Graphene oxide improved thermal and mechanical properties of electrospun methyl stearate/polyacrylonitrile form-stable phase change composite nanofibers

In the present work, a novel PAN-based form-stable composite phase change materials with the methyl stearate (MES) encapsulated in the supporting matrices of polyacrylonitrile (PAN) nanofibers were fabricated through electrospunning for the storage and retrieval of thermal energy. Influences of graphene oxide (GO) addition on the chemical properties, structural morphologies, mechanical properties, thermal energy storage properties, thermal stability, and thermal energy storage/retrieval rates of electrospun MES/PAN/GO phase change composite nanofibers were systematically investigated by FT-IR, FE-SEM, tensile testing, DSC, TG, and measurement of melting/freezing times, respectively. The results revealed that the incorporation of GO effectively enhanced the mechanical properties, thermal stability, as well as heat storage and release rates of the phase change composite nanofibers. The averaged tensile strength of electrospun MES/PAN/GO phase change composite nanofibers increased significantly by 573 % with 10 mass% loading of GO, while elongation at break had a maximum 107 % increment when adding 3 mass% of GO. The DSC results indicated that the electrospun PAN-based phase change composite nanofibers with various GO loadings had suitable phase transition temperatures with the latent heat ranging from about 92 to 109 kJ kg^?1 and exhibited good thermal reliability in terms of DSC measurements during 50 melting-freezing cycles. Moreover, the melting and freezing time were significantly decreased about 44 and 43 % for the MES/PAN/GO5, as well as 59 and 64 % for the MES/PAN/GO10 after introducing the GO into the composite nanofibers systems.     

Simple fabrication of cellulose nanofibers via electrospinning of dissolving pulp and tunicate

This work demonstrates a simple fabrication of cellulose nanofibers by direct electrospinning of dissolved cellulose solutions. The hard- and softwood pulps and the outer mantles of tunicate were dissolved in a mixture of trifluoroacetic acid and dichloroethane by stirring and ultrasonication to give highly viscoelastic, clear solutions. These solutions were electrospun to form continuous nanofibers made of unsubstituted cellulose, which were confirmed by scanning electron microscopy (SEM) and IR spectroscopy. Statistical analysis of the SEM images of the nanofibers suggested that there are positive correlations between diameters of the nanofibers and concentration of the cellulose solution. The mean diameters of the nanofibers obtained from softwood pulp (DP of cellulose ≈ 1200) solutions were larger than those from hardwood pulp (DP of cellulose ≈ 500) at the same concentrations. This indicates that the DP of cellulose is one of the important parameters to control the diameters of the electrospun cellulose nanofibers.     

Nonenzymatic hydrogen peroxide sensor based on a glassy carbon electrode modified with electrospun PdO-NiO composite nanofibers

A glassy carbon electrode was modified with PdO-NiO composite nanofibers (PdO-NiO-NFs) and applied to the electrocatalytic reduction of hydrogen peroxide (H₂O₂). The PdO-NiO-NFs were synthesized by electrospinning and subsequent thermal treatment, and then characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Factors such as the composition and fraction of nanofibers, and of the applied potential were also studied. The sensor exhibits high sensitivity for H₂O₂ (583.43 μA?·?mM^?1?·?cm^?2), a wide linear range (from 5.0 μM to 19 mM), a low detection limit (2.94 μM at an SNR of 3), good long term stability, and is resistant to fouling.

Structural characterization of nano-crystalline Co3O4 ultra-fine fibers obtained by sol–gel electrospinning

In this paper, we report the obtention of ultrafine fibers of cobalt oxide (Co₃O₄) by combining electrospinning method with high-temperature calcinations from the precursor sol of poly(2-ethyl-2-oxazoline) (PEtOx)/cobalt acetate tetrahydrate [Co(CH₃COO)₂·4H₂O] in water. The optimum electrospinning conditions for obtaining precursor composite nanofibers from PEtOx/Co(CH₃COO)₂·4H₂O solution in water, to produce ceramic nanofibers, were studied. The average fiber diameter of the precursor composite fibers measured by scanning electron microscopy (SEM) was approximately 200 nm. Thermogravimetric analysis of PEtOx was performed to estimate the suitable calcination temperature of the precursor fibers. SEM images of the ceramic fibers obtained after calcination revealed the shrinkage in diameter due to complete degradation of the polymer and Co(CH₃COO)₂·4H₂O. Fourier transform infrared spectroscopy was used to ensure the complete pyrolysis of polymer during calcinations of the composite fibers. Crystalline properties of the ceramic fibers were studied by X-ray diffraction and high resolution transmission electron microscopy. The ceramic fibers are polycrystalline with an average grain size of ≈40 nm obtained at a calcination temperature of 773 K. It was observed that the grain sizes increased as the calcination temperature was increased, due to self assembly mechanism.     

