Effect of heat treatment on the electrical properties of lead zirconate titanate/poly (vinylidene fluoride) composites

Ceramic/polymer composites are attracting increasing interest in materials research and practical applications due to the combination of excellent electric properties of piezoelectric ceramics and good flexibility of polymer matrices. In this case, the crystallization of the polymer has a significant effect on the electric properties of ceramic/polymer composites. Based on different heat treatment methods, the crystallization of poly(vinylidene fluoride) (PVDF) in composites of lead zirconate titanate (PZT) and PVDF can be controlled effectively. PZT/PVDF composites with various PVDF crystallizations exhibit distinctive dielectric and piezoelectric properties. When the crystallization of PVDF is 21%, the PZT/PVDF composites show a high dielectric constant (ε) of 165 and a low dielectric loss (tan δ) of 0.03 at 10³ Hz, and when the crystallization of PVDF reaches 34%, the piezoelectric coefficient (d₃₃) of PZT/PVDF composites can be up to ca 100 pC N^?1. By controlling the crystallization of PVDF, PZT/PVDF composites with excellent dielectric and piezoelectric properties were obtained, which can be employed as promising candidates in high‐efficiency capacitors and as novel piezoelectric materials. Copyright © 2010 Society of Chemical Industry     

Pyroelectric properties of a new family of synthetic polypeptidepolymers

The pyroelectric response of a triglycerol-gelatin film, belonging to a new family of pyroelectric modified polypeptides, is examined over a temperature range from-20°C to +85°C, by the dynamic Chynoweth¹ technique. The size of the observed pyroelectric coefficient of the film is found to be comparable to that of polyvinylidene fluoride (PVDF), the best known piezoelectric and pyroelectric polymer.     

Flexible and Conductive 3D Printable Polyvinylidene Fluoride and Poly(N,N‐dimethylacrylamide) Based Gel Polymer Electrolytes

In this work, 3D printable gel polymer electrolytes (GPEs) based on N,N‐dimethylacrylamide (DMAAm) and polyvinylidene fluoride (PVDF) in lithium chloride containing ethylene glycol solution are synthesized and their physicochemical properties are investigated. 3D printing is carried out with a customized stereolithography type 3D gel printer named “Soft and Wet Intelligent Matter‐Easy Realizer” and free forming GPE samples having variable shapes and sizes are obtained. Printed PVDF/PDMAAm‐based GPEs exhibit tunable mechanical properties and favorable thermal stability. Electrochemical proprieties of the printed GPEs are carried out via impedance spectroscopy in the temperature range of 25–90 °C by varying PVDF content. Ionic conductivity as high as 6.5 × 10^?4 S cm^?1 is achieved at room temperature for GPE containing low PVDF content (5 wt%) and conductivity of the GPEs is increased as temperature rises.     

Nanostructured piezoelectric polymers

Among the wide variety of piezoelectric materials available, polymers offer an interesting solution because of their high mechanical flexibility, easy processing, and conformable features; they maintain good ferroelectric and piezoelectric properties. The most prominent examples of these are poly(vinylidene fluoride) (PVDF) and its copolymer, poly(vinylidene difluoride–trifluoroethylene) [P(VDF–TrFE)]. An attractive prospective consists of the preparation of nanostructured polymers. It has been shown that the dimensional confinement of such macromolecules down to the nanoscale can improve their piezoelectric properties because the tailoring of the chemical structure is performed at the molecular level. In this review, we show how nanostructured polymers can be obtained and discuss reports on the ferroelectric and piezoelectric properties of nanostructured PVDF and P(VDF–TrFE) materials. In particular, we show how dimensional confinement leads to piezoelectric nanostructures with relevant performances, with a focus on the macromolecular structural arrangement that enhances their behavior. Experimental results and applications are also reported to compare the performances of different nanostructuration processes and the polymer efficiencies as piezoelectric materials. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41667.     

Master batch approach for developing PVDF/EVA/CNT nanocomposites with co-continuous morphology and improved electrical conductivity

Conducting polymer composites constituted by co-continuous poly (vinylidene fluoride) (PVDF)/ ethylene- vinyl acetate copolymer (EVA) blends with multiwalled carbon nanotube (CNT) were prepared by melt mixing using different procedures. The effect of the master batch approach on the conductivity, morphology, mechanical, thermal and rheological properties of PVDF/EVA/CNT nanocomposites was compared with that based on one step mixing strategy. The selective extraction experiments revealed that CNT was preferentially localized in the EVA phase in all situations, even when PVDF@CNT master batch was employed. Nanocomposites prepared with EVA@CNT master batch displayed higher conductivity, whose value reached around 10⁻¹ S m⁻¹ with the addition of 0.56 vol% of CNT. The better electrical performance was attributed to the better distribution of the filler, as indicated by transmission electron microscopy and rheological behavior. The electrical and rheological behavior were also investigated as a function of the CNT content.     

