Polymer ferroelectret based on polypropylene foam: piezoelectric properties prediction using dynamic mechanical analysis

Thin polypropylene (PP) foam films were produced by continuous extrusion using supercritical nitrogen (N₂) and then charged via corona discharge. The samples were characterized by dynamic mechanical analysis as a simple method to predict the piezoelectric properties of the cellular PP obtained. The results were then related to morphological analysis based on scanning electron microscopy and mechanical properties in tension. The results showed that the presence of a nucleating agent (CaCO₃) substantially improved the morphology (in terms of cell size and cell density) of the produced foam. Also, an optimization of the extrusion (screw design, temperature profile, blowing agent, and nucleating agent content) and post‐extrusion (calendering temperature and speed) conditions led to the development of a stretched eye‐like cellular structure with uniform cell size distribution. This morphology produced higher storage and loss moduli in the machine (longitudinal) direction than for the transverse direction, as well as higher piezoelectric properties. The morphological and mechanical results showed that higher cell aspect ratio led to lower Young's modulus, which is suitable to achieve higher piezoelectric properties. Finally, the best quasi‐static piezoelectric d₃₃ coefficient was 550 pC/N for a cellular PP ferroelectret having a uniform eye‐like cellular structure using N₂ as the ionizing gas inside the cells, while the highest value was only 250 pC/N when air was used. Hence, the value of d₃₃ can be improved by more than 100% just by replacing air with N₂ as the ionizing gas. Copyright © 2016 John Wiley & Sons, Ltd.     

A Semiconducting Organic–Inorganic Hybrid Perovskite‐type Non‐ferroelectric Piezoelectric with Excellent Piezoelectricity

Piezoelectric materials are a class of important functional materials applied in high‐voltage sources, sensors, vibration reducers, actuators, motors, and so on. Herein, [(CH₃)₃S]₃[Bi₂Br₉]( 1 ) is a brilliant semiconducting organic–inorganic hybrid perovskite‐type non‐ferroelectric piezoelectric with excellent piezoelectricity. Strikingly, the value of the piezoelectric coefficient d₃₃ is estimated as ≈18 pC N^?1. Such a large piezoelectric coefficient in non‐ferroelectric piezoelectric has been scarcely reported and is comparable with those of typically one‐composition non‐ferroelectric piezoelectrics such as ZnO (3pC N^?1) and much greater than those of most known typical materials. In addition, 1 exhibits semiconducting behavior with an optical band gap of ≈2.58 eV that is lower than the reported value of 3.37 eV for ZnO. This discovery opens a new avenue to exploit molecular non‐ferroelectric piezoelectric and should stimulate further exploration of non‐ferroelectric piezoelectric due to their high stability and low loss characteristics.     

Ferroelectric and piezoelectric properties of nylon 11/poly(vinylidene fluoride) bilaminate films

The ferroelectric and piezoelectric properties of a new class of polymer ferroelectric and piezoelectric materials, nylon 11/polyvinylidene fluoride (PVF₂) bilaminate films, prepared by a co-melt-pressing method, is presented. The bilaminate films exhibit typical ferroelectric D-E hysteresis behavior with a remanent polarization, P_r, of about 75 mC/m², which is higher than the value of 52 mC/m² observed for PVF₂ or nylon 11 films measured under the same conditions. The coercive field, E_c, of the bilaminate films is ～ 78 MV/m, which is higher than that of either PVF₂ or nylon 11 films. Measurements of the temperature dependence of the piezoelectric strain coefficient, d₃₁, and the piezoelectric stress coefficient, e₃₁, were also carried out. The bilaminate films exhibit a piezoelectric strain coefficient, d₃₁, of 41 pC/N at room temperature, which is significantly higher than the PVF₂ films (25 pC/N) and the nylon 11 films (3.1 pC/N). When the temperature is increased to 110°C, d₃₁ of the bilaminate films reaches a maximum value of 63 pC/N, more than five times that of PVF₂ (11 pC/N) and more than four times that of nylon 11 (14 pC/N) at the same temperature. The piezoelectric stress coefficient, e₃₁, of the bilaminate films shows a value of 109 mC/m² at room temperature, almost twice that of the PVF₂ films (59 mC/m²) and about 18 times that of the nylon 11 films (6.2 mC/m²). Measurement of the temperature dependence of the hydrostatic piezoelectric coefficient, d_h, of the bilaminate films also shows an enhancement with respect to the individual components, PVF₂ and nylon 11. ©1995 John Wiley & Sons, Inc.     