Sol-Gel Co-Electrospun LiNiO2 Hollow Nanofibers

Using a coaxial capillary spinneret electrospinning technique combined with the sol-gel method, the nickelic xerogel hollow nanofibers first were prepared and the polycrystalline LiNiO₂ hollow nanofibers were obtained after sintering. The obtained hollow nanofibers were about 500 nm to 4 µm in outer diameter, and were made up of 20 ～ 30 nm nanocrystals. The xerogel hollow nanofibers and those calcined at different temperatures were characterized by thermogravimetric (TG) analysis, Fourier transform infrared (FTIR) spectrum, x-ray diffractometry (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM).     

A composite polyaniline/graphene–coated polyamide6 nanofiber mat for electrochemical applications

In this study, polyamide6 (PA6) nanofiber mats were fabricated through the electrospinning process. The nanofibers were coated by polyaniline (PANI) using the in situ polymerization of aniline in the presence of graphene oxide. The composite of the PANI/graphene oxide–coated nanofiber mat was treated with hydrazine monohydrate to reduce graphene oxide to graphene, and this was followed by the reoxidation of PANI. Field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), wide angle X‐ray diffraction (WAXD), thermal gravimetric analysis (TGA), tensile strength tests, electrical conductivity measurements, cyclic voltammetry (CV), and charge/discharge measurements were conducted on the composite PA6/graphene nanofiber mats. It was found that the surface of the PA6 nanofibers was coated uniformly with the granular PANI and graphene oxide. Besides, the composite nanofibers showed good tensile and thermal properties. Their electrical conductivity and specific capacitance, when used as a separator in the cell, were 1.02 × 10^?4 S/cm and 423.28 F/g, respectively. Therefore, the composite PANI/reduced graphene oxide–coated PA6 nanofiber mats could be regarded as suitable candidates for application in energy storage devices.     

Microstructure of SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> hybrid electrospun nanofibers and their application in dye degradation

SiO₂/TiO₂ hybrid nanofibers were prepared by electrospinning and applied for photocatalytic degradation of methylene blue (MB). The phase structure, specific surface area, and surface morphologies of the SiO₂/TiO₂ hybrid nanofibers were characterized through thermogravimetry (TG), X-ray diffraction (XRD) analysis, Brunauer–Emmett–Teller (BET) analysis, scanning electron microscopy (SEM), etc. XRD measurements indicated that doping of silica into TiO₂ nanofibers can delay the phase transition from anatase to rutile and decrease the grain size. SEM and BET characterization proved that silica doping can remarkably enhance the porosity of the SiO₂/TiO₂ hybrid nanofibers. The MB adsorption capacity and photocatalytic activity of the SiO₂/TiO₂ hybrid nanofibers were distinguished experimentally. It was found that, although increased silica doping content could enhance the MB adsorption capacity, the intrinsic photocatalytic activity gradually dropped. The SiO₂ (10 %)/TiO₂ composite nanofibers exhibited the highest MB degradation rate, being superior to SiO₂ (20 %)/TiO₂ or pure TiO₂.     

静电纺丝法制备聚乳酸/纳米磷酸钙复合纳米纤维及其表征

首先合成了纳米磷酸钙(NCP),用扫描电镜(SEM)和X射线衍射(XRD)进行了表征.再利用静电纺丝法制备了PLA/NCP复合纳米纤维,对纤维进行了TEM,SEM,XRD以及单轴拉力测试的表征.TEM和XRD测试表明,NCP已成功掺杂到聚乳酸纤维中,获得的纤维为复合纤维.SEM测试表明,NCP在溶液中浓度较小时,复合纳米纤维的形貌变化不大;NCP浓度超过PLA质量的7%后,纤维表面出现粒状物;随着浓度继续增大,粒状物逐渐增多,最后很难成纤.拉伸实验结果表明,复合纤维拉伸强度先随着NCP浓度的增加而增大,但NCP浓度超过7%后拉伸强度随着浓度的增加反而减小.     

