Electrospinning of biopolymer nanofibers encapsulated with functional nanoparticles toward core-shell fluorescence encoding

Photochromism has been an efficient approach to improve authenticity of commercial products. In order to prepare an authentication nanofibrous film with mechanical reliability, it has been crucial to improve the engineering production route of the authentication materials. Herein, we electrospun photoluminescent nanofibrous film with a fiber diameter of 50–200 nm from the environmentally-friendly polylactic acid embedded with nanoparticles of rare-earth activated strontium aluminate (NRESA; 10–15 nm). The created nanocomposite film was colorless in daylight, and became an intense green in ultraviolet light. The strontium aluminate photochromic agent must be applied in the nanoparticle form to ensure film transparency by enhancing its dispersion without aggregation in the electrospun polylactic acid nanofiber bulk. An emission peak was observed at 518 nm after excitation of the pigment-polylactic acid nanofibers at 365 nm. Raising NRESA ratio increased the hydrophobic properties of the pigment-polylactic acid nanofibers without changing their visual or mechanical properties. The transparent films showed high photochromic reversibility without exhaustion under numerous exposure cycles of ultraviolet light and darkness. The nanofibrous mats were elastic and flexible. The current technique is an effective strategy for making a variety of anti-counterfeiting substances.     

Preparation of dual mode encoding photochromic electrospun glass nanofibers for anticounterfeiting applications

Photochromism has shown to be a promising tool for improving the authenticity of commercially available products. Additionally, improving the engineering process of authentication patterns has been crucial to offer mechanically reliable anticounterfeiting nanofibers. Herein, the electrospinning technology was applied to develop mechanically reliable and photoluminescent silicon dioxide-based electrospun glass nanofibers (80–110 nm) embedded with lanthanide-activated aluminate (LA) nanoparticles (NPs; 1–2 nm) for anticounterfeiting purposes. The produced nanocomposite films exhibited photochromism from colorless in visible spectrum to green under ultraviolet irradiation. The nanofibrous film transparency was maintained by presenting the strontium aluminate pigment as nano-scaled particles, which improves its distribution and prevents the formation of aggregates in the electrospun glass nanofibrous bulk. After being excited at 365 nm, the nanofibers made of phosphor@glass (LANPs@GLS) displayed an emission band at 519 nm. Increases in the pigment ratio enhanced the hydrophobicity of the LANPs@GLS nanofibers without altering their intrinsic characteristics. The LANPs@GLS films exhibited fast and reversible photochromism without fatigue when activated by UV light. Transparency and flexibility were shown by the nanofibrous mats. The proposed technique is reliable for making a wide range of anticounterfeiting materials.     

Preparation of luminescent polyethylene plastic composite nano-reinforced with glass fibers

Electrospun glass nanofibers (EGNFs) were prepared to reinforce polyethylene (PE) plastic waste towards the development of photochromic anti-counterfeiting patterns and long-persistent photoluminescent materials, such as smart windows and concrete. By physical integration of lanthanide-doped aluminate (LdA) nanoparticles (NPs) into polyethylene plastic reinforced with EGNFs, a transparent lanthanide-doped aluminate nanoparticles (LdANPs)/EGNFs@PE sheet was produced. The colorless EGNFs@PE hybrids became green under ultraviolet (UV) rays and greenish-yellow in a darkened room as proved by CIE Lab and photoluminescence analysis. In the luminescent LdANPs/EGNFs@PE hybrids, the identified photochromism was promptly reversed at low concentrations of LdANPs to designate fluorescence emission. Photoluminescence was maintained with slow reversibility for the high phosphor concentrations to designate afterglow emission. LdANPs exhibit diameters of 5–12 nm, whereas glass nanofibers have diameters of 70–120 nm. The morphologies of LdANPs/EGNFs@PE substrates were studied by energy-dispersive x-ray spectroscopy (EDX), scanning electron microscopy (SEM), and x-ray fluorescence (XRF). The mechanical properties of the prepared polyethylene plastic were enhanced by reinforcement with glass nanofibers as a roughening agent. The photoluminescent substrates showed markedly improved scratch resistance in comparison to LdANPs-free EGNFs@PE substrate. The obtained luminescence spectra displayed an emission band at 519 nm upon excitation at 365 nm. The results demonstrated that the luminous plastic has improved hydrophobicity and UV shielding upon increasing the LdANPs content.     

