Electrospun composite nanofiber yarns containing oriented graphene nanoribbons

Graphene Nanoplatelets-Based Textured Polymeric Fibrous Fabrics for the Next-Generation Devices

Graphene is a 2D crystal composed of carbon atoms in a hexagonal arrangement. From their isolation, graphene nanoplatelets (nCD) have revolutionized material science due to their unique properties, and, nowadays, there are countless applications, including drug delivery, biosensors, energy storage, and tissue engineering. Within this work, nCD were combined with PLA, a widely used and clinically relevant thermoplastic polymer, to produce advanced composite texturized electrospun fabric for the next-generation devices. The electrospinning manufacturing process was set-up by virtue of a proper characterization of the composite raw material and its solution. From the morphological point of view, the nCD addition permitted the reduction of the fiber diameter while the texture allowed more aligned fibers. After that, mechanical features of fabrics were tested at RT and upon heating (40 °C, 69 °C), showing the reinforcement action of nCD mainly in the texturized mats at 40 °C. Finally, mats' degradation in simulated physiological fluid was minimal up to 30 d, even if composite mats revealed excellent fluid-handling capability. Moreover, no toxic impurities and degradation products were pointed out during the incubation. This work gains insight on the effects of the combination of composite carbon-based material and texturized fibers to reach highly performing fabrics.

Nanocomposite pectin fibers incorporating folic acid-decorated carbon quantum dots

Pectin has recently attracted increasing attention as an alternative biomaterial commonly used in biomedical and pharmaceutical fields. It shows several promising properties, including good biocompatibility, health benefits, nontoxicity, and biodegradation. In this research, novel nanocomposite fibers composed of folic acid-decorated carbon dots (CDs) in pectin/PEO matrix were fabricated using the electrospinning technique, which was never reported previously. Nitrogen-doped and nitrogen, sulfur-doped CDs were synthesized with average diameters of 2.74 nm and 2.17 nm using the one-step hydrothermal method, studied regarding their physicochemical, optical, and biocompatibility properties. The relative Quantum yields of N-CDs and N, S doped CDs were measured to be 54.7 % and 30.2 %, respectively. Nanocomposite fibers containing CDs were prepared, and their morphology, physicochemical properties, conductivity, drug release behavior, and cell viability were characterized. The results indicated that CDs improve fibrous scaffolds' tensile strength from 13.74 to 35.22 MPa while maintaining comparable extensibility. Furthermore, by incorporation of CDs in the prepared fibers conductivity enhanced from 8.69 × 10^-9 S·m^-1 to 1.36 × 10^-4 S·m^-1. The nanocomposite fibrous scaffold was also biocompatible with controlled drug release over 212 h, potentially promising tissue regeneration.

State-of-the-art review of advanced electrospun nanofiber yarn-based textiles for biomedical applications

The pandemic of the coronavirus disease 2019 (COVID-19) has made biotextiles, including face masks and protective clothing, quite familiar in our daily lives. Biotextiles are one broad category of textile products that are beyond our imagination. Currently, biotextiles have been routinely utilized in various biomedical fields, like daily protection, wound healing, tissue regeneration, drug delivery, and sensing, to improve the health and medical conditions of individuals. However, these biotextiles are commonly manufactured with fibers with diameters on the micrometer scale (> 10 μm). Recently, nanofibrous materials have aroused extensive attention in the fields of fiber science and textile engineering because the fibers with nanoscale diameters exhibited obviously superior performances, such as size and surface/interface effects as well as optical, electrical, mechanical, and biological properties, compared to microfibers. A combination of innovative electrospinning techniques and traditional textile-forming strategies opens a new window for the generation of nanofibrous biotextiles to renew and update traditional microfibrous biotextiles. In the last two decades, the conventional electrospinning device has been widely modified to generate nanofiber yarns (NYs) with the fiber diameters less than 1000 nm. The electrospun NYs can be further employed as the primary processing unit for manufacturing a new generation of nano-textiles using various textile-forming strategies. In this review, starting from the basic information of conventional electrospinning techniques, we summarize the innovative electrospinning strategies for NY fabrication and critically discuss their advantages and limitations. This review further covers the progress in the construction of electrospun NY-based nanotextiles and their recent applications in biomedical fields, mainly including surgical sutures, various scaffolds and implants for tissue engineering, smart wearable bioelectronics, and their current and potential applications in the COVID-19 pandemic. At the end, this review highlights and identifies the future needs and opportunities of electrospun NYs and NY-based nanotextiles for clinical use.

