The effect of solvent dielectric properties on the collection of oriented electrospun fibers

A simple approach to electrospinning has been developed that enables the collection of polymer, ceramic, and multiphase composite fibers, in quantity, with a high degree of spatial orientation. It has been demonstrated that a careful choice of solvent effectively eliminates the onset of the characteristic “bending” instability that is commonly associated with the electrospinning process. This allows collection of spatially oriented submicron electrospun fibers on a rotating drum without the need for elaborate mechanical or electrostatic manipulation of the electrospinning jet and/or collection target (Deitzel, J. M.; Kleinmeyer, J. D. et al. Polymer 2001, 42, 8163, Zussman, E.; Theron, A.; et al. Appl Phys Lett 2003, 82, 973, and Li, D. Wang, Y. L.; et al. Nano Lett 2003, 3, 1167). Fibers have been electrospun from a series of model polyethylene oxide/CHCl₃ solutions with a range of conductivities. The experimental data confirms theoretical predictions that the onset of the bending instability is a function of the available “free” charge in the solution, which in turn is strongly influenced by the dielectric constant of the solvent. The results show that fiber orientation becomes random as the conductivity increases, indicating the need for the surface charge density to exceed a critical threshold in order for the bending instability to initiate. This method has been experimentally demonstrated with other low-dielectric constant solvents and other common polymer, ceramic, and composite materials. Furthermore, it has been demonstrated that fibers electrospun from these solutions can be mechanically drawn to submicron dimensions (∼ 200–500 nm) by controlling drum speed. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Fabrication of continuous nanofiber yarn using novel multi‐nozzle bubble electrospinning

A novel multi‐nozzle bubble electrospinning apparatus, including spinning unit, metering pump, constant flow pump, metal funnel and yarn winder, was designed for the preparation of continuous twisted polyacrylonitrile nanofiber yarns, and the principle of nanofiber yarn spinning was studied. An innovative spinning unit consisting of nozzle and air chamber was used to improve the production of nanofibers. Double conjugate electrospinning was developed using two pairs of oppositely charged spinning units to neutralize the charges. The effects of applied voltage, air flow rate, overall solution flow rate and funnel rotary speed on the fiber diameter, production rate and mechanical properties of the nanofiber yarns were analyzed. Nanofibers could be aggregated stably and bundled continuously, then twisted into nanofiber yarns uniformly at an applied voltage of 34 kV, air flow rate of 1200 mL min^?1 and overall solution flow rate of 32 mL h^?1. With an increase in the funnel rotary speed, the twist angle of the nanofiber yarns gradually increased when the take‐up speed was constant. The yarn tensile strength and elongation at break showed an increasing trend with increasing twist angle. Nanofiber yarns obtained using this novel method could be produced at a rate from 2.189 to 3.227 g h^?1 with yarn diameters ranging from 200 to 386 µm. Nanofiber yarns with a twist angle of 49.7° showed a tensile strength of 0.592 cN dtex^?1 and an elongation at break of 65.7%. © 2013 Society of Chemical Industry     

溶剂对电纺聚酯纳米纤维可纺性的影响

利用静电纺丝法制备聚酯(PET)纳米纤维,选择苯酚和四氯乙烷,三氟乙酸,三氟乙酸和二氯甲烷3种溶剂分别溶解PET切片进行静电纺丝,通过扫描电子显微镜(SEM)对纤维表面形态进行观察,结果表明:三氟乙酸和二氯甲烷混合溶剂溶解PET制备的电纺纤维较好。使用视频光学接触角测定仪测试PET电纺纤维膜与其流延膜的接触角,通过分析两者表面结构,证明PET电纺纤维膜能产生较强的疏水功能。     

Effect of solution properties on nanofibrous structure of electrospun poly(lactic‐co‐glycolic acid)

Electrospinning of poly(lactic‐co‐glycolic acid) (PLGA) in chloroform or 1,1,1,3,3,3‐hexafluoro‐2‐propanol (HFIP) was investigated, focusing on its solution parameters, to develop nonwoven biodegradable nanofibrous structures for tissue engineering. PLGA nanofibers were obtained by electrospinning of 15 wt % PLGA solution and the resulting average fiber diameters were varied with the range of 270–760 nm, depending on solution property. When small amounts of benzyl triethylammonium chloride (BTEAC) was added to the PLGA/chloroform solution, the average diameter was decreased from 760 to 450 nm and the fibers were densely amounted in a straight shape. In addition, the average fiber diameter (270 nm) of nanofibers electrospun from polar HFIP solvent was much smaller than that (760 nm) of nanofibers electrospun from nonpolar chloroform solvent. Therefore, it could be concluded that conductivity or dielectric constant of the PLGA solution was a major parameter affecting the morphology and diameter of the electrospun PLGA fibers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1214–1221, 2006     

