单轴拉伸对聚偏二氟乙烯薄膜压电响应性能的影响

采用溶液涂覆成膜工艺制备聚偏二氟乙烯(PVDF)薄膜，对其进行单轴拉伸制得不同拉伸比(R=3, 5, 7)的PVDF薄膜.研究了不同拉伸比对薄膜化学结构、结晶行为、铁电性能及压电响应性能的影响，实现了对PVDF结晶相的本征压电响应性能的增强.单轴拉伸使PVDF结晶度提高，同时促使其结晶相由α相向β相转变；拉伸比越大，极性β相相对含量越高，当拉伸比为7时，薄膜β相的相对含量最高达到85.12%，此时薄膜的电输出性能最佳：外加电场为200 MV/m时，其剩余极化强度为2.69μC/cm~2；应变为5%时，其平均闭路电流密度为58.92 nA/cm~2，平均开路电压为89.70 mV.     

聚偏氟乙烯共混体系的压电性及其分子运动

聚偏氧乙烯(PVDF)的压电效应近年来引起了人们的极大兴趣,为了探索PVDF共混体系中第二组分对薄膜压电性能的影响及开发新的压电材料,我们研究了PVDF的三个共混体系的压电性及其分子运动。这三个共混体系是: 1.PVDF+PMMA(聚甲基丙烯酸甲酯);2.PVDF+F₂₆(偏氟乙烯-全氟丙烯共聚物),3. PVDF+F₂₄(偏氟乙烯-四氟乙烯共聚物)。     

聚偏氟乙烯基含氟聚合物介电和储能研究进展

聚偏氟乙烯（PVDF）和偏氟乙烯（VDF）／三氟乙烯（TrFE）二元共聚物以其优异的铁电、压电性能而备受关注。近年来,该类聚合物经物理／化学改性后表现出非常优异的介电、储能性能,尤其在高储能放电电容器领域被寄予厚望。经分子组成优化和挤出拉伸处理的PVDF基含氟聚合物在室温下具有高介电常数（12～60）,高击穿电场强度,...     

铁电高分子聚偏氟乙烯-三氟乙烯的凝聚态结构与性能调控研究进展

高分子的凝聚态结构具有多层次性,在微纳米尺度上有效地控制高分子的凝聚态结构,进而探索在微纳米尺度上凝聚态结构与性能的关系,将为高分子分子层次和宏观层次的结构与性能之间架起桥梁。本文综述了近年来我们课题组在铁电高分子聚偏氟乙烯-三氟乙烯共聚物方面的研究及其进展。发展了在纳米尺度上控制高分子片晶取向的新方法并应用到聚偏氟乙烯-三氟乙烯体系,构筑了取向高度有序的铁电高分子纳米结构阵列,分析了片晶取向与聚偏氟乙烯-三氟乙烯微观铁电和压电性能之间的关系,有效降低了以聚偏氟乙烯-三氟乙烯为主要材料的有机铁电非易失性存储器的读写电压。     

偏氟乙烯-四氟乙烯共聚物热释电性的研究

本实验室合成了一系列不同组成的偏氟乙烯-四氟乙烯共聚物(F_(24)),并通过浇铸与极化制成了热电薄膜. 实验结果表明F_(24)薄膜的热释电系数依赖于极化温度,极化电场,极化时间。选用适当的极化条件可以提高薄膜的热释电性。热释电系数还与共聚物组成有关,当共聚物中,偏氟乙烯的克分子百分数为80～85时,热释电系数最高.此外,还测定了F_(24)的电滞回线。     

聚偏氟乙烯共混体系的压电性及其分子运动

聚偏氟乙烯(PVDF)的压电效应近年来引起了人们的极大兴趣,用它制成的各种换能器已得到了广泛应用,关于它的压电性及其分子运动已有报道。为了探索PVDF共混体系中第二组分对薄膜压电性能的影响及开发新的压电材料,我们研究了PVDF的三个共混体系的压电性及其分子运动。这三个共混体系是:     

偏氟乙烯的聚合反应

本文研究了用有机引发剂引发偏氟乙烯的水相聚合,并对制得的聚偏氟乙烯的性质进行了研究。有机引发剂引发聚合的聚偏氟乙烯的热稳定性、强度、结晶度和熔点均比用过硫酸盐引发聚合的聚偏氟乙烯高。     