PVDFBaTiO3/carbon nanotubes ternary nanocomposites: Effect of nanofillers and processing

Ternary thermoplastic systems based on poly(vinylidene fluoride), PVDF, filled with barium titanate, BaTiO₃, submicrometric particles and carbon nanotubes, CNT, were prepared. Their structure and morphology were studied as a function of composition and finally correlated with thermal and mechanical properties. High energy ball milling, HEBM, under cryogenic conditions and subsequent hot pressing were used to obtain films with quite uniform dispersion of the nanofillers. The presence of BaTiO₃ particles and CNT did not modify the thermodegradation mechanism of the PVDF. However, enough amount of BaTiO₃ seemed to inhibit the volatility of the products of pyrolysis, hindering the decomposition of PVDF. The presence of CNT favored the PVDF thermodegradation probably due to improved heat transmission by an increase in the thermal conductivity. Variations in PVDF thermal transitions were more dependent of processing conditions. Improvements in the mechanical properties of PVDF were ascribed to a reinforcing effect of the fillers. This effect only happened below the fraction of percolation of CNT, pointing out that CNT reinforce through an optimum load transfer from the PVDF matrix to the nanofillers. POLYM. COMPOS., 38:227–235, 2017. © 2015 Society of Plastics Engineers     

Reinforcement of electroactive characteristics in polyvinylidene fluoride electrospun nanofibers by intercalation of multi-walled carbon nanotubes

This research work reports on development and characterization of multi-walled carbon nanotube (MWCNT)-doped polyvinylidene difluoride (PVDF) nanofibers by the electrospinning method. PVDF is an extensively studied polymer both theoretically and experimentally due to its appealing ferroelectric, piezoelectric, and pyroelectric properties which strongly favors its promising applications in the development of micro/nanostructure devices. The foremost reason for its ferroelectric and piezoelectric behaviors has been attributed to its crystalline structure, specifically the presence of β-phase; however, the existence of the small percentage of β-phase in pristine PVDF limits its applications. To enhance the electroactive features in the PVDF, MWCNTs have been doped in it to prepare electrospun nanofibers, as electrospinning is a single-step approach. These nonwoven nanofibers were prepared at a DC voltage of 20 kV which were subsequently calcined at 100 °C for 12 h. The estimation of crystal structure and phase identification in these nanofibers have been determined by attenuated FT-IR and XRD, while the morphology, microstructure, mean diameter, and length have been examined by FE-SEM. The observed electrical conductivity, capacitance, permittivity (ε), conductivity (δ), and impedance (Z) in these samples have been tailored by doping a range of MWCNT contents and optimizing the experimental conditions.     

Employing Nitrogen Doping as Innovative Technique to Improve Broadband Dielectric Properties of Carbon Nanotube/Polymer Nanocomposites

Undoped carbon nanotubes (CNTs) and N‐CNTs are synthesized by chemical vapor deposition using Fe catalyst, and then melt‐mixed in an APAM mixer with polyvinylidene fluoride (PVDF) to prepare the nanocomposites. The morphology, crystallinity, aspect ratio, nitrogen content, and nitrogen bonding type of CNTs, and the broadband dielectric properties of undoped CNT/PVDF and N‐CNT/PVDF nanocomposites are analyzed. The results show that while undoped CNTs present a crystalline structure with open channels, doping with nitrogen results in CNTs with a bamboo‐like configuration, inferior crystallinity, smaller length, and larger dia­meter. The N‐CNT/PVDF nanocomposites, thus, have a higher percolation threshold (≈ 3.5 wt%) compared to that of the undoped CNT/PVDF nanocomposites (≈ 0.5 wt%). Comparison of the broadband dielectric properties of the generated nanocomposites reveals that nitrogen doping improved the dielectric properties in the insulative region. This is ascribed to the role of nitrogen atoms and their sequent defects in the nanotubes, which act as scattering centers and provide additional polarization sites. For instance, 1.0 wt% N‐CNT/PVDF nanocomposites exhibit a real permittivity of ε′ = 22 and a dissipation factor of tan δ = 0.03 at 1 kHz, a combination superior to that of 0.5 wt% undoped CNT/PVDF nanocomposite with ε′ = 11.2 and tan δ = 3.8, and 1.0 wt% undoped CNT/PVDF nanocomposites with ε′ = 40 and tan δ = 1.4 × 10⁵.

