Polyvinylidene Fluoride Fibers Research Articles

The Radial Piezoelectric Response from Three-Dimensional Electrospun PVDF Micro Wall Structure.

The ability of electrospun polyvinylidene fluoride (PVDF) fibers to produce piezoelectricity has been demonstrated for a while. Widespread applications of electrospun PVDF as an energy conversion material, however, have not materialized due to the random arrangement of fibers fabricated by traditional electrospinning. In this work, a developed 3D electrospinning technique is utilized to fabricate a PVDF micro wall made up of densely stacked fibers in a fiber-by-fiber manner. Results from X-ray diffraction (XRD) and Fourier transform infrared spectra (FTIR) demonstrate that the crystalline structure of this PVDF wall is predominant in the β phase, revealing the advanced integration capability of structural fabrication and piezoelectric poling with this 3D electrospinning. The piezoelectric response along the radial direction of these PVDF fibers is measured while the toppled micro wall, comprised of 60 fibers, is sandwich assembled with a pair of top/bottom electrodes. The measured electrical output is ca. 0.48 V and 2.7 nA. Moreover, after constant mechanical compression happening over 10,000 times, no obvious reduction in the piezoelectric response has been observed. The combined merits of high-precision 3D fabrication, in situ piezoelectric poling, and high mechanical robust make this novel structure an attractive candidate for applications in piezoelectric energy harvesting and sensing.

Luminescent PVDF nanocomposite films and fibers encapsulated with La2Hf2O7:Eu3+ nanoparticles

Luminescent films and fibers are in high demand in display devices and optoelectronics owing to their higher flexibility and mechanical strength compared to powder samples. Keeping that in mind, we have encapsulated La2Hf2O7:Eu3+ (LHOE) nanoparticles (NPs) synthesized by a molten salt method into polyvinylidene fluoride (PVDF) films and fibers. The LHOE-PVDF nanocomposite fibers were manufactured using a Forcespinning® technology while the counterpart films were fabricated by a drop-casting technique. Their photophysical properties were analyzed and compared. Specifically, the red emission with optimum lifetime, color coordinates, and branching ratio of the LHOE NPs can be reproduced even when incorporated inside the PVDF films and fibers. Our studies demonstrate that the LHOE-PVDF films have better emission output, excited-state lifetime, quantum yield, and color purity than the fibers. This is attributed to lower defect density and better surface texture of the LHOE-PVDF films compared to the fibers. Based on the Judd–Ofelt analysis, we have also elucidated that the Eu–O bond is more polarizable and has a higher degree of covalency in the LHOE-PVDF films compared to that in the fibers. The trend of the Judd–Ofelt parameters suggested that Eu3+ has a more asymmetric environment in the films compared to the fibers which impart higher red color purity to the former.

Enhanced Piezoelectricity of Electrospun Polyvinylidene Fluoride Fibers for Energy Harvesting.

Piezoelectric polymers are promising energy materials for wearable and implantable applications for replacing bulky batteries in small and flexible electronics. Therefore, many research studies are focused on understanding the behavior of polymers at a molecular level and designing new polymer-based generators using polyvinylidene fluoride (PVDF). In this work, we investigated the influence of voltage polarity and ambient relative humidity in electrospinning of PVDF for energy-harvesting applications. A multitechnique approach combining microscopy and spectroscopy was used to study the content of the β-phase and piezoelectric properties of PVDF fibers. We shed new light on β-phase crystallization in electrospun PVDF and showed the enhanced piezoelectric response of the PVDF fiber-based generator produced with the negative voltage polarity at a relative humidity of 60%. Above all, we proved that not only crystallinity but also surface chemistry is crucial for improving piezoelectric performance in PVDF fibers. Controlling relative humidity and voltage polarity increased the d33 piezoelectric coefficient for PVDF fibers by more than three times and allowed us to generate a power density of 0.6 μW·cm–2 from PVDF membranes. This study showed that the electrospinning technique can be used as a single-step process for obtaining a vast spectrum of PVDF fibers exhibiting different physicochemical properties with β-phase crystallinity reaching up to 74%. The humidity and voltage polarity are critical factors in respect of chemistry of the material on piezoelectricity of PVDF fibers, which establishes a novel route to engineer materials for energy-harvesting and sensing applications.

