Fabrication of Aligned Poly(L‐lactide) Fibers by Electrospinning and Drawing

A new target collector was designed for taking up aligned nanofibers by electrospinning. The collector consists of a rotor around which several fins were attached for winding electrospun filaments continuously in large amounts. The alignment of the nanofibers wound on the collector was affected by the electrospinning conditions, such as the needle‐to‐collector distance and the applied voltage, but not by the rotation speed of the collector. At a voltage of 0.5 kV · cm^?1, about 60% of the fibers were found to be aligned within an angle of ± 5° relative to the rotational direction of the collector. The fiber alignment was improved to 90% by drawing the fiber bundle 2–3 times at 110 °C. The drawing was also effective for crystal orientation of the fibers as revealed by WAXD. The drawn fibers show improved mechanical properties.

     

Electrospinning superhydrophobic–superoleophilic PVDF-SiO2 nanofibers membrane for oil–water separation

Oil–water separation has attracted research interest due to the damages of oily wastewater caused to the environment and human beings. Electrospun fiber membrane has high oil–water separation performance. A nanofibers membrane with multi-stage roughness was prepared by electrospinning using poly(vinylidene fluoride)(PVDF)-silica blend solution as raw material. The result shows that the water contact angle (WCA) of the nanofibers membrane was promoted from 138.5 ± 1° to 150.0 ± 1.5° when the SiO₂ content was increased from 0 to 3 wt%. The nanofibers membranes exhibited excellent separation efficiency (99 ± 0.1%) under gravity drive, with high separation flux of 1857 ± 101 L·m⁻²·h⁻¹. More importantly, the obtained PVDF-SiO₂ nanofibers membranes showed excellent multi-cycle performance and stable chemical resistance, which would make them great advantages for the practical application of oil–water separation.     

Fabrication of high-efficiency anatase TiO2 photocatalysts using electrospinning with ultra-violet treatment

In metal oxide nanofiber fabrication using the electrospinning method, heat treatment is performed at temperatures of 500°C or higher for crystallization and polymer desorption. Therefore, it is difficult to fabricate low-temperature phase metal oxides that crystallize at low temperatures. TiO₂, a representative metal oxide often used as photocatalysts, is known to have higher photocatalytic activity in the low-temperature phase (anatase structure) than in the high-temperature phase (rutile structure). Studies on the fabrication of TiO₂ anatase nanofibers using conventional electrospinning have reported disadvantages such as the partial expression of rutile structures and low crystallinity. This study developed an anatase TiO₂ nanofiber as a high-efficiency catalyst based on the electrospinning method and a residual organic matter cleaning method that employs ultra-violet (UV) light. We fabricated nanofibers using the electrospinning method and implemented TiO₂ nanofibers with the anatase structure through heat treatment at 260°C. Residual organics remaining after heat treatment of the fabricated crystalized TiO₂ nanofibers were removed by exposing them to UV light, thereby improving photocatalytic efficiency. The photocatalytic efficiency of the fabricated TiO₂ nanofibers was confirmed through a methylene blue (MB) decomposition experiment under visible light irradiation. The photocatalytic efficiency (time taken for the concentration of the MB solution to reach 50%) of the UV-treated TiO₂ nanofibers was approximately six times higher than of P25 and the heat-treated nanofibers.     

Fabrication of superhydrophobic and self cleaning PVA-silica fiber coating on 304L SS surfaces by electrospinning

In this work superhydrophobic coating with self cleaning property is fabricated on 304L SS samples directly using a simple one step electrospinning process followed by silane treatment by using polyvinyl alcohol (PVA) and tetraethyl orthosilicate solution. A maximum water contact angle of 169.2° ± 2.1° is obtained at an electrospinning potential of 15 kV for 2 h, with a distance of 18 cm between the collector and needle. The hierarchical nanostructures thus formed on 304L SS composed of poly(vinyl alcohol)-silica microbeads and nanofibers. The surface morphologies are optimized by varying the electrospinning voltage, time, distance between needle and the collector and aging duration of the precursors. Attenuated total reflectance-infrared spectroscopy studies at different stages of preparation confirmed the presence of PVA/SiO₂ composite nanofibers deposited on the 304L SS surface. The reaction of SiO₂ nanofibers with hexamethyl disilazane resulted in the formation of Si O Si bonds that provided water repellent property. The developed SHP surface coating on 304L SS sample showed dynamic bouncing of water droplets and excellent self cleaning performance. The sample retained the SHP behavior in chloride solutions with different ionic strengths and pH.     

