Electrochemical properties and morphology of composite fibers based on silicon and carbon obtained by electroforming

Pyrolized Si/C composite fibers and films were studied in the processes of lithium intercalation-extraction during the operation of rechargeable lithium-ion batteries and supercapacitors. It was found that their electrochemical characteristics differ from those of pure silicon and pure carbon. Analysis of these parameters under charge-discharge conditions allowed us to determine the optimum composition of precursors: FM-1 and TEOS mixtures used as silicon-containing components. The optimum modes and temperatures of fiber pyrolysis were found to have a Si/C ratio of 3/2 in the pyrolyzed fibers and an oxygen content not much greater than 20 at %. The prospects for applying fibers in the form of film electrodes (the best stability in cycling) and adhesives with developed structural networks are shown.     

Poly(ethylene terephthalate)/carbon black composite fibers prepared by electrospinning

Poly(ethylene terephthalate)(PET)/carbon black(CB) composite fibers with improved mechanical properties in tensile modulus and tensile strength are prepared by eletrospinning. Stable dispersions suitable for electrospinning are obtained by dispersing melt pre-compounded PET/CB composites in hexafluoroisopropanol. The fiber morphology and CB dispersion are investigated by FESEM and TEM. The addition of CB has no obvious effect on fiber diameter, and the average fiber diameters for all the samples are around 2-3 μm. CB in the fibers is in the form of submicron-sized clusters. The thermal properties of the PET/CB composite fibers are evaluated by DSC, showing almost unchanged melting temperature and crystallinity. Uniaxial tensile tests are used to measure the mechanical properties of the PET/CB composite fiber mats. The fiber mats containing 1 wt%-8.5 wt% CB have significantly improved tensile modulus compared to neat PET fiber mat, showing reinforcing effect of CB. The electrical conductivity of the fiber mats has also been tested.     

Emulsion electrospinning: composite fibers from drop breakup during electrospinning

We evaluate the feasibility of electrospinning oil‐in‐water type emulsions. The emulsions had an aqueous solution of polyethylene oxide (PEO) as the continuous phase, and either mineral oil or a polystyrene (PS) in toluene solution as the drop phase. The Taylor cones and electrified liquid jets were stable even when the emulsion drops were as large as a few‐ten microns in diameter. The resulting electrospun PEO fibers incorporated the dispersed phase of the emulsion in the form of drops (in case of mineral oil), or in the form of solid particles (in case of PS). Mineral oil drops appear to be completely encapsulated in the PEO fibers, whereas the PS particles are either incompletely encapsulated, or covered by only a very thin layer of PEO. Calculations show that in both cases, the initially large emulsion drops are broken during the electrospinning process. Copyright © 2007 John Wiley & Sons, Ltd.     

静电纺羟基磷灰石/明胶微纳复合纤维

本文从仿生角度出发,模拟细胞外基质独特结构,采用静电纺丝法成功制备出HA均匀分布的HA/Gelatin复合纤维。根据影响静电纺丝的主要因素,分别考察了聚合物浓度、无机物含量、溶剂浓度、电纺电压等因素对纤维形貌和结构的影响。研究结果表明:聚合物浓度是制备复合纤维的首要影响因素,影响复合纤维的直径;无机物的添加使聚合物中的氢键减少,降低了电纺液的粘度,影响复合纤维中珠状物的形成;制备分布均匀的电纺纤维,溶剂起很大的作用,影响纤维的粘联;电纺电压增大使电场力过大,聚合物被强力拉伸,单根纤维出现卷曲。     

Photoluminescence properties of Re(I) complex doped composite submicron fibers prepared by electrospinning

In this paper, a Re(I) complex of Re(CO)3(Bphen)Br, where Bphen=4,7-diphenyl-1,10-phenanthroline is synthesized, and doped into poly(vinylpyrrolidone) submicron fibers through electrospinning technique. Their morphology, absorption, and emission spectra are investigated in detail. The composite fibers exhibit smooth and uniform morphology on the substrate, with an average diameter of ～800 nm. A bright yellow emission peaking at 543 nm is observed from these composite fibers, and this emission is attributed to the triplet emissive state of Re(CO)3(Bphen)Br. When doped into poly(vinylpyrrolidone) matrix, the emission shows a blue-shift tendency compared with that of bulk sample, correspondingly, the photostability is also largely improved. Detailed analysis suggests that Re(CO)3(Bphen)Br occupies a homogeneous site within poly(vinylpyrrolidone) matrix, and the matrix provides a rigid environment for Re(CO)3(Bphen)Br.     