P3HT loaded piezoelectric electrospun fibers for tunable molecular adsorption

Electrospinning is strongly attractive for the fabrication of fibrous platforms for a wide range of applications like electronic devices, electroactive wearables and wound healing scaffolds. Recently, this versatile, reliable and low-cost technique has been investigated with a wide selection of active materials to fabricate nonwoven meshes to be used as smart filters to control the adsorption/delivery of small molecules. In this work, electrospinning is proposed for the fabrication of polyvinylidene fluoride (PVDF)-based fibers able to control the adsorption of negatively charged molecules such as Methylene Blue (MB). It is demonstrated that PVDF fibers with pronounced surface roughness – from 126 nm to 1983 nm – are able to adsorb a higher amount of MB than smooth fibers made of PCL, used as a control. Moreover, the integration of a p-type conjugated polymer such as Poly (3-hexylthiophene) (P3HT), concurs influencing the adsorption mechanism of MB, mediated by the microscopic interactions among dipolar β phases in PVDF. In addition, an increase of MB absorption was measured in the presence of an externally applied voltage (10 kV), ascribable to the P3HT oxidation change that influences microscopic dipole interactions. Hence, we suggest the use of P3HT/Polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) fibers to design new filtering systems able to tune the absorption of negatively charged molecules for environmental and biomedical applications.

A comparative study of electrospun polyvinylidene fluoride and poly(vinylidenefluoride-co-trifluoroethylene) fiber webs: Mechanical properties, crystallinity, and piezoelectric properties

Energy scavenging has been attracting the consideration of researchers in recent years. In this study, the fabrication and characterization of electrospun randomly oriented and aligned grooved polyvinylidene fluoride (PVDF) and poly(vinylidenefluoride-co-trifluoroethylene) (PVDF-TrFE) fiber webs are studied. The fibers are generated with comparable diameters and the webs which are used as an active layer to directly make a piezoelectric nanogenerator are fabricated with the same thickness for accurate comparison. The results show that PVDF-TrFE fiber webs have better mechanical properties, crystallinity, and piezoelectric properties than PVDF fiber webs. Furthermore, the piezoelectric nanogenerator based on PVDF-TrFE fiber webs has higher electrical outputs than piezoelectric nanogenerator based on PVDF fiber webs owing to its high β phase content (F(β)). Moreover, the electrical outputs of the piezoelectric nanogenerator based on aligned fiber webs are higher than those based on randomly oriented fiber webs due to the increase in the friction area. We believe that our work can be served as a good reference for the comparison between the mechanical, physicochemical, and piezoelectric properties of PVDF and PVDF-TrFE fiber webs generated via electrospinning.

Electrospun polyvinylidene fluoride/polyacrylonitrile composite fibers: fabrication and characterization

The purpose of this study is to make use of the advantages of both polyvinylidene fluoride (PVDF) and polyacrylonitrile (PAN) to fabricate a flexible electronic device. Polyvinylidene fluoride (PVDF)/polyacrylonitrile (PAN) composite fibrous mats with different blend ratios were fabricated using electrospinning. The effects of PVDF and PAN mass ratio on fiber morphology, chemical structure, thermal stability, and piezoelectric properties of the produced composite fibers were investigated by scanning electron microscopy (SEM), X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG), and piezoelectric tester. The SEM images showed that the PVDF/PAN composite nanofibers were fabricated successfully and fiber diameters increased with the increase of PVDF content. The FTIR and XRD analyses showed that both the α- and β-crystal phases existed in PVDF/PAN composite fibers. The thermal stability of PVDF/PAN fibrous mats was less than that of neat PVDF fibers. The piezoelectric properties of PVDF/PAN fibrous mats were significant and a function of PVDF content. The output voltage of PVDF/PAN fibrous mats increased from 1.2 to 5.0 V as PVDF content increased from 20 to 100%. The piezoelectric voltages of PVDF/PAN composite nanofibers also increased with the increase of impacting force. Tensile and contact angle testing indicated that the PVDF/PAN fibrous mats were more flexible and hydrophilic than neat PVDF membrane. PVDF/PAN nanocomposite fiber mats were observed suitable for potential application in flexible electronic devices.

