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Summary: Objectives: The aim of this study was to explore novel polymeric dental restorative composites, in which polyhedral oligomeric silsesquioxane methacrylate monomer (POSS-MA) was used to partially (or completely) replace the commonly used base monomer 2,2′-bis-[4-(methacryloxypropoxy)-phenyl]-propane (Bis-GMA). Methods: The composites were cured (hardened) by photo-initiated free radical polymerization. Mechanical properties (i.e. flexural strength, Young''s modulus and diametral tensile strength) of the composites were tested by a universal mechanical testing machine; photopolymerization induced volumetric shrinkage was measured using a mercury dilatometer; and near infrared (NIR) technique was used to study the degree of methacrylate double bond conversion and photopolymerization rate. Results: Small percentage POSS-MA substitution of Bis-GMA (i.e. mass fraction of 10% or less) in the resin system improved the mechanical properties of the composites; while large amount substitution led to less desirable mechanical properties, lower methacrylate double bond conversion, and slower photopolymerization rate. Statistical examinations showed the maximum flexural strength of the composites occurred when 10% (mass fraction) of Bis-GMA was replaced by POSS-MA, while the highest modulus occurred when the mass fraction of POSS-MA was 2%. Significance: Polymeric dental restorative composites with improved mechanical properties may be designed by judicious choice of monomer (POSS-MA, Bis-GMA and TEGDMA) compositions. [Copyright &y& Elsevier]

Electrospun Nylon 6 nanofibers, in the form of nonwoven fabrics, were impregnated with the dental methacrylate of BIS-GMA/TEGDMA (50/50, mass ratio), to prepare the restorative composite resins. Three-point bending test results indicated flexural strength (FS), elastic modulus (EY) and work of fracture (WOF) of the nanofiber reinforced composite resins were all significantly increased with relatively small amounts of Nylon 6 nanofibers. The addition of 5% (mass fraction) nanofibers improved FS by 36%, EY by 26%, and WOF by 42% over those of the neat resin. SEM observations showed the fracture surface of the composite resin was rough, while the fracture surface of the neat resin was smooth and had large fracture steps. It is suggested that the presence of nanofibers deflected the crack. When the crack finally broke away from the nanofibers, numerous fracture lines and steps were created on the fracture surface, resulting in energy consumption during fracture. [Copyright &y& Elsevier]

Dissolution and reprocessing of exfoliated montmorillonite–nylon 6 (NLS) nanocomposite is demonstrated, illustrating the potential of using polymer nanocomposites as the foundation for fabricating nano- and mesoscopic structures, nanofibers in this case, and thus exerting hierarchical control of morphology and form through the combination of a nanostructured material and a nanoscale fabrication technique. Exfoliated morphology, present in the melt-fabricated NLS nanocomposite, was preserved in cast films and electrospun fibers from hexafluoroisopropanol solution. However, addition of a few percent N,N-dimethyl formamide resulted in agglomeration of the dispersed montmorillonite layers and an overall mixed morphology, demonstrating solvent partitioning and the delicate enthalpic balance necessary to maintain layer dispersion. Fibers and nanofibers of NLS nanocomposite (diameters between 100 and 500 nm) were electrospun from solution, and collected as non-woven fabrics, or as aligned yarns. Together with these cylindrical shaped fibers and nanofibers, ribbon shaped fibers (width∼10 μm, thickness∼100–200 nm) were also found in the products. The electrospinning process resulted in highly aligned montmorillonite layers (layer normal perpendicular to the fiber axis) and nylon 6 crystallites (layer normal parallel to fiber axis). [Copyright &y& Elsevier]

Presents an experimental prototype system designed to establish mutual hybrid fiber/coaxial (HFC) cable television network system that connects several departments in separate campuses. Multiple priority multiple channel local area network protocol; Construction and design of multimedia object-oriented real time enhanced network.

Nanofibers of polymers were electrospun by creating an electrically charged jet of polymer solution at a pendent droplet. After the jet flowed away from the droplet in a nearly straight line, it bent into a complex path and other changes in shape occurred, during which electrical forces stretched and thinned it by very large ratios. After the solvent evaporated, birefringent nanofibers were left. In this article the reasons for the instability are analyzed and explained using a mathematical model. The rheological complexity of the polymer solution is included, which allows consideration of viscoelastic jets. It is shown that the longitudinal stress caused by the external electric field acting on the charge carried by the jet stabilized the straight jet for some distance. Then a lateral perturbation grew in response to the repulsive forces between adjacent elements of charge carried by the jet. The motion of segments of the jet grew rapidly into an electrically driven bending instability. The three-dimensional paths of continuous jets were calculated, both in the nearly straight region where the instability grew slowly and in the region where the bending dominated the path of the jet. The mathematical model provides a reasonable representation of the experimental data, particularly of the jet paths determined from high speed videographic observations. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Lignin-derived ECNF substrates were surface-functionalized with Fe 2 O 3 nanoparticles. • Flexible ECNF/Fe 2 O 3 nanostructures were explored as binder-free LIB anodes. • The ECNF/Fe 2 O 3 (1:1) anode exhibited the highest electrochemical performance. • A new approach for making high-performance binder-free LIB anodes was demonstrated. Abstract To develop high-performance flexible anodes has become an emerging technological demand for the next generation of lithium-ion batteries (LIBs). In this study, flexible substrates consisting of randomly overlaid electrospun carbon nanofibers (ECNFs) with fiber diameters of ∼200 nm and BET specific surface area of ∼583 m2∙g−1 were made from lignin and polyvinyl alcohol by electrospinning followed by stabilization in air and carbonization in argon. After surface-functionalization with Fe 2 O 3 nanoparticles, the resulting flexible ECNF/Fe 2 O 3 nanostructures/electrodes exhibited enhanced lithiation/delithiation performance. Specifically, in lithium-ion half-cells with ∼35 wt% Fe 2 O 3 nanoparticles deposited on ECNF surfaces, the discharge capacities of ∼951 mA∙h∙g−1 in the first cycle and ∼715 mA∙h∙g−1 after 80 cycles were observed. This study presents a new approach for the fabrication of flexible LIB anodes by eliminating commonly used organic binders, metal substrates, and electrode slurries; furthermore, lignin that is a waste byproduct of cellulose industry has been successfully utilized in this approach. [ABSTRACT FROM AUTHOR]

Abstract: A newly developed electrospun polyimide nanofiber mat/membrane along with three commercial 0.22µm microfiltration membranes have been investigated for applications within a renewable biorefinery to complete solid–liquid clarification at two locations: (1) following enzymatic hydrolysis (pre-fermentation) and (2) post-ethanol fermentation. Performance was assessed by evaluating process flux, reversible and irreversible fouling, and the ability to completely remove insoluble solids. Lignin (the primary insoluble solid following enzymatic hydrolysis of a biomass feedstock), yeast cells, and cell debris (following fermentation to ethanol), along with soluble phenolic compounds, all being very hydrophobic in nature, caused extensive fouling, which led to permanent irreversible flux decline for the three commercial membranes. In addition, all three commercial membranes showed a small amount of insoluble solids in the permeate, indicating incomplete removal of the insoluble solids. In contrast, the polyimide nanofiber membrane showed virtually no irreversible fouling and complete retention of insoluble solids, suggesting the tremendous potential for biorefinery applications. [Copyright &y& Elsevier]

