A composite polyaniline/graphene–coated polyamide6 nanofiber mat for electrochemical applications

In this study, polyamide6 (PA6) nanofiber mats were fabricated through the electrospinning process. The nanofibers were coated by polyaniline (PANI) using the in situ polymerization of aniline in the presence of graphene oxide. The composite of the PANI/graphene oxide–coated nanofiber mat was treated with hydrazine monohydrate to reduce graphene oxide to graphene, and this was followed by the reoxidation of PANI. Field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), wide angle X‐ray diffraction (WAXD), thermal gravimetric analysis (TGA), tensile strength tests, electrical conductivity measurements, cyclic voltammetry (CV), and charge/discharge measurements were conducted on the composite PA6/graphene nanofiber mats. It was found that the surface of the PA6 nanofibers was coated uniformly with the granular PANI and graphene oxide. Besides, the composite nanofibers showed good tensile and thermal properties. Their electrical conductivity and specific capacitance, when used as a separator in the cell, were 1.02 × 10^?4 S/cm and 423.28 F/g, respectively. Therefore, the composite PANI/reduced graphene oxide–coated PA6 nanofiber mats could be regarded as suitable candidates for application in energy storage devices.     

Fabrication and electrochemical instrumentation of redox‐active nanofiber mat for polyaniline incorporated with poly(imide sulfonate)

In this study, we demonstrate the fabrication of an electrochemically active nanofiber mat that is a composite of high‐performance poly(imide sulfonate) (PIS) and polyaniline (PANI). First, a nonconductive nanofiber mat comprising nanofibers having diameters of ca. 300 nm was fabricated by the electrospinning of ionomeric PIS in N,N‐dimethylformamide (DMF). Then, the nanofibers were modified using PANI, which was synthesized by the oxidative polymerization of aniline, yielding an electrochemically active nanofiber mat having a diameter of ca. 350 nm. It was confirmed that PANI was successfully incorporated onto the PIS nanofiber mats by X‐ray photoelectron spectroscopy. Subsequently, we conducted electrochemical measurements of the PANI‐modified nanofiber mats using a tailor‐made attachment in which the working electrode gently comes in contact with the nanofiber mat surface. This attachment was observed to be widely useful in the cyclic voltammetry measurements related to redox‐active nanofibers. These observations are expected to contribute to the advancements in application development of the electrochemically active nanofiber mats.     

The tensile properties of electrospun nylon 6 single nanofibers

In this article, we have aimed to mechanically characterize the nylon 6 single nanofiber and nanofiber mats. We have started by providing a critical review of the developed mechanical characterization testing methods of single nanofiber. It has been found that the tensile test method provides information about the mechanical properties of the nanofiber such as tensile strength, elastic modulus and strain at break. We have carried out a tensile test for nanofiber/composite MWCNTs nanofiber mats to further characterize the effect of the MWCNTs filling fiber architecture. In addition, we have designed and implemented a novel simple laboratory set‐up for performing tensile test of single nanofibers. As a result, we have established the stress–strain curve for single nylon 6 nanofibers allowing us to define the tensile strength, axial tensile modulus and ultimate strain of this nanofiber. The compared values of the tensile strength, axial modulus and ultimate strain for nylon 6 nanofiber with those of conventional nylon 6 microfiber have indicated that some of the nylon 6 nanofiber molecule chains have not been oriented well along the nanofiber axis during electrospinning and through the alignment mechanism. Finally, we have explained how we can improve the mechanical properties of nylon 6 nanofibers and discussed how to overcome the tensile testing challenges of single nanofibers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1719–1731, 2010     

Solution Blowing of Poly（dimethylsiloxane）/Nylon 6 Nanofiber Mats for Protective Applications

