Β-phase PVDF Research Articles

Self-polarized cellulose nanofiber-reinforced PVDF-based piezoelectric composites via direct-ink-writing 3D printing for pressure sensing and energy harvesting

With their unique physicochemical properties, PVDF-based piezoelectric materials demonstrate significant potential in various fields. Nevertheless, their benign piezoelectric performance is usually obtained through polarization post-treatment after material formation. In this study, a self-polarized direct-ink-writing (DIW) 3D printing strategy is proposed for one-step fabrication of high-performance PVDF/cellulose nanofiber (CNF) piezoelectric composites with low energy consumption. Under the synergistic effects of shear/stretching from DIW and hydrogen bonding between PVDF and CNF, α-phase PVDF undergoes gauche-trans conformational transformation into β phase. And then β-phase PVDF is dragged by high aspect ratio CNF into bead-like small crystals to form a multilayered oriented structure, resulting in abundant oriented dipole moments. PVDF/CNF composites with different weight ratios are printed using this strategy, and the results show that the composite film with 5 wt% CNF content exhibits the best piezoelectric performance. Without additional polarization treatment, it achieves a sensitivity of 103 mV/N, 2.2 times higher than conventional cast films. The composite also demonstrates good linear response and durability, meeting the requirements for human motion monitoring and mechanical energy harvesting. This work has opened up new avenues for the efficient and low-energy fabrication of flexible wearable and energy-harvesting devices.

Piezo-to-piezo (P2P) conversion: simultaneous β-phase crystallization and poling of ultrathin, transparent and freestanding homopolymer PVDF films via MHz-order nanoelectromechanical vibration.

An unconventional yet facile low-energy method for uniquely synthesizing neat poly(vinylidene fluoride) (PVDF) films for energy harvesting applications by utilizing nanoelectromechanical vibration through a 'piezo-to-piezo' (P2P) mechanism is reported. In this concept, the nanoelectromechanical energy from a piezoelectric substrate is directly coupled into another polarizable material (i.e., PVDF) during its crystallization to produce an optically transparent micron-thick film that not only exhibits strong piezoelectricity, but is also freestanding-properties ideal for its use for energy harvesting, but which are difficult to achieve through conventional synthesis routes. We show, particularly through in situ characterization, that the unprecedented acceleration associated with the nanoelectromechanical vibration in the form of surface reflected bulk waves (SRBWs) facilitates preferentially-oriented nucleation of the ferroelectric PVDF β-phase, while simultaneously aligning its dipoles to pole the material through the SRBW's intense native evanescent electric field . The resultant neat (additive-free) homopolymer film synthesized through this low voltage method, which requires only -orders-of-magnitude lower than energy-intensive conventional poling methods utilizing high kV electric potentials, is shown to possess a 76% higher macroscale piezoelectric charge coefficient d33, together with a similar improvement in its power generation output, when compared to gold-standard commercially-poled PVDF films of similar thicknesses.

Large-Scale Fabrication of High β-Phase PVDF Films with Enhanced Piezoelectric and Electrode Formation Properties

Large-Scale Fabrication of High β-Phase PVDF Films with Enhanced Piezoelectric and Electrode Formation Properties

Lead-free Polymer Composite Film for Photon Energy Influenced Piezoelectric Nanogenerator based on Photoactive SnS2

Piezoelectric nanogenerators (PENGs) can power microelectronics, which convert weak mechanical vibrations to electrical impulses; however, low output voltage and poor mechanical durability limit PENG use. Thus, we provide photoactive SnS2 nanofillers in a PVDF matrix for piezoelectric nanogenerators (PPENGs). Raman spectroscopy demonstrates improvement of the electroactive β-phase of PVDF due to adding photoactive hexagonal SnS2 nanoparticles with a band gap of 2.4 eV. Sandwiching the PVDF-SnS2 composite between ITO-coated substrates with silver paste contacts fabricated the PPENG. The open-circuit voltage of PPENG is 24.4 V in the dark and 72.9 V under illumination with a short-circuit current of 0.75 μA, showing its outstanding photo responsiveness. The high light absorption of SnS2 and PVDF-SnS2 interfacial polarization caused the improved response. High-performance optoelectronic and energy harvesting applications may employ this photoactive piezoelectric nanogenerator development technique.