     

3D Printing of Polyvinylidene Fluoride Based Piezoelectric Nanocomposites: An Overview

Recently, polyvinylidene fluoride (PVDF) based nanocomposites have attracted much attention for next-generation wearable applications such as promising piezoelectric energy harvesters (nanogenerators), energy storage devices, sensing devices, and biomedical devices due to their high flexibility, and high dielectric and piezoelectric properties. 3D printing technology, PVDF based piezoelectric nanocomposites, the studies based on 3D printing of PVDF based piezoelectric nanocomposites by inkjet printing and fused deposition modeling, and enhancements of energy harvesting and storage performance of nanocomposites by structural design are comprehensively overviewed here. An insight is provided into 3D printing techniques, structure and properties of PVDF based polymers, various nanofillers and production methods for nanocomposites, solutions to enhance β phase (crystallinity) of PVDF, and improvements of nanocomposites’ breakdown strength, discharged energy density, and piezoelectric power output by mentoring structural design.     

Physico-Chemical Characterizations of Poly(vinylidene fluoride)/Cu3(BTC)2 Composite Membranes Prepared by In Situ Crystal Growth

In this work, we present a simple and fast method for elaborating hybrid membranes by growing metal–organic framework crystals inside a polymer solution. The solution thus obtained was casted then annealed at 90°C for 5 h. This method was tested with poly(vinylidene fluoride) (PVDF) as a piezoelectric polymer and the Cu₃(BTC)₂, BTC = 1,3,5-benzene tricarboxylate, as a filler. The characterization of the obtained membranes by attenuated total reflectance Fourier transform infrared spectroscopy and X-ray diffraction showed the presence of the characteristic signatures of Cu₃(BTC)₂ and the β-phase of PVDF. Moreover, scanning electron microscopy images reveal that the Cu₃(BTC)₂ crystallites have grown along the PVDF membranes. The effect of the filler on both thermal and mechanical properties of the membranes was also studied. POLYM. ENG. SCI., 60:464–473, 2020. © 2019 Society of Plastics Engineers     

Dielectric and piezoelectric properties of PVDF/PZT composites: A review

Smart materials, which exhibit piezoelectricity, find an eclectic range of applications in the industry. The direct piezoelectric effect has been widely used in sensor design, and the inverse piezoelectric effect has been applied in actuator design. Ever since 1954, PZT and BaTiO₃ were widely used for sensor and actuator applications despite their toxicity, brittleness, inflexibility, etc. With the discovery of PVDF in 1969, followed by development of copolymers, a flexible, easy to process, nontoxic, high density alternate with high piezoelectric voltage coefficient was available. In the past 20 years, heterostructural materials like polymer ceramic composites, have received lot of attention, since these materials combine the excellent pyroelectric and piezoelectric properties of ceramics with the flexibility, processing facility, and strength of the polymers resulting in relatively high dielectric permittivity and breakdown strength, which are not attainable in a single phase piezoelectric material. The current review article is an attempt to provide a compendium of all the work carried out with reference to PVDF‐PZT composites. The review article evaluates the effect of grain size, content and other factors under the purview of dielectric and piezoelectric properties while evaluating the sensitivity of the material for sensor application. POLYM. ENG. SCI., 55:1589–1616, 2015. © 2015 Society of Plastics Engineers     

Enhanced piezoelectric responses and crystalline arrangement of electroactive polyvinylidene fluoride/magnetite nanocomposites

The well distributed and electroactive polyvinylidene fluoride (PVDF)/magnetite nanocomposites were successfully fabricated using a mixed solvent system (THF/DMF). Dynamic mechanical properties of the fabricated PVDF/magnetite nanocomposites indicate significant enhancements in the storage modulus as compared with that of neat PVDF. By adding 2 wt % magnetite nanoparticles into the PVDF matrix, the thermal stability of nanocomposites could be enhanced about 26°C as compared with that of PVDF. The β‐phase fraction of PVDF is significantly enhanced with increasing the voltage of electric field poling. The piezoelectric responses of PVDF/magnetite films are extensively increased about five times in magnitude with applied strength of electrical field at 35 MV/m. The change of piezoelectric responses during the applied electric field may be due to the relative long arrangement of PVDF units along the direction of electric field poling and thus increases the values of L_p^* and l_c. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40941.     