This letter reports the fabrication and electrochemical properties of electrospun carbon nanofibers surface-grafted with vapor-grown carbon nanotubes (CNTs) as hierarchical electrodes for supercapacitors. The specific capacitance of the fabricated electrodes was measured up to 185 F/g at the low discharge current density of 625 mA/g; a decrease of 38% was detected at the high discharge current density of 2.5 A/g. The morphology and microstructure of the electrodes were examined by electron microscopy, and the unique connectivity of the hybrid nanomaterials was responsible for the high specific capacitance and low intrinsic contact electric resistance of the hierarchical electrodes. [ABSTRACT FROM AUTHOR]

Abstract: Due to recent advances in the production of biotherapeutics, high capacity, high throughput adsorption media for efficient and economic separation of these medically important products are in great demand. One option that has been evaluated extensively is membrane/mat adsorption. While these media allow for rapid adsorption (due to the decreased internal diffusion) and high throughput processing (due to the open porous structure), they often suffer from low capacity and poor enrichment factors. Herein, we report the fabrication, characterization, and protein adsorption evaluation of an innovative type of membrane/mat adsorption media based on electrospun carbon nanofibers. By surface-functionalization of these nanofibers with a weak acid cation-exchange ligand, the capacity was doubled for binding a model protein (i.e., lysozyme) compared to commercial products; and the capacity value was over 200mg lysozyme per gram of adsorption media. Meanwhile, the thin nanofibers (having diameters of ∼300nm) along with open pores among nanofibers in the mats (having sizes of ∼10–15μm) allowed for higher operating flow rates and lower pressure drops. Furthermore, the incorporation of higher ligand density and the addition of a non-ionic surfactant (i.e., Triton X-305) into the adsorption buffer eliminated the non-specific binding of a competing protein (bovine serum albumin). In combination, this study suggested that electrospun carbon nanofiber adsorption media would provide a promising alternative to packed resin beds for bioseparations. [Copyright &y& Elsevier]

Abstract: Adsorptive membranes have shown great promise for bioseparations as an alternative to packed bed chromatography. Here we evaluate an adsorptive membrane (felt) made from electrospun cellulose acetate nanofibers as an ion-exchange medium for protein separations. The as-electrospun cellulose acetate nanofibers had diameters ranging from tens of nanometers to microns, and the pore sizes within the nanofiber felts were in the range from sub-microns to microns. The cellulose acetate nanofibers were hydrolyzed/deacetylated to yield regenerated cellulose nanofibers, which were then surface functionalized with diethylaminoethyl (DEAE) anion-exchange ligand. SEM imaging, along with FT-IR spectroscopy, and nitrogen content analysis were used to follow each stage of the process. For comparison, a regenerated cellulose microfiber adsorption medium, a commercially available regenerated cellulose adsorptive membrane, and bleached absorbent cotton balls, were all similarly treated and evaluated. The results indicated that the functionalized nanofiber felt had the highest static binding capacity of 40.0mg/g for bovine serum albumin (BSA), compared to 33.5mg/g, 14.5mg/g, and 15.5mg/g for the functionalized commercial membrane, cellulose microfiber medium, and cotton balls, respectively; and the DEAE nanofiber felt had over five times higher permeability of 10mM Tris buffer, pH 8.0 than the DEAE commercial membrane. It was also found that detrimental system dispersion, as determined by calculation of the Peclet number, could be limited by increasing the number of felt layers used for the adsorption bed, without compromising pressure limitations. Dynamic adsorption of BSA, at 10% breakthrough, was higher for the DEAE nanofiber felt (26.9mg/g) compared to the DEAE commercial membrane (20.9mg/g). [Copyright &y& Elsevier]

Carbon nanofibrous nonwoven mats (CNFMs) prepared via electrospinning offer excellent electrical and structural properties and have been used as frameworks for electrodes in electrochemical energy storage devices. However, lack of mechanical strength hinders the broad applications of CNFMs in flexible electronics or industry use. In this work, a rapid stabilization method is developed to prepare high-strength and flexible CNFMs. Studies of the effects of stabilization time on the structures of the stabilized polyacrylonitrile (PAN) nanofibers and the subsequent carbon nanofibers reveal that there is an optimal stabilization time for making high-strength CNFMs. Long stabilization time results in excessive oxidation of the stabilized PAN nanofibers and unwanted defects in the carbon nanofibers. Short stabilization time results in carbon nanofibers with less crystalline structures due to insufficient formation of the thermally stable ladder-like structure. Robust and flexible CNFM with the highest tensile strength of 192.7 MPa is obtained using an optimized total stabilization time of 40 min. To demonstrate the application of the flexible CNFMs, they are fabricated as an electrode framework to load TiO2 nanoparticles without use of organic binders. Lithium ion half-cell based on this electrode demonstrates superior rate cycling performance owning to the porous structure and highly conductive fibrous carbon network of CNFM. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Highly porous HNTs sponges were prepared via a facile while innovative approach. • Short electrospun nanofibers acted as skeleton while PVA acted as binding agent. • The HNTs sponges with nanofibers-to-HNTs ratio of 1:8 possessed the best properties. • (1:8) HNTs sponges showed high performances as dye adsorbent and catalyst support. • This work would expand the applications of 3D sponges made of electrospun nanofibers. Abstract Naturally existing Halloysite nanotubes (HNTs) are promising dye adsorbent and catalyst support; however, to directly use the HNTs powder encounters a practical problem related to separation and regeneration. In this work, highly porous HNTs sponges (with weight ratios of nanofibers-to-HNTs being 1:2, 1:4, 1:6, and 1:8) were prepared via a facile while innovative approach (i.e. , homogenizing the HNTs-PVA-nanofibers suspension, fast freezing, freeze drying, and thermal stabilization). In these sponges, short electrospun polyacrylonitrile and polyimide nanofibers acted as skeletons, supported HNTs, and provided mechanical elasticity and stability, while poly(vinyl alcohol) was utilized as binding agent. The HNTs sponges with nanofibers-to-HNTs weight ratio of 1:8 had low density (43.4 mg/cm3), high porosity (97.9%), large BET surface area (25.0 m2/g), excellent mechanical elasticity, good thermal stability, and high HNTs loading amount (88.9%), and they demonstrated high performances as novel dye adsorbent and catalyst support. This work would not only provide a novel approach for the preparation of HNTs sponges but also expand the applications of three-dimensional sponges/structures made of short electrospun nanofibers. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Electrospun 3D scaffolds with different weight ratios of PCL/PLA were fabricated. • These 3D scaffolds were elastic and possessed interconnected and hierarchical pores. • The PLA80 nanofibrous scaffold exhibited the best overall properties. • They might be highly desired/favorable for the osteogenic differentiation of hMSCs. • Colloids and Surfaces B: Biointerfaces. Abstract Three-dimensional (3D) scaffolds as artificial ECMs have been extensively studied to mimic the critical features of natural ECMs. To develop more clinically relevant 3D scaffolds, electrospun nanofibrous scaffolds with different weight ratios of PCL/PLA (i.e. , 100/0, 60/40, and 20/80) were fabricated via the thermally induced (nanofiber) self-agglomeration (TISA) method. The hypothesis was that, with the weight ratio increase of stiffer and more bioactive PLA in the 3D PCL/PLA blend scaffolds, the osteogenic differentiation of human mesenchymal stem cells (hMSCs) would be enhanced. The results indicated that, all of the 3D scaffolds were elastic/resilient and possessed interconnected and hierarchical pores with sizes from sub-microns to ∼300 μm; therefore, the morphological structures of these scaffolds were similar to those of natural ECMs. The PLA80 scaffolds exhibited the best overall properties in terms of density, porosity, water absorption capacity, mechanical properties, bioactivity, and cell viability. Furthermore, with increasing the PLA weight ratio, the alkaline phosphatase (ALP) activity, calcium content, and gene expression level were also increased, probably due to the improved stiffness/bioactivity of scaffold. Hence, the novel 3D electrospun PLA80 nanofibrous scaffold might be desired/favorable for the osteogenic differentiation of hMSCs. [ABSTRACT FROM AUTHOR]

