Structure and properties of electrospun PLLA single nanofibres

An electrospinning method was used to spin semi-crystalline poly(L-lactide) (PLLA) nanofibres. Processing parameter effects on the internal molecular structure of electrospun PLLA fibres were investigated by x-ray diffraction (XRD) and differential scanning calorimetry (DSC). Take-up velocity was found as a dominant parameter to induce a highly ordered molecular structure in the electrospun PLLA fibres compared to solution conductivity and polymer concentration, although these two parameters played an important role in controlling the fibre diameter. A collecting method of a single nanofibre by an electrospinning process was developed for the tensile tests to investigate structure-property relationships of the polymer nanofibres. The tensile test results indicated that higher take-up velocity caused higher tensile modulus and strength due to the ordered structure developed through the process.     

Process optimization and alignment of PVA/FeCl<Subscript>3</Subscript> nano composite fibres by electrospinning

This paper describes the result of investigation on PVA/FeCl₃ nano composites fibres prepared by the electrospinning process. The effects of instrument parameters including solution concentration, electric voltage, tip–target distance, flow rate parameters on the morphology of electrospun PVA/FeCl₃ fibres were evaluated. The produced composite fibres were characterized by scanning electron microscopy (SEM) and transmission electron microscope (TEM). Fibre mats of (PVA)/FeCl₃ composite thin fibres, in the diameter of 500–1100 nm, were prepared by electrospinning. These microscopies show detailed morphologies of PVA/FeCl₃ nano composites incorporating magnetic power. These novel composite fibres could be used in biomedical, catalyst and magnetic purpose.     

Electrospinning of polymer nanofibres from multiple jets on a porous tubular surface

A novel method for the electrospinning of multiple polymer jets into nanofibres is presented. In this work, 20?wt% nylon 6 solution was electrified and pushed by air pressure through the walls of a porous polyethylene tube. Multiple jets formed on the porous surface and electrospun into nanoscale fibres. The length weighted fibre diameters have a similar mean diameter to those from a single jet but broader in distribution. The mass production rate from the porous tube is 250 times greater than from a typical single jet.     

Nanofibre fabrication in a temperature and humidity controlled environment for improved fibre consistency

Fabricating nanofibres with reproducible characteristics is an important demand in the membrane industry in order to establish commercial viability. In this study, the effect of controlled atmospheric conditions on electrospun cellulose acetate (CA) nanofibres was evaluated for temperatures ranging 17.5–32.5 °C and relative humidity ranging 20–70%. CA solution (0.2 g/mL) in a solvent mixture of acetone/dimethylformamide/ethanol (2:2:1) was electrospun into nonwoven fibre mesh with the fibre diameter ranging from 150 nm to 1 μm. The resulting nanofibres were analysed by differential scanning calorimetry, showing a correlation of reducing melt enthalpy with increasing atmospheric temperature. The opposite was seen with increasing atmospheric humidity, which conferred increasing melt enthalpy. Analysis of scanning electron microscopy images provided a correlation of reducing average fibre diameter with increasing atmospheric temperature and increasing fibre diameter with increasing atmospheric humidity. These results correlate with the melt enthalpy results, suggesting that finer CA nanofibres infer a lower melt enthalpy. Together these studies provide strong evidence that the controlled atmospheric conditions affect the fibre diameter of the resulting electrospun nanofibres. A salient observation in this study was that increased humidity reduced the effect of fibre beading yielding a more consistent and therefore better quality of fibre. This has apparent implications for the reproducibility of nanofibre production and offers a new method of controlling fibre morphology. This study has highlighted the requirement to control atmospheric conditions during the electrospinning process to fabricate reproducible fibre mats.     

Fabrication of a submicron-channel organic field-effect transistor using a controllable electrospun single fibre as a shadow mask

We demonstrate a simple and versatile method for the fabrication of a submicron channel for an organic field-effect transistor (OFET) using a single electrospun fibre as a shadow mask. A single electrospun fibre is produced by an alternative switching electrospinning method and is stretched 2.5-fold. The average diameter of the stretched fibres is 302 nm. The stretched fibre is placed on ultrathin dielectric layers of aluminium oxide and a self-assembled monolayer (SAM). During electrode deposition the fibre acts as a very small shadow mask. After removing the fibre, electrodes with very narrow gaps of around 350 nm and with high uniformity are easily obtained. We fabricate an OFET by depositing pentacene as an active layer onto the electrodes. The OFET is operable at low voltages, with a threshold voltage of - 1.1 V and a subthreshold swing of 0.27 V decade(-1), values which are one order of magnitude lower than those obtained with a channel length of 75 μm.     

