Ultrafine Nanofibers Research Articles

Flexible, ultrafine and abundant microporous carbon nanofibers prepared by electrospinning from resole-type liquefied biomass-based resin

In the present work, flexible porous carbon nanofibers (PCNFs) of 175 nm diameter were prepared by electrospinning process using resole-type liquefied biomass-based resin (RLBR) as precursor. The addition of defined amount of polyvinyl alcohol (PVA) is essential for the bead-free fibers forming. The final PCNFs were obtained after one-step carbonization of as-spun nanofibers, which presented abundant micropores (0.9 and 1.8 nm) and high specific surface area of 956 m2/g without any activation process. This indicates that the flexible RLBR-based PCNFs will be promising not only in adsorbent and catalyst support materials but also as materials in electrode capacitance application.

Sustainable and Antioxidant Lignin–Polyester Copolymers and Nanofibers for Potential Healthcare Applications

Lignin polymerization has been considered as an effective approach for lignin valorization. Herein we report the synthesis of a series of new lignin-based copolymers (lignin–poly(e-caprolactone-co-lactide), lignin–PCLLA) via solvent-free ring-opening polymerization. Lignin–PCLLA copolymers with tunable molecular weights (10 to 16 kDa) and glass transition temperatures (−40 to 40 °C) were obtained. Such copolymers were engineered into ultrafine nanofibers by blending with polyesters (polycaprolactone, PCL and poly(l-lactic acid), PLLA) via electrospinning. Both PCL/lignin–PCLLA and PLLA/lignin–PCLLA nanofibers displayed uniform and beadless nanofibrous morphology. The size (diameters ranging from 300 to 500 nm) and tensile tests of the obtained nanofibers indicated that the lignin copolymers are miscible with the polyester matrices and can significantly improve the mechanical properties of the nanofibers. Moreover, good antioxidant activity and biocompatibility of the lignin nanofibers were demonstrated in...

Preparation of Polydimethylsiloxane–Polyvinylidene Fluoride Composite Membranes for Phenol Removal in Extractive Membrane Bioreactor

The extractive membrane bioreactor (EMBR) system combining a membrane process and a biological process has been developed to extract and biodegrade recalcitrant organic pollutants in wastewater. Removal of the organics such as phenol by EMBR requires an effective membrane to selectively extract the organic compounds while rejecting water and other harsh inorganic components. In this work, novel composite membranes consisting of a highly porous substrate, made by tiered polyvinylidene fluoride (PVDF) nanofibers with ultrafine nanofibers on top (61 ± 12 nm in diameter), and a dense polydimethylsiloxane (PDMS) selective layer have been fabricated. We have investigated (1) the effect of the pore size of PVDF nanofibrous substrates, (2) the effect of PDMS preparation method, and (3) the effect of prewetting agent on the resultant composite membranes’ morphologies, mechanical properties, and phenol removal performance. Compared with the symmetric substrate with a nanofiber diameter of 129 ± 13 nm, the tiered su...

Synthesis of Helical Phenolic Resin Bundles through a Sol-Gel Transcription Method.

Chiral and helical polymers possess special helical structures and optical property, and may find applications in chiral catalysis and optical devices. This work presents the preparation and formation process of helical phenolic resins through a sol-gel transcription method. A pair of bola-type chiral low-molecular-weight gelators (LMWGs) derived from valine are used as templates, while 2,4-dihydroxybenzoic acid and formaldehyde are used as precursors. The electron microscopy images show that the phenolic resins are single-handed helical bundles comprised of helical ultrafine nanofibers. The diffused reflection circular dichroism spectra indicate that the helical phenolic resins exhibit optical activity. A possible formation mechanism is proposed, which shows the co-assembly of the LMWGs and the precursors.