Improving the energy storage efficiency and power density of polymer blend in combination with Ti3C2Tx for energy storage devices

Polymer blend-based dielectrics are extensively used because of their broad working temperature range, quick discharging speed, and high power density. The solution casting approach is used to prepare the PVDF/PMMA- Ti3C2Tx nanocomposite flexible energy storage films. The morphology results show that the composite has a homogeneous and dense microstructure. The structural study shows the composition of thin films and confirms the existence of the PVDF β-phase. The thermal analysis showed 31.36 % crystallinity for 20 wt% of nanocomposite (NCs). The values of band gap energy reduced from 3.07 eV to 2.65 eV with increasing Ti3C2Tx concentration (15 wt%). It was found that the almost high dielectric constant values of (̴205) at 100 Hz and loss of 0.078 were suggestive of increased interfacial polarization. The maximal energy density of the NCs is 1.28 J/cm3, and its power density is 4.86 MW/cm3 for 15 wt% NCs. The conductivities of 15 wt% composite increase to 10−9 –10−7 S.cm−1 at 100 Hz, and then it reaches nearly 10−3 S cm−1 when the frequency is raised to 1 MHz. The 2D MXene nanofiller and PVDF macromolecular chain have an improved interface interaction, which results in excellent complete electrical characteristics. The rise in residual polarization can be inhibited by adding PMMA. In this work, adding 2D Ti3C2Tx MXene to PVDF/PMMA blends offers a viable way to create materials that are highly effective at storing energy in capacitors.

Electrical Response of Different Crystalline Microregions in Poly(vinylidene fluoride).

The crystal structure has a great influence on the dielectric and piezoelectric performance of poly(vinylidene fluoride) (PVDF). In this work, we prepared PVDF films with two typical crystalline phases (α and β). In situ Kelvin probe force microscopy (KPFM) and Piezoelectric force microscopy (PFM) were employed to investigate the responses of different PVDF crystalline phases to charge mobility, polarization, and piezoelectric properties. We used a homemade Kelvin probe force microscope (KPFM) to inject charges into the two crystalline phases to investigate the differences in the response of different crystalline phases of PVDF to electrical excitation on a microscopic scale. It was found that the α-phase has a lower charge injection barrier and is more susceptible to charge injection and that the α-phase is accompanied by a faster charge dissipation rate, which makes it easier to accumulate charge at the interface between the α-phase and β-phase PVDF. Moreover, the PFM polarization manipulation showed no change in the amplitude and phase diagram of the α-phase under ±10 V bias. In contrast, the β-phase showed a clear polarization reversal phenomenon and a significant increase in piezoelectric amplitude, which is consistent with its polar intrinsic properties. This study provides valuable insights into the multiphase contributions and a reference for designing advanced PVDF dielectrics.

Scalable wet-spinning multilevel anisotropic structured PVDF fibers enhanced with cellulose nanocrystals-exfoliated MoS2 for high-performance piezoelectric textiles

The high-performance fabric-based piezoelectric nanogenerators (PENGs) is the ideal choice for the next generation of wearable electronics. However, large-scale fabrication of high-performance fabric-based PENGs remains a great challenge. In this study, cellulose nanocrystals (CNCs) exfoliated MoS2 (C@M) are integrated into the poly (vinylidene fluoride) (PVDF) matrix, which are successfully fabricated PVDF/C@M fibers (PCF) by wet-spinning and post-drawing processes. Accompanied by the stress-induced anisotropic alignment of C@M and PVDF molecular chains during post-drawing, the interfacial interactions between C@M and PVDF dipoles greatly promote the formation of the electroactive β-phase of PVDF as well as the orientation of the dipoles. The PCF demonstrate excellent mechanical performance with a tensile strength of 301 MPa and toughness of 68.5 MJ·m−3. Subsequently, the PCF are woven into fabrics and subsequently assembled into a flexible PENG (PCF-PENG), exhibiting excellent piezoelectric coefficient (d33 = 40.3 pC·N−1), power density of 56.25 μW·cm−2. Furthermore, scenarios such as energy harvesting, motion detection, and posture recognition of the PCF-PENG are demonstrated, providing a feasible proposal for the large-scale fabrication of electronic textiles.