Tension Sensor Based on Fluorescence Resonance Energy Transfer Reveals Fiber Diameter-Dependent Mechanical Factors During Myelination

Oligodendrocytes (OLs) form a myelin sheath around neuronal axons to increase conduction velocity of action potential. Although both large and small diameter axons are intermingled in the central nervous system (CNS), the number of myelin wrapping is related to the axon diameter, such that the ratio of the diameter of the axon to that of the entire myelinated-axon unit is optimal for each axon, which is required for exerting higher brain functions. This indicates there are unknown axon diameter-dependent factors that control myelination. We tried to investigate physical factors to clarify the mechanisms underlying axon diameter-dependent myelination. To visualize OL-generating forces during myelination, a tension sensor based on fluorescence resonance energy transfer (FRET) was used. Polystyrene nanofibers with varying diameters similar to neuronal axons were prepared to investigate biophysical factors regulating the OL-axon interactions. We found that higher tension was generated at OL processes contacting larger diameter fibers compared with smaller diameter fibers. Additionally, OLs formed longer focal adhesions (FAs) on larger diameter axons and shorter FAs on smaller diameter axons. These results suggest that OLs respond to the fiber diameter and activate mechanotransduction initiated at FAs, which controls their cytoskeletal organization and myelin formation. This study leads to the novel and interesting idea that physical factors are involved in myelin formation in response to axon diameter.

Rapid In Situ Polymerization of Polyacrylonitrile/Graphene Oxide Nanocomposites as Precursors for High-Strength Carbon Nanofibers

Graphene oxide (GO) has been widely used as an additive of polyacrylonitrile (PAN)-based carbon nanofibers (CNFs) to optimize its crystal structure and improve the mechanical performances of nanofibers. However, the homogeneous dispersion of GO nanosheets among entangled PAN molecular chains is always challenging, and the poor dispersion of GO severely limits its positive effects on both the structure and performances of CNFs. Considering this issue, this paper provides for the first time an effective solution to achieve rapid and uniform introduction of GO in PAN-based nanofibers via in situ polymerization, and the optimization of the nanofiber structure by GO is systematically studied in three consecutive stages (polymerization, electrospinning, and carbonization) of the production process. During in situ polymerization, PAN is tightly attached on GO nanosheets to form PAN/GO nanocomposites, and this interaction is maintained throughout the spinning process. Not only the arrangement of PAN molecular chains but also the crystal size of the final turbostratic structure of CNFs is considerably improved by the interaction between PAN and GO. Besides, the direct proof that GO nanosheets promote the crystallization and orientation of the nanofiber matrix is presented. As a result, the tensile strength of CNFs is remarkably increased by 2.45 times with 0.5 wt % addition of GO. In summary, this paper provides a method for efficiently introducing nanoscale additives into PAN-based nanofibers and gives insights into the production of high-performance CNFs with the addition of GO.

Functionalized magnetic composite nano/microfibres with highly oriented van der Waals CrI3 inclusions by electrospinning

This study reports on the synthesis of highly oriented chromium triiodide (CrI₃) magnetic inclusions inside nano/microfibres with a polyethylene oxide matrix, prepared by the electrospinning technique. The structural, microstructural and spectroscopic analysis shows uniformly dispersed CrI₃ nanosized inclusions inside the fibres, presenting a C2/m monoclinic structure at room temperature, where their c-axis is perpendicular to the fibre mat plane and the ab layers are in-plane. Analysis of the magnetic properties show that the samples have a ferromagnetic-paramagnetic phase transition at ∼55-56 K, lower than that of bulk CrI₃. Noticeably, a field-driven metamagnetic transition is observed below ∼45 K, from M versus H curves, when the applied magnetic field is perpendicular to the fibre mat plane, while it is strongly reduced when the field is in-plane. This anisotropic behaviour is attributed to the field-induced changes from antiferromagnetic to ferromagnetic interlayer magnetic moment alignment along the CrI₃ c-axis stacked layers. These CrI₃ electrospun fibres then show an efficient cost-effective route to synthesize magnetic composite fibres with highly oriented van der Walls inclusions, for spintronic applications, taking advantage of their anisotropic 2D layered materials properties.

