PVDF-based Composites Research Articles

The high energy density and efficiency of PVDF-based composites with double-shell Nd-BaTiO3 particles as fillers

Flexible dielectric capacitors are becoming shining stars in modern electronic devices. Ceramic particles with large dielectric constants and benign compatibility are attractive candidates to enhance the energy storage density of pristine polymer capacitors while guaranteeing their flexibility. In this work, double-shell structure of Al2O3 (AO) and dopamine (PDA) were successively coated on the Nd-doped BaTiO3 (NBT) particles and then introduced into the Poly(vinylidene fluoride) (PVDF) matrix. Obvious enhancement in dielectric constants was observed while the dielectric loss remained nearly constant. For the composite films with 1–4[Formula: see text]vol.% NBT@AO@PDA NPs, the maximum energy density of 9.1[Formula: see text]J/cm3 and energy efficiency of 65% was achieved at 430[Formula: see text]MV/m in the sample with 1[Formula: see text]vol.% filling ratio, which are 1.4 and 1.3 times larger than those of pristine PVDF at 450[Formula: see text]MV/m. The finite element simulation reveals the effective relief of the electric field concentration in the composite film induced by the AO and PDA layers. The greater improvement in the energy storage performance could be anticipated if the dispersity of NBT@AO@PDA NPs was further improved.

Two-dimensional sheet-like K0.5Na0.5NbO3 platelets and sandwich structure induced ultrahigh discharge efficiency in poly(vinylidenefluoride)-based composites

Polyvinylidene fluoride (PVDF) -based composites have received great attention in high-energy-density capacitors due to their high breakdown strength and ease of processing. In this work, sandwich structure K0.5Na0.5NbO3(KNN)/PVDF composite films with a middle of PVDF layer containing 2D sheet-like KNN platelets were prepared by a simple layer-by-layer casting process. Experimental results indicate that the reasonably distributed 2D sheet-like KNN platelets and sandwich structured are very effective for reducing the conductivity and dielectric loss of the composite film, manifested by a significant improvement of discharge efficiency (η = 80.2%), which is the highest η value reported so far. In addition, the finite element simulation results confirm that the synergy between the 2D sheet-like KNN platelets and the sandwich structure can effectively hinder the development of electric tree. The high breakdown strength of the composite film and high dielectric constant of KNN platelets result in high discharge energy density of 14.5 J cm−3. This work provides a new reference for PVDF-based polymer composites with excellent comprehensive energy storage performance for capacitive energy storage applications.

Graphitic-carbon nitride nanosheets as a new inorganic filler for improving energy storage density of PVDF-based dielectric composites

Graphitic-phase carbon nitride (g-C3N4) nanosheets with lateral size of 1000 nm, 500 nm, and 100 nm have been fabricated by a one-step thermal condensation method at different thermal treating temperatures and used as filler for poly(vinylidene fluoride) (PVDF)-based dielectric composites. The effects of its size and content on energy storage density of g-C3N4/PVDF composites are discussed. The experimental results show that the energy storage density of the composites containing 3 wt% g-C3N4 increases with the decrease of lateral size and could reach to 11.7 J cm−3 at 522 kV mm−1, much higher than pure PVDF of 5.8 J cm−3 at 386 kV mm−1. A finite element simulation is employed to describe electric field distribution within the composites and reveal further the role of g-C3N4 nanosheets on the energy storage behavior of the composites. This work provides a new inorganic filler for high energy storage density PVDF-based dielectric composites.

Multilayer Structured Poly(vinylidene fluoride)-Based Composite Film with Ultrahigh Breakdown Strength and Discharged Energy Density.

Poly(vinylidene fluoride)-based (PVDF) composites with high discharged energy density (Ue) have been considered as advanced dielectric materials for pulsed power systems and electrical weapon systems. However, further improvement of the Ue of PVDF-based composites with higher breakdown strength (Eb) is of utmost importance. Based on the principle of voltage distribution in the multilayer structure, the multilayer structure (five-layer structure) ceramic/polymer composite films consisting of pristine PVDF layers with high breakdown strength and PVDF layers doped with one-dimensional 0.15SrTiO3-0.85Na0.5Bi0.5TiO3 (1D SNBT) fibers where the two kinds of layers stacked alternately has been designed and fabricated. Accordingly, a series of analyses of the dielectric properties and energy storage performances are presented, and the related results are tentatively explained by finite element simulation. The energy storage characteristics of the composite films are greatly improved due to the newly designed structure. An excellent Ue of 20.82 J cm-3 is achieved at an ultrahigh electric field of 640 MV m-1 with the PVDF layers containing 6 vol % SNBT fibers. Therefore, this work provides a new strategy to design and fabricate advanced polymer-based energy storage materials.