To develop tissue engineering scaffolds that possess similar morphological structures to natural extracellular matrices (ECMs) is a major technological challenge. Herein, the feasibility of utilizing polycaprolactone (PCL) as biocompatible and biodegradable binding agent to fabricate electrospun three-dimensional (3D) scaffolds has been demonstrated. The obtained 3D scaffolds are soft while elastic, and they possess interconnected and hierarchically structured pores with sizes in the range from sub-microns to hundreds of microns; hence, they are morphologically similar to natural ECMs thus well suited for cell functions and tissue formation. It is envisioned that various thermoplastic polymers could be fabricated into 3D nanofibrous scaffolds/structures by first making blend nanofibers with PCL followed by processing via the thermally induced (nanofiber) self-agglomeration (TISA) method and finally being thermally stabilized, and the resulting electrospun 3D nanofibrous scaffolds/structures might to be useful for a variety of applications (particularly those related to tissue engineering). [ABSTRACT FROM AUTHOR]

In this study, an innovative nano-material was prepared, which was ultilized to removal of heavy metal ions from wastewater. Polyacrylonitrile/cellulose acetate (PAN/CA) composite nanofibrous membranes were generated by the electronspinning technique first, and then amidoxime ployarcylonitrile/regenerate cellulose (AOPAN/RC) composite nanofibrous membranes were prepared by combining hydrolysis and amidoximation modification. The modification of composite nanofibers (AOPAN/RC) were consequently used in heavy metal ions adsorption. The characterizations of various different nanofibers were analyzed using scanning electron microscopy, Fourier transform infrared spectroscopy, surface area and pore size distribution analyzer and energy dispersive X-ray spectroscopy. Meantime, the adsorption equilibrium studies were studied. In addition, the saturation adsorption amount of nanofibrous membranes (at 25 °C) for Fe(III), Cu(II) and Cd(II) of 7.47, 4.26 and 1.13 mmolg −1 , respectively. The effects of pH value of solution, adsorption time and ions concentration on adsorption capacity were also investigated. Furthermore, the composite nanofibrous membranes after five times consecutive adsorption and desorption tests, the desorption rate of the Fe(III), Cu(II) and Cd(II) mental ions maintained more than 80% of their first desorption rate, AOPAN/RC composite nanofibrous reflected excellent resuability. [ABSTRACT FROM AUTHOR]

The aim of this study is to develop high-performance carrier/support for immobilization of enzyme ( e.g. , laccase). The hypothesis is that electrospun blend nanofiber membrane consisting of polyurethane (PU), amidoxime polyarcylonitrile (AOPAN), and β-cyclodextrin (β-CD) would possess the desired morphological, mechanical, and chemical properties for the coordination/chelation of Fe(III) ions and the subsequent immobilization of laccase molecules. To test this hypothesis, the Fe(III)-PU/AOPAN/β-CD nanofiber membrane has been prepared and characterized first; thereafter, the membrane’s performance as laccase immobilization carrier/support has been investigated. The results indicate that the prepared nanofiber membrane can efficiently immobilize laccase, and it also possesses excellent morphological/mechanical properties and regeneration capability. In specific, the membrane’s immobilization amount of laccase reaches a high value of 186.34 mg/g; moreover, the immobilized laccase exhibits reasonably high catalytic activity and significantly improved resistance against the variations of temperature and p H value than the free laccase. Additionally, thermal stability, storage stability, and reusability of the immobilized laccase are substantially improved; and the membrane carrier/support can also be regenerated/reused for several times. Therefore, the developed electrospun PU/AOPAN/β-CD blend nanofiber membrane is a high-performance carrier/support for efficient and reusable immobilization of laccase. [ABSTRACT FROM AUTHOR]

Three-dimensional, cost-effective, and renewable/recyclable absorbent materials with high capacities on absorption of organic compounds are urgently in demand. Herein, a facile while innovative approach is reported to develop ultralight electrospun cellulose sponge (UECS). The prepared UECS exhibits super-high absorption capacity (up to 232 times of its own weight) towards absorption of organic compounds due to high porosity (99.57%), low density (6.45 mg/cm 3 ), and hydrophobic surface feature (with water contact angle of 141.2°). Furthermore, the UECS is mechanically robust thus can be readily cut into different shapes; and it also possesses excellent stability against various organic compounds. Intriguingly, upon absorption of an organic compound, the shape-stable UECS organic gel can be formed. Hence, the developed UECS would be promising as environmental friendly absorbent on high-performance separation of organic compounds from aqueous systems; while the UECS organic gel could be utilized for the applications such as drug delivery and sensor. [ABSTRACT FROM AUTHOR]

Mechanically flexible electrospun carbon nanofiber (ECNF) mats were prepared by electrospinning mixtures containing hydrothermal liquefaction (HTL) derived biochar and polyacrylonitrile (PAN) into precursor nanofiber mats followed by stabilization in air and then carbonization in argon. The resulting ECNF mats well retained the overall morphological structures of their precursors ( i.e. , biochar/PAN composite nanofiber mats), and the carbon nanofibers showed the enlarged specific surface area upon the increase of biochar loading amount in precursor nanofibers. The ECNFs (4/10), which were derived from composite nanofibers with the biochar/PAN weight ratio being 4/10, had the fiber diameters of ∼350 nm and the BET specific surface area of 30.12 m 2 ·g −1 ; and these ECNF mats exhibited the highest gravimetric capacitance of 37.60 F·g −1 at the current density of 500 mA·g −1 . Hence, the prepared ECNF mats could potentially be utilized for energy related ( e.g. , supercapacitor) applications. [ABSTRACT FROM AUTHOR]

In this study, nine types of polyacrylonitrile (PAN) nanofibrous membranes with varied fiber diameters and different membrane porosities are prepared by electrospinning followed by hot-pressing. Subsequently, these membranes are explored as Li-ion battery (LIB) separators. The impacts of fiber diameter and membrane porosity on electrolyte uptake, Li + ion transport through the membrane, electrochemical oxidation potential, and membrane performance as LIB separator (during charge/discharge cycling and rate capability tests of a cathodic half-cell) have been investigated. When compared to commercial Celgard PP separator, hot-pressed electrospun PAN nanofibrous membranes exhibit larger electrolyte uptake, higher thermal stability, wider electrochemical potential window, higher Li + ion permeability, and better electrochemical performance in LiMn 2 O 4 /separator/Li half-cell. The results also indicate that the PAN-based membrane/separator with small fiber diameters of 200–300 nm and hot-pressed under high pressure of 20 MPa surpasses all other membranes/separators and demonstrates the best performance, leading to the highest discharge capacity (89.5 mA h g −1 at C/2 rate) and cycle life (with capacity retention ratio being 97.7%) of the half-cell. In summary, this study has revealed that the hot-pressed electrospun PAN nanofibrous membranes (particularly those consisting of thin nanofibers) are promising as high-performance LIB separators. [ABSTRACT FROM AUTHOR]

