Hierarchical nanostructured electrospun carbon fiber/NiCo2O4 composites as binder-free anodes for lithium-ion batteries

Hierarchical structured composite materials consisting of NiCo₂O₄ and electrospun carbon fibers were fabricated through the coprecipitation of Ni Co compounds on electrospun carbon fibers. Post thermal treatment converted Ni Co compounds to NiCo₂O₄. We aimed to identify how different fiber diameters affect the structures and electrochemical performance of NiCo₂O₄/carbon fiber composites. Carbon fibers with diameters smaller than 400 nm resulted in the formation of NiCo₂O₄ needles, whereas those with diameters larger than 800 nm resulted in the development of NiCo₂O₄ flowers. The composites with needle-type NiCo₂O₄ exhibited richer mesopores and larger specific surface areas than fibers with flower-like NiCo₂O₄ did. When used as lithium-ion battery anodes, the needle-like and flower-like composites exhibited specific capacities of 639 and 498 mAh/g, respectively, at a current density of 200 mA/g after 100 cycles, which were much higher than pristine carbon fibers. The enhanced specific capacity resulted from the combinative effects of the efficient electron transfer in the carbon fiber networks and the high specific capacity of NiCo₂O₄. Furthermore, needle-like materials with large mesopore volume allowed for the accommodation of volume changes and favored fast lithium-ion transfer during continuous electrochemical reactions, leading to more favorable cycling stability and rate capability than the flower-like materials did.     

A study on UV-protection property of poly(vinyl alcohol)-montmorillonite composite nanofibers

The aim of this research is to investigate the possibility of barrier effect of poly(vinyl alcohol) (PVA)/montmorillonite (MMT) nanofiber, against the UV radiation in different electrospinning situations. For this purpose, nanofibers with different weight ratio of PVA and nanoclay (MMT) were electrospun under different circumstances, and the amount of protect that is created by the nanofiber web against UV radiation by examining the rate of degradation of methylene blue dye that was protected by the same web was estimated. The UV-vis spectrometry was used for the analysis of methylene blue color. In order to investigate the morphology and miscibility of PVA-MMT composite nanofiber, X-ray diffraction, scanning election microscope, and Fourier transform infrared spectrometer have been used. Thermal gravimetric analysis is used to investigate and explore how nanofibers behave against heat.     

液液两相流法制备海藻酸钠包覆的液态金属微滴

本文以室温液态金属(GaInSn)为分散相、海藻酸钠(NaAlg)溶液(1wt%)为连续相,采用液液两相流方法,在竖直共轴微通道中,制备得到NaAlg凝胶包覆的多个GaInSn微滴,具有单分散、尺寸一致的特点。GaInSn/NaAlg两相流存在四种流型:分散相滴流、分散相柱塞流、连续相滴流和连续相射流。GaInSn微滴的包覆模式三种:Squeezing、Dripping和Compound Jetting,其中Dripping和Compound Jetting是主要的包覆模式。在较低的GaInSn流量下,NaAlg流量增加到一定程度后,包覆模式由Dripping转变Compound Jetting。固定两相流量比,随着两相流量的同比例增加,GaInSn微滴的特征频率呈线性增加、包覆个数增加、特征长度变化不显著。     

Co_(0.5)Ni_(0.5)Fe_2O_4纳米纤维的静电纺丝法制备、表征及其磁性能

采用溶胶-凝胶法结合静电纺丝技术成功制备直径为150~400 nm的Co0.5Ni0.5Fe2O4铁氧体纳米纤维,并利用TG-DTA、XRD、FTIR、FESEM、TEM和VSM对样品进行表征。结果表明:前驱体纤维经450℃焙烧后可基本形成纯相晶态的目标产物Co0.5Ni0.5Fe2O4纳米纤维;随着焙烧温度的升高,纤维直径逐渐减小,晶粒尺寸逐渐增大,纤维表面粗糙度加强,其微观形貌由多孔结构向项链状结构转变;所制得的Co0.5Ni0.5Fe2O4纳米纤维的饱和磁化强度由450℃时的35.8 A.m2/kg单调增加到1 000℃时的80.2 A.m2/kg,而矫顽力呈现先增大后减小的趋势,在550℃附近时达到最大值,意味着其单畴临界尺寸约为30 nm,且发现在单畴尺寸范围内,矫顽力与平均晶粒尺寸的0.7次方成正比,与随机各向异性模型所预测的结果基本吻合。此外,低温(77 K)磁测量显示,与室温相比,样品的矫顽力和剩余磁化强度均大幅提高,但饱和磁化强度明显下降。     

高功率微波作用下单极天线瞬态响应特性研究

运用时域有限差分法(FDTD)结合同轴等效馈电模型计算了高功率微波(HPM)电磁脉冲作用下单极天线的感应电流的频域和时域响应,分析了单根单极天线感应电流频谱和时域响应与入射HPM间的关系,同时分析了两根天线间的距离对第一根天线末端感应电流的影响。计算结果表明,单根单极天线对HPM的感应电流频谱主要由入射HPM载波频率决定,感应电流波形与入射HPM波形相似;有其他天线存在时,对第一根天线会造成影响,且随距离增加影响减小。     

In Situ Electrospinning Wound Healing Films Composed of Zein and Clove Essential Oil

Electrospun fibrous membranes have the potential to be effective wound dressings for promoting wound healing. However, the fabrication and application of the common electrospun fibrous wound dressings are usually complicated and separated. Here, electrospun zein/clove essential oil (CEO) fibrous membranes are fabricated and applied as a potential wound dressing through in situ electrospinning process by a portable electrospinning device. The in situ electrospinning process can directly electrospin zein/CEO membranes onto a wound site to cover the wound well and improve the convenience and comfort in use. The as‐spun zein/CEO membranes show a porous structure and exhibit higher gas permeability at 168.2 ± 43.3 mm s^?1, with superhydrophilicity to absorb the wound exudate and good biocompatibility as well as antibacterial effects to protect from infection. Moreover, the mice wound model study suggests that in situ electrospun zein/CEO promotes the wound healing process.     

A General Strategy to Fabricate Flexible Oxide Ceramic Nanofibers with Gradient Bending-Resilience Properties

Inorganic materials assembled with rigid elements such as crystals or graphitized carbon generally show brittleness and hardness. However, it is found that both TiO₂ ceramic crystal nanofibers (NFs) and carbon NFs show superior flexibility, in which the former are surprisingly knottable and the latter exhibit excellent bending-resilience property. The different flexure mechanisms are revealed by fabricating composite NFs of these two constituents and find that the carbon NFs can be recovered to the original states after releasing the external force, while the bending-resilience is weakened and the softness of the composite NFs is enhanced upon increasing the TiO₂ content. The graphitized carbon can store mechanical deformation energy that enables the NFs with bending-resilience, while both the homogeneous interfaces between TiO₂ crystals and the heterogeneous interfaces between TiO₂ and carbon can alleviate stress concentration, which reduce the flexural modulus of the composite NFs. By filling different contents of elastic carbon into TiO₂ NFs, a series of flexible NFs that exhibit gradient bending-resilience properties are fabricated. This study provides a deeper understanding of the mechanical properties of inorganic materials.