Formation of high aspect ratio polyamide-6 nanofibers via electrically induced double layer during electrospinning

In the present study, the formation of high aspect ratio nanofibers in polyamide-6 was investigated as a function of applied voltage ranging from 15 to 25 kV using electrospinning technique. All other experimental parameters were kept constant. The electrospun polyamide-6 nanofibers were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF). FE-SEM images of polyamide-6 nanofibers showed that the diameter of the electrospun fiber was decreased with increasing applied voltage. At the critical applied voltage, the polymer solution was completely ionized to form the dense high aspect ratio nanofibers in between the main nanofibers. The diameter of the polyamide-6 nanofibers was observed to be in the range of 75-110 nm, whereas the high aspect ratio structures consisted of regularly distributed very fine nanofibers with diameters of about 9-28 nm. Trends in fiber diameter and diameter distribution were discussed for the high aspect ratio nanofibers. TEM results revealed that the formation of double layers in polyamide-6 nanofibers and then split-up into ultrafine fibers. The electrically induced double layer in combination with the polyelectrolytic nature of solution is proposed as the suitable mechanisms for the formation of high aspect ratio nanofibers in polyamide-6.     

Ultrasonic-assisted dyeing of Nylon-6 nanofibers

We first time report ultrasonic dyeing of the Nylon 6 nanofibers with two disperse dyes CI Disperse blue 56 and CI Disperse Red 167:1 by utilising ultrasonic energy during dyeing process. The Nylon 6 nanofibers were fabricated via electrospinning and dyed via batchwise method with and without sonication. Results revealed that ultrasonic dyeing produce higher color yield (K/S values) and substantially reduces dyeing time from 60 min for conventional dyeing to 30 min can be attributed to breakage of dye aggregate, transient cavitation near nanofiber surface and mass transfer within/between nanofibers. Color fastness results exhibited good to very good dye fixation. SEM images exhibit insignificant effect of sonication on morphology of the nanofibers. Our research results demonstrate ultrasonic dyeing as a better dyeing technique for Nylon 6 nanofibers with higher color yield and substantially reduced dyeing time.     

Using of sonochemically prepared SbSI for electrospun nanofibers

A novel polymeric, polyacrylonitrile (PAN) nanofibers containing ferroelectric and semiconducting antimony sulfoiodide (SbSI) have been made by electrospinning. SbSI nanowires, used as the filler, have been prepared sonochemically from antimony sulphide (Sb₂S₃) and antimony tri-iodide (SbI₃) for the first time. Nanocrystalline SbSI has been fabricated in ethanol under ultrasonic irradiation (20 kHz, 565 W/cm²) at 323 K within 2 h. The products have been characterized by using techniques such as powder X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, high-resolution transmission electron microscopy, selected area electron diffraction and optical diffuse reflection as well as transmission spectroscopy. The good quality of the nanocrystals and their dispersion in the nanofiber’s volume is important because this material is attractive for nanogenerators due to its ferroelectric and piezoelectric properties. The amplitude of the voltage pulse, generated under shock pressure of 3.0 MPa, has reached 180 V in the prototype PAN/SbSI piezoelectric nanogenerator. The peak output voltage of about 0.2 V was measured in bending/releasing conditions with the deformation frequency of 1 Hz.     

Fabrication of titanium dioxide nanofibers containing hydroxyapatite nanoparticles

In the present study, we introduce titanium dioxide (TiO₂) nanofibers that contain hydroxyapatite (HAp) nanoparticles (NPs) as a result of an electrospinning process. A simple method that does not depend on additional foreign chemicals has been employed to synthesize HAp NPs through calcination of bovine bones. Typically, a colloidal gel consisting of titanium isopropoxide/HAp was prepared to produce nanofibers embedded with solid NPs by electrospinning process. The SEM results confirmed well oriented nanofibers and good dispersion of HAp NPs over the nanofibers. XRD results demonstrated well crystalline feature of both TiO₂ and HAp. Physiochemical aspects of prepared nanofibers were characterized for TEM and TEM-EDS which confirmed nanofibers were well oriented and had good dispersion of HAp NPs. Accordingly, these results strongly recommend the use of obtained nanofiber mats as a future candidate for hard tissue engineering applications.     

