Large‐scale aligned fiber mats prepared by salt‐induced pulse electrospinning

In this article, a new large‐scale aligned fiber mats formation method called salt‐induced pulse electrospinning was developed. By electrospinning salted solution in a humid environment, traditional continuous electrospinning changed into pulse electrospinning and aligned fibers were thus formed. The possible mechanisms for the occurrence of salt‐induced pulse electrospinning and the formation of fiber alignment were studied. The continuous electrospinning changing into the pulse electrospinning was due to the change of viscosity and conductivity of salted polymer solution in a wet electrospinning condition. Fishing net‐shaped whipping region of the electrospinning jet during pulse electrospinning process was considered as the key factor for the formation of fiber alignment. The mechanical properties of the aligned fiber mat increased significantly compared with that of the random fiber mat. This aligned fiber preparation method only requires a very low rotating drum speed as the receiver and can produce large‐scale aligned fiber mats for many applications. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Elucidating the relationship between the spreading coefficient, surface-mediated partial coalescence and the whipping time of artificial cream

We studied the whipping of artificial creams composed of a blend of sunflower oil and hydrogenated palm fat stabilized by protein or a mixture or protein and low molecular weight (lmw) surfactant. It was found that an increased whipping speed, decreased protein concentration, and the addition of lmw surfactant leads to shorter whipping times. Further, shorter whipping times were observed for WPI-stabilized cream compared to cream stabilized by sodium caseinate. In all cases, the decrease in whipping time was due to a decrease in the length of the second stage of whipping, the stage characterized by the adhesion of fat droplets to the air bubble surface. The decrease in whipping time could be accounted for by considering the influence of the experimental variables on the fraction of bubble surface area at which fat droplet spreading is possible. The same changes in parameters that promote droplet spreading at the air/water interface cause a decrease in the whipping time of our model creams. Correlating the whipping time of cream with the spreading behavior of fat droplets at the air/water interface represents a new insight into the mechanisms involved in the whipping of cream.     

Preparation of polybenzoxazole fibers via electrospinning and postspun thermal cyclization of polyhydroxyamide

Polybenzoxazole (PBO) fibers with a submicron diameter were successfully prepared by electrospinning its precursor, polyhydroxyamide (PHA), solutions to obtain the PHA fibers first, followed by appropriate thermal treatments for cyclization reaction. BisAPAF‐IC PHA with two different molecular weights (MWs) were synthesized from a low temperature polymerization of 2,2′‐bis(3‐amino‐4‐hydroxyphenyl) hexafluoropropane (BisAPAF) and isophthaloyl chloride (IC). Using dimethylacetamide (DMAc) and tetrahydrofuran (THF), solvent effects on the electrospinnability of PHA solutions were investigated. For balancing the solution properties, it was found that DMAc/THF mixture with a weight ratio of 1/9 was the best cosolvent to prepare smooth PHA fibers; uniform PHA fibers with a diameter of 325–720 nm were obtained by using 20 wt % PHA/(DMAc/THF) solutions. For a fixed PHA concentration, solutions with a lower MW of PHA yielded thinner electrospun fibers under the same electrospinning condition. After obtaining the electrospun BisAPAF‐IC PHA fibers, subsequent thermal cyclization up to 350 °C produced the corresponding thermally stable BisAPAF‐IC PBO fibers with a diameter of 305–645 nm. The structure of the precursor fibers and the fully cyclized fibers were characterized by FTIR. For the cyclized BisAPAF‐IC PBO fibers, thermogravimetric analysis showed a 5% weight loss temperature at 523 °C in nitrogen atmosphere. The interconnected fiber structure in the BisAPAF‐IC PBO fiber mats was irrelevant to the curing process, but resulted from the jet merging during the whipping process as revealed by the high speed camera images. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8159–8169, 2008     

Light Electrospun Polyvinylpyrrolidone Blanket for Low Frequencies Sound Absorption

Light polymeric soundproofing materials(density = 63 kg/m~3) of interest for the transportation industry were fabricated through electrospinning. Blankets of electrospun polyvinylpyrrolidone(average fiber diameter =(1.6 ± 0.5) or(2.8 ± 0.5) μm) were obtained by stacking disks of electrospun mats. The sound absorption coefficients were measured using the impedance tube instrument based on ASTM E1050 and ISO 10534-2. For a given set of disks(from a minimum of 6) the sound absorption coefficient changed with the frequency(in the range 200–1600 Hz) following a bell shape curve with a maximum(where the coefficient is greater than 0.9) that shifts to lower frequencies at higher piled disks number and greater fiber diameter. This work showed that electrospinning produced sound absorbers with reduced thickness(2–3 cm) and excellent sound-absorption properties in the low and medium frequency range.     