聚偏氟乙烯/蒙脱土纳米复合材料的形态结构

采用有机改性的蒙脱土与聚偏氟乙烯熔融共混, 制备了聚偏氟乙烯/蒙脱土纳米复合材料. 利用X射线衍射分析、透射电子显微镜(TEM)和Molau实验研究了复合材料的微观结构. 通过X射线衍射、傅里叶变换红外光谱(FTIR)以及差热扫描(DSC)研究了有机改性蒙脱土对聚偏氟乙烯结晶结构的影响. 结果表明, 有机改性蒙脱土在聚偏氟乙烯中以插层、剥离和碎片的形式存在. 在X射线衍射谱中发现蒙脱土的(001)峰向低角方向移动, 在TEM中可见到剥离的片层碎 片.蒙脱土的引入改变了聚偏氟乙烯的结晶结构, 导致了具有压电性能的β相形成, 引起α相内应力的产生, 同时也导致了聚偏氟乙烯基体的结晶度下降, 球晶尺寸随蒙脱土含量明显减少. 蒙脱土引起的β相在 160℃退火表明是相当稳定的. 根据这些实验结果, 对由于蒙脱土的引入引起的聚偏氟乙烯结晶结构的变化提出了可能的解释.     

金属及其化合物掺杂PVDF介电/压电材料的研究进展

聚偏氟乙烯(PVDF)是一种具有热电性和压电性的聚合物,由于其具有良好的柔韧性、热稳定性和耐腐蚀性等优点,因此在电子电气领域具有广阔的应用前景,但相对于传统无机类压电材料来说,其介电常数和压电常数仍相对较低,因此提升PVDF的压电性能和介电性能已成为目前国内外的研究热点之一。本文对近年来国内外利用金属及其化合物来提高聚偏氟乙烯(PVDF)电性能的方法进行了概述,并对金属及其化合物掺杂PVDF的利弊及发展趋势进行了展望。     

偏氟乙烯-四氟乙烯共聚物的热电性及热刺激电流的研究

<正> 偏氟乙烯-四氟乙烯共聚物(F_(24))与偏氟乙烯(PVDF)都具有较高的热释电性,但F_(24)在一定组成范围内为β晶型,不像PVDF那样需要经过拉伸,所以制备热释电薄膜的工艺比较简单。本文比较了在无机及有机引发剂体系中所合成的F_(24)的热释电性,研究了不同极化方法对热循环曲线和热释电性的影响,并测定了F_(24)的TSC谱,由此观察     

Electrical impedance spectroscopy study of piezoelectric PVDF membranes

Piezoelectric poly (vinylidene fluoride) (PVDF) membranes were prepared from pre-fabricated membranes by electrically poling in an intense electric field. The electrical impedance of PVDF membranes measured over a frequency range of 10^?2–10⁵ Hz before and after poling is presented. The effect of pressure on the impedance characteristics of un-poled and poled PVDF membranes was also studied. A four element model circuit, including a constant phase element (CPE) was fitted to the impedance spectra. The elements of the circuit fitted to the poled sample were more conductive compared with those of the un-poled sample. Stronger CPE elements in the circuit were detected in the poled samples under pressure suggesting that the piezoelectric activity of PVDF is the major contributor to the constant phase angle seen at low frequencies.     

Broadband dielectric characterization of piezoelectric poly(vinylidene fluoride)thin films between 278 K and 308 K

This work describes the dielectric properties of piezoelectric poly(vinylidene fluoride) (PVDF) thin films in the frequency and temperature ranges relevant for usual applications. We measured the isothermal dielectric relaxation spectra of commercial piezoelectric PVDF thin films between 10 Hz to 10 MHz, at several temperatures from 278 K to 308 K. Measurements were made for samples in mechanically free and clamped conditions, in the direction of the poling field (perpendicular to the film). We found that the imaginary part of the dielectric relaxation spectra of free and clamped PVDF samples is dominated by a peak, above 100 kHz, that can be characterized by a Havriliak-Negami function. The characteristic time follows an Arrhenius dependence on temperature. Moreover, the spectra of the free PVDF samples show two additional peaks at low frequencies which are associated with mechanical relaxation processes. Our results are important for the characterization of piezoelectric PVDF, particularly after the stretching and poling processes in thin films, and for the design and characterization of a broad range of ultrasonic transducers.     