Longitudinal piezoelectric strain measurements of poly(vinylidene fluoride) films

The longitudinal piezoelectric strain of poly(vinylidene fluoride) (PVF₂) films has been measured at room temperature using a high-sensitivity ac capacitance-type dilatometer. The dc bias field dependence of the piezoelectric strain coefficient d₃₃ has been determined. The polarization-related electrostrictive coefficient Q₃₃ obtained is several hundred times larger than the value in normal piezoelectric oxide crystals and is of opposite sign.     

Improving piezoelectric performance of lead-free polymer composites with high aspect ratio BaTiO3 nanowires

Flexible and lead-free piezoelectric nanocomposites were synthesized with BaTiO₃ nanowires (filler) and poly(vinylidene fluoride) (PVDF) (matrix), and the piezoelectric performances of the composites were systematically studied by varying the aspect ratio (AR) and volume fraction of the nanowire and poling time. BaTiO₃ nanowires with AR of 18 were synthesized and incorporated into PVDF to improve the piezoelectric performance of the composites. It was found that high AR significantly increased the dielectric constant up to 64, which is over 800% improvement compared to those from the composites containing spheroid shape BaTiO₃ nanoparticles. In addition, the dielectric constant and piezoelectric coefficient were also enhanced by increasing the concentration of BaTiO₃ nanowires. The piezoelectric coefficient with 50-vol% BaTiO₃ nanowires embedded in PVDF displayed 61 pC/N, which is much higher than nanocomposites with spheroid shape BaTiO₃ nanoparticles as well as comparable to, if not better, other nanoparticle-filled polymer composites. Our results suggest that it is possible to fabricate nanocomposites with proper mechanical and piezoelectric properties by utilizing proper AR fillers.     

A study of the mechanical anisotropy of high-draw,low-draw,and voided PVDF

The mechanical anisotropy of oriented PVDF sheet is examined using a variety of experimental techniques. The mechanical behavior is similar to that observed previously for low-density polyethylene and nylon and consistent with a parallel lamellar crystalline structure. The s₃₁ compliance is reduced in magnitude by drawing to higher draw ratio, but the reduction in the piezoelectric coefficient d₃₁ is less marked, suggesting that the piezoelectric response cannot be related solely to dimensional changes under stress. Drawing to high draw ratio increases the s₃₃ compliance, and this is further increased by introducing voids. The corresponding d₃₃ piezoelectric coefficient is not changed significantly by drawing to high draw ratio, or by the introduction of voids, again indicating that the piezoelectric behavior relates to factors other than dimensional changes.     

Evaluation of piezoelectric poly(vinylidene fluoride) polymers for use in space environments. I. Temperature limitations

Smart materials, such as thin‐film piezoelectric polymers, are interesting for potential applications on Gossamer spacecraft. This investigation aims to predict the performance and long‐term stability of the piezoelectric properties of poly(vinylidene fluoride) (PVDF) and its copolymers under conditions simulating the low‐Earth‐orbit environment. To examine the effects of temperature on the piezoelectric properties of PVDF, poly(vinylidenefluoride‐co‐trifluoroethylene), and poly(vinylidenefluoride‐co‐hexafluoropropylene), the d₃₃ piezoelectric coefficients were measured up to 160 °C, and the electric displacement/electric field (D–E) hysteresis loops were measured from ?80 to +110 °C. The room‐temperature d₃₃ coefficient of PVDF homopolymer films, annealed at 50, 80, and 125 °C, dropped rapidly within a few days of thermal exposure and then remained unchanged. In contrast, the TrFE copolymer exhibited greater thermal stability than the homopolymer, with d₃₃ remaining almost unchanged up to 125 °C. The HFP copolymer exhibited poor retention of d₃₃ at temperatures above 80 °C. In situ D–E loop measurements from ?80 to +110 °C showed that the remanent polarization of the TrFE copolymer was more stable than that of the PVDF homopolymer. D–E hysteresis loop and d₃₃ results were also compared with the deflection of the PVDF homopolymer and TrFE copolymer bimorphs tested over a wide temperature range. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1310‐1320, 2005     