Fabrication of continuous nanofiber yarn using novel multi‐nozzle bubble electrospinning

A novel multi‐nozzle bubble electrospinning apparatus, including spinning unit, metering pump, constant flow pump, metal funnel and yarn winder, was designed for the preparation of continuous twisted polyacrylonitrile nanofiber yarns, and the principle of nanofiber yarn spinning was studied. An innovative spinning unit consisting of nozzle and air chamber was used to improve the production of nanofibers. Double conjugate electrospinning was developed using two pairs of oppositely charged spinning units to neutralize the charges. The effects of applied voltage, air flow rate, overall solution flow rate and funnel rotary speed on the fiber diameter, production rate and mechanical properties of the nanofiber yarns were analyzed. Nanofibers could be aggregated stably and bundled continuously, then twisted into nanofiber yarns uniformly at an applied voltage of 34 kV, air flow rate of 1200 mL min^?1 and overall solution flow rate of 32 mL h^?1. With an increase in the funnel rotary speed, the twist angle of the nanofiber yarns gradually increased when the take‐up speed was constant. The yarn tensile strength and elongation at break showed an increasing trend with increasing twist angle. Nanofiber yarns obtained using this novel method could be produced at a rate from 2.189 to 3.227 g h^?1 with yarn diameters ranging from 200 to 386 µm. Nanofiber yarns with a twist angle of 49.7° showed a tensile strength of 0.592 cN dtex^?1 and an elongation at break of 65.7%. © 2013 Society of Chemical Industry     

Alumina nanofibers obtained from poly(vinyl alcohol)/boehmite nanocomposites

Poly(vinyl alcohol) (PVA)/boehmite nanocomposite (precursor) nanofibers were formed by electrospinning using a PVA aqueous solution of dispersed boehmite nanoparticles as the spinning solution. The alumina nanofibers were obtained by calcination of the precursor nanofibers between 500 and 1200°C. The specific surface area of the precursor nanofibers was around 6 m²/g, and that of the γ‐alumina nanofibers calcined at 500°C was around 300 m²/g. The specific surface areas and the fiber diameters were not affected by the alumina contents in the precursors. Also, the diameter of the alumina nanofibers was not affected by the calcination temperature of the precursor nanofibers. The pore characteristics of the alumina nanofibers decreased with increased calcination temperature due to the sintering, and nonporous α‐alumina nanofibers were obtained by calcination of the precursor nanofibers at 1200°C. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effects of some electrospinning parameters on morphology of natural silk‐based nanofibers

Natural silk, from Bombyx mori solutions were electrospun into nanofibers, with diameters ranged from 60 to 7000 nm. The effects of electrospinning temperature, solution concentration and electric field on the formation nanofibers were studied. Optical and scanning electron microscope were used to study the morphology and diameter of electrospun nanofibers. It was observed that the nanofibers became flattened with ribbon‐like shape with increasing the electrospinning temperature. The nanofiber diameter increases with the increase in the concentration of silk solution at all electrospinning temperature. With increasing the voltage of electric field at 50°C, morphology of the nanofibers changes from ribbon‐like structure to circular cross section. Referring to the literature the probable mechanism responsible for the change of morphology is pointed out. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of nanocrystalline cellulose addition on needleless alternating current electrospinning and properties of nanofibrous polyacrylonitrile meshes

Needleless alternating current (AC)‐electrospinning is capable of achieving high nanofiber generation rates while adding more flexibility to the process development when compared to common direct current (DC)‐electrospinning. However, AC‐electrospinning process may produce very different results than DC‐electrospinning when using the same precursors. This study demonstrated that stable AC‐electrospinning of uniform and mechanically strong polyacrylonitrile (PAN) nanofibrous meshes can be achieved at 30 ± 5 kV rms voltage when 0.75–6.0 wt % of nanocrystalline cellulose‐II with respect to PAN is added to a typical PAN precursor solution. Efficient generation (up to 2 g/h rate or 0.7 g h^?1 cm^?2 mass flux) of nanofibers with 250–500 nm fiber diameters has been observed when using flat fiber‐generating electrodes with diameters up to 25 mm. Depending on the amount of nanocellulose, nanofibrous nanocellulose/PAN meshes revealed large variations in tensile modulus (90–273 MPa) and yield strength (1.0–2.5 MPa), whereas the fiber diameter, air permeability, air resistance, mesh porosity, and water absorption were less affected. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45772.     

