Polyvinylidene Difluoride Film Research Articles

Fabrication of Multilayered Polyvinylidene Difluoride Films for Dielectric Capacitor, Sensing, and Energy Harvesting Performance

Fabrication of Multilayered Polyvinylidene Difluoride Films for Dielectric Capacitor, Sensing, and Energy Harvesting Performance

In Situ Fabrication of Highly Efficient and Stable Cs2NaInCl6: Sb3+@PVDF Composite Films for Optoelectronic Devices.

Lead-free double perovskites (DPs) have superior phase stability and optical properties, which make them competitive for future applications in illumination and displays. However, the preparation of DPs was mainly based on high-temperature heating and hydrochloric acid as a solvent to form powders, which increased the risk and cost of the preparation process and limited its further application. In this study, the growth of Cs2NaInCl6: Sb3+ DPs in polyvinylidene difluoride (PVDF) films was achieved using an in situ fabrication strategy with DMSO as the solvent. The prepared Cs2NaInCl6: Sb3+@PVDF composite films (CFs) can achieve a bright blue emission under 302 nm irradiation. To achieve the optimal luminescent performance of CFs, the photoluminescence (PL) intensity of Cs2NaInCl6: Sb3+@PVDF CFs under various in situ preparation conditions was compared. In addition, the photoluminescence quantum yield (PLQY) of CFs was increased from 0.72% to 83.77% by adjusting the doping amount of Sb3+, and the fluorescence lifetimes t1 and t2 were 131.08 and 1048.52 ns, respectively. Temperature-dependent PL spectroscopy and density functional theory (DFT) calculations indicate that these excellent optical properties are derived from the self-trapped excitons (STEs) at the [SbCl6]3- octahedron and [InCl6]3- octahedron connected via Cl-Na-Cl. The CFs also demonstrated excellent environmental stability, maintaining a relatively stable PL intensity even under conditions of water immersion, high temperatures, and ultraviolet (UV) radiation. Finally, we used the CFs to assemble a blue light-emitting device (LED), which showed good and stable blue emission performance at different currents. This work can provide a new idea for preparing DPs, which is conducive to promoting their commercial application in high-performance optoelectronic devices.

Temperature Dependence of the Sensitivity of PVDF Pyroelectric Sensors to THz Radiation: Towards Cryogenic Applications.

The application of terahertz (THz) science in industrial technology and scientific research requires efficient THz detectors. Such detectors should be able to operate under various external conditions and conform to existing geometric constraints in the required application. Pyroelectric THz detectors are among the best candidates. This is due to their versatility, outstanding performance, ease of fabrication, and robustness. In this paper, we propose a compact pyroelectric detector based on a bioriented poled polyvinylidene difluoride film coated with sputtered metal electrodes for in situ absorption measurement at cryogenic temperature. The detector design was optimized for the registration system of the electron paramagnetic resonance (EPR) endstation of the Novosibirsk Free Electron Laser facility. Measurements of the detector response to pulsed THz radiation at different temperatures and electrode materials showed that the response varies with both the temperature and the type of electrode material used. The maximum signal level corresponds to the temperature range of 10-40 K, in which the pyroelectric coefficient of the PVDF film also has a maximum value. Among the three coatings studied, namely indium tin oxide (ITO), Au, and Cu/Ni, the latter has the highest increase in sensitivity at low temperature. The possibility of using the detectors for in situ absorption measurement was exemplified using two typical molecular spin systems, which exhibited a transparency of 20-30% at 76.9 cm-1 and 5 K. Such measurements, carried out directly in the cryostat with the main recording system and sample fully configured, allow precise control of the THz radiation parameters at the EPR endstation.

