Electrospun poly(vinyl alcohol)/phase change material fibers: morphology, heat properties, and stability

A phase change material (PCM) from a mixture of plant oils was incorporated into electrospun poly(vinyl alcohol) (PVA) nanofibers using an emulsion electrospinning technique. Effects of PCM and PVA content in the emulsions on nanofiber morphology, heat properties, and phase change stability were examined. Higher PCM loadings in the nanofibers led to increased fiber diameter, gouged fiber surfaces, and higher heat enthalpies. The fibers maintained their morphological integrity even if the PCM melted. They showed reliable heat-regulating performance which can undergo at least 100 cycles of phase change. Such PCM fibers may be used for the development of thermoregulating fabrics or in passive heat storage devices.

Self-assembled peptide nanostructures for the fabrication of cell scaffolds

The fabrication of artificial scaffolds that effectively mimic the host environment of the cell have exciting potential for the treatment of many diseases in regenerative medicine. In particular, appropriately designed scaffolds have the capacity to support, replace, and mediate the transplantation of therapeutic cells in order to regenerate damaged or diseased tissues. To achieve these goals for regeneration, the engineering of an environment structurally similar to the native extracellular matrix (ECM) is necessary in order to closely match the chemical and physical conditions found within the extracellular niche. Recently, self-assembled peptide (SAP) hydrogels have shown great potential for such biological applications due to their inherent biocompatibility, propensity to form higher order structures, rich chemical functionality and ease of synthesis. Importantly, it is possible to control the organization and properties of the target materials as the chemical structure is determined by amino acid sequence. Here, the development of SAP hydrogels as functional cell scaffolds and useful tools in tissue engineering is reviewed.

Thermal and rheological characteristics of biobased carbon fiber precursor derived from low molecular weight organosolv lignin

In the present work, electrospinnability as well as thermal, rheological, and morphological characteristics of low molecular weight hardwood organosolv lignin, as a potential precursor for carbon fiber, was investigated. Submicromter biobased fibers were electrospun from a wide range of polymer solutions with different ratios of organosolv lignin to polyacrylonitrile (PAN). Rheological studies were conducted by measuring viscosity, surface tension, and electrical conductivity of hybrid polymer solutions, and used to correlate electrospinning behavior of solutions with the morphology of the resultant electrospun composite fibers. Using scanning electron microscopy (SEM) images, the solutions that led to the formation of bead-free uniform fibers were found. Differential scanning calorimetry (DSC) analysis revealed that lignin-based fibers enjoy higher decomposition temperatures than that of pure PAN. Thermal stability of the lignin-based fibers was investigated by thermogravimetric analysis (TGA) indicating a high carbon yield of above 50% at 600 °C, which is highly crucial in the production of low-cost carbon fiber. It was also observed that organosolv lignin synergistically affects thermal decomposition of composite fibers. A significant lower activation energy was found for the pyrolysis of lignin-derived electrospun fibers compared to that of pure PAN.

Self-assembled V2O5 interconnected microspheres produced in a fish-water electrolyte medium as a high-performance lithium-ion-battery cathode

Interconnected microspheres of V2O5 composed of ultra-long nanobelts are synthesized in an environmental friendly way by adopting a conventional anodization process combined with annealing. The synthesis process is simple and low-cost because it does not require any additional chemicals or reagents. Commercial fish-water is used as an electrolyte medium to anodize vanadium foil for the first time. Electron microscopy investigation reveals that each belt consists of numerous nanofibers with free space between them. Therefore, this novel nanostructure demonstrates many outstanding features during electrochemical operation. This structure prevents self-aggregation of active materials and fully utilizes the advantage of active materials by maintaining a large effective contact area between active materials, conductive additives, and electrolyte, which is a key challenge for most nanomaterials. The electrodes exhibit promising electrochemical performance with a stable discharge capacity of 227 mAh·g–1 at 1C after 200 cycles. The rate capability of the electrode is outstanding, and the obtained capacity is as high as 278 at 0.5C, 259 at 1C, 240 at 2C, 206 at 5C, and 166 mAh·g–1 at 10C. Overall, this novel structure could be one of the most favorable nanostructures of vanadium oxide-based cathodes for Li-ion batteries. [Figure not available: see fulltext.]