Effect of glycerol on solution properties governing morphology,glass transition temperature,and tensile properties of electrospun zein film

An attempt was made to improve the tensile strength and elongation of electrospun zein film by addition of a plasticizer, namely, glycerol to the film forming solution. A surfactant viz. Tween®40 and NaCl were also added into the film solution to facilitate the electrospinning process. The effect of glycerol content on selected zein solution properties, i.e., surface tension, electrical conductivity, and viscosity, which in turn affect the mechanical property, morphology, and glass transition temperature (T_g) of the film were investigated. Morphology of the electrospun film was examined via scanning electron microscopy (SEM), whereas the film component was characterized by Fourier transform infrared (FTIR) spectroscopy. It was observed that as the glycerol content increased, the diameter of the electrospun fiber increased as a result of decreasing electrical conductivity with increasing surface tension of the solution. The flow‐behavior index of the solution indicated that glycerol had a significant impact on the solution flow property, hence improved fiber diameter uniformity. Besides, the tensile strength and elongation of the film were improved as glycerol content increased, but the reverse was noted at 10 wt %. T_g of the zein film decreased as the glycerol content increased. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and characterization of electrospun ultrafine polyamide‐6 nanofibers

We report on the preparation and characterization of ultrafine polyamide‐6 nanofibers by the electrospinning technique. The effect of electrospinning on the formation of ultrafine polyamide‐6 nanofiber structure was examined. The morphological and structural characterizations and thermal properties of the ultrafine polyamide‐6 nanofibers were investigated in comparison with bulk polyamide‐6 pellets. In order to accurately characterize the ultrafine polyamide‐6 nanofiber structure by direct identification of mass resolved components, we performed matrix‐assisted laser desorption ionization time‐of‐flight (MALDI‐TOF) mass spectrometry. Field emission scanning electron microscopy images revealed the presence of ultrafine polyamide‐6 nanofibers bound between the main fibers. The diameter of the polyamide‐6 nanofibers was observed to be in the range 75–110 nm, whereas the ultrafine structures consisted of regularly distributed very fine nanofibers with diameters of about 9–28 nm. The MALDI‐TOF spectra showed the presence of protonated and sodiated ions that were assigned to polyamide‐6 chains. Copyright © 2011 Society of Chemical Industry     

Crystalline order and mechanical properties of as‐electrospun and post‐treated bundles of uniaxially aligned polyacrylonitrile nanofiber

This study investigates the crystalline order and mechanical properties of as‐electrospun and posttreated polyacrylonitrile nanofibers. To keep the nanofibers under tension during the posttreatment, a modified method of preparing bundles such as multifilament yarn was used in which the alignment of the nanofibers and linear density of the bundles were controlled successfully. An increase in the nanofibers' diameter from 240 to 500 nm led to the E modulus, ultimate strength, and elongation at break of the bundles rising from 836 MPa, 45 MPa, and 38% to 1915 MPa, 98 MPa, and 120%, respectively. The crystallinity index (%) and coherence length of the nanofiber bundles were evaluated through wide‐angle X‐ray diffraction. The mechanical properties and crystalline order of the nanofiber bundles were both increased as a result of the posttreatment. Wide‐angle X‐ray diffraction patterns of annealed bundles showed equatorial diffraction from the (101 0) reflection at ～ 5.1 Å and from the (112 0) reflection at ～ 3 Å. The values of the coherence length, crystallinity index (%), ultimate strength, and E modulus of the bundles prepared from 240‐nm nanofibers increased from negligible, 2%, 1109 MPa, and 48 MPa to 54 Å, 35%, 2235 MPa, and 95 MPa after annealing at 85°C in a mixture of water (95 wt %) and N,N‐dimethylformamide (5 wt %), respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation and characterization of zein and zein/poly‐L‐lactide nanofiber yarns