Achieving thermally conductive low loss PVDF-based dielectric composites via surface functionalization and orientation of SiC nanowires

Achieving thermally conductive low loss PVDF-based dielectric composites via surface functionalization and orientation of SiC nanowires

Journey of Electroactive β-Polymorph of Poly(vinylidenefluoride) from Crystal Growth to Design to Applications

Electroactive polymers are ideal candidates for dielectric and piezoelectric applications due to their very high breakdown strength, good flexibility, and ease of processing. Among the various polymers, poly(vinylidenefluoride) (PVDF) is of special interest due to potential applications in sensors, capacitors, actuators, etc. PVDF exists in four different crystalline phases (α-, β-, γ-, and δ-phases). Among these, the electroactive β-phase is very important for dielectric and piezoelectric applications. In the recent past, research has been focused on obtaining the maximum amount of electroactive β-polymorph in PVDF. The piezoelectric and dielectric properties of PVDF are influenced by the amount and the possible orientation of the polar β-phase. However, the effect of orientation on the electroactive β-phase in the field direction toward improving dielectric and piezoelectric applications is still not clear. This review attempts to bring in mechanistic insights into various processes that induce the electroactive β-phase, orientation, and correlation with dielectric and piezoelectric properties in PVDF-based composites. Some of the challenges and possible solutions for the future fabrication of piezoelectric materials are also emphasized.

Effect of BaTiO3 nanowire distribution on the dielectric and energy storage performance of double-layer PVDF-based composites

A series of novel double-layer PVDF-based composites filled with different concentration of BaTiO3 nanowire were fabricated employing hot-pressing process. The effects of various BT-NWs concentrations in isolated layers on the dielectric properties, energy storage density of the composites were investigated. The experimental dielectric constants of double-layer composites are lower than expected. The breakdown strength (Eb) of double-layer composites was obtained in the experiment, and predicted via capacitance series formula (CSF) and finite element analysis (FEA). Results show that the data predicted by FEA are closer to the experimental values. Compared with dielectric constant, the enhancement of Eb induced by double-layer structure is more significant for the energy storage performance of composites. A design route including Eb measurement of single-layer composites, Eb prediction of double-layer composites via FEA, selection of single-layer material and composites fabrication is proposed to prepare the multi-layer composites with excellent dielectric properties and energy storage.

Fabrication and Characterization of a Flexible PVDF Fiber-based Polymer Composite for High-performance Energy Harvesting Devices

A flexible polyvinylidene fluoride (PVDF)/polydimethylsiloxane (PDMS) composite prototype with high piezoelectricity and force sensitivity was constructed, and its huge potential for applications such as biomechanical energy harvesting, self-powered health monitoring system, and pressure sensors was proved. The crystallization, piezoelectric, and electrical properties of the composites were characterized using an X-ray diffraction (XRD) experiment and customized experimental setups. The composite can sustain up to 100% strain, which is a huge improvement over monolithic PVDF fibers and other PVDF-based composites in the literature. The Young’s modulus is 1.64 MPa, which is closely matched with the flexibility of the human skin, and shows the possibility for integrating PVDF/PDMS composites into wearable devices and implantable medical devices. The 300 μm thick composite has a 14% volume fraction of PVDF fibers and produces high piezoelectricity with piezoelectric charge constants d31 = 19 pC/N and d33 = 34 pC/N, and piezoelectric voltage constants g31 = 33.9 mV/N and g33 = 61.2 mV/N. Under a 10 Hz actuation, the output voltage was measured at 190 mVpp, which is the largest output signal generated from a PVDF fiber-based prototype.

