PVDF Nanofibers Research Articles

Hybrid Piezoelectric/Triboelectric Wearable Nanogenerator Based on Stretchable PVDF-PDMS Composite Films.

Hybrid piezoelectric/triboelectric nanogenerators combine the merits of piezoelectric nanogenerators (PENGs) and triboelectric nanogenerators (TENGs), possessing enhanced electrical output and sensitivity. However, the structures of the majority of hybrid nanogenerators are rather complex in integrating both functions, limiting their practical application in wearable electronics. Herein, we propose to construct a piezoelectric/triboelectric hybrid nanogenerator (PT-NG) with a simple structure based on a composite film to simultaneously achieve the coupling of piezoelectric charge generation and triboelectrification with improved energy conversion efficiency. The composite film consists of electrospun PVDF nanofibers embedded in the surface of the PDMS film, which not only forms a rough nanomorphology on the surface of PDMS but also provides structural protection to the PVDF nanofibers by PDMS during compressive deformation. The results have shown that the PT-NG can generate much higher electrical outputs than individual TENG and PENG devices. The PT-NG devices exhibit a high level of mechanical-to-electrical energy conversion efficiency with superior performance in charging capacitors and functioning as self-powered wearable sensors for the detection of different signals from finger movement, the recognition of various gestures, and the monitoring of respiration. More importantly, the composite device possesses an impressive structure durability, maintaining its layered structure over 5000 testing cycles without noticing any obvious damage on the nanofibers or detachment between the layers. Our results have demonstrated that the combining of piezoelectric nanofibers and triboelectric substrate is an efficient way to fabricate highly efficient energy harvesting devices for intelligent identification and health monitoring.

Fully Transparent Flexible Piezoelectric Sensing Materials Based on Electrospun PVDF and Their Device Applications

AbstractAdvanced transducer materials have become increasingly important with the rapid development of the internet of things and flexible electronics. Herein, fully transparent flexible polyvinylidene fluoride/polydimethylsiloxane (PVDF/PDMS) composite piezoelectric films are fabricated using scrape coating techniques based on electrospun PVDF nanofiber films. Compared to the electrospun PVDF, the PVDF/PDMS not only owns high transparency and a more uniform and stable structure but also has superior piezoelectric properties. Based on the electrospun PVDF and the PVDF/PDMS films, flexible piezoelectric sensors are developed, which can effectively detect weak mechanical signals including finger tapping and bending signals, radial artery pulses, and environmental sound signals. The PVDF/PDMS sensor performs better than the electrospun PVDF sensor and presents great potential for applications in flexible sensors and transducers. Especially, thanks to their high transparency, the PVDF/PDMS composite piezoelectric films lend themselves easily to application fields requiring transparent sensors such as imperceptible sensors and human‐machine interfaces, display devices, electronic skins, intelligent windows, etc.

Developing a Model to Improve the Efficiency of Maintenance Management for Service Buildings Using BIM and Power BI: A Case Study

Developing a Model to Improve the Efficiency of Maintenance Management for Service Buildings Using BIM and Power BI: A Case Study

Preparation and Characterization of Polymer-Based Electrospun Nanofibers for Flexible Electronic Applications

This study was undertaken to synthesize and characterize PVDF/CB (polyvinylidene fluoride/carbon block) nanofiber composites for flexible, wearable electronic applications. Nanofibers were produced by electrospinning method and used to produce thin films. Fiber surface morphologies were investigated by FE-SEM and HR-TEM, crystalline structures by FT-IR and P-XRD, and thermal characteristics by TGA and DSC. The prepared materials are thermally stable up to 390 °C. Mechanical properties were ascertained using tensile characteristics, and results showed that the addition of carbon black (CB) powder to PVDF polymer solution decreased Young’s modulus values and reduced the dielectric constant of PVDF nanofiber films. The obtained dielectric constants of nanofibers loaded with various concentrations of CB were found from 1.4 to 2.0. Flexible electronics materials are essential for the production of wearable electronics and various biomedical engineering applications. The PVDF/CB nanofibers containing 1% showed maximum Young’s moduli of 101.29 ± 15.94. Nanofiber thin films offer various advantages, including simplicity of manufacture, low power consumption, flexibility, and exceptional stability, all of which are crucial for flexible, wearable device applications.