Zein and zein/poly‐L ‐lactide (PLLA) nanofiber yarns were prepared by conjugate electrospinning using coupled spinnerets applied with two high electrical voltages of opposite polarities in this article. Structure and morphology of zein yarns were investigated by SEM and X‐ray diffraction. The results showed that zein yarn consisted of large quantity of fibers with diameters ranging from several hundreds nanometers to a few microns, and zein concentration played a significant role on the diameter of nanofibers in yarns. To improve mechanical property of nanofiber yarns, PLLA was then incorporated with zein. Zein/PLLA composite nanofiber yarns conjugate electrospun from solution with concentration of 7.5% (zein, w/v)/7.5% (PLLA, w/v) exhibited tensile strength of 0.305 ± 0.014 cN/dtex. The composite yarns showed better nanofiber alignment along the longitudinal axis. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Morphology of electrospun nylon‐6 nanofibers as a function of molecular weight and processing parameters

In the present study, the morphology and mechanical properties of nylon‐6 nanofibers were investigated as a function of molecular weight (30,000, 50,000, and 63,000 g/mol) and electrospinning process conditions (solution concentration, voltage, tip‐to‐collector distance, and flow rate). Scanning electron micrographs (SEM) of nylon‐6 nanofibers showed that the diameter of the electrospun fiber increased with increasing molecular weight and solution concentration. An increase in molecular weight increases the density of chain entanglements (in solution) at the same polymer concentration; hence, the minimum concentration to produce nanofibers was lower for the highest molecular weight nylon‐6. The morphology of electrospun fibers also depended on tip‐to‐collector distance and applied voltage concentration of polymer solution as observed from the SEM images. Trends in fiber diameter and diameter distribution are discussed for each processing variable. Mechanical properties of electrospun nonwoven mats showed an increase in tensile strength and modulus as a function of increasing molecular weight. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Mechanical property enhancement of non‐bonding electrospun mats via adhesive

In the present study, the effect of adhesive on the morphology of different electrospun polymeric mats was investigated. The modification of two polymers, poly(methyl methacrylate) and poly(vinyl chloride), was carried out by blending the polymers with different amounts of poly(butyl acrylate) (PBA) adhesive to investigate the effect of different amounts of adhesive with heat hardener in hybrid mats. The introduction of various concentrations of PBA into different polymer solutions led to the formation of point‐bonded electrospun fibrous mats. Scanning electron microscopy images indicated that point‐bonded polymer/adhesive fibers were uniformly distributed throughout the mats. Fourier transform infrared spectrometry, contact angle measurements and thermogravimetric analysis were used to study the different properties of the hybrid mats. The tensile strength of the blended fibrous electrospun mats was increased effectively. This enhancement of the mechanical properties of the mats due to the presence of adhesive increases the number of potential applications of the electrospun mats, especially for mechanically weak polymers. Copyright © 2012 Society of Chemical Industry     

静电纺特殊形貌纳米纤维的应用研究进展

特殊形貌的纳米纤维可以通过控制静电纺丝过程工艺及参数条件来制备。特殊形貌的纳米纤维具有比普通纳米纤维更大的比表面积和更高的孔隙率,以及掺杂各类有机/无机材料后赋予纤维的多功能性,使其应用研究已经深入能源环境、催化过滤、生物工程、食品安全等诸多领域,成为纳米材料研究的热点领域之一。但特殊形貌纳米纤维存在研究体系不完善、量产化难度高、重现性差等问题。本文通过对多种特殊形貌纳米纤维的成形机理进行阐述,介绍了特殊形貌纳米纤维独特的形貌结构与性能优势,对其在粒子透过、粒子拦截与传输等领域的应用研究进行了概述。此外,本文对特殊形貌的纳米纤维从研究制备到应用过程中面临的局限性进行了讨论,提出建立完善的特殊形貌纳米纤维研究体系,针对应用领域开发功能性特殊形貌纳米纤维膜,从环保性、稳定性角度出发,推进特殊形貌纳米纤维的产业化发展进程。     

Fabrication and electrical characterization of electrospun polyacrylonitrile‐derived carbon nanofibers