Magnetic Fe doped ZnO nanofibers obtained by electrospinning

We demonstrate structural and room temperature magnetic properties of Fe doped ZnO nanofibers (NFs) obtained by electrospinning followed by calcination. The observed NFs, formed from crystalographically oriented, approximately 4.5?nm particles conglomerates, were approximately 200?nm in diameter. The reported synthesis of room temperature ferromagnetic Fe doped ZnO NFs is both facile and economical, and is therefore suggested as a generic method of fabricating biocompatible magnetic materials. The major substrates selected for the NFs synthesis (Zn, Fe) comprised of relatively low toxicity materials. Incorporating 10% Fe into ZnO does not modify the wurtzite crystal structure of the host material. No evidence of impurity phase was detected by either X-ray or electron diffraction. Magnetometry studies and Magnetic Force Microscopy imaging reveal a local ferromagnetic order that persists up to room temperature. We suggest that the observed phenomenon is either due to a mechanism mediated by presence of oxygen vacancies and/or is related to iron-rich precipitates.     

Nanoporous structured submicrometer carbon fibers prepared via solution electrospinning of polymer blends

A facile means for obtaining submicrometer carbon fibers with a nanoporous structure is presented. A mixture of polyacrylonitrile (PAN) and a copolymer of acrylonitrile and methyl methacrylate (poly(AN-co-MMA)) in dimethylformamide was electrospun into submicrometer fibers with a microphase-separated structure. During the followed oxidation process, the copolymer domains were pyrolyzed, resulting in a nanoporous structure that was preserved after carbonization. The microphase-separated structure of the PAN/poly(AN-co-MMA) electrospun fibers, the morphology, and porous structure of both the oxidized and the carbonized fibers were observed with scanning electron microscopy and transmission electron microscopy. The carbon fibers have diameters ranging from several hundred nanometers to about 1 microm. The nanopores or nanoslits throughout the fiber surface and interior with diameters of several tens of nanometers are interconnected and oriented along the longitudinal axis of the fibers. This unique nanoporous morphology similar to the microphase-separated structure in the PAN/poly(AN-co-MMA) fibers is attributed to the rapid phase separation, solidification, as well as the stretching of the fibers during electrospinning. The pore volume and pore size distribution of the carbonized fibers were investigated by nitrogen adsorption and desorption.     

Microstructure and composition of silicon carbide films deposited on carbon fibers by chemical vapor deposition

The microstructure and the composition of CVD silicon carbide films used as fiber coatings in composite materials were investigated by photoelectron spectroscopy and transmission electron microscopy. The films with a uniform thickness of 50 nm consisted of small SiC grains with a mean diameter of 15 nm and showed a stripe contrast in bright field images. Large grains with diameters in the dimension of the film thickness were used for imaging the lattice structure by high-resolution electron microscopy. The results are discussed as a polytype of cubic lamellae of a few nanometers and intermediate random stacking sequences of hexagonal structure. Received: 30 July 1997 / Accepted: 16 December 1997     

Humidity sensing properties of ZnO-based fibers by electrospinning

Zinc oxide (ZnO) based fibers with a diameter of 80-100 nm were prepared by electrospinning. Polyvinyl alcohol (PVA) and zinc acetate dihydrate were dissolved in water and the polymer/salt solution was electrospun at 2.5 kV cm⁻¹. The resulting electrospun fibers were subjected to calcination at 500 °C for 2 h to obtain ZnO-based fibers. Humidity sensing properties of the fiber mats were investigated by quartz crystal microbalance (QCM) method and electrical measurements. The adsorption kinetics under constant relative humidity (RH) between 10% and 90% were explained using Langmuir adsorption model. Results of the measurements showed that ZnO-based fibers were found to be promising candidate for humidity sensing applications at room temperature.     

