Nanofiber Webs Research Articles

Enhancement of β-Phase Crystal Content of Poly(vinylidene fluoride) Nanofiber Web by Graphene and Electrospinning Parameters

Electrospun poly(vinylidene fluoride) (PVDF) nanofiber web has been widely utilized as a functional material in various flexible sensors and generators due to its high piezoelectricity, ease processability, and low cost. Among all the crystalline phases of PVDF, β-phase is a key property for PVDF nanofiber web, because the content of β-phase is directly proportional to piezoelectric performance of PVDF nanofiber web. Herein, the impact of graphene content (GC), tip-to-collector distance (TCD), and rotational speed of collector (RSC), as well as their interactions on the β-phase formation of PVDF nanofiber web is systematically investigated via design of experimental method. The fraction of each crystalline phase of PVDF nanofiber web is calculated by FTIR spectra, and the crystallinity is determined by XRD patterns. The influences of GC, TCD, and RSC on both β-phase fraction and crystallinity of PVDF nanofiber are analyzed using Minitab program. The results show that GC, TCD, and RSC all have significant effect on the β-phase content of PVDF nanofiber web, and GC is the most significant one. In addition, an optimal electrospinning condition (GC = 1 wt%, TCD = 4 cm, and RSC = 2000 r-min−1) to fabricate high β-phase crystallinity of PVDF nanofiber web is drawn, under which the crystallinity can reach 41.7%. The contributions in this study could provide guidance for future research on fabricating high performance PVDF nanofiber web based sensors or generators.

Microstructure and Thermoelectric Characterization of Composite Nanofiber Webs Derived from Polyacrylonitrile and Sodium Cobalt Oxide Precursors

We report the microstructure and thermoelectric properties of composite nanofiber webs, which were fabricated by dual-electrospinning of polyacrylonitrile (PAN) and sodium cobalt oxide (NaCo2O4) precursor solutions with different input compositions and following heat-treatment at 600–900 °C for simultaneous carbonation and calcination. The SEM and EDS mapping images revealed that PAN-derived carbon nanofibers (CNFs) and NaCo2O4-based ceramic nanofibers coexisted in the composite nanofiber webs and that their relative contents could be controlled by the input compositions. The Seebeck coefficient increased from ~26.77 to ~73.28 μV/K and from ~14.83 to ~40.56 μV/K with increasing the relative content of NaCo2O4 nanofibers in the composite nanofiber webs fabricated at 700 and 800 °C, respectively. On the other hand, the electrical conductivity of the composite nanofiber webs increased with the decrement of the relative content of NaCo2O4 nanofibers as well as the increment of the heat-treatment temperature. Owing to the opposite contributions of NaCo2O4 nanofibers and CNFs to the Seebeck coefficient, electrical conductivity and thermal conductivity, a maximum power factor of ~5.79 μW/mK2 and a figure of merit of ~0.01 were attained for CNF/NaCo2O4-based composite nanofiber webs fabricated at 45 wt% input composition of NaCo2O4 and at heat-treatment of 700 °C.

Tuning energy harvesting devices with different layout angles to robust the mechanical-to-electrical energy conversion performance

This research presents an engineering approach to fabricate multilayered electrospun nanofiber mats with high conversion performance of mechanical to electrical energy as well as improved physical stability. Electrospun polyvinylidene fluoride nanofiber webs were prepared with predefined nanofiber alignments. Fiber alignments and layer-by-layer deposition angles are considered as a tool to adjust the piezoelectric responses of multi-layered fibrous mats. Samples with optimized drum speed and maximum aligned nanofibers were utilized to fabricate multi-layered mats in different layering angles from the fiber direction of base layer (0°, 30°, 60°, 90°, 120°, 150°, and 180[Formula: see text]). The effect of layering angle of multi-layered nanogenerators on their piezoelectric responses was investigated using an image analysis approach based on the fast Fourier transform. Multivariate analyses (ANOVA) performed to reveal the relationship between increasing drum speed and nanofibers alignment and the degree of crystallization as well as the formation of β-phase in the fiber crystalline structure. Results showed that increase in drum speeds had a relative improvement in the crystal structure and the formation of β-phase in the electrospun polyvinylidene fluoride nanofiber webs. Furthermore, electrical response of samples with well-aligned polyvinylidene fluoride nanofibers collected at 1800 r/min led to 94.49% improvement when they were exposed by a periodic mechanical impact compared to non-aligned polyvinylidene fluoride nanofiber webs. Piezoelectric response of multilayered samples with layering angles of 120[Formula: see text] showed 41% improvement in their electrical output compared to those with 0[Formula: see text]. These results teach us to establish engineering design rules for textile-based energy conversion devices with different piezoelectric coefficients.

