The separation and purification of chemical molecules from organic media under harsh chemical environments are of vital importance in the fields of water treatment, biomedical engineering, and organic recycling. Herein, we report the preparation of a flexible SiO2/SnO2 nanofibrous membrane (SiO2/SnO2 NFM) with high surface area and hierarchical porous structure by selecting poly(vinyl butyral) as pore-forming agent and embedding crystalline phase into amorphous matrix without using surfactant as sacrificial template. Benefiting from the uniform micropore size on the fibers and negatively charged properties, the membranes exhibit a precise selectivity toward molecules based on electrostatic interaction and size exclusion, which could separate organic molecule mixtures with the same electrostatic charges and different molecular sizes with a high efficiency of more than 97%. Furthermore, the highly tortuous open-porous structures and high porosity give rise to a high permeate flux of 288 000 L m–2 h–1. In addition, the membrane also displays excellent stability and can be reused for ten consecutive filtration–regeneration cycles. The integration of high filtration efficiency, large permeate flux, good reutilization, and easy to industrialization provides the SiO2/SnO2 NFM for potential applications in practical molecular purification and separation science.Keywords: electrospinning; flexible; high permeate flux; molecular filtration; porous SiO2/SnO2 nanofibrous membrane;

Flexible membranes created from porous carbon nanofibers (CNFs) hold great promise in the next generation wearable energy storage devices, but challenges still remain due to the poor mechanical properties of porous carbon nanofibers. Here, we report a facile strategy to fabricate elastic and hierarchical porous CNF membranes with NiFe2O4 nanocrystals embedded via multicomponent electrospinning and nano-doping methods. Benefiting from the scattering effect of NiFe2O4 nanocrystals and graphitized carbon layers for the condensed stress, the resultant CNF membranes exhibit an enhanced elasticity with a bending radius <12 μm, rapid recovery from the deformations, and a superior softness. Quantitative pore size distribution and fractal analysis reveal that the CNFs possessed tunable porous structures with a high surface area of 493 m2 g−1 and a pore volume of 0.31 cm3 g−1. Benefiting from the robust mechanical stability, hierarchical porous structures and good electrochemical properties, the NiFe2O4 doped CNF membranes demonstrate a high electrical capacitance of 343 F g−1, and good reversibility with a cycling efficiency of 97.4% even after 10000 cycles. The successful synthesis of elastic porous CNF membranes also provided a versatile platform for the design and development of functional CNF based materials for various applications.

The demand of water-resistant and breathable materials applied to a separation medium and protective garments is steadily increasing. Typical approaches to obtain these functional materials are based on hydrophobic agents and porous substrates with small fiber diameter, tiny pore, and high porosity. However, a fluorinated hydrophobic finishing agent usually employed in providing effective waterproofness is limited with respect to their environmental persistence and toxic potential. Herein, with the aim to keep a balance between the water-resistance and breathability as well as mechanical properties, we fabricate a novel fluoride-free functional membrane by electrospun polyacrylonitrile (PAN) nanofibers modified with polydimethylsiloxane (PDMS). As determined by morphological, DSC, and FT-IR analyses, the curing reaction of PDMS macromolecules formed an abundance of hydrophobic adhesive structures, which improved the waterproof performance dramatically and imparted relative good breathability at the same time. By systematically tuning the curing temperature as well as the concentration of PDMS, the modified PAN membranes with 4 wt % PDMS possessed good water-resistance (80.9 kPa), modest vapor permeability (12.5 kg m–2 d–1), and air permeability (9.9 mm s–1). Compared with pristine PAN membranes, the modified membranes were endowed with enhanced tensile stress of 15.7 MPa. The good comprehensive performance of the as-prepared membranes suggested their potential applications in protective clothing, membrane distillation, self-cleaning materials, and other medical products. Furthermore, the proposed relationship between porous structure and waterproof/breathable property as one considerable principle is applicable to designing functional membranes with different levels of protective and comfortable performance.Keywords: electrospinning; poly(dimethylsiloxane); polyacrylonitrile; surface modification; waterproof/breathable

Additive manufacturing features “direct” and “layer-by-layer” fabrication and has significantly facilitated the microstructural design and fabrication of a wide range of highly complex parts. To enable the application of additive manufacturing in major industries and composites, it is necessary to evaluate the microstructural features of additively manufactured parts. Among the various advanced characterization techniques, X-ray micro-computed tomography (μ-CT) showed unique advantages as a high resolution, nondestructive and 3D visualization and measurement technique for material characterization. In the research reported in this article, we have fabricated an array of multi-directional preforms and composites and have characterized their microstructural features via X-ray μ-CT. First, a solid specimen as well as 3D orthogonal and 3D braided preforms have been fabricated using fused filament fabrication (FFF) and inspected with X-ray μ-CT. Then, the fabricated preforms have been infused with silicone matrix and the multi-directional preforms and composites have been tested in compression at different strain levels, to reveal their damage evolution under compressive loading. The preliminary effort made in this research demonstrates the feasibility of characterizing microstructure of additively manufactured parts via X-ray μ-CT technique and enables an investigation of the microstructural features and damage evolution of multi-directional preforms and composites.

