Fabrication and Excellent Properties of Polyvinylidene fluoride/Graphene Composite Films as Thermal Interface Materials

The growing concern about thermal conductivityand electromagnetic shielding inelectronic equipment has promoted the development of interfacial film materials.In this work,polyvinylidene fluoride(PVDF)/graphene composite films with different graphene contents were fabricated by high-energy ball milling,cold isostatic pressing,scraping and coating,successively.High-energy ball milling is beneficial to the dispersion of graphene powder,while cold isostatic pressing can greatly enhance thermal conductivity and mechanical strength by reducing the voids in the film and increasing the contact area of graphene sheets.The thermal conductivity,tensile strength and electromagnetic shielding properties of the films were carefully investigated and compared.It was demonstrated that the thermal conductivity increased from 0.19 W·m^(-1).K^(-1) for pure PVDF to 103.9 W·m^(-1).K^(-1)for the composite film with PVDF:graphene=1:3.Meanwhile the electromagnetic shielding efficiency can reach 36.55 dB.The prepared PVDF/graphene composite films exhibit outstanding overall performance and have the potential for practical applications.

Wearable Triboelectric Nanogenerators Based on Printed Polyvinylidene Fluoride Films Incorporated with Cobalt-Based Metal-Organic Framework for Self-Powered Mobile Electronics

In this study,wearable triboelectric nanogenerators comprising bar-printed polyvinylidene fluoride(PVDF)films incorporated with cobalt-based metal-organic framework(Co-MOF)were developed.The enhanced output performance of the TENGs was attributed to the phase transition of PVDF from a-crystals toβ-crystals,as facilitated by the incorporation of the MOF.The synthesis conditions,including metal ion,concentration,and particle size of the MOF,were optimized to increase open-circuit voltage(VOC)and open-circuit current(I_(SC))of PVDF-based TENGs.In addition to high operational stability,mechanical robustness,and long-term reliability,the developed TENG consisting of PVDF incorporated with Co-MOF(Co-MOF@PVDF)achieved a VOC of 194 V and an I_(SC)of 18.8μA.Furthermore,the feasibility of self-powered mobile electronics was demonstrated by integrating the developed wearable TENG with rectifier and control units to power a global positioning system(GPS)device.The local position of the user in real-time through GPS was displayed on a mobile interface,powered by the battery charged through friction-induced electricity generation.

Effect of Packaging Material on Piezoelectric Response of Sensor with Electrospinning Polyvinylidene Fluoride (PVDF) Nanofiber Web

The polyvinylidene fluoride(PVDF)nanofiber web by electrospinning technology has the characteristics of fast response,high sensitivity,wide range of pressure,etc.,and provides new sensitive materials for the sensor testing the dynamic pressure such as foot pressure during walking.Because of the nanofiber mesh structure,it must be packaged to collect piezoelectric charge and bear strong mechanical behavior before industrial practice.The PVDF nanofiber web is usually packaged by incorporating a pair of flexible electrode as well as the lead of signal output.This present work will introduce the detailed packaging process and technology of PVDF nanofiber web,and three different types of packaging electrode materials(adhesive copper foil tape,indium tin oxide(ITO)thin plate,and adhesive conductive cloth)in previously published literatures are compared by the piezoelectric response of their sensor prototypes to a periodic mechanical activation.The results showed that the surface property of packaging material had a significant effect on the piezoelectric response of sensor by PVDF nanofiber web.For PVDF nanofiber web sensor,therefore,it needed a deep investigation on the specific packaging technology in terms of different working conditions.

Preparation and Properties of Electrospun Polyvinylidene Fluoride (PVDF)/Polyurethane (PU) Composite Nanofiber Membranes

Polyvinylidene fluoride(PVDF)/polyurethane(PU)composite nanofiber membranes were prepared by mixing PVDF and PU at different mass ratios.The microstructure and the crystal structure of the composite nanofiber membranes were analyzed by scanning electron microscopy(SEM),Fourier transform infrared(FTIR)spectroscopy and X-ray diffraction(XRD).The hydrophilicity,mechanical properties and piezoelectric properties were also tested.Results showed that when the mass ratio of PVDF to PU was 9∶1,the fiber membrane had the best microstructure,and the crystal form of PVDF changed fromαcrystal toβcrystal in the electrospinning.The addition of PU improved the hydrophilicity,mechanical properties,and piezoelectric signal of the fiber membrane.When the mass ratio of PVDF to PU was 9∶1,the tensile strength reached the peak value of(10.39±0.41)N,and the output voltage reached the maximum value of(1.98±0.12)V.