Carbon nanofibers were produced from a polyacrylonitrile/N,N‐dimethylformamide precursor solution by an electrospinning process and later pyrolysis at temperatures ranging from 500 to 1100°C in an N₂ atmosphere for about 1 h. The morphological structure of the nanofibers was studied with scanning electron microscopy. Scanning electron microscopy images of carbonized polyacrylonitrile nanofibers without a gold coating showed that the carbonized polyacrylonitrile nanofibers possessed electrical properties. The thermal behavior of the nanofibers was studied with thermogravimetric analysis. An indirect four‐point‐probe method was used for the measurement of the conductivity of nanofiber mats. The conductivity increased sharply with the pyrolysis temperature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effects of surface modification,carbon nanofiber concentration,and dispersion time on the mechanical properties of carbon‐nanofiber–polycarbonate composites

The time effect of ultrasonication was investigated for dispersing carbon nanofibers (CNFs) into a polycarbonate (PC) matrix on the mechanical properties of thus‐produced composites. The effects of CNF surface modification by plasma treatment and the CNF concentration in composites on their mechanical properties were also explored. The plasma coating was characterized by HRTEM and FT‐IR. Furthermore, the plasma polymerization (10 w) treatment on the CNF enhanced the CNF dispersion in the polymer matrix. The mechanical properties of the CNF–PC composites varied with the dispersion time, at first increasing to a maximum value and then dropping down. After a long ultrasonic treatment (24 h), the properties increased again. At a high concentration, the CNF‐PC suspension became difficult to disperse. Additionally, the possible mechanisms for these behaviors are simply proposed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3792–3797, 2007     

电子纺丝成形及纤维形态结构研究

电子纺丝是—种可能制备具有微细直径的纤维成形技术，本文介绍了电子纺丝技术的基本原理和电子纺丝成形工艺对纤维形态结构的影响以及电子纺纤维的应用前景等。     

Non‐ionic surfactants for enhancing electrospinability and for the preparation of electrospun nanofibers

BACKGROUND: Electrospinning is widely used to produce nanofibers; however, not every polymer can be electrospun into nanofibers. To enhance electrospinability, much effort has been made in designing new apparatus, such as vibration‐electrospinning, magneto‐electrospinning and bubble‐electrospinning. RESULTS: A representative non‐ionic surfactant, TritonR X‐100, is used to enhance electrospinability. The surfactant is added to an electrospun poly(vinyl pyrrolidone) polymer solution, and a dramatic reduction in surface tension is observed. As a result, a moderate voltage is needed to produce fine nanofibers, which are commonly observed during the conventional electrospinning procedure only at elevated voltage. CONCLUSION: The novel strategy produces smaller nanofibers than those obtained without surfactants, and the minimum threshold voltage is much decreased. Copyright © 2008 Society of Chemical Industry     

Mixed macrodiol‐based siloxane polyurethanes: Effect of the comacrodiol structure on properties and morphology

Two series of polyurethanes were prepared to investigate the effect of comacrodiol structure on properties and morphology of polyurethanes based on the siloxane macrodiol, α,ω‐bis(6‐hydroxyethoxypropyl) polydimethylsiloxane (PDMS). All polyurethanes contained a 40 wt % hard segment derived from 4,4′‐methylenediphenyl diisocyanate (MDI) and 1,4‐butanediol (BDO), and were prepared by a two‐step, uncatalyzed bulk polymerization. The soft segments were based on an 80/20 mixture of PDMS (MW 967) and a comacrodiol (MW 700), selected from a series of polyethers and polycarbonates. The polyether series included poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO), poly(tetramethylene oxide) (PTMO), poly(hexamethylene oxide), and poly(decamethylene oxide) (PDMO), whereas the polycarbonate series included poly (hexamethylene carbonate) diol (PHCD), poly [bis(4‐hydroxybutyl)‐tetramethyldisiloxy carbonate] diol (PSCD), and poly [hexamethylene‐co‐bis(4‐hydroxybutyl)‐tetramethyldisiloxy carbonate] diol (COPD). Polyurethanes were characterized by size exclusion chromatography, tensile testing, differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMTA). The results clearly demonstrated that the structure of the comacrodiol influenced the properties and morphology of siloxane‐based polyurethanes. All comacrodiols, except PEO, improved the UTS of the polyurethane; PHMO and PTMO were the best polyether comacrodiols, while PSCD was the best polycarbonate comacrodiol. Incorporation of the comacrodiol made polyurethanes more elastomeric with low modulus, but the effect was less significant with polycarbonate comacrodiols. DSC and DMTA results strongly supported that the major morphological change associated with incorporation of a comacrodiol was the significant increase in the interfacial regions, largely through the compatibilization with the hard segment. The extent of compatibilization varied with the comacrodiol structure; hydrophilic polyethers such as PEO were the most compatible, and consequently, had poor mechanical strength. Among the polyethers, PHMO was the best, having an appropriate level of compatibility with the hard segment for substantial improvement in mechanical properties. Siloxy carbonate comacrodiol PSCD was the best among the polycarbonates. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1071–1082, 2000     

