Electrospinning and mechanical characterization of gelatin nanofibers

This paper investigates electrospinning of a natural biopolymer, gelatin, and the mass concentration-mechanical property relationship of the resulting nanofiber membranes. It has been recognized that although gelatin can be easily dissolved in water the gelatin/water solution was unable to electrospin into ultra fine fibers. A different organic solvent, 2,2,2-trifluoroethanol, is proven suitable for gelatin, and the resulting solution with a mass concentration in between 5 and 12.5% can be successfully electrospun into nanofibers of a diameter in a range from 100 to 340 nm. Further lower or higher mass concentration was inapplicable in electrospinning at ambient conditions. We have found in this study that the highest mechanical behavior did not occur to the nanofibrous membrane electrospun from the lowest or the highest mass concentration solution. Instead, the nanofiber mat that had the finest fiber structure and no beads on surface obtained from the 7.5% mass concentration exhibited the largest tensile modulus and ultimate tensile strength, which are respectively 40 and 60% greater than those produced from the remaining mass concentration, i.e. 5, 10, and 12.5%, solutions.     

Relationship between surface concentration of amphiphilic quaternary ammonium biocides in electrospun polymer fibers and biocidal activity

Electrospinning was utilized to generate antimicrobial Nylon and polycarbonate fibers for potential applications including self-decontaminating fabrics, wound dressings, and filtration media. The effects of quaternary ammonium salt concentration on fiber morphology, diameter, and antimicrobial activity of the resulting fiber mats were investigated. Fibers were characterized utilizing scanning electron microscopy and X-ray photoelectron spectroscopy, while antimicrobial activity was evaluated against Staphylococcus aureus. The co-electrospinning of soluble quaternary ammonium biocides within polymeric solutions generated uniform fibers with diameters ranging from 91 to 278 nm for Nylon and 0.55–2.34 μm for polycarbonate. Fiber morphology and diameter of the resulting fibers were shown to be dependent on polymer type and biocide concentration. A positive correlation between surface concentration of quaternary ammonium salts and antimicrobial activity was observed as fibers loaded with biocides exhibited up to a 7 log reduction of viable bacteria.     

Electrospinning preparation and characterization of cadmium oxide nanofibers

Using a facile synthesis route, cadmium oxide (CdO) nanofibers in the diameter range of 50–60 nm have been prepared employing the electrospinning technique followed by a single-step calcination from the aqueous solution of polyvinyl alcohol (PVA) and cadmium acetate dihydrate. Electron microscopy (EM) and the Brunauer–Emmett–Teller (BET) technique were employed to characterize the as-spun nanofibers as well as the calcined product. The specific surface area of the product was calculated to be 42.6711 m² g⁻¹. Infrared (IR) absorbance spectroscopy and X-ray powder diffractometery were conducted on the samples to study their chemical composition as well as their crystallographic structure. The study on the optical properties based on the photoluminescence (PL) spectrum demonstrated that the emission peaks of CdO nanofibers are centered at 493 and 528 nm. The direct bandgap of the CdO nanofibers was determined to be 2.51 eV.     

Electrospinning jets and polymer nanofibers

In electrospinning, polymer nanofibers are formed by the creation and elongation of an electrified fluid jet. The path of the jet is from a fluid surface that is often, but not necessarily constrained by an orifice, through a straight segment of a tapering cone, then through a series of successively smaller electrically driven bending coils, with each bending coil having turns of increasing radius, and finally solidifying into a continuous thin fiber. Control of the process produces fibers with nanometer scale diameters, along with various cross-sectional shapes, beads, branches and buckling coils or zigzags. Additions to the fluid being spun, such as chemical reagents, other polymers, dispersed particles, proteins, and viable cells, resulted in the inclusion of the added material along the nanofibers. Post-treatments of nanofibers, by conglutination, by vapor coating, by chemical treatment of the surfaces, and by thermal processing, broaden the usefulness of nanofibers.     