A novel approach to extend microbiological stability of sea bass (Dicentrarchus labrax) fillets coated with electrospun chitosan nanofibers

We tested electrospun chitosan nanofibers (CN) and liquid smoke-loaded electrospun chitosan nanofibers (LSCN) in terms of limitation of Total Mesophilic Aerobic Bacteria (TMABc), Psychrophilic Bacteria (TPBc) and Yeast and Mold count (YMc) growth during storage period. CN and mixtures of CN and LS were electrospun to yield smooth, cylindrical, beadless and ultrafine polymeric nanofibers. Molecular (Fourier Transform Infrared Spectroscopy, FTIR), thermal (Thermogravimetric Analysis, TGA), zeta potential (Dynamic Light Scattering, DLS) and surface (Scanning Electron Microscopy, SEM) properties of CN and LSCN were determined. FTIR results revealed that the LS could be encapsulated within chitosan nanofibers. SEM images showed a smooth structure. TGA indicated thermal decomposition (a reduction in mass of CN and LSCN at temperatures below 150 °C, corresponding to 11.8 and 10.77%, respectively) and DLS demonstrated dispersion stability (ζ potential +22.3 and +27.1 mV for CN and LSCN, respectively) properties. Microbiological stability tests demonstrated that CN and LSCN were both effective against growth of the tested microorganisms, exhibiting almost 40–50% limitation of growth; but the antimicrobial effect of CN was more than that of LSCN. The results suggested that coating of the fish fillets with the nanofibers would be a promising technique to limit microbial growth in fish fillets.

Cellulose nanofiber intermediary to fabricate highly-permeable ultrathin nanofiltration membranes for fast water purification

Highly-permeable nanofiltration membranes are highly desired in water production and dissolved solutes removal due to environmental and energy concerns. Here a facile approach is presented to prepare ultrathin polymeric nanofiltration membrane using surface modification of ultrafine cellulose nanofiber (UCN) membrane via interfacial polymerization. The hydrophilic UCN membrane endows an interconnected nanoporous microstructure containing free spaces for the growth of the crosslinked-PEI layer creating narrow permeation channels that are responsible for the transport of water moleucles. The resultant membranes comprising an ultrathin selective layer intertwined with cellulose nanofiber matrix are smooth and allow fast permeation of water. Typically, the 77.4nm-thick membrane with a mean pore size of about 0.45nm and molecular weight cut-off of 824gmol−1 has a high pure water flux of 32.7Lm−2h−1bar−1 that is an order of magnitude higher than those of previously reported similar nanofiltration membranes. The membranes are also positively charged and display high permeation flux and sufficient rejections for inorganic salts and organic dyes in the water purification. Further performance evaluation using model synthetic wastewater demonstrates the membranes have a great potential in the wastewater treatment. This approach presents a promising strategy for the development of highly-permeable nanofiltration membranes for fast water purification and high-efficient separation of small molecules.

Fabrication and Characterization of Electrospun Thermoplastic Polyurethane/Fibroin Small-Diameter Vascular Grafts for Vascular Tissue Engineering.

The demand for small-diameter blood vessel substitutes has been increasing due to a shortage of autograft vessels and problems with thrombosis and intimal hyperplasia with synthetic grafts. In this study, hybrid small-diameter vascular grafts made of thermoplastic polyurethane (TPU) and silk fibroin, which possessed a hybrid fibrous structure of an aligned inner layer and a random outer layer, were fabricated by the electrospinning technique using a customized striated collector that generated both aligned and random fibers simultaneously. A methanol post-treatment process induced the transition of fibroin protein conformation from the water-soluble, amorphous, and less ordered structures to the water-insoluble β-sheet structures that possessed robust mechanical properties and relatively slow proteolytic degradation. The methanol post-treatment also created crimped fibers that mimicked the wavy structure of collagen fibers in natural blood vessels. Ultrafine nanofibers and nanowebs were found on the electrospun TPU/fibroin samples, which effectively increased the surface area for cell adhesion and migration. Cyclic circumferential tensile test results showed compatible mechanical properties for grafts made of a soft TPU/fibroin blend compared to human coronary arteries. In addition, cell culture tests with endothelial cells after 6 and 60 days of culture exhibited high cell viability and good biocompatibility of TPU/fibroin grafts, suggesting the potential of applying electrospun TPU/fibroin grafts in vascular tissue engineering.