Graphitic carbon nanofibers developed from bundles of aligned electrospun polyacrylonitrile nanofibers containing phosphoric acid

Graphitic carbon nanofibers (GCNFs) with diameters of approximately 300 nm were developed using bundles of aligned electrospun polyacrylonitrile (PAN) nanofibers containing phosphoric acid (PA) as the innovative precursors through thermal treatments of stabilization, carbonization, and graphitization. The morphological, structural, and mechanical properties of GCNFs were systematically characterized and/or evaluated. The GCNFs made from the electrospun PAN precursor nanofibers containing 1.5 wt.% of PA exhibited mechanical strength that was 62.3% higher than that of the GCNFs made from the precursor nanofibers without PA. The molecules of PA in the electrospun PAN precursor nanofibers initiated the cyclization and induced the aromatization during stabilization, as indicated by the FT-IR and TGA results. The stabilized PAN nanofibers possessed regularly oriented ladder structures, which facilitated the further formation of ordered graphitic structures in GCNFs during carbonization and graphitization, as indicated by the TEM, XRD, and Raman results.     

Synthesis of Porous NiO and ZnO Submicro- and Nanofibers from Electrospun Polymer Fiber Templates

Porous nickel oxide (NiO) and zinc oxide (ZnO) submicro- and nanofibers were synthesized by impregnating electrospun polyacrylonitrile (PAN) fiber templates with corresponding metal nitrate aqueous solutions and subsequent calcination. The diameter of the NiO and ZnO fibers was closely related to that of the template fibers and larger diameters were obtained when using the template fibers with larger diameter. SEM results showed that the NiO and ZnO fibers have a large amount of pores with diameters ranging from 5 nm to 20 nm and 50 nm to 100 nm, respectively. Energy dispersive X-ray (EDX) spectra and X-ray diffraction (XRD) patterns testified that the obtained materials were NiO and ZnO with high purity.     

Template‐Based Synthesis of Aluminum Nitride Hollow Nanofibers Via Plasma‐Enhanced Atomic Layer Deposition

Aluminum nitride (AlN) hollow nanofibers were synthesized via plasma‐enhanced atomic layer deposition using sacrificial electrospun polymeric nanofiber templates having different average fiber diameters (~70, ~330, and ~740 nm). Depositions were carried out at 200°C using trimethylaluminum and ammonia precursors. AlN‐coated nanofibers were calcined subsequently at 500°C for 2 h to remove the sacrificial polymeric nanofiber template. SEM studies have shown that there is a critical wall thickness value depending on the template's average fiber diameter for AlN hollow nanofibers to preserve their shapes after the template has been removed by calcination. Best morphologies were observed for AlN hollow nanofibers prepared by depositing 800 cycles (corresponding to ~69 nm) on nanofiber templates having ~330 nm average fiber diameter. TEM images indicated uniform wall thicknesses of ~65 nm along the fiber axes for samples prepared using templates having ~70 and ~330 nm average fiber diameters. Synthesized AlN hollow nanofibers were polycrystalline with a hexagonal crystal structure as determined by high‐resolution TEM and selected area electron diffraction. Chemical compositions of coated and calcined samples were studied using X‐ray photoelectron spectroscopy (XPS). High‐resolution XPS spectra confirmed the presence of AlN.     

