Pyroelectric performances of 1-3 ferroelectric composites based on barium titanate nanowires/polyvinylidene fluoride

Pyroelectric properties of 1–3 ceramic/polyvinylidene fluoride (PVDF) composites by using barium titanate nanowires (BTnws) and dopamine modified BTnws (DM-BTnws) as inclusions were firstly reported. 0–3 composites based on dopamine modified BT nanoparticles (DM-BTnps)/PVDF were also prepared for comparison. It was found that low contents of DM-BTnws in PVDF are beneficial for achieving high fraction of β-phase content based on the analysis results of X-ray diffraction (XRD), Fourier transform infrared (FTIR) and electric displacement-electric field (D-E) measurements. The enhancement of β-phase content in the DM-BTnws/composited film was believed to originate from strong hydrogen bonds interactions between poly-dopamine and PVDF molecules, which induced phase transition in PVDF from α-phase into β-phase. However, although DM-BTnws improved β-phase content and, accordingly, pyroelectric coefficient of the composites, they deteriorated dielectric performances of PVDF, reducing pyroelectric performances of the composites in terms of voltage and detectivity figures of merit.     

COOHMWCNTs‐induced BiFeO3‐poly(vinylidene fluoride) (PVDF) composites with enhanced dielectric and ferroelectric properties

In this work, flexible three phase composite films were prepared with surface functionalized multi‐walled carbon nanotubes (f‐MWCNTs) and bismuth ferrite (BiFeO₃;BFO) particles embedded into the poly(vinylidene fluoride) (PVDF) matrix via solution casting technique. The properties and the microstructure of prepared composites were investigated using an impedance analyzer and field emission scanning electron microscope. The micro‐structural study showed that the f‐MWCNTs and BFO particles were dispersed homogeneously within the PVDF matrix, nicely seated on the floor of the f‐MWCNTs separately. The dielectric measurement result shows that the resultant composites with excellent dielectric constant (≈96) and relatively lower dielectric loss (<0.23 at 100 Hz). Furthermore, the percolation theory is explored to explain the dielectric properties of the resultant composites. It says that the percolation threshold of f_MWCNTs = 0.9 wt % and the enhancement of the dielectric constant of the composite was also discussed. In addition, the remnant polarization of the un‐poled PVDF‐BFO‐f‐MWCNTs composites (2P_r ～1.34 µC/cm² for 1.1 wt % of f‐MWCNTs) is also improved. These three phase composites provide a new insight to fabricate flexible and enhanced dielectric properties as a promising application in modern electrical and electronic devices. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46002.     

COOH?MWCNTs‐induced BiFeO3‐poly(vinylidene fluoride) (PVDF) composites with enhanced dielectric and ferroelectric properties

In this work, flexible three phase composite films were prepared with surface functionalized multi‐walled carbon nanotubes (f‐MWCNTs) and bismuth ferrite (BiFeO₃;BFO) particles embedded into the poly(vinylidene fluoride) (PVDF) matrix via solution casting technique. The properties and the microstructure of prepared composites were investigated using an impedance analyzer and field emission scanning electron microscope. The micro‐structural study showed that the f‐MWCNTs and BFO particles were dispersed homogeneously within the PVDF matrix, nicely seated on the floor of the f‐MWCNTs separately. The dielectric measurement result shows that the resultant composites with excellent dielectric constant (≈96) and relatively lower dielectric loss (<0.23 at 100 Hz). Furthermore, the percolation theory is explored to explain the dielectric properties of the resultant composites. It says that the percolation threshold of f_MWCNTs = 0.9 wt % and the enhancement of the dielectric constant of the composite was also discussed. In addition, the remnant polarization of the un‐poled PVDF‐BFO‐f‐MWCNTs composites (2P_r ～1.34 µC/cm² for 1.1 wt % of f‐MWCNTs) is also improved. These three phase composites provide a new insight to fabricate flexible and enhanced dielectric properties as a promising application in modern electrical and electronic devices. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46002.     