Characterization of gelatin nanofibers electrospun using ethanol/formic acid/water as a solvent

Gelatin nanofibers were prepared via electrospinning using aqueous solutions of formic acid and ethanol as the solvent instead of cytotoxic solvents. The resulting mat was further crosslinked with glutaraldehyde (GTA). The influence of the storing time on the viscosity and gel point of the solution was investigated. The gelatin nanofibers were examined using a field emission scanning electron microscope (FESEM) for the fiber size and morphology. The lowest diameter of gelatin fiber (85 nm, without beads) was achieved when the gelatin concentration was 20 wt% and electrospinning was conducted with a voltage of 20 kV over a distance of 10 cm at ambient temperature. The results from differential scanning calorimetry (DSC) showed that the softening temperature of gelatin nanofibers crosslinked with GTA was elevated. In addition, GTA‐crosslinked gelatin nanofibers exhibited cell compatibility for mouse mesangial cells (CRL 1927). Copyright © 2008 John Wiley & Sons, Ltd.     

静电纺丝——从无规纳米纤维膜到取向连续长纱

静电纺丝是通过对聚合物溶液或熔体施加外电场制造纳米纤维的有效方法.电纺过程中,在静电力作用下聚合物射流快速鞭动,形成的纳米纤维无规堆砌,得到无纺布状的无规纳米纤维膜.这种纳米纤维膜具有极大的比表面积,已用于超高效过滤,在刨伤修复、组织工程、水处理等领域有广泛的应用前景.为了进一步拓展纳米纤维在纤维工业、纺织品、微制造等领域的应用,电纺纳米纤维的取向和连续长纱的制备研究受到科学家的重视,文献报道了多种纳米纤维取向方法.本文分析了纳米纤维膜无规堆砌结构的形成机理,总结了纳米纤维取向研究和连续长纱制备研究进展,特别介绍了基于静电作用分析提出的共轭电纺方法,讨论了取向纳米纤维的应用以及纳米纤维未来的研究方向.     

静电纺制备纳米孔结构聚乳酸(PLLA)超细纤维

采用静电纺丝法制备了孔径为40～150 nm的PLLA纳米孔结构超细纤维,纳米孔不仅分布在纤维表面,而且存在于纤维内部.通过扫面电镜观察了纤维表面形貌.探讨了混合溶剂二氯甲烷/N,N-二甲基甲酰胺的比例、PLLA浓度、电场强度对PLLA纤维纳米孔大小、分布密度、深度的影响.结果表明通过调节PLLA溶液性质和纺丝参数,PLLA纤维的表面形貌可以在3种状态即光滑无孔、疏浅凹坑、密集深孔之间可控.二氯甲烷/N,N-二甲基甲酰胺比例为1∶4,PLLA浓度9%,电场强度1 kV/cm,环境温湿度分别为30℃和52%,静电纺丝所得PLLA超细纤维表面孔洞直径为150 nm,孔洞分布密集.纳米孔PLLA纤维形成的主要机理是由于静电纺丝过程中溶剂的快速挥发引起纤维表面温度急剧降低导致热致相分离而产生多孔结构.PLLA纤维膜的疏水性与纤维表面孔洞结构密切相关,纤维膜接触角最高可达146.6°.由于PLLA纤维的多孔结构,这种高疏水性的PLLA纤维膜能够快速、大量地吸油,90 s内吸收柴油达到90 g/g,25 min内可以达到145 g/g.     