Ultra-flexible and foldable Cu mesh transparent electrodes for the electromagnetic shielding

Ultra-flexible and foldable transparent electrodes have been developed by embedding conductive Cu meshes into a thin polyvinylidene difluoride (PVDF) film. The prepared transparent electrodes exhibit excellent optical and electrical properties (transmittance of 91.5 % at a wavelength of 550 nm, sheet resistance of 0.9 Ω/sq). Particularly, the sheet resistance remains nearly a constant after 1500 bending cycles at a bending radius of 15 μm, demonstrating exceedingly good foldability. Moreover, the Cu meshes possess strong adhesion to the PVDF films, and there is no significant performance degradation after experiencing taping cycles and ultrasonication. To assess the application potentials, transparent shielding of radiofrequency with ＞30 dB attenuation in the range from 10 M to 9 GHz are achieved. Good optical and electrical performance, outstanding foldability, strong adhesion and low-cost material, suggest that the Cu mesh transparent electrode can be applied to the next generation of wearable optoelectronic systems.

An origami structure triboelectric nanogenerator based on PVDF/BaTiO3 for muscle strain monitoring in running sports

Wearable sensing devices for monitoring human muscle health have received much attention. Triboelectric nanogenerator (TENG), which is renewable, sustainable, and green, will promote the development of wearable electronic devices. However, there is still room for development in the material and structural design of wearable TENGs. In this work, we proposed a polyvinylidene difluoride (PVDF) film doped with BaTiO3, named PVDF/BaTiO3, for triboelectric nanogenerator (PB-TENG) fabrication. The PVDF/BaTiO3 film has a unique surface micro-structure of porous scales and a fluffy 3D network architecture, which is beneficial for enhancing triboelectric efficiency. The cross-elastic origami architecture of PB-TENG brings high stability and recoverable mechanical properties to PB-TENG devices. According to the results, the maximum output power of PB-TENG can reach 2.15 mW with a load of 25 MΩ. The transferred charge (Qsc) of PB-TENG can arrive at 541 nC. Besides, the PB-TENG can act as a self-powered sensor for muscle strain diagnosis and monitoring. This research provides a new path for intelligent sports development.

Significantly Enhanced the Energy Density of Dielectric Composites by Sandwich Structure with Highly Insulating Mica Nanosheets.

Dielectric polymer composites exhibit great application prospects in advanced pulse power systems and electric systems. However, the decline of breakdown strength by loading of single high dielectric constant nanofiller hinders the sustained increase in energy density of the composites. Here, a sandwich-structured nanocomposite prepared with mica nanosheets as the second filler exhibits decoupled modulation of dielectric constant and breakdown strength. The traditional layered clay mineral mica is exfoliated into nanosheets and filled into polyvinylidene difluoride (PVDF), which shows a special depolarization effect in the polymer matrix. In Kelvin probe microscopy characterization and thermally stimulated depolarization current indicates that the mica nanosheets provided space charge traps for the polymer matrix and effectively suppressed the carrier motion. A sandwich structure composite material with mica nanosheets as the central layer has achieved a high energy density of 11.48 Jcm-3, 2.4 times higher than the pure PVDF film. This is due to the fact that randomly oriented distribution of nanosheets in a polymer matrix provide better current blocking. This work provides an effective method to improve the energy density of dielectric polymer composites by synergistically introducing insulating nanosheets and high dielectric constant nanofillers.

Piezoelectric sensing method for segmental joint contact stress during shield tunnel construction

The emergence of curved shield tunnels poses a significant construction challenge. If the quality of the segment assembly is not guaranteed, many segment cracks and damage will result from the stress concentration. Sensing the contact stresses between segmental joints is necessary to improve the quality of segments assembled for shield tunnel construction. Polyvinylidene difluoride (PVDF) piezoelectric material was chosen for the sensor because it can convert contact stresses into electrical signals, allowing the state of the segmental joints to be effectively sensed. It matches the working environment between the segmental joints of the shield tunnel, where flexible structures such as rubber gaskets and force transfer pads are present. This study proposes a piezoelectric sensing method for segmental joints in shield tunnels and conducts laboratory tests, numerical analyses, and field tests to validate the feasibility of the method. The results indicate that the PVDF film sensor can effectively sense the entire compression process of the gasket with different amounts of compression. The piezoelectric cable sensor can effectively sense the joint offset direction of the gasket. For differently shaped sections, the variation in the force sensed by the piezoelectric cable sensors was different, as verified by numerical simulation. Through the field test, it was found that the average contact stress between the segmental joints was in the range of 1.2–1.8 MPa during construction of the curved shield tunnels. The location of the segmental joints and the type of segment affect the contact stress value. The field monitoring results show that piezoelectric sensing technology can be successfully applied during assembly of the segments for effective sensing of the contact stress.