Preparation and Characterization of the Modified Polyvinylidene Fluoride (PVDF) Hollow Fibre Microfiltration Membrane

A novel thermally induced graft polymerization technique was used to modify a polyvinylidene fluoride （PVDF） hollow fibre microfiltration membrane. An artificial neural network （ANN） was applied to optimize the prepared condition of the membrane. The optimized dosing of acrylic acid （AA）, acrylamide （AM）, N, N＇- methylenebisacrylamide （NMBA） and potassium persulphate （KSP） designed by ANN was that AA was 40.63 ml/L; AM acted as 6.25 g/L; NMBA was 1.72 g/L and KSP was 1.5 g/L, respectively. The thermal stability of the PVDF modified hollow fibre membrane （PVDF-PAA） was investigated by thermogravimetric （TG） and differential scanning calorimetry （DSC） analysis. The polycrystallinity of the PVDF-PAA membrane was evaluated by X-ray diffraction （XRD） analysis. The complex formation of the modified membrane was ascertained by Fourier transform infrared spectroscopy （FTIR）. The morphology of the PVDF-PAA membrane was studied by environmental scanning electron microscopy （ESEM）. The surface compositions of the membrane were analyzed by X-ray photoelectron spectroscopy （XPS）. The adsorption capacity of Cu^2＋ ion on the PVDF-PAA hollow fibre membrane was also investigated.

Effect of Nanostructures Addition and Enhancement of Poly (Vinylidene Difluoride) (PVDF) Energy Harvesting

With concerns in energy crisis and global warming, researchers are actively investigating alternative energy renewable solutions. Among the various methods, piezoelectric transduction stands out due to its impressive electromechanical coupling factor and coefficient. As a result, piezoelectric energy harvesting has garnered significant attention from the scientific community. In this study, we explored methods to enhance the piezoelectric properties of polyvinylidene fluoride (PVDF) through two distinct approaches. The first approach involved applying external high voltages at various stages during the mixture reaction. The goal was to determine whether this voltage application could alter or enhance PVDF’s piezoelectric conformation by improving the alignment of polarized dipoles. In the second part of our study, we investigated the effects of incorporating various nanostructures (including Iron Oxide, Magnesium Oxide, and Zinc Oxide) into PVDF. To analyze changes in PVDF’s crystalline structure, we utilized Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction (XRD) techniques. Additionally, we measured the electric polarization of samples using a Precision LC Meter and examined the morphology of nanofibers through Scanning Electron Microscopy (SEM).

Dye-sensitized Solar Cells with Higher J_(sc) by Using Polyvinylidene Fluoride Membrane Counter Electrodes

A flexible counter electrode(CE) for dye-sensitized solar cells(DSCs) has been fabricated using a micro-porous polyvinylidene fluoride membrane as support media and sputtered Pt as the catalytic material.Non-conventional structure DSCs have been developed by the fabricated CEs. The Pt metal was sputtered onto one surface of the membrane as the catalytic material. DSCs were assembled by attaching the Ti O2 electrode to the membrane surface without Pt coating. The membrane was with cylindrical pore geometry. It served not only as a substrate for the CE but also as a spacer for the DSC. The fabricated DSC with the flexible membrane CE showed higher photocurrent density than the conventional sandwich devices based on chemically deposited Pt/FTO glass, achieving a photovoltaic conversion efficiency of 4.43%. The results provides useful information in investigation and development of stable, low-cost, simple-design, flexible and lightweight DSCs.

PREPARATION AND CHARACTERIZATION OF ION EXCHANGE MEMBRANES BASED ON POLYVINYLIDENE FLUORIDE

A new ion exchange membrane based on polyvinylidene fluoride (PVDF) and sulfonated poly(styrene-divinylbenzene) was prepared by in-situ polymerization. The incorporation of sulfonic groups into the polyvinylidene fluoride composite membrane was confirmed by infrared spectroscopy (IR), ion exchange capacity (IEC) and energy dispersive X-ray analysis (EDAX). Area resistance, IEC and water uptake of the treated membrane were evaluated. When 20% of the crosslinked membrane was sulfonated at 80degreesC for 22 h, the PVDF ion exchange membrane can attain 0.8 Omega . cm(2) area resistance in NaCl aqueous solution at 25degreesC, IEC is as high as 2.43 millimoles per grain of the wet membrane. The hydrophilicity of PVDF membrane is also significantly improved after treatment. When 60% of crosslinked membrane was sulfonated at 80degreesC for 6 h, water uptake of the treated membrane can attain 64.7%.