Fabrication and characterization of NiTiO3 nanofibers by sol–gel assisted electrospinning

Continuous NiTiO₃ nanofibers have been successfully synthesized by a sol–gel assisted electrospinning method followed by calcination at 600 °C in air. These nanofibers were characterized for the morphological, structural and optical properties by scanning electron microscopy (SEM), energy-dispersive X-ray spectrum (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectra (XPS) and UV–visible (UV–vis) diffuse reflectance spectroscopy (DRS). SEM results reveal that the obtained NiTiO₃ nanofibers are 175 nm in diameter and several micrometers in length after annealing at 600 °C. The XRD analysis shows that the nanofibers possess highly crystalline structure with no impurity phase. In contrast, the NiTiO₃ nanoparticles synthesized at the identical conditions by a sol–gel route have impurities including TiO₂ and NiO. Moreover, the electrospun NiTiO₃ nanofibers are endowed with an obvious optical absorbance in the visible range, demonstrating they have visible light photoresponse.     

Thermal,morphological, and mechanical properties of ethyl vanillin immobilized in polyvinyl alcohol by electrospinning process

In this study, polyvinyl alcohol (PVA) nanofibers with ethyl vanillin as an active compound were prepared using electrospinning technique. The final products of electrospinning process were in the form of nanofibers films. PVA/ethyl vanillin nanofibers, having fibers diameters in the range 100–1700 nm, were successfully electrospun from ethanol/water mixture of PVA and ethyl vanillin. The effects of immobilization process on ethyl vanillin thermal properties were investigated by differential scanning calorimetry (DSC). The results of DSC showed significant influence of immobilization process on thermal properties of ethyl vanillin. It was noticed that melting point of immobilized ethyl vanillin was lower (~55 °C) compared to free flavor (~77 °C). Our results showed that films based on PVA/ethyl vanillin nanofibers are mechanically stable.     

聚乙烯吡咯烷酮/四氧化三铁复合纳米纤维的制备与表征

采用静电纺丝方法制备了聚乙烯吡咯烷酮/四氧化三铁复合纳米纤维, 并用透射电子显微镜(TEM)、X射线衍射(XRD)、热失重分析(TGA)和振动磁力分析进行了表征, 探讨了复合物的结构及其性能.     

In situ synthesis of ZnO nanocrystal/PET hybrid nanofibers via electrospinning

Hybrid nanofibers of ZnO precursors/PET were fabricated by electrospinning a nonaqueous poly(ethylene terephthalate) (PET) solution containing zinc acetate dihydrate. Scanning electron microscopy images showed that the as prepared nanofibers had smooth and uniform surfaces, and the diameter was decreased with increasing zinc acetate dihydrate content and reducing PET concentration. After the treatment by a mild process of immersing the fibers in ammonia‐ethanol mixtures (pH ≈ 9–11), the surface of the nanofibers became rough during the formation of ZnO nanocrystals in the fibers. High resolution transmission electron microscopy images showed that the mean particle size became smaller with increasing diameter of the polymer fibers and decreasing content of ZnO. Fourier transform infrared spectra confirmed the ZnO formation in the hybrid nanofibers. X‐ray diffractometry patterns indicated that ZnO had the Wurtzite structure. The formation and growth of ZnO nanocrystals in the nanofiber matrices was also influenced by the various other parameters, that is, the pH value of the reaction solution, the content of zinc acetate dihydrate within the fibers, the reaction time and temperature. Photoluminescence spectra under excitation at 300 nm revealed a broad and intense ultraviolet emission. The UV‐visible diffuse reflectance spectra demonstrated the blue shift in the absorbance curve, which was ascribed to the quantum confinement effects of ZnO nanoparticles in the hybrid materials. These hybrid nanofibers can potentially be used in light emitters, chemical sensors, photo‐catalysts and solar cells. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1360–1368, 2011     

Effect of pullulan/poly(vinyl alcohol) blend system on the montmorillonite structure with property characterization of electrospun pullulan/poly(vinyl alcohol)/montmorillonite nanofibers