A technique of electro-spinning/netting (ESN) has been investigated to prepare poly(vinyl alcohol) (PVA) nanofibrous membrane with unique morphological structure of nano-fiber/net (NFN). The prepared NFN membrane consists of both common electrospun nanofibers (with diameters in hundreds of nanometers) and two-dimensional nano-nets (with nanofibril diameters smaller than 50 nm). It is revealed that formic acid has dual effects ( i.e. , as solvent and crosslinking agent) on solution properties and membrane morphological structures, and systematic analyses on rheological properties of three different 10 wt% PVA solutions with solvents being water, formic acid, and their 1/1 (wt./wt.) mixture have been conducted. Results indicate that the molecular interactions (particularly hydrogen bonding) among water, formic acid, and PVA macromolecular chains, as well as the acetal formation ( i.e. , chemical crosslinking), have significant influences on macromolecular conformation, solution rheological properties, and morphological structure of membranes. The acetal formation, which leads to improved tensile strength of PVA NFN membrane, has been verified by FT-IR and DSC. Additionally, the PVA NFN membrane has been assembled into a gravity-driven filtration device; and the membrane exhibits high rejection ratio (> 99%) for polystyrene microspheres (with diameters of ~ 0.2 μm) and high water flux (3773 L/m 2 ∙ h) under the pressure of 40 kPa. [ABSTRACT FROM AUTHOR]

Electrospun nanofiber membranes (with varied fiber diameters and different membrane porosities and thicknesses) have been explored as innovative microfiltration media for the highly efficient and cost-effective removal of contaminations with particle sizes of 0.2 μm (even 0.1 μm) from water. For the first time, the membrane porosity has been judiciously adjusted/controlled by a facile hot-pressing method; and the relationships between membrane properties and microfiltration performances have been systematically investigated. Upon the hot-pressing process, the membrane porosity could be significantly decreased from ∼86% to as low as ∼34%, further leading to the substantial increase of rejection fraction from 0% to ∼100% for 0.2 μm particles; moreover, some of these membranes (consisting of small diameter nanofibers) that were hot-pressed with relatively high pressure could even reject all of 0.1 μm particles. As compared to conventional microfiltration media, these membranes exhibited significantly higher flux values and substantially lower degrees of fouling without distinguishably sacrificing particle rejection fractions. For example, the rejection fraction and permeate flux value of one membrane (fiber diameters: ∼150–250 nm, membrane porosity: ∼40%) were ∼99.3% and ∼71.2·L·h −1 ·m −2 ·psi −1 at 13 mL volume fed, respectively, indicating that electrospun nanofiber membranes might be highly promising for microfiltration applications (particularly water purification). [ABSTRACT FROM AUTHOR]

Nanofibrous scaffolds that are morphologically/structurally similar to natural ECM are highly interested for tissue engineering; however, the electrospinning technique has the difficulty in directly producing clinically relevant 3D nanofibrous scaffolds with desired structural properties. To address this challenge, we have developed an innovative technique of thermally induced nanofiber self-agglomeration (TISA) recently. The aim of this work was to prepare ( via the TISA technique) and evaluate 3D electrospun PCL/PLA blend (mass ratio: 4/1) nanofibrous scaffolds having high porosity of ∼95.8% as well as interconnected and hierarchically structured pores with sizes from sub-micrometers to ∼300 μm for bone tissue engineering. The hypothesis was that the incorporation of PLA (with higher mechanical stiffness/modulus and bioactivity) into PCL nanofibers would significantly improve human mesenchymal stem cells (hMSCs) osteogenic differentiation in vitro and bone formation in vivo. Compared to neat PCL-3D scaffolds, PCL/PLA-3D blend scaffolds had higher mechanical properties and in vitro bioactivity; as a result, they not only enhanced the cell viability of hMSCs but also promoted the osteogenic differentiation. Furthermore, our in vivo studies revealed that PCL/PLA-3D scaffolds considerably facilitated new bone formation in a critical-sized cranial bone defect mouse model. In summary, both in vitro and in vivo results indicated that novel 3D electrospun PCL/PLA blend nanofibrous scaffolds would be strongly favorable/desired for hMSCs osteogenic differentiation and cranial bone formation. [ABSTRACT FROM AUTHOR]

Aromatic polyimides (PIs) are high-performance polymers with rigid heterocyclic imide rings and aromatic benzene rings in their macromolecular backbones. Owing to excellent mechanical properties and thermal stability, as well as readily adjustable molecular structures, PIs have been widely adopted for many applications related to electronics, aerospace, automobile, and other industries. In recent years, PI fibers prepared by electrospinning of polyamic acid (PAA) precursor nanofibers followed by imidization (commonly known as electrospun PI nanofibers) have attracted growing interests. Herein, the preparation, evaluation, and application of electrospun PI nanofibers are reviewed. PI polymers and the electrospinning technique are introduced first followed by the preparation of electrospun nanofibers of homo-PI, co-PI, blend-PI, and PI composite. Subsequently, the mechanical and thermal properties of electrospun PI nanofibers are presented; in particular, the mechanical properties of individual electrospun PI nanofibers are highlighted. Thereafter, various applications of electrospun PI nanofibers are outlined, including reinforcement of composites, Li-ion battery separators, fuel cell proton exchange membranes, sensors, microelectronics, high-temperature filtration media, super-hydrophobic PI nanofibers, and PI-based carbon nanofibers. In the final section of conclusions and perspectives, future research endeavors and high-value applications of electrospun PI nanofibers are discussed. [ABSTRACT FROM AUTHOR]

The aim of this study is to explore innovative materials for the development of next-generation supercapacitor electrodes. The hypothesis is that, upon the surface-decoration with appropriate amount of MnO 2 nanowhiskers, freestanding and highly graphitic electrospun carbon nanofiber (ECNF) mats (with fiber diameters of ∼200 nm and BET specific surface areas of ∼583 m 2 g −1 ) derived from a natural product of lignin would be binder-free supercapacitor electrodes with high performance. To test the hypothesis, the ECNF mats have been prepared first; thereafter, the acquired ECNF mats have been surface-decorated with varied amounts of MnO 2 nanowhiskers to prepare three types of ECNF/MnO 2 mats. The morphological and structural properties of ECNF and ECNF/MnO 2 mats are characterized by SEM, TEM and XRD, the weight percentages of MnO 2 nanowhiskers in three ECNF/MnO 2 mats are determined by thermal gravimetric analysis; while the electrochemical performance of each mat/electrode is evaluated by cyclic voltammetry, galvanostatic charge/discharge method, and electrochemical impedance spectroscopy. This study reveals that, all of the three ECNF/MnO 2 mats/electrodes have significantly enhanced electrochemical performances compared to the ECNF mat/electrode; while the ECNF/MnO 2 (1:1) mat/electrode exhibits the highest gravimetric capacitance of 83.3 F g −1 , energy density of 84.3 W h kg −1 , and power density of 5.72 kW kg −1 . [ABSTRACT FROM AUTHOR]

The aim of this study was to prepare melt electrospun poly(L-lactic acid) (PLLA) fibers with relatively high macromolecular orientation and crystallinity (thus relatively high mechanical properties) for future biomedical studies. Upon melt electrospinning PLLA fibers in hot airflow, the elevated environmental temperature was acquired; and the filaments/fibers could be stretched by the hot airflow and/or for a prolonged period of time. The effects of speed and temperature of hot airflow on macromolecular orientation and crystallinity of PLLA fibers were investigated, and the results indicated that the PLLA fibers with higher degrees of macromolecular orientation and crystallinity could be prepared under the condition of hotter airflow having faster speed. [ABSTRACT FROM AUTHOR]

