Electrospinning/electrospray of polyvinylidene fluoride (PVDF): piezoelectric nanofibers

Polyvinylidene fluoride (PVDF) is one of the most studied polymer systems that exhibits piezoelectric, pyroelectric, and ferroelectric properties. It is well known that PVDF is able to crystallize in four different forms that involve three different chain conformations, namely α, β, γ, and δ phases. Among the four polymorphs, the β-phase has the largest spontaneous polarization per unit cell and thus exhibits the highest electro active properties. In the past few decades, many researches have been done to increase the β-phase content in PVDF using various processing techniques and additives. One of these processing methods is electrospinning/electrospray with organic/inorganic additives, nanoparticles or carbon nanotubes. Material and structural analyses on fabricated nanofibers using instruments such as X-ray diffraction, Fourier transform infrared, Differential Scanning Calorimetry, and Scanning Electron Microscope as the characterizations of piezoelectric nanofibers are carried out. This article attempts to have an overview on the electrospinning process of PVDF as a piezoelectric polymer, method of characterization of its β-phase and its application as a nanogenerator.     

碳纳米管/聚偏氟乙烯纳米纤维膜的制备及其压电性能

为提高聚偏氟乙烯(PVDF)的压电性能,采用静电纺丝法将碳纳米管(CNTs)引入到PVDF纳米纤维膜中制备CNTs/PVDF纳米纤维膜,并组装成三明治结构的柔性压电传感器,探究CNTs质量分数对CNTs/PVDF纳米纤维膜压电性能的影响。借助扫描电子显微镜、X射线衍射仪、傅里叶变换红外光谱仪、万能试验机以及数字示波器对纳米纤维的形貌、结构、力学性能及压电性能进行表征。结果表明:CNTs/PVDF纳米纤维膜具有良好的力学特性,CNTs的添加有利于晶体结构中β晶型的形成;当CNTs质量分数为5%时,CNTs/PVDF纳米纤维的晶体结构中β晶型含量最多,压电性能最强,此时柔性传感器的输出电压达到最大值7.5 V。     

静电纺钛酸钡/聚偏氟乙烯纳米复合柔性压电纤维膜

为进一步提高聚偏氟乙烯（PVDF）压电性能,采用具有铁电性能的钛酸钡(BaTiO3)纳米颗粒为无机填料,通过静电纺丝技术制备BaTiO3/PVDF纳米复合纤维膜。借助扫描电子显微镜、全反射红外光谱、差示扫描量热法、X射线衍射以及脉冲电压测试等仪器对纤维膜的结构和性能进行了表征及分析,探索了不同添加量的BaTiO3对复合纤维膜结晶结构及压电性能的影响。结果表明：静电纺丝过程中静电力的拉伸和纳米BaTiO3的成核作用促进了PVDF具有压电性的β晶型的形成;当BaTiO3质量分数为10%,复合纤维膜的β晶型含量达到90.8%,纤维膜的输出电压值由20 V增加至50 V;制得的BaTiO3/PVDF复合纤维薄膜具有良好的压电性。     

静电纺制备PVDF纳米纤维膜的应用

聚偏氟乙烯(PVDF)是一种新型高分子材料,通过静电纺丝法制备的PVDF纳米纤维膜具有压电系数高、生物相容性好、质轻柔软等优点,近年来在各领域得到广泛应用。为了充分认识PVDF纤维膜,简要对比了溶液流延法、静电纺丝法制作PVDF纤维膜的优缺点,详细介绍了溶液静电纺丝法制备聚偏氟乙烯纳米纤维膜的工艺过程。重点分析了当前PVDF纳米纤维膜在压电传感器、生物医学、过滤材料、电池隔膜等领域的应用现状。探索了在生产和应用领域上存在的问题,并提出了PVDF纳米纤维膜的发展前景。     

Modeling of electrospun PVDF/LiCl nanogenerator by the energy approach method: determining piezoelectric constant