•Waterproof-breathable membranes were prepared by electrospinning and heat treatment.•FPU enriched the PAN/FPU macroporous membranes with superhydrophobicity.•Heating induced inter-fiber adhesion structure and decreased pore size.•Heat treatment enhanced the waterproof-breathable and mechanical properties.•High hydrostatic pressure (114.6 kPa) and WVTR (10.1 kg m−2 d−1).Macroporous membranes with robust waterproofness, breathability and mechanical properties have attracted a great deal of attention. However, great challenges still remained in developing an effective and cost-efficient method to fabricate such materials. In this study, polyacrylonitrile (PAN)/fluorinated polyurethane (FPU) nanofibrous composite membranes with enhanced waterproof and breathable performance were fabricated by combination of electrospinning and heat post-treatment. The introduction of FPU enriched the nanofibrous membranes with superhydrophobic surface with water contact angle of 151°, optimized pore size and porosity. Moreover, the relationship among hydrostatic pressure, pore structure and surface wettability has proven to be in accordance with Young–Laplace equation. By employing the heat post-treatment, the pristine PAN/FPU composite membranes were endowed with physically adhesion structure, thereby significantly improved the waterproof-breathable performance as well as the mechanical property. Owing to these effects, the resulting thermal treated PAN/FPU composite membranes exhibited the integrated properties of high hydrostatic pressure (114.6 kPa), water vapor transmission rate (10.1 kg m−2 d−1) and good tensile strength (9.4 MPa). Furthermore, the reinforced PAN/FPU nanofibrous composite membranes have great potential to be used as functional materials for fabricating separation media, filter, outdoor sportswear, chemical protective clothing, and army combat uniforms.

Electrospun nanofibrous membranes with thin fiber diameter, small pore size, and high porosity have attracted a great deal of attention in the waterproof and breathable field. However, great challenges still remain in simultaneously reinforcing the mechanical and waterproof-breathable performance of such materials. In this study, a new type of fluorinated polyurethane/polyacrylonitrile/polyvinyl butyral nanofibrous membranes (FPU/PAN/PVB NFM) with a blocked isocyanate prepolymer (BIP) as chemical cross-linking agent were fabricated. The composite NFM, with robust mechanical, waterproof and breathable performance, has been prepared using an innovation strategy combining electrospinning with thermally induced physical bonding and chemical cross-linking. By systematically tuning the cross-linked temperature and time as well as the concentration of PVB and BIP, large breaking elongation (81.5%), good hydrostatic pressure (110 kPa) and modest WVTR (9.6 kg m−2 d−1) of the membranes were achieved. Meanwhile, the physically bonded structure and chemically cross-linked networks between PVB and BIP endowed the composite NFM with the robust tensile strength of 32.8 MPa, which was three times higher than that of pristine FPU/PAN membranes. Considering the excellent performance of the as-prepared membranes, this simple and intriguing approach may provide a versatile platform for exploring the applications of the bonded and cross-linked membranes in separation processes, membrane distillation, self-cleaning materials, and protective clothing.

Current additive manufacturing methods present the potential to construct net-shape structures with complicated architectures, thus eliminating the need for multi-step processing and fasteners/joints. Combined with these features is the ability to ascribe material properties at the sub-millimeter scale, inspiring multi-material, functionally graded designs. These features make additive manufacturing an attractive option for composite materials development. In an effort to extend this family of technologies beyond nano- and micro-composites, we explore the additive manufacture of multi-directional composite preforms. This exercise has served to highlight the aspects of additive manufacturing critical to composite and general materials processing, as well as to demonstrate the high fidelity between modeled and additively manufactured structures. Within the scope of composites development, we review the state-of-the-art and discuss challenges facing the broad adoption of additive manufacturing for directionally reinforced composites processing.