Nanofibers of the composite of pullulan (PULL), poly(vinyl alcohol) (PVA), and montmorillonite clay (MMT) were prepared using electrospinning method in aqueous solutions. Pullulan is an interesting natural polymer for many of its merits and good properties. Because of biocompatibility and non-toxicity of PVA, it could be used in numerous fields. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), X-ray diffraction (XRD), and thermal gravimetric analysis (TGA) were done to characterize the PULL/PVA/MMT nanofibers morphology and properties. XRD patterns and FTIR data demonstrated that there were good interactions between PULL and PVA caused by possibly hydrogen bonds. Moreover, XRD data and TEM images indicated that intercalated and exfoliated MMT nanoplatelets can be obtained within the PULL/PVA/MMT nanofibers depending on the PULL/PVA blend ratios. Furthermore, the thermal stability and mechanical property (tensile strength) of PULL/PVA/MMT nanofibers could be enhanced more by exfoliated MMT nanoplatelets than intercalated structures of that nanoplatelets.     

Fabrication of polyacrylonitrile/lignin-based carbon nanofibers for high-power lithium ion battery anodes

Low-cost carbon nanofibers are fabricated from lignin, the second most abundant raw material in wood after cellulose and polyacrylonitrile mixture as a carbon precursor by electrospinning, followed by suitable heat treatments. As the lignin content in the precursor increases, the carbon nanofibers become thinner, as seen from scanning electron microscopy images. However, their carbon structure and electrochemical performance are found to be very similar, even though surface functional groups on carbon nanofibers are slightly different from each other. For example, in the initial charge (lithium insertion) and discharge (lithium deinsertion) process, the reversible specific capacities of the various carbon nanofibers come from different precursor ratios of lignin and polyacrylonitrile are similar. Even at a fast (7 min) charge and discharge condition, the carbon nanofibers prepared from the lignin-containing precursors show a discharge capacity of 150 mAh g^?1. The lignin-based carbon nanofibers thus show promise for use in high-power lithium ion battery anodes with low price.     

Novel Hydrogen Peroxide Biosensor Based on Hemoglobin Combined with Electrospinning Composite Nanofibers

A facile strategy to construct an amperometric biosensor was described for the determination of hydrogen peroxide (H₂O₂). This biosensor relied on an electrospinning gold nanoparticle-chitosan-poly(vinyl alcohol) composite nanofibers modified ITO electrode, followed by immobilization of hemoglobin (Hb) on the surface. The introduction of nanofibers and gold nanoparticles in the modification of electrode surface not only enhanced the surface area of the modified electrode for enzyme immobilization but also facilitated the electron transfer rate. Under optimum conditions, the sensor was characterized in terms of its morphology by scanning electron microscopy and its electroactivity by cyclic voltammetry and chronoamperometry. Scanning electron microscopy revealed that the obtained nanofibers were uniform. The chronoamperometric behavior of the modified electrode indicated that the immobilized Hb retained electrochemical activity inside the electrospinning fibrous membranes. The electrode responded linearly to H₂O₂ in a wider concentration range of 5.6 × 10^?7 M to 5.2 × 10^?2 M with a low detection limit (S/N = 3) of 1.98 × 10^?7 M and a short response time of ～4 s, suggesting a much better performance than that of other sensors. Moreover, the biosensor achieved bulk production and exhibited superior properties for the sensitive determination of H₂O₂, studied namely, long-term stability, good reproducibility, and high selectivity.     

SnO2/TiO2复合纳米纤维的制备及光催化性能

采用静电纺丝技术,以聚乙烯吡咯烷酮和钛酸正丁酯为前驱体,制得锐钛矿相TiO2纳米纤维。以TiO2纳米纤维为模板,通过水热合成法,制备了具有异质结构的SnO2/TiO2复合纳米纤维。利用扫描电镜(SEM)、X射线能量色散光谱（EDS）、透射电镜(TEM)和X射线衍射(XRD)等分析测试手段对其形貌和结构进行了表征,结果表明,SnO2纳米粒子均匀地生长在TiO2纳米纤维表面,形成了异质结构的SnO2/TiO2复合纳米纤维材料。通过改变反应物浓度,能有效地实现SnO2/TiO2复合纳米纤维的可控合成。以罗丹明B为模拟污染物,考察了SnO2/TiO2复合纳米纤维的光催化性能,与纯TiO2纳米纤维相比光催化活性明显提高,初步探讨了光催化反应机理。     

Efficient method for fabrication of fluorescein derivative/PDAC composite nanofibers and characteristics of their photoluminescent properties