Electrospinning of complex oxide nanofibers

Electrospinning is a versatile process for drawing fibers of diverse materials including polymers, ceramics, and composites. We demonstrate here its application in the synthesis of complex ceramic oxide materials. The phase formation and morphology of BaTiO₃ nanofibers synthesized via electrospinning is investigated as a function of heat treatment conditions. Fully crystallized BaTiO₃ nanofibers with the perovskite structure are obtained after annealing at 750 °C and show an average grain size of about 30 nm. Tetragonal crystal structure of the fibers is indicated by XRD peak splitting (calculated c/a ratio=1.007), and confirmed by Raman spectroscopy. Furthermore, the advancement in heat treatment of the electrospun fibers yields single crystalline BaTiO₃ nanofibers with 50 nm in diameter and lengths up to 1 μm.     

Fabrication and characterization of electrospun orthorhombic InVO4 nanofibers

The novel orthorhombic InVO₄ nanofibers have been successfully synthesized by annealing electrospun precursor fibers. Citric acid was used as a ligand for it could react with metal salts to get a transparent homogeneous precursor solution and homogeneous precursor sol for electrospining. Polyvinyl pyrrolidone (PVP, K-30) was used as a binder and a structure guide reagent because it was one kind of water-soluble polymers. It is easy to gain one-dimensional materials while the viscosity of the citrate/PVP sol was suitable. The structure, morphology and photocatalytic properties of the nanofibers were characterized by X-ray diffraction (XRD), thermogravimetry analysis (TGA), scanning electron microscopy (SEM) analysis, UV-vis spectrophotometer and fluorescence spectrophotometer. The nanofibers calcined at 700 °C were orthorhombic InVO₄ with a width in the range of 30-100 nm and length in micron-grade. This one-dimensional pure orthorhombic InVO₄ had the higher photocatalytic activity under visible light irradiation. The photo-degradation rate of nitrobenzene aqueous solution under visible light reached 69% after 6 h. It is obvious that the orthorhombic InVO₄ nanofibers have a potential application in wastewater-treatment.     

A mathematical model of external electrostatic field of a special collector for electrospinning of nanofibers

This article focuses on the analysis of electrostatic field generated by a special collector consisting of two parallel cylindrical conductors used for electrospinning. Computed values of critical electrical potential obtained by an analytical model are compared with measurements. Here we show that the gap distance between the special collector and a spinning electrode, i.e., a syringe needle, has not substantial effect on the critical potential if the special collector distance from the syringe needle is higher than the gap distance between cylindrical conductors. The presented model is a good analytical approximation of electric field created by the used special collector.     

Modification of surface properties of electrospun polyamide nanofibers by means of a perfluorinated acridine

Polyamide 6 (PA6) nanofibers were prepared from formic acid solutions by using electrospinning technique. The fibers were smooth, defects free and with diameters smaller than 200 nm. Small amounts of a perfluorinated acridine were added as dopant to the feed solution to modify the wettability of the fibers. The effect of doping on the contact angle values is well apparent. The contact angle values go from 50° of pure PA6 to 120° when 6% of acridine is added. A comparison between fibers and films of pure and doped polyamide 6 was carried out in order to determine the effect of morphology on wettability. Thermal annealing near the T_g of the polymer promoted the segregation of the molecules to the surface, reaching contact angles of 131° with smaller amounts (4%) of acridine. The surface segregation was also promoted by time aging.     

