PVDF Mats Research Articles

Recent Advancement in Electrospun nanofibrous mats with emphasis on their applications

PVDF, which has four phases, is one of the most commonly used dielectric polymers. Among them the piezoelectric property that is accessible via an electrospinning synthesis method is only seen in its β phase. In this research solution was prepared at a concentration by taking the Polyvinylidene fluoride about 2.5 gm was dissolved in Dimethylformamide (DMF) and Acetone with a ratio of 6:4.The prepared solution has been loaded to the syringe pump and it has been electrospinned by using the electrospnning set up by having the parameters at a flow rate of 0.5ml/hr with a power supply of 20kv,at a distance of 100mm.The SEM Images of PVDF electrospuned nanofibrous mats clearly indicates that the beads were formed which decreased in number when concentration was increased whereas the diameter of beads got increased in the range of 647.39 to 1208.35nm. Average diameters of the Nano fiber obtained were in the range of 34.21 to 107.35nm in diameter, with a minimum diameter of 25.50nm to a maximum of 135.85nm. PVDF based Electrospuned nanofibers mats, have been tested by applying the Impact Energy, Due to the impact force, the sound frequency of 86-89 dB was induced, the generated acoustic waves were tracked and sensed by electro-sponsored PVDF Mats based sensors. During the trial, the voltage reached a limit of 100 mV and disappeared quickly due to the low power generated by the PVDF Mats based sensors. The created Lamb wave can be easily detected by this PVDF sensor, which allows this system to characterize the structural element’s properties and to detect cracks and structural defects as well.

An Ideal Structure for Li-Ion Battery Separators

Among all types of Li-ion battery (LIB) separators, fibrous mats have the advantage of low cost, low mass, and high porosity. Fibrous Poly(Vinylidene difluoride) (PVDF) shows promising results because of its stability and affinity for electrolytes commonly employed in Li-ion cells. Despite numerous studies published on LIB separators, none reports structure-property relationships for the identification of an ideal structure. We investigated the properties of a melt-blowable PVDF and produced meltblown PVDF mats in scale-up equipment with the objective of elucidating its performance as a LIB separator. We also present a new class of LIB separators, PVDF-based highly-branched, colloidal polymer particulates called soft dendritic colloids that are produced by shear-driven polymer precipitation within a highly turbulent nonsolvent flow, followed by filtration. We show that the morphology of the resulting PVDF particulates can be modulated from fibrous soft dendritic colloids (SDC) to thin and highly porous sheet-like particles.Through a scale-up system, we obtained high-quality meltblown PVDF with high homogeneity, low number of defects, an average fiber diameter of 1.4 μm, and pore size as low as 0.9 μm. Small fiber diameter provides high-surface area and high-electrolyte uptake. We show interactions of the meltblown PVDF with the electrolyte lead to a morphology change in the fibers. The highest ionic conductivity was ~ 9.6 mS/cm, and the first-cycle capacity was 140 mAh/g (Li/LiCoO2). After melt-pressing, the thickness and pore size decrease, but the mats electrolyte absorbency and conductivity decrease commensurately. PVDF SDC separators show high porosity (up to 80%) and high particle surface area, which results in high conductivity (1.2 mS/cm), high-electrolyte uptake (325%), and high-cell capacity (112 mAh/g in Li/LiCoO2 cell) with <10% loss after 50 cycles. Both processes yield separators with low thermal shrinkage (<5% at 90 ºC) and high tensile strength (<0.5% offset at 1000 psi), with the highest-performing separator possessing low average fiber diameter with a wide diameter distribution.Both meltblowing and shear-driven precipitation are facile and versatile processes for high-volume fabrication of LIB separators with one single polymer without necessarily requiring post-processing and with characteristics similar to commercially available battery separators. Our findings show that battery separators should be fabricated with a low pore size (<2 µm) but also with a wide pore distribution. When the strength and openness of the micropores are coupled with a dense net of nanopores, an ideal Li-ion battery separator is obtained.