Textile‐Compatible, Electroactive Polyvinylidene Fluoride Electrospun Mats for Energy Harvesting

AbstractPolymer piezoelectric nanogenerators have attracted attention for mechanical energy harvesting, for powering wearable electronics and movement sensing applications. Polyvinylidene fluoride (PVDF) is a flexible and efficient electroactive polymer, however, it is a polymorph for which only two phases (of five) are piezoelectric. Herein are produced breathable and flexible textile‐compatible electroactive mats via electrospinning, and the polymorphism of PVDF nanofibers during deposition is controlled, rather than post‐fabrication, meaning that this process is directly compatible with textile manufacturing. The electrospinning process combines mechanical stretching and electrical poling and results in the alignment of dipoles in the nanofibers. The local stretching of polymer chains at each position on the fibre point impacts the polymorph relative content in that area. It is found that finer PVDF fibres (ø < 50 nm) have a lower electroactive crystal phase content compared to medium thickness‐range fibres (100 nm < ø < 500 nm), whilst thicker fibres (ø > 1000 nm) show distinct areas of lower (fibres with beading) and higher (smooth fibres) electroactive phase content. Ultimately, fibrous mats produced using solutions with a high polymer concentration have a lower bead content and the most uniform medium‐range fibre thickness, consequently resulting in the highest content of the electroactive phase.

Rapid Li Diffusion By Ferroelectric Polarization for Smooth Lithium Deposition

we demonstrated smart protective web consisted of nanosized beta phase polyvinylidene fluoride (PVDF) fibers with ferroelectricity on copper (Cu) foil to suppress Li dendrite. The beta phase PVDF fiber provides a well-ordered molecular structure, which ensures rapid Li-ion migration along PVDF fiber. That guarantee homogeneous Li-ions flux on the Cu current collector, leading to smooth Li surface occurs during Li deposition. In addition, the fiber could physically inhibit Li dendrite formation, resulting in no short-circuit and Li dead particle formation. Thus, the electrode consisted of PVDF fiber forms dense Li film during deposition, achieving high volume metric energy density (1937 mAh cm-3). In full cell (LFP||PVDF electrode (PVDF web on Cu current collector), the electrode exhibits an excellent cycle performance (over 300 cycles) using conventional carbonate electrolytes at a current density of 1C.

Fabrication and Characterization of a Flexible PVDF Fiber-based Polymer Composite for High-performance Energy Harvesting Devices

A flexible polyvinylidene fluoride (PVDF)/polydimethylsiloxane (PDMS) composite prototype with high piezoelectricity and force sensitivity was constructed, and its huge potential for applications such as biomechanical energy harvesting, self-powered health monitoring system, and pressure sensors was proved. The crystallization, piezoelectric, and electrical properties of the composites were characterized using an X-ray diffraction (XRD) experiment and customized experimental setups. The composite can sustain up to 100% strain, which is a huge improvement over monolithic PVDF fibers and other PVDF-based composites in the literature. The Young’s modulus is 1.64 MPa, which is closely matched with the flexibility of the human skin, and shows the possibility for integrating PVDF/PDMS composites into wearable devices and implantable medical devices. The 300 μm thick composite has a 14% volume fraction of PVDF fibers and produces high piezoelectricity with piezoelectric charge constants d31 = 19 pC/N and d33 = 34 pC/N, and piezoelectric voltage constants g31 = 33.9 mV/N and g33 = 61.2 mV/N. Under a 10 Hz actuation, the output voltage was measured at 190 mVpp, which is the largest output signal generated from a PVDF fiber-based prototype.