Time and poling history dependent energy storage and discharge behaviors in poly(vinylidene fluoride-<Emphasis Type="Italic">co</Emphasis>-hexafluoropropylene) random copolymers

 We studied cycle time (0.01–10 s with triangular input waves) and poling history (continuous versus fresh poling) dependent electric energy storage and discharge behaviors in poly(vinylidene fluoride-co-hexafluoropropylene) [P(VDF-HFP)] films using the electric displacement ― the electric field (D-E) hysteresis loop measurements. Since the permanent dipoles in PVDF are orientational in nature, it is generally considered that both charging and discharging processes should be time and poling history dependent. Intriguingly, our experimental results showed that the charging process depended heavily on the cycle time and the prior poling history, and thus the D-E hysteresis loops had different shapes accordingly. However, the discharged energy density did not change no matter how the D-E loop shape varied due to different measurements. This experimental result could be explained in terms of reversible and irreversible polarizations. The reversible polarization could be charged and discharged fairly quickly (< 5 ms for each process), while the irreversible polarization depended heavily on the poling time and the prior poling history. This study suggests that it is only meaningful to compare the discharged energy density for PVDF and its copolymer films when different cycle times and poling histories are used.     

极化方式对聚偏氟乙烯(PVDF)驻极体压电性的影响

<正> 自1969年日本学者Kawai发现PVDF驻极体具有强压电性以来,PVDF作为一种换能材料已得到广泛重视,七十年代中期至今,在应用上获得了可喜的进展。 然而到目前为止,对其压电性机制的研究仍无定论,多数人认为PVDF的压电性是由它晶区的固有特性即体积极化度所引起,并且Scheinbeim等人的工作表明,PVDF的     

Improving piezoelectric performance of lead-free polymer composites with high aspect ratio BaTiO3 nanowires

Flexible and lead-free piezoelectric nanocomposites were synthesized with BaTiO₃ nanowires (filler) and poly(vinylidene fluoride) (PVDF) (matrix), and the piezoelectric performances of the composites were systematically studied by varying the aspect ratio (AR) and volume fraction of the nanowire and poling time. BaTiO₃ nanowires with AR of 18 were synthesized and incorporated into PVDF to improve the piezoelectric performance of the composites. It was found that high AR significantly increased the dielectric constant up to 64, which is over 800% improvement compared to those from the composites containing spheroid shape BaTiO₃ nanoparticles. In addition, the dielectric constant and piezoelectric coefficient were also enhanced by increasing the concentration of BaTiO₃ nanowires. The piezoelectric coefficient with 50-vol% BaTiO₃ nanowires embedded in PVDF displayed 61 pC/N, which is much higher than nanocomposites with spheroid shape BaTiO₃ nanoparticles as well as comparable to, if not better, other nanoparticle-filled polymer composites. Our results suggest that it is possible to fabricate nanocomposites with proper mechanical and piezoelectric properties by utilizing proper AR fillers.     

NMR investigations of polymer electrets

1H NMR investigations were performed on thin films of poly(vinylidene fluoride) (PVDF) and polyamide 11 (PA 11). The variation of the angle between the static magnetic B_o-field and preferred directions given by drawing and poling leads to characteristic dependences of T_20ff, which can be discussed in terms of Legendre polynomials of the orientational distribution functions of crystallographic c- and b-axis. A good c-axis alignment can be realized by uniaxial drawing. The tendency for b-axis to orient towards the direction of the applied electric field via the orientation of the electric dipoles is evident. The b-axis alignment can be “switched” periodically.     