A Study of Contact Electrification Process on PVDF–Metal Interface: Effect of β Phase Composition

AbstractRecently, triboelectric nanogenerators (TENGs) are getting considerable attention as an energy harvesting tool that can convert random mechanical energy into electricity due to the wide material selection, low cost, and easy fabrication. TENGs work by contact electrification on the interface and electrostatic induction on the electrodes when two surfaces contact and separate. Herein, the study of the contact electrification process on the metal–polyvinylidene difluoride (PVDF) interface is conducted focusing on the effect of β phase content on the electrical properties of the PVDF films. It is found through the EFM and KPFM surface electrical studies that a higher β phase promotes stronger electrostatic interactions and enhances electron‐cloud overlap with the metal coated cantilever tip that leads to higher amount of charge transfer. Additionally, there is overall enhancement of the TENGs electric output performance for a higher β phase containing PVDF films and the maximum electric output of 8.1 V and 12.2 nA is obtained for the TENG made with 79% β phase PVDF film.

A study on comparing method of motion classification using muscle bulging for control of powered prosthetic hand

AbstractAiming at the control of a powered prosthetic hand, this paper compares methods for the classification of intended hand motions using muscle bulging patterns caused by muscle contraction. Two sheets of Polyvinylidene Difluoride (PVDF) film were used as sensors to detect the muscle bulging on the forearm caused by intended hand motions. A neural network had been successfully trained for the classification of six types of hand motions using the muscle bulging pattern detected by the two PVDF sensors. In this paper, we further studied the motion classification methods of back propagation neural network (BPNN), k‐nearest neighbor algorithm (k‐NN), and support vector machine (SVM) to compare their classification performance. We found that all three methods had a similar classification rate of about 95% for six types of hand motions. Moreover, a regressive analysis comparison of the time for each classification method to converge to 95% of the total classification rate showed that SVM converged significantly earlier than BPNN and k‐NN. The time it takes for SVM to converge the classification rate to 95% is less than 0.1 s, suggesting that real‐time motion classification is possible by using SVM. In a similar manner, we found that SVM requires the least training data of the three methods at only nine trials for a type of motion. Furthermore, SVM had the highest classification rate at about 90% in practical experimental conditions. In conclusion, SVM was found to be the most practical of the three methods.

High-output soft-contact fiber-structure triboelectric nanogenerator and its sterilization application

Infectious diseases are spreading rapidly with the flow of the world’s population, and the prevention of epidemic diseases is particularly important for public and personal health. Therefore, there is an urgent need to develop a simple, efficient and non-toxic method to control the spread of bacteria and viruses. The newly developed triboelectric nanogenerator (TENG) can generate a high voltage, which inhibits bacterial reproduction. However, the output performance is the main factor limiting real-world applications of TENGs. Herein, we report a soft-contact fiber-structure TENG to avoid insufficient friction states and to improve the output, especially at a high rotation speed. Rabbit hair, carbon nanotubes, polyvinylidene difluoride film and paper all contain fiber structures that are used to guarantee soft contact between the friction layers and improve the contact state and abrasion problem. Compared with a direct-contact triboelectric nanogenerator, the outputs of this soft-contact fiber-structure TENG are improved by about 350%. Meanwhile, the open-circuit voltage can be enhanced to 3440 V, which solves the matching problems when driving high-voltage devices. A TENG-driven ultraviolet sterilization system is then developed. The bactericidal rate of this sterilization system can reach 91%, which significantly reduces the risk of disease spread. This work improves a forward-looking strategy to improve the output and service life of the TENG. It also expands the applications of self-powered TENG sterilization systems.

Multimode Dynamic Photoluminescence of Bi3+-Activated ZnGa2O4 for Optical Information Encryption.