Electrospun PCL and PLA hybrid nanofibrous scaffolds containing Nigella sativa herbal extract for effective wound healing

AbstractBlack seed (Nigella sativa [NS]) is used in traditional medicine as an antibacterial agent. In this study, novel hybrid scaffolds were manufactured from poly(ɛ‐caprolactone[PCL])/ Poly(lactic acid [PLA]) with NS extract by double‐nozzle electrospinning for wound healing application. Optimal conditions were found using response surface methodology including feed rate 0.8 ml/hr, voltage 20 kV and PLA 8% /PCL 10% concentrations. The effect of NS extract on the properties of the scaffold was evaluated by scanning electron microscopy, contact angle, and mechanical test. The PLA‐PCL/NS 20% beadles, and smooth nanofibrous web was obtained as the optimum scaffold with an average diameter of 638 ± 69 nm and the contact angle of 44°. In addition, the biological properties of the scaffolds such as antibacterial against Staphylococcus aureus (gram‐positive) and Escherichia coli (gram‐negative) bacteria, MTT assay, extract release, and cell growth (human mesenchymal stem cells) were examined. Incorporation of NS extract into the nanofibers caused to enhance the biological properties, cell viability and cell proliferation without toxicity.

Thermally Treated Graphene Oxide/Polyacrylonitrile Based Electrospun Carbon Nanofiber Precursor

Graphene oxide (GO) included polyacrylonitrile (PAN) composite electrospun nanofiber webs were fabricated, and thermal oxidation of PAN/GO composite nanofibers were performed at different temperatures (25, 250, 280, and 300 °C) for different time intervals (0, 1 and 3 h.) to investigate the oxidation process of PAN/GO nanofibers. The thermal oxidation process of PAN has a complex mechanism through the cyclization and dehydrogenation steps. For all oxidized samples, Electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared-Attenuated Total Reflectance (FTIR-ATR) Spectroscopic results were comparatively evaluated to investigate the effect of GO addition onto the nanofiber webs. After heat treatment, change in C1s spectra from virgin PAN to oxidized form was detected and sp² carbon is developed. The presence of GO accelerated the oxidation and development of the final structure. At shorter heat treatment time, less oxidized forms are obtained. The cyclization of nitrile pendant groups of PAN forming polyimine type structure is the main reaction occurs during stabilization. In addition to the imine sequences with three to six units long, the presence of polar groups C═O, OH and COOH in the chains facilitates the initiation of the cyclization process through a nucleophilic attack and accelerates the subsequent oxidative ring closure reactions which these newly formed bonds during thermal oxidation and stabilization steps play an essential role on the carbonization process as an intermediate form of PAN based structures.

Analysis of polyacrylonitrile nanofiber yarn formation in electrospinning by using a conical collector and two oppositely charged nozzles

Nanofiber production by electrospinning has become a common production method as it is an easy and flexible system producing nanofibrous webs. However, direct spinning of nanofibers into a yarn would lead to conversion of nanofibers into woven or knitted fabrics easily, therefore improving end-use possibilities of these fibers substantially. In this work a successful nanofiber yarn spinning system using polyacrylonitrile polymer is established and yarn formation by polymers ejected from two nozzles with opposite charges was analysed and potential of this system for bicomponent yarn production was shown. Fiber formation from each nozzle was also examined by high speed camera while distribution of the electric field strength and loads in the electrostatic state was analysed by electric field simulation . Finally, polyacrylonitrile nanofiber yarns produced at different collector and winding speeds were analysed in terms of fiber and yarn properties. Furthermore, the first fabric sample with nanofiber yarns woven manually was presented.

