Three-dimensional electrospun alginate nanofiber mats via tailored charge repulsions

The formation of 3D electrospun mat structures from alginate-polyethylene oxide (PEO) solution blends is reported. These unique architectures expand the capabilities of traditional electrospun mats for applications such as regenerative medicine, where a scaffold can help to promote tissue growth in three dimensions. The mat structures extend off the surface of the flat collector plate without the need of any modifications in the electrospinning apparatus, are self-supported when the electric field is removed, and are composed of bundles of nanofibers. A mechanism for the unique formations is proposed, based on the fiber-fiber repulsions from surface charges on the negatively charged alginate. Furthermore, the role of the electric field in the distribution of alginate within the nanofibers is discussed. X-ray photoelectron spectroscopy is used to analyze the surface composition of the electrospun nanofiber mats and the data is related to cast films made in the absence of the electric field. Further techniques to tailor the 3D architecture and nanofiber morphology by changing the surface tension and relative humidity are also discussed.     

Preparation and adsorption behavior of aminated electrospun polyacrylonitrile nanofiber mats for heavy metal ion removal

Polyacrylonitrile (PAN) nanofiber mats were prepared by electrospinning and they were further modified to contain amidino diethylenediamine chelating groups on their surface via heterogeneous reaction with diethylenetriamine (DETA). The obtained aminated PAN (APAN) nanofiber mats were evaluated for their chelating property with four types of metal ions, namely Cu(II), Ag(I), Fe(II), and Pb(II) ions. The amounts of the metal ions adsorbed onto the APAN nanofiber mats were influenced by the initial pH and the initial concentration of the metal ion solutions. Increasing the contact time also resulted in a monotonous increase in the adsorbed amounts of the metal ions, which finally reached equilibria at about 10 h for Cu(II) ions and about 5 h for Ag(I), Fe(II), and Pb(II) ions. The maximal adsorption capacities of the metal ions on the APAN nanofiber mats, as calculated from the Langmuir model, were 150.6, 155.5, 116.5, and 60.6 mg g(-1), respectively. Lastly, the spent APAN nanofiber mats could be facilely regenerated with a hydrochloric acid (HCl) aqueous solution.     

Multifunction ZnO/carbon hybrid nanofiber mats for organic dyes treatment via photocatalysis with enhanced solar-driven evaporation

ZnO-based photocatalytic materials have received widespread attention due to their usefulness than other photocatalytic materials in organic dye wastewater treatment. However, its photocatalytic efficiency and surface stability limit further applicability. This paper uses a one-step carbonization method to prepare multifunctional ZnO/carbon hybrid nanofiber mats. The carbonization creates a π-conjugated carbonaceous structure of the mats, which prolongs the electron recovery time of ZnO nanoparticles to yield improved photocatalytic efficiency. Further, the carbonization reduces the fiber diameter of the carbon hybrid nanofiber mats, which quadruples the specific surface area to yield enhanced adsorption and photocatalytic performance. At the same time, the prepared nanofiber mats can increase the evaporation rate of water under solar irradiation to a level of 1.46 kg·m⁻²·h⁻¹ with an efficiency of 91.9%. Thus, the nanofiber mats allow the facile incorporation of photocatalysts to clean contaminated water through adsorption, photodegradation, and interfacial heat-assisted distillation mechanisms.     

Formation of nano-columnar amorphous carbon films via electron beam irradiation

Electrical beam (EB) irradiation is used to chemically modify the amorphous carbon film, a-C:H, which is prepared by the DC magnetron sputtering. The starting a-C:H film has vague columnar structure with lower density intercolumns as predicted by Thornton structure model. The EB-irradiated a-C:H film has fine nano-columnar structure with the average columnar size of 10–15 nm. This size is equivalent to the measured in-plain correlation length by the Raman spectroscopy. Little change in the sp2/sp3 bonding ratio is observed in the columnar matrix before and after EB-irradiation. Increase of sp2/sp3 ratio is noted in the intercolumns of irradiated a-C:H films. No change is detected in the hydrogen content of a-C:H films before and after EB-irradiation: 35 at% hydrogen in a-C:H. Increase of the in-plain density via EB-irradiation, is attributed to the increase of local atomic density in the intercolumns, which is measured by the electron energy zero-loss spectroscopy. This local densification is accompanied with ordering or graphitization in the intercolumns of the EB-irradiated a-C:H film. The nano-columnar a-C:H film modified by EB-irradiation has non-linear elasticity where indentation displacement should be reversible up to 8% of film thickness. Owing to this ordering and densification via EB-irradiation, softening both in stiffness and hardness takes place with increasing the irradiation time.     

