Ultrafine fibers were spun from polyacrylonitrile (PAN)/N,N-dimethyl formamide (DMF) solution as a precursor of carbon nanofibers using a homemade electrospinning set-up. Fibers with diameter ranging from 200 nm to 1200 nm were obtained. Morphology of fibers and distribution of fiber diameter were investigated varying concentration and applied voltage by scanning electric microscopy (SEM). Average fiber diameter and distribution were determined from 100 measurements of the random fibers with an image analyzer (SemAfore 5.0, JEOL). A more systematic understanding of process parameters was obtained and a quantitative relationship between electrospinning parameters and average fiber diameter was established by response surface methodology (RSM). It was concluded that concentration of solution played an important role to the diameter of fibers and standard deviation of fiber diameter. Applied voltage had no significant impact on fiber diameter and standard deviation of fiber diameter. 相似文献
Summary: Uniform core‐sheath nanofibers are prepared by electrospinning a water‐in‐oil emulsion in which the aqueous phase consists of a poly(ethylene oxide) (PEO) solution in water and the oily phase is a chloroform solution of an amphiphilic poly(ethylene glycol)‐poly(L ‐lactic acid) (PEG‐PLA) diblock copolymer. The obtained fibers are composed of a PEO core and a PEG‐PLA sheath with a sharp boundary in between. By adjusting the emulsion composition and the emulsification parameters, the overall fiber size and the relative diameters of the core and the sheath can be changed. A mechanism is proposed to explain the process of transformation from the emulsion to the core‐sheath fibers, i.e., the stretching and evaporation induced de‐emulsification. In principle, this process can be applied to other systems to prepare core‐sheath fibers in place of concentric electrospinning and it is especially suitable for fabricating composite nanofibers that contain water‐soluble drugs.
Schematic mechanism for the formation of core‐sheath composite fibers during emulsion electrospinning. 相似文献
The electrospinning technique was used to spin ultra-thin fibers from several polymer/solvent systems. The diameter of the electrospun fibers ranged from 16 nm to 2 μm. The morphology of these fibers was investigated with an atomic force microscope (AFM) and an optical microscope. Polyethylene oxide) (PEO) dissolved in water or chloroform was studied in greater detail. PEO fibers spun from aqueous solution show a “beads on a string” morphology. An AFM study showed that the surface of these fibers is highly ordered. The “beads on a string” morphology can be avoided if PEO is spun from solution in chloroform; the resulting fibers show a lamellar morphology. Polyvinylalcohol (PVA) dissolved in water and cellulose acetate dissolved in acetone were additional polymer/solvent systems which were investigated. Furthermore, the electrospinning process was studied: different experimental lay-outs were tested, electrostatic fields were simulated, and voltage - current characteristics of the electrospinning process were recorded. 相似文献
Nowadays, quantification of the effects of basic parameters such as precursor, temperature oxidation, residence time, low temperature carbonization (LTC) and high temperature carbonization (HTC) on production process polyacrylonitrile based carbon fibers is not completely understood. In this way, there is not a completely theoretical model that accomplishes to quantitatively describe production process carbon fibers very accurately which needs to be used by engineers in design, simulation and operation of that process. This paper presents the development of a back propagation neural network model for the prediction of carbon fibers produced from PAN fibers. The model is based on experimental data. The precursors, temperature oxidation, residence time, LTC and HTC have been considered as the input parameters and the strength as output parameter to develop the model. The developed model is then compared with experimental results and it is found that the results obtained from the neural network model are accurate in predicting the strength of carbon fibers. 相似文献
Ultrafine nylon fibers were prepared by electrospinning of nylon-6,66,1010 terpolymer solution in 2,2,2-trifluoroethanol (TFE). The morphology, crystallinity and mechanical properties of the electrospun nylon-6,66,1010 fibers were investigated by scanning electron microscope (SEM), differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and tensile test. The effects of electrospun process parameters such as solution concentration, voltage and tip-to-collector distance on the morphology and the average size of the electrospun fibers were also studied. The results show that the spinnable concentration of nylon-6,66,1010/TFE solution is in the range of 6-14 wt%, and higher solution concentration favors the formation of uniform fibers without beads. The diameters of the electrospun fibers increase with increasing the solution concentration and decrease slightly with increasing the voltage and needle tip-to-collector distance. But no obvious morphology changes were found with the increase of the voltage and collection distance. DSC and WAXD results suggest that the electrospun nylon-6,66,1010 membranes have lower crystallinity than those of the corresponding casting films. The electrospun nylon-6,66,1010 membrane obtained from the 14 wt% concentration exhibits the largest tensile strength and elongation at break. 相似文献