While the emerging wire-shaped supercapacitors (WSS) have been demonstrated as promising energy storage devices to be implemented in smart textiles, challenges in achieving the combination of both high mechanical stretchability and excellent electrochemical performance still exist. Here, an asymmetric configuration is applied to the WSS, extending the potential window from 0.8 to 1.5 V, achieving tripled energy density and doubled power density compared to its asymmetric counterpart while accomplishing stretchability of up to 100% through the prestrainning-then-buckling approach. The stretchable asymmetric WSS constituted of MnO2/CNT hybrid fiber positive electrode, aerogel CNT fiber negative electrode and KOH-PVA electrolyte possesses a high specific capacitance of around 157.53 μF cm–1 at 50 mV s–1 and a high energy density varying from 17.26 to 46.59 nWh cm–1 with the corresponding power density changing from 7.63 to 61.55 μW cm–1. Remarkably, a cyclic tensile strain of up to 100% exerts negligible effects on the electrochemical performance of the stretchable asymmetric WSS. Moreover, after 10 000 galvanostatic charge–discharge cycles, the specific capacitance retains over 99%, demonstrating a long cyclic stability.Keywords: asymmetric configuration; carbon nanotube fibers; manganese oxides; stretchability; wire-shaped supercapacitors;

Due to their exceptional flexibility and transparency, CVD graphene films have been regarded as an ideal replacement of indium tin oxide for transparent electrodes, especially in applications where electronic devices may be subjected to large tensile strain. However, the search for a desirable combination of stretchability and electrochemical performance of such devices remains a huge challenge. Here, we demonstrate the implementation of a laminated ultrathin CVD graphene film as a stretchable and transparent electrode for supercapacitors. Transferred and buckled on PDMS substrates by a prestraininig-then-buckling strategy, the four-layer graphene film maintained its outstanding quality, as evidenced by Raman spectra. Optical transmittance of up to 72.9% at a wavelength of 550 nm and stretchability of 40% were achieved. As the tensile strain increased up to 40%, the specific capacitance showed no degradation and even increased slightly. Furthermore, the supercapacitor demonstrated excellent frequency capability with small time constants under stretching.Keywords: chemical vapor deposition; graphene films; high rate capability; stretchability; supercapacitors; transparency;

Since 2006, a rapid development has been achieved in a subject area, so called electro-spinning/netting (ESN), which comprises the conventional electrospinning process and a unique electro-netting process. Electro-netting overcomes the bottleneck problem of electrospinning technique and provides a versatile method for generating spider-web-like nano-nets with ultrafine fiber diameter less than 20 nm. Nano-nets, supported by the conventional electrospun nanofibers in the nano-fiber/nets (NFN) membranes, exhibit numerious attractive characteristics such as extremely small diameter, high porosity, and Steiner tree network geometry, which make NFN membranes optimal candidates for many significant applications. The progress made during the last few years in the field of ESN is highlighted in this review, with particular emphasis on results obtained in the author’s research units. After a brief description of the development of the electrospinning and ESN techniques, several fundamental properties of NFN nanomaterials are addressed. Subsequently, the used polymers and the state-of-the-art strategies for the controllable fabrication of NFN membranes are highlighted in terms of the ESN process. Additionally, we highlight some potential applications associated with the remarkable features of NFN nanostructure. Our discussion is concluded with some personal perspectives on the future development in which this wonderful technique could be pursued.

The pollution arising from oil spills is a matter of great concern due to its damaging impacts on the ecological environment, which has created a tremendous need to find more efficient materials for oil spill cleanup. In this work, we reported a sorbent for oil soak-up from a water surface with a high sorption capacity, good selectivity, and excellent reusability based on the hydrophobic–oleophilic fibrous mats that were fabricated via co-axial electrospinning polystyrene (PS) solution as the shell solution and polyurethane (PU) solution as the core solution. The fine structures of as-prepared fibers were regulated by manipulating the spinning voltages, core solution concentrations, and solvent compositions in shell solutions, which were also characterized by field emission scanning electron microscopy, transmission electron microscopy, nitrogen adsorption method, and synchrotron radiation small-angle X-ray scattering. The effects of inter-fiber voids and intra-fiber porosity on oil sorption capacities were well studied. A comparison of oil sorption capacity for the single fiber with different porous structures was also investigated with the help of scanning transmission X-ray microscopy. The results showed that the sorption capacities of the as-prepared sorbent with regards to motor oil and sunflower seed oil can be 64.40 and 47.48 g g−1, respectively, approximately 2–3 times that of conventional polypropylene (PP) fibers for these two same oils. Even after five sorption cycles, a comparable oil sorption capacity with PP fibers was still maintained, exhibiting an excellent reusability. We believe that the composite PS–PU fibrous mats have a great potential application in wastewater treatment, oil accident remediation and environmental protection.

Novel hierarchically aligned PMIA–MWCNT hybrid nanofibers with a robust tensile strength of 316.7 MPa were prepared by a facile electrospinning process. The critical roles of humidity and MWCNT contents in tuning hierarchically aligned structures were first proposed, and a two-step break mechanism upon external stress was confirmed.

