Effect of polarization switching on piezoelectric and dielectric performance of electrospun nanofabrics of poly(vinylidene fluoride)/Ca–Al LDH nanocomposite

At present, highly flexible, durable, and lightweight piezoelectric nanogenerators with high-power density and energy conversion efficiency are of great interest. The present study reports a new synthetic route for Ca–Al layered double hydroxide (LDH) nanosheets and incorporation of these two-dimensional nanosheets as filler material into poly(vinylidene fluoride) (PVDF) to produce composite nanofabrics by electrospinning. The polymorphism, crystallinity, and the interaction between PVDF and LDH were studied by Fourier transform infrared spectroscopy, X-ray diffraction, and differential scanning calorimetry techniques. The synergetic effect of PVDF–LDH interaction and in situ stretching due to electrospinning facilitates the nucleation of electroactive β phase up to 82.79%, which makes it a suitable material for piezoelectric-based nanogenerators. The piezoelectric performance of PVDF/Ca–Al LDH composite nanofabrics was demonstrated by hand slapping and frequency-dependent mechanical vibration mode, which delivered a maximum open circuit output voltage of 4.1 and 5.72 V, respectively. Moreover, the composite nanofabrics exhibited a high dielectric constant and low dielectric loss due to superior interfacial polarization at low-frequency region with LDH loading, promising its potential applications in electronic devices. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48697.     

不同相对湿度下亲疏水纳米纤维膜空气过滤性能实验研究

利用静电纺丝法制备了表面静态接触角为23.6°的具有亲水功能的PAN/PVP复合纳米纤维膜、接触角为81.2°的PAN纳米纤维膜、接触角为131.9°的具有疏水功能的PAN/PVDF复合纳米纤维膜。利用自行搭建的空气过滤实验台，在40%、55%、70%三种相对湿度下对三种纳米纤维膜进行空气过滤实验，对纳米纤维膜的过滤效率、阻力损失及品质因子进行分析。结果表明：三种纳米纤维膜的过滤效率随着相对湿度的增大而升高，PAN/PVP膜和PAN膜的阻力损失随着相对湿度的增大而增加，PAN/PVDF的阻力损失随着相对湿度的增大而减小；PAN/PVP膜和PAN膜的品质因子随着相对湿度的增大而减小，PAN/PVDF膜的品质因子随着相对湿度的增大而增大，湿度越大，PAN/PVDF纳米纤维膜的过滤性能越显著。     

Research on hydrophobicity of electrospun Fe3O4/PVDF nanofiber membranes under different preparation conditions

Abstract

Preparation condition can affect the structure and the properties of nanofiber membrane. In order to explore suitable conditions to prepare the Fe₃O₄/PVDF nanofiber membrane with good hydrophobicity, the hydrophobicity of Fe₃O₄/PVDF nanofiber membranes obtained by electrospinning was investigated by changing preparation conditions like weight percentage of Fe₃O₄ nanoparticles, blending quality concentration of poly (vinylidene fluoride) (PVDF) and Fe₃O₄ nanoparticles, and positive voltage. And the variations of hydrophobicity of Fe₃O₄/PVDF nanofiber membranes modified by 1H, 1H, 2H, 2H-perfluorodecyl trimethoxysilane were studied. The results show that the hydrophobicity of Fe₃O₄/PVDF nanofiber membranes has changed under different preparation conditions. The contact angles of samples increased after a modification by 1H, 1H, 2H, 2H-perfluorodecyl trimethoxysilane, which indicates that the hydrophobicity of Fe₃O₄/PVDF nanofiber membranes has been enhanced.     

静电纺丝法制备ZnO构建酪氨酸酶生物传感器检测邻苯二酚

电化学生物传感器在环境监测、生物与食品分析等领域应用广泛。本文采用静电纺丝法制备了氧化锌微纳米纤维材料，并负载酪氨酸酶（Tyr）构建了检测邻苯二酚的生物传感电极。利用X射线粉末衍射（XRD）、扫描电子显微镜（SEM）表征了氧化锌微纳米纤维的形貌结构，采用循环伏安法（CV）和计时电流法（IT）优化了检测邻苯二酚的工作条件。结果表明，制备的Tyr/ZnO/CS/GCE生物传感电极具有良好的电化学性能，在反应过程中为扩散控制，对邻苯二酚的检测在5～50μmol/L的浓度范围内具有较好的线性关系，最低检测限为1.9041μmol/L，灵敏度为376.31μA/(mmol·L·cm²)，氧化锌的加入可增强酪氨酸酶的稳定性，在尿素、多巴胺和葡萄糖3种电化学活性相近物质存在的情况下仍对邻苯二酚的检测有较好的选择性，且具有良好的循环稳定性。     