A new strategy was developed to fabricate superhydrophobic nylon 6 nanofibers, in which the blend solutions of poly(dimethylsiloxane)(PDMS) prepolymer and nylon 6 was spun using an innovative solution blowing process, and then the PDMS prepolymer contianning nanofibers were cured to obtain PDMS/nylon 6 nanofiber mats. Morphology, surface composition, non-wetting property and protective performance were investigated. The results showed that the addition of PDMS prepolymer improved the spinnability of the spinning solutions, and the PDMS/nylon 6 nanofibers had smooth surfaces and diameters from 100 nm to 350 nm. The presence of PDMS effectively enhanced the hydrophobicity of the nanofiber mats, showing water contact angles of 132° to 161° for PDMS contents of 1 wt% to 3 wt%. The PDMS/nylon 6 mats also possessed excellent protective and transport properties. The results indicated the potential application of the novel nanofiber mats in protective clothing.     

A novel method for a high‐strength electrospun meta‐aramid nanofiber by microwave treatment

Electrospun nanofibers have attracted great attention as potential reinforcements in composite application due to their high specific surface area, high porosity, and versatility. Because the electrospun nanofibers exhibit relatively low mechanical strength due to low crystallinity and random alignment, many researchers have tried to enhance the mechanical strength through various approaches, such as heat treatment and fiber orientation control. These methods, however, are difficult to control and require the use of high temperatures and sophisticated apparatuses, and high costs. In this study, we investigate a novel microwave technique to fabricate high‐strength electrospun meta‐aramid nanofiber mats. To optimize the microwave irradiation conditions, the electrospun nanofiber was treated at varying levels of moisture and for different irradiation times. Field emission scanning electron microscopy was used to observe the surface morphology of the electrospun nanofiber mats at the different irradiation times. The changes in the crystallinity and thermal properties were investigated using X‐ray diffraction and thermogravimetric analysis measurements. Tensile tests were performed to measure the mechanical strength of the meta‐aramid nanofiber mats with respect to each parameter. As a result, any residual solvents and salts were removed, and the degree of crystallization was dramatically increased by microwave irradiation under wet conditions. These effects led to a 2.8‐fold increase in the tensile strength of the nanofiber mats compared with an untreated mat. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 807–814     

Characterization of poly(methyl methacrylate) nanofiber mats by electrospinning process

In this study, the aim is to describe the influence of electrospinning parameters on the morphology, the water wetting property and dye adsorption property of poly(methyl methacrylate) nanofiber mats. Specifically, the effects of solution concentration, solvent type, applied voltage, distance between the electrodes and particulate reinforcement on the diameter and shape of the nanofibers were investigated. All poly(methyl methacrylate) nanofiber mats contained beaded nanofiber structures. With increasing the polymer solution concentration, the average fiber diameter also increased. Poly(methyl methacrylate) nanofiber mat electrospun from dimethylformamide solution resulted in thicker fibers when compared with the mat electrospun from acetone solution. Increasing the electric potential difference between the collector and the syringe tip did not increase the average fiber diameter. Besides increasing the distance between the electrodes resulted in a decrease in the average fiber diameter. When compared with PMMA nanofiber mat, thicker fibers were obtained with silica nanoparticles reinforced nanofiber mat. According to the water contact angle measurements, all poly(methyl methacrylate) nanofiber mats revealed hydrophobic surface property. PMMA nanofiber mat with the highest water contact angle gave rise to the highest dye adsorption capacity.     

Stabilization of electrospun poly(vinyl alcohol) nanofibrous mats in aqueous solutions

<正>The stability ofpoly(vinyl alcohol)(PVA) nanofibrous mats in water media was improved by post-electrospinning treatments.Bifunctional glutaraldehyde(GA) in methanol was used as a crosslinking agent to stabilize PVA nanofiber,but fiber twinning was observed frequently,and the highly porous structure of PVA nanofibrous mats was destroyed when the crosslinked fiber was soaked in water.To overcome this shortcoming,chitosan(CS) was introduced into the PVA spinning solution to prepare PVA/CS composite nanofibers.Their treatment in GA/methanol solution could retain the fiber morphology of PVA/CS nanofibers and porous structure of PVA/CS nanofibrous mats even if they were soaked in aqueous solutions for 1 month.Scanning electron microscopy(SEM),X-ray diffraction(XRD),thermal gravimetric analysis(TGA) and differential scanning calorimetry(DSC) were applied to characterize the physicochemical structure and thermal properties of PVA nanofibers.It was found that the water resistance of PVA nanofibrous mats was enhanced because of the improvement of the degree of crosslinking and crystallinity in the electrospun PVA fibers after soaking in GA/methanol solution.     

