Poled Polyvinylidene Fluoride Research Articles

Stretching, Tapping, or Compressing–What Role Does Triboelectricity Play in the Signal Output from Piezoelectric Nanogenerators?

AbstractPiezoelectric energy generation is relevant for developing advanced electronics. However, the poor understanding of the influence of triboelectricity as an alternate charge generation mechanism has, in many cases, resulted in the reporting of exaggerated piezoelectric outputs. Herein, the signal output is systematically investigated from a range of organic piezoelectric materials (poled polyvinylidene fluoride (PVDF)), moderately piezoelectric (heat‐treated PVDF), and non‐piezoelectric (non‐poled PVDF), polytetrafluoroelthylene (Teflon) and nylon) under tapping and compression (33 direction) and stretching (31 direction) in both encapsulated and non‐encapsulated forms. This findings reveal that regardless of their piezoelectric properties, all tested materials exhibit substantial voltage outputs (4.2–4.6 V) during tapping, primarily attributed to the triboelectric effect at the contact interface. The triboelectric contribution to the signal is reduced by 99% in compression mode for non‐piezoelectric materials and the piezoelectric signal is the primary contributor in the stretching mode with a high signal output of 7.71 V N−1 for poled PVDF and a negligible signal (0.01–0.12 V N−1) for non‐piezoelectric materials. Moreover, elastomeric encapsulation is demonstrated to markedly increase triboelectric signals in tapping mode. These results have important implications for the future design of piezoelectric‐triboelectric devices and the accurate interpretation of the data obtained from such devices.

Poling induced changes in polarization domain structure of polymer ferroelectrics for application in organic thin film transistors

While electrical poling of organic ferroelectrics has been shown to improve device properties, there are challenges in visualizing accompanying structural changes. We observe poling induced changes in ferroelectric domains by applying differential phase contrast (DPC) imaging in the scanning transmission electron microscope, a method that has been used to observe spatial distributions of electromagnetic fields at the atomic scale. In this work, we obtain DPC images from unpoled and electrically poled polyvinylidene fluoride trifluorethylene films and compare their performance in polymer thin film transistors. The vertically poled films show uniform domains throughout the bulk compared to the unpoled film with a significantly higher magnitude of the overall polarization. Thin film transistors comprising a donor–acceptor copolymer as the active semiconductor layer show improved performance with the vertically poled ferroelectric dielectric film compared with the unpoled ferroelectric dielectric film. A poling field of 80–100 MV/m for the dielectric layer yields the best performing transistors; higher than 100 MV/m is seen to degrade the transistor performance. The results are consistent with a reduction in deleterious charge carrier scattering from ferroelectric domain boundaries or interfacial dipoles arising from electrical poling.

Scalable Fabrication of MXene-PVDF Nanocomposite Triboelectric Fibers via Thermal Drawing.

In the data-driven world, textile is a valuable resource for improving the quality of life through continuous monitoring of daily activities and physiological signals of humans. Triboelectric nanogenerators (TENG) are an attractive option for self-powered sensor development by coupling energy harvesting and sensing ability. In this study, to the best of the knowledge, scalable fabrication of Ti3 C2 Tx MXene-embedded polyvinylidene fluoride (PVDF) nanocomposite fiber using a thermal drawing process is presented for the first time. The output open circuit voltage and short circuit current show 53% and 58% improvement, respectively, compared to pristine PVDF fiber. The synergistic interaction between the surface termination groups of MXene and polar PVDF polymer enhances the performance of the fiber. The flexibility of the fiber enables the weaving of fabric TENG devices for large-area applications. The fabric TENG (3 × 2 cm2 ) demonstrates a power density of 40.8mW m-2 at the matching load of 8 MΩ by maintaining a stable performance over 12 000 cycles. Moreover, the fabric TENG has shown the capability of energy harvesting by operating a digital clock and a calculator. A distributed self-powered sensor for human activities and walking pattern monitoring are demonstrated with the fabric.

Janus electro-microenvironment membrane with surface-selective osteogenesis/gingival healing ability for guided bone regeneration.