Fabrication of Multilayered Nanofiber Scaffolds with a Highly Aligned Nanofiber Yarn for Anisotropic Tissue Regeneration

Nanofibrous scaffolds were widely studied to construct scaffold for various fields of tissue engineering due to their ability to mimic a native extracellular matrix (ECM). However, generally, an electrospun nanofiber exhibited a two-dimensional (2D) membrane form with a densely packed structure, which inhibited the formation of a bulk tissue in a three-dimensional (3D) structure. The appearance of a nanofiber yarn (NFY) made it possible to further process the electrospun nanofiber into the desired fabric for specific tissue regeneration. Here, poly(l-lactic acid) (PLLA) NFYs composed of a highly aligned nanofiber were prepared via a dual-nozzle electrospinning setup. Afterward, a noobing technique was applied to fabricate multilayered scaffolds with three orthogonal sets of PLLA NFYs, without interlacing them. Thus the constituent NFYs of the fabric were free of any crimp, apart from the binding yarn, which was used to maintain the integrity of the noobing scaffold. Remarkably, the highly aligned PLLA NFY expressed strengthened mechanical properties than that of a random film, which also promoted the cell adhesion on the NFY scaffold with unidirectional topography and less spreading bodies. In vitro experiments indicated that cells cultured on a noobing NFY scaffold showed a higher proliferation rate during long culture period. The controllable pore structure formed by the vertically arrayed NFY could allow the cell to penetrate through the thickness of the 3D scaffold, distributed uniformly in each layer. The topographic clues guided the orientation of H9C2 cells, forming tissues on different layers in two perpendicular directions. With NFY as the building blocks, noobing and/or 3D weaving methods could be applied in the fabrication of more complex 3D scaffolds applied in anisotropic tissues or organs regeneration.

Bath Electrospinning of Continuous and Scalable Multifunctional MXene-Infiltrated Nanoyarns

Electroactive yarns that are stretchable are desired for many electronic textile applications, including energy storage, soft robotics, and sensing. However, using current methods to produce these yarns, achieving high loadings of electroactive materials and simultaneously demonstrating stretchability is a critical challenge. Here, a one-step bath electrospinning technique is developed to effectively capture Ti₃ C₂ T_x MXene flakes throughout continuous nylon and polyurethane (PU) nanofiber yarns (nanoyarns). With up to ≈90 wt% MXene loading, the resulting MXene/nylon nanoyarns demonstrate high electrical conductivity (up to 1195 S cm^-1 ). By varying the flake size and MXene concentration, nanoyarns achieve stretchability of up to 43% (MXene/nylon) and 263% (MXene/PU). MXene/nylon nanoyarn electrodes offer high specific capacitance in saturated LiClO₄ electrolyte (440 F cm^-3 at 5 mV s^-1 ), with a wide voltage window of 1.25 V and high rate capability (72% between 5 and 500 mV s^-1 ). As strain sensors, MXene/PU yarns demonstrate a wide sensing range (60% under cyclic stretching), high sensitivity (gauge factor of ≈17 in the range of 20-50% strain), and low drift. Utilizing the stretchability of polymer nanofibers and the electrical and electrochemical properties of MXene, MXene-based nanoyarns demonstrate potential in a wide range of applications, including stretchable electronics and body movement monitoring.

Graphene Nanoplatelets for the Development of Reinforced PLA-PCL Electrospun Fibers as the Next-Generation of Biomedical Mats

Electrospun scaffolds made of nano- and micro-fibrous non-woven mats from biodegradable polymers have been intensely investigated in recent years. In this field, polymer-based materials are broadly used for biomedical applications since they can be managed in high scale, easily shaped, and chemically changed to tailor their specific biologic properties. Nonetheless polymeric materials can be reinforced with inorganic materials to produce a next-generation composite with improved properties. Herein, the role of graphene nanoplatelets (GNPs) on electrospun poly-l-lactide-co-poly-ε-caprolactone (PLA-PCL, 70:30 molar ratio) fibers was investigated. Microfibers of neat PLA-PCL and with different amounts of GNPs were produced by electrospinning and they were characterized for their physicochemical and biologic properties. Results showed that GNPs concentration notably affected the fibers morphology and diameters distribution, influenced PLA-PCL chain mobility in the crystallization process and tuned the mechanical and thermal properties of the electrospun matrices. GNPs were also liable of slowing down copolymer degradation rate in simulated physiological environment. However, no toxic impurities and degradation products were pointed out up to 60 d incubation. Furthermore, preliminary biologic tests proved the ability of the matrices to enhance fibroblast cells attachment and proliferation probably due to their unique 3D-interconnected structure.