Increasing demands for harvesting energy from other sources of energy than fossil fuel and oil have led to an upsurge of interest in nano-structured materials such as piezoelectric nanofibers and nanowebs to harvest energy from environmental movements. Previous research introduced a suitable nanogenerator package to have higher output voltage needless of the post-treatment process. Electrospinning of PVDF (polyvinylidene fluoride) with LiCl (lithium chloride) increases the beta-crystalline phase and thus piezoelectric effect. This article presents an FEM (finite element method) model for the electrospun PVDF/LiCl nanogenerator to determine the piezoelectric constant base on the energy approach method. An experimental and analytical procedure has been developed to determine the piezoelectric coupling coefficient and results validation. The nanogenerator package was modeled as a multilayer structure. The excitation method for the nanogenerator package was dropping a ball on the sample from different heights. The determinations of electrospun nanogenerator coupling coefficients are an important factor in the final application of these types of nanogenerators that have not been studied yet.     

Effect of electrospinning parameters on piezoelectric properties of electrospun PVDF nanofibrous mats under cyclic compression

The high piezoelectric response capacity of electrospun PVDF nanofibers is currently a challenging area of research, and this study attempts to optimize the piezoelectric properties of electrospun PVDF nanofibrous mat under controlled electrospinning process. Some experiments were designed to study the relationship between electrospinning processing parameters and the piezoelectric properties of PVDF mats under cyclic compression, and this relationship was compared with the change of crystalline structure features with the electrospinning parameters. The excitation method is based on low velocity compression test by cyclically pressing flat contactor on samples. The impact of each of processing parameters has been investigated. It was found that three electrospinning parameters including: applied voltage, feeding volume flow rate and syringe needle tip diameter, are significant influential factors to the piezoelectric properties of the electrospun PVDF nanofibrous mats. However, the feeding volume flow rate has a greater effect on the piezoelectric responses to cyclic compression than both applied voltage and volume flow rate does, and its effect on the piezoelectric responses is different from that of β-phase fraction of crystalline structure within PVDF nanofiber. It was also observed that the relationship between the piezoelectric peak intensity and the applied voltage as well as the feeding volume flow rate is nonlinear.     

纺丝电压对静电纺PVDF纤维膜压电效应的影响

纺丝电压是影响静电纺聚偏氟乙烯(PVDF)纤维膜β相生成和压电效应的重要因素之一。目前不同文献中对电压影响的研究结果存在不同观点。采用静电纺丝方法,在不同电压(14.0~24.0 k V)条件下制备了PVDF纤维膜,测试了不同电压下PVDF纤维膜的压电响应,利用FTIR和XRD方法表征了不同电压下PVDF纤维膜的β相含量。结果表明,在给定的纺丝电压范围内,PVDF纤维膜的压电响应输出和β相含量均存在最大值。通过对比分析其他研究结果,对影响试验结果的因素展开了讨论。     

SiO2原位掺杂聚偏氟乙烯纳米纤维膜的制备及其性能

为提高聚偏氟乙烯(PVDF)的压电性能,以PVDF和正硅酸乙酯(TEOS)为原料,N,N-二甲基甲酰胺(DMF)和丙酮为混合溶剂,利用原位复合溶胶-凝胶法和高压静电纺丝技术制备纳米SiO₂原位掺杂PVDF复合纳米纤维膜,并分析纳米纤维膜的表面微观形貌、化学结构、力学性能以及压电性能等。结果表明:复合纳米纤维膜的面密度与厚度随TEOS质量的增加而增加;静电纺丝使PVDF中部分α相转变为β相,纯PVDF纳米纤维膜的β相含量是PVDF粉末的1.54倍,为(31.42±0.62)%;且原位掺杂SiO₂后β相含量进一步提高,拉伸强力与输出电压均呈先增大后降低的趋势,当TEOS质量为1.643 g时PVDF纳米纤维膜β相含量最高为(42.59±0.62)%,原位掺杂PVDF纳米纤维膜拉伸强力最大为(8.03±0.19) N,输出电压最高为(2.33±0.13) V。     