High Precision Deposition Electrospinning of nanofibers and nanofiber nonwovens

Electrospinning is known to produce nanofiber nonwovens with lateral dimensions in 10 cm up to the meter range meeting thus requirements characteristic of filter, textile or even tissue engineering applications. For particular applications other types of deposition pattern are of benefit (i) in which the deposition area is strongly limited in the lateral dimension, (ii) in which a linear deposition path is oriented along a specified direction or (iii) in which the nonwovens are deposited following a predesigned pattern. This paper reports experimental results for the High Precision Deposition Electrospinning (HPDE) approach introduced by us earlier. It is based on a syringe type die-counter electrode set-up used for conventional continuous electrospinning, the key feature being a reduction of the distance between the spinning die and the substrate from the conventional value of 10-50 cm down to the millimeter and below mm range in order to suppress the onset of bending instabilities and the corresponding spread of the deposition area. The architecture of the nonwovens is controlled in this case by buckling processes and deflections of the jet by transiently charged nanofibers on the substrate. A second important feature of the set-up is a counter electrode/substrate which can be subjected to precise motions in the deposition plane. Based on a careful optimization of the spinning parameters and a tight online control of the spinning process a deposition of individual nanofibers or nonwovens is achieved which meets all deposition requirements specified above. This opens the route towards novel applications among others in areas relying on specific surface architectures such as sensorics, microfluidics and possibly also surfaces of implants.     

Electrospinning preparation and characterization of alumina nanofibers with high aspect ratio

Alumina nanofibers were successfully prepared via an electrospinning technique combined with a sol–gel method. The electrospinning solution was prepared by dissolving aluminum isopropoxide (AIP) in distilled water and then mixing with a polyvinyl alcohol (PVA) aqueous solution. The as-spun fibers were calcined at different temperatures and characterized by TG–DTA, XRD, SEM–EDS, TEM–SAED, and BET analysis. Results showed that the average fiber diameter decreases with increasing calcination temperature. The as-spun nanofibers were amorphous. After calcination at 1000 °C, the nanofibers formed were composed of α-Al₂O₃ and γ-Al₂O₃, showing an average diameter of 30–90 nm and an aspect ratio of greater than 1000. The pore size of the obtained fibers was approximately 5 nm, which implies that these fibers are mesoporous materials.     

Electrospinning of polymer nanofibers loaded with noncovalently functionalized graphene

Pristine graphene/polyvinyl alcohol (PVA) nanofibers were prepared by electrospinning an aqueous solution of polyvinylpyrrolidone‐stabilized graphene and PVA. This is the first report of electrospun nanofibers reinforced with dispersed pristine graphene. We examine the relationship between graphene loading and critical electrospinning parameters. Microscopy indicates uniform fiber formation and excellent graphene dispersion within the fiber. Rheological data indicates that the excellent level of graphene dispersion enhances the modulus of the polymer by 205%. We also find that the graphene significantly increases the fibers' thermal stability (increase of 15°C) and crystallinity (59% increase) above the baseline. In fact, the graphene may act as nucleating points for increased crystallinity. These graphene/polymer nanofibers have the potential to serve in a variety of applications, including electrodes, conductive wires, and biomedical materials. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Electrospinning preparation and microstructure characterization of homogeneous diphasic mullite ceramic nanofibers

In this work, diphasic mullite (3Al₂O₃·2SiO₂) nanofibers with good homogeneity were prepared by electrospinning method. Aluminum nitrate (AN) and aluminum isopropoxide (AIP) were used as alumina sources, commercial colloidal silica as silica source, and polyvinyl alcohol (PVA) as polymer additive. Precursor nanofibers with continuous and uniform structures were acquired at mass ratio of PVA to precursor sol from 0.06 to 0.09. γ-Al₂O₃ phase was obtained at 878 ^°C and mullite phase formed at 1322 ^°C upon heating of the precursor under air atmosphere. Calcined samples suggested mullite as dominant phase at 1300 ^°C and amorphous SiO₂ could even exist at 1400 ^°C. As-prepared nanofibers possessed continuous structures with subequal average diameters at 900–1200 °C. However, such morphological characteristics were lost at temperatures above 1300 ^°C due to rapid growth of crystal grains. Al and Si elements were uniformly distributed in fibers and mixed at nanoscale, confirming homogeneity and diphasic features of nanofibers.     

Electrospinning synthesis and negative thermal expansion of one-dimensional Sc2Mo3O12 nanofibers