Effect of Polyvinylidene Fluoride Hollow Fiber Membranes on Mass Transfer of Samarium

The influence of swelling and stripping acidity on the mass transfer coefficient based on water phase and the inner diameters of membranes were studied with P507-HCl-Sm as working system in the two different kinds of hollow fiber membranes. Effects of extractant concentration, H+ concentration in aqueous phase and Sm3+ concentration on extraction rate were discussed and the corresponding reaction series were obtained. According to the investigations on the interfacial kinetics, the reaction kinetics equation and reaction rate constant were obtained.

Morphology of Polyvinylidene Fluoride Based Gel Polymer Electrolytes

Two series of polyvinylidene fluoride (PVDF) based gel polymer electrolytes, with different LiClO 4 or propylene carbonate (PC) content, were prepared and analyzed by infrared spectrometer, differential scanning calorimetry, scanning electron microscope and complex impedance spectrometer. The results show that there are great interactions between PVDF, PC and lithium cations. Both LiClO 4 and PC content lead to evident change of the morphology of the gel polymer electrolytes. The content of LiClO 4 and PC also influences the ionic conductivity of the samples, and an ionic conductivity of above 10 -3 S·cm -1 can be reached at room temperature.

Soft Template-Induced Porous Polyvinylidene Fluoride Membrane for Vanadium Flow Batteries

Vanadium flow batteries(VFBs)are considered ideal for grid-sc ale,long-duration energy storage applications owing to their decoupled output power and storage capacity,high safety,efficiency,and long cycle life.However,the widespread adoption of VFB s is hindered by the use of expensive Nafion membranes.Herein,we report a soft template-induced method to develop a porous polyvinylidene fluoride(PVDF)membrane for VFB applications.By incorporating water-soluble and flexible polyethylene glycol(PEG 400)as a soft template,we induced the aggregation of hydrophilic sulfonated poly(ether ether ketone),resulting in phase separation from the hydrophobic PVDF polymer during membrane formation.This process led to the creation of a porous PVDF membrane with controllable morphologies determined by the polyethylene glycol content in the cast solution.The optimized porous PVDF membrane enabled a stable VFB performance for 200 cycles at a current density of 80 mA/cm^(2),and the VFB exhibited a Coulombic efficiency of 95.2%and a voltage efficiency of 87.8%.These findings provide valuable insights for the development of highly stable membranes for VFB applications.

PVDF/PU共混纳米纤维膜的制备及其性能

为扩展不同原料纳米纤维膜在空气过滤领域的应用,综合聚偏氟乙烯(PVDF)和聚氨酯(PU)的特点,采用静电纺丝技术制备PVDF/PU共混纳米纤维膜。探讨PVDF/PU不同配比对纳米纤维膜形貌、化学结构、力学性能和空气过滤性能的影响。试验结果表明:PU的加入可显著增加PVDF/PU共混纳米纤维膜的力学性能,同时提高纤维膜的亲水性;当PVDF/PU配比为8∶2时,共混纳米纤维膜的形貌及空气过滤性能最佳,过滤效率达91.3%,过滤阻力仅51 Pa,达到高效低阻空气过滤材料的性能要求。

PEI/MIL-88@PVDF复合膜对典型畜禽抗生素废水的分离性能

为提高超滤膜对污染物的去除效果,以聚偏氟乙烯(PVDF)为支撑材料,采用共混法掺入金属有机骨架材料(MOFs)MIL-88对其进行修饰改性,并通过聚乙烯亚胺(PEI)和环氧氯丙烷(ECH)的表面交联反应来改善膜的亲水性,制备了PEI/MIL-88@PVDF表面交联复合膜,分析了复合膜的表面结构形貌特征和性能,并以盐酸四环素为模拟污染物,考察了PEI/MIL-88@PVDF复合膜对抗生素废水处理效果的影响。结果表明:掺杂MIL-88能使复合膜增强对抗生素的处理效果,盐酸四环素去除率相较于纯PVDF膜提升了30.4%;交联反应进行后,复合膜的纯水通量为309.15 L/(m^(2)·h),相较于PVDF膜提升了65.9%,其对抗生素的去除率也提高至74.6%;Langmuir模型能很好地拟合复合膜的等温吸附过程,表明盐酸四环素在复合膜表面的吸附以单层吸附为主;PEI/MIL-88@PVDF复合膜对于pH值变化表现出良好的耐受性,且具有优异的抗生素去除性能。