Electrospun type I collagen fibers are very promising materials for tissue scaffold applications, but are typically fabricated from toxic solvents. Recently, electrospinning of type I collagen fibers by using environmentally friendly phosphate buffer saline (PBS)/ethanol solution has been explored. PBS/ethanol solvent systems offer better cell compatibility, but the high surface tension and high boiling point of the solvent system make the collagen difficult to electrospin and can cause inferior fiber morphology. In this study, the influence of solvent surface tension on the morphology of electrospun collagen fibers has been experimentally investigated and analyzed from a thermodynamics perspective. The analytical results indicate that solvents with high surface tension drive the formation of beads along the smaller, thinner fibers. In addition, beads with relatively small angular eccentricity were thermodynamically favorable. The experimental results presented herein corroborate the theoretical analysis and conclusions drawn from this study. The surface tension of the solvent has significant influence on the bead formation, especially in an aqueous system. The environmental humidity for the electrospinning process and the collagen concentration were also investigated. These parameters may result in variations of the evaporation-solidification rates, which consequently impact the formation and morphologies of electrospun collagen fibers. According to the thermodynamic analysis, uniform electrospun collagen fibers without beads can be obtained by manipulating solvent surface tension during the electrospinning process. 相似文献
A facile three-step method is developed to prepare new titania fibers with various special structures using a standard electrospinning equipment. After the traditional electrospinning, a treatment process, such as storing in air and soaking in water, for electrospun composite fibers is added before the calcination. Based on a given electrospinning solution and corresponding composite fiber, the structure of titania fiber is easily adjusted to be rough surface, fiber-in-tube, or a string of many particles by controlling the treating parameters and the calcination temperature, so this method shows a great potential of producing ceramic nanofibers with controlled structures for a large-scale production using a standard electrospinning equipment. The origin behind the morphological change of titania electrospun fibers is intensely studied. The results indicate that the surface structure of titania electrospun fiber formed during the storing period, will become the key factor on the formation of special titania fiber structure during the calcination process with different temperatures. 相似文献
Submicron poly(vinyl alcohol) (PVA) fiber mats were prepared by electrospinning of aqueous PVA solutions in 6-8% concentration. Fiber morphology was observed under a scanning electron microscope and effects of instrument parameters including electric voltage, tip-target distance, flow rate and solution parameters such as concentration on the morphology of electrospun PVA fibers were evaluated. Results showed that, when PVA with higher degree of hydrolysis (DH) of 98% was used, tip-target distance exhibited no significant effect on the fiber morphology, however the morphological structure can be slightly changed by changing the solution flow rate. At high voltages above 10 kV, electrospun PVA fibers exhibited a broad diameter distribution. With increasing solution concentration, the morphology was changed from beaded fiber to uniform fiber and the average fiber diameter could be increased from 87 ± 14 nm to 246 ± 50 nm. It was also found that additions of sodium chloride and ethanol had significant effects on the fiber diameter and the morphology of electrospun PVA fibers because of the different solution conductivity, surface tension and viscosity. When the DH value of PVA was increased from 80% to 99%, the morphology electrospun PVA fibers was changed from ribbon-like fibers to uniform fibers and then to beaded fibers. The addition of aspirin and bovine serum albumin also resulted in the appearance of beads. 相似文献
This review deals with electrospun nanofibers and their applications in several fields. Nanofibers have mainly been produced via electrospinning technique due to the simple, cost-effective, and versatile setup. Electrospinning is defined as a process, which produces fibers from its polymer solutions under exposure of high electric field voltage. The technique needs optimization of several parameters such solution, processing and ambient parameters to refine nanofiber morphology, diameter and porosity. The basic technique has been modified to produce composite fibers and to increase production capacity. Nanofiber characterization methods are summarized with examples. The relation between electrospinning and electrospraying is discussed. Nanofibers have the ability to form highly porous mesh with large surface to volume ratio enhancing its performance for various applications such as water filtration, tissue engineering scaffold, wounds, fiber composites, drug release and protective clothes. Single nanofibers could potentially be used as soft microrobots for drug delivery. Finally, results from modeling and simulations are illustrated. 相似文献