Preparation and Optimization of Novel Anisotropic Proton-Exchange Membranes with Enhanced through-Plane Conductivity

Maximizing through-plane (TP) conductivity, as opposed to in-plane (IP), is desired for proton exchange membranes (PEMs) in fuel cells, electrolysis and electrodialysis. Nafion, the benchmark PEM material, owes conductivity to randomly oriented ion-channels. Channel alignment in electrospun nanofibers was shown to enhance conductivity along the fibres by an order of magnitude, but it proved challenging to convert this to desired stable TP conductance. Another challenge is that orientation proves unstable and returns to random after nanofiber consolidation.Previously, we reported fabrication of electrospun nanofiber-based membrane with a stable anisotropic TP alignment of proton conducting channels prepared by co-spinning, buckling and fusion of Nafion and PVDF nanofibers (Odess, Li et al, ACS Appl Mat Interfaces, 2021), as shown in Figure 1. PVDF nanofibers serve as a mechanical reinforcement as well as a stabilizing component to safeguard Nafion TP alignment during annealing and swelling, akin to a solid template. However, the prepared 50% Nafion membrane still showed a TP conductivity slightly inferior to Nafion.In this report, we systematically optimized the Nafion content in the 50-80% range, as well as buckling and consolidation procedure and its temperature regime, to achieve a maximal and sustained conductance, exceeding that of pure Nafion. It was found that the TP proton conductivity of the membrane with 60% Nafion already exceeded that of Nafion 117 and further increased with Nafion content (Figure 1), with decrease in anisotropy (TP/IP conductance ratio). As another attractive feature, compared with Nafion 117, the TP conductivity of aligned membranes decreased less at lower humidity, i.e., was less sensitivity to dehydration, apparently due to better channel connectivity. Anisotropic structure and nanoscopic alignment were further confirmed by TEM and SAXS. The results demonstrate the potential of the new buckling approach for making novel nanofiber-based anisotropic membranes with significantly improved performance in electromembrane applications. Figure 1

A Stretchable and Strain‐Limiting, Bio‐Inspired Nanofiber‐Reinforced Microfiber for Wearable Electronics

AbstractWith existing fiber‐based approaches for wearable electronics, devices with limited stretchability are not fully protected against large stretching when the wearer is participating in vigorous activities. A network of elastin and collagen fibers makes biological tissues elastic at low strains and strain‐limiting at high strains, showing a J‐shaped stress‐strain behavior. Stretchable systems can replicate a “J‐shaped stress‐strain/strain‐limiting” mechanical behavior of biological tissues under deformations and provide mechanical compliance and comfort to wearers. For mimicking this mechanical behavior of biological tissues, he developed a combined microfiber and nanofiber (NF)‐based approach. The soft polyurethane (PU) microfiber mimicking elastin of biological tissue is wrapped with stiff poly(vinylidene fluoride)(PVDF) NFs, mimicking collagen in tissue, and dip coated in polydimethylsiloxane (PDMS). Confocal images during stretching confirmed that the PU microfiber maintained stretchability, while the stiff PVDF NFs played a role in the strain‐limiting characteristics. By tailoring a loading ratio of the PVDF NFs on the PU microfiber, the elastic modulus is matched well with those of biological tissues. The stretchable conducting coating and temperature sensor on the bio‐inspired microfiber showed a negligible difference in a current‐time (I‐T) response during static and dynamic stretching which indicated the efficient absorption of stress by the bio‐inspired microfiber.

Ternary liquid separation using PVDF nanofiber membranes with tunable structure and surface tension

Ternary liquid separation using PVDF nanofiber membranes with tunable structure and surface tension

PVDF Nanofiber Modified with ZnO Nanowires/Polydopamine for the Treatment of Sewage Containing Heavy Metals, Organic Dyes, and Bacteria.