Cellulose fibers deposited with metallic nanoparticles as one kind of renewable, biocompatible and antimicrobial nanomaterials evoke much interest because of their versatility in various applications. Herein, for the first time, a facile, simple and rapid method was developed to fabricate TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical) selectively oxidized jute fibers in situ deposited with silver nanoparticles in the absence of reducing reagents. The average size of silver nanoparticles deposited on the fibers is 50.0 ± 2.0 nm by microwave heating for 5 min and 90.0 ± 4.7 nm for 10 min heating sample, respectively. The versatile jute–silver nanoparticles nanocomposites with superior thermal stability and high crystallinity would be particularly useful for applications in the public health care and biomedical fields.Highlights► For the first time, Ag nanoparticles were in situ deposited on TEMPO treated jute fibers. ► Ag nanoparticles were synthesized on jute without any reducing reagents. ► The size distributions of Ag nanoparticles on the jute fibers were narrow. ► Jute/nanosilver nanocomposites exhibited superior thermal stability and high crystallinity. ► Microwave heating provides a promising method for preparation of metallic nanoparticles.

A novel, sensitive, selective, and reproductive formaldehyde sensor has been developed by coating polyvinylamine (PVAm) modified electrospun polyacrylonitrile (PAN) nanofibrous membranes on quartz crystal microbalance (QCM) for the first time. Benefiting from the abundant primary amine groups in PVAm, large specific surface area, high porosity and hierarchal structure of PAN nanofibers, and the strong interaction between PVAm molecule and formaldehyde, the as-prepared QCM sensors achieved an extremely low detection limit of 500 ppb in a remarkably short period of time (120 s). Moreover, the sensitivity of the fibrous membranes based sensors are 2.5 times higher than that of flat film-based ones when upon exposure to 500 ppb formaldehyde. Furthermore, the as-prepared QCM sensors possess excellent reproducibility, reversibility, and good selectivity by virtue of the reversible nucleophilic addition reaction between formaldehyde molecule and primary amine group in PVAm. Hence, such promising QCM sensors could not only potentially allow for monitoring gaseous formaldehyde, but also pave a way for designing and development of novel QCM sensing systems based on functionalized nanofibrous membranes.

We report a facile method to control intra-fiber porosity via varying the relative humidity and inter-fiber voids through the blending of two different polymeric fibers via multi-nozzles spinning of electrospun fibers for selective adsorption of oil from water.

In this study, we conducted a subtle regulation of micro- and nanostructures of electrospun polystyrene (PS) fibers via tuning the molecular weights of the polymers with different sources, solvent compositions, and solution concentration. The surface morphology and porous structures of as-prepared PS fibers were characterized, and a full and intuitive observation of the porous structures as well as a tentative account of the formation of porous structures was presented. Additionally, the porous PS fibrous mats showed much higher oil absorption capacities than those of commercial polypropylene fibers in the form of a non-woven fabric, which displays a bight future for oil spill cleanups. We believe that such regulation of micro- and nanostructures of the PS fibers will widen the range of their applications in self-cleaning materials, ultra-high sensitivity sensors, tissue engineering, ion exchange materials, etc.

A novel airborne particulate filtration medium, consisting of a two-tier composite structure, i.e., a nano-fiber/net (NFN) top layer and a conventional nonwoven microfibrous support, was demonstrated for highly efficient and low pressure drop filtration for the first time. The polyamide-66 (PA-66) NFN structured top layer, which is composed of traditional electrospun nanofibers and two-dimensional (2D) spider-web-like nano-nets, was electro-spinning/netting (ESN) deposited on the nonwoven polypropylene (PP) scaffold for constructing this new concept of filter. The morphology of NFN architecture, including fiber diameter, coverage rate, pore-width and layer-by-layer packing structure of the nano-nets, can be finely controlled by regulating the solution properties and several ESN process parameters. Taking advantage of several fascinating features such as extremely small diameter, high porosity, controllable coverage rate, nano-nets bring to the NFN/nonwoven composite filtration medium several excellent filtration features such as high filtration efficiency (up to 99.9%), low pressure drop, facile filters cleaning, and more lightweight.

Cellulose nanowhiskers is a kind of renewable and biocompatible nanomaterials evoke much interest because of its versatility in various applications. Here, for the first time, a novel controllable fabrication of cellulose nanowhiskers from jute fibers with a high yield (over 80%) via a 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)/NaBr/NaClO system selective oxidization combined with mechanical homogenization is reported. The versatile jute cellulose nanowhiskers with ultrathin diameters (3–10 nm) and high crystallinity (69.72%), contains C6 carboxylate groups converted from C6 primary hydroxyls, which would be particularly useful for applications in the nanocomposites as reinforcing phase, as well as in tissue engineering, pharmaceutical and optical industries as additives.Highlights► For the first time, cellulose nanowhiskers are extracted from TEMPO oxidized jute. ► The dimension of the nanowhiskers is 3–10 nm in width and 100–200 nm in length. ► Carboxylate groups formed on cellulose nanowhiskers results in a negative charge. ► It is easily dispersed in water and forms stable and transparent suspension.