凝固浴温度对PVDF膜结构和性能的影响

通过溶剂相转化法制备聚偏氟乙烯(PVDF)平板膜,并深入探讨了凝固浴温度这一关键因素对膜微观结构及性能所产生的影响,结果表明:在一定范围内,随着凝固浴温度的逐步升高,制得的PVDF平板膜的厚度呈现出逐渐增加趋势,膜的孔隙率也相应地随之提高;进一步对膜的物理机械性能进行测试分析发现,制得的PVDF平板膜物理机械性能呈先提升后下降的趋势,并在凝固浴温度为60℃时达到最优值,此时,膜拉伸率达到105%,拉断力度达到3.17 N的较高水平;另外,值得注意的是,随着凝固浴温度的升高,铸膜液体系分相时间延长,致使膜的皮层结构变得更加致密,进而导致膜通量逐渐下降。

凝固浴的组成和温度对PVDF均质膜的影响

采用相转化法,配制聚偏氟乙烯、二甲基乙酰胺、添加剂为铸膜液,分别以不同浓度的二甲基乙酰胺的水溶液为芯液和外凝固液制备PVDF均质膜。分别考察了芯液和外凝固液中的溶剂质量分数和温度对均质膜性能和结构的影响。实验结果表明,当芯液溶剂质量分数为55%,温度为55℃,外凝固液溶剂质量分数为50%,温度为60℃时,膜丝可形成完整的海绵状结构,并且具有优异的过滤性能和力学性能。

康复机器人PVDF柔性关节设计与驱动特性研究

针对康复机器人本体柔顺性差的问题,提出了一种新型的聚偏氟乙烯(Polyvinylidene Fluoride,PVDF)凝胶基人工肌肉,将其作为康复机器人柔性关节致动器,期望实现类人动作。介绍了PVDF凝胶制备和电致变形机制,并由此设计了具备收缩和伸张功能的单体肌肉,进而将多个单体肌肉上下串联,组合构成层级人工肌肉;基于康复机器人柔性关节3层级人工肌肉,辨识其驱动数学模型,并进行了仿真与实验。结果表明,该人工肌肉能够有效地实现位置控制,具备电致收缩和扩张能力,作为致动器应用于柔性关节是可行的。

PVDF/PVA共混膜的制备及其在去除污水COD中的应用

以聚乙烯醇(PVA)、聚偏氟乙烯(PVDF)为原料,聚乙烯吡咯烷酮为溶剂,制备了PVDF/PVA共混膜。将该膜应用于膜生物反应器处理污水,测试化学需氧量(COD)去除率和膜的使用性能。结果表明:膜的水通量随PVA加入量的增加而逐渐增加,在牵伸比为1.7时,膜的水通量达到最大值;平板膜用清水清洗后,膜的水通量恢复率较高,膜的运行周期经第一次清洗后下降了18 h,经第二次和第三次清洗后,膜的运行周期基本稳定在6~8 h,COD去除率高于90%,表明该膜具有良好的使用性能。

PVDF纳米纤维膜对工业除尘滤料的性能强化

为了利用聚偏氟乙烯(PVDF)纤维膜的细直径和热/压电性提升过滤效率,用静电纺丝方法制备了PVDF纤维膜,通过SEM和XRD表征了PVDF纤维膜形貌和β晶相转化,并将PVDF纤维膜附着在PPS滤料上制备成PPS/PVDF复合滤料,对其过滤效率及压差特性进行了评估.结果表明:PVDF纤维膜无串珠结构,纤维直径分布在270~780 nm,中值427.3 nm,晶型结构以β晶相为主.随着风速升高,PPS/PVDF纤维膜复合滤料过滤效率下降更小,证明PVDF纤维膜的压电效应对微细粒子过滤效率有改善作用.随着温度的提高,PVDF纤维膜呈现热电性,复合滤料的过滤效率上升,当温度升高到70℃,其对小粒径0.3μm粒子过滤效率提升幅度最大为28.37%.

利用PVDF压电传感器实现接触滑动的快速检测

工业机器人在进行工件抓取过程中,往往存在夹持力过大使工件破损、夹持力过小导致工件滑落的矛盾。为此,提出一种接触滑动的快速检测方法,采用聚偏二氟乙烯(polyvinylidene fluoride, PVDF)压电传感器作为滑觉感知元件。首先,利用阿基米德优化算法(Archimedes optimization algorithm, AOA)优化变分模态分解(variational mode decomposition, VMD)对传感器信号进行分解与重构,降低噪声干扰;然后,提取信号的时频域特征,构建信号特征集;最后,使用蜣螂优化算法(dung beetle optimization, DBO)优化选取长短期记忆网络(long short-term memory networks, LSTM)参数,将DBO优化选取后的参数和信号特征集用于构建滑动检测识别模型。将所提滑动检测方法应用于电动夹爪抓取试验,结果表明,该方法实现了接触状态的精准快速识别,准确率达到100%,识别时间在20 ms以内,根据识别结果可实时调整电动夹爪夹持力大小。