Guided bone regeneration is widely applied in clinical practice to treat alveolar bone defects. However, the rate of healing of severe alveolar bone defects is slow, and there is a high incidence of soft tissue wound dehiscence. In this study, we propose a barrier membrane with a Janus electro-microenvironment (JEM) to achieve side-selective bone regeneration and soft tissue healing. The JEM membrane was constructed using a polarized polyvinylidene fluoride ferroelectric membrane with different surface potentials on either side. It promoted osteogenic differentiation and bone regeneration on the negatively polarized side (JEM-) and soft tissue regeneration on the positively polarized side (JEM+). Further investigation revealed that the JEM-mediated promotion of bone formation was related to mitochondrial autophagy, as indicated by depolarization of the mitochondrial membrane potential and the expression of LC3, Pink I, and Parkin. Moreover, the gingival healing promoted by JEM+ was related to oxidative phosphorylation in mitochondria, as indicated by the upregulation of mitochondrial complexes I-V and an increase in ATP generation. The design concept of the JEM provides a new avenue for regulating tissue regeneration between different tissue interfaces.

Effect of sampling duration on culturable and viable bioaerosol determination when using Rutgers Electrostatic Passive Sampler (REPS)

Rutgers Electrostatic Passive Sampler (REPS) is a passive bioaerosol sampler composed of a permanently polarized polyvinylidene fluoride (PVDF) film wound into a 3D printed film holder. In order to investigate the effect of sampling duration on its performance, REPS was deployed in an indoor and outdoor location in Spring and Fall over continuing sampling periods ranging from 24 h to 21 days. Reference concentrations were determined by an active, culture-based sampler twice daily. REPS samples were analyzed for culturable bacteria and fungi as well as adenosine triphosphate (ATP) activity. The number of culture forming units (CFU) determined by REPS exhibited strong and positive correlations with sampling duration for culturable bacteria (Pearson r > 0.899, p < 0.05) and fungi (r > 0.902, p < 0.05) for both test locations. Similar results were observed for ATP activity in outdoor samples (r > 0.844, p < 0.05). REPS showed an equivalent flow rate (Qeq) as high as 4.86 ± 4.90 L/min when sampling bacteria outdoors. When sampling bacteria indoors, the Qeq was lower: 0.37 ± 0.78 L/min. When sampling fungi, the Qeq outdoors was also higher than that indoors. Overall, the study demonstrated that REPS is able to effectively capture airborne culturable bacteria and fungi by passive means of collection in indoor and outdoor environments while maintaining bioaerosol culturability for over 21 days of continuous sampling. Further studies will explore methods to improve the sample detection limit by using different sample concentration techniques as well as the sampler's integration with the next-generation sequencing techniques.

Nonflammable, robust and flexible electrolytes enabled by phosphate coupled polymer–polymer for Li-metal batteries

Liquid organic electrolytes commonly employed in commercial Li-ion batteries suffer from safety issues such as flammability and explosions. Replacing liquid electrolytes with nonflammable electrolytes has become increasingly attractive in the development of safe, high-energy Li-metal batteries (LMBs). In this work, nonflammable, robust, and flexible composite polymer–polymer electrolytes (PPEs) were successfully fabricated by flame-retardant solution casting with polyimide (PI) and polyvinylidene fluoride (PVDF). The optimized nonflammable PPEs (e.g., PPE-50) demonstrate not only good mechanical properties (i.e., a high tensile strength of 29.6 MPa with an elongation at break of 87.2%), but also high Li salts dissolubility, the former of which ensures the suppression of Li dendrites, while the latter further improves the ionic conductivity (∼1.86 × 10−4 S cm−1 at 30 °C). The resulting symmetric cells (Li|PPE-50|Li) offer excellent Li stripping and plating stability for 1000 h at 0.5 mA cm−2/0.25 mAh cm−2 and 600 h at 2.0 mA cm−2/1.0 mAh cm−2. In addition, the LiFePO4|PPE-50|Li half cells show high cycling performance (e.g., a reversible discharge capacity of 135.9 mAh g−1 after 300 cycles at 1C) and rate capability (e.g., 117.2 mAh g−1 at 4C). The PPE-50 is also compatible with a high-voltage cathode (e.g., LiNi0.5Mn0.3Co0.2O2), and the resulting batteries demonstrate long-term cycling stability with a high cut-off voltage of 4.5 V vs. Li/Li+. Because of the incorporation of a mechanically robust and thermally stable PI, a polar PVDF, and flame-retardant trimethyl phosphate (TMP) within PPEs, as well as the coordination between Li salts and TMP, and the interaction between Li salts and polymers (especially between Li bis(oxalato)borate) and PI, as well as the bis(oxalato)borate anion and PI), PPEs show great potential for practical and high-energy LMBs without safety concerns.