The primary goal of the present study is to develop a quartz crystal microbalance (QCM) sensor functionalized by three-dimensional sensing membranes for heavy metal ion detection. The fibrous polystyrene (PS) membranes were stabilized on the QCM electrode and modified with subsequent gold sputtering, followed by the functionalization of the sensing polyethyleneimine. The morphology and specific surface area (SSA) of the PS membranes were controllable by adjusting the weight ratios of the blend solvents of tetrafuran, N,N-dimethylformamide. The resultant sensors with optimal structure showed excellent selectivity for Cr3+ with a detection limit of 5 ppb. Sensor sensitivity increased concurrently with both increasing PS loading and SSA on the electrode of QCM. The sensor responses showed good linearity in the 5–200 ppb concentration range. The results suggest that the fibrous membrane QCM sensors have potential for further applications in other sensors.

A mechanical robust and thermal tolerant nanofibrous membrane with hydrophilicity is presented by one step via electrospinning Nomex® solution. The nanofibrous membrane shows a high specific surface area of 21.46 m2/g, two orders of magnitude larger than that of the commercial Nomex® fibers. The experimental results demonstrate that the membrane has high efficient rejection for nanoparticles from aqueous solution, which reveals its feasibility used in liquid filtration. Additionally, the membrane displays high break strength of 31.34 MPa as well as very excellent thermal resistance, making it as good candidates for applications in reinforced nanomaterials, automobile air filters, template of structure coatings etc., requiring high strength and high thermal resistance.A mechanical robust and thermal tolerant nanofibrous membrane with hydrophilicity was prepared by one step via electrospinning poly(meta-phenylene isophthalamide) fibers solution which was commercialized by Dupont company under the trade name of Nomex®. The membrane exhibits high efficient rejection for nanoparticles from aqueous solution.Highlights► PMIA nanofibrous membrane is prepared by one step via electrospinning Nomex® solution. ► The membrane shows high break strength as well as very excellent thermal resistance. ► The membrane has a high efficient rejection for nanoparticles from aqueous solution.

A highly sensitive coating comprising 3-mercaptopropionic acid (MPA) monolayer modified electrospun polystyrene (PS) membranes was constructed on the electrode of quartz crystal microbalance (QCM) for Cu2+ detection. The three-dimensional fibrous PS membranes with high specific surface area (SSA) were deposited on the electrode of QCM via electrospinning. The PS membranes were sputter coated with gold, then modified with self-assembled monolayer of MPA. The PS-MPA sensors showed fast response (2–3 s) to Cu2+ and a detection limit down to 100 ppb. Additionally, sensor sensitivity increased concurrently with both increasing PS loading and SSA on QCM electrodes. The response of the PS-MPA sensors with a PS membrane loading of 978 Hz and SSA of 43.31 m2/g was 40 times larger than that without membranes when exposed to 1 ppm of Cu2+. The sensor responses were reproducible toward Cu2+ in the 100–5 ppm concentration range, whereas a linear response was found in the 100–1 ppm concentration range. The sensor response to Cu2+ showed a linear relationship with an increase in pH from 2 to 7. Moreover, the sensors also exhibited chelation selectivity for other transition metal ions in the descending order Cu2+ > Ni2+ > Zn2+ > Fe2+ at concentration between 1 and 5 ppm.

A novel strategy for highly sensitive colorimetric detection of gaseous formaldehyde was developed based on Methyl Yellow-impregnated electro-spinning/netting (ESN) nylon 6 nano-fiber/nets (NFN). The sensor presented a significant reflectance intensity decreasing band at 550 nm which induce the visual color changes from yellow to red after exposure to formaldehyde and allowed for the detection of formaldehyde with a low detection limit of 50 ppb. Upon exposure to a series of volatile organic compounds (VOCs), only formaldehyde could induce a yellow-to-red color change observable by the naked eye, which clearly exhibited that Methyl Yellow-impregnated nylon 6 NFN membranes could act as highly selective and sensitive strips to detect formaldehyde with minor interference from other VOCs. Additionally, the colorimetric sensor showed good reproducibility under cyclic sensing experiments. Furthermore, the colorimetric responses were visualized quantitative by using a color-differentiation map prepared form converted RGB (red, green and blue) values. As-prepared Methyl Yellow-impregnated nylon 6 NFN sensor strips successfully combined with the visualized detection of color map and fascinating structure of NFN membranes, which indicated promising composite materials as a simple and economical alternative to replace the traditional formaldehyde sensors and facilitated the design and development of other label-free colorimetric sensors toward various analytes based on the NFN template.

