Polyvinylidene Fluoride Electrospun Nanofibers Research Articles

Influence of non-woven antistatic substrate materials on polyvinylidene fluoride electrospun nanofibers: fabrication, characterization, and performance evaluation

Influence of non-woven antistatic substrate materials on polyvinylidene fluoride electrospun nanofibers: fabrication, characterization, and performance evaluation

Stem Cell Self‐Triggered Regulation and Differentiation on Polyvinylidene Fluoride Electrospun Nanofibers

AbstractSmart electroactive materials that can dynamically regulate stem cell fate without external stimuli have fascinated increasing attention. Meanwhile, noninvasive electrical stimulation has emerged as a less restrictive approach, generating considerable interest in its potential biomedical applications. The intricate interplay between cells and materials within complex microenvironments includes encompassing substrate response, ion exchange, and membrane potential alterations. However, the mechanisms by which smart materials influence stem cells have yet to be fully elucidated. Herein, electrospinning technology is utilized to fabricate bone‐mimicking microenvironments comprising disordered and highly oriented polyvinylidene fluoride (PVDF) nanofibers. The aligned annealed PVDF (AA) and random annealed PVDF (RA) membranes present high fractions of β‐phase. By comparing the osteogenic ability, calcium activity, and F‐actin distribution of bone marrow‐derived mesenchymal stem cells (BMSCs) cultured with these PVDF nanofibers, it is proposed that the stem cells autonomously regulate their differentiation by remodeling the cytoskeleton on the electrospun membranes. Electrical stimulation, more adhesion area, and active calcium influx support the greater osteogenesis of BMSCs on RA than AA. This mechanism can provide a basic theory for the design and preparation of bone tissue engineering scaffolds and contribute to the further study of cells and microenvironments.

AgNPs-thiols modified PVDF electrospun nanofiber membrane with a highly rough and pH-responsive surface for controllable oil/water separation

To develop a novel membrane with controllable wettability in response to external stimuli for intelligent oil/water separation is always in urgent demand. In this study, a pH-responsive nanofibrous membrane was prepared through the step-by-step modification of polyvinylidene fluoride (PVDF) electrospun nanofiber membrane, including mussel-inspired self-polymerization of polydopamine (PDA), immobilization of silver nanoparticles (AgNPs) and self-assembly of thiols. A rough membrane surface could be formed by the loading of AgNPs, and the subsequent introduction of HS(CH2)11CH3/HS(CH2)10COOH via metal-thiol coordination could endow the membrane with pH-responsive wettability. The surface of the membrane was able to quickly and reversely switch between superhydrophobicity and superhydrophilicity through simply applying pH stimulus at pH 7 and 13, respectively. The membrane can be applied for separating multiphase oil/water mixtures, achieving separation efficiency of over 99.2% for light oil/water mixture and 96.5% for heavy oil/water mixture with a stable flux of around 2500 L/m2·h for water and 11,000 L/m2·h for oil over the 10-cycle separation process. Meanwhile, the membrane exhibited separation efficiency of higher than 99% for all the tested oil-in-water emulsions, and the water flux of the membrane could be effectively recovered by water rinsing. Moreover, the membrane demonstrated a good structural stability against rigorous mechanical abrasion. The pH-responsive membrane could be potentially applied for smart and energy-saving separation and recycle of oil or water from oily wastewater.

Composite Polymer Electrolyte Membranes based on Nafion and Modified PVDF Electrospun Nanofiber Mats

We fabricated the nanofiber composite membranes by impregnating Nafion into the modified polyvinylidene fluoride(PVDF) electrospinning nanofiber mat for proton exchange membrane fuel cells applications. The hydrophobic PVDF nanofibers mat became to the hydrophilic state by alkali treatment for the full embedding of Nafion into the PVDF network. The fabricated composite membranes exhibit significantly enhanced thermal stabilities, swelling resistance, and observably improved mechanical property compared to the pristine Nafion membrane. When the content of PVDF nanofiber mat is 15.1wt% in the membrane, the proton conductivity of the nanofiber composite membrane is nearly equal to that of pristine Nafion membrane with the same condition. The experimental results show that the prepared composite membrane can be used as a promising polyelectrolyte membrane for fuel cell applications.