Fabrication of ultrafast temperature-responsive nanofibrous hydrogel with superelasticity and its 'on–off' switchable drug releasing capacity

The temperature-responsive bulky hydrogel with fast response rate and satisfactory mechanical property has fascinating application potential in many aspects, such as the implantable macroscale controlled drug release carrier for post-surgical therapy; however, creating such a smart hydrogel was proven extremely challenging. Here a novel type of temperature-responsive bulky hydrogel with ultrafast response rate and super compressible elasticity was fabricated by the fibrous freeze-shaping technique using shortened temperature-responsive polymer based electrospun hollow nanofibers as building blocks, followed by heat treatment for endowing the hydrogel with high stability in water. Because the hydrogel has hierarchical porous structure and its constituent nanofibers have hollow structure, which are beneficial to diffusion of its embodied water during temperature-induced volume phase transition, its temperature-response time is less than 30 s. In addition, the hierarchical porous structure benefits dissipation of the compression stress exerted on the hydrogel. Fluorescein isothiocyanate (FITC)-dextran as a model biomacromolecular drug, was loaded into the shells of the hollow nanofibers during coaxial electrospinning, and the ultimately obtained nanofibrous hydrogel can release its loaded FITC-dextran in a 'on–off' switchable fashion in response to temperature alternation between 15 and 47°C. Cell cytotoxicity test results demonstrate that the temperature-responsive nanofibrous hydrogel is biocompatible.     

Intermolecular interaction of thermoresponsive poly-2-isopropyl-2-oxazoline in solutions and interpolymer complex with fiber-forming polyethylene oxide

The cross-linked poly-2-isopropyl-2-oxazolines (PiPrOx) differing in cross-linker content have been synthesized and characterized by light scattering, chromatography, and rheometry. The dramatic influence of the cross-linker content on solubility and uni- or bimodality was observed. For the first time, the interpolymer complex of cross-linked PiPrOx with polyethylene oxide is manufactured in fibrous form by the electrospinning method. The role of intermolecular hydrogen bonds in the structure and properties of electrospun fibers (EF) was studied by infrared spectroscopy, differential scanning calorimetry, and scanning electron microscopy. It was established that these interactions allow to obtain a uniform fibrous membrane. At the same time, hydrogen bonding is responsible for the self-organization of PiPrOx in water.     

Synthesis,characterization, and DFT Raman study of pure and Mn-doped LiTaO3 nanofibers

Pure and Mn-doped lithium tantalate nanofibers, with Mn concentrations of 1%, 2.5%, and 5%, were synthesized by the electrospinning method. The morphology, microstructure, and crystal structure of as-spun and annealed composite nanofibers were characterized by scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. Raman spectroscopy has shown to be a powerful tool to detect either local variations or changes of the whole structure. Position and width of one Raman line can be used as markers of a structural change. Some vibrational modes are especially associated with the site of Li or Ta ions and so, they can be affected by the introduction of dopant ions. Any damages or local changes in the microstructure can be detected by a line broadening. With the use of Raman spectroscopy, the sites where Mn ions enter the doped structures were established by recording the shift and broadening of peaks in Mn-doped structures with respect to pure lithium tantalate. Thus it was proven that Mn ions enter the Li sites for low Mn concentration and, on the other hand, for higher concentrations, the dopant substitutes Li and Ta sites. First-principles calculations were performed within the density functional theory, including lattice-dynamic calculations of the phonon modes at the zone center (Γ point), for the pure structure, to find the irreducible representation of the modes.     

电子纺丝制备聚氧化乙烯纳米纤维

通过电子纺丝技术成功制备了分子量为9×105的聚氧化乙烯纳米纤维,并讨论了纺丝液的浓度范围,分析了纺丝条件对制备纳米纤维的影响,探讨了不同剪切粘度的聚氧化乙烯溶液制备的纳米纤维的差异和形成原因。随着聚氧化乙烯溶液零剪切粘度的增加,制备的纳米纤维直径逐渐变细而且表面也较平滑。其中,分子量为9×105的零剪切粘度为30 Pa.s的8 wt%的聚氧化乙烯溶液用电子纺丝技术制备的纳米纤维直径最小,分布在120~160nm,表面平滑。