Synthesis of Active Graphene with Para-Ester on Cotton Fabrics for Antistatic Properties

The excellent electrical properties of graphene provide a new functional finishing idea for fabricating conductive cotton fabrics with antistatic properties. This work develops a novel method for synthesizing active graphene to make cotton fabrics conductive and to have antistatic properties. The graphite was oxidized to graphene oxide (GO) by the Hummers method, and was further acid chlorinated and reacted with the para-ester to form the active graphene (JZGO). JZGO was then applied to cotton fabrics and was bonded to the fiber surface under alkaline conditions. Characterizations were done using FT-IR, XRD and Raman spectroscopy, which indicated that the para-ester group was successfully introduced onto JZGO, which also effectively improved the water dispersibility and reactivity of the JZGO. Furthermore, this study found that the antistatic properties of the fabric were increased by more than 50% when JZGO was 3% by weight under low-humidity conditions. The washing durability of the fabrics was also evaluated.

Graphene Quantum Dot Reinforced Electrospun Carbon Nanofiber Fabrics with High Surface Area for Ultrahigh Rate Supercapacitors

High surface area, good conductivity, and high mechanical strength are important for carbon nanofiber fabrics (CNFs) as high-performance supercapacitor electrodes. However, it remains a big challenge because of the trade-off between the strong and continuous conductive network and a well-developed porous structure. Herein, we report a simple strategy to integrate these properties into the electrospun CNFs by adding graphene quantum dots (GQDs). The uniformly embedded GQDs play a crucial bifunctional role in constructing an entire reinforcing phase and conductive network. Compared with the pure CNF, the GQD-reinforced activated CNF exhibits a greatly enlarged surface area from 140 to 2032 m² g^-1 as well as a significantly improved conductivity and strength of 5.5 and 2.5 times, respectively. The mechanism of the robust reinforcing effect is deeply investigated. As a freestanding supercapacitor electrode, the fabric performs a high capacitance of 335 F g^-1 at 1 A g^-1 and extremely high capacitance retentions of 77% at 100 A g^-1 and 45% at 500 A g^-1. Importantly, the symmetric device can be charged to 80% capacitance within only 2.2 s, showing great potential for high-power startup supplies.

Electrostatic grafting of graphene onto polyamide 6,6 yarns for use as conductive elements in smart textile applications

Electrostatic graphene-grafted conductive yarns were prepared based on a scalable manufacturing method using conventional polyamide 6,6 (PA 6,6) multifilament yarns, common in the textile industry.

Hybrid carbon nanostructured fibers: stepping stone for intelligent textile-based electronics

The journey of smart textile-based wearable technologies first started with the attachment of sensors to fabrics, followed by embedding sensors in apparels. Presently, garments themselves can be transformed into sensors, which demonstrates the tremendous growth in the field of smart textiles. Wearable applications demand flexible materials that can withstand deformation for their practical use on par with conventional textiles. To address this, we explore the potential reasons for the enhanced performance of wearable devices realized from the fabrication of carbon nanostructured fibers with the use of graphene, carbon nanotubes and other two-dimensional materials. This review presents a brief introduction on the fabrication strategies to form carbon-based fibers and the relationship between their properties and characteristics of the resulting materials. The likely mechanisms of fiber-based electronic and storage devices, focusing mainly on transistors, nano-generators, solar cells, supercapacitors, batteries, sensors and therapeutic devices are also presented. Finally, the future perspectives of this research field of flexible and wearable electronics are discussed. The present study supplements novel ideas not only for beginners aiming to work in this booming area, but also for researchers actively engaged in the field of fiber-based electronics, dealing with advanced electronics and wide range of functionalities integrated into textile fibers.