Mechanical,electrical, and dielectric properties of polyvinylidene fluoride/short carbon fiber composites with low‐electrical percolation threshold

In this investigation, polyvinylidene fluoride (PVDF)/short carbon fiber (SCF) composites have been prepared by solution casting technique to enhance electrical and dielectric properties with very low‐electrical percolation threshold (0.5 phr SCF). The effect of SCF content on mechanical, thermal and morphological properties of the composites have also been investigated. The mechanical properties of the composites are found to reduce compared to neat PVDF due to poor polymer–filler interaction which can be concluded from FESEM micrographs showing poor bonding between PVDF and SCF. The PVDF/SCF composites exhibit either positive temperature coefficient effect of resistivity or negative temperature coefficient effect of resistivity depending on the loading of SCF in the polymer matrix. The change in conductivity during heating–cooling cycle for these composites shows electrical hysteresis along with electrical set. The melting point of the composites marginally increases with the increase in fiber loading in PVDF matrix as evidenced from DSC thermograms. X‐ray diffraction analysis reveals the crystallinity of PVDF decreases with the increase in SCF loading in matrix polymer. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39866.     

Improved dispersion of carbon nanotubes in poly(vinylidene fluoride) composites by hybrids with core–shell structure

Core–shell structure hybrids of carbon nanotubes (CNTs)/BaTiO₃ (H‐CNT‐BT) and commercial multi‐wall CNTs are respectively incorporated into poly(vinylidene fluoride) (PVDF) for preparing the composites near the percolation thresholds. A comprehensive investigation for CNT's dispersion and composite's conductivity is conducted between H‐CNT‐BT/PVDF and CNT/PVDF at different depths vertical to the injection's direction. Gradual increases of the conductivity in two composites are observed from the out‐layer to the core part which infers an inhomogeneous CNT's dispersion in the interior of composites due to their migration under flow during the injection. However, the use of H‐CNT‐BT fillers with core–shell structure enables to reduce this inhomogeneous dispersion in the composite. Furthermore, the conductive network of CNTs in H‐CNT‐BT/PVDF is less sensitive to the thermal treatment than the one in CNT/PVDF composite, which infers the core–shell structure of hybrids can ameliorate the sensitivity of the conductive network. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45693.     

Enhancement in pyroelectric properties of PZT‐PVA polymer nanocomposites with addition of PAA

Composites comprising of pyroelectric ceramics and electro‐active polymers have gained importance currently as materials for thermal sensing applications, as their unique features and relevant properties can be tailored easily. In this work nanoparticles of PZT have been embedded into PVA/PAA copolymer matrix to form 0 to 3 nanocomposites. Films of the composites are prepared following solvent cast method after dispersing ceramic nanopowder homogeneously in the copolymer matrix with different wt % of the PZT powder. Relevant properties such as dielectric constant and loss factor, pyroelectric coefficients, thermal conductivity, and specific heat capacity as well as Shore hardness have been measured. The material figures of merit for pyroelectric detection have also been determined and reported. It is found that pyroelectric sensing properties of a film of the composite with 20 wt % PZT are comparable to those of commercially used β‐PVDF film for the same application, but with a lower figure of merit. However, it provides greater mouldability and simpler processibility for the fabrication of bulk sensors and actuators. So this composite can be considered as a potential material for the design and fabrication of mouldable pyroelectric detectors and actuators. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41142.     

Electroactive phases of poly(vinylidene fluoride): Determination,processing and applications

Poly(vinylidene fluoride), PVDF, and its copolymers are the family of polymers with the highest dielectric constant and electroactive response, including piezoelectric, pyroelectric and ferroelectric effects. The electroactive properties are increasingly important in a wide range of applications such as in biomedicine, energy generation and storage, monitoring and control, and include the development of sensors and actuators, separator and filtration membranes and smart scaffolds, among others. For many of these applications the polymer should be in one of its electroactive phases. This review presents the developments and summarizes the main characteristics of the electroactive phases of PVDF and copolymers, indicates the different processing strategies as well as the way in which the phase content is identified and quantified. Additionally, recent advances in the development of electroactive composites allowing novel effects, such as magnetoelectric responses, and opening new applications areas are presented. Finally, some of the more interesting potential applications and processing challenges are discussed.     

