Polyvinylidene Difluoride Fibers Research Articles

Comparative study between bulk and surface modification on hy-drophobic membrane for dyeing and oily wastewater treatment

Surface modification could remarkably improve the oil–water separation ability of membrane, but suffers from limited survival positive effect layer after long-term operation. Herein, we report a systematic comparative study between bulk and surface modification (i.e., synchronous or sequential electrospun/elecrospraying) on hydrophobic polyvinylidene difluoride (PVDF) membrane. A hydrophilic UiO-66-NH2@polyacrylic acid micro/nanospheres (UiO@PAA) was selected as functional layer to improve the separation and adsorption capability of PVDF. The surface modification (SMM) and bulk modification membranes (BMM) exhibited the similar water wetting behavior in air as the same surface layer. The spider filament-like nanofibers of BMM could enhance the mechanical stability and dispersion uniformity of active sites among the PVDF fibers. In terms of oil-in-water emulsions separation ability, the BMM was superior to the SMM with the maximumly increase of separation efficiency and filtration flux to 1.3 % and 192.6 L m-2h−1, respectively. As for dye absorption, the BMM showed better adsorption capacity with a removal efficiency over 96 %. For the low concentration of methylene blue, the removal efficiency of SMM was only 94 %, while the removal efficiency of the BMM reached 98 % at room temperature. In addition, the BMM exhibited higher removal efficiency over 94 % compared with that less than 84 % of SMM after eight cycling tests, confirming its advantages in repeatability. This study demonstrates that the bulk modification can endow the initial membrane with better performance and durability, showing more promising prospects in actual wastewater treatment.

Graphene Nanoplatelet Integrated Thermally Drawn PVDF Triboelectric Nanocomposite Fibers for Extreme Environmental Conditions

AbstractTriboelectric nanogenerators (TENGs) utilize the synergetic effect of triboelectrification and electrostatic induction to guide electrons through an external circuit, enabling low‐frequency mechanical and biomechanical energy harvesting and self‐powered sensing. Integrating 2D material with a high specific surface area into flexible ferroelectric polymers such as polyvinylidene difluoride (PVDF) has proven to be an efficient strategy to improve the performance of TENG devices. Scalable fabrication of graphene‐integrated PVDF nanocomposite fiber using thermal drawing process is demonstrated for the first time in this study. The open‐circuit voltage and short‐circuit current show 1.41 times and 1.48 times improvement with the integration of 5% graphene in the PVDF fibers, respectively. The TENG fabric shows a maximum power output of 32.14 µW at a matching load of 7 MΩ and a power density of 53.57 mW m−2. The fibers exhibit excellent stability in harsh environmental conditions such as alkaline medium, high/low temperature, multi‐washing cycle, and long‐time usage.

Experimental feasibility investigation on wearability of cloth-type electronic devices composed of functional polyvinylidene difluoride (PVDF) fibers

In the fabrication of fabric-type electronic devices, especially mobile wearable devices, various electrical functions such as sensing, actuation, and energy harvesting can be realized using complex fibrous electrical components and the associated techniques such as weaving and wiring. This study introduces a hybrid cloth-type electronic device composed of PVDF and ordinary fiber yarns. Moreover, experimental protocols for evaluating the electrical performances of cloth-type electronic devices are used to check the feasibility of the proposed wearable electronic device. The magnitude of the generated voltage signal depending on the weaving pattern and types of functional fibers under impact loading were experimentally investigated, and the most appropriate weaving pattern was suggested. To check the serviceability of the proposed cloth-type wearable device, its performance was tested under various hygrothermal environmental conditions. After conducting several electro-mechanical tests and a washing test, the proposed hybrid cloth-type electronic device was found to have adequate potential for use in self-powered wearable electronic devices.