Electrospun Polyvinylidene Fluoride-Based Fibrous Scaffolds with Piezoelectric Characteristics for Bone and Neural Tissue Engineering.

Polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE) with excellent piezoelectricity and good biocompatibility are attractive materials for making functional scaffolds for bone and neural tissue engineering applications. Electrospun PVDF and P(VDF-TrFE) scaffolds can produce electrical charges during mechanical deformation, which can provide necessary stimulation for repairing bone defects and damaged nerve cells. As such, these fibrous mats promote the adhesion, proliferation and differentiation of bone and neural cells on their surfaces. Furthermore, aligned PVDF and P(VDF-TrFE) fibrous mats can enhance neurite growth along the fiber orientation direction. These beneficial effects derive from the formation of electroactive, polar β-phase having piezoelectric properties. Polar β-phase can be induced in the PVDF fibers as a result of the polymer jet stretching and electrical poling during electrospinning. Moreover, the incorporation of TrFE monomer into PVDF can stabilize the β-phase without mechanical stretching or electrical poling. The main drawbacks of electrospinning process for making piezoelectric PVDF-based scaffolds are their small pore sizes and the use of highly toxic organic solvents. The small pore sizes prevent the infiltration of bone and neuronal cells into the scaffolds, leading to the formation of a single cell layer on the scaffold surfaces. Accordingly, modified electrospinning methods such as melt-electrospinning and near-field electrospinning have been explored by the researchers to tackle this issue. This article reviews recent development strategies, achievements and major challenges of electrospun PVDF and P(VDF-TrFE) scaffolds for tissue engineering applications.

Plasmon-Enhanced Blue-Light Emission of Stable Perovskite Quantum Dot Membranes.

A series of stable and color-tunable MAPbBr3−xClx quantum dot membranes were fabricated via a cost-efficient high-throughput technology. MAPbBr3−xClx quantum dots grown in-situ in polyvinylidene fluoride electrospun nanofibers exhibit extraordinary stability. As polyvinylidene fluoride can prevent the molecular group MA+ from aggregating, MAPbBr3−xClx quantum dots are several nanometers and monodisperse in polyvinylidene fluoride fiber. As-prepared MAPbBr3−xClx quantum dot membranes exhibit the variable luminous color by controlling the Cl− content of MAPbBr3−xClx quantum dots. To improve blue-light emission efficiency, we successfully introduced Ag nanoparticle nanofibers into MAPbBr1.2Cl1.8 quantum dot membranes via layer-by-layer electrospinning and obtained ~4.8 folds fluorescence enhancement for one unit. Furthermore, the originality explanation for the fluorescence enhancement of MAPbBr3−xClx quantum dots is proposed based on simulating optical field distribution of the research system.

Direct Three-Dimensional Visualization of Membrane Fouling by Confocal Laser Scanning Microscopy.

Membrane-based separation is an important technique for removing emulsified oil from water. However, the mechanisms of fouling are complex because of the deformability and potential for coalescence and break-up of the oil droplets. Here, we report for the first time direct, three-dimensional (3D) visualization of oil droplets on electrospun fiber microfiltration membranes after a period of membrane-based separation of oil-in-water emulsions. High-resolution 3D images were acquired by a dual-channel confocal laser scanning microscopy (CLSM) technique in which both the fibers and the oil (dodecane) were fluorescently labeled. The morphology of dodecane as the foulant was observed for two different types of fibers, an oleophobic nylon (PA6(3)T), and oleophilic polyvinylidene fluoride (PVDF). Through direct visualization, the rejected oil was found to form droplets of clam-shell shape on the PA6(3)T fibers, whereas the oil tended to wet the PVDF fibers and spread across the membrane. The morphology was also analyzed as a function of separation time (i.e., "4D" imaging), as the oil accumulated within and upon the membranes. The observations are qualitatively consistent with a transition from blocking of individual pores in the membrane to coalescence of oil droplets into coherent liquid films with increasing filtration time. Analysis of permeate flux using blocking filtration models corroborate the transition of fouling modes indicated by the 3D images. This direct, 3D visualization CLSM technique is a powerful tool for characterizing the mechanisms of fouling in membranes used for liquid emulsion separations.