Structure and performance of electroblown PVDF‐based nanofibrous electret filters

AbstractPoly(vinylidene fluoride) (PVDF)‐based nanofibrous mats were produced via electrically assisted solution blowing (electroblowing). Morphology and filtration properties of the nanofibrous mats were investigated as a function of polymer concentration and applied voltage. The average fiber diameter was reduced from 727 ± 366 nm to 408 ± 143 nm and from 424 ± 233 nm to 328 ± 105 nm, using 16 wt% and 12 wt% concentrations, respectively, with an increase of electric voltage from 0 to 30 kV. In addition, the pore size of the mats produced from 12 wt% concentration decreases with the increase of electric voltage. Results showed that electroblown mats possess high filtration properties and performance. Enhancement of mechanical capturing efficiency is attributed to the reduction in fiber diameter and pore size. The enhancement of electrostatic capturing efficiency is thought to be from the improved electret property of the mats, which eliminates the need for a second step to polarize nanofibrous mats. As a result, both mechanical and electrostatic capture efficiency of the mats is enhanced compared to solution blown PVDF mats. The emerging electret property might be due to the accumulation of the electrostatic charges at high voltage and the enhanced polarized β phase, which is the result of the high drawing ratio applied to the polymer jet during the spinning process.

Dielectric and energy storage density studies in electrospun fiber mats of polyvinylidene fluoride (PVDF)/zinc ferrite (ZnFe2O4) multiferroic composite

Flexible free standing electrospun poly (vinylidene fluoride)/ZnFe2O4 composite fiber mats were synthesized through electrospinning technique. Structural and morphological studies of PVDF/ZnFe2O4 composite fibers were examined by X-ray diffraction and scanning electron microscopy. The functional groups and the percentage of β phase were analysed using FTIR studies. 92% beta phase was achieved with the incorporation of ZnFe2O4 filler. The enhancement in dielectric and ferroelectric properties of the composite fiber mats were observed with a maximum dielectric constant and polarization values of 15 and 0.72 μC/cm2 respectively for 20 wt% filler loading. The domain switching behaviour of the mats were analysed using DC-EFM. Vibration sample magnetometry results revealed the antiferromagnetic nature of the composite fiber mats with a maximum magnetization of 0.18 emu/cm3. Further, the energy storage density of the mats was studied and a maximum energy storage density of 239 mJ/cm3 was obtained which was 1.4 times than that of pure PVDF mat.

Bio-inspired hydrophobic/cancellous/hydrophilic Trimurti PVDF mat-based wearable triboelectric nanogenerator designed by self-assembly of electro-pore-creating

Electrical performances, output stability and use of comfort are three crucial indexes for the rapid advancements in wearable power generators. However, there exist few studies that can simultaneously improve the three aforementioned indexes in a simple manner. Here, a bio-inspired Trimurti poly(vinylidene fluoride) (PVDF) tribo-material with a transcendent electrical performance, excellent output stability in high environmental humidity, and increased use of comfort under a sweating condition is designed, by simple self-assembly of electro-pore-creating. The nanoporous cancellous-bone-like, hydrophobic lotus-leaf-like, and hydrophilic root-xylem-like structures are assembled respectively in the interior, on the upper surface and on the bottom surface of Trimurti PVDF mat, endowing the fabricated Trimurti triboelectric nanogenerator (T-TENG) with outstanding electrical performances and availability in different application environments. With a high power density of 10.6 W m−2, the T-TENG can directly drive 714 light-emitting-diodes and small electronics. Additionally, under the relative humidity of 85%, the output retention rate of the T-TENG reaches up to 22%. Under the simulated sweating condition, the Trimurti PVDF mat can absorb sweat into its bottom region to accelerate evaporation of sweat. This work indicates a substantial progress of wearable high-performance power sources for dealing with various complex conditions in practical applications.