Photo responsive single layer MoS2 nanochannel membranes for photocatalytic degradation of contaminants in water

The major polluting aspects of our global fashion industries are the textile wastewater that turns black all our freshwater reservoirs. Nano-filtration through membrane technology is one of the biggest solutions of industrial wastewater treatment but the fouling of membrane is the major limitation of previous work. In this research, novel PVDF/MoS2-TNT (PMT) nanocomposite membranes were fabricated through a modified In-situ polymerisation phase inversion method. X-ray diffraction (XRD) analysis also confirmed the β-phase of PVDF within the developed PVDF/MoS2-TNT membrane. XPS analysis provides evidence about the presence of a specific chemical states of titanium nanotube and molybdenum disulphide which is involved in the photocatalytic degradation of pollutant molecules. Scanning electron microscope (SEM) shows that our membranes are porous in nature. PVDF/MoS2-TNT membranes exhibit excellent filtration efficiency (∼97%) for textile wastewater. The results and outcomes of the research demonstrate that PMT membranes have enormous potential in the commercial application of textile wastewater treatment.

Synergistic Molecular Alignment and Dipole Polarization in Stretched Nafion/Poly(vinylidene fluoride) Blend Membranes for High Proton Conduction in PEMFCs.

The nanostructure of Nafion and poly(vinylidene fluoride) (PVDF) blend membranes is successfully aligned through a mechanical uniaxial stretching method. The phase-separated morphology of Nafion molecules distinctly forms hydrophilic proton channels with increased connectivity, resulting in enhanced proton conductivity. Additionally, the crystalline phase of PVDF molecules undergoes a successful transformation from the α- to β-phase during membrane stretching, demonstrating an alignment of fluorine and hydrogen atoms with a TTTT(trans) structure. The aligned nanostructure of the blend film, combined with the dipole polarization of the β-phase PVDF, synergistically enhances the proton conduction through the membrane for operating proton-exchange membrane fuel cells (PEMFCs). The controlled structures of the blend membranes are thoroughly investigated using atomic force microscopy and small-angle X-ray scattering. Furthermore, the improved in-plane proton conductivity facilitates increased proton conduction at the interface between the membrane and catalyst layer in the membrane-electrode assembly, ultimately enhancing the power generation of PEMFCs.

Preparation of PVDF/PVA composite films with micropatterned structures on light-cured 3D printed molds for hydrophilic modification of PVDF

Abstract Polyvinylidene fluoride (PVDF) is widely used in biotechnology due to its excellent biocompatibility, high temperature and pressure resistance, and outstanding mechanical properties. However, the hydrophobic nature of PVDF surface hinders the attachment of biological proteins. In order to enhance the wettability of PVDF surfaces, this study prepared composite films by blending PVDF with polyvinyl alcohol (PVA), and micro-patterned structures were fabricated on the material surface using a mold-replication method based on digital light processing (DLP) photopolymerization printing technology. A series of characterization techniques including surface morphology analysis, chemical composition analysis, and wettability testing were employed. The surface morphology analysis results indicated that the method of using DLP photopolymerization technology to print mold replicas and create micro-patterned structures was indeed effective in creating micro-patterned structures on both PVDF and PVDF/PVA composite films. The chemical composition analysis showed that the spin-coating of PVDF powder material resulted in PVDF β-phase crystalline structure, which has a positive effect on cell growth. Furthermore, the introduction of hydrophilic groups was achieved by mixing PVDF with PVA. Wetting test results indicate that the incorporation of the hydrophilic material PVA and micro-patterned surfaces both contribute to the improved hydrophilicity of the material. The water contact angle of the micro-patterned PVDF/PVA composite film reached 30.8°, exhibiting excellent hydrophilic properties. This study achieved the optimization of PVDF surface properties through micro-patterned surface modification and material composition design, providing novel insights for the further development of PVDF materials in the field of biotechnology.

