Electrospun PVDF-HFP Research Articles

Biocompatible Silk/Polymer Energy Harvesters Using Stretched Poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) Nanofibers.

Energy harvested from human body movement can produce continuous, stable energy to portable electronics and implanted medical devices. The energy harvesters need to be light, small, inexpensive, and highly portable. Here we report a novel biocompatible device made of poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanofibers on flexible substrates. The nanofibers are prepared with electrospinning followed by a stretching process. This results in aligned nanofibers with diameter control. The assembled device demonstrates high mechanical-to-electrical conversion performance, with stretched PVDF-HFP nanofibers outperforming regular electrospun samples by more than 10 times. Fourier transform infrared spectroscopy (FTIR) reveals that the stretched nanofibers have a higher β phase content, which is the critical polymorph that enables piezoelectricity in polyvinylidene fluoride (PVDF). Polydimethylsiloxane (PDMS) is initially selected as the substrate material for its low cost, high flexibility, and rapid prototyping capability. Bombyx Mori silkworm silk fibroin (SF) and its composites are investigated as promising alternatives due to their high strength, toughness, and biocompatibility. A composite of silk with 20% glycerol demonstrates higher strength and larger ultimate strain than PDMS. With the integration of stretched electrospun PVDF-HFP nanofibers and flexible substrates, this pilot study shows a new pathway for the fabrication of biocompatible, skin-mountable energy devices.

A facile approach to fabricate superhydrophobic membranes with low contact angle hysteresis

A robust superhydrophobic polyvinyldene fluoride-co-hexafluoropropylene (PVDF-HFP) electrospun membrane was fabricated by using a modest and versatile coating technique. Inspired by the natural phenomenon of thin layer formation of dust particles on the surfaces. Electrospun mats of PVDF-HFP were coated with tetrafluoroethylene oligomers (OTFE) particles. Dust of the OTFE was created in a closed chamber and used to form a thin layer of OTFE particles on the surface of the electrospun PVDF-HFP membranes. Hot pressing was used then to infuse the loose OTFE deposited layer on the surface of the PVDF-HFP membrane. Scanning electron microscopy images indicate that OTFE particles infused ~2–3µm in the electrospun non-woven network. Static contact angle of water on the PVDF-HFP surface improved from 125° ± 2 to 156° ± 2 after OTFE coating. In addition, OTFE coating did not alter the pore size distribution of PVDF-HFP membrane and permeation flux, whereas it significantly helped in improving the water liquid entry pressure. The prepared membranes were tested in direct contact membrane distillation (DCMD) applied to desalination and reported to achieved 99.9% salt rejection with permeation flux of 13–14kg/m2h. In addition to increasing the hydrophobicity of the membranes, OTFE coating significantly reduces the contact angle hysteresis from ~90° ± 2° to ~10° ± 2°. To show the significance of contact angle hysteresis on membrane performance, high fidelity modeling based on computational fluid dynamic in thermal coupled membrane flow was developed. Results of the temperature, polarization coefficient (TPC) and heat transfer coefficient (h) clearly show the favorable impact of the reduced value of hysteresis and its implication of inducing slip. Under total slip, considerable gain in the TCP is observed and reaching as high as 25%.

Membrane-based detection of wetting phenomenon in direct contact membrane distillation

Advances in membrane distillation are limited by the wetting phenomenon. Wetting is typically determined by examining the permeate water quality. In this work, we apply an electrically conductive membrane to direct contact membrane distillation combined with an electrochemical system. The membrane was fabricated by heat pressing a carbon cloth with electrospun PVDF-HFP mat. The membrane acts not only as a barrier to reject salt with 99.6% rejection, but also as an electrode where in the current through the system is used to detect wetting which allows Na+ and Cl− ions to complete the cell. It was found that the membrane has an LEP of 36psi and mean pore size of 0.2µm. A continuous voltage of +1V was applied during the direct contact membrane distillation process, and a sharp increase in current was observed at the point where wetting was induced.