A simple and straightforward strategy of depositing a nanostructured complex, based on a polyethyleneimine (PEI) functionalized polyamide 6 (PA 6) (PEI-PA 6) nano-fiber/net (NFN), on a quartz crystal microbalance (QCM) sensor for humidity detection is demonstrated. The PA 6 NFN substrate, comprising common electrospun nanofibers and spider-web-like nano-nets fabricated by a versatile electro-spinning/netting (ESN) process, exhibits several fundamental characteristics, such as a remarkable specific surface area, high open porosity and good interconnectivity. Therefore, the sensors based on PEI-PA 6 NFN membranes show high sensitivity and fast response/recovery time to humidity, which outperform current porous structure-based sensors. The frequency changes by approximately three orders of magnitude with relative humidity (RH) varying from 2% to 95%. Moreover, the resultant sensors also presents relatively small hysteresis and long-term stability. For low RH levels, the response of the QCM sensor is dependent on water molecules adsorbed/desorbed masses on NFN membranes, whereas for increasing RH levels variations in interlayer expansion stress of NFN membranes derived from the swelling effect become prevalent. This study demonstrates that NFN structured materials are have potential applications for fabricating high performance humidity sensors.

A nanostructured complex, polyethyleneimine (PEI) functionalized polyamide 6 (PA 6) (PEI-PA 6) nano-fiber/net (NFN), is developed as a novel sensing coating on quartz crystal microbalance (QCM) for highly sensitive formaldehyde detection. The NFN structured substrate comprising common electrospun nanofibers and two-dimensional (2D) spider-web-like nano-nets fabricated by a facile electro-spinning/netting (ESN) process, exhibit large specific surface area, high porosity and large stacking density, which make them optimal candidates for sensing applications. The responses of the sensors in response to formaldehyde were analyzed in terms of PA 6 NFN membranes morphologies, PA 6 substrate and sensing PEI coating loads, and the comparison with nanoporous fibers. Experimental results show that this new PEI-PA 6 NFN nanostructure based QCM sensor exhibits excellent formaldehyde sensing performances in terms of remarkably low detection limit (50 ppb), rapid response, superior selectivity and good reproducibility. We expect the highly sensitive and robust NFN-based QCM sensor may serve as a practical and powerful tool for gas sensing and chemical analysis.

A novel, ultrasensitive, selective and flexible sensor strip based on polyaniline/polyamide-6 (PANI/PA-6) nano-fiber/net (NFN) membranes for naked-eye colorimetric detection of Cu2+ ions in water is successfully prepared by a facile electro-spinning/netting (ESN) process. The sensing mechanism involves the transformations between different oxidation and doping forms of PANI. Upon exposure to Cu2+ aqueous solution, the sensors exhibit two significant reflectance intensity decreasing bands at 435 and 650 nm which induce the color changes from white to blue dramatically. This new sensor shows colorimetric response specifically to Cu2+ ions (white-to-blue color change) over other possible interfering metal cations and allows for detection of Cu2+ in aqueous solution with a low detection limit of 1 ppb observing by naked eye. Additionally, the colorimetric responses are visualized quantitative by using a color-differentiation map prepared from converted RGB (red, green and blue) values. Furthermore, the as-prepared PANI/PA-6 NFN sensor strips could successfully combine with the color map, which suggested a promising analytical method as an economical alternative to traditional Cu2+ sensors and also provided a new insight into the design and development of a novel colorimetric sensing system based on the NFN platform.

A number of fascinating properties of micro/nano-fibers can be obtained as their fine-structures are tuned. Here, we report a one-step procedure to construct nanoporous polystyrene (PS) fibers loaded with controllably distributed silica nanoparticlesvia tuning the solvent compositions in electrospinning. With decreasing solvent vapor pressure in electrospinning, the silica nanoparticles were clearly observed to be transferred from the interior of the PS fiber to its surface due to the phase separation of fluid jet in varying degrees. The silica nanoparticles embedded in the fibers exhibited porous cores contributing to an increase in Brunauer–Emmett–Teller surface area of the as-spun fibers. The presence of silica nanoparticles on the fiber surfaces enhanced the surface roughness with numerous papillae. Water droplets on a typical fiber surface readily sat on the apex of papillae because the air filled in these hierarchically roughened fibrous mats as a cushion, and therefore, displayed superhydrophobicity with a water contact angle of 156.7°. We believe that the exploitation of such a simple method for fine-controlling structures of micro/nano-fibers will endow these materials with new properties for some special applications such as in novel easy-cleaning coatings, microfluidic devices, and even smart membranes.