Simultaneous enhancement of specific capacitance and potential window of graphene-based electric double-layer capacitors using ferroelectric polymers

Despite their high power density, aqueous-based electric double-layer capacitors (EDLCs) possess relatively low energy density due to the limitation of potential window (~1.0 V) and low specific capacitance of active materials. To increase the energy density without sacrificing the power density, it is highly desired to achieve a simultaneous improvement of both specific capacitance and potential window of EDLCs. However, this remains a major challenge that is not been solved up to date. This work demonstrates that by inserting a polarized-polyvinylidene fluoride (PVDF) ferroelectric layer underneath the graphene, a simultaneous enhancement of both areal capacitance and potential window is achieved, in which the areal capacitance increases from 5.5 to 7.5 μF/cm 2 ( i.e. , 36%) (or 55 F/cm 3 to 75 F/cm 3 in terms of volumetric capacitance), and the potential window expands from 1.0 V to 1.5 V. This results in a threefold increase in the areal energy density of the capacitor. The enhancement in capacitance can be explained by the Gouy–Chapman–Stern model. The widening of potential window is due to the shift of the Fermi level of graphene caused by the doping effect of the polarized-PVDF layer. • Graphene capacitor is designed with polarized PVDF. • Increases the areal capacitance and potential window of graphene capacitors. • The areal capacitance increases 36% compared to without polarized PVDF. • The potential window increases from 1.0 V to 1.5 V.

Design and simulation of piezoelectric nano cylindrical hollow structure for energy harnessing applications

Abstract This article investigates piezoelectric materials for harnessing vibrational energy. A nano hollow cylindrical structure based on various piezoelectric materials was designed and utilised to generate the voltage. An accurate and efficient model is developed here, so as to optimized the efficiency of the piezoelectric energy harvester. This work analyses the piezoelectric actuator deflection and involves the Eigen frequency computation. A measurement methodology for investigating the mechanical and electrical behaviour of vibrational harvester's was modelled and analysed by finite element method using COMSOL software. The energy harvesting structure was developed and tested with different piezoelectric materials to attain appreciable voltage through a small deflection. The Simulated results predicts that for the same pressure range, different piezoelectric materials have the different output voltage and Eigen frequencies. The maximum voltage was observed for Barium Titanate (3.0847 V at 250 µm), along with poled Polyvinylidene fluoride. In addition, a comparison was made with different piezoelectric materials ideally suited to intelligent cantilever structure. For optimizing the performance of the piezoelectric energy harvester an accurate and efficient model is required, which was developed in this simulation study. A high voltage value with a small deflection through a cylindrical hollow structure was designed and tested using various piezoelectric materials in this study.

Diphenylalanine-Derivative Peptide Assemblies with Increased Aromaticity Exhibit Metal-like Rigidity and High Piezoelectricity.

Diphenylalanine (FF) represents the simplest peptide building block that self-assembles into ordered nanostructures with interesting physical properties. Among self-assembled peptide structures, FF nanotubes display notable stiffness and piezoelectric parameters (Young’s modulus = 19–27 GPa, strain coefficient d33 = 18 pC/N). Yet, inorganic alternatives remain the major materials of choice for many applications due to higher stiffness and piezoelectricity. Here, aiming to broaden the applications of the FF motif in materials chemistry, we designed three phenyl-rich dipeptides based on the β,β-diphenyl-Ala-OH (Dip) unit: Dip-Dip, cyclo-Dip-Dip, and tert-butyloxycarbonyl (Boc)-Dip-Dip. The doubled number of aromatic groups per unit, compared to FF, produced a dense aromatic zipper network with a dramatically improved Young’s modulus of ∼70 GPa, which is comparable to aluminum. The piezoelectric strain coefficient d33 of ∼73 pC/N of such assembly exceeds that of poled polyvinylidene-fluoride (PVDF) polymers and compares well to that of lead zirconium titanate (PZT) thin films and ribbons. The rationally designed π–π assemblies show a voltage coefficient of 2–3 Vm/N, an order of magnitude higher than PVDF, improved thermal stability up to 360 °C (∼60 °C higher than FF), and useful photoluminescence with wide-range excitation-dependent emission in the visible region. Our data demonstrate that aromatic groups improve the rigidity and piezoelectricity of organic self-assembled materials for numerous applications.