Efficient adsorption and antibacterial properties of electrospun CuO-ZnO composite nanofibers for water remediation

On the face of impending global water resources, developing low-cost and efficient water treatment technologies and materials thereof is highly important. Herein, we explore the adsorption capacity and antibacterial properties of CuO-ZnO (CZ) composite nanofibers. The ultrafine nanofibers were fabricated using simple and inexpensive electrospinning technique and were further characterized using Field Emission-Scanning Electron Microscope (FE-SEM), Transmission electron microscope (TEM) and X-Ray Diffraction (XRD), Thermogravimetric analysis (TGA), Fourier transform Infrared Spectroscopy (FTIR). When employed as nanoadsorbents, CZ nanofibers exhibited excellent adsorption capacity for congo red dye. Adsorption Isotherms and kinetics were performed to determine the maximum adsorption capacity and the rate of adsorption, respectively, depicting the better efficiency of composite nanofibers as compared to their single counterparts. The mechanism of adsorption is also proposed with the evaluation of diffusion studies. The second part of this study deals with the examination of antibacterial activity of CZ composite nanofibers against antibiotic resistant GFP-E.coli and S. aureus. The antibacterial efficacy was monitored by visual turbidity assay, SEM analysis and reactive oxygen species (ROS) determination. Hence, such nanofibers have been explored as a single platform for the removal of biological as well organic contaminants so as to make them potential in the field of water remediation.

Pool boiling of Novec 7300 and DI water on nano-textured heater covered with supersonically-blown or electrospun polymer nanofibers

In this work we study pool boiling of Novec 7300 and DI water on bare copper surface and copper surface covered with supersonically-blown or electrospun polymer nanofibers. In distinction from the previous works nanofibers were not metal-plated. The elimination of the electroplating makes nano-texturing process extremely simple and applicable to a wide variety of surfaces. On the other hand, it comes with the price of a lower heat removal rate compared to that on metal-plated nanofibers, albeit the present experiments revealed that the reduction is not that drastic as it would be expected. It is also demonstrated that the supersonically-blown polymer nanofibers also outperformed the electrospun nanofiber-coated surface. Supersonically-blown nanofibers provide a larger number of nucleation sites than electrospun nanofibers or bare copper surface, and thus, facilitate nucleate boiling much stronger. The ultrafine supersonically-blown polymer nanofibers are very robust and did not delaminate from the heater surface either in Novec 7300 or DI water after prolonged vigorous boiling process. Overall, the enhancement of heat removal due to the ultrafine supersonically-blown polymer nanofibers on the heater surface in Novec 7300 is more significant than in DI water, which is associated with the smaller bubble size in the former case.

Simplified modeling of the electrospinning process from the stable jet region to the unstable region for predicting the final nanofiber diameter

ABSTRACTElectrospinning allows the production of ultrafine nanofibers through the stretching of a charged polymer jet with an external electrostatic field. In this study, we derived a simplified and accurate model relating the processing parameters, including the solution volumetric flow rate (Q), the applied electric field (E), and the polymer concentration, to the final fiber diameter. The model takes into consideration the jet behavior starting at the stable region and moving to the bending instability region. We validated the model experimentally by performing the electrospinning process with a polyacrylonitrile/N,N‐dimethylformamide solution with different ranges of concentrations (8–11 wt %), Qs (900–1320 μL/h), and Es (88,889–113,889 V/m). The final fiber diameter was measured with scanning electron microscopy. The model predicted the fiber diameter with a relative error of less than 10%. Moreover, a 30% increase in Q resulted in a 15% increase in the fiber diameter, whereas a 30% increase in E resulted in a 14% decrease in the fiber diameter. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44112.