Dimensional stability and electrochemical behaviour of ZrO2 incorporated electrospun PVdF-HFP based nanocomposite polymer membrane electrolyte for Li-ion capacitors

Different weight percentages of ZrO2 (0, 3, 5, 7 and 10 wt%) incorporated electrospun PVDF-HFP nanocomposite polymer membranes (esCPMs) were prepared by electrospinning technique. They were activated by soaking in 1 M LiPF6 containing 1:1 volume ratio of EC : DMC (ethylene carbonate:dimethyl carbonate) to get electrospun nanocomposite polymer membrane electrolytes (esCPMEs). The influence of ZrO2 on the physical, mechanical and electrochemical properties of esCPM was studied in detail. Finally, coin type Li-ion capacitor cell was assembled using LiCo0.2Mn1.8O4 as the cathode, Activated carbon as the anode and the esCPME containing 7 wt% of ZrO2 as the separator, which delivered a discharge capacitance of 182.5 Fg−1 at the current density of 1Ag−1 and retained 92% of its initial discharge capacitance even after 2,000 cycles. It revealed that the electrospun PVdF-HFP/ZrO2 based nanocomposite membrane electrolyte could be used as a good candidate for high performance Li-ion capacitors.

High Performance Electrospun PVdF-HFP/MMT Nanofibrous Composite Membrane Electrolyte for Li-Ion Capacitors

The electrospun poly(vinylidene fluoride-co-hexafluoropropylene)/montmorillonite nanofibrous composite membranes (esCPMs) were prepared by electrospinning technique using a mixture of different amounts of montmorillonite (0, 3, 5, 7 and 10 wt%) into 16 wt% of PVDF-HFP polymer solution in 7:3 wt% of acetone and dimethylacetamide as the solvent. The effect of montmorillonite (MMT) on electrospun PVdF-HFP membrane has been studied by XRD, DSC, TGA and tensile strength analysis. It is found that electrospun PVDF-HFP/MMT nanofibrous composite membrane obtained using 5wt% MMT has a higher porosity, electrolyte uptake, ionic conductivity, electrochemical stability window and showed higher specific capacitance and good compatibility with electrode materials.

Montmorillonite embedded electrospun PVdF–HFP nanocomposite membrane electrolyte for Li-ion capacitors

The electrospun poly(vinylidene fluoride-co-hexafluoropropylene)/montmorillonite nanofibrous composite membranes (esCPMs) were prepared by electrospinning technique using a mixture of different amounts of montmorillonite (0, 3, 5, 7 and 10wt%) into 16wt% of PVDFHFP polymer solution in 7:3wt% of acetone and dimethylacetamide as the solvent. The effect of montmorillonite (MMT) on electrospun PVdF–HFP membrane has been studied by XRD, DSC, TGA and tensile strength analysis. The average diameter of the electrospun nanofibrous composite membrane was about ∼400nm. The physical properties such as porosity, electrolyte uptake and mechanical strength of the electrospun nanofibrous composite membrane were studied in detail. The ionic conductivity and electrochemical stability windows of the electrospun nanofibrous composite membrane containing 1M LiPF6 in EC:DMC (1:1, v/v%) as an electrolyte (esCPME) were studied by AC-impedance and linear sweep voltammetry studies, respectively. It is found that electrospun PVDF–HFP/MMT nanofibrous composite membrane obtained using 5wt% MMT has a higher porosity, electrolyte uptake, ionic conductivity and electrochemical stability window than the other nanofibrous composite membrane systems and are found to be 88.1%, 428%, 2.330×10−3S/cm and 3.1V, respectively. Finally, the charge–discharge studies were carried out by fabricating a prototype Li-ion supercapacitor by sandwiching PVDF–HFP/MMT (5wt%) nanofibrous composite membrane electrolyte in between a carbon anode and LiCo0.2Mn1.8O4 cathode. It showed higher specific discharge capacitance and good compatibility with electrode materials suggesting that the electrospun PVdF–HFP/MMT nanofibrous composite membrane electrolyte could be used as the best candidate for high performance Li-ion capacitors.