New vacuum electron beam processing method based on temperature closed-loop control

This is a novel combination of vacuum electron beam (EB) processing and automatic control theory. The concept of full EB processing method was presented. The digital control system for temperature closed-loop control in EB processing based on scanning track control was realized. The method of controlling electron beam current and heating power by real-time adjusting grid bias voltage is feasible. EB processing methods consist of two stages: heating-up stage and temperature maintaining stage. In the former stage, a fuzzy controller was used to control the temperature rising velocity, the sensitivity of the control was evaluated; in the latter stage, an integral separation PID controller was used to keep the workpiece's temperature constant, ideal static and dynamic performances were obtained. The temperature rising velocity control and the maintaining control compose the full EB processing method, the transition of the two stages is bumpless.     

Hybrid multi-scale epoxy composite made of conventional carbon fiber fabrics with interlaminar regions containing electrospun carbon nanofiber mats

Herein we report the development and evaluation of hybrid multi-scale epoxy composite made of conventional carbon fiber fabrics with interlaminar regions containing mats of electrospun carbon nanofibers (ECNs). The results indicated that (1) the interlaminar shear strength and flexural properties of hybrid multi-scale composite were substantially higher than those of control/comparison composite without ECNs; in particular, the interlaminar shear strength was higher by ∼86%; and (2) the electrical conductivities in both in-plane and out-of-plane directions were enhanced through incorporation of ECNs, while the enhancement of out-of-plane conductivity (∼150%) was much larger than that of in-plane conductivity (∼20%). To validate the data reduction procedure, a new shear stress formula was formulated for composite laminates, which took into account the effect of layup and inter-layers. The study suggested that ECNs could be utilized for the development of high-performance composites, particularly with the improved out-of-plan properties (e.g., interlaminar shear strength).     

Poly(vinyl alcohol)-perfluorinated sulfonic acid nanofiber mats prepared via electrospinning as catalyst

Well-formed poly (vinyl alcohol) (PVA)-perfluorinated sulfonic acid (PFSA) nanofiber mats were fabricated via electrospinning process. Homogenous PFSA-PVA solutions were prepared by mixing PFSA-N, N-dimethylacetamide (DMAc) solution with PVA aqueous solution at different weight ratio. Increasing the weight ratio of PFSA in solution greatly increased the viscosity of the solution and slightly decreased the conductivity, which increased the diameter of the resulting PVA-PFSA nanofiber. The operating parameters such as tip to collector distance (TCD) and flow rate have a limited effect on the morphology of nanofibers, but high flow rate can improve the productivity. Ethyl acetate synthesis catalyzed by PVA-PFSA nanofiber mats was investigated, the results showed that all nanofibers have significantly catalytic activity, but the catalytic efficiency is related to the specific surface of PVA-PFSA nanofibers.     

Vertically oriented carbon nanofiber based nanoelectromechanical switch

We present a proof-of-principle study of a vertically aligned carbon nanofiber switch and study relevant parameters via a model for a static switch. Vertically aligned freestanding carbon nanofibers are produced by plasma-enhanced chemical vapor deposition (PECVD) and their deflection under applied voltage is measured using an optical microscope. The deflection is compared with a static force balance model, which successfully predicts the switching behavior assuming a nanofiber modulus of 40 GPa, which is consistent with independent modulus measurements made in our laboratory. The model is then extended to explore constraints for implementing a vertically aligned nanotube switch into present CMOS process flow. Carbon nanofibers of less than 40 nm in diameter, which may be grown by current PECVD technology, are shown to be acceptable for device integration for current and future CMOS scaling. To accommodate varying tube sizes and architectures, a basic scaling relationship is developed to relate CMOS via parameters and nanofiber characteristics to programming voltage.     