Coassembled nanostructured bioscaffold reduces the expression of proinflammatory cytokines to induce apoptosis in epithelial cancer cells

The local inflammatory environment of the cell promotes the growth of epithelial cancers. Therefore, controlling inflammation locally using a material in a sustained, non-steroidal fashion can effectively kill malignant cells without significant damage to surrounding healthy cells. A promising class of materials for such applications are the nanostructured scaffolds formed by epitope containing minimalist self-assembled peptides (SAPs), as they are bioactive on a cellular length scale, whilst presenting as an easily handled hydrogel. Here, we show that the assembly process distributes an anti-inflammatory polysaccharide, fuccoidan, localised to the nanofibers to function as an anti-inflammatory biomaterial for cancer therapy. We show that it supports healthy cells, whilst inducing apoptosis in cancerous endothelial cells, as demonstrated by the downregulation of the proinflammatory gene and protein expression pathways associated with epithelial cancer progression. Our findings highlight an innovative material approach with potential applications as local epithelial cancer immunotherapy and drug delivery vehicles.

Epoxy nanocomposites with aligned carbon nanofillers by external electric fields

This paper presents systematic studies on aligning carbon nanofillers in epoxy by external fields, either electric fields or magnetic fields, to create nanocomposites with greatly improved mechanical and electrical properties. Carbon nanofibers (CNFs) and graphene nanoplatelets (GnPs) were observed to align along the field direction in the epoxy resin. Compared to the unmodifed epoxy and those with randomly-oriented carbon nanofillers, the nanocomposites with aligned carbon nanofillers showed significantly higher fracture toughness and electrical conductivity along the direction of the external field. Compared with randomly-oriented nanofillers, aligned GnPs and CNFs produced 40% and 27% improvement in fracture energy at 1.0 wt%, bringing the total increase in fracture energy over the neat polymer to more than 10 times. Several key toughening mechanisms were identified through fractographic analysis, which was used to develop predictive models to quantify the increases in the value of GIc as a result of 1-D and 2D carbon nanofillers. The present findings suggest that aligning carbon nanofillers presents a very promising technique to create multi-scale reinforcement with greatly increased electric conductivity and fracture toughness.

Rapid and sensitive ethanol sensor based on hollow Au/V2O5 nanotubes via emulsion-electrospinning route

Hollow electrospun V2O5 and Au/V2O5 nanotubes have been successfully synthesized by combining emulsion electrospinning (EE) and post calcination treatment. Immiscible polyvinyl pyrrolidone (PVP)/metal salts/dimethylformamide (DMF) solution and polystyrene (PS)/DMF solution are chosen for the EE to form PS PVP/metal salts) core-sheath nanofibers, in which PS nanorods were formed and encapsulated within in the PVP/metal salts nanofibers owing to the stretching forces and de-emulsified force during the electrospinning. Excellent sensitivity and rapid response-recovery behaviors against ethanol have been successfully achieved based on our hollow ceramic (V2O5 and Au/V2O5) nanotubes.

High performance PP/SEBS/CNF composites: evaluation of mechanical, thermal degradation, and crystallization properties

Nanocomposites comprising carbon nanofibers (CNF) were prepared and evaluated in terms of morphology, mechanical performance, thermal stability and crystallization properties. It was found that addition of CNF reinforced polypropylene (PP) matrix by marginally increasing the strength and modulus, but at the expense of toughness and ductility. To improve the toughness of the composites, polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) was used. Presence of SEBS remarkably improved the toughness and ductility of the composites. The optimum level of reinforcement was observed at 0.1 wt% of CNF in the composites. Phase morphology studies revealed that at this concentration, CNF were well dispersed in polymer phases and beyond it, agglomeration occurred. PP/SEBS/CNF (0.1 wt%) nanocomposites exhibited good strength, excellent toughness and decent modulus, which make them suitable for cost effective, light-weight, tough and stiff material for engineering applications. It was observed that thermal stability of composites is only marginally improved whereas crystallinity of PP drastically reduced by the addition of CNF.

Effect of vapor-phase glutaraldehyde crosslinking on electrospun starch fibers

In this work, we have proven that starch nanofibrous membranes with high tensile strength, water stability and non-cytotoxicity can be produced by electrospinning of starch solution and post-treatment with GTA in vapor phase. GTA vapor phase crosslinking plays a key role in forming water-stable nanofiber membrane and improving the mechanical properties. Comparing with non-crosslinked starch fibers, the crosslinked fibers are increased by nearly 10 times in tensile strength. The crosslinked starch fibrous membranes are non-cytotoxic. They may find applications in the fields of tissue engineering, pharmaceutical therapy and medical.