The ultimate goal of this research is to develop continuous carbon nanofibers with superior mechanical strength. The hypothesis is that aligned and stretched polyacrylonitrile (PAN) copolymer nanofibers may be an innovative type of precursor, because the nanofibers possess high degrees of morphological and structural perfections; and due to size effect ( i.e. , the nanofibers are ~ 20 times thinner than the conventional microfibers), the formation of structural heterogeneities ( e.g. , sheath/core structure) can be effectively prevented/mitigated. In this study, a bundle consisting of aligned PAN copolymer nanofibers was first prepared by electrospinning (with nanofibers collected by a flowing water system) followed by 3 times stretching; the oxidative stabilization of precursor nanofiber bundle was then investigated. Compared to conventional microfibers, electrospun nanofibers had smoother surface, higher density, and higher degrees of crystallinity and macromolecular orientation. As a result, the activation energy for cyclization of nitrile groups was higher; nevertheless, the diffusion of oxygen molecules was easier and the distribution of oxygen was more uniform particularly when the stabilization temperature was 240 °C or higher. Such a situation led to the reduction of activation energy for oxidative dehydrogenation, facilitated the structural conversion into aromatic and supra-molecular structures, and also prevented the formation of sheath/core structure. [ABSTRACT FROM AUTHOR]

A flexible felt consisting of electrospun anatase TiO 2 and amorphous SiO 2 nanofibers together with anatase TiO 2 nanoparticles was explored as an innovative anode material for lithium ion battery. The electrochemical characterization of the half-cell of the composite felt ( vs. Li metal) showed that the felt had a high initial discharge capacity of 170 mAh/g and an excellent rate capability; furthermore, the capacity was retained at 84% of initial value after 100 cycles at fast charge/discharge rate of 1 A/g. The binder-free composite felt maintained superior flexibility/robustness and good electrochemical performance after 5,000 continuous bending cycles. [ABSTRACT FROM AUTHOR]

The aim of this study was to explore the development of lead-free X-ray shielding rubber nanocomposites with improved mechanical properties. In specific, gadolinium oxide (Gd[sub 2]O[sub 3]) nano-flakes (with thickness of ~20 nm and sizes being tens of nanometers) were first prepared via the co-precipitation spray drying method; subsequently, the prepared Gd[sub 2]O[sub 3] nano-flakes were uniformly dispersed into nitrile butadiene rubber (NBR) followed by vulcanization for the fabrication of flexible and lightweight X-ray shielding nanocomposites. Compared with the Gd[sub 2]O[sub 3]/NBR conventional composites made from a Gd[sub 2]O[sub 3] powder with particle sizes in the range of 5-20 µm, the fabricated Gd[sub 2]O[sub 3]/NBR nanocomposites exhibited significantly higher tensile strength, Shore A hardness, and X-ray shielding properties while the rubbery characteristic (i.e. elasticity) was retained. [ABSTRACT FROM AUTHOR]

Electrospun polyacrylonitrile (PAN) copolymer nanofibers (particularly those after the post-spinning stretching process) are expected to be an innovative type of precursors for making continuous carbon nanofibers with superior mechanical properties. In this study, three types of unidirectionally aligned PAN-based nanofibers including homo-PAN, binary-PAN (a PAN copolymer with itaconic acid units), and ternary-PAN (a PAN copolymer with itaconic acid and methyl acrylate units) were prepared by the electrospinning technique; thereafter, the nanofibers (in the form of bundles) were stretched into 3 times of their original lengths in hot water at 97 °C. The effects of chemical composition and post-spinning stretching process on morphological, structural, and thermo-chemical properties of these precursor nanofibers were investigated. The results indicated that, the stretched electrospun binary-PAN nanofibers possessed the most desired thermo-chemical properties, macromolecular regularity, crystal and macromolecule orientations, and dimensional stability; and thus they are suitable for the development of high-performance carbon nanofibers. [ABSTRACT FROM AUTHOR]

Electrospun SiO 2 nanofibers (in the form of overlaid mat) absorbed with fatty acid eutectics were studied to fabricate form-stable phase change materials (PCMs) for storage and retrieval of thermal energy. The SiO 2 nanofibers were made via electrospinning of precursor nanofibers followed by pyrolysis, while four fatty acid eutectics of capric acid–lauric acid (CA–LA), capric acid–myristic acid (CA–MA), capric acid–palmitic acid (CA–PA), and capric acid–stearic acid (CA–SA) were studied as the model PCMs. The morphological structure, absorption capacity, thermal energy storage property, and thermal energy storage/retrieval rates of the developed form-stable composite PCMs were characterized by scanning electron microscopy, differential scanning calorimetry, and measurement of melting/freezing time. The results indicated that the electrospun SiO 2 nanofibrous mats were highly porous and capable of absorbing a large amount of PCMs, and the absorption capacities of SiO 2 nanofibers for the four fatty acid eutectics ( i.e. , CA–LA, CA–MA, CA–PA and CA–SA) were 82.0, 83.7, 84.2, and 83.1%, respectively. The experimental values of heat enthalpy for the fabricated composite PCMs were slightly lower than the corresponding theoretical values, whereas there were no appreciable changes on phase transition temperatures. In comparison with fatty acid eutectics (without supporting materials), the melting and freezing time periods of the corresponding CA–LA/SiO 2 , CA–MA/SiO 2 , CA–PA/SiO 2 , CA–SA/SiO 2 were shortened by 28.6% and 30.8%, 20.0% and 44.4%, 62.5% and 50.0%, and 50.0% and 33.3%, respectively. This study suggested that the fabricated form-stable composite PCMs possessed appropriate phase transition temperatures and high heat enthalpy values; hence, they would have potential applications for low-temperature thermal energy storage/retrieval. [ABSTRACT FROM AUTHOR]

CNTs were grown on iron-modified mesoporous graphitized carbon aerogel (GCA) at 700 °C, 800 °C and 900 °C using catalytic CVD method. Resultant CNT/GCA materials composition, morphology and structure were studied to understand their electrochemical stability and performance for oxygen reduction reaction (ORR) in acidic medium. CNT growth was increased from 700 °C to 800 °C, dominated by MWCNTs formation. In the temperature range from 800 °C to 900 °C, the growth was reduced by forming nanofiber/nanoribbon structures accompanied by MWCNTs. Mesoporosity of CNT/GCA composites declined at 700 °C and 800 °C due to MWCNT formation. However, CNT/GCA growth at 900 °C improved mesoporosity with substantial increase in pore volume (∼3 times of GCA) due to formation of nanofibers and nanoribbons. The structure of CNT/GCA materials revealed nitrogen doping and dispersion of FeN x phase. A synergistic contribution of CNT/GCA material structure and morphology to ORR activity was noticed. Among CNT/GCA materials, CNT-800 °C/GCA material showed ORR activity at lowest onset potential of 0.5 V. However, CNT-900 °C/GCA exhibits the highest ORR mass activity, with a half-wave onset potential difference of 120 mV with Pt (40 wt.%)/C. Moreover, CNT-900 °C/GCA demonstrates high selectivity (>3.97) to 4 electron ORR path, excellent methanol tolerance and electrochemical durability which makes it a potential DMFC cathode candidate. [ABSTRACT FROM AUTHOR]