Porous electrospun polycaprolactone fibers: Effect of process parameters

The effect of electrospinning process parameters (solution flow rate, applied voltage, spinning distance) on the size and surface morphology of porous electrospun poly(ε‐caprolactone) was investigated in this study. Response surface methodology was implemented for the design and conduction of electrospinning experiments. The feed solution was a 12.5% w/v poly(ε‐caprolactone) (PCL) solution in a binary solvent mixture of 90%v/v chloroform/dimethyl sulfoxide. Spinning distance of 10–25 cm, applied voltage of 10–25 kV and feed flow rate of 0.5–5 mL/h were the range of limiting values of the independent variables used for the development of a central composite design. Second‐order polynomial equations, correlating electrospinning process parameters to relative pore coverage, and fiber average diameter were developed and validated. An increase in any of the investigated parameters (solution flow rate, applied voltage, spinning distance) resulted in the increase of both, pore formation on electrospun fibers, and produced fiber average diameter. Under the experimental conditions investigated, the relative pore surface coverage was 15.8–31.9% and the average fiber diameter was in the range of 1.6–3.3 μm. Applied voltage was proven to be the parameter with the strongest impact on both, fiber diameter and surface morphology. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1878–1888     

Aeration of emulsions by whipping

During aeration of food emulsions such as dairy cream and ice cream, small gas bubbles are introduced, which are often stabilized by a layer of adsorbed emulsion droplets. It is shown that the maximum achievable volume of gas bubbles that can be incorporated by whipping depends on the effectiveness of the introduction of gas during the first stage of whipping and is furthermore limited by packing constraints. The main factors relevant for the latter limitation are the thickness of the coating of emulsion droplets at the bubble surface, the ratio between the droplet and bubble radii, and the fat content of the emulsion. It is hypothesized that, during whipping, a dynamic process of bubble break-up and coalescence adjusts the average bubble size and the volume of gas incorporated in the foam to the constraint of close packing of the bubbles. The consequences of this mechanism for whipping of emulsions are discussed.     

Melt-electrospinning of PMMA

<正>The melt electrospinning of PMMA was investigated.The averaged fiber diameter thus obtained was reduced from 34.0μm to 19.7μm by adding di-(2-ethylhexyl)phthalate to reduce viscosity of the molten PMMA,and it further lowered down to 4.0μm when a KCl/ice-water solution was used as collection media.A comparison study on the PMMA fibers made through melt electrospinning and done by solution electrospinning was made.It was found that solution electrospinning was capable of fabricating very thin fibers as small as to a nanometer size,but resulted in a much wider fiber diameter range than melt-electrospinning did.In general,within some extent an increase in applied voltage and amount of the additive or a decrease in collection distance can give rise to a decreased fiber diameter and improved mechanical performance for the PMMA fibers by melt electrospinning.It was also indicated that the mechanical properties of the PMMA fibers made through melt-electrospinning were superior to those by solution elctropspinning.     

Free surface electrospinning of fibers containing microparticles

Many materials have been fabricated using electrospinning, including pharmaceutical formulations, superhydrophobic surfaces, catalysis supports, filters, and tissue engineering scaffolds. Often these materials can benefit from microparticles included within the electrospun fibers. In this work, we evaluate a high-throughput free surface electrospinning technique to prepare fibers containing microparticles. We investigate the spinnability of polyvinylpyrrolidone (PVP) solutions containing suspended polystyrene (PS) beads of 1, 3, 5, and 10 μm diameter in order to better understand free surface electrospinning of particle suspensions. PS bead suspensions with both 55 kDa PVP and 1.3 MDa PVP were spinnable at 1:10, 1:5, and 1:2 PS:PVP mass loadings for all particle sizes studied. The final average fiber diameters ranged from 0.47 to 1.2 μm and were independent of the particle size and particle loading, indicating that the fiber diameter can be smaller than the particles entrained and can furthermore be adjusted based on solution properties and electrospinning parameters, as is the case for electrospinning of solutions without particles.     