The Photovoltaic Performances of PVdF-HFP Electrospun Membranes Employed Quasi-Solid-State Dye Sensitized Solar Cells.

The PVdF-HFP nanofiber membranes with different molecular weight were prepared by electrospinning technique and were investigated as solid state electrolyte membranes in quasi solid state dye sensitized solar cells (QS-DSSC). The homogeneously distributed and fully interconnected nanofibers were obtained for all of the prepared PVdF-HFP electrospun membranes and the average fiber diameters of fabricated membranes were dependent upon the molecular weight of polymer. The thermal stability of electrospun PVdF-HFP membrane was decreased with a decrement of molecular weight, specifying the high heat transfer area of small diameter nanofibers. The QS-DSSC fabricated with the lower molecular weight PVdF-HFP electrospun nanofiber membrane exhibited the power conversion efficiency of 1 = 5.38%, which is superior over the high molecular weight membranes and is comparable with the liquid electrolyte. Furthermore, the electrospun PVdF-HFP membrane exhibited long-term durability over the liquid electrolyte, owing to the higher adsorption and retention efficiencies of liquid electrolyte in its highly porous and interconnected nanofibers. Thus the proposed electrospun PVdF-HFP membrane effectively tackled the volatilization and leakage of liquid electrolyte and provided good photoconversion efficiency associated with an excellent stability, which constructs the prepared electrospun membranes as credible solid state candidates for the application of QS-DSSCs.

Highly Aligned Poly(vinylidene fluoride-co-hexafluoro propylene) Nanofibers via Electrospinning Technique

We report on the simple way of obtaining aligned poly(vinylidiene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanofibers by electrospinning process. The collector drum rotation speed was adjusted to prepare well aligned PVDF-HFP nanofibers. The degree of alignment and the orientation of PVDF-HFP nanofibers can be significantly altered by varying the speed of collector drum rotation. The resultant PVDF-HFP nanofibers were systematically characterized. From the scanning electron microscopy data, it was found that the electrospun PVDF-HFP nanofibers were formed with well-aligned nature. The X-ray diffraction results revealed that the electrospun PVDF-HFP nanofibers with β-phase can be formed by the increased collector drum rotation speed. Overall, the collector rotation speed during the electrospinning process plays an important role in obtaining well-aligned and improved characteristics of PVDF-HFP nanofibers.

Underwater superoleophobic cellulose/electrospun PVDF–HFP membranes for efficient oil/water separation

Electrospun polyvinylidene fluoride-co-hexafluoropropylene (PVDF–HFP) nanofibers have been modified with cellulose regenerated from ionic liquid solution. Three-dimensional impregnation of cellulose provides greater control over porosity, pore size, wettability as well as the mechanical and thermal properties of the electrospun membrane. Formation of smaller pores with narrower pore size distribution is achieved as the fibers are coated with cellulose matrix. At 15wt.% cellulose, the mechanical properties of electrospun PVDF–HFP are enhanced as the elastic modulus increases from 17MPa to 54MPa and the tensile strength also improves from 5.5MPa to 8.6MPa. The resulting membrane exhibits superhydrophilicity and underwater supoeroleophobicity and is successfully applied for selective separation of water from oil with efficiencies up to 99.98%.

Fabrication and characterization of reinforced electrospun poly(vinylidene fluoride-co-hexafluoropropylene) nanofiber membranes

In this study, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanofiber membranes with different amounts of polyethylene glycol (PEG) and polyethylene glycol dimethacrylate (PEGDMA) oligomer were fabricated via electrospinning. The obtained nanofiber membranes were subsequently thermal treated to produce physically bonded structures and chemically cross-linked networks, which were confirmed by scanning electron microscopy (SEM), Fourier transform infrared spectra (FT-IR) and wide-angle X-ray diffraction (WAXD). Young’s modulus of electrospun nanofiber membrane with the composition of PVDF-HFP/PEG/PEGDMA (6/1/3, w/w/w) was approximately three times for the case of nanofiber membrane and four times for the case of single nanofiber higher than that of pure PVDF-HFP nanofiber, respectively. The characteristic of cell cycling performance was demonstrated as the possibility of its application at ambient temperature. The electrospun PVDF-HFP nanofiber membrane presented great electrolyte uptake because the membrane had higher porosity due to the structural features of nonwoven fabric, and the amorphous regions in PVDF-HFP could trap large amounts of liquid electrolyte. Also, the cell performance of the membrane as the separator declared high discharge capacity. As the result, the reinforced electrospun composite nanofiber membrane was found to be a promising candidate as a separator for lithium-ion batteries.