Electrospinning is a simple and cost-effective approach for the production of nanofibers and assemblies with controllable structures. In this work, the pure poly (diallyldimethylammonium chloride) (PDAC) nanofibers with smooth surface and uniform morphology were successfully fabricated by electrospinning. On this basis, fluorescein/PDAC, dibromofluorescein/PDAC, diidofluorescein/PDAC and fluorescein sodium/PDAC composite nanofibers were also fabricated using the same method. The average diameters of the pure PDAC nanofibers increased with the applied field strength and the amount of PDAC in the solutions; and the average diameters ranged from 280 to 450 nm. The morphology of pure PDAC nanofibers has been observed by scanning electron microscopy (SEM) and the photoluminescent properties of fluorescein derivative/PDAC composite nanofibers have been characterized by fluorescence microscopy.     

静电纺丝法制备Mn2O3纳米纤维及其磁性研究

采用溶胶-凝胶过程和静电纺丝技术相结合方法, 以聚丙烯腈和醋酸锰为前驱物, 制得了PAN/Mn(CH₃COO)₂复合纳米纤维. 将该复合纤维高温煅烧, 获得了Mn₂O₃纳米纤维. 采用扫描电镜(SEM)、红外光谱(FTIR)、差热-热重(TG-DTA)和X射线衍射(XRD)分析等对样品进行了表征. 结果表明, Mn₂O₃纳米纤维为规则的一维结构, 直径分布均匀, 具有铁磁性-反铁磁性-顺磁性相互转化的特性.     

The effect of diameter on the thermal properties of the modeled shape-stabilized phase change nanofibers (PCNs)

The main objective of the present study is to investigate the effect of diameter on thermal properties of phase change fibers at nanoscale in order to develop a shape-stabilized phase change material (PCM). In this regard, polyethylene glycol/cellulose acetate (PEG/CA) electrospun nanofibers as a model of PCM/polymer structure were electrospun. The electrospinning process was optimized using response surface methodology (RSM) to produce phase change nanofibers (PCNs) with achievable minimum and maximum diameter at nanoscale range. Therefore, PCNs with minimum and maximum diameter (223 nm and 545 nm, respectively) were successfully prepared. According to differential scanning calorimetry (DSC) results, the PCNs sample with maximum diameter exhibited higher efficiency of enthalpy (49.41 %) than the PCNs sample with minimum diameter (46.24 %). On the other hand, a test based on the T-history method revealed that PCNs with maximum diameter enjoy higher thermal insulation effect. Scanning electron microscopy (SEM) as well as DSC results showed that the PCNs samples exposed to thermal cycling test not only preserved their structural durability, but also exhibited about twofold increasing in the efficiency of enthalpy than the non-exposed samples. According to thermogravimetric analysis (TG) results, due to successful entrapping, a fraction of PCMs within the structure of polymer matrix, PCNs sample display greater thermal stability comparing to the pure PCM. The present work emphasises that at nanoscale range, higher diameter of PCNs can present more favorable thermal behavior; suggesting a great potential for advanced applications of thermal energy storage and thermal regulating materials fields.     

Investigation of nanomechanical and morphological properties of silane-modified halloysite clay nanotubes reinforced polycaprolactone bio-composite nanofibers by atomic force microscopy

There is remarkable interest in the fabrication of polymeric composite nano/micro-fibers by electrospinning for many applications ranging from bioengineering to water/air filtration. In almost all of these applications, the mechanical properties of both the polymer fibers and their assemblies, are significant. In this study, unmodified, 3-Glycidoxypropyltrimethoxysilane (GPTMS) or 3-Aminopropyltriethoxysilane (APTES) modified halloysite clay nanotube (HNT) reinforced polycaprolactone (PCL) nanofibers were successfully synthesized via the electrospinning. The morphology and mechanical features of the obtained electrospun fibers were investigated by atomic force microscopy (AFM) and AFM-based nanoindentation for single fibers in nanoscale, respectively. Besides, scanning electron microscopy and tensile strength tests were used to investigate whole fibrous structures in microscale. The AFMresults, accompanied by SEM and tensile strength, support the conclusion that silane-modification affected positively the morphology and mechanical characteristics of electrospun PCL nanofibers. Therefore, it was concluded that the morphological and mechanical features from the single fibers in the nanofiber mats were related to the whole fibrous structure.