Dependence of dielectric,ferroelectric, and piezoelectric properties on crystalline properties of p(VDF‐co‐TrFE) copolymers

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 (P_r) and coercive electric field (E_c) 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     

Ferroelectric behavior and polarization mechanism in odd‐odd polyamide 11,11

Ferroelectric and piezoelectric behavior in odd‐odd polyamide 11,11 are successfully detected for the first time. The maximum coercive field (E_c) of 90 MV/m, and a remnant polarization (P_r) of 40 mC/m² are obtained at room temperature. A piezoelectric strain coefficient (d₃₃) value as high as ?3.9 pC/N has been found in stretched polyamide 11,11 film. The structural change of samples before and after poling is investigated by wide‐angle X‐ray diffraction patterns, differential scanning calorimetry, and Fourier transform infrared spectroscopy. The results indicate that the nature of the ferroelectricity originates from amide group dipoles in the γ‐form crystal regions. Hysteresis behavior appears to result from the crystallites reversal mechanism. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1094–1099     

Tailoring poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) microstructure and physicochemical properties by exploring its binary phase diagram with dimethylformamide

Poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) (PVDF‐CTFE) membranes were prepared by solvent casting from dimethylformamide (DMF). The preparation conditions involved a systematic variation of polymer/solvent ratio and solvent evaporation temperature. The microstructural variations of the PVDF‐CTFE membranes depend on the different regions of the PVDF‐CTFE/DMF phase diagram, explained by the Flory‐Huggins theory. The effect of the polymer/solvent ratio and solvent evaporation temperature on the morphology, degree of porosity, β phase content, degree of crystallinity, mechanical, dielectric, and piezoelectric properties of the PVDF‐CTFE polymer were evaluated. In this binary system, the porous microstructure is attributed to a spinodal decomposition of the liquid‐liquid phase separation. For a given polymer/solvent ratio, 20 wt % , and higher evaporation solvent temperature, the β phase content is around 82% and the piezoelectric coefficient, d₃₃, is ? 4 pC/N © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 761–773     

High‐Temperature Elastic Moduli of Flux‐Grown α‐GeO2 Single Crystal

From high‐precision Brillouin spectroscopy measurements, six elastic constants (C₁₁, C₃₃, C₄₄, C₆₆, C₁₂, and C₁₄) of a flux‐grown GeO₂ single crystal with the α‐quartz‐like structure are obtained in the 298–1273 K temperature range. High‐temperature powder X‐ray diffraction data is collected to determine the temperature dependence of the lattice parameters and the volume thermal expansion coefficients. The temperature dependence of the mass density, ρ, is evaluated and used to estimate the thermal dependence of its refractive indices (ordinary and extraordinary), according to the Lorentz–Lorenz equation. The extraction of the ambient piezoelectric stress contribution, e₁₁, from the C′₁₁–C₁₁ difference gives, for the piezoelectric strain coefficient d₁₁, a value of 5.7(2) pC N^?1, which is more than twice that of α‐quartz. As the quartz structure of α‐GeO₂ remains stable until melting, piezoelectric activity is observed until 1273 K.     

Flexible and environment-friendly regenerated cellulose/MoS2 nanosheet nanogenerators with high piezoelectricity and output performance

Flexible piezoelectric nanogenerators for energy harvesting are getting more and more attention nowadays by converting the mechanical energy to electric energy. Here, an environment-friendly piezoelectric nanogenerator based on the regenerated cellulose (RC)/MoS₂ nanosheet nanocomposite successfully exhibited a relative high output voltage of 2 V and current of 150 nA under slight press which were 5 and 7.5 times higher than those of the neat RC film, i.e. 0.4 V and 20 nA, respectively. In particular, the MoS₂ nanosheets were obtained through a simple, facile and low-cost pathway by mechanical exfoliation in triethanolamine. The nanocomposite film with MoS₂ nanosheets content of 4% exhibited a high piezoelectric constant (d₃₃) of 19 pC/N, which was 6.3 times higher than that of the neat RC film (i.e. 3 pC/N). Thus, the RC/MoS₂ piezoelectric nanogenerator has great potential applications in the fields of energy harvester, sensors and is of great significance to environment protection.