Optical storage technology for information encryption is a popular means of safeguarding information. Herein, a Bi3+-activated ZnGa2O4 multimode dynamic photoluminescence (PL) material is developed. Upon being irradiated with an ultraviolet lamp at a fixed excitation wavelength of 254 nm, the ZnGa2O4: x% Bi3+ (x = 0.5-5.0) samples exhibit varying degrees of dynamic PL emission due to a distinct Bi3+ doping effect. The mechanism underlying the dynamic PL of ZnGa2O4: Bi3+ associated with Bi3+-activated trap concentration modulation is investigated using thermoluminescence spectra. Additionally, the ZnGa2O4: 5% Bi3+ sample shows a reversible thermally responsive dynamic PL with a color variation from blue to red upon heating from 283 to 393 K. Predesigned procedures based on single-wavelength-mediated photochromic and thermochromic dynamic PL emissions of ZnGa2O4: Bi3+ are designed for rewritable optical data storage and high-level information encryption. Also, an enhanced encryption scheme with a mask encoding technique applying a ZnGa2O4: Bi3+ hybridized polyvinylidene difluoride film is then proposed to increase the security level. Accordingly, this work provides a feasible way to rationally design dynamic PL material offering more creative designs for safeguarding information via encryption.

Multicolor Display Fabricated via Stacking CW Laser-Patterned Perovskite Films

Direct laser patterning enables precise tailoring of perovskites at the microscale, which is of vital importance to a variety of advanced optoelectronic devices. However, thermal ablation triggered by nonlinear absorption could cause imprecise crystallization, which significantly limits the resolution of the patterning technique. Here, the perovskite nanoparticles (NPs) are crystallized inside the polyvinylidene difluoride (PVDF) matrix by continuous wave (CW) laser illumination. The underlying crystallization of perovskite NPs is fundamentally triggered by the photon effect rather than the thermal ablation, avoiding undesired crystallizations and the destruction of the perovskite. This technique enables the fabrication of multicolor perovskite PVDF films with high transparency, high-resolution, and high stability. Significantly, the multilayer film resulting from the stacking of the patterned colorful perovskite PVDF films presents potential applications in flexible multicolor displays. This work opens a new avenue for precise manufacturing of perovskite films and potentially expands their applications in various integrated optoelectronic devices in displays and micro light-emitting diodes.

Considerably enhanced electrochemical and thermomechanical performance of lithium battery (LIB) separators of PVDF/vermiculite nanosheets (VNs) composites via constructing well-defined hierarchical microstructure

In this study, polyvinylidene difluoride (PVDF) lithium battery (LIB) separators were prepared by nonsolvent- induced phase separation (NIPS) technique, and effect of vermiculite nano-sheets (VNs) on the performance of PVDF separator was studied by altering the proportions of VNs added. The microscopic morphologies of PVDF films were observed by scanning electron microscope (SEM), and it was found that the incorporation of two-dimensional VNs greatly improved the thermodynamic instability of PVDF/N, N-dimethylacetamide (DMAc) solution, which further induced the formation of long finger-like pore structure, leading to improved porosity and electrolyte uptake rate of the prepared separators. Meanwhile, differential scanning calorimeter (DSC) analysis showed that the presence of VNs decreased PVDF's crystallinity and greatly improved the thermal stability of the separators primarily owing to VNs’ two-dimensional structure as well as excellent thermal stability. When the VNs content reached 7.0 wt%, the ionic conductivity of the separator increased from 0.300 mS⋅cm−1 to 1.679 mS⋅cm−1, coupled with significant improvement in both mechanical properties and battery performance. The present study provides a facile method for preparing LIB separators with high safety and superior performance.

Preparation and application of high performance PVDF/PS electrospinning film-based triboelectric nanogenerator

In this research, polyvinylidene difluoride(PVDF)/polystyrene(PS) blends were prepared by the torque blending method, and the PVDF/PS electrospinning films obtained by electrospinning can be used to prepare a triboelectric nanogenerator with high output performance. Compared with the TENG made by pristine PVDF film, the short-circuit current, open-circuit voltage, and transferred charge of the PVDF/PS electrospinning film-based triboelectric nanogenerator increased from 4.89 μA, 57.7 V, and 17.1 nC to 11.1 μA, 165.9 V, and 53.8 nC, which increased by 2.27 times,2.88 times, and 3.15 times, respectively. At the same time, combined with the structural characteristics of the electrospinning film, it was proposed to use the PVDF/PS electrospinning film as the filter layer of the mask. Compared with the filtering ability of PP melt-blown nonwoven that was used as a commercial mask filter layer, the PVDF/PS electrospinning film had a better filtering effect for particles of various diameters in the air, and after PVDF/PS electrospinning film loses charge, it can recharge by friction to restore filtering performance, and the recharged PVDF/PS film still offered excellent protection, filtering up to 95 % of air particles between 0.3 and 10 μm.