Effects of ultrasonic-assisted pH shift treatment on physicochemical properties of electrospinning nanofibers made from rapeseed protein isolates

Electrospinning nanofibers (NFs) made from natural proteins have drawn increasing attention recently. Rapeseed meal is a by-product that rich in protein but not fully utilized due to poor properties. Therefore, modification of rapeseed protein isolates (RPI) is necessary to expand applications. In this study, pH shift alone or ultrasonic-assisted pH shift treatment was adopted, the solubility of RPI, along with the conductivity and viscosity of the electrospinning solution were detected. Moreover, the microstructure and functional characteristics of the electrospinning NFs, as well as the antibacterial activity of clove essential oil loaded-NFs were investigated. The tested parameters were remarkably improved after different treatments compared with the control, and synergistic effects were observed, especially under alkaline conditions. Hence, pH_12.5 + US showed the maximum value of solubility, conductivity, and viscosity, which was more than 7-fold, 3-fold, and almost 1-fold higher than the control respectively. Additionally, SEM and AFM images showed a finer and smoother surface of NFs after treatments, and the finest diameter of 216.7 nm was obtained after pH_12.5 + US treatment in comparison with 450.0 nm in control. FTIR spectroscopy of NFs demonstrated spatial structure changes of RPI, and improved thermal stability and mechanical strength of NFs were achieved after different treatments. Furthermore, an inhibition zone with a diameter of 22.8 mm was observed from the composite NFs. This study indicated the effectiveness of ultrasonic-assisted pH shift treatment on the physicochemical properties improvement and functional enhancement of NFs made from RPI, as well as the potential antibacterial application of the composite NFs in the future.     

Synthesis of praseodymium oxide nanofiber by electrospinning

Well-defined and uniform Pr₆O₁₁ nanofibers were synthesized by electrospinning of an aqueous sol-gel consisting of praseodymium nitrate hexa-hydrate and polyvinyl acetate. The synthesized Pr₆O₁₁ nanofibers mat was dried at 80 °C for 24 h under vacuum and finally annealed at 600 °C for 2 h in static air furnace. From crystalline properties, the synthesized Pr₆O₁₁ nanofibers XRD analysis revealed the typical cubic structure. The morphological observation showed that the synthesized Pr₆O₁₁ nanofibers composed of fibers length in several 100 nm and diameter of ∼20 nm. Similarly, transmission electron microscope (TEM) measurement revealed the good crystalline nature of the synthesized Pr₆O₁₁ nanofibers with the average diameter of ∼20 nm. Photoluminescence (PL) demonstrated a strong green-blue emission peak at 521 nm, suggesting that the Pr₆O₁₁ nanofiber exhibited good crystal quality with very less structural defects.     

Electron energy-loss spectroscopy of V2O5 nanofibers synthesized by electro-spinning

The dielectric properties of V₂O₅ nanofibers, synthesized by the electrospinning method, are studied by analyzing the low-loss region of the electron energy loss spectroscopy (EELS) in a transmission electron microscope. A comparison of experimental EELS spectra and ab initio density-functional theory calculations (WIEN2k code) within the Generalized Gradient Approximation (GGA) is presented, having found an excellent agreement between them. Although the experimental EELS has been acquired for the nanoparticles composing the fibers, and numerical calculations were carried out for bulk material, agreement between experimental and calculated results shows that no difference exists between the electronic structure in calculated bulk material and the nanoparticles. Furthermore, our results from EELS confirm that we accomplished the expected crystalline phase. The origins of interband transitions are identified in the electronic band structure by calculating the partial imaginary part of the dielectric function and the partial density of states.     

Preparation and photoluminescence properties of electrospun nanofibers of C60/PVK

Ultrafine fullerene (C60)/poly(N-vinylcarbazole) (PVK) composite fibers with 1 μm diameter were prepared by electrospinning C60/PVK blend solutions in solvent mixtures of N,N-dimethylformamide (DMF)/toluene. The UV absorption spectra of nanofibers have a similar behavior as observed in the thin films for the same doping condition. It is interesting to observe that the PVK nanofibers have a very strong blue-violet luminescence, while ‘bright spots’ due to C60 can be observed on the C60/PVK fibers under UV irradiation in a fluorescence optical microscope. Compared to the emission spectra of PVK thin films, the photoluminescence of the PVK nanofibers shows a new emission peak at 437 nm. Efficient energy transfer was observed in C60/PVK thin films, as well as in blend nanofibers.     