Power enhancement of piezoelectric energy harvester using ZnOnf-PDMS composite with PVDF filler

This work aims to fabricate a piezoelectric energy harvester using Polydimethylsiloxane (PDMS) with Zinc Oxide nanoflower (ZnOnf) and Poly(vinylidene fluoride) (PVDF). ZnOnf is synthesised via the hydrothermal method by varying the reaction time. The long nanoflowers resulting from the reaction time of 2 h are utilized to prepare the piezoelectric composite. Two energy harvesters are fabricated: ZnOnf-PDMS (ZP) and ZnOnf-PVDF-PDMS (ZPP), to harvest mechanical energy. The incorporation of PVDF into the ZnOnf-PDMS composite enhances the active polar β-phase of PVDF, leading to improved piezoelectric activity. The output voltage of the piezoelectric harvesters is measured under various impact forces applied using a self-designed impact force setup. The addition of PVDF to the ZnOnf-PDMS composite results in an increase in the dielectric constant and, consequently, in the energy harvester's output. Thus, at an applied impact force of 2.64 N, the output power harvested is 11.4 µW for ZP, and is amplified to 14.27 µW for ZPP. Furthermore, the incorporation of PVDF enhances the thermal stability and delays the decomposition temperature of the energy harvester.

High-Performance Hybrid Triboelectric Generators Based on an Inversely Polarized Ultrahigh β-Phase PVDF

High-Performance Hybrid Triboelectric Generators Based on an Inversely Polarized Ultrahigh β-Phase PVDF

Molecular Mechanism of the Piezoelectric Response in the β-Phase PVDF Crystals Interpreted by Periodic Boundary Conditions DFT Calculations.

A theoretical approach based on Periodic Boundary Conditions (PBC) and a Linear Combination of Atomic Orbitals (LCAO) in the framework of the density functional theory (DFT) is used to investigate the molecular mechanism that rules the piezoelectric behavior of poly(vinylidene fluoride) (PVDF) polymer in the crystalline β-phase. We present several computational tests highlighting the peculiar electrostatic potential energy landscape the polymer chains feel when they change their orientation by a rigid rotation in the lattice cell. We demonstrate that a rotation of the permanent dipole through chain rotation has a rather low energy cost and leads to a lattice relaxation. This justifies the macroscopic strain observed when the material is subjected to an electric field. Moreover, we investigate the effect on the molecular geometry of the expansion of the lattice parameters in the (a, b) plane, proving that the rotation of the dipole can take place spontaneously under mechanical deformation. By band deconvolution of the IR and Raman spectra of a PVDF film with a high content of β-phase, we provide the experimental phonon wavenumbers and relative band intensities, which we compare against the predictions from DFT calculations. This analysis shows the reliability of the LCAO approach, as implemented in the CRYSTAL software, for calculating the vibrational spectra. Finally, we investigate how the IR/Raman spectra evolve as a function of inter-chain distance, moving towards the isolated chain limit and to the limit of a single crystal slab. The results show the relevance of the inter-molecular interactions on the vibrational dynamics and on the electro-optical features ruling the intensity pattern of the vibrational spectra.