Thermoplastic polyurethane/silica nanocomposite fibers by electrospinning

Thermoplastic polyurethane/silica nanocomposite fibers with good mechanical properties were prepared by electrospinning, using colloidal silica as the source of silica and dimethyl formamide as the solvent. The fiber morphology was examined by field emission scanning electron microscopy. The average fiber diameter is about 0.8 μm with 0–10 wt % silica, and silica nanoparticles were observed on all fiber surfaces. X‐ray photoelectron spectroscopy analysis of Si in combination with transmission electron microscopy observation suggest that silica nanoparticles have a fairly uniform distribution in the fibers rather than enriching on the fiber surfaces. Tensile tests show that the incorporation of silica nanoparticles can bring about a significant reinforcing effect without decreasing the ductility. The reinforcing effect is further confirmed by dynamic mechanical analysis. The thermoplastic polyurethane/silica composite fiber mats can adsorb gold nanoparticles after further treatment with 3‐aminopropyltriethoxysilane, demonstrating that the composite fibers could be used as functional fibers by using the properties of silica nanoparticles. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Synthesis of polymer-stabilized magnetic nanoparticles and fabrication of nanocomposite fibers thereof using electrospinning

Polymer-stabilized magnetic nanoparticles were obtained using two biocompatible polyelectrolytes: N-carboxyethylchitosan (CECh) and poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS). The size of the particles (mean diameter 10 or 30 nm, respectively) and the stability of the dispersions could be effectively controlled depending on the polyelectrolyte nature. The presence of polyelectrolyte shell was proved by transmission electron microscopy (TEM) studies and confirmed by thermogravimetric analyses. Depending on the polyelectrolyte nature the magnetic nanoparticles existed in different magnetic states - superparamagnetic or intermediate state between superparamagnetic and ferrimagnetic one, as evidenced by the measurements of the magnetization and Mössbauer analyses. Fabrication of nanocomposite magnetic fibers with mean diameter in the range 100-500 nm was achieved using electrospinning of the system CECh/ferrofluid/non-ionogenic polymer.     

Liquid crystal fibers produced by using electrospinning technique

This paper investigates the electrospinning process of liquid crystalline polysiloxane with cholesterol as side chain (LCPC) and the influence on the morphology of the formed fibers by mixing LCPC solution with small-molecule liquid crystal, triethylamine, and poly(ethylene oxide)(PEO). The mechanical properties of single fibers were characterized by a novel approach. The results indicate that, under appropriate conditions, fine liquid crystal fibers can be obtained and the preferable mechanical properties can be achieved, especially after annealing. WXRD was used to investigate the orientation of polymer molecules in the formed fibers, suggesting that strong interaction exists between LCPC and PEO molecule in the resulting composite fibers, and polymer molecular tends to arrange regularly during electrospinning processing. This research work provides a new and facile method of using electrospinning to prepare liquid crystal fibers, which would be useful for designing the related high-performance materials.     

Structural analysis of hexagonal and solid carbon fibers composite

This paper is showed to explore the relationship between materials and their properties. The elements are defined by their features. It identifies the composition of the pyrolysis products obtained through pyrolysis in the structure of different designs. Two design specimens of carbon fibers structure with different directional load were fabricated, solid carbon fibers and hexagonal carbon fibers structure. The deformation behavior is well-known and has been analyzed. 3D finite element (FE) models were used to investigate both structures. There was some impact on the specimens used, and the behavior of the strain and stress line was captured. These results show that the positive Poisson's ratio of both composites structures obtained when appropriate yarn structure in the 3D material system is adopted in both designs. The main purpose of the experiment was to define and test the structure's use in industries that require carbon fiber material that has excessively excellent mechanical and thermal properties. DMA tests have been conducted, and both the thermal and mechanical properties investigated. The compositions can improve carbon vs the adhesion of the polymer matrix for carbon fibers structure, which allows the use of such fibers for the reinforcement of plastics without extra processing.     