Theoretical Model and Outstanding Performance from Constructive Piezoelectric and Triboelectric Mechanism in Electrospun PVDF Fiber Film

AbstractFlexible materials with high electromechanical coupling performance are highly demanded for wide applications for electromechanical sensors and transducers, including mechanical energy harvesters. Here, outstanding electromechanical performance is obtained in electrospun‐aligned polyvinylidene fluoride (PVDF) fiber film. A theoretical model is developed from systematic theoretical analyses to clarify the underlying constructive piezoelectric‐triboelectric mechanism in the polarized PVDF fiber films that explains the experimental observations well. The electrospinning process induces polarization alignment and thus tunes the electron affinity for PVDF fibers with different polarization terminals, which results in the constructive piezoelectric and triboelectric responses in the obtained PVDF fiber films. Extremely large effective piezoelectric performance properties are achieved in the direct piezoelectric measurements, reaching the maximum effective piezoelectric strain and voltage coefficients of −1065 pm V−1 and −9178 V mm N−1, respectively, at 100 Hz. In the converse piezoelectric measurements without a significant contribution from reversible triboelectric effect, the maximum effective piezoelectric strain and voltage coefficients are −166 pm V−1 and −1499 V mm N−1, respectively. The theoretical analyses and experimental results show the great potential of the electrospun aligned polar PVDF fiber material for various electromechanical device applications, particularly for mechanical energy harvesting.

A wearable solar-thermal-pyroelectric harvester: Achieving high power output using modified rGO-PEI and polarized PVDF

Abstract Harvesting solar energy via pyroelectric technology is highly desired because it is a sustainable and clean solution to yield electricity. However, the low power output (below 5mW/m2) and bulky device design of traditional devices hinder their practical applicability. Herein, we demonstrate a highly efficient sunlight-triggered pyroelectric nanogenerator (S-PENG) design that achieves unprecedented performance of 21.3 mW/m2 under one sun irradiation. This is achieved via enhancing both the solar harvesting properties and the pyroelectric efficiencies rationally by employing polyethyleneimine (PEI) chemically modified reduced graphene oxide (rGO-PEI), and a pyroelectric layer based on a polarized polyvinylidene fluoride (PVDF) film respectively. Moreover, we demonstrate its practical application by adapting the S-PENG into a wearable outdoor bracelet. Using a facile hand-waving motion to replace the traditional bulky sunlight-alternating device, our compact bracelet can charge a fitness tracker after only 1 h of outdoor exposure, demonstrating its capability to be seamlessly integrated with outdoor sports activities. We expect our rational design to promote the development of S-PENG and pave the way for the utilization of sunlight as a viable on-the-go electrical source.

Calibration of polyvinylidene fluoride based dust detectors in response to varying grain density and incidence angle.

Permanently polarized Polyvinylidene Fluoride (PVDF) films have been used on a variety of spacecraft as in situ dust detectors to measure the size and spatial distributions of micron and sub-micron dust particles. The detectors produce a short electric pulse when impacted by a hypervelocity dust particle. The pulse amplitude depends on the mass and relative speed of the dust grain. This relationship has been studied both empirically and numerically to better understand the film's principle of operation, as well as the effects of film thickness, film temperature, and particle penetration depth. However, little work has been done to constrain the effects of varying particle density and incidence angle despite the frequent occurrence of such configurations in most space-based applications. We present calibrations of non-penetrating impacts on 28 μm thick films at varying incidence angles ranging from 0° to 75° for iron and aluminum particles in the mass and speed range of 10-12 ≤ m ≤ 10-8 g and 0.5 ≤ v ≤ 7 km/s, respectively. The study was carried out at the 3 MV dust accelerator laboratory at the University of Colorado at Boulder. The results show that PVDF signals are largely independent of particle density and incidence angle up to 75° for non-penetrating impacts.