Piezoelectric properties of noncovalently functionalized 2D nanomaterials incorporated poly(vinylidene fluoride) nanocomposites

We report here for the first time the role of noncovalently functionalized 2D nanomaterials on the ferroelectric and piezoelectric behavior of poly(vinylidene fluoride) (PVDF) nanocomposites. Graphene oxide (GO), expanded graphite (EG) and hexagonal boron nitride (h-BN) were noncovalently modified via Li-salt of 6-amino hexanoic acid (Li-AHA), denoted as m-GO, m-EG and m-BN, in order to de-agglomerate and de-stack them, which were subsequently incorporated into the PVDF matrix via solution mixing, followed by compression molding. Simultaneously, PVDF nanocomposites with unmodified 0.08 wt% of 2D nanomaterials were also prepared using the same methodology. PVDF/m-BN nanocomposite showed a higher extent of polar phase (~36%) associated with PVDF phase as compared to PVDF/m-GO and PVDF/m-EG nanocomposites. Further, the highest permittivity (~58 at 10⁻¹ Hz) was achieved in PVDF/m-BN nanocomposite, which was also reflected in higher remnant polarization (~61 nC/cm²) and a significantly higher d₃₃ value (~53 pm/V). Moreover, a higher output peak to peak voltage (~13 V) was obtained for the sensor device fabricated from PVDF/m-BN nanocomposite. Thus, the role of Li-AHA-modified 2D nanomaterials in improving the morphology, dielectric, ferroelectric, and piezoelectric characteristics of the PVDF nanocomposites was clearly established.     

Novel composites of copper nanowire/PVDF with superior dielectric properties

Novel copper nanowires (CuNWs)/poly(vinylidene fluoride) (PVDF) nanocomposites with high dielectric permittivity (ε′) and low dielectric loss (ε″) were prepared by a precipitation technique followed by melt compression. Their dielectric properties over the broadband frequency range, i.e. 10¹–10⁶ Hz, were compared with multi-walled carbon nanotubes (MWCNT)/PVDF nanocomposites prepared by the same technique. It was observed that the CuNWs/PVDF nanocomposites had higher dielectric permittivity, lower dielectric loss and thus significantly lower dissipation factor (tan δ) than the MWCNT/PVDF nanocomposites at room temperature. This behavior was ascribed to a higher conductivity of the fresh core of the CuNWs relative to the MWCNT, which provided the composites with a higher amount of mobile charge carriers participating in the interfacial polarization. Moreover, the presence of oxide layers on the CuNWs surfaces diminished the conductive network formation leading to a low dielectric loss.     

Simultaneously improving thermal conductivity and dielectric properties of poly(vinylidene fluoride)/expanded graphite via melt blending with polyamide 6

Poly(vinylidene fluoride)/polyamide 6/expanded graphite (PVDF/PA6/EG) composite is prepared via one-step melt extrusion. The EG is well dispersed with the addition of PA6 and mainly distributed in the PA6 phase due to the stronger affinity between them. As a result, the PVDF/PA6/EG sample presents higher dielectric permittivity than the PVDF/EG sample and maintain a low dielectric loss due to its sea-island phase structure, which impedes the formation of conductive path in the composite. The mean interlayer spacing of the EG in the polymer matrix decreases obviously due to its improved dispersion state, which is in favor of the phonon transportation in the composite. As a result, the PVDF/PA6/EG sample exhibits a significantly improved thermal conductivity of about 0.48 W m⁻¹ K⁻¹, which is 140% higher than that of the PVDF sample and 37% higher than that of the PVDF/EG sample. Moreover, the PVDF/PA6/EG sample presents higher Young's modulus and tensile strength than the PVDF/EG sample. While the elongation at break of the PVDF/PA6/EG sample is only a little lower than that of the PVDF/EG sample. This means that the tensile properties of the composite are not destroyed obviously by melt blending with the immiscible PA6.     

Development of Multiferroism in PVDF with CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Nanoparticles

Thin films of some polymer-ceramic nanomultiferroic composites (in 0–3 connectivity) of compositions (1-x) PVDF-xCoFe₂O₄ (x?=?0.05, 0.1, 0.5) have been fabricated through a solution casting route. Based on X-ray diffraction pattern and data, basic crystal structure and unit cell parameters were obtained. The surface morphology of the materials was studied using a scanning electron microscopy (SEM) technique. Structural investigation confirms the presence of a polymeric electro-active β-phase of matrix (PVDF) and nano filler spinel phase of the incorporated nano-ceramics. The observed SEM micrographs confirm that the nanoparticles are well distributed in the PVDF matrix without any agglomeration with a lesser spherulitic microstructure. The flexible nano-composites fabricated with polymer (PVDF) and CoFe₂O₄ provide high permittivity (relative dielectric constant) and low loss tangent. An impedance spectroscopy (IS) technique was employed to study the effect of grain and grain boundary in the resistive properties of the composite materials in terms of electric circuit. The study of AC conductivity as a function of frequency follows Jonscher’s power law. The improved conductivity and dielectric, magnetic, and measured first-order magnetoelectric coefficients suggest some promising applications in the embedded capacitors as well as in multifunctional devices.     