Three types of carbon nanoscale reinforcements (CNRs) including the shortened electrospun carbon nanofibers (ECNFs, with diameters and lengths of ~200 nm and ~15 µm, respectively), carbon nanofibers (CNFs), and graphite nanofibers (GNFs) were electrophoretically deposited on carbon fiber (CF) fabrics for the fabrication of hybrid multi-scale epoxy composites. The results indicated that the electrophoretic deposition (EPD) of CNRs onto CF fabrics led to substantial improvements on mechanical properties of hybrid multi-scale epoxy composites; in particular, the hybrid multi-scale epoxy composite containing surface-functionalized ECNFs (with amino groups) exhibited the highest mechanical properties. The study also indicated that some agglomerates of CNRs (particularly GNFs) could form during the EPD process, which would decrease mechanical properties of the resulting composites. Additionally, the reinforcement mechanisms were investigated, and the results suggested that continuous (or long) ECNFs would outperform short ECNFs on the reinforcement of resin-rich interlaminar regions in the composites. [ABSTRACT FROM AUTHOR]

Highlights: [•] Electrospun carbon nanofiber mats were prepared from a natural product of lignin. [•] The freestanding mats were flexible with BET specific surface area of ∼583 m2/g. [•] The mats were surface-deposited with Ag nanoparticles via the scCO2 method. [•] Novel electrocatalytic systems of Ag/ECNFs exhibited high activities towards ORR. [ABSTRACT FROM AUTHOR]

Abstract: A hybrid mat consisting of anatase-phase TiO2 nanofibers (~75wt.%) and structurally amorphous SiO2 nanofibers (~25wt.%) was prepared for the first time by electrospinning with dual spinnerets followed by pyrolysis in air at 500°C. Unlike many other TiO2 nanostructures, the TiO2/SiO2 hybrid mat was mechanically flexible; after being sensitized with N719 dye, the dye-sensitized mat was then assembled as a photo-detector for visible light. The fabricated photo-detector was also flexible; it exhibited excellent sensitivity and reproducibility/reversibility under varied light intensities, and it also showed high performance under the bending condition. Additionally, it is envisioned that the reported method could be a general approach for the preparation of flexible hybrid mats with different electrospun nanofibers of semiconducting metal oxides (e.g., TiO2 and ZnO) for various applications. [Copyright &y& Elsevier]

Abstract: For the first time, electrospun carbon nanofibers (ECNFs, with diameters and lengths of ∼200nm and ∼15μm, respectively) were explored for the preparation of nano-epoxy resins; and the prepared resins were further investigated for the fabrication of hybrid multi-scale composites with woven fabrics of conventional carbon fibers via the technique of vacuum assisted resin transfer molding (VARTM). For comparison, vapor growth carbon nanofibers (VGCNFs) and graphite carbon nanofibers (GCNFs) were also studied for making nano-epoxy resins and hybrid multi-scale composites. Unlike VGCNFs and GCNFs that are prepared by bottom-up methods, ECNFs are produced through a top-down approach; hence, ECNFs are more cost-effective than VGCNFs and GCNFs. The results indicated that the incorporation of a small mass fraction (e.g., 0.1% and 0.3%) of ECNFs into epoxy resin would result in substantial improvements on impact absorption energy, inter-laminar shear strength, and flexural properties for both nano-epoxy resins and hybrid multi-scale composites. In general, the reinforcement effect of ECNFs was similar to that of VGCNFs, while it was higher than that of GCNFs. [Copyright &y& Elsevier]

Abstract: Mechanically flexible mats consisting of electrospun carbon nanofibers (ECNFs) were prepared by first electrospinning aqueous mixtures containing a natural product of alkali lignin together with polyvinyl alcohol (PVA) into composite nanofiber mats followed by stabilization in air and carbonization in an inert environment. Morphological and structural properties, as well as specific surface area, total pore volume, average pore size, and pore size distribution, of the lignin-based ECNF mats were characterized; and their electrochemical performances (i.e., capacitive behaviors) were evaluated by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. The lignin-based ECNF mats exhibited outstanding performance as free-standing and/or binder-free electrodes of supercapacitors. For example, the ECNFs made from the composite nanofibers with mass ratio of lignin/PVA being 70/30 (i.e., ECNFs (70/30)) had the average diameter of ∼100 nm and the Brunauer–Emmett–Teller (BET) specific surface area of ∼583 m2 g−1. The gravimetric capacitance of ECNFs (70/30) electrode in 6 M KOH aqueous electrolyte exhibited 64 F g−1 at current density of 400 mA g−1 and 50 F g−1 at 2000 mA g−1. The ECNFs (70/30) electrode also exhibited excellent cycling durability/stability, and the gravimetric capacitance merely reduced by ∼10% after 6000 cycles of charge/discharge. [Copyright &y& Elsevier]

Carbon nanofibers with diameters that fall into submicron and nanometer range have attracted growing attention in recent years due to their superior chemical, electrical, and mechanical properties in combination with their unique 1D nanostructures. Unlike catalytic synthesis, electrospinning polyacrylonitrile (PAN) followed by stabilization and carbonization has become a straightforward and convenient route to make continuous carbon nanofibers. This paper is a comprehensive and state-of-the-art review of the latest advances made in development and application of electrospun PAN-based carbon nanofibers. Our goal is to demonstrate an objective and overall picture of current research work on both functional carbon nanofibers and high-strength carbon nanofibers from the viewpoint of a materials scientist. Strategies to make a variety of carbon nanofibrous materials for energy conversion and storage, catalysis, sensor, adsorption/separation, and biomedical applications as well as attempts to achieve high-strength carbon nanofibers are addressed. [ABSTRACT FROM AUTHOR]

A series of counter electrodes (CEs) for dye-sensitized solar cells (DSSCs) was fabricated using different weight ratios of electrospun carbon nanofibers (ECNs) and carbon nanoparticles (CNPs). The conductivity of neat ECN was 838 S/m, which is more than twice than that of neat CNP, and the bulk resistance of CEs decreased as the ECN ratios increased in the composite, leading to lower transport resistance in the CEs. However, as the concentration of CNPs increased, the surface area of CEs also improved because CNPs have a much smaller dimension than ECNs, leading to higher electrocatalytic property. The CEs with higher ratio of CNPs possessed several superiorities compared with those with higher ratio ECNs, such as larger surface area for triiodide reduction, faster reaction rate, and less charge transfer resistance at the interface of CE and electrolyte. Evidenced from cyclic voltammograms and electrochemical impedance spectroscopy, the devices with higher ratio CNPs exhibited lower Nernst diffusion impedance and higher efficiency electrocatalytic performance than those with higher ratio ECNs. When the materials of CE switched from neat ECN to those with a higher concentration of CNPs, the DSSC fill factor, current density, and efficiency were improved. [ABSTRACT FROM PUBLISHER]

Abstract: Two types of electrospun TiO2 nanotubes were prepared by the technique of co-axial electrospinning followed by pyrolysis of electrospun core–shell nanofibers at 500°C. The SEM/TEM images showed that both types of TiO2 nanotubes were polycrystalline with diameters of ~400–500nm and crystallite/grain sizes of ~10nm. The XRD results indicated that the TiO2 nanotubes possessed the anatase crystalline phase/structure. Upon sonication, both types of TiO2 nanotubes could be shortened; whereas the average lengths were different (i.e., shorter and longer TiO2 nanotubes). The dye-sensitized solar cell (DSSC) with photoanode based on the shorter TiO2 nanotubes had higher short-circuit current density and device efficiency while lower open-circuit voltage than the DSSC with photoanode based on the longer TiO2 nanotubes. The results are discussed in terms of dye loading amount and electron recombination lifetime. [Copyright &y& Elsevier]