     

Harnessing Plasticity in an Amine-Borane as a Piezoelectric and Pyroelectric Flexible Film

We demonstrate that trimethylamine borane can exhibit desirable piezoelectric and pyroelectric properties. The material was shown to be able operate as a flexible film for both thermal sensing, thermal energy conversion and mechanical sensing with high open circuit voltages (>10 V). A piezoelectric coefficient of d₃₃≈10–16 pC N⁻¹, and pyroelectric coefficient of p≈25.8 μC m⁻² K⁻¹ were achieved after poling, with high pyroelectric figure of merits for sensing and harvesting, along with a relative permittivity of 6.3.     

Harnessing Plasticity in an Amine‐Borane as a Piezoelectric and Pyroelectric Flexible Film

We demonstrate that trimethylamine borane can exhibit desirable piezoelectric and pyroelectric properties. The material was shown to be able operate as a flexible film for both thermal sensing, thermal energy conversion and mechanical sensing with high open circuit voltages (>10 V). A piezoelectric coefficient of d₃₃≈10–16 pC N^?1, and pyroelectric coefficient of p≈25.8 μC m^?2 K^?1 were achieved after poling, with high pyroelectric figure of merits for sensing and harvesting, along with a relative permittivity of 6.3.     

Enhanced β‐phase in PVDF polymer nanocomposite and its application for nanogenerator

Harvesting energy from the ambient mechanical energy by using flexible piezoelectric nanogenerator is a revolutionary step toward achieving reliable and green energy source. Polyvinylidene fluoride (PVDF), a flexible polymer, can be a potential candidate for the nanogenerator if its piezoelectric property can be enhanced. In the present work, we have shown that the polar crystalline β‐phase of PVDF, which is responsible for the piezoelectric property, can be enhanced from 48.2% to 76.1% just by adding ZnO nanorods into the PVDF matrix without any mechanical or electrical treatment. A systematic investigation of PVDF‐ZnO nanocomposite films by using X‐ray diffractometer, Fourier transform infrared spectroscopy, and polarization‐electric field loop measurements supports the enhancement of β‐phase in the flexible nanocomposite polymer films. The piezoelectric constant (d₃₃) of the PVDF‐ZnO (15 wt%) film is found to be maximum of approximately −1.17 pC/N. Nanogenerators have been fabricated by using these nanocomposite films, and the piezoresponse of PVDF is found to enhance after ZnO loading. A maximum open‐circuit voltage ~1.81 V and short‐circuit current of 0.57 μA are obtained for 15 wt% ZnO‐loaded PVDF nanocomposite film. The maximum instantaneous output power density is obtained as 0.21 μW/cm² with the load resistance of 7 MΩ, which makes it feasible for the use of energy harvesting that can be integrated to use for driving small‐scale electronic devices. This enhanced piezoresponse of the PVDF‐ZnO nanocomposite film‐based nanogenerators attributed to the enhancement of electroactive β‐phase and enhanced d₃₃ value in PVDF with the addition of ZnO nanorods.     

Piezoelectric PVDF-TrFE nanocomposite mats filled with BaTiO3 nanofibers: The effect of poling conditions

BaTiO₃ nanofibers (BT NFs), prepared by electrospinning, were used as a filler for electrospun poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) nanocomposite mats. The phase structure and the effect of poling conditions on the piezoelectric properties of PVDF-TrFE/BT nanocomposites were investigated. The results showed an improved degree of crystallinity (78.6%) and a high β-crystal phase (up to 98.3%) in all electrospun samples, independent of the nanofiber content. The two-step poling method, applying electric fields of opposite polarity, led to significantly improved piezoelectric constants d₃₃ (−31.7 pC N⁻¹), strongly dependent on the added BaTiO₃ nanofibers. The inclusion of piezoelectric ceramic nanofibers into a polymer matrix, easily carried out by means of electrospinning, followed by an ad hoc optimized poling treatment, allowed to develop flexible materials with enhanced piezoelectric properties, potentially exploitable in innovative conversion systems used in wearable and sensing devices.     