Splashing needleless electrospinning of nanofibers

This article proposes a new needleless electrospinning apparatus applying the method of splashing polymer solution onto the surface of a metal roller spinneret. When a high voltage is applied, many spinning jets form on the free surface of polymer solutions. Multiple electrified jets undergo strong stretching and bending instability, solvent evaporates, and solidified nanofibers deposit on the collector, as in an ordinary single‐needle electrospinning process. The production of nanofibers is enhanced by 24–45 times comparing with a single‐needle system. And the productivity is easy to scale up. The effects of processing parameters, including solution concentration, applied voltage, distance between spinneret to collector, and rotational speed of the roller spinneret on the morphology of nanofibers are investigated in this article. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

Low Temperature Carbothermal Reduction Synthesis of ZrC Nanofibers via Cyclized Electrospun PVP/Zr(OPr)4 Hybrid

The fabrication capability of zirconium carbide (ZrC) nanofibers by a novel polymeric solution was examined using electrospinning method. The electrospinnable solution was prepared from the reaction of zirconium n‐propoxide (Zr(OPr)₄) with acetylacetone and acetic acid followed by the addition of polyvinylpyrrolidone (PVP) solution. By utilizing thermal and microstructural analyses such as differential scanning calorimetry–thermogravimetry (DSC–TG), field emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD), and Brunauer–Emmett–Teller (BET), the effect of heat treatment type on the morphology and crystallinity of as‐spun PVP/Zr(OPr)₄ hybrid fibers was examined. The results showed that direct carbonization treatment of as‐spun fibers under argon atmosphere led to spherical ZrC aggregates in lack of fibrillar morphology, whereas carbonization coupled with cyclization could be recognized as the unique template to govern the morphology and crystallinity of ZrC nanofibers. Carbonization of the cyclized fibers at 1550°C in flowing argon atmosphere produced the thick, fragmented rosary‐like fibers with a diameter of 357 nm, while through a 100°C decrease in carbonization temperature to 1450°C, the thin, smooth, long, and uniform ZrC nanofibers with 176 nm diameter and a medium surface area of 23 m²/g were obtained.     

Morphology of electrospun nylon‐6 nanofibers as a function of molecular weight and processing parameters

In the present study, the morphology and mechanical properties of nylon‐6 nanofibers were investigated as a function of molecular weight (30,000, 50,000, and 63,000 g/mol) and electrospinning process conditions (solution concentration, voltage, tip‐to‐collector distance, and flow rate). Scanning electron micrographs (SEM) of nylon‐6 nanofibers showed that the diameter of the electrospun fiber increased with increasing molecular weight and solution concentration. An increase in molecular weight increases the density of chain entanglements (in solution) at the same polymer concentration; hence, the minimum concentration to produce nanofibers was lower for the highest molecular weight nylon‐6. The morphology of electrospun fibers also depended on tip‐to‐collector distance and applied voltage concentration of polymer solution as observed from the SEM images. Trends in fiber diameter and diameter distribution are discussed for each processing variable. Mechanical properties of electrospun nonwoven mats showed an increase in tensile strength and modulus as a function of increasing molecular weight. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation of poly(ether sulfone) nanofibers by gas‐jet/electrospinning

Poly(ether sulfone) (PES) nanofibers were prepared by the gas‐jet/electrospinning of its solutions in N,N‐dimethylformamide (DMF). The gas used in this gas‐jet/electrospinning process was nitrogen. The morphology of the PES nanofibers was investigated with scanning electron microscopy. The process parameters studied in this work included the concentration of the polymer solution, the applied voltage, the tip–collector distance (TCD), the inner diameter of the needle, and the gas flow rate. It was found from experimental results that the average diameter of the electrospun PES fibers depended strongly on these process parameters. A decrease in the polymer concentration in the spinning solutions resulted in the formation of nanofibers with a smaller diameter. The use of an 18 wt % polymer solution yielded PES nanofibers with an average diameter of about 80 nm. However, a morphology of mixed bead fibers was formed when the concentration of PES in DMF was below 20 wt % during gas‐jet/electrospinning. Uniform PES nanofibers with an average diameter of about 200 nm were prepared by this electrospinning with the following optimal process parameters: the concentration of PES in DMF was 25 wt %, the applied voltage was 28.8 kV, the gas flow was 10.0 L/min, the inner diameter of the needle was 0.24 mm, the TCD was 20 cm, and the flow rate was 6.0 mL/h. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Fabrication of Au/PVP nanofiber composites by electrospinning