Electrospun Superhydrophobic Poly(vinylidene fluoride-co-hexafluoropropylene) Fibrous Membranes for the Separation of Dispersed Water from Ultralow Sulfur Diesel

One of the major causes of diesel engine maintenance problems is water contamination in fuels. This paper discusses fabrication, characterization, and testing of non-woven glass fiber mats augmented with an electrospun layer of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) fibers for the separation of secondary water dispersions from ultralow sulfur diesel. The PVDF-HFP fibers had an average fiber diameter of 334 nm. All PVDF-HFP layers had water contact angles greater than 150° with relatively low hysteresis values, making them superhydrophobic. Water separation experiments showed that glass fiber media augmented with electrospun PVDF-HFP fiber mats significantly improved water separation, with water removal efficiencies reaching 99%, as compared to glass fiber media without the PVDF-HFP layer.

Dye-sensitized solar cells based on electrospun poly(vinylidenefluoride-co-hexafluoropropylene) nanofibers

Poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) nanofibers were prepared by the electrospinning method and used as polymer electrolytes in dye-sensitized solar cells (DSSCs). The electrolyte uptake and ionic conductivity of electrospun PVDF-HFP nanofibers with different diameters changed significantly, regardless of the nanofiber thickness. The PVDF-HFP nanofibers prepared from a 15 wt% spinning solution showed high ionic conductivity (1.295 S/cm) and electrolyte uptake (947 %). DSSCs based on the 15 wt% PVDF-HFP nanofiber electrolyte showed an electron transit time of 6.34 × 10−3 s, electronic recombination time of 5.88 × 10−2 s, and conversion efficiency of 3.13 %. Thus, we concluded that the electrospun PVDF-HFP nanofibers can be used as polymer electrolytes in flexible DSSCs as well.

Constructing high energy density non-aqueous Li-ion capacitors using monoclinic TiO2-B nanorods as insertion host

We report the construction and electrochemical performance of a high power Li-ion hybrid electrochemical capacitor (Li-HEC) using monoclinic TiO2-B nanorods as anodes with activated carbon cathodes. First, TiO2-B nanorods are synthesized by a conventional hydrothermal approach and a subsequent ion-exchange reaction with protons. Phase formation and morphological features are investigated through X-ray diffraction and scanning and transmission electron microscopy, respectively. Li-insertion properties are evaluated in half-cell configurations and reversible insertion of 0.52 moles of Li at a current density of 100 mA g−1 were found. The Li-HEC is constructed with optimized mass loading of the electrodes along with Whatman and electrospun PVdF–HFP membranes. Among them, electrospun PVdF–HFP comprising Li-HEC is found to be superior in terms of cyclability, higher energy and power densities. The electrospun PVdF–HFP comprising Li-HEC delivered the maximum energy and power densities of 23 W h kg−1 and 2.8 kW kg−1, respectively, with a capacitance retention of ∼73% after 1200 cycles at a current density of 1.5 A g−1.