Electromagnetic interference shielding effectiveness of compression molded carbon nanofiber‐reinforced polyvinylidene difluoride film

AbstractIn this study, vapor grown carbon nanofiber (VGCNF) reinforced polyvinylidene difluoride (PVDF) composites were developed. Composites were fabricated by high shear mixing using a Banbury type mixer. The material was then subjected to compression molding resulting in films with an average thickness of 0.82 mm. The developed films were subjected to physico‐thermal, and electrical characterization including analysis of the shielding effectiveness (SE) of electromagnetic interference (EMI). Morphological analysis was conducted by scanning electron microscopy and characterization complemented with Fourier transform infrared spectroscopic and X‐ray diffraction analyses. The thermal properties were studied by differential scanning calorimetry and thermogravimetric analysis, which revealed the influence of carbon nanofibers on thermal stability and phase transitions. The electrical conductivity for in‐plane and through‐plane was gradually enhanced by increasing the concentration of VGCF loading; a percolation threshold was initiated at 5 wt% loadings. In plane and through plane resistivity decreased from 1011 Ω‐cm to 103 Ω‐cm and 102 Ω‐cm, respectively. An in‐depth EMI SE study was conducted depicting the influence of VGCNFs on skin depth, EMI power coefficients for reflection, absorption and transmission, and EMI SE for reflection, absorption, and total. The total SE of the developed nanocomposite films was observed to range between 6.6–16.4 dB in a frequency range of 30 kHz to 1.5 GHz. This study presents the processing‐structure–property relationships for lightweight and flexible NC films with enhanced electrical conductivity.

PVDF/RGO based piezoelectric nanocomposite films for enhanced mechanical and dielectric properties

Polymer nanocomposites are dominating today in the global scenario due to their diverse applications. The study involves the investigation of the role of Reduced graphene oxide (RGO) as nanofiller on mechanical and dielectric properties of Polyvinylidene difluoride (PVDF). Flexible piezoelectric thin films of PVDF loaded with RGO nanofillers were synthesized using a solvent casting technique. The crystal structure of neat PVDF and RGO loaded PVDF films were analysed using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and Fourier transform infrared spectroscopy (FTIR). Tensile strength and Young’s modulus of polymer nanocomposite films were analysed by performing tensile testing on a universal testing machine (UTM). The results showed an improvement in elastic modulus up to a certain nanofiller percentage (2 wt% RGO). Measurement of dielectric properties of thin films was conducted using an impedance and material analyser (IMA). The dielectric constant of the film increases with increment in RGO loading. Thus, overall increment in piezoelectric properties take place. This nanocomposite can be used for developing flexible and highly sensitive sensors and actuators.

Hybrid Nanofillers Creating the Stable PVDF Nanocomposite Films and Their Effect on the Friction and Mechanical Properties.

The solvent casting method was used for five types of polyvinylidene difluoride (PVDF) nanocomposite film preparation. The effect of nanofillers in PVDF nanocomposite films on the structural, phase, and friction and mechanical properties was examined and compared with that of the natural PVDF film. The surface topography of PVDF nanocomposite films was investigated using a scanning electron microscope (SEM) and correlative imaging (CPEM, combinate AFM and SEM). A selection of 2D CPEM images was used for a detailed study of the spherulitic morphologies (grains size around 6–10 μm) and surface roughness (value of 50–68 nm). The chemical interactions were evaluated by Fourier transform infrared spectroscopy (FTIR). Dominant polar γ-phase in the original PVDF, PVDF_ZnO and PVDF_ZnO/V, the most stable non-polar α-phase in the PVDF_V_CH nanocomposite film and mixture of γ and α phases in the PVDF_V and PVDF_ZnO/V_CH nanocomposite films were confirmed. Moderately hydrophilic PVDF nanocomposite films with water contact angle values (WCA) in the range of 58°–69° showed surface stability with respect to the Zeta potential values. The effect of positive or negative Zeta-potential values of nanofillers (ζn) on the resulting negative Zeta-potential values (ζ) of PVDF nanocomposite films was demonstrated. Interaction of PVDF chains with hydroxy groups of vermiculite and amino and imino groups of CH caused transformation of γ-phase to α. The friction properties were evaluated based on the wear testing and mechanical properties were evaluated from the tensile tests based on Young’s modulus (E) and tensile strength (Rm) values. Used nanofillers caused decreasing of friction and mechanical properties of PVDF nanocomposite material films.