Ag-Nanoparticle-Bearing Poly(vinylidene fluoride) Nanofiber Mats as Janus Filters for Catalysis and Separation.

Hydrophilic Ag nanoparticles were pattern-deposited onto one side of an electrospun poly(vinylidene fluoride) (PVDF) nanofiber mat, yielding a Janus filter. The filter was used to separate a receiver cell from a reactor cell that contained an aqueous 4-nitrophenol/NaBH4 solution. Upon contact with this solution, the Ag nanoparticles catalyzed the reduction of 4-nitrophenol to 4-aminophenol. After the reaction reached completion, ethyl acetate was added into the reactor to extract the product. During this process, the ethyl acetate containing 4-aminophenol also selectively permeated regions of the hydrophobic yet oleophilic PVDF mat that were not covered by Ag nanoparticles. The product was obtained after the evaporation of ethyl acetate. This paper demonstrates the first use of a Janus filter in a catalytic separatory reactor that catalyzes a chemical reaction and then facilitates the eventual separation of the formed product via filtration.

Effect of electrospinning parameters on piezoelectric properties of electrospun PVDF nanofibrous mats under cyclic compression

The high piezoelectric response capacity of electrospun PVDF nanofibers is currently a challenging area of research, and this study attempts to optimize the piezoelectric properties of electrospun PVDF nanofibrous mat under controlled electrospinning process. Some experiments were designed to study the relationship between electrospinning processing parameters and the piezoelectric properties of PVDF mats under cyclic compression, and this relationship was compared with the change of crystalline structure features with the electrospinning parameters. The excitation method is based on low velocity compression test by cyclically pressing flat contactor on samples. The impact of each of processing parameters has been investigated. It was found that three electrospinning parameters including: applied voltage, feeding volume flow rate and syringe needle tip diameter, are significant influential factors to the piezoelectric properties of the electrospun PVDF nanofibrous mats. However, the feeding volume flow rate has a greater effect on the piezoelectric responses to cyclic compression than both applied voltage and volume flow rate does, and its effect on the piezoelectric responses is different from that of β-phase fraction of crystalline structure within PVDF nanofiber. It was also observed that the relationship between the piezoelectric peak intensity and the applied voltage as well as the feeding volume flow rate is nonlinear.

Electrospun PVDF/MWCNT/OMMT hybrid nanocomposites: preparation and characterization

Electrospinning technique was employed to prepare neat PVDF, nanoclay-PVDF and carbon nanotube (MWCNT)-PVDF nanocomposites, and nanoclay-carbon nanotube-PVDF hybrid nanocomposites. A mixture of dimethyl formamide/acetone (60/40) was used to fluidize the polymer and nanofillers. Electrospinning process was conducted under optimized conditions. Maximum modification was achieved at 0.15 wt% nanofiller. Rheological measurements on the prepared solutions revealed decreased material functions in the presence of nanoclay, whereas the rheological properties of MWCNT-PVDF solution did not show any significant reduction compared with those of neat PVDF solution. The behaviors of the hybrid nanocomposite solutions, though dependent on their composition and their material functions, increased with MWCNT concentration. These differences, together with variations in electrical properties of nanoclay and MWCNT, led to changes in morphology of the fiber during electrospinning process. Under electrospinning conditions designed for neat PVDF solution, mats with beads and with the highest fiber diameter were produced. Meanwhile, incorporation of both nanoclay and MWCNT into the solutions resulted in bead-free fibers with thinner diameter. Fourier transformed infrared spectrophotometry (FTIR) and X-ray diffractometry (XRD) were used to measure the β-phase crystalline content in electrospun mats. Complete agreement was found between the FTIR and XRD results. The lowest and highest β-phase contents were obtained for neat PVDF mat and hybrid nanocomposite mat containing 0.1 wt% clay, respectively. The mixing procedure of nanofillers and the PVDF solution was also found to be important. In case of hybrid nanocomposites, more β-crystals were formed when the nanoclay was first mixed in the absence of MWCNT.

