluidic chips. The working principle, fabrication materials and manufacturing technologies will be introduced in detail. Finally, the present challenges and the development trend in the future of these approaches are also put forward. [ABSTRACT FROM AUTHOR]

A lead‐free tetragonal‐phase (Ba0.94Ca0.06)(Ti0.95Zr0.05)O3 (BCTZ) micro sheet is prepared by molten‐salt growth method, which exhibits a polarizing behavior of relaxor ferroelectricity and possesses a high dielectric constant (εr) of ~2400. Subsequently, the BCTZ sheet is evenly doped into ferroelectric copolymer P(VDF‐TrFE)55/45 mol% with different mass fractions, and the flexible BCTZ/P(VDF‐TrFE) composite films are prepared using a conventional solution casting process. εr of BCTZ/P(VDF‐TrFE) increases with the mass content of BCTZ, and reaches 23.8 in 20 wt% BCTZ sample. Meanwhile, at a high electrical field of 30 MV/m, the strain and electric field of BCTZ/P(VDF‐TrFE) are in the opposite direction, indicating a negative value of piezoelectric strain coefficient (d33) caused by inverse piezoelectric effect. In addition, d33 of different BCTZ/P(VDF‐TrFE) films are fitted using a strain‐electrical field curve, which firstly increases and then decreases with increases in BCTZ content. As such, a high d33 of −47.3 pC/N is obtained in BCTZ/P(VDF‐TrFE)15/85 wt% film. Thus, this research concerning the inverse piezoelectric effect may provide a reference for designing a piezoelectric composite using in transducers and actuators. [ABSTRACT FROM AUTHOR]

A group of ferroelectric polyvinylidene‐trifluoroethylene (P(VDF‐TrFE)) with 6, 9, 20, and 50 mol% trifluoroethylene (TrFE) is synthesized by an hydrogenation process using a new catalyst (SiMe3)3SiH from polyvinylidene‐chlorotrifluoroethylene. We find the crystalline region of hydrogenated P(VDF‐TrFE) 80/20 mol% is β crystal phase predominant, which is responsible to the favorable ferroelectric property. Moreover, polyvinylidene fluoride (PVDF) blending is used to fabricate the ferroelectric and relaxor ferroelectric properties of P(VDF‐TrFE) 80/20 mol%. Interestingly, with the increasing of PVDF content, PVDF/P(VDF‐TrFE) has three successional conversion stages of ferroelectricity, antiferroelectricity, and relaxor ferroelectricity, respectively, indicating that the β crystal domains in hydrogenated P(VDF‐TrFE) films gradually reduces with the introduction of PVDF. Otherwise, after an unidirectional stretching process, the ferroelectricity of relaxor PVDF/P(VDF‐TrFE) blend film is reformed. As such, the maximum polarization (Pm) and remnant polarization (Pr) of stretched PVDF/P(VDF‐TrFE) with 90 wt% PVDF reached to 13.8 and 7.5 μC/cm2 under 200 MV/m, respectively. Thus, the three methods proposed in this work including fabricating configuration by changing TrFE content, physical blending by introduction of PVDF, and simple stretching can modify the ferroelectric performances of this hydrogenated P(VDF‐TrFE), which also provides a reference of application of this polymer on ferroelectric areas. [ABSTRACT FROM AUTHOR]