Preparation of amidoxime-modified polyacrylonitrile (PAN-oxime) nanofibers and their applications to metal ions adsorption

Polyacrylonitrile (PAN) nanofibers were applied to metal adsorption. PAN nanofibers (prepared by an electrospinning technique) were chemically modified with amidoxime groups, which are suitable for metal adsorption due to their high adsorption affinity for metal ions. The adsorption of the amidoxime-modified PAN (PAN-oxime) (25% conversion) nanofibers followed Langmuir isotherm. The saturation adsorption capacities for Cu(II) and Pb(II) of 52.70 and 263.45 mg/g (0.83 and 1.27 mmol/g), respectively, indicating that the monolayer adsorption occurred on the nanofiber mats. In addition, over 90% of metals were recovered from the metal-loaded PAN-oxime nanofibers in a 1 mol/L HNO₃ solution after 1 h.     

Processing and characterization of oriented electrospun poly(vinylidene fluoride) mats

Mats of highly oriented poly(vinylidene fluoride) nanofibers were electrospun by means of a conventional electrospinning equipment; the orientation, however, was obtained using a disk collector rotating at a speed of 4000 rpm and a device that reduced the influence of air displacement during nanofiber orientation. Thermal transitions of the mats were determined by differential scanning calorimetry, the predominant crystalline phase by Fourier transform infrared spectroscopy and wide‐angle X‐ray scattering and the nanofiber orientation and morphology by scanning electron microscopy. Relative permittivity, loss index, stable remnant polarization, and coercive field of the mats were also determined and compared with those obtained for a mat electrospun at 2000 rpm and an oriented commercial film. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 000: 000–000, 2012     

Electrospun core–sheath fibers for integrating the biocompatibility of silk fibroin and the mechanical properties of PLCL

In the process of preparing core–sheath fibers via coaxial electrospinning, the relative evaporation rates of core and sheath solvents play a key role in the formation of the core–sheath structure of the fiber. Both silk fibroin (SF) and poly(lactide‐co‐ε‐caprolactone) (PLCL) have good biocompatibility and biodegradability. SF has better cell affinity than PLCL, whereas PLCL has higher breaking strength and elongation than SF. In this work, hexafluoroisopropanol (HFIP)‐formic acid (volume ratio 8:2), HFIP and HFIP–dichloromethane (volume ratio 8:2) were used to dissolve PLCL as the core solutions, and HFIP was used to dissolve SF as the sheath solution. Then, core–sheath structured SF/PLCL (C‐SF/PLCL) fibers were prepared by coaxial electrospinning with the core and sheath solutions. Transmission electron microscopy images indicated the existence of the core–shell structure of the fibers, and energy dispersive X‐ray analysis results revealed that the fiber mat with the greatest content of core–shell structure fibers was obtained when the core solvent was HFIP–dichloromethane (volume ratio 8:2). Tensile tests showed that the C‐SF/PLCL fiber mat displayed improved tensile properties, with strength and elongation that were significantly higher than those of the pure SF mat. The C‐SF/PLCL fiber mat was further investigated as a scaffold for culturing EA.hy926 cells, and the results showed that the fiber mat permitted cellular adhesion, proliferation and spreading in a manner similar to that of the pure SF fiber mat. These results indicated that the coaxial electrospun SF/PLCL fiber mat could be considered a promising candidate for tissue engineering scaffolds for blood vessels. Copyright © 2014 John Wiley & Sons, Ltd.     