In various countries worldwide, the issue of wastewater contamination poses a significant threat due to its intricate composition of heavy metals, organic dyes, and microorganisms, thereby complicating the purification process. Consequently, researchers have expressed considerable interest in materials capable of eliminating organic, heavy metal, and microbial pollutants. This study focuses on the fabrication of a water purification membrane (PDA/ZnO-NWs/PVDF) with a hierarchical structure and the ability to remove multiple pollutants. The membrane was created by modifying poly(vinylidene fluoride) (PVDF) nanofiber with zinc oxide nanowires (ZnO-NWs) and reinforcing it with polydopamine (PDA). The experimental results demonstrate that the PDA/ZnO-NWs/PVDF membrane exhibits a range of functionalities, including long-lasting superhydrophilicity, Cu(II) adsorption, photocatalytic degradation, and antibacterial ability. The manipulation of the DA synthesis procedure allows for the adjustment of the wettability, adsorption, and photocatalytic and antibacterial activities of the PDA/ZnO-NWs/PVDF composite. According to the Langmuir isotherm, the maximum Cu(II) adsorption capacity of the PDA/ZnO-NWs/PVDF membrane is determined to be 65.75 mg/g, which is significantly higher (27.26 mg/g) than that of the ZnO-NWs/PVDF membrane (38.49 mg/g). The PDA/ZnO-NWs/PVDF composite exhibited a notable degradation capacity toward rhodamine B under natural sunlight, reaching a maximum of 5.97 mg/g. Additionally, the degradation rate achieved during daylight hours was as high as 90.42%. Furthermore, the antibacterial efficacy of the PDA/ZnO-NWs/PVDF composite against both Gram-positive and Gram-negative bacteria approached 100%. This work presents a promising approach for the treatment of wastewater containing various coexisting contaminants.

Self‐standing piezoelectric nanogenerator fabrics from ZnO‐doped PVDF nanofiber yarns

AbstractToday a wide variety of wearable electronics are in our daily lives and their uses are increasing. The development of portable, flexible, lightweight, cost‐effective, and stable devices that produce sustainable energy with renewable approaches in the field of wearable electronics, as in every field, is one of the important issues of today. According to their volume and weight, the use of nanofibers with high surface area in energy‐generating devices may bring them advantages such as lightness and higher energy density. Therefore, in recent years, researchers have focused on the development of nanofiber‐based nanogenerators that produce energy using mechanical energy in a sustainable and renewable way. In this paper, self‐standing piezoelectric nanogenerator (PENG) fabrics were obtained by developing flexible composite poly(vinylidene fluoride) (PVDF) nanofiber yarns doped with zinc oxide (ZnO) nanoparticles at different rates to provide higher power output. It has been characterized from electromechanical, structural, and morphological aspects. The most successful self‐standing PENG fabric obtained (at 5% ZnO loading) doubled the energy output of the fabric made from pure PVDF nanofiber yarn and provided a peak total power of 81 μW and a power density of 30 μW/cm2. The present results open up the field for the development of PVDF/ZnO‐based nanomats and their use in sensors and actuators in the healthcare and engineering industries.

Statistical Modeling and Optimization of Electrospinning for Improved Morphology and Enhanced β-Phase in Polyvinylidene Fluoride Nanofibers.

The fabrication of PVDF-based nanofiber mats with enhanced β-phase using electrospinning and post processing was optimized using Taguchi design methodology. The parameters studied include the concentration of PVDF in the DMF (Dimethylformamide) solvent, applied voltage, flow rate, and drum speed. A reliable statistical model was obtained for the fabrication of bead-free PVDF nanofibers with a high fraction of β-phase (F(β)%). The validity of this model was verified through comprehensive regression analysis. The optimized electrospinning parameters were determined to be a 23 wt% PVDF solution, 20 kV voltage, a flow rate of 1 mL/h, and a drum speed of 1200 revolutions per minute.