Design and performance of flexible polymeric piezoelectric energy harvesters for battery-less tyre sensors

A piezoelectric energy harvester for battery-less tyre sensors has been developed. It consists of two key elements: (a) a piezoelectric material—polyvinylidene difluoride (PVDF) film and (b) an electrode—a conductive elastomer filled with carbon black and single-wall carbon nanotubes (SWCNTs). It was designed as a flexible patch in a sandwich-like configuration, which can be mounted onto the inner liner of a tyre. The patch was fabricated by inserting a PVDF film in between two conductive elastomer sheets. The development started with improving the conductivity of the elastomer by adding 6 wt% of SWCNT masterbatch. The adhesion between the interfaces was improved through surface modification of the PVDF film by introducing oxygen functional groups via a plasma treatment and further modification with a thiocyanate silane. The successful surface modification of the PVDF film was affirmed by x-ray photoelectron spectroscopy. T-peel and fatigue tests showed durable and stable adhesion between PVDF and conductive elastomer, confirming that the silane can effectively bridge the two components. A glueing method is proposed to adhere the patch to the tyre inner liner compound. The harvester is estimated to sufficiently power a reference tyre sensor, producing 28 μW cm−2.

Modeling and electromechanical performance analysis of polyvinylidene difluoride/textile‐system for energy harvesting from the human body toward a novel class of self‐powered sensors

AbstractBecause batteries' ability to power portable and wireless devices is limited, a great deal of research has been conducted on energy harvesting technology as a self‐power source for portable devices. Harvesting mechanical energy from human motion is an attractive approach to obtaining green and renewable energy by converting wasted ambient energy to electrical power. Hence, integrating an energy harvester into shoes is among the most interesting possibilities for harvesting energy from the body. In this paper, we explore the effect of flexible substrate mechanical parameters on the energy harvesting capability of a flexible piezoelectric film. Analytical modeling and simulations of a smart structure composed by polyvinylidene fluoride film stuck on three different textiles substrates have been done to evaluate the ability of this approach to harvest energy and its application within shoes to transform mechanical energy generated by the foot while walking into electrical energy. The maximum harvested power of the polyvinylidene difluoride film under 200 N compressive force was found to be 5.37 μW on a Cotton textile, which is a potentially useful amount of energy.

Broadband Model‐Based Optoacoustic Mesoscopy Enables Deep‐Tissue Imaging beyond the Acoustic Diffraction Limit

AbstractOptoacoustic mesoscopy (OAM) retrieves anatomical and functional contrast in vivo at depths not resolvable with optical microscopy. Recent progress on reconstruction algorithms have further advanced its imaging performance to provide high lateral resolution ultimately limited by acoustic diffraction. In this work, a new broadband model‐based OAM (MB‐OAM) framework efficiently exploiting scanning symmetries for an enhanced performance is presented. By capitalizing on the large detection bandwidth of a spherical polyvinylidene difluoride film while accurately accounting for its spatial impulse response, the new approach significantly outperforms standard OAM implementations in terms of contrast and resolution, as validated by functional in vivo experiments in mice and human volunteers. Furthermore, L1‐norm regularization enables resolving structures separated by less than the theoretical diffraction‐limited resolution. This unique label‐free angiographic performance demonstrates the general applicability of MB‐OAM as a super‐resolution deep‐tissue imaging method capable of breaking through the limits imposed by acoustic diffraction.