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[en] High-performance microwave absorbers with excellent absorption ability and superhydrophobic property are extremely significant for the application of stealthy techniques, especially in high-humidity environment. In this research, high-performance Co-C nanofibers (NFs) were prepared via electrospinning mathod by using of poly (vinyl alcohol) (PVA) and Cobalt acetate tetrahydrate (CoAc) solution as precursor with subsequent PVA pyrolyzation and carbonization process. The electromagnetic (EM) parameters and microwave absorption performance of the prepared NFs were investigated with the microwave frequency ranging from 2.0 GHz to 18.0 GHz. Analysis and comparison were performed on the impedance matching and loss mechanisms of each sample. The experimental results indicated that the sample calcinated at 950 °C achieved an optimal reflection loss (RL) of − 33.1 dB and an effective frequency bandwidth of 4.1 GHz under a thickness of 1.5 mm; and that the Co-C NFs membrane with the optimal absorption performance exhibited superhydrophobic property with a contact angle (CA) of 152°, suggesting their promising application to water-resistant stealthy materials.
[en] Poly(lactic acid) (PLA) nanocomposite films reinforced with acetylated bacterial cellulose nanoribbons were prepared by solvent casting. Acetylation of bacterial cellulose (BC) was performed by an innovative and sustainable direct solvent-free route catalyzed by citric acid. The effect of derivatization and its extent on the morphological, optical, thermal and mechanical properties of the nanocomposites was analyzed. Data collected from the above studies showed that acetylation of BC nanoribbons clearly improved the nanofibers dispersion in the PLA matrix with respect to unmodified BC, which in turn resulted in increased transparency and mechanical properties of the nanocomposites produced.
[en] In this study, gelatin–polyethylenimine blend nanofibers (GEL/PEI) were fabricated via electrospinning with different ratios (9:1, 6:1, 3:1) to integrate the properties of both the polymers for evaluating its biomedical application. From scanning electron microscopy, the average diameter of blend nanofibers (265 ± 0.074 nm to 340 ± 0.088 nm) was observed to be less than GEL nanofibers (403 ± 0.08 nm). The incorporation of PEI with gelatin resulted in improved thermal stability of nanofibers whereas the Young’s modulus was observed to be higher at 9:1 ratio when compared with other ratios. The in vitro studies showed that the GEL/PEI nanofibers with 9:1 ratio promoted better cell adhesion and viability. GEL/PEI nanofibers with 9:1 and 6:1 showed hemolysis within the permissible limits. From the results, it could be interpreted that GEL/PEI nanofibers with 9:1 ratio proved to be a better scaffold thereby making them a potential candidate for tissue engineering applications.
[en] The helical micro/nanofiber arrays of polyvinylpyrrolidone (PVP) were successfully prepared by Near-field electrospinning(NFES) with different concentrations of PVP and different voltages by a gradient of per 0.5 kV from 1 kV to 2.2 kV. It is found that the morphology of the arrayed fibers evolved with regularity with the increase of the working voltage, and the uniformity of the fiber arrays also increased. The formation mechanism of the arrayed helical micro/nanofibers was analyzed. This may be a cost-effective method for the large-scale production of morphologically controllable spiral fibers, which opens up an effective way for the precise and controlled deposition of electrospun helical fibers and the integration of single or array spiral fibers with functional devices. (paper)
[en] Highlights: • Ba-doped LaFeO3 nanofibers (NFs) were prepared by a facile electrospinning process. • Ba-doping promotes the sensing response of LaFeO3 NFs toward ethanol gas. • Ba-doped LaFeO3 NFs have a relatively low optimum operating temperature. • La0.75Ba0.25FeO3 NFs show the highest sensitivity and rapid response-recovery. • The good performance is attributed to the unique structure and morphology feature of NFs.
[en] A new type of hydrophobic polyacrylonitrile (PAN) nanofiber is fabricated by solution blowing of a blend solution of fluorine-containing polyacrylate (FPA) and PAN. The nanofibers’ surface composition, hydrophobicity, and protection ability were evaluated to clarify the effects of FPA addition. Results revealed that FPA addition increased the nanofiber diameter, as well as enhanced the hydrophobicity and transport properties of the nanofiber mats. The mats had average water contact angles of 123.44°, 132.11°, and 137.11° for FPA contents of 0.66 wt%, 1.98 wt%, and 3.30 wt%, respectively. All these results suggested the potential of the solution blowing nanofiber mats as protection materials.