PVDF-based composites filled with PZT@Ag core-shell structured particles for enhanced dielectric properties

Polymer-based composites with high dielectric constant and suppressed dielectric loss were successfully fabricated by using PZT@Ag core-shell structured particles as fillers and PVDF as polymer matrix. The PZT@Ag core-shell structured particles were synthesized via conventional solid-state method. The results indicate that the fillers dispersed in the polymer matrix prominently enhance the dielectric constant while keeping the dielectric loss unchanged simultaneously. Composites with high dielectric constant result from the high dielectric constant of PZT itself, the superior interfacial polarization of PZT@Ag core-shell structure and the conductivity of Ag according to percolation theory, while the dielectric loss is suppressed due to the tunneling current decreasing among Ag particles and Coulomb blockade effect.

Core-shell structured PVDF@BT nanoparticles for dielectric materials: A novel composite to prove the dependence of dielectric properties on ferroelectric shell

The design of core-shell structure is considered as a facile approach to obtain polymer composites with excellent dielectric properties and high breakdown strength (Eb). In this work, thiol-terminated poly(vinylidene fluoride) (PVDF-SH) and polystyrene (PS-SH) are synthesized by a two-step process. The as-prepared polymers are applied to modify BaTiO3 (BT) nanoparticles. The subsequent morphologies, dielectric properties, and Eb of PVDF-based composites are investigated systematically. PVDF encapsulated BT (PVDF@BT) fillers carries more desirable compatibility with matrix compared with PS encapsulated BT (PS@BT) and raw BT. For instance, the Eb of the 30 vol% PVDF@BT composites slightly decreased from 150.6 to 117 kV/mm for PVDF matrix, as compared to the raw and PS@BT composites, for those the values intensively reduced to 58.5 kV/mm and 107 kV/mm, respectively. It is also observed that PVDF polymer shells play a significant role in the improvement of composites dielectric constant (εr). Moreover, the design of the polymer shell also contributes to the suppression of dielectric loss. The results are of great importance for understanding the effect of polymer shells and fluorinated filler on composite properties. This study provides a strategy for preparing composites with high εr while maintaining high Eb for the next generation of dielectric capacitors.

High tribology performance of Poly(vinylidene fluoride) composites based on three-dimensional mesoporous magnesium oxide nanosheets

Three-dimensional mesoporous MgO nanosheets (MgO_NS) were synthesized by a facile non-hydrothermal method for the improvement of the tribological properties of poly(vinylidene fluoride) (PVDF) composites. The interactions and structural properties of the MgO_NS composites were systematically compared with those of commercially available MgO beads (MgO_B). It was found that the incorporation of MgO_NS decreased the polar β phase of the PVDF crystallinity owing to an intimate contact and good interactions between the mesoporous MgO_NS filler and PVDF matrix. Recipro-mode tribology tester results for a long measurement time of 3 h showed that the friction coefficients of the PVDF composites decreased with the increasing filler content for both MgO_B and MgO_NS, indicating an important role of MgO as a self-lubricating material. In particular, the PVDF/MgO_NS 5.0% composite exhibited an outstanding initial friction coefficient of 0.091 and specific wear rate of 1.8 × 10−5 mm3/N m as compared with MgO_B, this performance being among the best for PVDF-based composites. The results indicated that mesoporous MgO_NS composites with their small crystal size, large surface area, good dispersion, and intimate contact with the PVDF matrix were more effective than randomly organized MgO_B.

Polyhedral oligomeric silsesquioxane functionalized carbon nanotubes for high thermal conductive poly(vinylidene fluoride) composite membrane

To achieve high thermal conductivity of polymer-based composites at low filler loading is still a challenge because of the insufficient contact area and incomplete thermal percolation pathway. In this work, PVDF composite membrane with high thermal conductivity is fabricated using polyhedral oligomeric silsesquioxane (POSS) functionalized carbon nanotubes (CNTs) as fillers. Surface modification promotes the uniform dispersion of CNT-POSS in PVDF matrix and enlarges the contact area. Through the thermal analysis of the CNT-COOH/PVDF and CNT-POSS/PVDF composites, the results indicate that the nucleation effect of CNTs increases the crystallinity of the pure PVDF from 42.9% to 51.2%. In addition, the addition of POSS nanoparticles to the CNT-PVDF composites significantly improves its thermal stability, mechanical and thermal conductivity properties. The CNT-POSS/PVDF composite membrane with 15 wt% CNT-POSS presents an extremely high thermal conductivity of 1.12 W/m·K (vs. 0.15 W/m·K for pure PVDF) and exhibits great superiority in comparison with the thermally conductive PVDF-based composites reported before.