The tribo-piezoelectric microscopic coupling mechanism of ferroelectric polymers and the synchronous online monitoring of load distribution/roller speed for intelligent bearings

The tribo-piezoelectric microscopic coupling mechanism of ferroelectric polymers remains elusive due to the complicated interfacial electron transfer behavior and dipole-dipole interactions, limiting the development of high-performance tribo-piezoelectric hybrid nanogenerators. Herein, we take PVDF-Cu as an example to investigate the tribo-piezoelectric coupling mechanism at the ferroelectric polymer/metal interface under compression via first-principles calculations and KPFM experiments. It is revealed that the local deformation of the ferroelectric β-phase PVDF molecular chain not only concentrates the LUMO (lowest unoccupied molecular orbital) in the deformed region and lowers the LUMO energy level, but also changes the orientation and polarity of the dipoles, thus enhancing the triboelectric and piezoelectric charges. Furthermore, this work identifies dipole-dipole interactions and intramolecular/intermolecular electron transfer as the key intrinsic factors that promote the synergistic enhancement of triboelectricity and piezoelectricity. Specifically, the intramolecular and intermolecular electron transfer within the β-phase PVDF induced by the interfacial electron transfer enhances the dipole polarization, thus enhancing the piezoelectric effect, which in turn generates stronger dipole-dipole interactions to provide additional electrostatic potential energy for electrons in the polymer, finally enhancing the interfacial triboelectric effect again. On this basis, we propose the microscopic coupled electrification model at the ferroelectric polymer/metal interface and clarify that the triboelectric and piezoelectric effects dominate at low and high pressures, respectively. Inspired by the above microscopic mechanism, we regulate the ferroelectric β phase of PVDF film to develop a tribo-piezoelectric coupled pressure sensor(T-PPS) with high sensitivity(0.95 V/kPa) and wide measurement range(>10 MPa). In addition, benefiting from the excellent sensing characteristics of T-PPS, we propose a novel strategy based on pressure fluctuation detection of the bearing outer ring, enabling the high-precision synchronous online testing of load distribution and roller speed for intelligent bearings. This method can address the problems of existing measurements such as the destruction of bearings structure, interference with cage motion, and low integration.

Fused filaments of PVDF/PLA blends for biomedical applications

Artificial materials with piezoelectric properties have been increasingly investigated as potential candidates for replacing various living tissues. In this manuscript, results of studies on the synthesis and characterization PVDF/PLA blend filaments containing piezoelectric/ferroelectric PVDF β-phase are reported. SEM images reveal that all studied filaments are immiscible blends, while FTIR results reveal blends with a predominance of PVDF β-polar phase whose highest percentage (75%) was observed for the mass ratio of 80% of PVDF to 20% of PLA. This blend shows adequate characteristics for biomedical applications when processed by filament fabrication techniques.

Responsive polymer thin films

Responsive polymer thin films

Ultrastrong-polar cyano-Prussian blue analogs hybrid tribomaterials for biomechanical energy harvesting and self-powered sensing

Triboelectric nanogenerators (TENGs) are green energy devices that can convert mechanical energy into electrical energy. However, lower output power density currently hinders its realistic applications. Introducing functional materials into dielectric polymers layer is an efficient approach to enhance TENG output. Herein, a low-cost, biocompatible Prussian blue analog (KxMn[FeCN)6]y·zH2O, MnFePBA) is proposed as a functional component for high-performance hybrid tribomaterials of TENGs. Numerous highly polar CN groups found in MnFePBA can interact dipole-dipole with the C-F bond in PVDF, promoting the formation of electroactive β-phase PVDF and enhancing the capacity for charge induction and charge capture. Simultaneously, the weak interface fusion between the inorganic material and the organic polymer can be improved as the O-H bond in MnFePBA can establish a stronger hydrogen bond with the C-F bond in PVDF. Additionally, high dielectric MnFePBA can enhance the dielectric properties of PVDF/MnFePBA to boost the TENG output. Consequently, the PVDF/MnFePBA can achieve evidently increased short-circuit current of 31.2 µA, output voltage of 1580 V and ultra-high power density of 12.8 W/m2 (4 ×4 cm2). Moreover, the assembled TENG could also be efficiently utilized for human motion capture and sensing applications. This work enriches the range of functional components for high-performance tribomaterials of TENGs.