Reversible Immobilization of Urease by Using Bacterial Cellulose Nanofibers

In this work, bacterial cellulose nanofibers were produced by using the Gluconacetobacter hansenii HE1 strain. These nanofibers were derivatized with dye affinity ligand Reactive Green 5, and these newly synthesized dye-attached nanofibers were used for affinity adsorption of urease. Reactive Green 5-attached nanofibers were characterized by Fourier transform infrared spectroscopy, SEM, and energy-dispersive x-ray spectroscopy analysis. Some adsorption conditions which significantly affect the adsorption efficiency were investigated. The maximum urease adsorption capacity was found to be 240 mg/g nanofiber in pH 6.0 and at room temperature. Dye-free plain nanofibers also used for studying nonspecific urease adsorption onto plain nanofibers and nonspecific adsorption were found to be negligible (3.5 mg/g nanofiber). Prepared dye-attached nanofibers can be used in five successive adsorption/desorption steps without any decrease in their urease adsorption capacity. The desorption rate of the adsorbed urease was found to be 98.9 %. The activity of the urease was also investigated, and it was found that free and desorbed urease from the dye-attached nanofibers showed similar specific activity.     

Preparation and characterization of polytetrafluoroethylene‐polyacrylate core–shell nanoparticles

Polytetrafluoroethylene (PTFE)‐polyacrylate core–shell nanoparticles were produced by using PTFE micropowder and acrylate via seeded emulsion polymerization in the presence of fluorosurfactant. The properties of emulsion under various polymerization conditions were investigated and optimized. The chemical composition of the PTFE‐polyacrylate nanoparticles was characterized by Fourier‐transform infrared spectrometry (FTIR). The particle size and core–shell structure of the resulting PTFE‐polyacrylate nanoparticles were confirmed by transmission electron microscopy (TEM). Wettability of the PTFE‐polyacrylate core–shell particles was higher than the pristine PTFE. The formation of this kind of PTFE‐polyacrylate core–shell nanoparticles could improve the compatibility of PTFE with other materials because PTFE is covered by polyacrylate shell, which make them promising in various fields. Copyright © 2007 John Wiley & Sons, Ltd.     

Enhancing the Mechanical Properties of Electrospun Nanofiber Mats through Controllable Welding at the Cross Points

This communication describes a simple and effective method for welding electrospun nanofibers at the cross points to enhance the mechanical properties of their nonwoven mats. The welding is achieved by placing a nonwoven mat of the nanofibers in a capped vial with the vapor of a proper solvent. For polycaprolactone (PCL) nanofibers, the solvent is dichloromethane (DCM). The welding can be managed in a controllable fashion by simply varying the partial pressure of DCM and/or the exposure time. Relative to the pristine nanofiber mat, the mechanical strength of the welded PCL nanofiber mat can be increased by as much as 200%. Meanwhile, such a treatment does not cause any major structural changes, including morphology, fiber diameter, and pore size. This study provides a generic method for improving the mechanical properties of nonwoven nanofiber mats, holding great potential in various applications.

     

Conducting core‐sheath nanofibers for electroactive shape‐memory applications

Conducting nanofibers coated with polypyrrole (PPy) and poly(3‐hexylthiophene) (P3HT) exhibiting core‐sheath structures were prepared by vapor‐phase polymerization of the conducting polymers on electrospun polyurethane nanofibers. The synthesis of the conducting polymers was confirmed by Fourier transform infrared spectroscopy and energy‐disperse X‐ray spectroscopy. The surfaces of the PPy‐coated nanofibers were slightly rough, while very smooth and regular surfaces were observed in the case of the P3HT‐coated nanofibers. The initial polymerization rate of PPy was higher than that of P3HT. In addition, the electrical conductivities of the core‐sheath structured nanofiber webs of both types increased with polymerization time. The maximum sheet conductivity of the PPy and P3HT‐coated nanofiber webs was 5 × 10^?3 S/cm and 1 × 10^?2 S/cm, respectively. The webs of the conducting core‐sheath structured nanofibers were effective in generating sufficient electrical heating necessary for harnessing these materials for electroactive shape‐memory‐based applications. Copyright © 2013 John Wiley & Sons, Ltd.     