Ultrasonic dyeing of cellulose nanofibers

Textile dyeing assisted by ultrasonic energy has attained a greater interest in recent years. We report ultrasonic dyeing of nanofibers for the very first time. We chose cellulose nanofibers and dyed with two reactive dyes, CI reactive black 5 and CI reactive red 195. The cellulose nanofibers were prepared by electrospinning of cellulose acetate (CA) followed by deacetylation. The FTIR results confirmed complete conversion of CA into cellulose nanofibers. Dyeing parameters optimized were dyeing temperature, dyeing time and dye concentrations for each class of the dye used. Results revealed that the ultrasonic dyeing produced higher color yield (K/S values) than the conventional dyeing. The color fastness test results depicted good dye fixation. SEM analysis evidenced that ultrasonic energy during dyeing do not affect surface morphology of nanofibers. The results conclude successful dyeing of cellulose nanofibers using ultrasonic energy with better color yield and color fastness results than conventional dyeing.     

Electrospinning of non-woven poly(styrene-co-acrylonitrile) nanofibrous webs for corrosive chemical filtration: Process evaluation and optimization by Taguchi and multiple regression analyses

Nano-fibrous ultra-filtration membranes of poly(styrene-co-acrylonitrile) were produced from n-butanone solution by electrospinning. Effects of governing parameters on morphology and variation in diameter of the electrospun fibers were experimentally investigated by orthogonal experimental design. The process parameters were selected by Taguchi's method. Multiple regression analysis was used to obtain a quantitative relationship between selected electrospinning parameters and average fiber diameter and ANOVA was used to identify the statistically significant parameters and set the optimal level for each parameter. Confirmation experiment revealed a good agreement between the predicted values of the response obtained from optimum level parameters and the observed experimental values.     

Preparation of NiZn-ferrite nanofibers by electrospinning for DNA separation

We present the synthesis, magnetic and UV spectrometry of NiZn-ferrite nanofiber. The single phase of spinel ferrite was obtained at 600 °C. The NiZn-ferrite fibers fabricated by an electrospinning process were formed as a polygonal grain growth with firing temperature in fiber matrix. It appeared that the saturation magnetization (M_S) of NiZn-ferrite nanofiber was dependent on Ni/Zn molar ratio which is similar to that of the inverse spinel ferrites. The NiZn-ferrite fibers showed good DNA adsorption efficiency that can be modified and utilized for DNA separation with magnetic nanofiber as a novel material in clinical applications.     

一种尼龙老化评价的新方法

作为一种广泛使用的工程塑料,尼龙的老化备受关注。当作为电力系统芯片的封装材料时,尼龙在自然环境下的老化有可能会导致封装失效,从而影响芯片使用的可靠性,严重时甚至导致芯片的失效,给电力行业带来巨大损失。常规的自然老化和人工加速老化评价周期非常漫长,不同因素对尼龙老化的影响机理十分复杂,且这种影响难以研究,使得评价尼龙的老化稳定性成为一大难题。采用自主开发的原位老化评价系统,对尼龙6（PA6）和尼龙66（PA66）的老化稳定性及湿度对老化的影响进行了研究。该系统可以实现光照/温度/湿度/氧气等环境因素的加载,通过高灵敏度地测定材料在综合环境因素作用下产生的气相降解产物来评价材料的老化稳定性,评价时间缩短到几小时。实验表明,PA6和PA66的气相降解产物以H₂O和CO₂为主,由于H₂O在气相中的浓度不稳定,因此以CO₂的产生量作为老化评价指标。通过对不同自然老化时间PA6和PA66的原位老化评价,并与其ATR-FTIR红外光谱图进行对照,证明了原位老化评价方法能够较好地反映尼龙的老化程度,自然老化时间越长,PA6和PA66的稳定性越低,CO₂的产生量越大。进一步,采用该方法研究了湿度对PA6和PA66老化反应的影响,证明增大湿度对尼龙老化存在促进作用,而且升高温度会进一步促进湿度对老化的促进作用。研究表明,原位老化评价方法是一种快速评价尼龙老化稳定性及环境因素影响的有力手段。     