Orthorhombic Sc₂(MoO₄)₃ nanofibers have been prepared by ethylene glycol assisted electrospinning method. The effects of annealing temperature, precursor concentration, spinning distance and solvent on the preparation of Sc₂(MoO₄)₃ nanofibers were characterized by XRD, SEM, HRTEM, EDX and high-temperature XRD. XRD analysis shows as-prepared nanofibers are amorphous. Orthorhombic Sc₂(MoO₄)₃ nanofibers can be fabricated after annealing at different temperatures in 500–800 °C for 2 h. The crystallinity of Sc₂(MoO₄)₃ nanofibers improves and the nanofiber diameter decreases gradually as the annealing temperature increases. However, the nanofiber structure was destroyed at the annealing temperature above 700 °C. Higher precursor concentration results in a slight increase of diameter and decrease in destroying temperature of Sc₂(MoO₄)₃ nanofibers. Spinning distance also affects the diameter of nanofibers, and the nanofiber diameter decreases as the distance increases. One-dimensional orthorhombic Sc₂(MoO₄)₃ nanofibers exhibit anisotropic negative thermal expansion. In 25–700 °C, the coefficients of thermal expansion (CTE) of α_a, α_b and α_c are ?5.81 × 10^?6 °C^?1, 4.80 × 10^?6 °C^?1 and -4.33 × 10^?6 °C^?1, and the α_l of Sc₂(MoO₄)₃ nanofibers is ?1.83 × 10^?6 °C^?1.     

Synthesis, characterization, and properties of a novel acrylic terpolymer with pendant perfluoropolyether segments

A novel acrylic terpolymer with pendant perfluoropolyether (PFPE) segments has been synthesized and fully characterized. By hexamethylene diisocyanate functional groups PFPE monofunctional macromonomers have been grafted on a poly(butyl methacrylate-co-hydroxyethyl acrylate-co-ethyl acrylate) random terpolymer. Such grafted copolymer behaves like an interface-active material, since the perfluoropolyether segments in solvent cast films rearrange themselves at the air-polymer interface by surface segregation. In addition, blends of the above graft copolymer with acrylic base polymers (either the terpolymer itself or a commercial copolymer) have been examined in terms of surface segregation and fluorine enrichment of the external layers.The critical surface tension, γ_c, of solid films made of the neat graft copolymer as well as of the polymer blend has been evaluated by contact angle measurements and Zisman plots. Even a small addition (5 wt%) of the fluorinated copolymer to the acrylic component has been found very effective in lowering the surface tension. The outermost surface composition has been investigated by XPS technique, confirming the strong fluorine enrichment. Furthermore, SEM and EDX analyses have been performed on cross-sectioned films, showing that in the above polymer blends macrophase surface segregation has originated a thick layer made of fluorinated copolymer close to the air-polymer interface.     

Electrospinning of chitosan-poly(ethylene oxide) blend nanofibers in the presence of micellar surfactant solutions

Nanofibers were fabricated by electrospinning a mixture of cationic chitosan and neutral poly(ethylene oxide) (PEO) at a ratio of 3:1 in aqueous acetic acid. Chitosan ((1 → 4)-2-amino-2-deoxy-β-d-glucan) is a multifunctional biodegradable polycationic biopolymer that has uses in a variety of different industrial applications. Processing conditions were adjusted to a flow rate of 0.02 ml/min, an applied voltage of 20 kV, a capillary tip-to-target distance of 10 cm and a temperature of 25 °C. To further broaden the processing window under which nanofibers are produced, surfactants of different charge were added at concentrations well above their critical micellar concentrations (cmc). The influence of viscosity, conductivity and surface tension on the morphology and physicochemical properties of nanofibers containing surfactants was investigated. Pure chitosan did not form fibers and was instead deposited as beads. Addition of PEO and surfactants induced spinnability and/or yielded larger fibers with diameters ranging from 40 nm to 240 nm. The presence of surfactants resulted in the formation of needle-like, smooth or beaded fibers. Compositional analysis suggested that nanofibers consisted of all solution constituents. Our findings suggest that composite solutions of biopolymers, synthetic polymers, and micellar solutions of surfactants can be successfully electrospun. This may be of significant commercial importance since micelles could serve as carriers of lypophilic components such as pharmaceuticals, nutraceuticals, antimicrobials, flavors or fragrances thereby further enhancing the functionality of nanofibers.     

Electrospinning of cyclodextrin functionalized poly(methyl methacrylate) (PMMA) nanofibers

Cyclodextrin functionalized PMMA nanofibers (PMMA/CD) were successfully produced by electrospinning technique with the goal to develop functional nanowebs. Bead-free uniform electrospun PMMA/CD nanofibers were obtained from a homogeneous solution of CDs and PMMA in dimethylformamide (DMF) using three different types of CDs, α-CD, β-CD and γ-CD. The electrospinning conditions were optimized in order to form bead-free PMMA/CD nanofibers by varying the concentrations of PMMA and CDs in the solutions. The concentration of CDs was varied from 5% up to 50% w/w, with respect to the PMMA matrix. We find that the presence of the CDs in the PMMA solutions facilitates the electrospinning of bead-free nanofibers from the lower polymer concentrations and this behavior is attributed to the high conductivity and viscosity of the PMMA/CD solutions. The X-ray diffraction (XRD) spectra of PMMA/CD nanowebs did not show any significant diffraction peaks indicating that the CD molecules are homogeneously distributed within the PMMA matrix and does not form any phase separated crystalline aggregates. Furthermore, attenuated total reflection Fourier transform infrared (ATR-FTIR) studies elucidate that some CD molecules are located on the surface of the nanowebs. This suggests that these CD functionalized nanowebs may have the potential to be used as molecular filters and/or nanofilters for waste treatment purposes.     