High Energy Density Dielectrics Based on PVDF‐Based Polymers

AbstractMany applications, such as hybrid vehicles, pulsed power generators, and power factor correction, require capacitors with high energy density to reduce the size or weight of the related systems. For these applications, dielectric film capacitors are often used because of their fast discharge speed and high power density. The energy density of commercial available film capacitors is relatively low and cannot meet the demands for those applications. In the past decade, different polymer‐based dielectric materials have been intensively investigated to improve the energy density of the materials. Here, the progress in developing high energy density polymer‐based dielectric materials is reviewed, and strategies to improve the energy density of dielectric polymers are summarized and discussed. Because polyvinylidene fluoride (PVDF)‐based polymers have relatively high dielectric properties and have been intensively studied for the energy storage applications, the discussion focuses mainly on PVDF‐based polymers and composites. An outlook for the future directions and problems that will be tackled to further improve the energy density of dielectrics is also provided.

Microstructure and dielectric properties of BZT-BCT/PVDF nanocomposites

In this paper, the 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 nanofibers (BZT-BCT NFs) with high aspect ratio were synthesized by electrospinning technique, and the PVDF-based composites filled with the BT NPs or BZT-BCT NFs were fabricated. Obviously, compared to the BT NPs/PVDF composite, the dielectric properties of BZT-BCT NFs/PVDF composites are improved at given volume fraction. The electric modulus formalism indicated that the BZT-BCT NFs could effectively enhance the interfacial polarization of the BZT-BCT NFs/PVDF composites than that of the BT NPs/PVDF composite. In addition, the BZT-BCT NFs with large aspect ratio can make the composites polarize at a higher field strength, thus the composites obtain higher polarization strength. The energy density of 3 vol% BZT-BCT NFs/PVDF composite is 3.08 J/cm3 at 240 kV/mm, which is 2.01 times higher enhancement than the BT NPs/PVDF composite (1.53 J/cm3 at 180 kV/mm). These results also provide a simple but effective method to achieve the materials with high capacitance for energy storage.

Dielectric and energy storage performances of PVDF-based composites with colossal permittivitied Nd-doped BaTiO3 nanoparticles as the filler

The energy storage density of pure polymers is usually limited by their low intrinsic dielectric constants (εeff). Integrating polymer matrix with ceramic particles with high εeff values has been one powerful approach to enhance the εeff values of polymer composites and thus their energy storage density. In this study, we report a flexible polymer-based composite by introducing Nd-doped BaTiO3 (NBT) nanoparticles (εeff over 3×105) into the poly(vinylidene fluoride) (PVDF). The phase of PVDF and its dielectric behavior could be adjusted by varying the NBT loadings. Composites including less than 5 vol.% NBT loading exhibited enhanced dielectric constants and maintained high breakdown strength. With a quenching process, the composite delivers a discharged energy density up to 7.91 J/cm3 at an electric field of 350 kV/mm with 2.5 vol.% NBT loading, which is 140% more than that of pure PVDF at the same electric field.

Synergism between carbon materials and Ni chains in flexible poly(vinylidene fluoride) composite films with high heat dissipation to improve electromagnetic shielding properties

We prepared poly(vinylidene fluoride) (PVDF)/carbon/Ni-chain composites by dispersing Ni chains, and either carbon nanotubes (CNTs) or graphene nanoplatelets (GNPs) into a PVDF solution. The electrical conductivity and the electromagnetic interference (EMI) shielding properties of the PVDF/CNT/Ni-chain and the PVDF/GNP/Ni-chain composites were increased by increasing the Ni-chain filler content. The electrical conductivity of the PVDF/CNT/10 wt%Ni-chain composite was lower than the PVDF/CNT/6 wt%Ni-chain composite. We attributed this abnormality to the Ni chains having blocked the CNT connections, when there was a high Ni-chain content. Furthermore, the PVDF-based composites' EMI shielding properties were effectively tuned by controlling the films' thicknesses. The total shielding of the PVDF/CNT/6 wt%Ni-chain and the PVDF/GNP/8 wt%Ni-chain composite films increased from 23.6 to 57.3 dB and from 22.7 to 55.8 dB, as their thicknesses were increased from 0.3 mm to 0.6 mm, respectively. The synergetic relationship between the Ni chains and the carbon materials (CNT or GNP), meant that the main EMI shielding mechanisms of the PVDF/carbon/Ni-chain composites had resulted from the absorption process. Moreover, these composites possessed high thermal conductivity, which can convert microwave energy into Joule heating systems. Thus, these PVDF-based composite films can be used to make high-efficiency EMI shielding devices that can rapidly dissipate heat.