聚偏氟乙烯/导电TiO2复合压电薄膜的制备

为探究提高聚偏氟乙烯压电性能的方法,采用静电纺丝结合填料共混的方法制备了聚偏氟乙烯/导电TiO2复合纳米纤维压电薄膜,并讨论了不同添加量的导电二氧化钛晶须对纤维薄膜直径、形貌、结晶形态和β相和γ 相含量的影响。用扫描电子显微镜、傅里叶变换红外光谱和差示扫描量热仪测试方法表征纤维薄膜材料的微观形态结构和结晶结构。对复合纳米纤维薄膜的压电性能测试结果表明：静电纺丝是提高聚偏氟乙烯中β 相含量的有效方法。导电TiO2的添加除了诱导结晶取向,促进更多β 相和γ 相的形成,而且有助于将纺丝过程中形成的构相固定起来,从而达到提高产物压电性的目的。除此之外,添加导电TiO2后,聚偏氟乙烯纤维膜的力学性能也有一定的提高。     

高压电性静电纺柔性氧化锌/聚偏氟乙烯复合纤维膜

为了获得环保、柔软、透气和高压电性的材料,增加压电材料在纳米发电机,传感器,可穿戴电子器件等方面的应用,采用静电纺丝技术制备出了高压电性的氧化锌/聚偏氟乙烯（ZnO/PVDF）复合纤维膜材料。通过扫描电子显微镜、全反射傅里叶变换红外光谱仪、X射线衍射仪及示波器对压电复合纤维膜的形貌、结构和压电性进行了表征。结果表明：在PVDF基材中加入适量的氧化锌纳米颗粒(ZnO NPs)可在一定程度上提升PVDF纤维膜的结晶度和电活性β晶型含量增加,使PVDF中总的β晶型含量增加;同时,ZnO NPs自身具有压电性,也可进一步提升复合材料的压电性,使复合纤维膜的输出电压显著提高。当ZnO NPs质量分数为30%时,复合膜的输出电压高达60V,与纯PVDF纤维膜的输出电压相比,复合纤维膜的压电性提升了200%。     

Comparative evaluation of piezoelectric response of electrospun PVDF (polyvinilydine fluoride) nanofiber with various additives for energy scavenging application

Energy harvesting using piezoelectric nanomaterial provides an opportunity for advancement toward self-powered electronics. The fabrication complexity and limited power output of these nano/micro generators have hindered these advancements. This paper introduced a ?exible and light weight nanogenerator package that was obtained by variety of additives (ZnO, CNT, LiCl, PANI) and try to have comparisons between them to choose appropriate one base on final application. Performances of these additives were evaluated using Fourier Transform Infrared, Scanning Electron Microscopy, Impedance analyzer, and traction-compression machine. The excitation method is based on low velocity impact test by falling down a ball on samples. Results show that for all additives there is a direct connection between β phase formation and output voltage. CNT nanoparticles lead to have more β Phase formation and higher output voltage (0.9 V) for electrospun web with 230 μm thickness. The results imply promising applications, as an enhanced efficiency energy-scavenging interface, for various wearable self-powered electrical devices and systems.     

载药聚偏氟乙烯伤口敷料的制备及其性能

为获得轻薄柔软的伤口敷料,并使其具备优异的压电和抗菌性能,以聚偏氟乙烯(PVDF)为原料,掺杂不同质量分数的盐酸恩诺沙星(Enro),采用静电纺丝技术制备载药PVDF复合纳米纤维膜。分析了复合纳米纤维膜的形貌、化学结构对其压电性能、药物缓释和抗菌性能的影响。结果表明:PVDF质量分数为8%时,纤维平均直径为(753±128) nm,纤维网成膜良好,复合纳米纤维膜直径随着Enro质量分数的增加呈先增大后减小趋势;纺丝过程中PVDF由α晶型转变为β晶型,使纤维膜具备了压电性能,可产生9 mV的输出电压;当 Enro质量分数为15%时,纤维膜释药速度平稳、持续时间长且具备优异的抗菌性能,适合用作伤口敷料。     

Fabrication of electrically conductive and improved UV-resistant aramid fabric via bio-inspired polydopamine and graphene oxide coating

Abstract

This study presents the fabrication of woven aramid fabric (AF) with integrated properties, especially with improved surface activity, UV resistance, electrical conductivity and thermal properties. A biomimicry surface functionalization with polydopamine (PDA) and a further modification by graphene oxide (GO) coating of the AF was demonstrated. The surface properties of AF were changed by repeated reduce graphene oxide (rGO) coating process. The scanning electron microscope (SEM) results showed that the rGO sheets were successfully formed on the surface of AF, and the deposition of GO/rGO was proven by X-ray photoelectron spectroscopy (XPS). The electrical conductivity was ascertained by the electrical surface resistance value of the AF. A low surface resistance value of 6.43 K?cm^?1 was obtained after five times of modification, resulting in an excellent conductivity. The ultraviolet protection factor (UPF) value of the modified AF increased to 73 in comparison to 37 for the original AF.     