Fabrication and Characterization of High Performance PVDF-based flexible piezoelectric nanogenerators using PMN-xPT (x:30, 32.5, and 35) particles

Flexible piezoelectric nanogenerators based on polyvinylidene difluoride (PVDF) and lead magnesium niobate-lead titanate Pb(Mg1/3Nb2/3)O3–PbTiO3(PMN-xPT compositions for x between 30 and 35) particles with various filler ratios from 10 to 30 vol% were fabricated through the electrospinning method. The phase and microstructural characterizations revealed that the homogenous and continuous fiber-shaped composite structure with good interfacial interaction between the PMN-PT particles and the PVDF matrix was achieved. It was found that the diameter of the neat PVDF fibers was approximately 354 nm, whereas the PVDF/PMN-35PT fibers with ceramic particle concentrations of 10, 20, and 30 vol% had average diameters of 317, 249, and 163 nm, respectively. The piezoelectric performance tests indicated that the 30 vol%PVDF/PMN-35PT nanogenerator had a 3 times greater electrical power efficiency (10.59 μW) at 20 Hz compared to that of the pure PVDF nanogenerator (3.56 μW) at 15 Hz under the same resistance load of 1 MΩ. All in all, the incorporation of PMNT-PT particles into the PVDF appears to be a good approach for the fabrication of high-performance flexible piezoelectric nanogenerator applications for biomechanical energy harvesting of devices converting the mechanical movements of organs such as cardiac and lung into electrical energy.

A Self-Powered Strain Sensor Applied to Real-Time Monitoring for Movable Structures.

This study uses near-field electrospinning (NFES) technology to make a novel self-powered strain sensor and applies it to the real-time monitoring of a bending structure, so that the measurement equipment can be reduced in volume. A self-powered strain sensor consists of polyvinylidene difluoride (PVDF) fibers, a PDMS fixed substrate, and an aluminum electrode. PVDF fibers are spun with DMSO and acetone using NFES technology, with a diameter of about 8 μm, Young’s modulus of 1.1 GPa, and piezoelectric effect of up to 230 mV. The fixed substrate is a film made of PDMS by thermal curing, then adhered to the PDMS film surface of the sheet Al metal as an Al electrode, and then combined with PVDF fiber film, to become a self-powered strain sensor. As a result, the XRD β value of the self-powered strain sensor reaches 2112 and the sensitivity is increased by 20% over a traditional strain sensor. The cumulative angle algorithm can be applied to measure the angular change of the object over a unit of time or the cumulative displacement of the object over the entire period of motion. The experimental results demonstrate that the self-powered strain sensor combined with the angle accumulation algorithm may be applied to monitor the bending structure, thereby achieving continuous measurements of bending structure changes, and improving on traditional piezoelectric sensors, which can only be sensed once. In the future, self-powered strain sensors will have the ability to continuously measure in real-time, enabling the use of piezoelectric sensors for long-term monitoring of structural techniques.

Development of Bionic Semicircular Canals and the Sensation of Angular Acceleration.

To study the sensing process of the human semicircular canals (HSCs) during head rotation, which is difficult to directly measure due to physiological reasons. A 1-BSC (one-dimensional bionic semicircular canal) and 3-BSC were prepared with soft SMPFs (symmetric electrode metal core polyvinylidene difluoride fibers), which could sense deformations similar to human sensory cells. Based on these models, experiments were carried out to study the principle of the HSCs. Deformations of the bionic ampulla (BA) depended on the angular acceleration. Gravity had a strong influence on the deformation of the BA in the vertical plane. When the 3-BSC was subjected to angular acceleration around one of its centerlines, the three BAs all deformed. The deformation of the BAs was linearly related to the angular acceleration. The deformation of the BA in the main semicircular canal was exactly three times that of the other two BAs.

Piezoelectric and magnetoelectric properties of PVDF/NiFe2O4 based electrospun nanofibers for flexible piezoelectric nanogenerators

In this study, flexible piezoelectric nanogenerators (PNGs) were fabricated using the composite fibers which were prepared by combining polyvinylidene difluoride (PVDF) and nickel ferrite (NiFe2O4) nanoparticles (NPs) at a concentration of 1, 3, 5, 7, and 10 wt%. The piezoelectric properties of PNG indicate that the PVDF/NiFe2O4 fibers containing NiFe2O4 NPs at a concentration of 10 wt% has a higher power efficiency of 5.4% at 20 Hz compared to that of the pure PVDF fibers at 10 Hz, under the same resistive load of 2.5 MΩ. The magnetoelectric properties of PNG show that the PNG with PVDF+7 wt%NiFe2O4 supplied the highest electrical power of 0.40 μW under a resistive load of 750KΩ while it reached a maximum voltage value of 17.50 mV at the same load resistive load for a low-level magnetic field of 50 Hz frequency.