Mussel-Inspired Defect Engineering of Graphene Liquid Crystalline Fibers for Synergistic Enhancement of Mechanical Strength and Electrical Conductivity

Inspired by mussel adhesive polydopamine (PDA), effective reinforcement of graphene-based liquid crystalline fibers to attain high mechanical and electrical properties simultaneously is presented. The two-step defect engineering, relying on bioinspired surface polymerization and subsequent solution infiltration of PDA, addresses the intrinsic limitation of graphene fibers arising from the folding and wrinkling of graphene layers during the fiber-spinning process. For a clear understanding of the mechanism of PDA-induced defect engineering, interfacial adhesion between graphene oxide sheets is straightforwardly analyzed by the atomic force microscopy pull-off test. Subsequently, PDA could be converted into an N-doped graphitic layer within the fiber structure by a mild thermal treatment such that mechanically strong fibers could be obtained without sacrificing electrical conductivity. Bioinspired graphene-based fiber holds great promise for a wide range of applications, including flexible electronics, multifunctional textiles, and wearable sensors.

Reduced Graphene Oxide-Incorporated SnSb@CNF Composites as Anodes for High-Performance Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are promising alternatives to lithium-ion batteries because of the low cost and natural abundance of sodium resources. Nevertheless, low energy density and poor cycling stability of current SIBs unfavorably hinder their practical implementation for the smart power grid and stationary storage applications. Antimony tin (SnSb) is one of the most promising anode materials for next-generation SIBs attributing to its high capacity, high abundance, and low toxicity. However, the practical application of SnSb anodes in SIBs is currently restricted because of their large volume changes during cycling, which result in serious pulverization and loss of electrical contact between the active material and the carbon conductor. Herein, we apply reduced graphene oxide (rGO)-incorporated SnSb@carbon nanofiber (SnSb@rGO@CNF) composite anodes in SIBs that can sustain their structural stability during prolonged charge-discharge cycles. Electrochemical performance results shed light on that the combination of rGO, CNF, and SnSb alloy led to a high-capacity anode (capacity of 490 mAh g^-1  at the 10th cycle) with a high capacity retention of 87.2% and a large Coulombic efficiency of 97.9% at the 200th cycle. This work demonstrates that the SnSb@rGO@CNF composite is a potential and attractive anode material for next-generation, high-energy SIBs.

Nanostructured Electrospun Hybrid Graphene/Polyacrylonitrile Yarns

Novel nanostructured hybrid electrospun polyacrylonitrile (PAN) yarns with different graphene ratios were prepared using liquid crystal graphene oxide (LCGO) and PAN. It was found that the well-dispersed LCGO were oriented along the fiber axis in an electrified thin liquid jet during electrospinning. The graphene oxide sheets were well dispersed in the polar organic solvent, forming nematic liquid crystals upon increasing concentration. Twisted nanofibers were produced from aligned nanofibrous mats prepared by conventional electrospinning. It was found that the mechanical properties of the twisted nanofiber yarns increased even at very low LCGO loading. This research offers a new approach for the fabrication of continuous, strong, and uniform twisted nanofibers which could show promise in developing a novel carbon fiber precursor.

Manganese dioxide nanowires on carbon nanofiber frameworks for efficient electrochemical device electrodes

Hierarchically nanostructured composite electrodes were prepared by the electrodeposition of manganese dioxide nanowires (MnO₂ NWs) with 5–20 nm diameters on electrospun carbon nanofiber (CNF) webs with diameters of 250 and 650 nm.

Superflexibility of graphene oxide

Graphene oxide (GO), the main precursor of graphene-based materials made by solution processing, is known to be very stiff. Indeed, it has a Young's modulus comparable to steel, on the order of 300 GPa. Despite its very high stiffness, we show here that GO is superflexible. We quantitatively measure the GO bending rigidity by characterizing the flattening of thermal undulations in response to shear forces in solution. Characterizations are performed by the combination of synchrotron X-ray diffraction at small angles and in situ rheology (rheo-SAXS) experiments using the high X-ray flux of a synchrotron source. The bending modulus is found to be 1 kT, which is about two orders of magnitude lower than the bending rigidity of neat graphene. This superflexibility compares with the fluidity of self-assembled liquid bilayers. This behavior is discussed by considering the mechanisms at play in bending and stretching deformations of atomic monolayers. The superflexibility of GO is a unique feature to develop bendable electronics after reduction, films, coatings, and fibers. This unique combination of properties of GO allows for flexibility in processing and fabrication coupled with a robustness in the fabricated structure.