Dual-mode dichromatic SrBi4Ti4O15: Er3+ emitting phosphor for anti-counterfeiting application

Fluorescent materials have been widely used for anti-counterfeiting of important documents and currencies, wherein their anti-counterfeit abilities could be improved through multi-mode excitation. Herein, dual-mode-excited double-colour-emitting Er³⁺doped SrBi₄Ti₄O₁₅ up-conversion (UC) phosphors (SBTO: Er³⁺) were synthesised, and their UC spectra included green (2H11/2/4S3/2 → 4I15/2) and red (4F9/2 → 4I15/2) emissions from Er3+ ions under 980 or 1550 nm excitation. However, the green emission colour of phosphors was independent of dopant concentration under 980 nm laser irradiation; whereas the final emission colour was dominated by red emission and significantly affected by contents of Er3+ under 1550 nm excitation. These observations demonstrated potential application in dual-mode double-colour anti-counterfeiting. The possible UC mechanisms and emission characteristics of the phosphors using different 980 and 1550 nm irradiation source were contrastively investigated, and some fluorescent security patterns were also designed to demonstrate the potential applications in anti-counterfeiting and concealing important information.     

Nanofibers from recycle waste expanded polystyrene using natural solvent

Summary A new recycling technique has been developed. In this method, EPS (expanded polystyrene), generally called Styrofoam, is dissolved with natural solvent, d-limonene and electrospun. This method can economically produce the nanofibers. The electrospinning process produces a nonwoven mat of long polymer fibers with diameters in the range of 10–500 nm and high surface areas per unit mass. PS (Polystyrene) polymer dissolved in different solvents such as THF (Tetrahydrofuran), DMF (Dimethylformaide), and DMAc (Dimethylacetamide) etc. may all be electrospun into nanofibers. These solvents cause environmental problem and difficulty of process handling. Natural solvent, d-limonene is used for dissolving PS. PS nanofibers are produced with PS solution using d-Limonene. This paper describes the use of polystyrene (PS) nanofibers electrospun from recycled EPS solution dissolved in d-limonene. The electrospun polystyrene nanofiber diameters vary from 300 to 900 nm, with an average diameter of about 700 nm.     

Rare earth doped double perovskite nanocrystals with controllable emission wavelength and model for high-level anti-counterfeiting

Fluorescent anti-counterfeiting technology has become one of the most commonly used anti-counterfeiting technologies because of its simple preparation, low cost and high safety. However, there are still some key technical problems to be solved in developing multi-mode and polychromatic fluorescent materials for high-level anti-counterfeiting. Herein, Yb³⁺/Er³⁺ codoped Cs₂AgIn_0.99Bi_0.01Cl₆ double perovskite nanocrystals (DPNCs) with dual-mode polychromatic emission were developed. Under the irradiation of 365 nm ultraviolet (UV) light, the DPNCs emitted a bright downshifting (DS) yellow light, which comes from the self-trapping excitons (STEs) recombination. While the DPNCs produced upconversion (UC) green fluorescence under the 980 nm laser excitation, which is attributed to the transitions of ²H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2 of Er³⁺ ions. In view of its dual-mode and polychromatic fluorescence characteristics, a high-level anti-counterfeiting based on this fluorescent material is designed. Moreover, the brightness of the anti-counterfeiting pattern based on this material decreases very little after three months. These results indicated that the dual-mode and polychromatic DPNCs reported have potential application in information encryption and identity recognition.     

Preparation and photochromic behavior of borosilicate aluminate glass for smart window and curtain wall applications

Sunlight-induced photochromic glass exhibits attractive application prospects in the field of architecture materials. In this work, a series of borosilicate aluminate photochromic glasses containing AgCl nanocrystals were prepared. The photochromic property and mechanisms were systematically investigated. The color of the glass turned from transparent to black (or dark grey) under the irradiation of 365 nm ultraviolet light (or sunlight). Placing in a dark environment, the color of photochromic glass gradually restores to its initial state. From the results of in situ TEM and XPS measurement, it is found that the photochromic and self-bleaching behavior of borosilicate aluminate glass originated from the formation and decomposition of silver nanoparticles. Utilizing the photochromic and self-bleaching properties of the glass, the transmittance of the glass could be reversibly modulated. The cycle measurement shows excellent repeatability, demonstrating the potential application of AgCl-contained borosilicate aluminate photochromic glass in the fields of smart building windows and curtain walls.     