Efficient near infrared to visible light upconversion from Er/Yb codoped PVDF fibrous mats synthesized using a direct polymer doping technique

Upconverting-materials are capable of converting near infra-red (NIR) excitation into lower wavelengths. These materials could have a myriad of promising potential applications. However, in some areas, its use has been hindered by its low upconversion luminescence (UCL) efficiency and processing/handling disadvantages from luminescent materials in powder form. This work presents a step towards overcoming this limitation, by developing polymer-based fiber membranes without adding external luminescent powders. Herein, we report on the synthesis of Yb3+ and Er3+ codoped polyvinylidene difluoride (PVDF) and its development into fiber membranes using the Forcespinning® technique. X-ray diffraction (XRD), Fourier transformed infrared (FTIR) spectroscopy were performed to confirm the phase formation, crystallinity and the presence of vibrational bands of the corresponding PVDF matrix. Scanning Electron microscopy (SEM) and thermogravimetric analysis were conducted to investigate the morphological and thermal properties of the codoped nanofibers while the X-ray photoelectron spectroscopy (XPS) showed efficient doping of the lanthanides in the PVDF fiber. Under exposure to 980 nm NIR illumination, the PVDF:Yb3+,Er3+ fibrous mats exhibited efficient UCL emission in the visible wavelength region (523, 540 and 656 nm). The observed results show a NIR to visible UCL process where the Yb3+ ions act as the sensitizer for the generation of visible upconversion emission from Er3+ ions through an excited state absorption (ESA) and two photon energy transfer (ET) mechanisms. The developed material further opens potential lighting and imaging related applications given the ease of preparation, handling, and flexibility of the developed membranes.

Electrospun rhodamine@MOF/polymer luminescent fibers with a quantum yield of over 90%

SummaryTailored luminescent guest@metal-organic framework (Guest@MOF) materials with outstanding photophysical properties are enabling materials for emergent technologies in smart sensors and optoelectronics. However, the practical utility of Guest@MOF currently is impaired by its poor stability and difficult-to-handle powder form. Here, we combine a luminescent-sensing Guest@MOF system with a non-luminescent polymer matrix and, for the first time, demonstrated the easy-to-apply electrospinning of luminescent fibers comprising nanocrystals of RhB@ZIF-71 (rhodamine B@zeolitic imidazolate framework-71) homogeneously dispersed in a polyvinylidene difluoride (PVDF) matrix. The luminescence of RhB@ZIF-71/PVDF fiber is tunable and exhibits a quantum yield exceeding 90%. Compared with RhB fluorophore in PVDF fiber, the ZIF-71 (host) protects the nanoconfined RhB guest molecules (especially the J-aggregates of RhB), giving the composite fiber its unique thermofluorochromic response and enhanced thermal stability to 200°C. Our results reveal the exciting opportunities for implementing electrospun luminescent fibers functionalized with bespoke Guest@MOF nanocrystals for multifunctional device applications.

Piezoelectric Nanogenerator Based on In Situ Growth All‐Inorganic CsPbBr3 Perovskite Nanocrystals in PVDF Fibers with Long‐Term Stability

AbstractInorganic lead halide perovskite has become an emerging material for modern photoelectric and electronic nanodevices due to its excellent optical and electronic properties. In view of its huge dielectric and electrical properties, inorganic CsPbBr3 perovskite is introduced into the piezoelectric nanogenerator (PENG). Based on one‐step electrospinning of solutions containing CsPbBr3 precursors and polyvinylidene difluoride (PVDF), in situ growth of CsPbBr3 nanocrystals in PVDF fibers (CsPbBr3@PVDF composite fibers) with highly uniform size and spatial distribution are synthesized. The CsPbBr3@PVDF composite fibers based PENG reveals an open‐circuit voltage (Voc) of 103 V and a density of short‐circuit current (Isc) of 170 µA cm−2, where the Voc is comparable to the state‐of‐the‐art hybrid composite piezoelectric nanogenerators (PENGs) and the density of Isc is 4.86 times higher than that of lead halide perovskites counterpart ever reported. Moreover, CsPbBr3@PVDF composite fibers based PENG exhibits fundamentally improved thermal/water/acid–base stabilities. This study suggests that the CsPbBr3@PVDF composite fiber is a good candidate for fabricating high‐performance PENGs, promising application potentials in mechanical energy harvesting and motion sensing technologies.