Branched nanofibers with tiny diameters for air filtration via one-step electrospinning

Engineering the surface morphology of fibers has been attracting significant consideration in various areas and applications. In this study, polyvinylidene fluoride (PVDF) branched nanofibers with a diameter of less than 50 nm are electrospun directly at a low relative humidity by adding tetrabutylammonium chloride. The effects of the branched structure on the specific surface area and pore size distribution are investigated, and the filtration properties of the air filter based on branched nanofiber webs with different basis weights are studied. The results exhibit that the air filter based on PVDF branched nanofibers with the basis weight of 1 g/m2 has an outstanding filtration efficiency (99.999%) to 0.26 µm sodium chloride particles under the pressure drop of 126.17 Pa. We believe that this study can be used as a useful reference for the preparation of branched nanofibers through one-step electrospinning.

Synthesis of highly ordered mesoporous carbons nanofiber web based on electrospinning strategy for supercapacitor

Abstract Ordered mesoporous carbons fiber webs (OMCWs) with 2-D hexagonal (p6mm) pore structure were prepared by the electrospinning method using low molecular resin as carbon precursors, F127 as structure directed agent and PVP (polyvinyl pyrrolidone, Mw = 1,300,000) as fiber forming agent under wide range various electrospinning speed (0.1–0.5 ml/h) and voltages (15–25 kv). The microstructure of OMCWs could be tunable from cylinder to nano ribbon by carefully controlling the amount of PVP. OMCWs could be directly used in supercapacitor as electrode materials without any binders or conductive additives. The specific capacitance of OMCWs could reach as high as 119 F/g under the current density of 0.5 A/g, demonstrating the great potential application for electrode for supercapacitor.

Characterization of PU Nanofiber Web Treated with Non-oxidized Graphene and Silver Nanowire

The purpose of this study was to investigate the applicability of polyurethane nanofiber webs as smart textiles by evaluating electrical properties, surface properties, chemical properties, and thermal properties after imparting electrical conductivity by treating non-oxidized graphene/silver nanowire. For this purpose, three specimens were prepared by mixing non-oxidized graphene and silver nanowire at ratios of 3:1, 2:1, and 3:2, in order to impart conductivity to the polyurethane nanofiber web. The prepared specimens were named G/Ag31, G/Ag21 and G/Ag32 according to the ratio. The linear resistance and the surface resistance of each specimen was measured to estimate electrical properties of each specimen. The surface characteristics of the specimens were observed by FE-SEM photographs. HR-XRD analysis and Raman analysis were performed in order to determine whether the non-oxidized graphene and silver nanowires were properly processed in the fabricated specimens respectively. DSC and TGA analysis were also performed to investigate the thermal properties. As the results, the higher ratio of silver nanowires coated on the specimen, the lower the electrical resistance value. In the surface characteristics analysis, it was confirmed that the density of the silver nanowire was higher than that of the specimen having the higher silver nanowire ratio. In HR-XRD analysis, it was confirmed that non-oxidized graphene and silver nanowire existed in all specimens. In Raman analysis, it was confirmed that the intensity of 2D-peak was lower in specimens with high silver nanowire ratio. However, the difference in intensity between G/Ag21 and G/Ag32 was relatively small. In thermal analysis, it was found that the thermal stability of the specimen was higher than that of the untreated polyurethane nanofiber web because the thermogravimetric after 600 oC of all the specimens was larger than the untreated specimen. Therefore, in this study, it was confirmed that G/Ag32 specimen is best suited as a smart textile and it is confirmed that it can be applied as a textile sensor in the future.