Reinforcement of styrene-acrylonitrile polymer bulk with glass nanofibers to introduce photoluminescent bricks

Transparent and mechanically reliable plastic was developed by reinforcing styrene-acrylonitrile polymer (SAP) with electrospun glass nanofibers (EGN). The physical inclusion of strontium aluminate nanoparticles (SAN) produced long-persistent photoluminescent and photochromic EGN@SAP bricks or smart windows. EGN were fabricated by electrospinning technique and incorporated as a toughening mediator into styrene-acrylonitrile plastic to boost its mechanical properties. Transparency of EGN@SAP with the capacity to shift to green under ultraviolet (UV) illumination was verified using photoluminescence analysis and CIE Lab parameters. EGN@SAP with low content of SAN exhibited immediate reversibility of the photochromic feature, proving fluorescence emission. Afterglow emission from EGN@SAP embedded with high concentration of SAN persisted for longer time and was less easily reversed. After excitation at 365 nm, the emission peaked at 519 nm. Increasing the SAN content resulted in improved hydrophobicity and UV protection. Diameter measurements of SAN (6–14 nm) and EGN (75–300 nm) were taken utilizing transmission electron microscopy and scanning electron microscopy, respectively. EGN and EGN@SAP bricks were analyzed for their morphological characteristics using a variety of analytical techniques. The scratch resistance of EGN@SAP bricks containing SAN was enhanced in comparison to SAN-free EGN@SAP bricks.     

Thermo-chemical reactions occurring during the oxidative stabilization of electrospun polyacrylonitrile precursor nanofibers and the resulting structural conversions

Thermo-chemical reactions occurring during the oxidative stabilization of electrospun polyacrylonitrile (PAN) precursor nanofibers with diameters of approximately 300 nm were investigated as well as the resulting structural conversions, and the results were compared to those of conventional SAF 3K (Courtaulds) precursor fibers. The study revealed that: (1) the nitrile groups in the electrospun nanofibers possessed a higher reactivity than those in the SAF 3K fibers; (2) the macromolecules in the electrospun nanofibers predominantly underwent inter-molecular cyclization/crosslinking while those in the SAF 3K fibers underwent intra-molecular cyclization during the early stages of stabilization; and (3) under the same stabilization conditions, the structural conversion from linear macromolecules to aromatic ring/ladder structures in the electrospun nanofibers occurred faster and more thoroughly than in the SAF 3K fibers. These characteristics combined with other properties, including small diameter and high degree of structural perfection, suggest that electrospun PAN precursor nanofibers may be used to develop continuous nano-scale carbon fibers with superior mechanical strength, especially if the electrospun nanofibers could be further aligned and stretched.     

Designing lanthanide-doped nanocrystals with both up- and down-conversion luminescence for anti-counterfeiting

The widespread forgery in all kinds of paper documents and certificates has become a real threat to society. Traditional fluorescent anti-counterfeiting materials generally exhibit unicolor display and suffer greatly from substitution, thus leading to a poor anti-counterfeiting effect. In this work, unseen but significant enhanced blue down-conversion emission from oleic acid-stabilized lanthanide-doped fluoride nanocrystals is first present and the mechanism is proposed and validated. This not only endows these nanocrystals with dual-mode fluorescence, but also offers a simplified synthesis approach for dual-mode fluorescent nanocrystals involving no further complicated assembly or coating procedures, unlike the traditional methods. Furthermore, by changing the host/dopant combination or the content of dopant, these nanocrystals can exhibit simultaneously multicolor up-conversion emission under excitation at near-infrared light and unalterable blue down-conversion emission under ultraviolet light. A preliminary investigation of their anti-counterfeiting performance has been made, and the results indicate that this color tuning capability and high concealment makes these nanocrystals behave in a similar way to chameleons and can provide a strengthened and more reliable anti-counterfeiting effect.     