Does the Type of Polymer and Carbon Nanotube Structure Control the Electromagnetic Shielding in Melt-Mixed Polymer Nanocomposites?

A suitable polymer matrix and well dispersed conducting fillers forming an electrically conducting network are the prime requisites for modern age electromagnetic shield designing. An effective polymer-based shield material is designed that can attenuate 99.9% of incident electromagnetic (EM) radiation at a minimum thickness of &lt;0.5 mm. This is accomplished by the choice of a suitable partially crystalline polymer matrix while comparing non-polar polypropylene (PP) with polar polyvinylidene fluoride (PVDF) and a best suited filler nanomaterial by comparing different types of carbon nanotubes such as; branched, single-walled and multi-walled carbon nanotubes, which were added in only 2 wt %. Different types of interactions (polar-polar and CH-π and donor-acceptor) make b-MWCNT more dispersible in the PVDF matrix, which together with high crystallinity resulted in the best electrical conductivity and electromagnetic shielding ability of this composite. This investigation additionally conceals the issues related to the thickness of the shield material just by stacking individual thin nanocomposite layers containing different carbon nanotube (CNT) types with 0.3 mm thickness in a simple manner and finally achieves 99.999% shielding efficiency at just 0.9 mm thickness when using a suitable order of the different PVDF based nanocomposites.

Dielectric Properties of γ‐Iirradiated, Stretched, and Poled PVDF Thin Films

AbstractThe effects of γ‐irradiation on the dielectric properties of stretched and poled polyvinylidene fluoride thin films synthesized by solvent cast method are reported. The films are subjected to γ‐irradiation with different doses (25, 50, and 75 kGy). XRD pattern is obtained to identify the presence of α/β phases. Dielectric constant and loss values of the stretched and poled films have been measured, before and after irradiation, and their nature of variation has been studied. β phase is retained even after the irradiation thereby confirming that the radiation damage is not significant. The dielectric loss is minimum in the frequency range 102 to104 Hz, giving the preferable frequency range of operation for devices

Hand clapping inspired integrated multilayer hybrid nanogenerator as a wearable and universal power source for portable electronics

We report a human skin-based wearable and hybrid triboelectric-piezoelectric nanogenerator (HTEPENG) for harvesting biomechanical energy from hand clapping to eliminate the need for batteries to drive portable electronic devices. Through smart integration of polyimide encapsulated polarized polyvinylidene fluoride (PVDF) film between two nanopillar polydimethylsiloxane (n-PDMS) films, the hybrid nanogenerator can produce two triboelectric outputs and one piezoelectric output simultaneously upon a single clap. The output performances of the HTEPENG have been optimized through systematic analysis and experimental validation of the surface morphology and coupling effect of interfacing materials. The as-fabricated HTEPENG device delivers a peak power density of 3.7 W/m2 at a matched resistance of 23.08 MΩ. After the use of a custom-designed power conversion and management system (PCMS), the nanogenerator was able to drive a commercial pedometer and successfully recharged a trimmer, pocket Wi-Fi router, and smartphone individually, which might speed up commercialization of the wearable nanogenerators. Furthermore, the HTEPENG possesses a unique characteristic of modulated multi-level outputs, which has the potential to bring extensive application prospects in the field of logic devices, power supply, prosthetics, antistatic protection, and self-powered sensor networks. Even though clapping is a natural human activity to applaud somebody which is very common in many environments like a concert, theatre, and stadium, it is also well known to improve the overall human health by improving the blood circulation to various organs. Thereby, other than serving as a universal power source, the proposed hybrid nanogenerator can promote additional health benefit for the human.

Hybrid local piezoelectric and conductive functions for high performance airborne sound absorption

A concept of hybrid local piezoelectric and electrical conductive functions for improving airborne sound absorption is proposed and demonstrated in composite foam made of porous polar polyvinylidene fluoride (PVDF) mixed with conductive single-walled carbon nanotube (SWCNT). According to our hybrid material function design, the local piezoelectric effect in the PVDF matrix with the polar structure and the electrical resistive loss of SWCNT enhanced sound energy conversion to electrical energy and subsequently to thermal energy, respectively, in addition to the other known sound absorption mechanisms in a porous material. It is found that the overall energy conversion and hence the sound absorption performance are maximized when the concentration of the SWCNT is around the conductivity percolation threshold. For the optimal composition of PVDF/5 wt. % SWCNT, a sound reduction coefficient of larger than 0.58 has been obtained, with a high sound absorption coefficient higher than 50% at 600 Hz, showing their great values for passive noise mitigation even at a low frequency.