A Novel Method for Electrospinning Nanofibrous 3-D Structures

The fast and precise fabrication of three-dimensional (3-D) structures made of nanofibers is an important development trend in the electrospinning technique. This paper describes a new and facile method of electrospinning to fabricate nanofibrous 3-D structures. The nanofibrous 3-D structures can be engineered to have the desired layer thicknesses, where the fiber spacing, density (i.e., fiber volume/unit volume), as well as shape of the structure may be controlled. While innumerable structural variations are possible with this method, this paper discusses, as proof-of-concept, a few cases that illustrate how 3-D nanofiber webs can be made for filtration application. Computerized automation of the method will make it possible to build almost any 3-D web structure suitable for a myriad of applications including ultra-light-weight insulation and scaffolds for hydrogel preparation and tissue.

Polyaniline-coated titanium oxide nanoparticles and simvastatin-loaded poly(ε-caprolactone) composite nanofibers scaffold for bone tissue regeneration application

Poly(ε-caprolactone) (PCL) nanofibers loaded with polyaniline coated titanium oxide nanoparticles (TiO2/PANI) and simvastatin (SIM) drug were produced by the electrospinning method. As-prepared samples were investigated in terms of morphology characterization, mechanical properties, physiochemical properties, drug release, biomimetic mineralization, and biocompatibility. in vitro drug release studies were conducted in the phosphate buffer saline (PBS) at pH 7.4. The results suggest that varying the concentrations of TiO2/PANI nanoparticles could change the rate of drug release. The release mechanism was studied using several kinetic models, including the Higuchi model, the Hixson–Crowell model, and the Korsmeyer–Peppas model, to clarify the mechanism of SIM release from the composite nanofibers. The assessment of in vitro mineralization of the composite nanofibers for the growth of hydroxyapatite was performed in simulated body fluid (SBF). Field scanning electron microscopy (FE-SEM) imagery and energy-dispersive X-ray spectroscopy (EDS) analyses indicated that after soaking in SBF, a hydroxyapatite layer was formed on the surface of the nanofibrous webs. These novel composite nanofibers release simvastatin in a controlled manner with profound cell proliferation and attachment compared to that in pure PCL nanofiber, which indicates their potential for bone regeneration applications.

Electrospun ion gel nanofibers for high-performance electrochromic devices with outstanding electrochromic switching and long-term stability

Here we present the enhanced electrochemical properties of ion gel nanofiber-based electrochromic devices (ECDs) prepared by electrospinning. The ECDs were fabricated by sandwiching prepared electrospun nanofiber webs between two transparent electrodes. The electrochromic behaviors of the ECDs were investigated using cyclic voltammetry, spectroelectrochemistry, and kinetic stability measurements. In order to determine the origin of the enhanced EC behaviors, the morphological structures of the nanofiber were examined by a scanning electron microscope, which showed that an ionic liquid (IL) region enclosed the pores between the nanofibers in the solid phase. The increased IL contents in the interstices of the nanofibers were noted, which would induce higher ionic mobility. Consequently, the fabricated nanofiber-based ECDs showed greatly enhanced device performance in terms of switching speed, cyclic stability, and coloration efficiency. Furthermore, flexible ECDs were fabricated by sandwiching the electrospun webs between two plastic electrodes consisting of silver nanowire/PEDOT:PSS hybrid electrodes. The fabricated device revealed a color switching over the large active area, with the transmittance changes maintained over repeated bending cycles. These nanofiber-based ECDs are evidence of a practical approach by which to realize large-area electrochromic devices with excellent chromatic switching and long-term cyclic stability, suitable both for rigid and flexible devices.

Functional Nanofibers and Their Applications

The methods to provide functions to nanofiber webs and applications, characterization, evaluation methods, market value, and future directions of nanofiber webs are summarized and presented in this...

Nano- And Microfiber-Based Fully Fabric Triboelectric Nanogenerator For Wearable Devices.