For the first time, two-dimensional (2D) gelatin nano-nets are fabricated by regulating the solution properties and several process parameters during electrospinning/electro-netting. The spider-web-like nano-nets that comprise interlinked one-dimensional (1D) ultrathin nanowires (10–35 nm) are stacked layer-by-layer and widely distributed in the three-dimensional (3D) porous membranes. The final morphology of the gelatin nano-nets, including nanowire diameter, area density and pore-width of the nano-nets, is highly dependent on the solution concentration, salt concentration, kinds of solvents, applied voltage, ambient temperature and relative humidity (RH). The occurrence of rapid phase separation on the splitting-film and the formation of hydrogen bond among gelatin molecules during electro-netting are proposed as the possible mechanisms for the formation of these spider-web-like nano-nets.Graphical abstractHighlights► Large-scale spider-web-like gelatin nano-nets (∼35 nm) were successfully fabricated via electro-netting. ► The formation of nano-net could be well controlled by regulating the solution properties and several process parameters during electrospinning/electro-netting. ► Nano-nets create enhanced interconnectivity and additional surface area which may have potential application in the field of biomaterials, tissue engineering and ultra-fine filters.

Poly(butylene succinate-co-terephthalate) (PBST) copolyesters, with rigid butylene terephthalate (BT) units varying from 50 to 70 mol%, were synthesized via direct esterification route. The chemical structure and comonomer composition were characterized by 1H NMR. The weight-average molecular weights (Mw) of the prepared products measured by GPC spanned a range of 1.39 × 105–1.93 × 105 with corresponding Mw/Mn value of 2.23–2.42. Based on the WAXD analysis, PBST copolyesters were identified to have the same crystal structure as that of poly(butylene terephthalate) (PBT). The researches on the thermal properties showed that the melting temperature and decomposed temperature of PBST copolyesters increased with the increasing content of rigid BT units through DSC and TGA measurement. Furthermore, the tensile test results presented that the copolyester with higher content of BT units had higher initial modulus, higher breaking strength but lower elongation at break. Additionally, the viscoelastic properties of the prepared PBST films were analyzed by DMA measurement. It was found that both storage modulus (E′) and loss modulus (E″) corresponding to the peak tended to heighten with the increase of BT units, indicating the copolyester with higher BT units content had the more prominent viscoelasticity. The peak of loss factor (tan δ) curve shifted to higher temperature as the content of rigid BT units increased due to the increasing of the glass transition temperature (Tg).

Mechanisms of unit yarn-reduction braiding were investigated and preform microstructures were characterized by digital image photography and topological analysis. Flexural properties and failure mechanisms of the unit yarn-reduction composites, cut composites and uniform composites were compared. Results indicated that continuity of the braiding process must be ensured after yarn reduction and distribution of the reduction units should be uniform. A smoothly trapezoidal profile appeared near the unit yarn-reduction cross-section and braiding angles and yarn lengths in the surface or interior yarn-reduction control volumes all increased. Flexural properties of the unit yarn-reduction composites were significantly higher than those of the cut composites and slightly lower than the uniform composites. The damage process of the yarn-reduction composites can be divided into the initial, developing and serious damage stages with yarn breakage being the dominant failure mechanism, while the primary failure mechanisms of the cut composites were matrix microcracking and fiber pulling-out.

Aqueous mixture of NaOH/urea/thiourea at a 8/8/6.5 composition and pre-cooled at −10 °C readily dissolved cellulose to produce stable solutions at relatively high concentrations. The exothermic dissolution process was favored at −2 to 0 °C. Aqueous NaOH/urea/thiourea solution as non-derivatizing solvent broke the intra- and inter-molecular hydrogen bonding of cellulose and prevented the approach toward each other of the cellulose molecules, leading to the good dispersion of cellulose to form solution. The strength of the solvent network structure as well as the interaction between cellulose and solvent decreased as a function of increasing solution temperature. In the semi-dilute entangled solutions (>3.5% concentration), the entropy-driven gelation occurred, and the gel temperature dropped with increasing cellulose contents in the solution. The NaOH/urea/thiourea/H2O was demonstrated to be the most powerful solvent among all aqueous NaOH solutions and this novel solvent does not degrade cellulose even after storage times of up to 1 month.

The two-parameter Weibull distribution does not always adequately describe the experimental bast fibre strength at different gauge lengths. For this reason, it was modified by incorporating the diameter variation of jute fibres in this paper. The fibre diameter was measured with an optical microscope. The three-parameter Weibull model was also used to compare with the modified model. It was found that as the fibre diameter variation increased the tensile strength of the jute fibre decreased. The strength predicted by modified Weibull distribution was more accurate than that of the two conventional models. In addition, the breaking strength of jute fibre was less sensitive to gauge length than that of cotton fibre because the breaking of jute filament involves ultimate cells breaking repeatedly and matrix cracking.