Negative dielectric permittivity of PVDF nanocomposites induced by carbon nanofibers and polymer crystallization

Negative permittivity is a key characteristic of the distinctive metamaterials, a novel class of artificial materials with particular electromagnetic properties. Negative permittivity has been realized in metallic structures with special designs, but rarely achieved in polymer nanocomposites. Our recent studies discover that negative permittivity can be attained from randomly distributed carbon nanofiber (CNF) filled poly(vinylidene fluoride) (PVDF) composites over a wide frequency range, and the negative permittivity values are strongly influenced by CNF and PVDF crystalline structures. The effects of CNF on the crystallization of PVDF, and the resultant negative dielectric permittivity of CNF/PVDF composites influenced by crystallization of PVDF and CNF, are investigated. It is revealed that the introduction of CNF not only affects the dielectric permittivity directly, but also causes indirect effects to the dielectric permittivity through influencing the crystallization of PVDF. In particular, due to addition of more CNF, a α- to β-phase transformation in PVDF is found to affect permittivity of the nanocomposites. Furthermore, the permittivity of CNF/PVDF composites are increased considerably (“more negative”) with more CNF, and is affected noticeably by crystalline structures of PVDF. The lowest negative permittivity achieved is −2,500 for the nanocomposite with 5 wt% CNF at 5 kHz.     

Electrical conductivity properties of expanded graphite–polycarbonatediol polyurethane composites

Conductive polymer composites of segmented polycarbonatediol polyurethane and expanded graphite (EG) have been synthesized with different amounts of EG conductive filler (from 0 to 50 wt%). SEM, X‐ray diffraction measurements, Fourier transform infrared and Raman spectroscopies demonstrated a homogeneous dispersion of the EG filler in the matrix. The dielectric permittivity of the composites showed an insulator to conductor percolation transition with increase in EG content. Significant changes in the dielectric permittivity take place when the weight fraction of EG is in the range 20–30 wt%. Special attention has been paid to the dependence of the conductivity on frequency, temperature and EG content. The addition of EG to the matrix causes a dramatic increase in the electrical conductivity of 10 orders of magnitude, which is an indication of percolative behavior. A percolation threshold of ca 30 wt% was evaluated by using the scaling law of percolation theory. © 2014 Society of Chemical Industry     

Enhanced dielectric properties of poly(vinylidene fluoride)–surface functionalized BiFeO3 composites using sodium dodecyl sulfate as a modulating agent for device applications

In this work, we prepared a series of poly(vinylidene fluoride) (PVDF)–surface functionalized BiFeO₃ (h‐BFO)–Sodium dodecyl sulfate (SDS) composite films by solvent casting method to investigate the effect of SDS in the composites. The X‐ray diffraction confirmed that the structure of h‐BFO significantly changed in the PVDF‐(h‐BFO)‐SDS composite in comparison with the rhombohedral structure of pure BiFeO₃. The microscopic study illustrated that the composite with a higher percentage of SDS content facilitated the dispersion as well as proper distribution of ceramic particles in the polymer matrix. The presence of different functionalities of respective polymer and the modified fillers was confirmed by FTIR Spectrophotometer. The dielectric and electrical study done by Impedance Analyzer revealed that the SDS treated surface functionalized composites showed relatively higher dielectric properties than that of two phase composites and pure polymer. Finally, the ferroelectric properties of the composite films done by P‐E loop tracer revealed that the SDS‐treated composites showed an enhanced remanent polarization. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45040.     

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     

Dielectric properties of multiwalled carbon nanotube/clay/polyvinylidene fluoride nanocomposites: Effect of clay incorporation

This study investigates the effect of clay addition on the broadband dielectric properties of multi‐walled carbon nanotube/polyvinylidene fluoride (MWCNT/PVDF) composites, that is, frequency range of 10¹−10⁶ Hz. Different loadings of MWCNT and clay were used for the preparation of three‐phase (MWCNT/Clay/PVDF) nanocomposites via melt‐mixing method. The crystalline structure and morphology of nanocomposites were examined by employing characterization techniques such as X‐ray diffraction, transmission electron microscopy, and differential scanning calorimetry. The dielectric spectroscopy showed that introducing clay into the MWCNT/PVDF nanocomposites at a critical MWCNT concentration improved dielectric properties tremendously. It was interestingly observed that the incorporation of a specific amount of clay, that is, 1.0 wt%, into the (MWCNT/PVDF) nanocomposite at a critical MWCNT loading, that is, 0.5 wt% MWCNT, resulted in a huge increase in the dielectric permittivity (670% at 100 Hz) and a considerable reduction in the dissipation factor (68% at 100 Hz). POLYM. COMPOS., 161–167, 2016. © 2014 Society of Plastics Engineers     