Lead-free bimetallic oxide loaded on reduced graphene oxide‒poly(dopamine) hybrid nanocomposite with enhanced crystallinity and piezoelectric performance

The increased demand for electricity with low environmental impact has prompted researchers to find solutions to obtain the maximum output. This effort has imparted a significant focus on piezoelectric materials owing to their high piezoelectric coefficient and electromechanical coupling factor. In this study, reduced graphene oxide encapsulated with polydopamine and incorporated with zinc manganate hybrid nanocomposite (rGO‒pDA‒ZnMnO 3 HNC) was prepared. The as-prepared HNC, of different weight percentages, was blended with 15 wt% poly(vinylidene fluoride) (PVDF) to form different PVDF@rGO‒pDA‒ZnMnO 3(R) thin films. Subsequently, the flexible piezoelectric sensors (FPSs) were fabricated by a solution-casting method. The as-prepared HNC and thin films were characterized by powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDX), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The PXRD data revealed the increased degree of crystallinity of the thin films from 54% to 68% with the increase in filler loading. The β-phase of PVDF also increased, as obtained from the FT-IR analysis. Electrical characterization of the prepared FPSs was carried out by estimating the sensitivity of the devices on different loads. The acquired response at a force of 1 N for PVDF@rGO‒pDA‒ZnMnO 3(0.2 wt%) improved by 44% than that of PVDF@rGO‒pDA‒ZnMnO 3(0 wt%) . The force applied by the finger on the device also generated voltages, which were used to charge the capacitor, thereby used to glow the light-emitting diodes with amplifications. These promising results demonstrate the potential for developing lead-free efficient piezoelectric nanogenerators for energy-harvesting applications and self-powered devices.

Crash precipitation of nanoscale β-phase PVDF particles

• A simple approach to transform α-phase poly(vinylidene fluoride) (PVDF) to its crystalline β-phase is outlined. • The process also led to a decrease in the size of PVDF particles. • Early results from adjusting the ratio of PVDF to solvent indicate the possibility to tailor the crystalline phase of PVDF. Poly(vinylidene fluoride) exhibits coupling between the electrical and mechanical domains while in its crystalline β-phase. The electromechanical coupling effect is known as piezoelectricity, wherein a voltage is generated from a uniform stress or strain. While several techniques have been developed to crystallize PVDF in the β-phase, the processes usually produce films or fibers with few processes producing β-phase particles. The reported processes to produce particles generally require specialized equipment that is not readily available. In this work, nano-sized β-phase PVDF particles (<100 nm) are precipitated from solution using commercially available materials. The size of the particles was observed using scanning electron microscopy (SEM) and dynamic light scattering (DLS) techniques. The phase was characterized using Fourier transform infrared spectroscopy (FTIR) and powder x-ray diffraction (PXRD). These nano-sized β-phase particles have the potential to act as inclusions in composite materials to improve electrical and mechanical properties, while the method represents a potential route to control the phase and size of PVDF particles to meet specific applications.

Spatially Confined LiF Nanoparticles in an Aligned Polymer Matrix as the Artificial SEI Layer for Lithium Metal Anodes.

The uncontrollable growth of lithium (Li) dendrites and the instability of the Li/electrolyte interface hinder the development of next-generation rechargeable lithium metal batteries. The combination of inorganic nanoparticles and polymers as the artificial SEI layer shows great potential in regulating lithium-ion flux. Here, we design spatially confined LiF nanoparticles in an aligned polymer matrix as the artificial SEI layer. A high dielectric polymer matrix homogenizes the electric field near the surface of lithium metal. Aligned pores with LiF nanoparticles promote the lithium-ion transport across the artificial SEI layer. The synergistic effect of the highly polar β-phase PVDF and LiF nanoparticles provides high stability over 900 h for the Li//Li symmetrical cell. Besides, a Li//LFP full battery equipped with this artificial layer shows good performance in the commercial carbonate electrolyte, demonstrating the great potential of this protective film in lithium metal batteries.