Measuring of foot plantar pressure—possible applications in quantitative analysis of human body mobility

The paper presents an evaluation of human mobility by gait analysis, carried out in natural conditions (outside of the laboratory). Foot plantar pressure is measured using a shoe insole with 8 sensors placed in different anatomical zones of the foot, and placed inside a sports shoe. Polarized polyvinylidene fluoride (PVDF) foil is used as a sensor material. A wireless transmission system is used to transmit voltage values to the computer. Miniaturization was the priority during the design of the system. Due to the linear relationship between force and transducer voltage, energy and power released during walking in arbitrary units can be calculated as an integral of the square of the transducer voltage over time. Gait measurements were carried out over several days on healthy persons during normal walking and slow walking. The performed measurements allowed for the determination of walking speed (number of steps per second), gait rhythm and manner of walking (applying force to inside versus outside part of the sole). It was found that switching from normal to slow walk increases gait energy by 25% while the pressure distribution across the anatomical regions of the foot remains unchanged. The results will be used to develop a programme for the evaluation of patients with orthopedic diseases or even with cardiac failures, for an estimation of the results of health recovery and training efficiency in many sports activities.

Polyvinylidene fluoride/hydroxyapatite/β-tricalcium phosphate multifunctional biocomposite: Potentialities for bone tissue engineering

Bioactive ferroelectric composites based on polyvinylidene fluoride, hydroxyapatite and β-tricalcium phosphate have been synthesized and their structural, microstructural, bioactive, and ferroelectric properties are characterized. Structural and FTIR investigations showed the presence of the polar polyvinylidene fluoride (β2) phase, while ferroelectric characterizations revealed remnant polarizations and coercive field, around 0.04 μC/cm2 and 28 kV/cm, respectively, for these biocompatible samples. Structural and microstructural analysis of samples previously immersed in simulated body fluid for 7 days revealed a large apatite phase growth (1.45 μm) on the composites' surfaces as a strong indication of their elevated bioactivity and potentialities for bone tissue engineering.

Free-standing nanocrystalline-Cadmium sulfide/Polyvinylidene fluoride composite thin film: synthesis and characterization

Nanocrystalline Cadmium sulfide (CdS) impregnated polyvinylidene fluoride (PVDF) composite free-standing flexible films were prepared by sol–gel technique. The films were poled in vacuum under high electric field. Effect of CdS loading in PVDF host matrix on the optical properties was studied critically for the as-deposited and poled samples. The reduction in the relative intensities of the peaks arising out of α -PVDF as compared to that of β-PVDF for the poled samples was observed in X-ray diffraction (XRD) studies. This type of observation indicates a possible transition from α to β phase due to poling. Modulation of optical and microstructural properties with CdS loading was also addressed. Bonding environment was studied by X-ray photoelectron spectroscopy (XPS) and Fourier transformed infrared spectroscopy measurements. XPS studies indicated the presence of highly aligned CdS nanocrystallites in the poled PVDF matrix which may effectively modulate the piezoelectric behavior of the composite film. The Photoluminescence (PL) spectra recorded as above for a representative unpoled and poled nano-CdS/PVDF composite film.

Dipole-moment-induced effect on contact electrification for triboelectric nanogenerators

Triboelectric nanogenerators (TENGs) have been demonstrated as an effective way to harvest mechanical energy to drive small electronics. The density of triboelectric charges generated on contact surfaces between two distinct materials is a critical factor for dictating the output power. We demonstrate an approach to effectively tune the triboelectric properties of materials by taking advantage of the dipole moment in polarized polyvinylidene fluoride (PVDF), leading to substantial enhancement of the output power density of the TENG. The output voltage ranged from 72 V to 215 V under a constant contact force of 50 N. This work not only provides a new method of enhancing output power of TENGs, but also offers an insight into charge transfer in contact electrification by investigating dipole-moment-induced effects on the electrical output of TENGs.