Poly(vinylidene fluoride) (PVDF)/potassium sodium niobate (KNN)–based nanofibrous web: A unique nanogenerator for renewable energy harvesting and investigating the role of KNN nanostructures

In the recent era, finding renewable energy sources that are environmentally benign the main focus of scientific community around the globe. There is a plenty of renewable energy sources that are currently being researched such as solar power, thermal energy, wind energy, salinity gradients, and kinetic energy. Polymer‐ceramic–based nanocomposite piezoelectric material is known for quite some time for energy harvesting, but the real challenge lies as it requires very high loading of the ceramic part to obtain the required property and thus almost makes the system nonflexible. Developed material needs to be poled later on to use it as an electric energy generator from ambient mechanical movement. This current study is the first time attempt to produce a simple yet unique lightweight energy harvester using polyvinylidene fluoride (PVDF)/potassium sodium niobate (KNN) nanostructures–based nanocomposite flexible fibrous web where the material is in situ poled during its production using an electrospinning setup. At the beginning, various parameters were identified to synthesize and modulate KNN as nanostructural materials having higher aspect ratio, which is intended to provide a unique connection between KNN once these are embedded within the fibrous matrix. The incorporated KNN nanostructure having higher aspect ratio was also found to act as a beta nucleating agent in PVDF matrix and enhances the β‐phase crystal into the resultant fibrous web, which in turn increases the piezoelectric energy‐harvesting capacity manifold as compared with bare PVDF fibrous web. The in situ alignment of the nanostructured KNN (with a minimum loading, 5% only) into the fibrous nanocomposite is another achievement to obtain higher output. X‐ray diffraction and Fourier transform infrared analysis confirmed the mixture of α‐ and β‐crystalline phase of pure PVDF, which gets converted into β phase once KNN nanostructures are incorporated inside the nanofibrous web. An output voltage of 1.9 V was obtained from PVDF/KNN nanocomposite–based web, which is significantly higher (38 times) than generated voltage (50 mV) from the pure PVDF nanoweb without any subsequent poling operation.     

钛酸铅与偏氟乙烯-三氟乙烯共聚物形成的铁电复合物相变过程的热释电研究

研究了偏氟乙烯-三氟乙烯共聚物与钛酸铅形成的铁电复合物PT/P[VDF(70)-TrFE(30)]的热释电流行为。P[VDF(70)-TrFE(30)]室温下存在两个铁电相,即较无序的铁电相和较有序的铁电相,升温经过各自的相转变点后转变成较有序的顺电相和较无序的顺电相。热释电流谱上出现在95℃和108℃的两个电流峰,分别由两个铁电相的结构陷阱以及部分取向的偶极所贡献。采用Tc以上温度极化并冷却到不同温度的方法可明确鉴别出该试样两个顺电相降温转变过程,转变点分别为62℃和50℃。实验证实陷阱仅存在于铁电相而不存在于顺电相中。钛酸铅的引入虽不导致新电流峰出现,但可使共聚物的Tc降低、电流加大。热释电流方法可非常灵敏地跟踪铁电共聚物的相变过程。     

聚偏氟乙烯-磺化聚醚砜相容性及其成膜性能

研究了聚偏氟乙烯(PVDF)-磺化聚醚砜(SPES)的相容性及其成膜性能.首先通过溶解度参数、粘度法和目测法研究共混溶液的相容性,接着采用浊度法测定了共混溶液的热力学性质,最后采用浸没沉淀法制备了共混膜并探讨了成膜性能.结果显示,PVDF和SPES为部分相容体系,随着SPES含量的增加,共混溶液相容性逐渐减小,当SPES含量增加到50wt%时,体系发生分相.共混溶液的成膜性能良好,SPES含量增加有利于体系发生液液分相,生成高孔隙率膜,并且极大的提高了PVDF膜的亲水性和水通量.     

Photocrosslinkable second-order nonlinear optical polymers synthesized by cationic copolymerization

Photocrosslinkable second-order nonlinear optical (NLO) polymers were synthesized from cationic copolymerization of a vinyl ether monomer bearing 4′-nitrobiphenyl-4-oxy group as the NLO chromophore with a vinyl ether monomer bearing cinnamoyl group as the photoreactive moiety. To obtain a suitable poling method involving photocrosslinking, which is capable of inducing a higher and more stable second-order nonlinear coefficient, d₃₃, for NLO polymer films, some poling procedures were investigated. An optimized poling method was as follows. Ultraviolet (UV) irradiation is performed for 90 sec during poling at 50°C for 20 min, followed by poling at 150°C for 20 min. By using this poling method NLO polymer films exhibited a higher and considerably stable d₃₃ value at room temperature, even though they had rather lower glass transition temperatures before photocrosslinking. Some photocrosslinking mechanism for NLO polymers investigated here were considered.