Characterization of electron beam welded AA2024

For aerospace manufacturing, the perseverance for improving performance (high strength to density ratio) and reducing weight and costs has motivated consideration of welding techniques applicable to aluminum alloys. During fusion welding of aluminum alloy (AA) 2024, the avoidance of defects (e.g., porosity, oxides, solidification cracking, undercutting) and the optimization of the microstructure-property characteristics are of critical concern. In this work, AA2024 was electron beam (EB) welded as part of a study to determine the influence of parametric conditions on the characteristics of the weldment to optimize the joining process. Specifically, the evolution in the weld geometry, microstructure and mechanical properties was examined as a function of the process conditions, including beam current, beam focus, beam oscillation, and welding speed. For optimized parametric conditions, microstructural examination of the joints revealed narrow fusion and heat-affected zones comprising of dendritic structures without the occurrence of defects that enabled a maximized joint efficiency.     

Synthesis of gelatin-containing PHBV nanofiber mats for biomedical application

Electrospinning is one of the fabrication method to form ultra-fine fiber in a nano-scale made of synthetic and natural extracellular matrix components for tissue-engineering applications. In this study, a nanofibrous scaffold was obtained by co-electrospinning poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and gelatin in 2,2,2-trifluoroethanol (TFE) at a ratio of 50/50. The resulting fiber diameters were in the range of 400-1,000 nm without any beads. The nanofiber surfaces were characterized by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), electron spectroscopy for chemical analysis (ESCA), and atomic force microscopy. It was found, from cell culture experiments, that NIH 3T3 cells on the PHBV/gelatin nanofibrous scaffold more proliferated than on the PHBV nanofibrous scaffold.     

Preparation and electrochemical properties of carbon nanofiber composite dispersed with silver nanoparticles using polyacrylonitrile and beta-cyclodextrin

A simple one-step method was used for preparing the beta-cyclodextrin/polyacrylonitrile (PAN) nanofibers deposited with silver nanoparticles by electrospinning and followed by the reduction of the Ag+ ions. The nano-composite fibers were stabilized at 280 degrees C in air and activated at 800 degrees C for 1 h in steam/N2. The structures of nano-composite fibers were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), fourier-transform infrared (FTIR) spectroscopy, and X-ray diffraction analysis (XRD). The electrochemical behaviors of the composite of carbon nano-fibers were investigated by cyclic voltammetry and charge/discharge tests.     

含氟聚合物纳米多孔纳米纤维膜的制备

采用"电纺-相分离-沥滤"方法制备了聚(偏氟乙烯-co-六氟丙烯)(PVDF-HFP)以及聚偏氟乙烯(PVDF)纳米多孔纳米纤维膜.首先,将PVDF-HFP或PVDF和致孔剂聚乙烯吡咯烷酮(PVP)混合电纺,得到共混物纳米纤维膜.然后,将纳米纤维膜在水中沥洗出共混物中的PVP,获得纳米多孔纳米纤维膜.用场发射扫描电子显微镜(FESEM)观察水洗前后纤维表面精细结构.结果表明,纳米多孔纳米纤维表面呈多孔结构,孔径数10 nm.PVP的分子量对水洗后纤维表面结构有明显影响.致孔剂含量不同获得的PVDF-HFP纳米多孔纤维膜力学性能相近.     

Carbon nanotube reinforced small diameter polyacrylonitrile based carbon fiber

Polyacrylonitrile (PAN) and PAN/carbon nanotube (CNT) composite (99/1) based carbon fibers with an effective diameter of about 1 μm have been processed using island-in-a-sea bi-component cross-sectional geometry and gel spinning. PAN/CNT (99/1) based carbon fibers processed using this approach exhibited a tensile strength of 4.5 GPa (2.5 N/tex) and tensile modulus of 463 GPa (257 N/tex), while these values for the control PAN-based carbon fiber processed under the similar conditions were 3.2 GPa (1.8 N/tex) and 337 GPa (187 N/tex), respectively. Properties of these 1 μm diameter carbon fibers have been compared to the properties of the larger diameter (>6 μm) PAN and PAN/CNT based carbon fibers.     