Unusually Huge Charge Storage Capacity of Mn3O4-Graphene Nanocomposite Achieved by Incorporation of Inorganic Nanosheets

Remarkable improvement in electrode performance of Mn3O4-graphene nanocomposites for lithium ion batteries can be obtained by incorporation of a small amount of exfoliated layered MnO2 or RuO2 nanosheets. The metal oxide nanosheet-incorporated Mn3O4-reduced graphene oxide (rGO) nanocomposites are synthesized via growth of Mn3O4 nanocrystals in the mesoporous networks of rGO and MnO2/RuO2 2D nanosheets. Incorporation of metal oxide nanosheets is highly effective in optimizing porous composite structure and charge transport properties, resulting in a remarkable increase of discharge capacity of Mn3O4-rGO nanocomposite with significant improvement of cyclability and rate performance. The observed enormous discharge capacity of synthesized Mn3O4-rGO-MnO2 nanocomposite (∼1600 mA·h·g(-1) for the 100th cycle) is the highest value among reported data for Mn3O4-rGO nanocomposite. Despite much lower electrical conductivity of MnO2 than RuO2, the MnO2-incorporated nanocomposite at optimal composition (2.5 wt %) shows even larger discharge capacities with comparable rate characteristics compared with the RuO2-incorporated homologue. This finding underscores that the electrode performance of the resulting nanosheet-incorporated nanocomposite is strongly dependent on its pore and composite structures rather than on the intrinsic electrical conductivity of the additive nanosheet. The present study clearly demonstrates that, regardless of electrical conductivity, incorporation of metal oxide 2D nanosheet is an effective way to efficiently optimize the electrode functionality of graphene-based nanocomposites.

Hierarchical Graphene-Containing Carbon Nanofibers for Lithium-Ion Battery Anodes

We present a method to produce composite anodes consisting of thermally reduced graphene oxide-containing carbon nanofibers (TRGO/CNFs) via electrospinning a dispersion of polyacrylonitrile (PAN) and graphene oxide (GO) sheets in dimethylformamide followed by heat treatment at 650 °C. A range of GO (1-20 wt % GO relative to polymer concentration) was added to the polymer solution, with each sample comprising similar polymer chain packing and subsequent CNF microstructure, as assessed by X-ray diffraction. An increase from 0 to 20 wt % GO in the fibers led to carbonized nonwovens with enhanced electronic conductivity, as TRGO sheets conductively connected the CNFs. Galvanostatic half-cell cycling revealed that TRGO addition enhanced the specific discharge capacity of the fibers. The optimal GO concentration of 5 wt % GO enhanced first-cycle discharge capacities at C/24 rates (15.6 mA g(-1)) 150% compared to CNFs, with a 400% capacity increase at 2-C rates (750 mA g(-1)). We attribute the capacity enhancement to a high degree of GO exfoliation. The TRGO/CNFs also experienced no capacity fade after 200 cycles at 2-C rates. Impedance spectroscopy of the composite anodes demonstrated that charge-transfer resistances decreased as GO content increased, implying that high GO loadings result in more electrochemically active material.

Fabrication of conductive polymer nanofibers through SWNT supramolecular functionalization and aqueous solution processing

Polymeric thin films and nanostructured composites with excellent electrical properties are required for the development of advanced optoelectronic devices, flexible electronics, wearable sensors, and tissue engineering scaffolds. Because most polymers available for fabrication are insulating, one of the biggest challenges remains the preparation of inexpensive polymer composites with good electrical conductivity. Among the nanomaterials used to enhance composite performance, single walled carbon nanotubes (SWNTs) are ideal due to their unique physical and electrical properties. Yet, a barrier to their widespread application is that they do not readily disperse in solvents traditionally used for polymer processing. In this study, we employed supramolecular functionalization of SWNTs with a conjugated polyelectrolyte as a simple approach to produce stable aqueous nanotube suspensions, that could be effortlessly blended with the polymer poly(ethyleneoxide) (PEO). The homogeneous SWNT:PEO mixtures were used to fabricate conductive thin films and nanofibers with improved conductivities through drop casting and electrospinning. The physical characterization of electrospun nanofibers through Raman spectroscopy and SEM revealed that the SWNTs were uniformly incorporated throughout the composites. The electrical characterization of SWNT:PEO thin films allowed us to assess their conductivity and establish a percolation threshold of 0.1 wt% SWNT. Similarly, measurement of the nanofiber conductivity showed that the electrospinning process improved the contact between nanotube complexes, resulting in conductivities in the S m(-1) range with much lower weight loading of SWNTs than their thin film counterparts. The methods reported for the fabrication of conductive nanofibers are simple, inexpensive, and enable SWNT processing in aqueous solutions, and offer great potential for nanofiber use in applications involving flexible electronics, sensing devices, and tissue engineering scaffolds.