Enhanced piezoelectric properties of polyvinylidene fluoride nanofibers using carbon nanofiber and electrical poling

Abstract In this study, for the first time we report the combined impact of electrospinning, carbon nanofiber (CNF) addition and electrical poling in the polyvinylidene fluoride (PVDF) polymer on its beta phase transition and enhancement of piezoelectric effect. CNF (0.25%, 0.5%, 0.75% and 1% (w/w)) dispersed PVDF electrospun nanofibers were characterized for their morphology, functional group and electrical properties using SEM, FTIR, Raman, XRD and impedance analyzer. The developed nanofibers showed promising results in beta phase transition and 0.5% (w/w) CNF filled PVDF nanofibers were found to possess high beta phase crystals compared to other studied samples. After 30 V/μm electrical polling at 30 °C for 6 h, piezoelectric property of 0.5% (w/w) CNF based nanocomposite nanofiber showed highest open circuit voltage and short circuit current (5.8 ± 0.17 V and 1.2 ± 0.1 µA, respectively, at 35 µm compression). In future, these matrices can be used for development of affordable and nontoxic energy converters in biomedical wearable sensors.

Electrospun Nanofibers Embedding ZnO/Ag2CO3/Ag2O Heterojunction Photocatalyst with Enhanced Photocatalytic Activity

The immobilization of photocatalyst onto substrate has a great potential for energy-intensive separation to avoid the costly separation process and unwanted release of photocatalyst into the treated water. In this study, electrospun nanofiber composed of polyvinylidene fluoride (PVDF) with the immobilized ZnO, ZnO/Ag2CO3, ZnO/Ag2CO3/Ag2O, and ZnO/Ag2O photocatalysts were prepared via the electrospinning process. The immobilized ZnO and heterojunctioned ZnO in the PVDF electrospun nanofiber were proven via X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The electrospinning allowed high chemical binding of the nanofiber composite with good physical interaction between the photocatalyst and the electrospun nanofiber. AFM images obtained for the nanofibers were found to be rougher than that of the pristine PVDF electrospun nanofiber. Among the photocatalyst embedded, the immobilized ZnO/Ag2CO3/Ag2O had endowed the nanofiber with an excellent photocatalytic activity and recyclability for the degradation of the RR120 under UV light irradiation. Based on the results, effective immobilization of ZnO/Ag2CO3/Ag2O in PVDF nanofiber with 99.62% photodegradation in 300 min compared to PVDF-ZnO, PVDF-ZnO/Ag2CO3, and PVDF-ZnO/Ag2O of 28.14%, 90.49%, and 96.34%, respectively. The effective ZnO/Ag2CO3/Ag2O immobilization into polymers with affinity toward organic dye pollutants could both increase the efficiency and reduce the energy requirements for water treatment via the photocatalytic application.

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.

TiO2-FTCS modified superhydrophobic PVDF electrospun nanofibrous membrane for desalination by direct contact membrane distillation

The major challenges for electrospun membranes used in direct contact membrane distillation (DCMD) process are insufficient pore wetting resistance related with hydrophobicity and pore structure of membrane surface. A novel super-hydrophobization method containing first coating TiO2 nanoparticles on membrane surface by the low temperature hydrothermal process and then the TiO2 coated membrane being fluorosilanized with low surface energy material of 1H, 1H, 2H, 2H-perfluorododecyl trichlorosilane (FTCS) was employed to modify the virgin polyvinylidene fluoride electrospun nanofiber membrane (PVDF ENM). Results showed that this TiO2-FTCS modified membrane possessed high hydrophobicity (157.1°), high mean roughness (4.63μm), considerable wetting resistance (158kPa), well-distributed pore size (0.81μm), reasonable surface porosity (57%) and modest membrane thickness (55μm). These combined properties made the modified PVDF ENM an attractive candidate for DCMD. High flux and stable desalination performances were achieved during short-term DCMD process (73.4LMH permeate flux, 99.99% salt rejection) using 3.5wt% NaCl solution. Long-term DCMD process with actual reverse osmosis brine as feed solution also showed high performance (40.5LMH, 99.98%). These results exceeded those of commercial PVDF membrane and unmodified PVDF ENM significantly, suggesting the potential for PVDF ENM in DCMD applications.