The combination of the triboelectric effect and static electricity as a triboelectric nanogenerator (TENG) has been extensively studied. TENGs using nanofibers have advantages such as high surface roughness, porous structure, and ease of production by electrospinning; however, their shortcomings include high-cost, limited yield, and poor mechanical properties. Microfibers are produced on mass scale at low cost; they are solvent-free, their thickness can be easily controlled, and they have relatively better mechanical properties than nanofiber webs. Herein, a nano- and micro-fiber-based TENG (NMF-TENG) was fabricated using a nylon 6 nanofiber mat and melt blown nonwoven polypropylene (PP) as triboelectric layers. Hence, the advantages of nanofibers and microfibers are maintained and mutually complemented. The NMF-TENG was manufactured by electrospinning nylon 6 on the nonwoven PP, and then attaching Ni coated fabric electrodes on the top and bottom of the triboelectric layers. The morphology, porosity, pore size distribution, and fiber diameters of the triboelectric layers were investigated. The triboelectric output performances were confirmed by controlling the pressure area and basis weight of the nonwoven PP. This study proposes a low-cost fabrication process of NMF-TENGs with high air-permeability, durability, and productivity, which makes them applicable to a variety of wearable electronics.

Tensile testing and fracture mechanism analysis of polyvinyl alcohol nanofibrous webs

AbstractA tensile properties testing study was conducted to understand the influence of thickness, cross‐head speed (speed of testing), gauge length (GL; specimen test length), and sample shape on important tensile properties of polyvinyl alcohol (PVA) nanofiber webs. The effects of each testing parameter on load at break, extension at break, Young's modulus, and tensile stress–strain curve of PVA nanofiber webs are analyzed. The Welch two samplet‐tests show the significant difference among tested data. Using interaction plots, two‐way analysis of variance, and margin mean plots, the interaction effects among testing parameters have been analyzed. Of all the factors, cross‐head speed, the interaction among GL, and sample thickness (GL: Thickness) and the interaction among GL, testing speed and sample thickness (GL: Speed: Thickness) have significant influence on the tensile properties of PVA nanofiber webs. Moreover, the hypothesized model of mechanism of tensile strain–stress curve of PVA nanofiber webs has been proposed. Based on the model, the tensile strain–stress curve can be split into three stages: linear elastic, partial break up, and complete breakage. This study will provide a better understanding of tensile testing parameters' effects and their interaction effects on the tensile properties of nanowebs.

Nonflammable pre-carbonized polyacrylonitrile nanofiber webs

For non-flammability usages, composite structures with nano-additives or carbonized form of polyacrylonitrile (PAN) are generally preferred. In this study, a pre-carbonized form of nanofiber webs (OxPAN) is firstly proposed as a non-flammable material to eliminate the need for carbonization. The thermal oxidative stabilization process is applied to the PAN nanofibers to achieve high structural stability. This prevents melting and fusing during the thermal treatments and thereby improves the thermal stability of the web. PAN nanofiber webs were successfully obtained via the electrospinning technique and the thermal oxidation process was then applied. The structural properties of the oxidized PAN nanofiber webs were investigated by Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy, Raman Spectroscopy and X-Ray Photoelectron Spectroscopy and Electrochemical Impedance Spectroscopy. The surface morphology of the OxPAN was examined by scanning electron microscopy and the average fiber diameter was measured as 265 ± 64 nm. The thermal properties were analyzed with a differential scanning calorimeter and a thermal gravimetric analyzer. The flammability performance was tested via the Limiting Oxygen Index (LOI), and it was found that in addition to being lightweight, OxPAN nanofiber webs exhibit splendid performance with a LOI value of 48–49%.