A novel, ultrasensitive, selective and flexible sensor strip based on polyaniline/polyamide-6 (PANI/PA-6) nano-fiber/net (NFN) membranes for naked-eye colorimetric detection of Cu2+ ions in water is successfully prepared by a facile electro-spinning/netting (ESN) process. The sensing mechanism involves the transformations between different oxidation and doping forms of PANI. Upon exposure to Cu2+ aqueous solution, the sensors exhibit two significant reflectance intensity decreasing bands at 435 and 650 nm which induce the color changes from white to blue dramatically. This new sensor shows colorimetric response specifically to Cu2+ ions (white-to-blue color change) over other possible interfering metal cations and allows for detection of Cu2+ in aqueous solution with a low detection limit of 1 ppb observing by naked eye. Additionally, the colorimetric responses are visualized quantitative by using a color-differentiation map prepared from converted RGB (red, green and blue) values. Furthermore, the as-prepared PANI/PA-6 NFN sensor strips could successfully combine with the color map, which suggested a promising analytical method as an economical alternative to traditional Cu2+ sensors and also provided a new insight into the design and development of a novel colorimetric sensing system based on the NFN platform.

A nanostructured complex, polyethyleneimine (PEI) functionalized polyamide 6 (PA 6) (PEI-PA 6) nano-fiber/net (NFN), is developed as a novel sensing coating on quartz crystal microbalance (QCM) for highly sensitive formaldehyde detection. The NFN structured substrate comprising common electrospun nanofibers and two-dimensional (2D) spider-web-like nano-nets fabricated by a facile electro-spinning/netting (ESN) process, exhibit large specific surface area, high porosity and large stacking density, which make them optimal candidates for sensing applications. The responses of the sensors in response to formaldehyde were analyzed in terms of PA 6 NFN membranes morphologies, PA 6 substrate and sensing PEI coating loads, and the comparison with nanoporous fibers. Experimental results show that this new PEI-PA 6 NFN nanostructure based QCM sensor exhibits excellent formaldehyde sensing performances in terms of remarkably low detection limit (50 ppb), rapid response, superior selectivity and good reproducibility. We expect the highly sensitive and robust NFN-based QCM sensor may serve as a practical and powerful tool for gas sensing and chemical analysis.

A simple and straightforward strategy of depositing a nanostructured complex, based on a polyethyleneimine (PEI) functionalized polyamide 6 (PA 6) (PEI-PA 6) nano-fiber/net (NFN), on a quartz crystal microbalance (QCM) sensor for humidity detection is demonstrated. The PA 6 NFN substrate, comprising common electrospun nanofibers and spider-web-like nano-nets fabricated by a versatile electro-spinning/netting (ESN) process, exhibits several fundamental characteristics, such as a remarkable specific surface area, high open porosity and good interconnectivity. Therefore, the sensors based on PEI-PA 6 NFN membranes show high sensitivity and fast response/recovery time to humidity, which outperform current porous structure-based sensors. The frequency changes by approximately three orders of magnitude with relative humidity (RH) varying from 2% to 95%. Moreover, the resultant sensors also presents relatively small hysteresis and long-term stability. For low RH levels, the response of the QCM sensor is dependent on water molecules adsorbed/desorbed masses on NFN membranes, whereas for increasing RH levels variations in interlayer expansion stress of NFN membranes derived from the swelling effect become prevalent. This study demonstrates that NFN structured materials are have potential applications for fabricating high performance humidity sensors.

A novel airborne particulate filtration medium, consisting of a two-tier composite structure, i.e., a nano-fiber/net (NFN) top layer and a conventional nonwoven microfibrous support, was demonstrated for highly efficient and low pressure drop filtration for the first time. The polyamide-66 (PA-66) NFN structured top layer, which is composed of traditional electrospun nanofibers and two-dimensional (2D) spider-web-like nano-nets, was electro-spinning/netting (ESN) deposited on the nonwoven polypropylene (PP) scaffold for constructing this new concept of filter. The morphology of NFN architecture, including fiber diameter, coverage rate, pore-width and layer-by-layer packing structure of the nano-nets, can be finely controlled by regulating the solution properties and several ESN process parameters. Taking advantage of several fascinating features such as extremely small diameter, high porosity, controllable coverage rate, nano-nets bring to the NFN/nonwoven composite filtration medium several excellent filtration features such as high filtration efficiency (up to 99.9%), low pressure drop, facile filters cleaning, and more lightweight.