Enhanced bone formation in electrospun poly(l-lactic-co-glycolic acid)–tussah silk fibroin ultrafine nanofiber scaffolds incorporated with graphene oxide

To engineer bone tissue, it is necessary to provide a biocompatible, mechanically robust scaffold. In this study, we fabricated an ultrafine nanofiber scaffold by electrospinning a blend of poly(l-lactic-co-glycolic acid), tussah silk fibroin, and graphene oxide (GO) and characterized its morphology, biocompatibility, mechanical properties, and biological activity. The data indicate that incorporation of 10wt.% tussah silk and 1wt.% graphene oxide into poly(l-lactic-co-glycolic acid) nanofibers significantly decreased the fiber diameter from 280 to 130nm. Furthermore, tussah silk and graphene oxide boosted the Young's modulus and tensile strength by nearly 4-fold and 3-fold, respectively, and significantly enhanced adhesion, proliferation in mouse mesenchymal stem cells and functionally promoted biomineralization-relevant alkaline phosphatase (ALP) and mineral deposition. The results indicate that composite nanofibers could be excellent and versatile scaffolds for bone tissue engineering.

Sub‐10 nm Wide Cellulose Nanofibers for Ultrathin Nanoporous Membranes with High Organic Permeation

There are increasing requirements for highly efficient and solvent‐resistant nanoporous membranes in various separation processes. Traditional membranes usually have a poor solvent resistance and a thick skin layer leading to a low permeation flux. Currently, the major challenge lies in fabrication of ultrathin few‐nanometers‐pore membranes for fast organic filtration. Herein, a facile approach is presented to prepare ultrafine cellulose nanofibers for fabrication of ultrathin nanoporous membranes. The obtained nanofibers have a uniform diameter of 7.5 ± 2.5 nm and are homogeneously dispersed in aqueous solutions that are favorable to the fabrication of ultrathin nanoporous membranes. The resulting cellulose nanoporous membranes have an adjustable thickness down to 23 nm and pore sizes ranging from 2.5 to 12 nm. They allow fast permeation of water and organics during pressure‐driven filtration. Typically, the 30 nm thick membrane has high fluxes of 1.14 and 3.96 × 104 L h−1 m−2 bar−1 for pure water and acetone respectively. Furthermore, the as‐prepared cellulose nanofibers are easily employed to produce a novel syringe filter with sub‐10 nm pores that have a wide application in fast separation and purification of nanoparticles on few‐nanometers scale.

Electrical Properties of Conductive Nylon66/Graphene Oxide Composite Nanofibers.

In this paper, we report on the structural and electrical properties of graphene oxide (GO) incorporated Nylon66 (N66) composite nanofibers prepared via electrospinning technique. Different types of composite nanofibers were electrospun by varying the weight percentage of GO in the polymer solution. Scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy, as well as current-voltage (I-V) measurements were used to characterize the N66/GO composite nanofibers. The morphology of the N66/GO composite nanofibers exhibited densely arranged mesh-like ultrafine nanofibers which were strongly bound in between the main fibers. The I-V characteristics of the N66/GO composite nanofibers demonstrated that the blending of GO in to N66 nanofibers led to a dramatic improvement of the electrical conduction compared to that of pristine N66 nanofibers which can be utilized for the various technological applications.

Recent progress in electrospun nanofibers: Reinforcement effect and mechanical performance

ABSTRACTComposite materials are becoming increasingly important as structural materials for aeronautical and space engineering, naval, automotive, and civil engineering, sporting goods, and other consumer products. Fiber‐based reinforcement represents one of the most effective manufacturing strategies for enhancing the mechanical strength and other properties of composite materials. Electrospinning has gained widespread interest in the last two decades because of its ability to fabricate continuous ultrafine nanofibers with unique characteristics. The impact of electrospinning on fiber synthesis and processing, characterization, and applications in drug delivery, nanofiltration, tissue scaffolding, and electronics has been extensively studied in the past. In this article, the authors have focused on a comprehensive review of the mechanical performance and properties of electrospun nanofibers as potential reinforcements as well as their advanced nanocomposites. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1171–1212

Ultrafine polystyrene nanofibers and its application in nanofibrous membranes

Polymer nanofibers have raising increasing interest for a wide class of applications due to the excellent properties. Here novel ultrafine (about 19nm) nanofibers are prepared from very dilute polystyrene (PS) solution via a facile approach based on the fast freeze technique. The molecular weight (Mw) and solvents have significant influences on the nanofiber formation. The resulting PS nanofibers are consisted of several inter-connected PS chains and monodispersed in ethanol solution. Meanwhile, the nanofibers are used to fabricate the high porous membrane by direct filtration. The as-fabricated membranes have a high porosity up to 87%, a super-hydrophobic and super-lipophilic surface, as well as show a fast and high-efficiency adsorption for methylene blue. The newly developed PS nanofibers have a great potential application in nanofabrication and wastewater treatment.

