Preparation of efficient piezoelectric PVDF–HFP/Ni composite films by high electric field poling

Poly(vinylidene fluoride) (PVDF) and its copolymers have been widely studied due to their excellent piezoelectricity and ferroelectricity. In this study, composite films are prepared by adding Ni nanoparticles (0.00–0.3 wt%) into poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF–HFP) matrix by solution casting, uniaxial stretching, and high electric field poling. It is found that when the maximum electric field E max for poling is 130 MV m−1, the calibrated open circuit voltage of the pure PVDF–HFP films reaches 3.12 V, which is much higher than those poled by a lower electric field (70 MV m−1: 1.40 V; 90 MV m−1: 2.29 V). This result shows that the effect of poling on the generated output voltage is decisive. By adding 0.1 wt% Ni nanoparticles, it increases to 3.84 V, 23% higher than that of the pure PVDF–HFP films. To further understand the enhancement mechanism, the effects of Ni nanoparticles on initial crystallization, uniaxial stretching, and high electric field poling are investigated by X-ray diffraction, scanning electron microscope, Fourier transform infrared spectroscopy, and differential scanning calorimetry.

Excellent hydrophilicity of polyurethane modified polyvinylidene fluoride

Polyvinylidene fluoride (PVDF) is a promising membrane material in ultrafiltration (UF) applications; its extensive application however is limited due to the disadvantage in hydrophilicity and low surface energy. Herein, a sort of TPU-modified PVDF membrane is prepared by blending method and its hydrophilicity is compared with a series of pure/modified PVDF membranes. The contact angle and pure water flux (PWF) results demonstrate that the hydrophilicity of the TPU-modified PVDF membrane is enhanced, and the performance is not inferior to that of traditional pore-modified PVDF membranes. SEM image shows that the TPU-modified PVDF membrane maintains morphology of the pure PVDF membrane, indicating that TPU molecules have excellent compatibility with PVDF molecules and can maintain the mechanical property of PVDF membrane to a certain extent. Finally, we explore the effects of TPU molecules and PVDF molecules on water molecules, respectively, from a microscopic perspective involving first principles. This investigation not only establishes that PVDF membrane has been prepared with enhanced hydrophilicity, but also provides a novel avenue for the modification of membrane properties.

The Effect of CoFe2O4, CuFe2O4 and Cu/CoFe2O4 Nanoparticles on the Optical Properties and Piezoelectric Response of the PVDF Polymer.

Cobalt ferrite, Copper ferrite and cobalt doped copper ferrite nanoparticles have been synthesized and characterized using different characterization methods (XRD, FTIR and FESEM). The prepared nanoparticles have been used as promising fillers of the polyvinylidene fluoride (PVDF) polymer. The PVDF/(Cu-CoFe2O4, CoFe2O4, and CuFe2O4) nanocomposites films have been prepared via a simple solution casting technique. The optical properties and the piezoelectric response of the prepared nanocomposite films have been studied. The study showed that Cu-CoFe2O4, CoFe2O4, and CuFe2O4 have enhanced the interfacial polarization density and dielectric constant. The optical conductivity value of PVDF/ (Cu-CoFe2O4 and CoFe2O4) increased five times compared with the pure PVDF. Also, an increase in the piezoelectric response has been recorded by adding the nano-fillers to the pure PVDF.

Modification of the Surface Morphology and Properties of Graphene Oxide and Multi-Walled Carbon Nanotube-Based Polyvinylidene Fluoride Membranes According to Changes in Non-Solvent Temperature

The effect of changes in non-solvent coagulation bath temperature on surface properties such as morphology and hydrophilicity were investigated in multi-walled carbon nanotubes (MWCNTs) and graphene oxide (GO)-based polyvinylidene fluoride (PVDF) membranes. The properties of pores (size, shape, and number) as well as membrane hydrophilicity were investigated using field emission scanning electron microscopy, Raman spectroscopy, optical microscopy, water contact angle, and water flux. Results showed that the pore size increased with an increase in coagulation temperature. The hydrophilic functional groups of the added carbon materials increased the solvent and non-solvent diffusion rate, which significantly increased the number of pores by 700% as compared to pure PVDF. Additionally, these functional groups changed the hydrophobic properties of pure PVDF into hydrophilic properties.