Effects of the molecular format of collagen on characteristics of electrospun fibres

Electrospinning is a process that is used to create nanofibres, which have the potential to be used in many medical and industrial applications. The molecular structure of the raw material is an important factor in determining the structure and quality of the electrospun fibres. In this study, we extracted collagen from a cold water fish species, hoki (Macruronus novaezelandiae), and prepared it in several different molecular formats (native triple helical collagen, denatured whole chains, denatured atelocollagen chains and gelatin) for electrospinning. Low molecular weight gelatin and atelocollagen did not form fibres. Treatment with 1,1,1,3,3,3 hexafluoro-2-propanol or 40% acetic acid denatured collagen molecules into intact α-chains prior to the electrospinning process. When using intact denatured collagen chains, 10% acetic acid was an effective aqueous-based solvent for producing uniform fibres. This information will be useful for the development of a non-toxic, aqueous solvent system suitable for industrial scale-up of the electrospinning process. Our results show that this low imino marine collagen is a suitable biopolymer for producing electrospun fibres.     

Solvent control of cellulose acetate nanofibre felt structure produced by electrospinning

Non-woven structures of cellulose acetate (CA) fibres of 90 nm–5 μm in diameter (spinning parameters 90 nm beaded fibres: 12% CA in EtOH-DMSO 1/1, 22 kV, 30 cm, 0.5 mL/h; maximum 5 μm diameter fused fibres spun with 14% CA in Ac-BenzOH 2/1, 22 kV, 24 cm, 13 mL/h) were produced by electrospinning. On the basis of Hansen solubility theory, composition of binary solvent mixtures (ketones—acetone, methyl ethyl ketone (MEK), and alcohols—benzyl alcohol, propylene glycol and dimethylsulphoxide) was optimized with respect to control of fibre felt morphology. Fibre networks of high packing density were obtained with binary low-volatile alcohols/MEK solvent mixtures, a decreased spinning distance and an increased feed rate. Substituting MEK by acetone in the solvent mixture resulted in the formation of nanofibre felt with a low degree of fibre cross-links. Thus, solvent control is a key aspect for control of electrospun fibre felt structures, which may serve as scaffolds for tissue engineering.     

Fabrication and characterization of electrospun PVDF-aliquat 336 fibre membrane for removal of cadmium from hydrochloric acid solutions

The use of polyvinylidene fluoride (PVDF) electrospun fibre membrane incorporating aliquat 336 for the removal of cadmium from hydrochloric acid solutions was investigated. Scanning electron microscopy (SEM) was used to determined fibre diameter and to observe the fibre morphology. Energy dispersive spectroscopy (EDS) analysis was carried out to follow the fate of the aliquat 336 in the fibre membrane formed via electrospinning process and to detect the presence of cadmium in fibre membrane after it has acted as an ion exchange media. The amount of cadmium removed by the fibre membranes was determined by flame atomic absorption spectroscopy. The maximum capacity of the PVDF-aliquat 336 electrospun fibre membranes was determined to be 0.46 mg/g.     

Electrospun green fibres from lignin and chitosan: a novel polycomplexation process for the production of lignin-based fibres

Novel lignin-chitosan polyelectrolyte fibres were produced through a reactive electrospinning process. Polyelectrolyte formation between the anionic lignin and cationic chitosan was controlled through the pH of the solution. Through manipulating the polyelectrolyte complex formation, fibres could be effectively produced from two biopolymers, which are normally very difficult to electrospin on their own. Though minimal amounts of the petroleum-derived polyethylene oxide were introduced into the solution to enhance the spinnability of the polyelectrolyte solution, it could be easily removed from the fibres post spinning by washing with water. Thus, pure biopolymer fibres could be produced. The optimum composition of lignin to chitosan was identified through SEM, FTIR and TGA analysis of the electrospun fibres. Fluorescence spectra of the electrospun fibres reveal the homogeneous distribution of lignin and chitosan components throughout the fibre network.     