Gold nanoparticles prepared by trisodium citrate reduction of HAuCl₄ in poly(vinylpyrrolidone) (PVP) ethanol solution were dispersed into PVP nanofibers by electrospinning. The optical property of Au nanoparticles before and after electrospinning was measured by UV‐Vis. The morphology and distribution of gold nanoparticles in PVP nanofibers were observed by transmission electron microscopy (TEM). The influence of the amount of Au added to and the concentration of PVP in electrospinning solution over the morphology of Au/PVP nanofibers were studied. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Densifying and strengthening of electrospun polyacrylonitrile‐based nanofibers by uniaxial two‐step stretching

The effects of alignment of polyacrylonitrile (PAN) nanofibers and a two‐step drawing process on the mechanical properties of the fibers were evaluated in the current study. The alignment was achieved using a high‐speed collector in electrospinning synthesis of the nanofibers. Under optimal two‐step drawing conditions (e.g., hot‐water and hot‐air stretching), the PAN nanofiber felts exhibited large improvements in both alignment and molecular chain‐orientation. Large increase in crystallinity, crystallite size, and molecular chain orientation were observed with increasing draw ratio. Optimally, stretched PAN‐based nanofibers exhibited 5.3 times higher tensile strength and 6.7 times higher tensile modulus than those of the pristine one. In addition, bulk density of the drawn PAN nanofibers increased from 0.19 to 0.33 g/cm³. Our results show that fully extended and oriented polymer chains are critical in achieving the highest mechanical properties of the electrospun PAN nanofibers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43945.     

Fabrication and SERS application of the thermoresponsive nanofibers with monodisperse Au@Ag bimetallic nanorods loaded shells

Monodisperse Au@Ag bimetallic nanorods (Au@AgNRs) with gold nanorod core and silver shell were introduced into the shells of the thermoresponsive nanofibers with core‐shell structure by coaxial electrospinning technique using poly(N ‐isopropylacrylamide‐co ‐N ‐hydroxymethylacrylamide) aqueous solution as core fluid and its Au@AgNRs mixture as shell fluid, followed by heat treatment. Their core‐shell structure and the oriented alignment of the Au@AgNRs embedded within their shells along their axes were confirmed by transmission electron microscopy observation. The produced composite nanofibrous membrane has high stability in aqueous medium and more remarkable and faster thermoresponsiveness than our previously reported composite nanofibrous membrane with homogeneous Au@AgNRs distribution inside its constituent nanofibers. The smart composite nanofibrous membrane as a free‐standing surface enhanced Raman spectroscopy substrate with temperature‐dependent surface enhanced Raman spectroscopy efficiency from 25 to 50 °C and good reproducibility is able to be used to detect 10^?14 mol/L 4‐mercaptobenzoic acid in aqueous solution at 50 °C. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45375.     

Electrospinning of solvent‐resistant nanofibers based on poly(acrylonitrile‐co‐glycidyl methacrylate)

This article reports on the preparation of novel solvent‐resistant nanofibers by electrospinning of poly(acrylonitrile‐co‐glycidyl methacrylate) (PANGMA) and subsequent chemical crosslinking. PANGMA nanofibers with diameters ranging from 200 to 600 nm were generated by electrospinning different solutions of PANGMA dissolved in N,N‐dimethylformamide. Different additives were added to reduce the fiber diameter and improve the morphology of the nanofibers. The as‐spun PANGMA nanofibers were crosslinked with 27 wt % aqueous ammonia solution at 50°C for 3 h to gain the solvent resistance. Swelling tests indicated that the crosslinked nanofibers swelled in several solvents but were not dissolved. The weight loss of all the crosslinked nanofibrous mats immersed in solvents for more than 72 h was very low. The characterization by electron microscopy revealed that the nanofibrous mats maintained their structure. This was also confirmed by the results of the pore size measurements. These novel nanofibers are considered to have a great potential as supports for the immobilization of homogeneous catalysts and enzymes. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Needleless Electrospinning from a Tube with an Embedded Wire Loop

Enhancing the production rate while maintaining control in electrospinning has been a challenge for years. This work proposes a novel spinneret from a tube with a single wire loop embedded in its one end. With the feeding of solution precisely controlled and the spinning process stablized, multiple polymer jets can be continuously generated from the wire loop. The as‐spun fibers show nanofibrous structure and its fiber diameter is greatly affected by the applied voltage and polymer concentration. As compared to needle electrospinning, the wire loop spinneret generates a stronger electric field with a larger spinnable area due to its special geometrical structure and a higher applied voltage it is connected to. Slightly coarser nanofibers are fabricated as compared to the nanofibers from needle electrospinning and the production rate is as high as 0.48 g h^?1.     