Synthesis and Characterization of Lead-Free Ferroelectric 0.5[Ba(Zr0.2Ti0.8)O3]–0.5[(Ba0.7Ca0.3)TiO3]—Polyvinylidene Difluoride 0–3 Composites

0.5[Ba(Zr_0.2Ti_0.8)O₃]–0.5[(Ba_0.7Ca_0.3)TiO₃]/[BZT–BCT]–polyvinylidene difluoride/[PVDF] 0–3 composites were prepared by uniaxial hot-press method for different volume fractions of BZT–BCT ceramic powder in a PVDF polymer matrix. The structural, microstructural and dielectric properties were investigated and discussed. There was an increase in relative permittivity (ε_r) and dielectric loss (tan δ) of the composites with increase in the volume fraction of the ceramics. At room temperature and at 1 kHz frequency, 0.25[BZT–BCT]–0.75[PVDF] composite showed a highest relative permittivity (ε_r) ~41.     

Nickel‐multiwalled carbon nanotubes/polyvinylidene fluoride composites with high dielectric permittivity

Composites with nickel particles coated multiwalled carbon nanotubes (Ni‐MWNTs) embedded into polyvinylidene fluoride (PVDF) were prepared by solution blending and hot‐press processing. The morphology, structure, crystallization behavior, and dielectric properties of composites were studied. The results showed that the crystallization of PVDF was affected by Ni‐MWNTs. With the increment of Ni‐MWNTs, the content of β‐phase in PVDF increased. The dielectric permittivity was as high as 290 at 10³ Hz when the weight fraction of Ni‐MWNTs was 10%. The results can be explained by the space charge polarization at the interfaces between the insulator and the conductor, and the formation of microcapacitance structure. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3746–3752, 2013     

Polytetrafluorethylene-based high-k composites with low dielectric loss filled with priderite (K1.46Ti7.2Fe0.8O16)

Composite materials with a high permittivity (high-k) and low dielectric loss represent an important research direction for the rapid development of modern electronic. This article is about high-k composite with low dielectric loss (dielectric constant is approximately 11, and dielectric loss is only 0.02 at 1 MHz and about 50 wt % of filler) based on a polytetrafluorethylene (PTFE) compounded with priderite (K_1.46Ti_7.2Fe_0.8O₁₆). The dielectric permittivity about ε' ≈ 10³ and the dielectric loss of tgδ ≈ 2 have been found for filler content about 50 wt % (30 vol %) and, respectively, ε' ≈ 11 and tgδ ≈ 0.02 for 1 MHz. To produce filler, amorphous potassium polytitanate was synthesized by molten salt method, modified in aqueous solution of iron sulfate, crystallized at 700 °C and further treated in the aqueous dispersion of PTFE. The obtained product was pressured, dried and investigated by X-ray diffraction and scanning electron microscopy. Dielectric properties of the composite with different ceramic filler content (1–90 wt %) were studied using impedance spectroscopy in the frequency range of 10⁻² to 10⁶ Hz. The influence of frequency on electric conductivity, permittivity, and dielectric losses was analyzed taking into account the experimental data on porosity, apparent density obtained for the composites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48762.     

New potassium sodium niobate/poly(vinylidene fluoride) functional composite films with high dielectric permittivity

New and homogeneous KNN/PVDF functional hybrid films loaded with 2 vol.%, 4 vol.%, 9 vol.%, 21 vol.%, 30 vol.%, and 40 vol.% Na_0.5K_0.5NbO₃ (KNN) have been prepared by a solution casting process. The effects of the doping KNN particles on the structure, morphology, and dielectric properties of KNN/PVDF hybrid films were investigated. The introduction of KNN fillers has a remarkable influence on the α-, β-, γ-phase structure and the crystallinity of the polymer matrix. And it is also effective in improving the dielectric performance. A dielectric permittivity as high as 250 is obtained at 10 Hz when the concentration of the KNN filler reaches 30 vol.%, which is 28 times higher than that of the pure PVDF matrix. The conductivity of the hybrid film with 40 vol.% KNN concentrations is lower than 8 × 10^?10 (S cm^?1) at 10² Hz and at room temperature, which shows its excellent insulativity and the potential to be applied into the electronic industry.     