Online stretching of directly electrospun nanofiber yarns

Nanofiber yarns are important building blocks for making three-dimensional nanostructures, e.g. through a knitting or weaving process, with better mechanical properties than nanofiber nonwovens and well-controlled fibrous construction. However, it still remains challenging to produce quality nanofiber yarns in a sufficient rate. In this study, we have proven that online stretching during electrospinning of nanofiber yarns can considerably improve fiber alignment and molecular orientation within the yarn and increase yarn tensile strength, but reduce fiber/yarn diameters. By compensating twist during online stretching, the device can prepare nanofiber yarns with different stretch levels, but maintaining the same twist multiplier. This allows us to examine the effect of stretching on fiber and yarn morphology. It was interesting to find that on increasing the stretching ratio from 0% to 95%, the yarn diameter reduced from 135.1 ± 20.3 μm to 46.2 ± 10.2 μm, and the fiber diameter reduced from 998 ± 141 nm to 631 ± 98 nm, whereas the yarn tensile strength increased from 48.2 ± 5.6 MPa to 127.7 ± 5.4 MPa. Such an advanced yarn electrospinning technique can produce nanofiber yarn with an overall yarn production rate as high as 10 m min−1. This may be useful for production of nanofiber yarns for various applications.

Tailoring of interface of polypropylene/polystyrene/carbon nanofibre composites by polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene

Mechanical and physical properties of polypropylene (PP)/polystyrene (PS) blend, PP/PS/polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) ternary blend and their composites with carbon nanofibers (CNF) were investigated. Composites of ternary blend exhibited superior properties compared to those of binary blends. Mechanical performance of nanocomposites was intimately related to their phase morphology. PP/PS/SEBS/0.1 wt% CNF hybrid composites exhibited excellent impact strength (Four-fold increase compared to PP/PS blend) and ductility (12-fold increase in elongation at break, with respect to PP/PS blend). Moreover, these composites displayed good tensile strength and modulus (15% increase in Young's modulus, compared to PP/PS/SEBS blend) and are suitable for various end-use applications including automobile applications. Although crystallinity of PP phase is decreased by the incorporation of CNF, thermal stability of the composites remained almost unaffected. Contact angle measurements revealed that ternary composites exhibited maximum hydrophobicity.

Effect of solvent treatment on morphology, crystallinity and tensile properties of cellulose acetate nanofiber mats

Aligned nanofiber mats were prepared from cellulose acetate using an electrospinning technique. The nanofiber mats were then immersed in an ethanol/acetone mixture. The solvent treatment led to denser, more compact fibrous structure and slight decrease in fiber alignment. It increased fiber diameter and polymer crystallinity within fibers. These effects resulted in increase in the tensile strength of fibrous mats. Solvent treatment may offer a simple, efficient approach to improve the mechanical strength of nanofibrous mats.

Progress in nanostructured photoanodes for dye-sensitized solar cells

Solar cells represent a principal energy technology to convert light into electricity. Commercial solar cells are at present predominately produced by single- or multi-crystalline silicon wafers. The main drawback to silicon-based solar cells, however, is high material and manufacturing costs. Dye-sensitized solar cells (DSSCs) have attracted much attention during recent years because of the low production cost and other advantages. The photoanode (working electrode) plays a key role in determining the performance of DSSCs. In particular, nanostructured photoanodes with a large surface area, high electron transfer efficiency, and low electron recombination facilitate to prepare DSSCs with high energy conversion efficiency. In this review article, we summarize recent progress in the development of novel photoanodes for DSSCs. Effect of semiconductor material (e.g. TiO2, ZnO, SnO2, N2O5, and nano carbon), preparation, morphology and structure (e.g. nanoparticles, nanorods, nanofibers, nanotubes, fiber/particle composites, and hierarchical structure) on photovoltaic performance of DSSCs is described. The possibility of replacing silicon-based solar cells with DSSCs is discussed.

Removal of copper ions from aqueous solution by adsorption onto novel polyelectrolyte film-coated nanofibrous silk fibroin non-wovens

In this approach, polyelectrolyte film-coated nanofibrous silk fibroin (SF) nonwovens were prepared from the alternate deposition of positively charged polyethylenimine (PEI) and negatively charged SF using electrostatic layer-by-layer (LBL) self-assembled technology. The composite membranes were characterized by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectrometer. The SF-PEI multilayer-assembled nanofibers (less than five layers) were fine and uniform with the fiber diameter from 400 nm to 600 nm, and had very large surface area and high porosity (more than 70%). The amino groups of PEI were proved to be deposited onto SF nonwovens, which granted the coated nonwovens with potential applicability for copper ions adsorption. The PEI films coated SF substrate showed much higher copper ions adsorption capacity than that of ethanol treated SF nanofibers. Adding the number of PEI coated could enhance the Cu²⁺ adsorption capacity significantly. The maximum milligrams per gram of copper ions adsorbed reached 59.7 mg/g when the SF substrate was coated with 5 bilayers of SF-PEI. However, the copper ions adsorption capacity had no obvious change as the number of PEI continued to increase. These results suggest potential for PEL film-coated nanofibrous nonwovens as a new adsorbent for metal ions.