Chitosan fiber is one of the potential fibers that can be used as absorbable monofilament suture in biomedical application. In chitosan synthesis, aside from deproteination and deacetylation, demineralization is a crucial step where the major minerals within crustacean shells are removed. This demineralization process is carried out with two parameters, i.e. time and temperature. This research studies the influence of demineralization time on the diameter, tensile properties and biodegradability of chitosan fibers. Chitosan was synthesized from shrimp shells using 1 × 2 h and 3 × 2 h demineralization process. Chitosan fibers were produced by means of wet spinning. The chemical properties of chitosan fibers were characterized by means of Fourier Transform Infrared (FTIR) spectroscopy and X-Ray Diffractometry (XRD) technique. Physical properties characterization was carried out to measure the fibers’ diameter, density and viscosity. Tensile properties were evaluated by means of tensile test. The results were compared to standard of absorbable suture from the United States Pharmacopoeia (USP). Furthermore, in vitro degradation testing was also performed for analyzing biodegradation properties. Chitosan fibers were successfully made with diameter and maximum tensile force of chitosan fibers in a range of 364 - 460 μm and 5.6 - 8.3 N, respectively. The results of this research pointed that adding demineralization time would increase the diameter of chitosan fiber. However, the degradation occurred in prolonged demineralization process broke the bonds within the fiber which lead to a decrease in fiber's density. It is due to the degradation of chitosan occurred during extended demineralization process, which leads to degree of crystallinity reduction. Extensive demineralization process has been found to lower fibers’ tensile strength from 80.4 MPa to 38.4 MPa (52.2%), but increase their biodegradability by 17% and maximum elongation from 6.9% to 16.2% (136%). Despite that extensive demineralization process lowered chitosan fiber's tensile strength, both fibers made could still fit the standard for synthetic absorbable suture from USP number 0 and 1. 相似文献
This paper elucidates the means to control precisely the morphology of electrospun liquid crystal/polymer fibers formed by phase separation. The relative humidity, solution parameters (concentration, solvent), and the process parameter (feed rate) were varied systematically. We show that the morphology of the phase‐separated liquid crystal can be continuously tuned from capsules to uniform fibers with systematic formation of beads‐on‐a‐string structured fibers in the intermediate ranges. In all cases, the polymer forms a sheath around a liquid‐crystal (LC) core. The width of the polymer sheath and the diameter of the LC core increase with increasing feed rates. This is similar to the results obtained by coaxial electrospinning. Because these fibers retain the responsive properties of liquid crystals and because of their large surface area, they have potential applications as thermo‐, chemo‐, and biosensors. Because the size and shape of the liquid‐crystal domains will have a profound effect on the performance of the fibers, our ability to precisely control morphology will be crucial in developing these applications. 相似文献
Cellulose was dissolved rapidly in a NaOH/thiourea aqueous solution (9.5:4.5 in wt.-%) to prepare a transparent cellulose solution, which was employed, for the first time, to spin a new class of regenerated cellulose fibers by wet spinning. The structure and mechanical properties of the resulting cellulose fibers were characterized, and compared with those of commercially available viscose rayon, cuprammonium rayon and Lyocell fibers. The results from wide angle X-ray diffraction and CP/MAS 13C NMR indicated that the novel cellulose fibers have a structure typical for a family II cellulose and possessed relatively high degrees of crystallinity. Scanning electron microscopy (SEM) and optical microscopy images revealed that the cross-section of the fibers is circular, similar to natural silk. The new fibers have higher molecular weights and better mechanical properties than those of viscose rayon. This low-cost technology is simple, different from the polluting viscose process. The dissolution and regeneration of the cellulose in the NaOH/thiourea aqueous solutions were a physical process and a sol-gel transition rather than a chemical reaction, leading to the smoothness and luster of the fibers. This work provides a potential application in the field of functional fiber manufacturing. 相似文献
This work presents a numerical simulation of an ultrafiltration process of bovine serum albumin in solution, using hollow-fiber membranes. Such membranes are constituted of tiny polymer cylinders disposed in a tube-and-shell arrangement. The concentrate flows through the interior of the fibers and the pure solvent is recovered in the shell, assuming perfect solute rejection. In modeling the process, the flow of concentrate inside the fibers was considered to be laminar, with constant density, viscosity and solute diffusivity. Axial diffusion and angular effects were ignored. The model combines the effect of concentration polarization and adsorption, which are the two main limiting phenomena in ultrafiltration processes. The pressure on the shell side was considered constant and inside the fibers a linear pressure profile, dependent on the axial position, was adopted. The solution of the problem was achieved with the method of orthogonal collocation, with adequate choice of the weight function in the radial direction. In the axial direction, a finite-difference method was used. The numerical results were compared with experimental data available in the literature. 相似文献
Aggregation‐induced emission luminogens (AIEgens) are a new class of luminophors, which are non‐emissive in solution, but emit intensively upon aggregation. By properly designing the chemical structures of the AIEgens, their aggregation process can be tuned towards a desired direction to give diverse novel luminescent architectures of micelles, rods, and helical fibers. AIEgens represent a kind of promising building block for the fabrication of luminescent micro/nanostructures with controllable morphologies. In this review, we describe our recent work in this research area, focusing on the molecular design, circularly polarized luminescence properties, and helical self‐assembly behavior of AIEgens. 相似文献