Crystal polymorphism in electrospun composite nanofibers of poly(vinylidene fluoride) with nanoclay

We investigated for the first time the morphology and crystal polymorphism of electrospun composite nanofibers of poly(vinylidene fluoride) (PVDF) with two nanoclays: Lucentite™ STN and SWN. Both nanoclays are based on the hectorite structure, but STN has organic modifier in between the layers of hectorite while SWN does not. PVDF/nanoclay was dissolved in N,N-dimethylformamide/acetone and electrospun into composite nanofiber mats with fiber diameters ranging from 50-800 nm. Scanning electron microscopy shows that addition of STN and SWN can greatly decrease the number of beads and make the diameter of the nanofibers more uniform due to the increase of electrospinning solution conductivity brought by the nanoclay. Infrared spectroscopy and X-ray diffraction confirm that both STN and SWN can induce more extended PVDF chain conformers, found in beta and gamma phase, while reducing the alpha phase conformers in electrospun PVDF/Nanoclay composite nanofibers. With the attached organic modifier, even a small amount of STN can totally eliminate the non-polar alpha crystal conformers while SWN cannot. The ionic organic modifier makes STN much more effective than SWN in causing crystallization of the polar beta and gamma phases of PVDF. An ion-dipole interaction mechanism, suggested by Ramasundaram, et al. is utilized to explain the crystal polymorphism behavior in electrospun PVDF/nanoclay composite nanofibers.     

Simple preparation of long-persistent luminescent paint with superhydrophobic anticorrosion efficiency from cellulose nanocrystals and an acrylic emulsion

Novel photoluminescent paint was prepared for safety marking purposes using an emulsion system composed of an acrylic polymer, cellulose nanocrystals and lanthanide-doped strontium aluminate (LdSA) nanopaticles. The effect of LdSA concentration in the paint formula was investigated. Cellulose nanocrystals (CNCs) have been an attractive reinforcement material that can be incorporated into protective coatings due to their distinctive properties, such as biocompatibility, biodegradability, and renewability. The produced acrylic/cellulose nanocrystals/lanthanide-doped strontium aluminate paints were applied onto different surfaces of asphalt concrete and tinplate panels. LdSA was developed in the nano-scale form as described by transmission electron microscope (TEM) to allow a better dispersion in the paint formula. The applied paints were studied by energy-dispersive X-ray spectroscopy (EDS), X-ray fluorescence (XRF), scan electron microscopy (SEM), and infrared spectra (FTIR). Both transparency and coloration measurements of the applied paints were investigated by luminescence spectra and CIE Lab. The resistance to scratching, hydrophobic and corrosion resistivity were investigated. CNCs were monitored to be a key component for the anti-corrosion activity. The best long-lived luminescence was monitored for more that 60 min in the dark for LdSA concentration of 12% w/w. The paints containing cellulose nanocrystals and sodium hexametaphosphate demonstrated satisfactory results upon mixing with acrylic emulsion.     

Electrospun ZnO Nanofibers‐Based Ultraviolet Detector with High Responsivity

In this report, a metal–semiconductor–metal (MSM) ultraviolet photodetector based on ZnO nanofiber film with Au electrodes was demonstrated. The ZnO nanofibers were synthesized via effective electrospinning process and characterized by means of XRD, SEM, XPS, and UV–visible absorption spectra. At 5 V bias, the dark current of the device was 17.8 nA. Under the irradiation of 260 nm ultraviolet light, the photocurrent could reach 11.5 μA and a high responsivity of 790 A/W was achieved due to the large internal gain. The mechanism of the high internal photoconductive gain was discussed in the article. The experiment presented a general and simple approach to integrate electrospun nanomaterials into photodevices directly.     