Mechanical and dielectric behavior of poly(vinylidene)–poly(arylene ether nitrile) composites as film capacitors for energy storage applications

Novel polymer composites PEN/PVDF were prepared from poly(arylene ether nitrile) (PEN) and poly(vinylidene fluoride) (PVDF) via solution mixing. Due to the toughening effect of PVDF, PEN/PVDF blends with 5 wt % PVDF exhibit higher tensile strength (106 MPa) and breaking elongation (8.09%) than pure PEN does. Because of introduction of PVDF and interfacial polarization, the dielectric constant of PEN/PVDF blends at 1 kHz and room temperature increases from 3.3 to 4.5 with increasing content of PVDF. The dissipation factor (tanδ) of PEN/PVDF blends is relatively low (<0.04) in a very wide frequency range from 250 Hz to 100 kHz. The PEN/PVDF blends show certain piezoelectric behavior (d ₃₃ from 0.9 to 1 pC/N) due to the contribution of PVDF. After polarization, the piezoelectric coefficient d ₃₃ somewhat increases. The results suggest that PEN/PVDF blends will have potential application in electronic information fields, especially in film capacitors.     

Dielectric and piezoelectric properties of dense and porous PZT films prepared by sol-gel method

PZT films with different microstructure and Zr:Ti ratios were fabricated on ITO/glass and platinized silicon wafer substrates by dip-coating. A dense film of 2% porosity and a porous film of 19% porosity were obtained by repetition of thin and thick coatings, respectively. Development of pores during heating the film was examined and heating process factors were investigated. In the film fabricated on ITO/glass substrates, an existence of non-perovskite and low permittivity layer was confirmed by measurement of film thickness dependence of the dielectric constant. Among the films studied, the film with molar composition of Ti:Zr = 5:5 exhibited the largest dielectric constant and apparent piezoelectric coefficient, d ₃₃, though the values were small. Apparent piezoelectric coefficients of d ₃₃ and g ₃₃ of the porous films were larger than those of the dense films.     

MgNb2O6 Modified K0.5Na0.5NbO3 Eco-Piezoceramics: Scalable Processing,Structural Distortion and Complex Impedance at Resonance

In this work, piezoceramics of the lead-free composition K_0.5Na_0.5NbO₃ with an increasing amount of MgNb₂O₆ (0, 0.5, 1, 2 wt.%) were prepared through conventional solid-state synthesis and sintered in air atmosphere at 1100 °C. The effect of magnesium niobate addition on structure, microstructure and piezoelectric properties was evaluated. The ceramics maintain the orthorhombic Amm2 phase for all compositions, while an orthorhombic Pbcm secondary phase was found for increasing the concentration of MgNb₂O₆. Our results show that densification of these ceramics can be significantly improved up to 94.9 % of theoretical density by adding a small amount of magnesium-based oxide (1 wt.%). Scanning electron microscopy morphology of the 1 wt.% system reveals a well-packed structure with homogeneous grain size of ∼2.72 μm. Dielectric and piezoelectric properties become optimal for 0.5–1.0 wt.% of MgNb₂O₆ that shows, with respect to the unmodified composition, either higher piezoelectric coefficients, lower anisotropy and relatively low piezoelectric losses (d₃₃=97 pC N⁻¹; d₃₁=−36.99 pC N⁻¹ and g₃₁=−14.04×10⁻³ mV N⁻¹; Q_p(d₃₁)=76 and Q_p(g₃₁)=69) or enhanced electromechanical coupling factors (k_p=29.06 % and k₃₁=17.25 %).     

On the piezoelectricity of collagen/natural rubber blend films

We studied the physicochemical, piezoelectric and dielectric properties of collagen-natural rubber (NR) films. The piezoelectric strain tensor element d₁₄, and the dielectric permittivity ε₁₁ were obtained for the collagen-NR blends. Resonance measurement of the piezoelectric strain constant d₁₄ of collagen gives 0.057 pC/N. It was observed that for the addition of 10% of NR we have a decrease of the piezoelectricity to 0.042 pC/N. Our results also show that the presence of NR contributes to the increase of the thermal stability of the collagen films. The denaturation temperatures of collagen increases with the presence of NR. For the blend with 25% of NR (S2--Col75bn25), one has the highest denaturation temperature (109.6 °C). We also believe that the presence of NR lead to the decrease of the organization of the microscopic structure of the films, which results in the decrease of the piezoelectricity.