Extraordinary long-term cycleability of TiO2-B nanorods as anodes in full-cell assembly with electrospun PVdF-HFP membranes

One dimensional TiO2-B nanorods are synthesized by a conventional hydrothermal approach under highly concentrated alkali hydroxide solutions. Various characterization techniques such as X-ray diffraction, Raman studies, BET surface area measurements, scanning electron microscopy and transmission electron microscopy (TEM) are utilized. Electrochemical Li-insertion properties are evaluated by means of half-cell configuration (Li/TiO2-B) which delivered a discharge capacity of 195 mA h g−1 at a current density of 150 mA g−1 under ambient temperature conditions. The test cell, Li/TiO2-B, displayed good cycling profiles up to 500 cycles with columbic efficiency over 99.5%. Full-cell, LiMn2O4/TiO2-B, is fabricated and tested both in conventional liquid and PVdF-HFP membranes at a current density of 150 mA g−1 and exhibited an excellent cycleability up to 1000 cycles at an operating potential of ∼2.5 V. The results demonstrate the improved electrochemical performance and durability of one dimensional nanostructures i.e. TiO2-B nanorods and electrospun membranes during prolonged cycling. In addition, ex-situ TEM analysis revealed the retention of nanorod morphology along with the crystalline structure after 1000 cycles in full-cell assembly, which ensures excellent long-term cycleability of TiO2-B anodes.

A novel strategy to construct high performance lithium-ion cells using one dimensional electrospun nanofibers, electrodes and separators

We successfully demonstrated the performance of novel, one-dimensional electrospun nanofibers as cathode, anode and separator-cum-electrolyte in full-cell Li-ion configuration. The cathode, LiMn2O4 delivered excellent cycle life over 800 cycles at current density of 150 mA g(-1) with capacity retention of ~93% in half-cell assembly (Li/LiMn2O4). Under the same current rate, the anode, anatase phase TiO2, rendered ~77% initial reversible capacity after 500 cycles in half-cell configuration (Li/TiO2). Gelled electrospun PVdF-HFP exhibits liquid-like conductivity of ~3.2 mS cm(-1) at ambient temperature conditions (30 °C). For the first time, a full-cell is fabricated with enitrely electrospun one-dimensional materials by adjusting the mass loading of cathode with respect to anode in the presence of gelled PVdF-HFP membrane as a separator-cum-electrolyte. Full-cell LiMn2O4|gelled PVdF-HFP|TiO2 delivered good capacity characteristics and excellent cyclability with an operating potential of ∼2.2 V at a current density of 150 mA g(-1). Under harsh conditions (16 C rate), the full-cell showed a very stable capacity behavior with good calendar life. This clearly showed that electrospinning is an efficient technique for producing high performance electro-active materials to fabricate a high performance Li-ion assembly for commercialization without compromising the eco-friendliness and raw material cost.

Characterization of N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide-based polymer electrolytes for high safety lithium batteries

Poly(vinylidene difluoride-co-hexafluoropropylene) (PVdF-HFP) membrane was prepared by electrospinning. The membranes served as host matrices for the preparation of ionic liquid-based polymer electrolytes (ILPEs) by activation with non-volatile, highly thermally stable, and safe room temperature ionic liquid (RTIL) electrolytes; N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide (Py14TFSI) complexed with 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). In this work, the first combination of electrospun PVdF-HFP fiber polymer host and pyrrolidinium-based ionic electrolyte was employed for highly stable lithium batteries. The ILPE exhibited low Li+–TFSI coordination, low crystallinity, high thermal stability, high electrochemical stability, and high ionic conductivity with a maximum of 1.1 × 10−4 S cm−1 at 0 °C. The ILPE exhibited good compatibility with a LiFePO4 electrode on storage and good charge–discharge performance in Li/ILPE/LiFePO4 cells at room temperature, delivering specific capacities of 143 and 115 mA h g−1 at 0.1 and 1 C-rates. The ILPE also exhibited stable cycle properties and have therefore been demonstrated to be suitable for lithium battery applications.