Core/shell-like structured ultrafine branched nanofibers created by electrospinning

Novel core/shell-like structured ultrafine branch nanofibers were successfully fabricated by a phase-separation process using simple polymer blend (polyacrylonitrile (PAN) and fluorinated polyimide (PI)) solutions with electrospinning. The obtained core/shell-like structured branch nanofibrous membranes showed strong hydrophobicity based on the hydrophobic shell polymer and ultrafine branch nanostructures. This simple process could be used to prepare core/shell structured branch nanofibers composed of other blend polymers and would also provide novel opportunities for industrial applications, such as nanocoating, nanoreinforcement, nanocomposite, nanomedicine and a drug-release system.

Luminescence and Microstructure of Nd Doped Y2Si2O7 Electrospun Fibers

Y2Si2O7:Nd3+ nanofibers were synthesized for the first time through a combination of sol–gel and electrospinning methods. Annealing effects on the Y2Si2O7 polymorph transformation and fiber morphology were examined under a scanning electron microscope. About 901, 1061, and 1337 nm emission bands were observed in the ultrafine nanofibers, while the rough fibers with pinholes and a larger grain size exhibited only slight photoluminescence. The one‐dimensional surface stress and low‐temperature crystalline distortion shifted the emission bands of the Nd3+‐ doped Y2Si2O7 fibers.

Fabrication of unique ribbon-like porous LaFeO3 nanofibers photocatalyst via electrospinning

Novel LaFeO3 ribbon-like porous nanofibers have been fabricated by electrospinning utilizing sol–gel precursors, followed by heat treatment at 600 °C for 2 h. The crystal structure, surface morphology, and microstructure were investigated by thermogravimetry–differential thermal analysis, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, respectively. The photocatalytic activity was investigated for the photodegradation of methylene blue aqueous solution. The result shows that the ribbon-like porous nanofibers exhibit excellent photocatalytic activity compared with ultrafine LaFeO3 nanofibers and LaFeO3 powders.

Single-handed helical carbonaceous bundles prepared using a chiral polybissilsesquioxane

Left-handed helical polybissilsesquioxane bundles were prepared through a self-templating approach. After carbonization and removal of silica, left-handed helical carbonaceous bundles constructed by fine nanofibers were obtained. They were characterized using transmission electron microscopy, field-emission scanning electron microscopy, powder X-ray diffraction, Raman spectrophotoscopy, N2 sorptions and diffuse reflectance circular dichroism (DRCD). The Raman spectra and X-ray diffraction pattern indicated that the carbon was amorphous. Mesoporous were identified, which can be originated from the voids among the ultra-fine nanofibers. The DRCD spectrum indicated that they exhibited optical chirality. This material may have potential as catalyst supports, chirality sensors and adsorbents.

Tuning the oxidation states and crystallinity of copper oxide nanofibers by calcination

Cu oxide/polyvinyl alcohol (PVA) nanofibers were synthesized by sol–gel and electrospinning technique. The obtained Cu oxide/PVA nanofibers were heated to remove the PVA compound at 673 and 873 K. The ultrafine Cu oxide nanofibers were characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray diffraction (XRD), and x-ray photoelectron spectroscopy (XPS). The SEM images showed that the Cu oxide nanofibers were successfully synthesized by electrospinning and calcination and the average diameters of the electrospun Cu/PVA nanofibers were 268.9 ± 97.2 nm. After the nanofibers were calcined at higher temperature than rt, the morphologies of the nanofibers changed. XRD results indicated that the crystalline structure changed from amorphous phase to monoclinic CuO through cubic Cu2O. TEM images also verified the crystal phase of Cu oxide nanofibers. XPS spectra revealed that the thermal oxidation of Cu proceeded during calcination.