纺丝参数对聚偏氟乙烯静电纺纤维膜β相含量的影响

β相聚偏氟乙烯(PVDF)因其具有良好的压电、热电性能而受到广泛的关注。采用静电纺丝的方法一步得到高β相含量的PVDF纤维膜,利用X射线衍射(XRD)谱图以及后续的处理分析静电纺过程中的纺丝参数对制备的PVDF纤维膜的结晶度以及结晶部分中β相含量的影响,从而得到了制备高β相含量PVDF的最优化的静电纺丝条件。     

Resistivity–temperature characteristics of filler-dispersed polymer composites

Composites containing carbon nano tube (CNT) or carbon black (CB) conductive particle filler have the special characteristics of positive-temperature-coefficient (PTC) effects of resistivity. We quantitatively studied the relationship between poly(vinylidene fluoride) (PVDF) polymer's thermal volume expansion and the PTC effects of PVDF/CNT and PVDF/CB. The equation to revise filler content at each temperature due to the considerable thermal volume expansion rate of PVDF polymer indicates that filler content decreased with rising temperature. The graphs of filler content at room temperature plotted against apparent filler content with PTC effect were linear and their slopes were constant. From these graphs, we can determine the filler content necessary to occurring PTC effects. For example, the CNT content was 89% at room temperature, and the CB content was 93%. To our knowledge, this study is the first to report such phenomena.     

Melt electrowriting of electroactive poly(vinylidene difluoride) fibers

Poly(vinylidene difluoride) (PVDF) has piezoelectric properties suitable for numerous applications such as flexible electronics, sensing and biomedical materials. In this study, individual fibers with diameters ranging from 17 to 55 µm were processed using melt electrowriting (MEW). Electroactive PVDF fibers can be fabricated via MEW, while the polymer can remain molten for up to 10 h without noticeable changes in the resulting fiber diameter. MEW processing parameters for PVDF were investigated, including applied voltage, pressure and temperature. A rapid fiber characterization methodology for MEW that automatically determines the fiber diameters from camera images taken of microscope slides was developed and validated. The outputs from this approach followed previous MEW processing trends already identified with different polymers, although overestimation of fiber diameters <25 µm was observed. The transformation of the PVDF crystalline phase to the electroactive β phase was confirmed using piezo‐force microscopy and revealed that the PVDF fibers possess piezoelectric responses showing d₃₃ ≈ 19 pm V^–1. © 2018 Society of Chemical Industry     

Electron beam‐induced piezoelectric phase in poly(vinylidene fluoride) nanohybrid: effect at the molecular level

A nanohybrid has been synthesized by incorporating organically modified layered silicate in a poly(vinylidene fluoride) (PVDF) matrix. Molecular‐level phenomena have been explored after exposing PVDF and its nanohybrid to an electron beam of varying doses. The electron beam interacts with polymer chains and thereby generates different free radicals, the number of which is quite high in nanohybrid as compared to pure PVDF. The stability of free radicals has been confirmed through density functional theory energy minimization, predicting stable β‐phase free radicals in the nanohybrid. Quantitative analyses of chain scission, crosslinking and double bond formation are reported and compared after irradiation for both PVDF and its nanohybrid using UV‐visible and Fourier transform infrared spectroscopies, sol–gel analyses and gel permeation chromatography, revealing both chain scission and crosslinking phenomena in irradiated PVDF and its nanohybrid, but at higher dose (>90 Mrad) crosslinking dominates in the nanohybrid due to more free radicals and proximity of radical chains on top of templated system in the nanohybrid as compared to pure PVDF. The enhanced crosslinking alters the nanostructure causing disappearance of the peak at 2θ ≈ 3°. Moreover, the electron beam induces significant piezoelectric β‐phase in the nanohybrid against only α‐phase in pure PVDF at a similar dose and raises the possibility for the use of electron‐irradiated nanohybrid as an electromechanical device. β‐Phase formation is also supported through solid‐state NMR, scanning electron microscopy and differential scanning calorimetry studies. The thermal properties in terms of heat of fusion and degradation temperature have been verified indicating steady decrease of melting point and heat of fusion for pure PVDF while considerably less effect is observed for the nanohybrid. The combined effect of chain scission and crosslinking makes both PVDF and its nanohybrid brittle, but with greater stiffness with respect to unirradiated specimens. © 2014 Society of Chemical Industry