Ultrafine porous carbon fibers for SO2 adsorption via electrospinning of polyacrylonitrile solution

This work describes the potential capability of ultrafine porous carbon fibers (UPCF) prepared via electrospinning in the removal of SO2 from a mixture gas stream. A series of conventional PCF (CPCF) and ultrafine PCF (UPCF) were produced under the identical conditions and UPCF was also modified. Compared to the CPCF, experimental results showed that the UPCF had a better adsorption capacity for SO2 due to its higher surface area and microporous volume. After the modification of the UPCF, adsorption capacities of UPCF for SO2 were improved further via increasing the N-containing amount of UPCF and substrate which was followed by few changes in its specific surface area. The optimum concentration of modified reagent is 10%. From the results of the fatigue test, it has been found that both the UPCF and the modified UPCF showed a good durability.     

基于镍/氮掺杂碳复合材料的双功能电催化剂合成及电化学性能研究

通过高温热解氢氧化镍/聚苯胺前驱体,制备了镍/氮掺杂碳复合材料,并作为双功能电催化剂应用于可充电锌-空气电池.利用X射线衍射、透射电镜、拉曼光谱、X射线光电子能谱等对样品的形貌与结构进行表征,并利用电化学工作站与旋转圆盘电极对样品的氧还原与氧析出电催化性能进行测试.线性扫描伏安曲线的结果表明,在0.1 M KOH水溶液...     

Interaction of solid and polymeric lithium electrolytes with composites based on carbon fibers and silicon nanoclusters: Quantum-chemical modeling

In the framework of the search for promising electrodes and membranes for lithium-ion batteries, quantum-chemical modeling of the contact area of the solid (Li₁₀GeP₂S₁₂) and polymeric LiNafion · nDMSO-based electrolytes with an anode as carbon fibers coated with silicon nanoclusters (Si _n C _m ) has been performed by the density functional theory method with inclusion of gradient correction and periodic conditions (PBE/PAW). It has been found that the polymeric electrolytes form a better contact with the electrode surface than the solid electrolytes. The barriers to lithium transport in the polymeric LiNafion · nDMSO-based electrolyte have been estimated at 0.3 eV, and those to Li migration from the electrolyte into the electrode have been estimated at 0.4 eV.     

Formation of carbon nanotubes from a silicon carbide/carbon composite

The reaction of a SiC/C composite powder in an arcing plasma forms carbon nanotubes in good yield. Besides carbon nanotubes, a Si/C composite composed of β SiC covered with a shell of graphite is formed. The graphitic carbon surface layers of the carbon shell of this composite reacts further to form carbon nanotubes when heated to 600 °C. This process seems highly effective since only a small overall low weight loss, indicative for a complete carbon shell oxidation is observed by thermal analysis. The formation of the carbon nanotubes from SiC is unlikely since no SiO₂ has been found when heating the SiC/C core shell composite to its reaction temperature of 600 °C under O₂. The CNTs formed are of good quality with 3 to 6 concentric walls and high aspect ratio. Occasionally even single walled carbon naotubes have been observed.     

Highly porous fibers by electrospinning into a cryogenic liquid

Highly porous fibers of various polymers were created by electrospinning with a modified collector. A bath of liquid nitrogen was used to freeze the fibers, inducing a phase separation between the polymer and the solvent. When the solvent was removed in vacuo, highly porous fibers were obtained. Poly(styrene), poly(acrylonitrile), poly(vinylidene fluoride), and poly(epsilon-caprolactone) were all electrospun into porous fibers using this simple method. These porous fibers have a range of potential applications in encapsulation, controlled release, superhydrophobic coating, and lightweight reinforcement.     

Facile fabrication of cerium niobate nano-crystalline fibers by electrospinning technology

In this study, one-dimensional (1D) cerium niobate nano-crystalline fibers were first prepared by a facile sol–gel and electrospinning process, followed by heat treatment. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TG), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HR-TEM) were used to characterize the samples. It can be seen from SEM images that the as-prepared xerogel samples and those annealed at 900 °C presented uniform fibrous morphology, with the diameter of 100–300 nm and length of several centimeters. The XRD and FT-IR results showed that cerium niobate samples had well-crystallized phase of CeNbO_4.25 with the crystallite size of about 28.6 nm at a heat treatment temperature of 900 °C, which can also be validated with the TEM image. The AC impedance of annealed disks made from the CeNbO_4.25 nano-crystalline fibers has been probed.