Core–shell structure PEO/CS nanofibers based on electric field induced phase separation via electrospinning and its application

Core–shell structured PEO‐chitosan nanofibers have been produced from electric field inducing phase separation. Chitosan, a positive charged polymer, was dissolved in 50 wt % aqueous acetic acid and the amino group on polycation would protonize, which would endow chitosan electrical properties. Chitosan molecules would move along the direction of the electric field under the electrostatic force and formed the shell layer of nanofibers. Preparation process of core – shell structure is quite simple and efficient without any post‐treatment. The core–shell structure and existence of chitosan on the shell layer were confirmed before and after post‐treatment by TEM and further supported by SEM, FTIR, XRD, DSC, and XPS studies. Blending ratio of PEO and chitosan, molecular weight of chitosan for the mobility of chitosan are thought to be the key influence factors on formation of core–shell structure. Drug release studies show that the prepared core–shell structure nanofibers has a potential application in the biomedical fields involving drug delivery. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2298–2311     

Green,ultrafine cellulose-based porous nanofibrous membranes for efficient heavy metal removal through incorporation of chitosan by various electrospinning ways

Rapid global industrialization has worsened the heavy metal contamination of aquatic ecosystems globally. In this study, green, ultrafine cellulose-based porous nanofibrous membranes for efficient heavy metal removal were obtained by incorporating chitosan (CS) and using conventional and core–shell electrospinning ways. The relationship between the parameters of the electrospinning solution, the micro-morphology and porosity, the chemically active sites, the thermal stability, and the adsorption performance of the biocomposite nanofibrous membranes were analyzed. The adsorption effects of the copper ions, including the initial concentration, solution pH, and interaction time, were investigated. The results show that the average diameters of the conventional and core–shell ultrafine nanofibers with 50% and 30% CS loading are 56.22 nm and 37.28 nm, respectively. The core–shell cellulose acetate (CA)/CS biocomposite nanofibrous membranes showed the weaker thermal stability with a 48.2 °C lower maximum thermal decomposition temperature and induced the surface aggregation of more copper ions compared to the conventional one. A more uniform distribution of the chemical adsorption sites is obtained by conventional single-nozzle electrospinning than by core–shell electrospinning, which effectively promotes the adsorption performance of copper ions and decreases the surface shrinkage of the nanofibrous membranes during adsorption. The 30% CS conventional nanofibrous membranes at an aqueous solution pH of 5 showed the optimum adsorption capacity of copper ions (86.4 mg/g). The smart combination of renewable biomass with effective chemical adsorption sites, electrospinning technology that produces an interwoven porous structure, and an adsorption method with low cost and facile operation shows a promising prospect for water treatment.

     

Chitosan–poly(acrylic acid) nanofiber networks prepared by the doping induction of succinic acid and its ammonia‐response studies

Chitosan–poly(acrylic acid) (CS–PAA) composite membrane with a 3D network nano‐structure was prepared using an electrostatic interaction process by adding succinic acid as a branch promoter. Variations of the final solution pH values, concentration of CS, and PAA/CS volume ratio were examined systematically for their effects on average fiber diameter size, intensity of surface charge, and tendency of network formation. It was found that nanofiber size was affected by the mixing ratio of PAA and CS, the concentration of CS, and the final pH of the CS–PAA solution. The smallest diameter size distribution of the scaffold can be obtained when the PAA/CS ratio is in the range of 2:1–1:2 in a pH 3 environment. Negative charge nanofibers prepared using PAA and CS in a ratio of 2:1 in pH 3 environments had an average diameter of 215 nm. The formation of the interconnecting 3D self‐organized network structure can be built up with limited parasitic branching by crystallized succinic acid. The gas response to ammonia, including sensitivity and response time, was evaluated using impedance spectroscopy at room temperature. The results of sensing experiments indicate that the sensitivity of nanofibrous membrane (NM)‐coated sensors was eight times higher than that of continuous film‐coated sensors. NM‐coated sensors exhibited high sensitivity towards a low concentration of ammonia, as low as 50 ppm at a relative humidity of 45%. Copyright © 2008 John Wiley & Sons, Ltd.     