Electrically Conductive Polyaniline-Coated Electrospun Poly(Vinylidene Fluoride) Mats

Electrically conductive polyaniline (PANI)-coated electrospun poly(vinylidene fluoride) (PVDF) mats were fabricated through aniline (ANI) oxidative polymerization on electrospun PVDF mats. The effect of polymerization condition on structure and property of PVDF/PANI mats was investigated. The electrical conductivity and PANI content enhanced significantly with increasing ANI concentration due to the formation of a conducting polymer layer that completely coated the PVDF fibers surface. The PANI deposition on the PVDF fibers surface increased the Young Modulus and the elongation at break reduced significantly. Attenuated Total Reflectance-Fourier Transform Infrared spectroscopy (ATR-FTIR) revealed that the electrospun PVDF and PVDF/PANI mats display a polymorph crystalline structure, with absorption bands associated to the β, α and γ phases.

Highly hydrophobic nanofibrous surfaces genearated by poly(vinylidene fluoride)

Lotus-leaf-like nanofibrous surfaces were prepared by electrospinning hydrophobic poly(vinylidene fluoride) (PVDF) from a mixed solvent of N,N-dimethylformamide (DMF) and acetone. PVDF fibrous mats with a bead-on-string morphology were generated because the nonpolar acetone decresed the viscosity of the PVDF solution and promoted the evaporation of the solution during electrospinning process. The morphology of the nanofibirous surface was examined by scanning electron microscopy. Micron-sized beads were introduced to the electrospun PVDF mats, resulting in enhanced hydrophobicity of the electrospun mats. The addition of a small amount (0.05 vol%) of acetic acid to the polymer solution effectively improved the bead-on-string morphology of the electrospun mats, and led to a higher water contact angle (WCA). The electrospun PVDF fibrous mat showed a maximum WCA of 148.5° due to the appropriate surface roughness.

Understanding Cellular Energy Harvesting through Piezoelectric Polymers with Cellular Interfaces

There is emerging interest in designing systems that are capable of harvesting energy from living tissue. These systems have potential applications in powering medical implants such as microdevices, actuators, and electronically active tissue engineering grafts. Specific attention has focused on the manipulation of system and substrate geometries to control biomimetic tasks using external electric fields1. To make these devices more feasible for in vivo usage without the need for external energy sources or stimuli, the concept of a cardiomyocyte pump has beendemonstrated using only chemical energy input to cells as a driver2. The current work describes advances in materials design and cellular integration to produce a piezoelectric system that is powered by mechanical cell contractions. Poly(vinylidene fluoride) (PVDF) is a piezoelectric material that will be driven by cardiomyocytes. Nanofibrous PVDF mats are fabricated with an electrospinning process. The chemical and electrical properties of piezoelectric PVDF films are characterized by FT-IR and voltage measurements under controlled deflection, respectively. Mimicking the highly oriented nature of human tissue and muscles may improve control/cell response; achievable with films of anisotropically aligned nanofibers. In addition to affecting the mechanical properties of such films, this macroscopic alignment has been shown to improve cell adhesion, proliferation and alignment. Anisotropic PVDF films are fabricated by modified electrospinning methods. Murine cardiomyocytes were differentiated on these films and the generated electrophysiological response of the cells was measured using a highly sensitive ammeter. This work demonstrates that aligned piezoelectric substrates are suitable for cell-based energy harvesting. These materials are conformal, can be potentially integrated with organ scale systems, and may be scaled to power microelectronic medical implants.1 Feinberg, A. et al., Science 317, 1366-1370 (2007).2 Tanaka, Y. et al., Lab on a chip 7, 207-212 (2007).