Influence of Modified Cationic Starch in a Mixed Poly(Vinyl Alcohol)/Cationic Starch Solution on the Electrospinning Process and Web Structure

Abstract Nanofibers were electrospun from bicomponent poly(vinyl alcohol) (PVA) and modified cationic starch (CS) mixed solution PVA/CS with different mass ratios (75/25, 50/50 and 35/65) at a total concentration of 12 wt% for all polymer compositions. For comparison, pure PVA solution was used. Electrospinning technique Nanospider (Elmarco, Czech Republic) with a rotating electrode with tines was used to obtain nanofibrous web. The influence of prepared polymer solution compositions on the structure and morphology of nanofibers and webs were investigated. Analyzing the structure and morphology of the formed nanofiber webs, it was noticed that the fineness nanofibers were formed from the PVA/CS solution with a mass ratio of 50/50. This ratio of solution also lets us to obtain the nanofibrous web with less sticked nanofibers on spunbond. The increase in the CS ratio by more than 50/50 had a negative influence on the diameter of nanofibers and the structure of nanofibrous web.

Nanocomposites of polyvinylidene fluoride copolymer-functionalized carbon nanotubes prepared by electrospinning method

Electrospun nanofiber membranes (ENM) have been utilized in varied applications like filters, sensors, scaffolds for tissue engineering, electronics and so on. In this study, polyvinylidene fluoride (PVDF) copolymer nanofiber was reinforced with functionalized multiwall carbon nanotubes (f-MWCNT) via electrospinning method with N,N-dimethylacetamide (DMAc) as the solvent. To ensure the dispersion of f-MWCNT in polymer solution, it was sonicated prior to addition of PVDF copolymer into the dispersion. The results showed that tensile strength and elongation at break increased by 9 % and 79 %, respectively, with the addition of f-MWCNT, when compared to pure PVDF copolymer nanofiber web. Incorporated f-MWCNT into PVDF copolymer nanofiber also resulted in an increase in the average nanofiber diameter from 312 nm to 445 nm but decrease the hydrophobicity. FTIR spectra and XRD pattern confirmed the increase of PVDF β-phase structure as the results of electrospinning process and addition of MWCNT.

Fast-dissolving antioxidant curcumin/cyclodextrin inclusion complex electrospun nanofibrous webs

Curcumin/Hydroxypropyl-beta-Cyclodextrin (HP-β-CyD) and Curcumin/Hydroxypropyl-gamma-Cyclodextrin (HP-γ-CyD) inclusion complex nanofibrous webs were produced using electrospinning technique for the purpose of orally fast-dissolving antioxidant food supplement. Curcumin was totally preserved without any loss during the electrospinning process. The aqueous solutions of curcumin/HP-β-CyD and curcumin/HP-γ-CyD were yielded uniform fiber morphology with ~200 nm and ~900 nm average fiber diameter, respectively. Both Curcumin/CyD webs were produced in the form of free-standing and flexible character. Curcumin is a natural bioactive compound with poor water-solubility, however, the phase solubility test and dissolution/disintegration tests (water and artificial saliva) revealed that the water-solubility of curcumin was prominently improved by inclusion complexation with CyD. The antioxidant effect of curcumin in Curcumin/CyD webs was also enhanced due to higher solubility of curcumin by CyD inclusion complex. The results showed that HP-γ-CyD is significantly more effective than HP-β-CyD in order to enhance the solubility and antioxidant property of curcumin in Curcumin/CyD webs.

Fabrication of Antibacterial Nanofibers Composites by Functionalizing the Surface of Cellulose Acetate Nanofibers

AbstractThe surface modification of nanofibers web enables the invention of wound dressings by using the simple materials substrate without altering the mechanical properties of foundation materials or nanofibers web. Herein, authors fabricated the novel antibacterial wound dressings by functionalizing the surface of cellulose acetate (CA) nanofibers. This surface treatment was done through facile method. The silver sulfadiazine (SSD) nanoparticles were successfully synthesized on the surface of cellulose acetate nanofibers web by in‐situ facile method in which nanofibers webs were immersed in the solution of sodium sulfadiazine salt and silver nitrate (AgNO3) for three different interval of times (hrs). The resultant CA/SSD nanofibers were characterized by scan electron microscope, transmission electron microscope, FT‐IR, XPS, XRD, water contact angle and antibacterial agar disc diffusion test. All characterization results supported that this composite can be used for antibacterial wound dressings, especially for gram negative E. Coli bacteria because SSD has great potential against E. Coli bacteria.