Electrospinning of polyurethane/organically modified montmorillonite nanocomposites

Polyurethane/organically modified montmorillonite (PU/O‐MMT) nanocomposites were electrospun and the effect of O‐MMT on the morphology and physical properties of the PU/O‐MMT nanofiber mats were investigated for the first time. The average diameters of the PU/O‐MMT nanofibers were ranged from 150 to 410 nm. The conductivities of the PU/O‐MMT solutions were linearly increased with increasing the content of O‐MMT, which caused a decrease in the average diameters of the PU/O‐MMT nanofibers. The as‐electrospun PU and PU/O‐MMT nanofibers were not microphase separated. The exfoliated MMT layers were well distributed within the PU/O‐MMT nanofibers and oriented along the fiber axis. When the PU/O‐MMT nanofibers were annealed, the exfoliated MMT layers hindered the microphase separation of the PU. The electrospinning of PU/O‐MMT nanocomposites resulted in PU nanofiber mats with improved Young's modulus and tensile strength. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3171–3177, 2005     

Adsorption of Human Serum Albumin onto PVA-coated Affinity Microporous PTFE Capillary

Affinity dye-ligand Cibacron Blue F3GA（CB F3GA） was covalently coupled with poly（vinyl alcohol）（PVA） coated on the inner surface of microporous poly（tetra-fluoroethylene）（MPTFE） membranous capillary. The PVA-coated PTFE capillary surface was characterized by XPS and FESEM. The grafting degree of PVA and the amount of CB F3GA immobilized onto the membranous capillary were 23.5 mg/g and 89.6 pmol/g, respectively. These dyed membranous capillaries were chemically and mechanically stable, and could be reproducibly prepared. Human serum albumin（HSA） was selected as model protein. The saturation adsorbance of the dye attached membranous capillary was 85.3 mg HSA/g, while the capacity of non-specific adsorption for HSA was less than 0.3 mg/g.     

Chitosan/PEO nanofibers electrospun on metallized track-etched membranes: fabrication and characterization

The development of next-generation adsorption, separation, and filtration materials is growing with an increased research focus on polymer composites. In this study, a novel blend of chitosan (CS) and polyethylene oxide (PEO) nanofiber mats was electrospun on titanium (Ti)-coated polyethylene terephthalate (PET) track-etched membranes (TMs) with after-treatment by glutaraldehyde in the vapor phase for enhancing the nanofiber stability by crosslinking. The prepared composite, titanium-coated track-etched nanofiber membrane (TTM-CPnf) was characterized by Fourier transform infra-red (FTIR), water contact angle, and scanning electron microscopy (SEM) analyses. Smooth and uniform CS nanofibers with an average fiber diameter of 156.55 nm were produced from a 70/30 CS/PEO blend solution prepared from 92 wt. % acetic acid and electrospun at 15 cm needle to collector distance with 0.5 mL/h flow rate and an applied voltage of 30 kV on the TTM-CPnf. Short (15 min) and long (72 h)-term solubility tests showed that after 3 h, crosslinked nanofibers were stable in acidic (pH = 3), basic (pH = 13), and neutral (pH = 7) solutions. The crosslinked TTM-CPnf material was biocompatible based on the low mortality of freshwater crustaceans Daphnia magna. The composite membranes comprised of electrospun nanofiber and TMs proved to be biocompatible and may thus be suitable for diverse applications such as dual adsorption–filtration systems in water treatment.