In situ synthesis of iron oxide nanoparticles on poly(ethylene oxide) nanofibers through an electrospinning process

Iron oxide nanoparticle coated poly(ethylene oxide) nanofibers as organic–inorganic hybrids with 200–400‐nm diameters were prepared by the in situ synthesis of iron oxide nanoparticles on poly(ethylene oxide) nanofibers through the electrospinning of a poly(ethylene oxide) solution having Fe²⁺ and Fe³⁺ ions in a gaseous ammonia atmosphere. Transmission electron microscopy analysis proved the presence of iron oxide nanoparticles on the polymer nanofibers. The thermal properties of the nanofiber mat were also studied with differential scanning calorimetry and thermogravimetric analysis techniques. X‐ray diffraction showed that the formed iron oxide nanoparticles were maghemite nanoparticles. The results were compared with those of the electrospinning of a poly(ethylene oxide) solution having Fe²⁺ and Fe³⁺ ions and a pure poly(ethylene oxide) solution in an air atmosphere. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Studies on the synthesis of electrospun PAN‐Ag composite nanofibers for antibacterial application

We have successfully synthesized polyacrylonitrile (PAN) nanofibers impregnated with Ag nanoparticles by electrospinning method at room temperature. Briefly, the PAN‐Ag composite nanofibers were prepared by electrospinning PAN (10% w/v) in dimethyl formamide (DMF) solvent containing silver nitrate (AgNO₃) in the amounts of 8% by weight of PAN. The silver ions were reduced into silver particles in three different methods i.e., by refluxing the solution before electrospinning, treating with sodium borohydride (NaBH₄), as reducing agent, and heating the prepared composite nanofibers at 160°C. The prepared PAN nanofibers functionalized with Ag nanoparticles were characterized by field emission scanning electron microscopy (FESEM), SEM elemental detection X‐ray analysis (SEM‐EDAX), transmission electron microscopy (TEM), and ultraviolet‐visible spectroscopy (UV‐VIS) analytical techniques. UV‐VIS spectra analysis showed distinct absorption band at 410 nm, suggesting the formation of Ag nanoparticles. TEM micrographs confirmed homogeneous dispersion of Ag nanoparticles on the surface of PAN nanofibers, and particle diameter was found to be 5–15 nm. It was found that all the three electrospun PAN‐Ag composite nanofibers showed strong antibacterial activity toward both gram positive and gram negative bacteria. However, the antibacterial activity of PAN‐Ag composite nanofibers membrane prepared by refluxed method was most prominent against S. aureus bacteria. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Electrospun Bead‐On‐String Hierarchical Fibers for Fog Harvesting Application

Quest for efficient fog harvesting methods has drawn immense attention in recent times. In this study, electrospinning is used to fabricate three different sets of membranes that are based on pristine poly(N‐isopropylacrylamide) (PNIPAM) fibers, pristine polyvinylidene fluoride (PVDF) fibers, and PNIPAM‐PVDF bead‐on‐string fibers. The wettability of these membranes is investigated as a function of temperature and the effect of their wettability on the fog collection efficiency is determined. Membranes based on pristine PNIPAM and pristine PVDF fibers are fabricated using conventional electrospinning and are shown to have a smooth surface morphology. On the other hand, PNIPAM‐PVDF bead‐on‐string fibers are fabricated using core–shell electrospinning. Water collection efficiency of the membranes is compared to investigate the influence of microstructures and wettability gradient on fog harvesting ability of the samples. Among the three samples, the bead‐on‐string hierarchical fibrous membrane demonstrates the highest fog harvesting rate of 1150 ± 28 mg cm⁻² h⁻¹ at 25 °C and 909 ± 31 mg cm⁻² h⁻¹ at 40 °C. Furthermore, the results demonstrate that the presence of microstructures on the nanofibers improve the fog harvesting efficiency of PNIPAM‐PVDF bead‐on‐string fibers.