Mechanically Robust and Electrically Stable High-Performance Triboelectric Nanogenerator Based on Fluffy-Free EC/Nylon-11 and PTFE/PVDF Nanofibers.

Electrospun nanofiber (NF)-based triboelectric nanogenerators (TENGs) have attracted significant attention in recent years due to their high specific surface area, flexibility, and facile fabrication. However, these TENGs' triboelectric (TE) layers composed of electrospun NFs fail easily due to the poor mechanical properties and fluffy characteristics of the NFs. Herein, electropositive and electronegative TE layers based on ethylcellulose-coated nylon-11 (EC/nylon-11) NFs and polytetrafluoroethylene-coated poly(vinylidene fluoride) (PTFE/PVDF) NFs are prepared via electrospinning and postcoating processes. The obtained EC/nylon-11 and PTFE/PVDF NFs are fluffy-free and exhibit 12.26 and 20.33-fold enhancements of Young's modulus compared with those of pure nylon-11 and PVDF NFs, respectively. The optimized TENG exhibits not only superior performance, including an open-circuit voltage (VOC) of 212 V, a short-circuit current (ISC) of 18.5 μA, and a maximum power density of 1.76 W/m2 but also excellent electrical durability for over 100,000 cycles. The TENG's capability is further demonstrated by continuously driving electronics for over 5 min and by being integrated into a self-powered sensor array of electric skin to detect different in vitro stimuli. This work provides an effective approach to obtaining mechanically robust and electrically stable NF-based high-performance TENGs, which may have potential applications in durable, wearable, and self-powered nanoelectronics.

Production of Ultrafine PVDF Nanofiber-/Nanonet-Based Air Filters via the Electroblowing Technique by Employing PEG as a Pore-Forming Agent.

Particles with diameters smaller than 2.5 μm (PM2.5) can penetrate the respiratory system and have negative impacts on human health. Filter media with a porous surface and nanofiber/nanonet structure demonstrate superior filtration performance compared to traditional nano- and microfiber-based filters. In this study, nanostructured filters were produced using the electroblowing method from solutions containing different ratios of poly(vinylidene fluoride) (PVDF) and polyethylene glycol (PEG) polymers for the first time. By increasing the water-soluble PEG ratio in PVDF/PEG blend nanofibers and employing a water bath treatment to the produced mat afterward, a more porous fibrous structure was obtained with a lower average fiber diameter. Notably, the removal of PEG from the PVDF/PEG (3-7) sample, which had the highest PEG content, exhibited clustered nanofiber-/nanonet-like structures with average diameters of 170 and 50 nm at the points where the fibers intersect. Although this process resulted in a slight decrease in the filtration efficiency (-1.3%), the significant reduction observed in pressure drop led to a 3.2% increase in the quality factor (QF). Additionally, by exploiting the polarizability of PVDF under an electric field, the filtration efficiency of the nanostructured PVDF filters enhanced with a ratio of 3.6% after corona discharge treatment leading to a 60% improvement in the QF. As a result, the PVDF/PEG (3-7) sample presented an impressive filtration efficiency of 99.57%, a pressure drop (ΔP) of 158 Pa, and a QF of 0.0345 Pa-1.

A biocompatible and antibacterial all-textile structured triboelectric nanogenerator for self-powered tactile sensing

With the rapid development of cutting-edge technologies, self-powered breathable wearable electronic textiles have received significant attention because of portable and convenient power sources. In this work, a biocompatible and antibacterial all-textile structured triboelectric nanogenerator was designed for self-powered tactile sensing, constructed by the MXene doped PVDF (P/M) nanofibers and the antibacterial Ag nanoparticles modified nylon 6,6 (Ag@nylon 6/6) nanofibers as the triboelectric negative and positive materials, respectively. The effect of MXenes in PVDF nanofibers for its mutual interaction, surface potential, breathability, tensile strength, biocompatibility, and triboelectric performance was evaluated thoroughly through experimental and theoretical investigations. As developed P/M nanofiber film was paired with tribopositive Ag@nylon 6/6 nanofibers to fabricate the TENG, exhibiting a high output voltage of 362 V and an output current of 38.5 μA. The triboelectric harvesting properties were further demonstrated by capacitor charging and the operation of low power devices such as the clock, 95 commercial LEDs. In addition, a self-powered tactile sensor based on the Ag@nylon 6,6 and P/M fibrous membranes realizes ultrasensitive motion and pulse detection from different arteries, and the fabricated tactile sensor array shows a great potential in the application of smart wearable keyboard as well as high-resolution tactile mapping.