Twist-based cooling of polyvinylidene difluoride for mechanothermochromic fibers

• High-efficiency cooling was realized by changing twist in a PVDF fiber. • Reversible crystal structure transformation was found during cooling. • An inverse twistocaloric cooling was realized for a heterochiral PVDF coil. • A strain sensitive mechanothermochromic fiber was demonstrated. Developing new cooling strategies of solid-state cooling materials is highly desired in order to meet the high energy demand and new application scenarios for multicaloric cooling. Polyvinylidene difluoride (PVDF) is a typical ferroelectric polymer that shows electrocaloric effect, and general strategies for improving the cooling performance of PVDF-based polymers include material composition design, device optimization, etc . In this work, cooling was realized by changing twist of PVDF fibers. Cooling of −1.1 K was achieved by twist removal from a PVDF fiber, and −3.0 K cooling was realized by stretch release of a self-coiled PVDF fiber. During twist insertion and removal of the PVDF fiber, reversible transformation of crystal structure from orthorhombic to monoclinic phase was observed, which was ascribed as the origin of such twist-based cooling effect. Both coil stretching and releasing can realize cooling by using opposite and the same chirality of fiber twisting and coiling, respectively. A strain sensitive mechanothermochromic fiber was demonstrated to show different colors during stretching and releasing of a PVDF coil. The current research provides new era for improving the performance and finding new applications for PVDF-based cooling.

Development of MMG sensors using PVDF piezoelectric electrospinning for lower limb rehabilitation exoskeleton

In this study, a new type of fiber-based mechanomyography (MMG) sensor was developed and used as a motion on/off trigger sensor for a lower limb rehabilitation exoskeleton (LLRE). Piezoelectric material, polyvinylidene difluoride (PVDF), was applied to fabricate a MMG sensor, using the near-field electrospinning technology to electrically spin PVDF fibers to ∼5-10 μm in diameter. PVDF fibers attached on an interdigitated (IDT) electrode with different pole pairs and interspaces were packaged into a MMG sensor. This MMG sensor was stuck on the thigh muscles to detect and acquire human motion intention signal, then trigger the controller and actuate the LLRE. The LLRE multi-axis control system included a master and four slave controllers. The master controller released the command signal to control the slave controllers via controller area network (CAN). A multi-axis control system was developed to actuate the joints of hips and knees of both legs by the LLRE. In the study, commercial electromyography (EMG) sensors were also to compare with the as-made MMG sensors. Results showed that the maximum signal amplitude of the commercail EMG sensor was about ∼0.2 V, whereas the MMG sensor was about ∼2.8 V. The signal-to-noise ratio (SNR) of EMG was about ∼4, while that of MMG was about ∼25. From physiological signals captured from the MMG sensor for the human walking with the LLRE, this new sensor improved the sensitivity in driving the LLRE.

Effect of Electrospinning on the Ferroelectric Phase Content of Polyvinylidene Difluoride Fibers

Polyvinylidene difluoride (PVDF) fibers were prepared by electrospinning from dimethyl formamide (DMF) solutions. The effects of the electrospinning processing conditions on the formation of the alpha and beta phases of PVDF were studied using infrared spectroscopy and differential scanning calorimetry. We have shown that beta-phase PVDF fibers can be electrospun directly from a dimethyl formamide (DMF) solution with a maximum fraction of beta phase, F(beta)max, of 0.75. The fraction of beta phase is found to be greater for smaller-diameter fibers and those spun at an increased voltage.

Electrospinning of polyvinylidene difluoride-based nanocomposite fibers

Polyvinylidene difluoride fibers and composite fibers with Ni–Zn ferrite nanoparticles and rutile nanoparticles were prepared by electrospinning dimethyl formamide (DMF) solutions. To prevent agglomeration, the ferrite nanoparticles were coated with silica, allowing the formation of a stable ferrofluid in DMF as well as the formation of homogeneous fibers. The rutile nanoparticles could be spun with a uniform distribution within the fiber without silica coating. The effects of various solution properties (viscosity and solids loading for composite fibers) and processing parameters (flow rate and voltage) on fiber morphology and diameter were studied to identify a processing window that resulted in the formation of smooth, defect-free fibers. Of the variables examined, fiber diameter was found to be the most strongly dependent on the viscosity of the electrospinning solution. Infrared spectroscopy revealed that the inclusion of well-dispersed nanoparticles in the electrospun fibers enhanced the presence of the ferroelectric phase in the composite fibers.