Aligned and molecularly oriented semihollow ultrafine polymer fiber yarns by a facile method

In this work, aligned and molecularly oriented bone‐like PLLA semihollow fiber yarns were manufactured continuously from an optimized homogeneous polymer‐solvent‐nonsolvent system [PLLA, CH₂Cl₂, and dimethyl formamide (DMF)] by a single capillary electrospinning via self‐bundling technique. Here, it should be emphasized that the self‐bundling electrospinning technique, a very facile electrospinning technique with a grounded needle (which is to induce the self‐bundling of polymer nanofibers at the beginning of electrospinning process), is used for the alignment and molecular orientation of the polymer fiber, and the take‐up speed of the rotating drum for the electrospun fiber yarn collection is very low (0.5 m/s). PLLA can be dissolved in DMF and CH₂Cl₂ mixed solvent with different ratios. By varying the ratios of mixed solvent system, PLLA electrospun semihollow fiber with the porous inner structure and compact shell wall could be formed, the thickness of the shell and the size of inner pores could be adjusted. The results of polarized FTIR and wide angle X‐ray diffraction investigations verified that as‐prepared PLLA semihollow fiber yarns were well‐aligned and molecularly oriented. Both the formation mechanism of semihollow fibers with core‐shell structure and the orientation mechanism of polymer chains within the polymer fibers were all discussed. The as‐prepared self‐bundling electrospun PLLA fiber yarns possessed enhanced mechanical performance compared with the corresponding conventional electrospun PLLA fibrous nonwoven membranes. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1118–1125, 2010     

Optical birefringence and molecular orientation of electrospun polycaprolactone fibers by polarizing-interference microscopy

The potential of polarizing-interference Pluta microscope for determination of optical birefringence of individual nanofibers formed by electrospinning was shown. This technique can be applied for measurements of fiber birefringence, practically at diameter above 300 nm. The molecular orientation of individual polycaprolactone (PCL) nanofibers was determined from birefringence assuming the same orientation of both phases, crystal and amorphous. The molecular orientation was determined using DSC crystallinity, crystal intrinsic birefringence calculated for the first time for PCL from bond polarizabilities as well as estimated value of amorphous intrinsic birefringence. Our results indicate that the birefringence and thus molecular orientation are strongly inhomogeneous along the nanofibers, reflecting a complex nature of forces acting during electrospinning process. The average molecular orientation is weak if any, being dependent together with fiber thickness and crystallinity on electrospinning parameters, like applied voltage, concentration and type of solvent. The obtained results indicate that the average molecular orientation displays similar dependence on applied voltage as fiber diameter. Relatively low melting temperature of electrospun nanofibers suggests low crystal size and/or high concentration of defects in crystals. This observation corresponds with low crystallinity and molecular orientation, indicating together relatively low degree of crystal ordering due to high rate of cooling and solvent evaporation during electrospinning, limiting thus crystallization process.     

A comparative study of jet formation in nozzle‐ and nozzle‐less centrifugal spinning systems

Centrifugal spinning, a recently developed approach for ultra‐fine fiber production, has attracted much attention as compared with the electrospinning, due to its high yield, no solution polarity and high‐voltage electrostatic field requirements, etc. In this study, the jet formation process and spinning parameters on jet path are explored and compared in nozzle‐ and nozzle‐less centrifugal spinning systems. For nozzle‐less centrifugal spinning, fingers are formed at the front of thin liquid film due to the theory of Rayleigh–Taylor instability. We find that the lower solution concentration and higher rotational speed favor the formation of thinner and longer fingers. Then, the critical angular velocity and initial jet velocity for nozzle‐/nozzle‐less centrifugal spinning are obtained in accordance with the balance of centrifugal force, viscous force, and surface tension. When jet leaves the spinneret, it will undergo a series of motions including necking and whipping processes, and then, a steady spiral jet path is formed with its radius getting tighter. Finally, we experimentally study the effect of rotational speed and solution concentration on jet path, which shows that the higher rotational speed results in a larger radius of jet path while the solution concentration has little effect on it. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1547–1559     

Preparation and properties of thermoresponsive and conductive composite fibers with core‐sheath structure