Improved dielectric properties of poly(vinylidene fluoride)–BaTiO3 composites by solvent-free processing

Composites of poly(vinylidene fluoride) (PVDF) and BaTiO₃ nanoparticles (average diameter ca. 125 nm) are fabricated by a solvent-free and industrially scalable technique, that is, melt blending, followed by compression molding. The effect of processing parameters on the spectroscopic, microstructural, thermal, mechanical and dielectric properties are evaluated as a function of composition (loading up to 30 vol%). The presence of nanoparticle inclusions as well as specific compression molding parameters demonstrate both to affect the molecular relaxations of the PVDF matrix, studied by correlating the results of different techniques, and to induce the PVDF crystallization as β phase. Processing parameters also play a key role for optimizing the dielectric properties. An improved dielectric behavior of the composites is obtained in terms of both permittivity, whose value increases up to four times that of neat PVDF, and dielectric losses, lower than 5% between 10 and 3·10⁴ Hz. The obtained performances resulted enhanced compared to analogous composites prepared with the use of solvents.     

Dielectric properties of PMMA/KCTO(H) composites for electronics components

Polymethyl methacrylate/hollandite-like copper doped potassium titanate high-k ceramics composites with different filler content (20–60 vol.%) are prepared by simple method of mixing of the polymer solution and ceramics dispersion followed evaporation of the solvent and hot pressing. The particle morphology and size are estimated by SEM. The composites obtained are studied by XRD, FTIR, and TGA methods. The influence of the additive and the concentration of hollandite-like copper doped potassium titanate high-k ceramics on dielectric properties (permittivity, conductivity, dielectric loss tangent) are investigated at frequency range from 10⁻¹ to 10⁶ Hz. It is shown that the increasing of ceramics concentration cause the increasing of main dielectric characteristics, namely permittivity up to 40 and dielectric loss up to 0.13 at 60 vol.% of filler and 0.1 Hz. Conductivity percolation threshold for PMMA/KCTO(H) composites was estimated (v_c = 0.0773 vol. [20.9 wt. %]). Experimental data on permittivity are compared with different theoretical models (Lichtenecker's model and the Effective Medium Theory model).     

Exceptional dielectric properties of chlorine-doped graphene oxide/poly (vinylidene fluoride) nanocomposites

Herein, we report a facile method to significantly enhance the dielectric performance of reduced graphene oxide-based polymer composites. Addition of thionyl chloride into graphene oxide (GO) dispersion induces synergistic modifications of the structure, chemistry, charge carrier density and electrical conductivity of GO, as well as the interfacial interaction and phase of the surrounding matrix in the poly (vinylidene fluoride) (PVDF) composite. The composites reinforced with a very low reduced chlorinated GO (Cl-rGO) content of 0.2 vol% deliver an exceptional dielectric constant of 364 with a moderate dielectric loss of 0.077 at 1 kHz. These values are well contrasted with the corresponding properties of the neat PVDF polymer with a constant of 28 and a loss of 0.0029. Synergistic effects arising from chlorination are identified, including the much enhanced electrical conductivity of Cl-GO sheets by more than 3 orders of magnitude through introducing charge-transfer complexes, the improved interfacial interactions between the fillers and the PVDF matrix through hydrogen bonds, and the transformation of PVDF to β-phase with an inherently high dielectric constant due to dipolar interaction. The comparison with the literature data confirms superior dielectric performance of the present Cl-rGO/PVDF composites.     

MWCNTs-TiO<Subscript>2</Subscript> core-shell nanoassemblies for fabrication of poly(vinylidene fluoride) based composites with high breakdown strength and discharged energy density

Dielectric polymer composites with high breakdown strength and discharged energy density have potential applications in modern electric power systems. In this study, composites comprising MWCNTs-TiO₂ core-shell nanoparticles and poly(vinylidene fluoride) (PVDF) were fabricated by a solution casting method, followed by a melting and quenching process. The obtained composites are γ-phase PVDF dominated and present a dense structure. By the incorporation of MWCNTs-TiO₂ core-shell nanoparticles, the dielectric constant of composites can be significantly enhanced while the dielectric loss of composites remains low. Because of the core-shell structure of well-dispersed MWCNTs-TiO₂ and their strong interactions with matrix, high breakdown strength above 175 V/μm can be achieved in the composites. Additionally, the composites exhibit enhanced discharged energy density, which can be as high as 6.4 J/cm³ at 250 V/μm, while the maximum discharged energy density obtained in pure PVDF is only 2.6 J/cm³ (270 V/μm).