Lipid-modifying activity of curcuminoids: A systematic review and meta-analysis of randomized controlled trials

Objective: The aim of this systematic review and meta-analysis was to determine and clarify the impact of curcuminoids on serum lipid levels. Methods: Randomized controlled trials (RCTs) investigating the effects of curcuminoids on plasma lipids were searched in PubMed-Medline, Scopus, Web of Science databases (from inception to April 3^rd, 2017). A random-effects model and generic inverse variance method were used for quantitative data synthesis. Sensitivity analysis was conducted using the leave-one-out method. A weighted random-effects meta-regression was performed to evaluate the impact of potential confounders on lipid concentrations. Results: A meta-analysis of 20 RCTs with 1427 participants suggested a significant decrease in plasma concentrations of triglycerides (WMD: ?21.36 mg/dL, 95% CI: ?32.18, ?10.53, p < 0.001), and an elevation in plasma HDL-C levels (WMD: 1.42 mg/dL, 95% CI: 0.03, 2.81, p = 0.046), while plasma levels of LDL-C (WMD: ?5.82 mg/dL, 95% CI: ?15.80, 4.16, p = 0.253) and total cholesterol (WMD: ?9.57 mg/dL, 95% CI: ?20.89, 1.75, p = 0.098) were not altered. The effects of curcuminoids on lipids were not found to be dependent on the duration of supplementation. Conclusion: This meta-analysis has shown that curcuminoid therapy significantly reduces plasma triglycerides and increases HDL-C levels.     

Advances in electrospinning: The production and application of nanofibres and nanofibrous structures

The use of electrospun nanofibres in applications such as medical products, fuel cells, photocatalysis, filtration, sensors and actuators is reviewed. Yarn production is classified into two types, namely hollow and core-shell structures; the methods used for producing the two structures for different polymers are discussed. Explanations are given for the various arrangements for producing nanofibre yarns and bundles in non-twisted or twisted forms to suit their end use. Natural and synthetic polymer products for biomedical uses and their applications in the form of polymer nanofibres are reviewed and polymeric optical fibres for use in photonic devices and optical circuits are evaluated. The production and development of nanofibrous filtration devices is explored with specific reference to water treatment and the control of air pollution. Particular attention is then given to the evaluation of different electrospinning methods for PVDF (polyvinylidene fluoride), a piezoelectric polymer widely used in sensor applications in terms of their ability to harvest more energy after agitation of the sensor and the effects of different additives on the piezoelectric properties of PVDF. Priorities for further research are then outlined.     

可嵌入服装的PVDF压电传感器的研制与应用

用聚偏二氟乙烯(PVDF)薄膜制成适应大幅度形变的柔性传感器。设计了前置电路,选出与该电路相适合的反馈电阻和电容,测试PVDF薄膜传感器的幅频响应特性。将PVDF薄膜传感器应用在手指关节上,记录手指关节的动作,实验证明PVDF薄膜可制成检测大幅度形变的柔性传感器。     

LC-MS/MS method for the determination of the fungal pigment bikaverin in maize kernels as an indicator of ear rot

Bikaverin is a polyketide-derived pigment produced by multiple species of the fungus Fusarium, some of which can cause ear and kernel rot of maize. A method was developed for the analysis of bikaverin by high-performance liquid chromatography (LC) coupled to electrospray ionisation tandem mass spectrometry (MS/MS). The quantitative nature of the LC-MS/MS method was demonstrated over a range of concentrations of bikaverin in maize. For spike-recovery experiments utilising maize spiked with bikaverin to a level 5?µg?g^?1 of maize, the measured recovery (%) was 70.6?±?10.4. Based on the utilised method, the limit of detection (based on a signal-to-noise ratio (S/N)?>?3) was better than 0.5?µg?g^?1 from bikaverin spiked into uncontaminated ground maize. Further, the limit of quantitation (LOQ) was 3?µg?g^?1 (based on S/N?>?10) from bikaverin spiked into ground maize. The method was applied to assess contamination of maize with bikaverin following inoculation of developing maize ears with Fusarium verticillioides under agricultural field conditions.     