Preparation of Mineralized Electrospun Fibers as a Biomimetic Nanocomposite

Mineralization of gelatin electrospun nano and micro fiber was investigated in order to prepare a biomimetic bone nanocomposite. For this aim, at first, calcium containing gelatin nanofibers were electrospun by a novel ethanol/water/salt solution. Fibers with mean diameters varying from 300 to 3000 nm were acquired. Then, fiber mats were exposed to phosphate ions by soaking them in phosphate solution or laminating them between phosphate containing gelatin films. SEM micrographs demonstrated the presence of nano to micro sized minerals on gelatin fibers. FTIR and XRD results illustrated that the calcium phosphates in all samples are combinations of brushite and hydroxyapatite.     

Preparation of Aligned Ultra-long and Diameter-controlled Silicon Oxide Nanotubes by Plasma Enhanced Chemical Vapor Deposition Using Electrospun PVP Nanofiber Template

Well-aligned and suspended polyvinyl pyrrolidone (PVP) nanofibers with 8 mm in length were obtained by electrospinning. Using the aligned suspended PVP nanofibers array as template, aligned ultra-long silicon oxide (SiOx) nanotubes with very high aspect ratios have been prepared by plasma-enhanced chemical vapor deposition (PECVD) process. The inner diameter (20–200 nm) and wall thickness (12–90 nm) of tubes were controlled, respectively, by baking the electrospun nanofibers and by coating time without sacrificing the orientation degree and the length of arrays. The micro-PL spectrum of SiOx nanotubes shows a strong blue–green emission with a peak at about 514 nm accompanied by two shoulders around 415 and 624 nm. The blue–green emission is caused by the defects in the nanotubes.     

Ultrafine electrospun nanofiber created from cross-linked polyimide solution

This paper reports a novel study focused on the preparation of non-beaded ultrafine uniform nanofibers with a narrow fiber diameter distribution from fluorinated polyimide by electrospinning. Increasing the viscosity of the polymer solutions by the addition of hexamethylenediamine (HMDA) as a cross-linking agent can result in electrospun nanofibers with a smaller diameter. The cross-linking reaction between the polyimide and HMDA was examined by FTIR-ATR and GPC under different cross-linking times. The ultrafine uniform nanofibers were achieved with the use of HMDA. Finally, we successfully prepared the non-beaded ultrafine uniform nanofibers within a narrow nano-range (27 ± 5 nm).     

Photoluminescent electrospun polymeric nanofibers incorporating germanium nanocrystals

The photoluminescent germanium nanocrystals (Ge-NCs) were successfully incorporated into electrospun polymeric nanofiber matrix in order to develop photoluminescent nanofibrous composite web. In the first step, the synthesis of Ge-NCs was achieved by nanosecond pulsed laser ablation of bulk germanium wafer immersed in organic liquid. The size, the structural and the chemical characteristics of Ge-NCs investigated by TEM, XPS, XRD and Raman spectroscopy revealed that the Ge-NCs were highly pure and highly crystalline having spherical shape within 3–20 nm particle size distribution. In the second step, Ge-NCs were mixed with polyvinyl alcohol (PVA) polymer solution, and then, Ge-NC/PVA nanofibers were obtained via electrospinning technique. The electrospinning of Ge-NCs/PVA nanoweb composite structure was successful and bead-free Ge-NCs/PVA nanofibers having average fiber diameter of 185 ± 40 nm were obtained. The STEM analysis of the electrospun Ge-NCs/PVA nanofibers elucidated that the Ge-NCs were distributed homogeneously in the polymeric nanofiber matrix. The UV–Vis absorption and photoluminescence spectroscopy studies indicated the quantum confinement effect of Ge-NCs on the optical properties of the electrospun Ge-NCs/PVA nanoweb.