Reinforcement of electroactive characteristics in polyvinylidene fluoride electrospun nanofibers by intercalation of multi-walled carbon nanotubes

This research work reports on development and characterization of multi-walled carbon nanotube (MWCNT)-doped polyvinylidene difluoride (PVDF) nanofibers by the electrospinning method. PVDF is an extensively studied polymer both theoretically and experimentally due to its appealing ferroelectric, piezoelectric, and pyroelectric properties which strongly favors its promising applications in the development of micro/nanostructure devices. The foremost reason for its ferroelectric and piezoelectric behaviors has been attributed to its crystalline structure, specifically the presence of β-phase; however, the existence of the small percentage of β-phase in pristine PVDF limits its applications. To enhance the electroactive features in the PVDF, MWCNTs have been doped in it to prepare electrospun nanofibers, as electrospinning is a single-step approach. These nonwoven nanofibers were prepared at a DC voltage of 20 kV which were subsequently calcined at 100 °C for 12 h. The estimation of crystal structure and phase identification in these nanofibers have been determined by attenuated FT-IR and XRD, while the morphology, microstructure, mean diameter, and length have been examined by FE-SEM. The observed electrical conductivity, capacitance, permittivity (e), conductivity (δ), and impedance (Z) in these samples have been tailored by doping a range of MWCNT contents and optimizing the experimental conditions.

Composite membranes of Nafion and poly(styrene sulfonic acid)-grafted poly(vinylidene fluoride) electrospun nanofiber mats for fuel cells

Surface-initiated atom transfer radical polymerization has been performed on poly(vinylidene fluoride) electrospun nanofibers (PVDFNF) to incorporate poly(styrenesulfonic acid) (PSSA) chains tethered on PVDFNF surfaces. The obtained PSSA-g-PVDFNF nanofibers are used as reinforcement for Nafion to prepare Nafion/PSSA-g-PVDFNF composite membrane (Nafion/NF-CM). The PSSA chains tethered on the nanofiber surfaces improve the interfacial compatibility between the nanofiber reinforcement and the Nafion matrix, and might provide a proton-conducting pathway along the nanofibers. As a result, the proton conductivity of Nafion/NF-CM membrane is 2.5-fold of the value recorded with the nanofiber-free recasting Nafion membrane. The H2/O2 single cell employing Nafion/NF-CM membrane shows a maximum power density of 770mWcm−2 which is 1.5-fold of the value recorded with the commercial Nafion 212 membrane and a current density at 0.6V of 940mAcm−2 which is about 2.7-fold of the value recorded with Nafion 212. The Nafion/NF-CM membrane is also suitable for direct methanol fuel cell, in which it could be operated at a 5M methanol solution to show a cell performance of 91.2mWcm−2 for maximum power density and 464mAcm−2 for current density at 0.2V, which are about 1.5-fold of the values recorded with the commercial Nafion 117 membrane at 2M methanol solution.

Self-sustained webs of polyvinylidene fluoride electrospun nano-fibers: Effects of polymer concentration and desalination by direct contact membrane distillation