Fabrication of titanium dioxide nanofibers via anodic oxidation

In this work, titanium dioxide (TiO₂) nanofibers were obtained from anodic oxidation process. A piece of titanium sheet was anodized in 1.0 M sodium chloride (NaCl) solution, at 30 V. The as-anodized sample was calcinated at 400 °C for one hour. Subsequently the sample was characterized using field-emission scanning electron microscopy (FE-SEM), high resolution X-ray diffraction (HR-XRD), and Raman spectroscopy. Interestingly, results showed rutile phase dominates over anatase phase, which is rarely reported. In addition, the possible chemical reactions that lead to the formation of nanofibers were proposed. It was found that the nanofibers having an average length of 3 μm, also diameter of 83 nm.     

Recyclable aligned carbon nanotube-sheet-based particulate air filter with high filtration efficiency and low pressure drop

There is an increasing demand for particulate matter filters to primarily block viruses and fine particulate matter floating in the air from entering the human body. The most commonly used microfiber-based filter has a technical flaw in which the filtration efficiency cannot be maximized as there is a trade-off in terms of performance; the pressure drop increases when the filtration efficiency increases. Here, we report the development of a recyclable macroscopic carbon nanotube (CNT)-based filter consisting of unidirectionally arranged multi-walled carbon nanotube sheets. Owing to the uniform arrangement of the 10–20 nm carbon nanotubes, uniform nanopores are formed. As a result, the CNT-sheet-based particulate matter filter exhibited low pressure drop characteristics, even at a high filtration efficiency. In addition, it was confirmed that the collected particulate matter could rapidly be removed through heat generated by applying a voltage to the conductive CNT sheet.     

Surface functionalization, morphology and thermal properties of polyamide6/O-MMT composite nanofibers by Fe2O3 sputter coating

In the present work, the pure polyamide6 (PA6) nanofiber and PA6/organically modified montmorillonite (O-MMT) composite nanofiber were firstly prepared by a facile compounding process with electrospinning, and then coated by nanosize Fe₂O₃ using magnetron sputter technique. The effects of Fe₂O₃ sputter coating on structures, surface morphology and thermal stability were characterized by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), atomic force microscope (AFM) and thermogravimetric analyses (TGA), respectively. The SEM images showed that the diameters of composite nanofiber were decreased with the loadings of O-MMT and the nanosize Fe₂O₃ is well coated on the surface of the homogeneous and cylindrical nanofibers. The XPS spectra reflected the chemical features of the deposited nanostructures. The EDX confirmed the presence of the O-MMT and Fe₂O₃ in the fibers. The AFM observation revealed that there was a remarkable difference in the surface morphology of composite nanofiber before and after sputter coating. The TGA analysis indicated the barrier effects of silicate clay layers and catalysis effects of Fe₂O₃ improved thermal stability properties of the composite nanofiber.     

Instability controlled synthesis of tin oxide nanofibers and their gas sensing properties

Instability dependent electrospinning process has been controlled to obtain tin oxide nanofibers with morphological variation. The effect of spinning parameters such as viscosity, conductivity, flow rate, distance and applied voltage on growth rate of different instabilities was simulated and different deposition conditions were defined from the simulation results. The structural morphology was analyzed using X-Ray Diffraction (XRD) and Scanning Electron microscope (SEM). The sensing behavior of different structures was investigated. The branched structure obtained due to axisymmetric instabilities exhibited best sensing performance owing to high surface to volume ratio.