Construction of a Three-Dimensional BaTiO3 Network for Enhanced Permittivity and Energy Storage of PVDF Composites

Three-dimensional BaTiO3 (3D BT)/polyvinylidene fluoride (PVDF) composite dielectrics were fabricated by inversely introducing PVDF solution into a continuous 3D BT network, which was simply constructed via the sol-gel method using a cleanroom wiper as a template. The effect of the 3D BT microstructure and content on the dielectric and energy storage properties of the composites were explored. The results showed that 3D BT with a well-connected continuous network and moderate grain sizes could be easily obtained by calcining a barium source containing a wiper template at 1100 °C for 3 h. The as-fabricated 3D BT/PVDF composites with 21.1 wt% content of 3D BT (3DBT–2) exhibited the best comprehensive dielectric and energy storage performances. An enhanced dielectric constant of 25.3 at 100 Hz, which was 2.8 times higher than that of pure PVDF and 1.4 times superior to the conventional nano–BT/PVDF 25 wt% system, was achieved in addition with a low dielectric loss of 0.057 and a moderate dielectric breakdown strength of 73.8 kV·mm−1. In addition, the composite of 3DBT–2 exhibited the highest discharge energy density of 1.6 × 10−3 J·cm−3 under 3 kV·mm−1, which was nearly 4.5 times higher than that of neat PVDF.

Significantly Enhanced Dielectric Properties of Ag-Deposited (In1/2Nb1/2)0.1Ti0.9O2/PVDF Polymer Composites

The enhanced dielectric permittivity (ε′) while retaining a low loss tangent (tanδ) in silver nanoparticle−(In1/2Nb1/2)0.1Ti0.9O2/poly(vinylidene fluoride) (Ag-INTO/PVDF) composites with different volume fractions of a filler (fAg-INTO) was investigated. The hybrid particles were fabricated by coating Ag nanoparticles onto the surface of INTO particles, as confirmed by X-ray diffraction. The ε′ of the Ag−INTO/PVDF composites could be significantly enhanced to ~86 at 1 kHz with a low tanδ of ~0.044. The enhanced ε′ value was approximately >8-fold higher than that of the pure PVDF polymer for the composite with fAg-INTO = 0.5. Furthermore, ε′ was nearly independent of frequency in the range of 102–106 Hz. Therefore, filling Ag−INTO hybrid particles into a PVDF matrix is an effective way to increase ε′ while retaining a low tanδ of polymer composites. The effective medium percolation theory model can be used to fit the experimental ε′ values with various fAg-INTO values. The greatly increased ε′ primarily originated from interfacial polarization at the conducting Ag nanoparticle–PVDF and Ag–INTO interfaces, and it was partially contributed by the high ε′ of INTO particles. A low tanδ was obtained because the formation of the conducting network in the polymer was inhibited by preventing the direct contact of Ag nanoparticles.

Novel Core-Shell Structured Ironbark-Like TiO2 as Fillers for Excellent Discharged Energy Density of Nanocomposites

The perpendicular orientation of nanowires to electric fields would greatly improve the breakdown strengths (Eb) of polymer-based nanocomposites, however, the relatively small polarization at small filler fraction, and thus the unsatisfactory discharged energy density (Ud), greatly restrict their further application. In this study, x vol.% TO@TO/PVDF nanocomposites with superior energy storage performances have been fabricated, where the ironbark-like TiO2 fillers (TO@TO) with core-shell structures lead to greatly enhanced polarization and Eb simultaneously. The former is due to the coupling effects of the increased interfacial polarization, the latter is due to the enhanced path tortuosity of electric tree growing at small TO@TO fraction. Strikingly, an excellent Ud of 13.1 J/cm3 was achieved in the 1.5 vol % TO@TO/PVDF nanocomposite at 383 MV/m, which is greatly increased by 220% compared with that of pure PVDF (5.98 J/cm3). The primary results might provide a strategy to design and fabricate nanocomposites with satisfactory energy storage performances as well as the flexible and easy-processing ability at small filler fraction.