Continuous bundles of aligned electrospun polyacrylonitrile (PAN) copolymer nanofibers were prepared via collection with flowing water at varied temperatures. The morphological and structural properties, as well as the density and residual solvent amount, of electrospun nanofibers in different bundles were investigated. The results indicated that with the increase of water temperature, both diffusion coefficients of solvent (i.e., N,N-dimethylformamide) and non-solvent (i.e., H2O) increased; the surface roughness of nanofibers also increased, and the cross-section of electrospun nanofibers changed in shape from circular to irregular. With the decrease of water temperature from 25 to 2 °C, the average radius of gyration value (related to the average size of micro-voids in the nanofibers) decreased from 10.9 to 6.8 nm, the crystallinity value increased from 54.6% to 57.9%, and the nanofiber density increased from 1.191 to 1.202 g/cm3. It is envisioned that the continuous bundles of aligned electrospun PAN copolymer nanofibers collected with the flowing water bath at a low temperature (e.g., 2 °C) might be an innovative type of precursor for making the carbon nanofibers with superior mechanical strength. [ABSTRACT FROM AUTHOR]

Simultaneously achieving both bifunctional catalysts and flexible self-supported electrodes are urgently in demand to satisfy rechargeable lithium-oxygen (Li-O 2) batteries, particularly for wearable devices. Herein, we propose a novel strategy embracing electrospinning and hot-pressing to develop Co-based composites embedded in porous nitrogen-rich carbon nanofibers (ZnCo-NC/NCF) as a freestanding cathode for Li-O 2 batteries. The fabricated electrode is obtained through pyrolysis of bimetallic (ZnCo) zeolitic imidazolate frameworks/polyacrylonitrile (PAN) nanofibers (BMZIF/PAN). Benefiting from outstanding mechanical strength of electrospun carbon matrix and abundant porosity originated from decomposition of ZIFs as well as fully exposed Co-N x active sites, the achieved cathode is capable of excellent flexibility, high specific surface area, great conductivity and good catalytic behaviors towards both oxygen reduction/evolution reactions. Consequently, the corresponding Li-O 2 batteries exhibit remarkably decreased voltage gap (0.49 V), high specific areal capacity (9.52 mAh cm−2) and long-term cycling capability (around 42 cycles under a curtailing capacity of 0.25 at 0.04 mA cm−2). Besides, the evolution of the morphology and electrochemical impedance spectroscopy at various reaction states are further investigated, which confirms that ZnCo-NC /NCF cathode enables formation and decomposition of lithium peroxide during charge-discharge period. [ABSTRACT FROM AUTHOR]

Abstract: Electrospun anatase-phase TiO2 nanofibers with desired morphological structure and relatively high specific surface area are expected to outperform other nanostructures (e.g., powder and film) of TiO2 for various applications (particularly dye-sensitized solar cell and photo-catalysis). In this study, systematic investigations were carried out to prepare and characterize electrospun anatase-phase TiO2 nanofibers with different morphological structures (e.g., solid, hollow/tubular, and porous) and specific surface areas. The TiO2 nanofibers were generally prepared via electrospinning of precursor nanofibers followed by pyrolysis at 500°C. For making hollow/tubular TiO2 nanofibers, the technique of co-axial electrospinning was utilized; while for making porous TiO2 nanofibers, the etching treatment in NaOH aqueous solution was adopted. The results indicated that the hollow/tubular TiO2 nanofibers (with diameters of ∼300–500nm and wall-thickness in the range from tens of nanometers to ∼200nm) had the BET specific surface area of ∼27.3m2/g, which was approximately twice as that of the solid TiO2 nanofibers (∼15.2m2/g) with diameters of ∼200–300nm and lengths of at least tens of microns. Porous TiO2 nanofibers made from the precursor of Al2O3/TiO2 composite nanofibers had the BET specific surface area of ∼106.5m2/g, whereas porous TiO2 nanofibers made from the precursor of ZnO/TiO2 composite nanofibers had the highest BET specific surface area of ∼148.6m2/g. [Copyright &y& Elsevier]

SUMMARY In this study, four fatty acids of lauric acid (LA), myristic acid (MA), palmitic acid (PA), and stearic acid (SA) were selected to prepare six binary fatty acid eutectics of LA-MA, LA-PA, LA-SA, MA-PA, MA-SA, and PA-SA; thereafter, electrospun ultrafine composite fibers with the binary fatty acid eutectics encapsulated in the supporting matrices of polyethylene terephthalate (PET) were prepared as innovative form-stable phase change materials for storage and retrieval of thermal energy. The morphological structures and thermal energy storage properties of the ultrafine composite fibers were characterized by scanning electron microscope (SEM) and differential scanning calorimeter (DSC), respectively. The SEM results indicated that the fibers had the cylindrical morphology with diameters of 1-2 µm; some had smooth surfaces, while others had wrinkled surfaces with grooves. The DSC results indicated that the phase transition temperatures of binary fatty acid eutectics were lower than those of individual fatty acids; the enthalpy values associated with melting and crystallization for the eutectics encapsulated in the composite fibers were considerably reduced, whereas there were no appreciable changes on the phase transition temperatures. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The form-stable phase change materials (PCMs) with fatty acid eutectics absorbed in and/or supported by the overlaid mats of electrospun polyacrylonitrile (PAN) nanofibers or the derived carbon nanofibers were explored for storage and retrieval of thermal energy. The carbon mats were made from the PAN mats through stabilization in air followed by carbonization in nitrogen. Three fatty acid eutectics of capric acid–lauric acid, capric acid–palmitic acid, and capric acid–stearic acid were studied as model PCMs; for comparison, the individual fatty acid of capric acid was also studied. The results indicated that electrospun nanofibrous mats were highly porous and capable of absorbing a large amount of PCMs, and the maximum absorption capacities of PAN and carbon mats were ∼99wt% and ∼81wt%, respectively. The composite materials (i.e., the form-stable PCMs) could well-retain their overall shapes when the PCMs were in the molten stage; i.e., they would not flow/leak from the mats. The conversion of PAN mats into carbon mats increased the thermal energy storage/retrieval rates of the resulting composite PCMs; nonetheless, the thermal treatments of stabilization and carbonization also made the mats to be less fluffy, leading to the reduction of absorption amount. Morphological structures, as well as the properties of thermal energy storage, absorption capacity, and thermal energy storage/retrieval rates, of electrospun nanofibrous mats and the resulting composite PCMs were studied by scanning electron microscopy, differential scanning calorimetry, and measurement of melting/freezing times. The results indicated that the melting temperatures and enthalpies of the prepared composite PCMs were in the range of 19.8–31.4°C and 120.1–165.4kJ/kg for PAN mats, and 18.8–30.7°C and 92.1–128.0kJ/kg for carbon mats, respectively. In comparison with melting times of CA–PA/PAN and freezing times of CA–SA/PAN, the melting times of CA–PA/carbon and freezing times of CA–SA/carbon were shortened by about 49.5% and 41.0%, respectively. It is envisioned that this innovative type of form-stable PCMs could be utilized for potential applications in building energy conservation. [Copyright &y& Elsevier]