Electrospinning combined with hydrothermal synthesis and lithium storage properties of ZnFe2O4-graphene composite nanofibers

ZnFe₂O₄-graphene composite nanofibers were prepared through electrospinning technique, then with graphene oxide by the facile solvothermal method to get the final products for the first time. The obtained ZnFe₂O₄ nanofibers composed of numerous same size nanoparticles wrapped by graphene sheets to form a unique nanostructure. When the ZnFe₂O₄-graphene electrode was evaluated as anode for lithium-ion batteries, good rate capability and long-term cycling stability could be achieved. The ZnFe₂O₄-graphene electrode exhibited a first discharge capacity of 2166 mAh g⁻¹ cycling at 0.05 C, remained an average reversible capacity of 1000 mAh g⁻¹ after 50 cycles, and kept the high rate capacities of 899, 822, 760 and 711 mAh g⁻¹ at the current rates of 0.5, 1, 2 and 5 C, respectively. The excellent electrochemical performance could be ascribed to the following reasons: the large electrochemical active surface area provided by the composite nanofibers; the graphene sheets decreased the internal resistance of the lithium-ion batteries, which resulted from the electrical conductivity of the graphene sheets; the graphene sheets as conductive network could effectively restrain the agglomeration of ZnFe₂O₄ nanopaiticals.     

Electrospinning of nanofibers

Nanotechnology is the study and development of materials at nano levels. It is one of the rapidly growing scientific disciplines due to its enormous potential in creating novel materials that have advanced applications. This technology has tremendously impacted many different science and engineering disciplines, such as electronics, materials science, and polymer engineering. Nanofibers, due to their high surface area and porosity, find applications as filter medium, adsorption layers in protective clothing, etc. Electrospinning has been found to be a viable technique to produce nanofibers. An in‐depth review of research activities on the development of nanofibers, fundamental understanding of the electrospinning process, and properties of nanostructured fibrous materials and their applications is provided in this article. A detailed account on the type of fibers that have been electrospun and their characteristics is also elaborated. It is hoped that the overview article will serve as a good reference tool for nanoscience researchers in fibers, textiles, and polymer fields. Furthermore, this article will help with the planning of future research activities and better understanding of nanofiber characteristics and their applications. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 557–569, 2005     

Electrospinning of circumferentially aligned polymer nanofibers floating on rotating water collector

This work outlines a novel electrospinning process using a rotating water collector. The circumferentially aligned nanofibers are successfully fabricated using this process. The movement and conductivity of the liquid collector are considered as the two prime factors to investigate the interaction between electrospun nanofibers and liquid surface. Through the theoretical analysis of the movement of liquid collector, it is confirmed that the liquid flow velocity demonstrates a tendency to decline from the center of the vortex to the edge of the container. Experimental results show that as the fluid flow velocity increases, the alignment of the nanofibers increases as well. In addition, it is discovered that the conductivity of the water collector demonstrates no significant effect on the alignment of nanofibers. However, the solution with higher conductivity can produce a nanofiber mat with smaller dimension. The present study confirms the versatility of the liquid collector and can be used to prepare nanofiber mats with complicated structures. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48759.     

The surface chemistry of water-reducible polymer solutions/dispersions 1. Surface tension behavior

Both static tension and dynamic surface tension of water-reducible (W/R) polymer solutions were carefully examined. It is shown that the cosolvent and its concentration are controlling factors in surface tension behavior for most concentration regions of W/R polymer solutions. This is true for both static and dynamic surface tensions. The polymer and its concentration have a much smaller effect on static surface tension than does the cosolvent. Much of the dynamic surface tension correlates with the bulk shear viscosity of W/R polymer solutions. The examination of cosolvent /water mixtures shows a critical solution concentration (CSC) for most cosolvents, analogous to the critical micelle concentration (CMC) in surfactant solutions. Both CSC and CMC originate from the same structural characteristics, i.e. molecules having a hydrophilic head and hydrophobic tail. Typically cosolvents have a less hydrophobic nature so values of CSC are higher than those typical of CMC for surfactants. This CSC plays a unique role in the surface tension of W/R polymer solutions. Above the CSC, constant surface tension is observed, while below the CSC a rapid increase in surface tension with decrease of cosolvent concentration occurs.     