Performance Comparison between Polyvinylidene Fluoride and Polytetrafluoroethylene Hollow Fiber Membranes for Direct Contact Membrane Distillation.

Increasing water demand coupled with projected climate change puts the Southwestern United States at the highest risk of water sustainability by 2050. Membrane distillation offers a unique opportunity to utilize the substantial, but largely untapped geothermal brackish groundwater for desalination to lessen the stress. Two types of hydrophobic, microporous hollow fiber membranes (HFMs), including polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), were evaluated for their effectiveness in direct contact membrane distillation (DCMD). Water flux and salt rejection were measured as a function of module packing density and length in lab-scale systems. The PVDF HFMs generally exhibited higher water flux than the PTFE HFMs possibly due to thinner membrane wall and higher porosity. As the packing density or module length increased, water flux declined. The water production rate per module, however, increased due to the larger membrane surface area. A pilot-scale DCMD system was deployed to the 2nd largest geothermally-heated greenhouse in the United States for field testing over a duration of about 22 days. The results demonstrated the robustness of the DCMD system in the face of environmental fluctuation at the facility.

Electrospun polyvinylidene fluoride/SiO2 nanofibrous membranes with enhanced electret property for efficient air filtration

Abstract There is a critical need for air filters with the abilities of removing particles effectively and allowing air to pass through easily to protect the public from increasingly serious air pollution; however, creating such a filter medium has proven to be extremely challenging. Herein, an air filtration material equipped with remarkable electrostatic effect is fabricated by electrospining polyvinylidene fluoride (PVDF) as the matrix polymer and silicon dioxide nanoparticles (SiO 2 NPs) modified by γ-glycidoxypropyl trimethoxysilane (GPS) as the charge enhancer. The premise of the design is that GPS modified SiO2 NPs can be uniformly distributed in PVDF fibers, generating abundant stable interfacial charges. Benefiting from the monodisperse state of GPS@SiO2 NPs, the resultant PVDF/GPS@SiO2 nanofibrous membrane exhibits remarkable electret effect with a surface potential of 12.4 kV and high filtration performance with a quality factor of 0.14, which has never been reported before. We envision that this work can provide new insight into the design and development of electret air filter media for various applications.

Surface-Potential-Controlled Cell Proliferation and Collagen Mineralization on Electrospun Polyvinylidene Fluoride (PVDF) Fiber Scaffolds for Bone Regeneration.

This study represents the unique analysis of the electrospun scaffolds with the controlled and stable surface potential without any additional biochemical modifications for bone tissue regeneration. We controlled surface potential of polyvinylidene fluoride (PVDF) fibers with applied positive and negative voltage polarities during electrospinning, to obtain two types of scaffolds PVDF(+) and, PVDF(-). The cells' attachments to PVDF scaffolds were imaged in great details with advanced scanning electron microscopy (SEM) and 3D tomography based on focus ion beam (FIB-SEM). We presented the distinct variations in cells shapes and in filopodia and lamellipodia formation according to the surface potential of PVDF fibers that was verified with Kelvin probe force microscopy (KPFM). Notable, cells usually reach their maximum spread area through increased proliferation, suggesting the stronger adhesion, which was indeed double for PVDF(-) scaffolds having surface potential of -95 mV. Moreover, by tuning the surface potential of PVDF fibers, we were able to enhance collagen mineralization for possible use in bone regeneration. The scaffolds built of PVDF(-) fibers demonstrated the greater potential for bone regeneration than PVDF(+), showing after 7 days in osteoblasts culture produce well-mineralized osteoid required for bone nodules. The collagen mineralization was confirmed with energy dispersive X-ray spectroscopy (EDX) and Sirius Red staining, additionally the cells proliferation with fluorescence microscopy and Alamar Blue assays. The scaffolds made of PVDF fibers with the similar surface potential to the cell membranes promoting bone growth for next-generation tissue scaffolds, which are on a high demand in bone regenerative medicine.