Effects of some electrospinning parameters on morphology of natural silk‐based nanofibers

Natural silk, from Bombyx mori solutions were electrospun into nanofibers, with diameters ranged from 60 to 7000 nm. The effects of electrospinning temperature, solution concentration and electric field on the formation nanofibers were studied. Optical and scanning electron microscope were used to study the morphology and diameter of electrospun nanofibers. It was observed that the nanofibers became flattened with ribbon‐like shape with increasing the electrospinning temperature. The nanofiber diameter increases with the increase in the concentration of silk solution at all electrospinning temperature. With increasing the voltage of electric field at 50°C, morphology of the nanofibers changes from ribbon‐like structure to circular cross section. Referring to the literature the probable mechanism responsible for the change of morphology is pointed out. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of fatigue loading on wicking properties of polyamide 66 nanofiber yarns

The wicking phenomenon is of prime importance with regards to biomedical applications of nanofiber yarns such as suture yarns and tissue scaffolds. In such applications, the yarns are usually subjected to cyclic tensile forces and biological tensile stresses. There is a lack of science behind the effect of fatigue on wicking properties of nanofiber yarns and this work aims at exploring this venue. Wicking properties of polyamide 66 nanofiber yarns are investigated by tracing the color change in the yarn structure resulting from pH changes during the capillary rise of distilled water. Results show that applying cyclic loading increases equilibrium wicking height in the Lucus–Washburn equation, which is attributed to changes in the overall pore structure in the cyclic loaded yarn. The likely causes of these changes are studied by scanning electron microscope, which reveals disentangled, more or less aligned and parallel nanofibers with a smaller radius in the nanofibrous structure. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47206.     

The influence of electrospinning parameters on the structural morphology and diameter of electrospun nanofibers

Electrospinning is a simple method of producing nanofibers by introducing electric field into the polymer solutions. We report an experimental investigation on the influence of processing parameters and solution properties on the structural morphology and average fiber diameter of electrospun poly ethylene oxide (PEO) polymer solution. Experimental trials have been conducted to investigate the effect of solution parameters, such as concentration, molecular weight, addition of polyelectrolyte in PEO solution, solvent effect, as well as governing parameter, such as applied voltage. The concentration of the aqueous PEO solution has shown noteworthy influence on the fiber diameter and structural morphology of electrospun nanofibers. At lower concentrations of PEO polymer solution, the fibers showed irregular morphology with large variations in fiber diameter, whereas at higher concentrations, the nanofibers with regular morphology and on average uniform fiber diameter were obtained. We find that the addition of polyelectrolytes, such as sodium salt of Poly acrylic acid (PAA) and Poly allylamine hydrochloride (PAH), increases the conductivity of PEO solutions and thereby decreases the bead formation in electrospun nanofibers. The increase in applied voltage has been found to affect the structural morphology of nanofiber while the addition of ethanol in PEO solution diminishes the bead defects. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Production of Synthetic,Para‐Aramid and Biopolymer Nanofibers by Immersion Rotary Jet‐Spinning

Nanofiber production platforms commonly rely on volatile carrier solvents or high voltages. Production of nanofibers comprised of charged polymers or polymers requiring nonvolatile solvents thus typically requires customization of spinning setup and polymer dope. In severe cases, these challenges can hinder fiber formation entirely. Here, a versatile system is presented which addresses these challenges by employing centrifugal force to extrude polymer dope jet through an air gap, into a flowing precipitation bath. This voltage‐free approach ensures that nanofiber solidification occurs in liquid, minimizing surface tension instability that results in jet breakup and fiber defects. In addition, nanofibers of controlled size and morphology can be fabricated by tuning spinning parameters including air gap length, spinning speed, polymer concentration, and bath composition. To demonstrate the versatility of our platform, para‐aramid (e.g., Kevlar) and biopolymer (e.g., DNA, alginate) nanofibers are produced that cannot be readily produced using standard nanofiber production methods.