Nafion electro-spun reinforced membranes for polymer electrolyte fuel cell

The introduction of different reinforcement materials (yarns, fibrils, etc) into the membranes has been investigated with the aim of maintaining adequate membrane properties in terms of mechanical strength, good chemical stability, low swelling at critical temperatures and a stable electrochemical performance in PEFC. An innovative technique for the development of membranes is based on polymeric films containing polymeric nanofibres obtained through electrospinning. The electrospinning of Nafion blends with polyvinylpirrolidone (PVP) and polystyrene (PS) was investigated in this work. In particular, the morphology and diameter of electrospun fibres as a function of the electrospinning parameters and solution preparation have been studied and in both cases, a critical concentration of blend solution was found. Beaded fibres were obtained above such a concentration and, below it, only fibre mats were observed. Reinforced Nafion-based membranes were realised by using the obtained spun films. Preliminary proton conductivity and fuel cell results have shown the capability of operating in a fuel cell environment with a slightly higher performance than pure Nafion but having an improved stability at high temperatures.     

Modeling and optimization of electrospun polyvinylacetate (PVAc) nanofibers by response surface methodology (RSM)

Response surface methodology (RSM), a collection of statistical and mathematical techniques, has been widely used to optimize and design operating conditions. Although this method is suitable for optimizing experimental conditions, very few attempts have been made on the electrospinning process. In this work, RSM was used to model and optimize of the electrospinning parameters for polyvinylacetate (PVAc) nanofibers. PVAc solution in acetone was electrospun under various conditions such as concentration of spinning solution and applied voltage. The experimental results indicate that concentrations of solution and applied voltage played an important role on the diameter size of PVAc nanofibers. The second order polynomial function was used to correlate the fiber diameter with the production variables. The predicted fiber diameters were in good agreement with the experimental results.     

A new recycling method for expanded polystyrene

A new recycling method was investigated in this work, in which polystyrene (PS) sub‐µm fibres were electrospun from recycled expanded polystyrene (EPS). The experimental results in this work show that fibres with diameters of around 500 nm were produced by the electrospinning method. The fibres were produced to form a non‐woven mat. Non‐woven mats of electrospun fibres have large surface areas and small pore sizes compared to commercial textiles, making them excellent materials for use in filtration applications. Copyright © 2005 John Wiley & Sons, Ltd.     

Statistical optimization of the electrospinning process for chitosan/polylactide nanofabrication using response surface methodology

In this study, chitosan/polylactide (CP) blend solutions in trifluoroacetic acid as a co-solvent with different blend ratio were electrospun. Effects of different CP ratio and process parameters on the diameter of electrospun nanofibers were experimentally investigated. The fiber morphology and the distribution of fiber diameter were investigated by scanning electron microscopy. Response surface methodology (RSM) was used to define and evaluate a quantitative relationship between electrospinning parameters, average fiber diameters and its distribution for each chitosan–polylactide ratio. Applied voltage and polymer solution extrusion rate are the process variables which control the fiber diameter at similar spinning distances (15 cm). Fiber diameter was correlated to these variables by using a second-order polynomial function. The fibers were of diameter ranging from 94 to 389 nm. The predicted fiber diameters were in good agreement with the experimental results. Contour plots were obtained to identify the processing variables suitable for producing nanofibers. It was concluded that ratio of polylactide and chitosan in the blend polymer played an important role to the diameter of fibers and standard deviation of fiber diameter. The processing factors were found statistically significant in the production of nanofibers.     

静电纺聚乳酸纳米纤维复合滤料的过滤性能研究

将聚乳酸颗粒加入到质量比为8:2的三氯甲烷与N-N-二甲基甲酰胺的混合溶剂中,室温下配置质量分数为10%的纺丝液,采用静电纺丝法制备了平均直径在620nm左右的聚乳酸纤维。以聚乳酸熔喷非织造布为基布,通过控制纺丝时间的不同得到了负载不同厚度纳米纤维层的可生物降解的复合过滤材料。通过对各试样的孔隙率、孔径及孔径分布、过滤效率的测试发现:随着纺丝时间的增加,复合材料孔隙率不断下降,孔径不断减小,纺丝3h时,孔径基本减小到原先的一半,且分布相对集中,大大地提高了普通过滤材料的过滤效率。     