Light driven PVDF fibers based on photochromic nanosilica@naphthopyran fabricated by wet spinning

Photoresponsive polyvinylidene fluoride (PVDF) fibers doped with naphthopyran-functionalized silica nanoparticles (SiO2@NPT) were successfully prepared by dry–jet wet spinning. The incorporated photochromic nanomaterials, SiO2@S1 and SiO2@S2, were previously prepared by covalent post-grafting of the silylated NPTs – 2H-naphtho[1,2-b]pyran derivatives, S1 and S2 – onto nano-sized SiO2 (15 ± 3 nm).The morphological and chemical characterization of the resulting doped fibers PVDF@SiO2@S1 and PVDF@SiO2@S2 was evaluated by scanning electron microscopy with energy dispersive spectroscopy and Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR). Both PVDF@SiO2@S1 and PVDF@SiO2@S2 fibers presented average diameters of 133 ± 8 μm and 98 ± 7 μm, respectively, and a porous outer surface. The presence of the SiO2@NPT within the fibers was confirmed through the observation of dense clusters embedded within the polymeric matrix. Furthermore, the FTIR-ATR spectra of the fibers revealed that the PVDF matrix was composed of α and β crystalline and amorphous phases.The PVDF@SiO2@S1 and PVDF@SiO2@S2 fibers showed photoresponsive properties under UV and sunlight irradiation, exhibiting fast coloration kinetics and good optical contrast (ΔE*ab = 7.2 and 15.1, respectively), and changing from a pale orange and an off-white color to a more intense yellow-orange and purple coloration, respectively, in less than 1 min. Moreover, they showed an initial fast bleaching, losing half of their color in less than 30 min (t1/2 = 28 and 20 min for PVDF@SiO2@S1 and PVDF@SiO2@S2 fibers, respectively), but displaying a residual coloration that took 1 and 2 h to return to the initial uncolored state (t3/4 = 95 and 49 min, respectively). The PVDF@SiO2@S2 fibers presented the best photochromic performance.

Static-Aligned Piezoelectric Poly (Vinylidene Fluoride) Electrospun Nanofibers/MWCNT Composite Membrane: Facile Method.

Polyvinylidene Fluoride (PVDF) piezoelectric electrospun nanofibers have been intensively used for sensing and actuation applications in the last decade. However, in most cases, random PVDF piezoelectric nanofiber mats have moderate piezoelectric response compared to aligned PVDF nanofibers. In this work, we demonstrate the effect of alignment conducted by a collector setup composed of two-metal bars with gab inside where the aligned fiber can be formed. That is what we called static aligned nanofibers, which is distinct from the dynamic traditional technique using a high speed rotating drum. The two-bar system shows a superior alignment degree for the PVDF nanofibers. Also, the effect of added carbon nanotubes (CNTs) of different concentrations to PVDF nanofibers is studied to observe the enhancement of piezoelectric response of PVDF nanofibers. Improvement of β-phase content of aligned (PVDF) nanofibers, as compared to randomly orientated fibers, is achieved. Significant change in the piezoelectricity of PVDF fiber is produced with added CNTs with saturation response in the case of 0.3 wt % doping of CNTs, and piezoelectric sensitivity of 73.8 mV/g with applied masses down to 100 g.