[en] In this study, a flexible highly sensitive strain sensor was fabricated using thermoplastic polyurethane (TPU) and carbonized woven fabric based on polyacrylonitrile nanofiber yarn (PNY). The carbonized PNY fabric was prepared according to the following steps: filaments fabricated by electro spinning were twisted into a yarn; the yarn was treated by a sizing agent and weaved as a weft yarn; subsequently, the woven fabric was washed, pressed, and dried; finally, the carbonized PNY woven fabric was obtained through stabilization and carbonization. The effects of the thickness of the TPU film and the structure of the fabric on the sensing properties are discussed. The flexible strain sensor exhibits excellent sensitivity in the high-sensing strain range (average gauge factor = 77.3 within 12% strain) and high durability and stability (more than 1000 stretching cycles at 5% strain). Moreover, the strain sensor exhibits an excellent linear relationship between the strain and relative resistance change and accurately detects a full range of human activities (both vigorous and subtle). Such flexible highly sensitive strain sensors can be easily incorporated onto the surfaces of textiles and within electronics for use in various applications, toward applications such as smart textiles and health monitoring.
[en] Highlights: • Miscibility of wool keratin/PA6 blends and electrospun fibres were investigated in depth. • Chemical structures and viscometric measurements revealed immiscibility between the two polymers in all blending ratios. • Immiscibility was confirmed by the observation of segregation phases between polymers in the cast films. • Due to kinetic effects, homogeneous nanofibers are obtained from the keratin/PA6 immiscible system,by electrospinning. • The PCA analysis highlighted the keratin percentage, as critical variable which influences the nanofibers diameter. Blends of wool keratin and polyamide 6 (PA6) have shown interesting adsorbent properties in filtration. In this work, the miscibility of keratin and PA6 was studied for the first time through rheological measurements of diluted blend solutions. In particular, the immiscibility between the two polymers in different blend proportions was observed by the segregation of phases in the cast films. Nevertheless, notwithstanding the immiscibility, we demonstrate here that homogeneous keratin/PA6 blend nanofibers can be obtained by electrospinning as a result of rapid solvent evaporation, where kinetic effects prevail on thermodynamic effects, thereby avoiding phase segregation. The obtained nanofibers have diameters ranging from 100 to 250 nm, depending on the experimental conditions. We show, through a principal component analysis (PCA) that the percentage of keratin represents the most important variable to determine nanofiber diameters. Collectively, this study represents a successful case of immiscible electrospinning system for production of useful nanofibers as adsorbent material for different applications.
[en] Spontaneous decay rates of atoms into guided modes of an optical nanofiber are found for atomic transitions between the hyperfine structure sublevels. The decay rates are evaluated for the hyperfine structure transitions in Rb atoms. The efficiency of the guided mode excitation by spontaneous decay of the specific hyperfine atomic states is examined for both the fundamental fiber mode HE11 and the higher-order modes TE01, TM01, and HE21.
[en] Highlights: • Zn(OAc)2 contents affected morphology and size of PVA/HA/Zn(OAc)2 nanofibers. • meso-HA/ZnO nanofibers were fabricated from PVA/HA/Zn(OAc)2 nanofibers. • Morphology and structure of meso-HA/ZnO nanofibers were investigated. • Antimicrobial activity of meso-HA/ZnO nanofibers depended on ZnO/HA ratio. • S. aureus was more sensitive to meso-HA/ZnO nanofibers than E. coli. - Abstract: The aim of this study is to develop antimicrobial mesoporous hydroxylapatite/zinc oxide (meso-HA/ZnO) nanofibers from polyvinyl alcohol/hydroxylapatite/zinc acetate (PVA/HA/Zn(OAc)2) electrospun nanofibers by calcination process. The antibacterial activities of meso-HA/ZnO nanofibers towards Staphylococcus aureus (S. aureus, ATCC6538) and Escherichia coli (E. coli, 8099) were evaluated. The meso-HA/ZnO nanofibers were composed of hexagonal HA and wurtzite ZnO phases. The representative meso-HA/ZnO nanofibers with ZnO/HA ratio at 1:5 showed a wormhole-like shape, main pore diameter around 25 nm and specific surface area at 24.81 m2/g. The inhibition efficiency of meso-HA/ZnO nanofibers increased with the increase of ZnO/HA ratio, however, S. aureus was more sensitive to meso-HA/ZnO nanofibers than E. coli. The meso-HA/ZnO nanofibers with ZnO/HA ratio at 1:10 exhibited effective antibacterial activity towards S. aureus, whereas, the ZnO/HA ratio was raised up to 1:5 towards E. coli. The experimental results suggested that the meso-HA/ZnO nanofibers might have potential as an antimicrobial activity material in biomaterial applications.