Fabrications of Poly(vinylidenefluoride-co-hexafluoropropylene) Nanofibers Containing Inorganic Filler by Electrospinning Technique and Its Application to Dye-Sensitized Solar Cells

We prepared Poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) nanofibers containing nano-sized inorganic BaTiO3 filler by electrospinning technique, and applied to the dye sensitized solar cells (DSSCs). This technique compensates the draw back of leakage of the electrolyte in DSSCs. Moreover, electrospun PVDF-HFP nanofibers containing inorganic filler have better ionic conductivity than those of without filler, and the DSSC device using inorganic filler showed better efficiency than without inorganic filler. The best result of Voc, Jsc, FF, and η of the DSSC devices using the electrospun PVDF-HFP nanofibers containing 20 wt% inorganic BaTiO3 filler were the values of 0.70 V, 12.9 mA/cm2, 0.58 and 5.15% under AM 1.5, respectively. We also measured up-take, ionic conductivity and porosity to investigate the effect of electrolyte in the electrospun nanofibers.

Modification of electrospun poly(vinylidene fluoride‐co‐hexafluoropropylene) membranes through the introduction of poly(ethylene glycol) dimethacrylate

AbstractFor the modification of an electrospun poly (vinylidene fluoride‐co‐hexafluoropropylene) (PVDF–HFP) membrane for its potential use as an electrolyte or separator in lithium batteries, poly(ethylene glycol) dimethacrylate (PEGDMA) was introduced into a polymer solution for electrospinning. A post heat treatment of the as‐electrospun membrane at an elevated temperature was performed for PEGDMA polymerization, and this was verified by Fourier transform infrared spectroscopy. The results showed that no significant variations in the membrane morphology were detected when a small amount of PEGDMA (PVDF–HFP/PEGDMA mass ratio = 4/1) was incorporated. This electrospun membrane after heat treatment at 130°C for 2 h exhibited a significantly higher tensile strength (6.26 ± 0.22 MPa) than that of an electrospun PVDF–HFP membrane (3.28 ± 0.35 MPa) without PEGDMA. The porosity and liquid absorption of the electrospun PVDF–HFP/PEGDMA (4/1) membrane were 70.0 ± 1.6% and 267 ± 11%, respectively, lower than those of the electrospun PVDF–HFP membrane (76.5 ± 0.3% and 352 ± 15%) because of the introduction of PEGDMA. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Effect of electrolyte in electrospun poly(vinylidene fluoride- co-hexafluoropropylene) nanofibers on dye-sensitized solar cells

We prepared poly(vinylidene fluoride- co-hexafluoropropylene) (PVDF-HFP) nanofibers by the electrospinning method and applied to the polymer matrix in polymer electrolytes for dye-sensitized solar cells (DSSCs). The uptake, ionic conductivity, and porosity of the electrospun PVDF-HFP nanofiber films showed 653±50%, 4.53±1.3×10 −3 S/cm, and 70±2.3%, respectively, regardless of the diameter and morphology of nanofibers. In addition, several DSSC devices using the electrospun PVDF-HFP nanofiber films as the polymer matrix were prepared to investigate the photovoltaic effect of iodine (I 2) concentrations on DSSC devices. With an increase of I 2 concentration in electrolyte solutions, the ionic conductivity increased, while the photocurrent density of DSSC devices decreased.

Antibacterial activities of surface modified electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) fibrous membranes

Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) membrane, with its excellent chemical and mechanical properties, has good potential for broad applications. However, due to its hydrophobic nature, microbial colonization is commonly encountered. In this work, electrospun PVDF-HFP fibrous membranes were surface modified by poly(4-vinyl-N-alkylpyridinium bromide) to achieve antibacterial activities. The membranes were first subjected to plasma pretreatment followed by UV-induced surface graft copolymerization of 4-vinylpyridine (4VP) and quaternization of the grafted pyridine groups with hexylbromide. The chemical composition of the surface modified PVDF-HFP electrospun membranes was studied by X-ray photoelectron spectroscopy (XPS). The morphology and mechanical properties of pristine and surface modified PVDF-HFP fibrous membranes were characterized by scanning electron microscopy (SEM) and tensile test, respectively. The antibacterial activities of the modified electrospun PVDF-HFP fibrous membranes were assessed against Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli). The results showed that the PVDF-HFP fibrous membranes modified with quaternized pyridinium groups are highly effective against both bacteria with killing efficiency as high as 99.9999%.