A sulfonated polydopamine coated-PVDF membrane development for oil/water separation via eco-friendly methodology

Here we report on the successful super-oleophobic membrane, a key approach to improving the reusable oil-water separation with high water flux abilities avoiding the critical drawbacks of super-oleophilic membranes such as oil-retention and low water flux. In the development, we used a durable hydrophilic-based PVDF membrane modified by sulfonated polydopamine via the in-situ polymerization method using an eco-friendly solvent, ethanol. In this study, an ultra-thin sulfonated polydopamine (SPD) layer was coated onto PVDF nanofiber creating PVDF-SPD by varying coating time for obtaining improved super-hydrophilic membrane. The final 24 h in-situ polymerized coated membrane, PVDF-SPD24h exhibited excellent oil/water separation performed with 36,000 Lm−2h−1 of water flux and 99% of separation efficiency. It remains at ∼97.8% of separation efficiency even after 30 filtration recycles with test mixture. In addition, the PVDF-SPD24h membrane also demonstrated relevant performance in harsh acid and alkaline media with less than 3 wt% of weight loss after 48 h of treatment at 80 °C. These results suggest that PVDF-SPD24h could be sustainable membrane for oily wastewater treatment purposes.

Oil-water receiving membrane with sub-10 nm surfactant layer for long-lasting oil-water separation

Oil fouling is an inherent threaten of membrane-based separation of oil-water emulsion, while common physical sieving membrane separation and coalescence demulsification fail to achieve long term applications and combat severe water flux declines. We hereby report an “oil-water-receiving” membrane with anomalous wettability constructed by sub-10 nm Tween 80 assembly on hydrophobic PVDF nanofibers to establish independent water and oil transmembrane passageway. Water can go through the membrane freely along the hydrophilic nanofiber surface. While emulsified oils were diverted beneath the ultra-thin hydrophilic layer and captured by PVDF bulk to form coalesced oil phase and discharged out of the nanofibrous membrane as continuous macroscopic oil phase. The membrane showed stable permeate flux as high as 536 ± 40 L m−2 h−1 bar−1 after 10 h of continuously filtering oil-in-water emulsions. The conformation assembly of surfactants with hydrophilic and hydrophobic chains provides a new strategy to fabricate anti-fouling membranes for oil/water separation.

Flexible Self-Powered Friction Piezoelectric Sensor Based on Structured PVDF-Based Composite Nanofiber Membranes.

With the rapid development of the economy and technology, intelligent wearable devices have gradually entered public life. Flexible sensors, as the main component of wearable devices, have been widely concerned. However, traditional flexible sensors need an external power supply, lacking flexibility and sustainable power supply. In this study, structured poly(vinylidene fluoride) (PVDF)-based composite nanofiber membranes doped with different mass fractions of MXene and zinc oxide (ZnO) were prepared by electrospinning and were then assembled to flexible self-powered friction piezoelectric sensors. The addition of MXene and ZnO endowed PVDF nanofiber membranes with better piezoelectric properties. The structured PVDF/MXene-PVDF/ZnO (PM/PZ) nanofiber membranes with a double-layer structure, interpenetrating structure, or core-shell structure could further enhance the piezoelectric properties of PVDF-based nanofiber membranes through the synergistic effects of filler doping and structural design. In particular, the output voltage of the self-powered friction piezoelectric sensor made of a core-shell PM/PZ nanofiber membrane showed a good linear relationship with the applied pressure and could produce a good piezoelectric response to the bending deformation caused by human motion.