Porous Carbon Nanofibers from Electrospun Biomass Tar/Polyacrylonitrile/Silver Hybrids as Antimicrobial Materials

A novel route to fabricate low-cost porous carbon nanofibers (CNFs) using biomass tar, polyacrylonitrile (PAN), and silver nanoparticles has been demonstrated through electrospinning and subsequent stabilization and carbonization processes. The continuous electrospun nanofibers had average diameters ranging from 392 to 903 nm. The addition of biomass tar resulted in increased fiber diameters, reduced thermal stabilities, and slowed cyclization reactions of PAN in the as-spun nanofibers. After stabilization and carbonization, the resultant CNFs showed more uniformly sized and reduced average diameters (226-507 nm) compared to as-spun nanofibers. The CNFs exhibited high specific surface area (>400 m(2)/g) and microporosity, attributed to the combined effects of phase separations of the tar and PAN and thermal decompositions of tar components. These pore characteristics increased the exposures and contacts of silver nanoparticles to the bacteria including Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli, leading to excellent antimicrobial performances of as-spun nanofibers and CNFs. A new strategy is thus provided for utilizing biomass tar as a low-cost precursor to prepare functional CNFs and reduce environmental pollutions associated with direct disposal of tar as an industrial waste.

Nanostructured Electrode Materials for Electrochemical Capacitor Applications

The advent of novel organic and inorganic nanomaterials in recent years, particularly nanostructured carbons, conducting polymers, and metal oxides, has enabled the fabrication of various energy devices with enhanced performance. In this paper, we review in detail different nanomaterials used in the fabrication of electrochemical capacitor electrodes and also give a brief overview of electric double-layer capacitors, pseudocapacitors, and hybrid capacitors. From a materials point of view, the latest trends in electrochemical capacitor research are also discussed through extensive analysis of the literature and by highlighting notable research examples (published mostly since 2013). Finally, a perspective on next-generation capacitor technology is also given, including the challenges that lie ahead.

Polyacrylonitrile fibers containing graphene oxide nanoribbons

Graphene oxide nanoribbon (GONR) made by the oxidative unzipping of multiwalled carbon nanotube was dispersed in dimethylformamide and mixed with polyacrylonitrile (PAN) to fabricate continuous PAN/GONR composite fibers by gel spinning. Subsequently, PAN/GONR composite fibers were stabilized and carbonized in a batch process to fabricate composite carbon fibers. Structure, processing, and properties of the composite precursor and carbon fibers have been studied. This study shows that GONR can be used to make porous precursor and carbon fibers. In addition, GONR also shows the potential to make higher mechanical property carbon fibers than that achieved from PAN precursor only.

Antibacterial continuous nanofibrous hybrid yarn through in situ synthesis of silver nanoparticles: preparation and characterization

Nanofibrous hybrid yarns of polyvinyl alcohol (PVA) and poly-l-lactide acid (PLLA) with the antibacterial activity were prepared that contains 0, 5, 10, 20, and 30 wt.% of silver nanoparticles according to the PVA polymer content. This was performed by electrospinning using distilled water and 2, 2, 2-trifluoroethanol as a solvent for PVA and PLLA respectively, and sodium borohydride was used as a reducing agent. The scanning electron microscope observation confirmed the formation of AgNPs into the PVA nanofiber structure, and they were uniform, bead free, cylindrical and smooth. The diameter of hybrid yarns and their nanofiber component was decreased as the silver nitrate concentration in electrospinning solutions was increased. The differential scanning calorimetry results indicated that the silver nanoparticles can form interactions with polymer chains and decrease the melting enthalpy. The mechanical analysis showed a lower stress and strain at break of the AgNP-loaded nanofibrous hybrid yarns than the unloaded hybrid yarn. However, there wasn't a statistically significant difference between the strain at break of electrospun nanofibrous hybrid yarns. Moreover, the bactericidal efficiency of all loaded samples was over 99.99%.