Large‐scale mechanical stretching has been performed to modify the crystal phase structures of the pristine poly(vinylidene fluoride) (PVDF) and its copolymer poly(vinylidene fluoride‐hexafluoropropylene) [P(VDF‐HFP)] with various molar contents HFP in an attempt to improve their energy storage performances. It is found that the physical stretched PVDF and P(VDF‐HFP) 95.5/4.5 mol % films have a phase transition from the nopolar α‐phase to highly polar β‐phase, which is different from the P(VDF‐HFP) films with relative high HFP molar contents (α to γ phases). The following results show that the phase transition in these PVDF‐based polymers has a significant effect on their dielectric and energy storage performances. On account of the reformation of the crystalline property and elimination of the impurity defects, an ultra‐high breakdown electric field of ∼900 MV/m has been obtained in all the stretched samples. Consequently, the higher discharged energy densities of 27.1 and 27.7 J/cm3 are calculated from the D–E loops of the β‐PVDF and β‐P(VDF‐HFP) 95.5/4.5 mol % films, respectively. Regarding their excellent discharging energy density of ∼10 J/cm3 under 600 MV/m for thousands of times, the stretched PVDF and its copolymer P(VDF‐HFP)s are promising candidates for high power capacitors applications. [ABSTRACT FROM AUTHOR]

ABSTRACT Different thermal processing methods were used to fabricate the crystalline properties of poly(vinylidene fluoride- co-chlorotrifluoroethylene) [P(VDF- co-CTFE)] films. We observed that the crystallinity and crystal grain size of the various samples decreased with the quenching temperature. Compared to that of the annealed P(VDF- co-CTFE) sample, a higher dielectric constant of 13.9 at a frequency of 100 Hz was obtained in the film with liquid nitrogen quenching because the increasing small crystalline regions were susceptible to the excitation of external electric field. Meanwhile, the breakdown electric strength of the low-temperature-quenched film increased to 530 MV/m when the depth of shallow electronic energy level decreased, as depicted by Fröhlich collective electron approximated electric breakdown theory. Moreover, when we introduced the leakage current density curves, the effect of the space charges on the electric displacement was proven. As a result, the discharged energy density of the liquid-nitrogen-quenched P(VDF- co-CTFE) film was enhanced to 15.32 J/cm3 at an electric field of 530 MV/m; this provided an effective way in addition to chemical modification to achieve a high energy storage ability in this poly(vinylidene fluoride)-based fluoropolymer. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42794. [ABSTRACT FROM AUTHOR]

ABSTRACT 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. [ABSTRACT FROM AUTHOR]

Three series of poly (vinylidene fluoride-chlorotrifluoroethylene)/barium titanate (BT) nanocomposites with varied compositions were fabricated via solution cast process followed by thermally treated in different ways. Quenching the composite samples at lower temperature could effectively enhance their dielectric constant, breakdown strength as well as the energy density. The highest energy density (13.6 J/cm3) is observed in the sample quenched from 200°C to −94°C with 5 vol% BT, which is much higher than nanocomposites reported in the current literature. The addition of ceramic particles leads to the improvement of dielectric permittivity and energy density measured under the same electric field. However, the dielectric breakdown strength and the energy density measured at breakdown strength of the resultant composites are reduced as a function of BT content. The fixed maximum electric displacement and reduction of saturation electric field suggest that the addition of ceramic particles with high dielectric constant may help increase the energy density of composites under low electric field but not for high electric field. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers. [ABSTRACT FROM AUTHOR]

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 [ABSTRACT FROM AUTHOR]

Thermal processing at various temperatures has been used to fabricate poly(vinylidene fluoride- co-trifluoroethylene) [P(VDF- co-TrFE)] films with varied crystalline properties in an attempt to improve their piezoelectric properties. Although the dielectric constant of the films annealed at higher temperature is smaller than that of cooled and quenched ones, it has been shown that the annealed films possess larger crystallinity and stacked lamellar crystal grain size. The ferroelectric domains deriving from crystal region in all the samples are effectively improved by hot polarization. As a result, the remnant polarizations ( Pr) and coercive electric field ( Ec) of the corresponding films are improved at a low frequency due to the response of dipoles in crystal phase, and the largest piezoelectric constant in the longitudinal thickness mode ( d33=−25 pC/N) is obtained in an annealed copolymer film. The results illustrate improving the crystal structure of P(VDF- co-TrFE) is an effective way to realize high electromechanical properties, which provides broadly applied scenery for this kind of copolymer in piezoelectric components. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012 [ABSTRACT FROM AUTHOR]