Surface-enhanced fully nanofiber-based self-cleanable ultraviolet resistive triboelectric energy harvester for wearable smart garments

Wearable triboelectric nanogenerators (TENGs) with high electrical performance have recently prompted great expectations. However, charge diffusion and recombination affect the electric field strength, resulting in a weak electrostatic potential in the displacement region. Current research on film-type dielectric interlayers indicates that charge trapping can prevent charge recombination, although surface charge air breakdown has not been addressed, and becomes a crucial demand in wearable energy applications. In the present study, the surface charge density of poly(vinylidene fluoride) (PVDF) nanofibers is greatly improved by co-electrospraying PDMS-PVDF (PDPV) charge-trapping microbeads; this new approach prolongs the lifetime of surface charges. In particular, the PDPV beads prevent charge recombination, and the interlocking mechanism enhances the tensile property of the PVDF nanofibers. These result in a two-fold increase in the open-circuit voltage and peak power density to 305 V and 124.3 mW m−2, respectively. The device is successfully employed in portable electronic gadgets. Ag-nanoparticle-grafted styrene-butadiene-styrene (SBS) fiber is used as an electrode because it has favorable stretchability with low resistance and is antibacterial. The addition of TiO2/multiwalled carbon nanotube to PVDF nanofiber membrane shows excellent electricfield-induced photocatalyst and ultraviolet protection. Our surface-enhanced fully fiber-based TENG is a promising energy harvester for flexible smart garments applications.

Flexible piezoelectric PVDF/TPU nanofibrous membranes produced by solution blow spinning

Poly (vinylidene fluoride) (PVDF) nanofibers have been applied in producing piezoelectric membranes for energy harvesting in wearable devices under strenuous service conditions due to its outstanding properties such as piezoelectricity, flexibility, stability, and biocompatibility. Therefore, a processing technique with mass production capability and generating the highest possible piezoelectric properties of PVDF nanofibers is required. To achieve such requirements, this study presented a novel flexible piezoelectric membrane based on PVDF/TPU nanofibers using solution blow spinning (SBS). The addition of TPU into PVDF has been proven to increase the flexibility of the polymeric membranes. The produced membranes showed high piezoelectric response and sensitivity compared to other PVDF-based membranes in the literature especially at 5wt.% TPU concentration, owing to its small nanofiber diameter, high β fraction, and inducing reorientation of electric dipoles. The addition of TPU also significantly enhanced tensile strength and elasticity of the produced membranes. Based on those, this work has shown a promising method to produce high elastic-piezoelectric nanofibrous membrane using SBS.

Machine Learning-Aided All-Organic Air-Permeable Piezoelectric Nanogenerator

All-organic piezoelectric mechanical energy harvesters display an excellent electrical output with higher sensitivity due to the superior electrode compatibility between active materials and organic electrodes in comparison to that of metal electrodes. Herein, a stretchable, breathable, and flexible all-organic piezoelectric nanogenerator, made up of PVDF nanofibers and δ-PVDF nanoparticles, fabricated through the electrospinning process in a single step, has been demonstrated for prospective machine learning applications. The δ-phase PVDF nanoparticles serve as efficient active piezoelectric and ferroelectric components with a piezoelectric coefficient of ∼13 pm/V. In terms of electrical response, a peak-to-peak ∼VOC of 4 V, ISC of 1.8 μA, and maximum power density of ∼1600 μW/m2 were obtained. The fabricated device also exhibits excellent stretchability and air permeability, enabling the properties of robust wearable devices with a water vapor transmission rate of ∼250 g m–2 day–1. Here, we have shown that a machine learning algorithm proposed for the different finger motion responses can predict with 94.6% accuracy. Thus, it could recognize different finger gestures efficiently with the highest possible accuracy and predict the possible source point. This feature could be advantageous for prospective health care and security purposes apart from the device and sensor applications.

Flexible piezoelectric PVDF nanofiber film sensor by blow spinning

Flexible piezoelectric PVDF nanofiber film sensor by blow spinning