The effects of the polymer polyvinylidene fluoride (PVDF) concentration on the characteristics and direct contact membrane distillation (DCMD) desalination performance of self-sustained electrospun nano-fibrous membranes (ENMs) have been studied. Different polymer concentrations ranging from 15 to 30wt% were considered in the solvent mixture N,N-dimethyl acetamide and acetone, while all other electrospinning parameters were maintained the same. Viscosity, electrical conductivity and surface tension of the polymer solutions were measured and the effects of the PVDF concentration on fiber diameter, thickness, water contact angle, inter-fiber space, void volume fraction, liquid entry pressure, mechanical and thermal properties of the ENMs were investigated. The minimum polymer concentration, critical chain entanglement concentration, required for electrospinning beaded fibers and the concentration needed for the formation of bead-free fibers were localized. Two groups of ENMs were identified based on the surface structure of the ENMs, their void volume fraction and inter-fiber space. Bead-free ENMs, prepared with PVDF concentration higher than 22.5wt%, exhibit higher DCMD permeate flux than the beaded ENMs. Beaded ENMs can be used in desalination by DCMD. Among the prepared ENMs, the optimized membrane exhibiting the highest DCMD performance was prepared with 25wt% PVDF concentration.

Self-sustained webs of polyvinylidene fluoride electrospun nanofibers at different electrospinning times: 1. Desalination by direct contact membrane distillation

Self-sustained electrospun nanofibrous membranes (ENMs) were prepared using the polymer polyvinylidene fluoride (PVDF) and applied for desalination by direct contact membrane distillation (DCMD). Different electrospinning times were considered to prepare the PVDF ENMs of different thicknesses ranging from 144.4 to 1529.3μm. A systematic experimental study on the effects of membrane thickness on the DCMD performance is carried out for the first time. The surface and cross-section of the ENMs were studied by scanning electron microscopy and the mean size of the fibers together with its distribution was determined. The water contact angle, the inter-fiber space, the void volume fraction and the liquid entry pressure of water inside the inter-fiber space were determined by different characterization techniques. It was observed an enhancement of the thickness and the liquid entry pressure of water with the increase of electrospinning time, a decrease of the mean size of the inter-fiber space, whereas no significant changes were observed for the diameter of the electrospun fibers (1.0–1.3μm), the void volume fraction (0.85–0.93) and the water contact angle (137.4–141.1°). The size of the inter-fiber space is not uniform throughout the thickness of the ENMs. The effects of the ENMs thickness on the DCMD performance was studied for different feed temperatures and sodium chloride feed aqueous solutions with concentrations up to 60g/L, which is about two times greater than a typical seawater concentration. The permeate flux of the ENMs is lower for longer electrospinning time and the obtained permeate fluxes in this study are higher than those reported so far for PVDF ENMs.

Self-sustained webs of polyvinylidene fluoride electrospun nanofibers at different electrospinning times: 2. Theoretical analysis, polarization effects and thermal efficiency

A novel theoretical model that considers the gas transport mechanisms through the inter-fiber space of self-sustained electrospun nanofibrous membranes (ENMs) is developed for direct contact membrane distillation (DCMD). The theoretical model involves the structural characteristics of the ENMs, the heat transfer mechanisms and the nature of mass transport through the self-sustained web. The permeate fluxes of different ENMs prepared with different electrospinning times and therefore different thicknesses were predicted for different feed temperatures and sodium chloride salt concentrations up to 60g/L. The used ENMs exhibit different parameters such as liquid entry pressure of water, inter-fiber space, void volume fraction, thickness, etc. In contrast to what reported in other theoretical MD studies considering Bosanquet equation with equal mass transport contributions for Knudsen diffusion and ordinary molecular diffusion, in this study the contribution of each mass transport mechanism was determined. It was found that the Knudsen contribution increases with the increase of the ratio of the mean electrospun fiber diameter to the inter-fiber space. The predicted permeate fluxes were compared with the experimental ones and reasonably good agreements between them were found. The temperature polarization coefficient (θ) and the vapor pressure polarization coefficient (ψ) both increase with the thickness of the ENMs, whereas the concentration polarization coefficient (β) decreases indicating the dominant effect of the temperature polarization effect. β was found to be higher for the ENMs having higher permeate fluxes and for greater feed temperatures, whereas it decreases slightly with the increase of the feed salt concentration. The thermal efficiency (EE) is enhanced with the increase of the feed temperature being in all cases for all studied ENMs greater than 78.8% and the heat transfer by conduction less than 20% of the total heat transferred through the ENMs.