Maneuvering surface structures of polyvinylidene fluoride nanofibers by controlling solvent systems and polymer concentration

The surface evolution of fibers has been attracting great attention in many areas. In this work, we demonstrated the feasibility of directly electrospinning grooved and porous polyvinylidene fluoride fibers by varying polymer concentration and using both single/binary solvent systems. We discovered that grooved fibers can be generated from a variety of binary solvent systems, whereas porous fibers can be achieved using low boiling point solvent (LBPS) systems. The results indicated that the key factors for the formation of grooved fibers are the polymer concentration, the difference of evaporation rate (the difference of boiling points between each of the two studied solvents) between the two solvents, and the solvent ratio. While the polymer concentration, the presence of LBPS, and the solvent ratio are the decisive factors for the formation of porous structures. The formation mechanism of grooved fibers was attributed to void-based elongation, wrinkle-based elongation, and collapsed jet-based elongation. The mechanism for the formation of porous fibers was ascribed to the coexistence of both thermally induced phase separation and vapor induced phase separation. These structures can be used in different applications, such as harvesting energy and filtration. Importantly, we believe our work can serve as guidelines for the preparation of grooved and porous nanofibers through electrospinning.

Polyvinylidene fluoride/polystyrene hybrid fibers with high ionic conductivity and enhanced mechanical strength as lithium-ion battery separators

Ionic conductivity is an important separator parameter influencing the cycle life and rate capability of lithium-ion batteries (LIBs). To improve the ionic conductivity of polyvinylidene fluoride (PVdF) fibers, polystyrene (PS) was added into the PVdF electrospinning solution for the fabrication of PVdF/PS hybrid fibers. The morphology and electrochemical property were regulating by tuning the PS dosage. Owing to the increasing mass ratio of the adhesion structure, not only the porosity, uptake, and average pore size of PVdF/PS hybrid fibers simultaneously decreased but also the mechanical strength enhanced (15.9 MPa) with the increasing PS content. In addition, the ionic conductivity increased with increasing PS content (1.58 mS cm−1 for PVdF/PS hybrid fiber with 20-wt% PS) ascribing to the increase of the amorphous region. Benefiting from the characteristic of PVdF, the as-prepared PVdF/PS hybrid fibers with non-flammability can significantly improve the LIBs safety. Significantly, the cells with PVdF/PS hybrid fibers (15-wt% PS) displayed satisfactory cycling performance (159.9 mAh g−1 at 0.2 C for 45 cycles after testing at 0.1 C for 5 cycles) and rate capability, indicating that PVdF/PS hybrid fibers are the promising separator candidates for the applications in LIBs.

Self-powered pressure sensor based on the triboelectric effect and its analysis using dynamic mechanical analysis

Since 2012 there has been a rapid rise in the development of triboelectric nanogenerators due to their potential applications in the field of energy harvesting and self-powered sensors for vibrations, accelerations, touches, pressures and other mechanical motions. This study suggests a novel triboelectric nanogenerator based on the interaction between polyvinylidene fluoride and polyvinylpyrrolidone submicron fibers. Polyvinylpyrrolidone is introduced as a new material for the TENG because of its tendency of losing electrons easily, while polyvinylidene fluoride is selected for its strong-electron attracting ability. Electrospinning is suggested as a fabrication method for the nanofibers due to its simplicity, versatility and low-cost. Furthermore, the paper explores the possibility to use this triboelectric nanogenerator as a self-powered pressure sensor. For this purpose, the nanogenerator is subjected to dynamic mechanic analysis which produces controlled pressure forces applied with a certain frequency. This is the first work to suggest the use of dynamic mechanical analyzer to study the relation between the applied mechanical stimulus and the electric responses of the triboelectric nanogenerator. Eventually the sensitivity of the nanogenerator to different pressures is analyzed. A directly proportional relationship is found between the pressure applied and the resultant voltage and current amplitudes. The developed nanogenerator reacts to pressure in real time and as a sensor it exhibits a very high sensitivity and low experimental error for repeated measurements. The main contributions of this study are the development of a novel nanogenerator based on the triboelectric effect between polyvinylidene fluoride and polyvinylpyrrolidone electrospun fibers and the investigation for its potential use as a self-power pressure sensor. Eventually, the paper explores the advantages of dynamic mechanical analyzer for pressure analysis.