In this research, thermoresponsive and conductive fibers with core‐sheath structure were fabricated by coaxial electrospinning. For preparing the spinning sheath solution, poly‐(N‐isopropylacrylamide‐co‐N‐methylolacrylamide) (PNN) copolymer having thermoresponsive and cross‐linkable properties was synthesized by free‐radical polymerization using redox initiators; it was then mixed with the conductive poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) at different weight ratios in water. On the other hand, poly(butyl acrylate‐co‐styrene) (PBS) copolymer synthesized by emulsion polymerization was dissolved in chloroform and used as the spinning core solution. After electrospinning, the fibers were treated at 110 °C for 1 h to cross‐link the PNN portion in the sheath for strengthening the fibers. Well‐defined core‐sheath fibers were observed from SEM pictures; the outside and inside (core) diameters were 568 ± 24 and 290 ± 40 nm, respectively, as determined from TEM pictures. The fiber mats were further doped by DMSO to enhance their conductivity. For the fiber mat with the weight ratio of PEDOT:PSS/PNN at 0.20 in the sheath, its surface conductivity could reach 29.4 S/cm. In addition, the fiber mats exhibited thermoresponsive properties that both swelling ratio and electric resistance decreased with temperature. Furthermore, the fiber mats exhibited improved flexibility as evaluated via bending test. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1299–1307     

Large-scale fabrication of aligned single-walled carbon nanotube array and hierarchical single-walled carbon nanotube assembly

Aligned single-walled carbon nanotubes (SWNTs) and hierarchical SWNT assembly were fabricated by electrospinning. The high fiber elongation and high DC electric field applied during the electrospinning process result in the orientation of the SWNTs along the axial direction of the fiber. The alignment of the electropsun composite fiber transfers this local SWNT orientation to macroscopically aligned SWNTs. After removing the polymer component from the aligned composite fiber, we produced large area aligned SWNTs. The results show that the directional control of SWNT alignment and debundling of SWNTs into individual tubes can be simultaneously realized.     

Facilely preparing various new titania electrospun fibers with controllable nanostructures using a three-step method

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.     

PVA/SiO2-TiO2杂化电纺纤维膜的形态与性能

以正硅酸乙酯(TEOS)、钛酸四丁酯(TBT)和聚乙烯醇(PVA)为原料, 用溶胶凝胶法制备了PVA/(SiO2-TiO2)杂化纺丝液, 将其电纺成纤维膜. 红外光谱结果证实, PVA的羟基与TEOS和TBT水解后的羟基发生了缩合反应, 杂化电纺纤维膜以网络结构形式相结合; X射线衍射分析表明, 杂化电纺纤维膜的结晶度比纯PVA电纺纤维膜小; 扫描电镜表明, 随杂化纤维膜中无机相含量的增加, 纤维的直径不断增加, 纤维出现一定的弯曲和扭曲, 并伴有少量带状结构的纤维; 紫外-可见光谱结果表明, TiO2的引入增加了纤维膜的抗紫外性; TGA热分析结果表明, 杂化纤维膜的耐热性能优于纯PVA电纺纤维膜的; 耐水性和稳定性测试表明, 杂化纤维膜的耐水性和稳定性优于纯PVA和PVA/SiO2电纺纤维膜的.     

Electrospinning P(LLA-CL) Nanofiber: A Tubular Scaffold Fabrication with Circumferential Alignment

In this paper a synthetic Poly(L-lactic-co-ϵ-caprolactone) [P(LLA-CL)] (75:25) copolymer has been fabricated into a nanofibrous structure by electrospinning. The polymer crystal structure has been investigated by DSC and x-ray diffraction method. During electrospinning at room temperature, a crystallization of LLA sequence in the P(LLA-CL) copolymer could not form, while a relatively regular arrangement of CL sequence was observed. In order to obtain a tubular scaffold, a rotating mandrel was designed to collect the fiber, so that the tubular scaffold can be retrieved from the mandrel with an inner diameter same as that of the outer diameter of the mandrel. An auxiliary electrode with a sharp edge and a negative charge was set under the mandrel to guide the fiber deposition on the mandrel. When the sharp edge bar was vertical to the rotating axle of the mandrel and just beneath the spinning nozzle, nanofibers with circumferential alignment were obtained. With this method it is possible to obtain a tubular scaffold with suitable fiber alignment for blood vessel tissue engineering.     

Process optimization and empirical modeling for electrospun polyacrylonitrile (PAN) nanofiber precursor of carbon nanofibers

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.