Improvement of Dielectric Performance and Temperature-Dependent Behavior of Polyvinylidene Fluoride Composite with KTa0.5Nb0.5O3@Ag Nanoparticles

The effects of KTN and KTN@Ag nanoparticles on dielectric behavior and temperature-dependent dielectric mechanisms of PVDF-based composites were studied. It was found that relatively high dielectric permittivity, low loss tangent, and outstanding dielectric stability were simultaneously achieved in the Nano-KTN@Ag/PVDF hybrid films. In this study, we found that the effect of interfacial polarization on the permittivity of Nano-KTN@Ag/PVDF hybrid film becomes more and more significant with the increase of temperature. The calculated conductivity activation energy (EA) proved that the migration of charge carriers requires more energy to overcome the potential barrier in the Nano-KTN@Ag/PVDF hybrid films than that in the Nano-KTN/PVDF hybrid films. A complete and systematic study of the dielectric mechanism is necessary, which can be a significant guide to the preparation of dielectric materials applied in the electronics industry.

Greatly enhanced dielectric permittivity in poly(vinylidene fluoride)-based polymeric composites induced by Na1/3Ca1/3Bi1/3Cu3Ti4O12 nanoparticles

Greatly enhanced dielectric permittivity (e′) in poly(vinylidene fluoride) (PVDF) polymeric composites was induced by incorporating Na1/3Ca1/3Bi1/3Cu3Ti4O12 (NCB) nanoparticles. The NCB/PVDF composites were fabricated by conventional mixed powders and hot pressing. Nanosized (NCB-NPs) and microsized-powders (NCB-MPs) prepared, respectively, by chemical combustion and solid state reaction methods were used as fillers. The dispersion of NCB-NPs was quite good in the PVDF matric. A greatly improved e′ of PVDF-based polymeric composites can be induced by filling with NCB-NPs compared to that of the NCB-MPs/PVDF composite. Interestingly, at 103 Hz, the nanocomposite with 50 vol% of NCB-NPs can exhibit good dielectric properties with high e′ of about 210.8 and low loss tangent (tanδ ≈ 0.83). This enhanced e′ value is much larger than that of PVDF polymer by a factor of ≈20. The increase in e′ in the nanocomposites is attributed to large interfacial areas and very short interparticle distance. These can cause a great increase in the interfacial polarization intensity.

Excellent dielectric properties of PVDF-based composites filled with carbonized PAN/PEG copolymer fibers

Weak interfacial bonding between carbon materials and polymer matrix impedes the formation of homogeneous composites, challenging to the enhancement of dielectric properties of such systems. In this work, we designed novel carbonized polyacrylonitrile/polyethylene glycol copolymer fibers (CPCFs) and then used them as fillers to enhance the dielectric properties of poly(vinylidene fluoride) (PVDF)-based composites. These CPCFs are rich in nitrogen (8.55%) and oxygen (3.94%) atoms on the surface of them. The results of molecular dynamic (MD) simulations indicate that the existence of these atoms significantly increase the interaction energy between CPCFs and PVDF matrix from −45.13kcal/mol to −62.22kcal/mol, which promotes the intercalation of conductive CPCFs into insulated PVDF matrix to form ultrathin microcapacitors. As a result, the largest dielectric constant of CPCFs/PVDF composites can reach 1583 (1kHz), which is about 150times higher than that of pure PVDF.

Enhanced dielectric performance of polyvinylidene fluoride composites with an all-carbon hybrid architecture: vertically aligned carbon nanotube arrays on graphite nanoplatelets

The dielectric properties of PVDF-based percolative composites can be strongly improved by loading novel conductive units with a well-designed micro-architecture.