Fabrication of the silver/polypyrrole/polyacrylonitrile composite nanofibrous mats

The AgNO₃/polyacrylonitrile hybrid nanofibers were prepared by using electrospinning technique, then the hybrid fibers of AgNO₃/polyacrylonitrile were treated with pyrrole in the boiling toluene medium, finally, the silver/polypyrrole/polyacrylonitrile composite fibrous mats were obtained. The scanning electron microscopy, transmission electron microscopy, X-ray diffraction and Raman spectra were used to characterize the obtained silver/polypyrrole/polyacrylonitrile composite fibrous mats. And the results indicated that the morphologies of the composite fibers were influenced by the content of AgNO₃ in the AgNO₃/polyacrylonitrile fibers. The silver/polypyrrole composite dispersed in the fibrous mats exhibited core-shell structure, and the conductivity of the optimum silver/polypyrrole/polyacrylonitrile composite fibrous mats is relatively high.     

Irradiation of carbon nanotubes with a focused electron beam in the electron microscope

The paper reviews in-situ electron irradiation studies of carbon nanotubes in electron microscopes. It is shown that electron irradiation at high specimen temperature can lead to a variety of structural modifications and new morphologies of nanotubes. Radiation defects such as vacancies and interstitials are created under irradiation, but the cylindrically closed graphene layers reconstruct locally and remain coherent. The generation of curvature in graphene layers with non-hexagonal rings allows us to alter the topology of nanotubes. Several examples of irradiation-induced modifications of single- and multi-wall nanotubes are shown. Conclusions about the mobility of interstitials and vacancies are drawn which are important to explain the behaviour and the properties of nanotubes with an atomic arrangement deviating from the hexagonal network of graphene.     

Ultraflat carbon film electrodes prepared by electron beam evaporation

A facile method for the preparation of thin-film carbon electrodes by electron beam evaporation onto highly doped silicon is presented. The physical and electrochemical properties of these films both before and after postdeposition pyrolysis are investigated. Raman spectroscopy establishes the amorphous structure of the nonpyrolyzed carbon films and confirms the formation of graphitic carbon after pyrolysis at 1000 degrees C. Scanning force microscopy reveals the root-mean-square roughness of nonpyrolyzed films to be approximately 1 A, while pyrolyzed films exhibit an increased roughness of approximately 4 A. The electrochemical behavior of the electrodes resembles glassy carbon, with measured heterogeneous electron-transfer rate constants among the highest measured for thin carbon films. These carbon film electrodes will potentially find applications in such fields as molecular electronics and scanning probe microscopy of adsorbed species.     

Preparation of polyurethane cationomer nanofiber mats for use in antimicrobial nanofilter applications

In this study, polyurethane cationomers (PUCs) containing different amounts of quaternary ammonium groups were synthesized and successfully electrospun into non-woven nanofiber mats for use in antimicrobial nanofilter applications. The PUCs showed very strong antimicrobial activities against Staphylococcus aureus and Escherichia coli. The average diameters of the electrospun PUCs fibers decreased with increasing quaternary ammonium group content due to the increased charge density of the PUC solutions. The PUC nanofibers showed adhesion between nanofibers with various bonding sites, yielding mats with a film-like character and structural integrity.     

Surface modification of steel surfaces by electron beam excited plasma processing

The nitriding performance of low power electron beam excited plasma is investigated by characterizing the surface of nitrided low alloy Cr-Mo steels. In this research, a particular attention was given to the effect of the acceleration voltage and processing time on the composition and hardness of the processed samples. In an attempt to maximize the dissociation of N₂, the acceleration voltages applied in our experiments were set within a range that corresponds to the maximum dissociation cross-section of N₂. The results show that the peak intensity of the alpha Fe observed for the unprocessed sample decreases as the acceleration voltage increases. Moreover, the peak intensities depicting the formation of the nitride compound layers, Fe₄N and Fe₃N phases, increases with the acceleration voltage of the electron beam. Consequently, the surface hardness of the treated low alloy steel was increased by more than two times that of the unprocessed specimen.