Fabrication of silicon based glass fibres for optical communication

Silicon based glass fibres are fabricated by conventional fibre drawing process. First, preform fabrication is carried out by means of conventional MCVD technique by using various dopants such as SiCl₄, GeCl₄, POCl₃, and FeCl₃. The chemicals are used in such a way that step index single mode fibre can be drawn. The fibre drawing process consists of various steps such as heating the preform at elevated temperature, diameter monitor, primary and secondary coating, and ultra violet radiation curing. The fibres are then characterized for their geometrical and optical properties. The drawn fibre has diameter of core and cladding to be 8.3 μm and 124.31 μm, respectively whereas non-circularity is found to be 4.17% for core and 0.26% for cladding as seen from phase plot. Mode field diameter is found to be 8.9 μm and 9.2 μm using Peterman II and Gaussian method, respectively. The fabricated fibres showed the signal attenuation of 0.35 dB/km and 0.20 dB/km for 1310 nm and 1550 nm, respectively as measured by the optical time domain reflectometer (OTDR).     

Wafer-scale patterning of sub-40 nm diameter and high aspect ratio (>50:1) silicon pillar arrays by nanoimprint and etching

We demonstrate wide-area fabrication of sub-40?nm diameter, 1.5?μm tall, high aspect ratio silicon pillar arrays with straight sidewalls by combining nanoimprint lithography (NIL) and deep reactive ion etching (DRIE). Imprint molds were used to pre-pattern nanopillar positions precisely on a 200?nm square lattice with long range order. The conventional DRIE etching process was modified and optimized with reduced cycle times and gas flows to achieve vertical sidewalls; with such techniques the pillar sidewall roughness can be reduced below 8?nm (peak-to-peak). In some cases, sub-50?nm diameter pillars, 3?μm tall, were fabricated to achieve aspect ratios greater than 60:1.     

Preparation of CuS nanoparticles embedded in poly(vinyl alcohol) nanofibre via electrospinning

Poly(vinyl alcohol) (PVA)/CuS composite nanofibres were successfully prepared by electrospinning technique and gas-solid reaction. Scanning electron microscopic (SEM) images showed that the average diameter of PVA/CuS fibres was about 150–200 nm. Transmission electron microscopy (TEM) proved that a majority of CuS nanoparticles with an average diameter of about 15–25 nm are incorporated in the PVA fibres. X-ray diffraction (XRD) analyses and electron diffraction pattern also revealed the forming of CuS crystal structure in the PVA fibres.     

Fabrication and in vitro biomineralization of bioactive glass (BG) nanofibres

Bioactive glass nanofibres have excellent bioactivity and cell compatibility, and are regarded as a promising next-generation biomaterial in the bone-regeneration field. This paper is concentrated on the effect of electrospinning parameters on the diameter and morphology of bioactive glass nanofibres, and the process of in vitro biomineralization. In this work, sol-gel glass nanofibres with high bioactivity were prepared by electrospinning processing in the presence of poly(vinyl pyrrolidone) (PVP) and pluronic P123 (EO(20)-PO(70)-EO(20)) as chain entanglements. The influence of the polymer concentration, types of polymer and electric field strength on the fibre diameter was examined. The average diameter of these BG nanofibres could be controlled in the range from 85 to 400?nm. The addition of PVP resulted in sufficient chain entanglement and the formation of smooth BG nanofibres, and the addition of P123 led to a further decrease of the diameter with appropriate electric field strength, which held the balance between the electrostatic repulsive force and surface tension of the electrospinning solution. Furthermore, the early stage of in vitro biomineralization of the BG nanofibres in the simulated body fluid (SBF) was studied in this work. The behaviour of in vitro biomineralization of bioactive glass nanofibres was different to the conventional ones, and the structure of bioactive glasses contributed to the formation process of hydroxyapatite.     

Syndiotactic 1,2-polybutadiene fibers produced by electrospinning

Syndiotactic 1,2-polybutadiene (s-PB) is a typical thermoplastic elastomer with various applications because of its high reactivity. In the past, it is difficult to form s-PB fibers with a diameter below 10 μm because of the limitation of the conventional method such as melt spinning. Here, we report for the first time on the production of s-PB nanofibers by using a simple electrospinning method. Ultrafine s-PB fibers without beads were electrospun from s-PB solutions in dichloromethane and characterized by environmental scanning electron microscope (ESEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). At 4 wt.% concentration of s-PB, the average diameter of s-PB was about 130 nm. We found that dichloromethane was a unique suitable solvent for the electrospinning of s-PB fibers, and the structure of syndiotactic was changed through the electrospinning process.