Understanding the Percolation Effect in Triboelectric Nanogenerator with Conductive Intermediate Layer

Introducing the conductive intermediate layer into a triboelectric nanogenerator (TENG) has been proved as an efficient way to enhance the surface charge density that is attributed to the enhancement of the dielectric permittivity. However, far too little attention has been paid to the companion percolation, another key element to affect the output. Here, the TENG with MXene-embedded polyvinylidene fluoride (PVDF) composite film is fabricated, and the dependence of the output capability on the MXene loading is investigated experimentally and theoretically. Specifically, the surface charge density mainly depends on the dielectric permittivity at lower MXene loadings, and in contrast, the percolation becomes the degrading factor with the further increase of the conductive loadings. At the balance between the dielectric and percolation properties, the surface charge density of the MXene-modified TENG obtained 350% enhancement compared to that with the pure PVDF. This work shed new light on understanding the dielectric and percolation effect in TENG, which renders a universal strategy for the high-performance triboelectronics.

Isothermal and Non-Isothermal Crystallization Kinetics of PVDF and PVDF/PMMA Blends

Background: poly(vinylidene fluoride) PVDF and PVDF/PMMA blends have been investigated with a focus on the crystal structure, immiscibility and mechanical properties. However, few reports were found on the crystallization behaviors of PVDF and PVDF/PMMA blends, especially on crystallization kinetics. The article is to report the research on isothermal and nonisothermal crystallization kinetics for PVDF and PVDF/PMMA blends using differential scanning calorimetry (DSC). Results: Besides crystallization temperature and isothermal crystallization activation energy, the Avrami equation exponent of PVDF in blends decreased compared with pure PVDF. The nonisothermal crystallization kinetics of PVDF and PVDF/PMMA (70:30) blends were investigated by Ozawa equation, Jeziorny method and crystallization rate constant (CRC) in detail. The nonisothermal crystallization energy of pure PVDF and its blends were determined by the Kissinger and Vyazovkin’s method. Conclusion: The nucleation and growth mechanism of PVDF in blends changed compared with pure PVDF. The Ozawa equation is not applicable in nonisothermal crystallization kinetics of PVDF and PVDF/PMMA blends. The decreasing of crystallization ability of PVDF in blends were found and confirmed by CRC and the decline of crystallization rate constant in Jeziorny method. Such is opposite to the results of Kissinger’s and Vyazovkin’s method, chances are that these two methods were not used to calculate the nonisothermal crystallization activation energy where the nucleation process was influenced.

Effect of sol–gel synthesized Al0.1Zr0.9O1.95 nanoparticles and PVP on PVDF-based separators in lithium-ion battery performance: The RSM study

In this study, the simultaneous effects of Al0.1Zr0.9O1.95 nanoparticles (NPs) and polyvinyl pyrrolidone (PVP) on the ion-conductivity of poly (vinylidene fluoride) (PVDF)-based separator were investigated. The ion-conductivity of PVDF/PVP/Al0.1Zr0.9O1.95 was optimized by using response surface methodology combined with central composite design. The Al0.1Zr0.9O1.95 as a nanofiller was synthesized by the sol–gel auto-combustion method. The PVDF/PVP/Al0.1Zr0.9O1.95 separators were prepared by phase inversion method. The properties and structure of optimal separator were compared with pure PVDF as a reference. The ion-conductivity of optimal separator has increased by 30.73% related to pure PVDF separator. The porosity and electrolyte uptakes of optimal separator were increased from 41% to 57% and from 246% to 384%, respectively, compared to the pure PVDF separator. Moreover, the optimal separator has a better anti-thermal shrinkage than pure PVDF separator over a wide temperature range. It is found that optimal separator (4.6 V) has a higher electrochemical stability window than pure PVDF separator (3.75 V). Also, compared with the pure PVDF separator, the optimal separator has a better discharge capacity. NPs were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy. The separators were investigated by XRD, surface and cross-section SEM, atomic force microscopy, and water contact angle.