Fabrication of electronspun porous CeO2 nanofibers with large surface area for pollutants removal

The porous CeO₂ nanofibers with diameter of 100–140 nm were successfully synthesized by single-capillary electrospinning of a Ce(NO₃)₃·6H₂O/PVP precursor solution, followed by calcination. The preparation parameters, including solution parameters and process parameters, affecting the spinnability and the morphology of nanofibers were investigated and discussed systematically. And the effects of different calcination temperatures on the microstructure CeO₂ nanofibers were also studied. A plausible mechanism was proposed to explain the formation process of the CeO₂ nanofibers. The N₂ adsorption-desorption isotherm analysis showed that the specific surface area and average pore size of the nanofibers were 195.75 g/m² and 2.4 nm, respectively. Moreover, as absorbent, the porous CeO₂ nanofibers adsorbed the MO effectively. The adsorption experiment indicated that the adsorption process can be divided into two stages, including quick adsorption and gradual adsorption. And the adsorption capacities were not only determined by the specific surface area, but closely related to the pore size. Finally, the adsorption data were modeled by the pseudo-first-order and pseudo-second-order kinetics equations. The results showed that the pseudo-second order kinetics could best describe the adsorption of MO onto the porous CeO₂ nanofibers.     

Electrospinning of polyacrylonitrile nanofibers

Polyacrylonitrile (PAN) was electrospun in dimethylformamide as a function of electric field, solution flow rate, and polymer concentration (C). The fiber diameter increased with C and ranged from 30 nm to 3.0 μm. The fiber diameter increased with the flow rate and decreased when the electric field was increased by a change in the working distance; however, it did not change significantly when the electric field was varied by a change in the voltage at a given working distance. The fibers below about 350 nm diameter contained beads, whereas above this diameter, bead‐free fibers were obtained. For PAN with a molecular weight of 100,000 g/mol, the fiber diameter scaled as C^1.2 and C^7.5 at low (5.1–16.1 wt %) and high (17.5–22.1 wt %) C values, respectively. Both concentrations were in the semidilute entangled regime, where the specific viscosity scaled as C^4.4, consistent with De Gennes's scaling concepts. In the semidilute unentangled regime (0.5–3.1 wt %), where the viscosity scaled as C^1.3, microscopic or nanoscopic particles rather than fibers were obtained. Concentration‐ dependent electrospinning studies were also carried out for higher molecular weight PAN (250,000 and 700,00 g/mol). The results of these studies are also presented and discussed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1023–1029, 2006     

Electrospinning fabrication of partially crystalline bisphenol A polycarbonate nanofibers: The effects of molecular motion and conformation in solutions

Partially crystalline bisphenol A polycarbonate (BPAPC) nanofibers were successfully fabricated using a combination of a centrifugal field (1800 rpm) and an electrostatic field (25 kV). The BPAPC solution properties are key factors for adequately electrospinning the partially crystalline BPAPC nanofibers. The correlation times (τ_c) of methyl (τ_c = 9.3 ns) and of benzene-ring (τ_c = 15.3 and 15.8 ns) motions in the 14 wt.% BPAPC/THF solution were longer than in CH₂Cl₂ and CHCl₃, as determined by NMR. The distribution-peak maximum of the hydrodynamic radius of BPAPC in the 14 wt.% THF solution (R_h = 15 Å) was higher than in CH₂Cl₂ (R_h = 9.2 Å) and CHCl₃ (R_h = 7.9 Å), as evidenced by DLS data. We conclude that the BPAPC assumed a denser, more worm-like chain conformation in THF solvation.     

Electrospinning of polyurethane fibers

A segmented polyurethaneurea based on poly(tetramethylene oxide)glycol, a cycloaliphatic diisocyanate and an unsymmetrical diamine were prepared. Urea content of the copolymer was 35 wt%. Electrospinning behavior of this elastomeric polyurethaneurea copolymer in solution was studied. The effects of electrical field, temperature, conductivity and viscosity of the solution on the electrospinning process and morphology and property of the fibers obtained were investigated. Results of observations made by optical microscope, atomic force microscope and scanning electron microscope were interpreted and compared with literature data available on the electrospinning behavior of other polymeric systems.