Abstract: This paper reports the fabrication and mechanical properties of hybrid multi-scale epoxy composites reinforced with conventional carbon fiber (CF) fabrics surface-attached with electrospun carbon nanofiber (ECN) mats. The ECNs were prepared via thermal treatments of polyacrylonitrile copolymer nanofibers, which were produced by the electrospinning technique and collected as overlaid mats on the T300 CF fabrics. The ECN-CF fabrics/mats were used as innovative reinforcement fillers for the fabrication of hybrid multi-scale composites (with SC-15 epoxy resin) through the composite-manufacturing technique of vacuum assisted resin transfer molding. Three-point bending test and short-beam shear test were carried out to evaluate the strengthening/toughening effects of ECNs on mechanical properties of the novel composites. The results indicated that out-of-plane mechanical properties of the ECN-CF/epoxy composites were considerably higher than the control sample of traditional CF/epoxy composites. [Copyright &y& Elsevier]

Abstract: The ultrafine composite fibers based on the composites of binary fatty acid eutectics and polyethylene terephthalate (PET) with varied fatty acid eutectics/PET mass ratios (50/100, 70/100, 100/100 and 120/100) were fabricated using the technique of electrospinning as form-stable phase change materials (PCMs). The five binary fatty acid eutectics including LA–MA, LA–PA, MA–PA, MA–SA and PA–SA were prepared according to Schrader equation, and then were selected as an innovative type of solid–liquid PCMs. The results characterized by differential scanning calorimeter (DSC) indicated that the prepared binary fatty acid eutectics with low phase transition temperatures and high heat enthalpies for climatic requirements were more suitable for applications in building energy storage. The structural morphologies, thermal energy storage and thermal stability properties of the ultrafine composite fibers were investigated by scanning electron microscope (SEM), DSC and thermogravimetric analysis (TGA), respectively. SEM images revealed that the electrospun binary fatty acid eutectics/PET ultrafine composite fibers possessed the wrinkled surfaces morphologies compared with the neat PET fibers with cylindrical shape and smooth surfaces; the grooves or ridges on the corrugated surface of the ultrafine composite fibers became more and more prominent with increasing fatty acid eutectics amount in the composite fibers. The fibers with the low mass ratio maintained good structural morphologies while the quality became worse when the mass ratio is too high (more than 100/100). DSC measurements suggested that the heat enthalpies of melting and crystallization of the ultrafine composite fibers increased gradually with increasing fatty acid eutectics amounts, but their phase transition temperatures had almost no obvious variation as relative to the corresponding fatty acid eutectics. Meanwhile, the characteristic temperatures and heat enthalpies of the ultrafine composite fibers varied with the different types of binary fatty acid eutectics. TGA results indicated that the degradation of electrospun binary fatty acid eutectics/PET ultrafine composite fibers with representative mass ratio of 100/100 had two steps and corresponded respectively to the degradations of binary fatty acid eutectics and PET polymer chains; and the charred residue at 700°C of the composite fibers was lower than that of the neat PET fibers. It could be envisioned that the electrospun binary fatty acid eutectics/PET composite fibers would be extensively used for latent heat storage in the field of building energy conservation. [Copyright &y& Elsevier]

The development of novel nanomaterials with well-controlledmorphologies/structuresto achieve excellent activities/sensitivities in surface-enhancedRaman scattering (SERS) is crucial in advancing the high-performanceSERS detections of chemical and biological species. In this study,amidoxime surface-functionalized polyacrylonitrile (ASFPAN) nanofibrousmembranes surface-decorated with silver nanoparticles (Ag NPs) wereprepared via the technique of electrospinning followed by the methodof seed-mediated electroless plating. High SERS activities/sensitivitieswere observed from the ASFPAN-Ag NPs nanofibrous membranes, whilethe density and size of Ag NPs had an important impact on the SERSactivity/sensitivity. The results confirmed that the enhancement ofRaman signals is due to the presence of hot spots between/among AgNPs on the nanofiber surfaces. Electrospun nanofibrous membranes surface-decoratedwith Ag NPs were mechanical flexible/resilient and could be used ashighly active/sensitive SERS substrates for a broad range of applications. [ABSTRACT FROM AUTHOR]

Abstract: Herein we report an effective method for the preparation of composite nanofibers of polybutadiene rubber (BR) containing uniformly distributed Ag nanoparticles (Ag NPs). These nanofibers were morphologically stable and were made from electrospun core–sheath nanofibers with the sheath component being polyvinyl pyrrolidone (PVP) and the core component being BR, in situ synthesized Ag NPs, and a photo-curing agent of camphorquinone. The method included (1) co-axial electrospinning of core–sheath nanofibers, (2) in situ chemical crosslinking of BR in the core component of nanofibers, and (3) removal of the sheath component of PVP from nanofibers. The experimental observation indicated that, when the flow rate of inner spin dope was slower than that of the outer spin dope, the co-axial electrospinning process would be stable, the resulting nanofibers would not be curled; and there were few conglutination locations among the core–sheath nanofibers. Both electrospun core–sheath nanofibers and the resulting composite nanofibers possessed the cylindrical morphology with smooth surface. The study also revealed that the Ag in the composite nanofibers primarily existed in the elemental form. [Copyright &y& Elsevier]

Abstract: Objective: To investigate the reinforcement of Bis-GMA/TEGDMA dental resins (without conventional glass filler) and the corresponding composites (with conventional glass filler) containing varied mass fractions of halloysite nanotubes (HNTs). Methods: Three dispersion methods were studied to separate the silanized halloysite as individual HNTs and to uniformly distribute them into dental matrices. Photopolymerization induced volumetric shrinkage was measured by using a mercury dilatometer. Real time near infrared spectroscopy was adopted to study the degree of vinyl double bond conversion and the photopolymerization rate. Mechanical properties of the composites were tested by a universal mechanical testing machine. Analysis of variance (ANOVA) was used for the statistical analysis of the acquired data. Morphologies of halloysite/HNTs and representative fracture surfaces of the reinforced dental resins/composites were examined by SEM and TEM. Results: Impregnation of small mass fractions (e.g., 1% and 2.5%) of the silanized HNTs in Bis-GMA/TEGDMA dental resins/composites improved mechanical properties significantly; however; large mass fractions (e.g., 5%) of impregnation did not further improve the mechanical properties. The impregnation of HNTs into dental resins/composites could result in two opposite effects: the reinforcing effect due to the highly separated and uniformly distributed HNTs, and the weakening effect due to the formation of HNT agglomerates/particles. Significance: Uniform distribution of a small amount of well-separated silanized HNTs into Bis-GMA/TEGDMA dental resins/composites could result in substantial improvements on mechanical properties. [Copyright &y& Elsevier]

Abstract: In this study, electrospun immiscible blend fibers of poly(vinylidene fluoride) (PVDF)/polysulfone (PSF) were prepared. Due to the strong shearing during electrospinning, cocontinuous fibers of PVDF in the PSF matrix were obtained despite the minor composition of PVDF (5–30 wt.%) in the blend. After annealing these electrospun blend fibers above the melting temperature of PVDF (170 °C) and the glass transition temperature of PSF (185 °C), nanosized droplets (primarily 200–300 nm) of PVDF were developed inside the PSF matrix from the breaking up of PVDF nanofibers because of the Plateau–Rayleigh instability. Fractionated crystallization occurred in these PVDF nanodroplets with the heterogeneously nucleated crystallization in the range of 105–135 °C and the homogeneous nucleation at 55–60 °C. The mechanism of homogeneous nucleation was confirmed by the study of crystallization kinetics using differential scanning calorimetry. Only the nonpolar α-phase was observed by wide-angle X-ray diffraction despite of the homogeneously nucleated crystallization at a high supercooling in these PVDF nanodroplets. This study leads to a conclusion that nanoconfined crystallization at a moderate crystallization rate is less important than the local electric field to induce the ferroelectric phases of PVDF. [Copyright &y& Elsevier]