Enhanced piezoresponse of electrospun PVDF mats with a touch of nickel chloride hexahydrate salt

PVDF nanofibers are prepared using electrospinning. The effect of addition of a hydrated salt, nickel chloride hexahydrate (NiCl(2)·6H(2)O), on the phase formation is examined. Addition of the hydrated salt (NC) is found to enhance the polar β phase by about 30%. The peak to peak piezo-voltage generated for PVDF NC is almost 0.762 V, a factor of 3 higher than that for PVDF. The fiber mats exhibit a significantly enhanced dynamic strain sensor response. The voltage generated per unit micro-strain developed during the free vibration test for PVDF was 0.119 mV whereas it was 0.548 mV for PVDF NC, exhibiting a non-linearly enhanced performance vis a vis the increase in the β phase component.

Mechanical properties and biocompatibility of electrospun polylactide/poly(vinylidene fluoride) mats

Polylactide (PLA) was mixed with poly(vinylidene fluoride) (PVDF) and spun into nonwoven mats via electrospinning technique using a co-solvent system of N,N-dimethylformamide (DMF) and acetone. The resulting mats were subject to characterization including contact angle, infrared spectrometry (IR), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), tensile test, and examined using scanning electron microscope (SEM). With such a co-solvent system, the viscosity was measured, and the average fiber diameter achievable without beads for PLA, PLA/PVDF, and PVDF mats was 252 nm, 209 nm, and 355 nm, respectively. Infrared spectra showed that electrospinning can induce crystallization of PVDF. Both α and β phases were observed from the IR and WAXD results. From the results of DSC, the PLA/PVDF mats exhibited higher melting temperature but lower crystallinity than both PLA and PVDF. The tensile strength of PLA/PVDF was lower than those of PLA and PVDF. By applying stretching during eletrospinning, the ratio of strength in machine direction (MD) to that in cross direction (CD) was increased to 2. In addition, electrospun PLA/PVDF mats exhibited higher cell proliferation for L929 fibroblasts than both PLA and PVDF mats.

NOVEL POLYMER ELECTROLYTE BASED ON POLY(VINYLIDENE FLUORIDE) AND POLY(4-VINYL PYRIDINE) HAVING A NANO-CHANNEL FOR ION TRANSPORTATION

The micro-porous polymer electrolytes membranes(PEMs), notably electro-spun fiber mats, have been suggested to give an improved ionic conductivity. However, the mat-type PEMs have a poor mechanical and dimensional stability because of their inevitable porous nature. In this study, we suggest a new PEM system based on poly(vinylidene fluoride)(PVdF) mats, which can overwhelm such shortcomings of the porous mats by introducing another component, poly(4-vinyl pyridine)(P4VP), into the mats. The tensile strength of PVdF / P 4 VP membrane was considerably improved compared with that of pristine PVdF membrane under dry and wet conditions. The ionic conductivity was also improved by about 10 times than that of PVdF mat. A micro- to nano-size gap was formed at the interfaces between PVdF nanofiber and P 4 VP , and this may act as a channel for fast ion transportation under wet condition.

Novel microporous poly(vinylidene fluoride)‐graft‐poly(tert‐butyl acrylate) electrolytes for secondary lithium batteries

AbstractBACKGROUND: Much interest has recently been shown in improving the performance of lithium‐ion polymer batteries with gel polymer electrolytes (GPEs) due to a rapid expansion in industrial demand. Novel GPEs based on poly(vinylidene fluoride)‐graft‐poly(tert‐butyl acrylate) (PVDF‐g‐tBA) microporous mats are suggested in this study.RESULTS: Microfibrous polymer electrolytes were prepared using electrospinning and characterized for extent of grafting, morphology, crystallinity, electrochemical stability, ionic conductivity, interfacial resistance and cell cycleability. The degree of crystallinity was lower for tBA‐grafted PVDF mats than that of neat PVDF. The PVDF‐g‐tBA showed an improvement in the ionic conductivity, electrochemical stability, interfacial resistance and cyclic performance.CONCLUSION: The tBA‐grafted PVDF microporous electrolytes are promising candidates for enhancing the performance of lithium‐ion polymer batteries. Copyright © 2008 Society of Chemical Industry