Evaluating the fabric performance and antibacterial properties of 3-D piezoelectric spacer fabric

The increasing need of on-demand power for enabling portable low-power devices and sensors has necessitated work in novel energy harvesting materials and devices. In a recent work, we demonstrated the production and suitability of three-dimensional (3-D) spacer all fibre piezoelectric textiles for converting mechanical energy into electrical energy for wearable and technical applications. The current work investigates the textile performance properties of these 3-D piezoelectric fabrics including porosity, air permeability, water vapour transmission and bursting strength. Furthermore, as these textiles are intended for wearable applications, we have assessed their wear abrasion and consequently provide surface resistance measurements which can affect the lifetime and efficiency of charge collection in the piezoelectric textile structures. The results show that the novel smart fabric with a measured porosity of 68% had good air (1855 l/m²/s) and water vapour permeability (1.34 g/m²/day) values, good wear abrasion resistance over 60,000 rotations applied by a load of 12 kPa and bursting strength higher than 2400 kPa. Moreover, the antibacterial activity of 3-D piezoelectric fabrics revealed that owing to the use of Ag/PA66 yarns, the textiles exhibit excellent antibacterial activity against not only Gram-negative bacteria E. coli but they are also capable of killing antibiotic methicillin-resistant bacteria S. aureus.     

Studies on cotton–acrylic bulked yarns produced from different spinning technologies. Part I: yarn characteristics

The effects of different factors, namely spinning technologies (ring, rotor and DREF-II, i.e. Group A yarns), position of shrinkable acrylic feed sliver in DREF-II friction spinning system (Group B yarns) and proportion of shrinkable acrylic core fibre in core-sheath type DREF-III friction spun yarns (Group C yarns) on various properties of cotton-acrylic–blended bulked yarns have been studied. The bulk in the yarns was developed by relaxing shrinkable acrylic component of the yarns using boiling water treatment. All the above factors have a significant impact on various properties of cotton–acrylic blended bulked yarns. For all the yarns, after boiling treatment, there is lengthwise shrinkage of yarns and the specific volume also increases. Tenacity and breaking elongation of all the yarns of Group A and Group B increase after hot water treatment, whereas in case of core-sheath type DREF-III yarns (Group C yarns) there is drop in tenacity and breaking elongation after similar treatment. In general, for all the yarns the flexural rigidity of the yarns reduces and compressibility and compressional recovery of increases after bulking treatment.     

热致相变分离法制备PVDF微孔膜及其性能研究

本以邻苯二甲酸二甲酯（DMP）为稀释剂,聚偏氟乙烯（PVDF）为原料,通过热致相变分离法,制备了PVDF微孔膜。采用扫描电镜（SEM）、差示扫描量热法（DSC）、拉伸压缩材料试验机等手段对PVDF微孔膜的性能及热力学特征进行了表征。结果表明：DMP作为稀释剂时与PVDF有很好的相容性;铸膜液中DMP质量分数由50%增加到80%时,PVDF微孔膜的纯水通量和孔隙率分别由65 L/(m2?h)和34%增加到230 L/(m2?h)和77%,分别增加了135%和254%;而随着铸膜液中DMP含量的上升,PVDF微孔膜的断裂伸长率以及断裂强度都是逐渐下降的;此外,用有机非溶剂处理微孔膜后,膜通量可以提高3~4倍;同时,热力学研究表明当DMP含量不断上升时,PVDF结晶颗粒变得越来越模糊,而且球晶之间的空洞变大,球晶间的结合则更为稀疏,球晶尺寸也呈现出了变小的趋势。