电场极化与振荡剪切对聚偏氟乙烯β相形成的影响

通过电场极化、振荡剪切及以上两种外场同时作用于聚偏氟乙烯(PVDF)熔体,借助红外光谱仪对PVDF在外场作用下结晶形成β相的行为进行了研究。结果表明,电场极化作用能促进PVDF极性β相的形成,随着电场强度提高,β相含量逐渐增加。振荡剪切对β相的形成也有一定促进作用,β相含量随振荡频率的提高略有增加;但两种外场的同时作用,却并不表现出协同效果。     

PVF_2/PMMA共混物高取向薄膜的形态结构研究 Ⅰ.PMMA对高取向PVF_2晶相结构的影响

本文用傅里叶变换红外光谱和电子显微镜方法研究了聚甲基丙烯酸甲酯对高取向聚偏氟乙烯晶相结构的影响。在熔体拉伸的高取向聚偏氟乙烯薄膜中,聚甲基丙烯酸甲酯的存在导致了聚偏氟乙烯片晶尺寸减小,针状晶形成和β相结晶含量增加。     

铁电聚合物可制成更快捷更有效的电源

宾夕法尼亚州立大学正在开发一种铁电聚合物制成的电容器,可以比常用的电池速度更快,但是重量却轻许多。研究人员开发出了聚偏1,1-二氟乙烯和三氟乙烯,其中掺有一氯三氟乙烯。这种材料在室温下拥有很高的介电常数。介电常数是描述一种材料在给定电场下能储存多少电荷的一个参数。这个参数也是当电容器进行储能时,这种材料的效率如何的一个量度。     

掺铌Pb(Zr,Sn,Ti)O3反铁电-铁电转换电场的研究

研究了掺铌PZST反铁电陶瓷中组份和温度对诱导反铁电－铁电相变转换电场的影响,测定了Pb0.99Nb0.02((Zr0.80Sn0.20)1-yTiy)0.98O3系中正向转换电场EF与组份y(Ti)的关系和电极化前后的反铁电／铁电相界。实验测量结果显示,某组份y(Ti)的反映电－铁电转换强度大小取决于该组份与铁电／铁电相界组份的差距。在Pb0.99Nb0.02((Zr0.80Sn0.20)1-yTiy)0.98O3系中随着试样温度升高,反向转换电场EB保持不变,正向转换电场EF和电滞△E降低。这一现象表明温度有助于降低反铁电－铁电相变的应能使得电场诱导反铁电－铁电相变容易进行,因此可以采用加热电极化方法来降低极化电场强度。     

聚偏氟乙烯及其共聚物的分子链旋转势能计算

文章计算了聚偏氟乙烯和三氟乙烯共聚物分子链旋转时势能曲线。结果表明势能曲线不存在“六阱势”理论所预防假设的准六度对称性。由此推论“六阱势”理论不是描述这种有机铁电共聚物极化反转的适合的理论模型。     

聚合物驻极体材料研究的新进展

综述了几种电活性聚合物近年来的迅猛发展状况。其中之一是空间电荷型聚合物压电膜，例如聚丙稀蜂窝膜(PP cellular)和聚四氮乙烯多孔膜(porous PTFE)，它们呈现出高达200～600pC／N的压电d33系数。另一类是经缺陷结构修正的弛豫铁电聚合物偏氟—三氟乙烯共聚物，它们在150MV／m的电场作用下可能诱导出约5％的高应变量和1J/cm^3的高弹性能密度。而全有机复合材料则且现出十分高的介电系数(＞900)，和在13MV／m的较低电场下形成的2％的高应变量及接近1GPa的高弹性模量。     

核-壳结构界面对纳米Ag掺杂BaTiO3@PDA/P(VDF-HFP)复合膜介电和储能性能影响

为改善聚偏氟乙烯（PVDF）基复合材料界面相容性,提高其电性能,利用聚多巴胺（PDA）成功包覆了纳米钛酸钡（BaTiO₃）,并引入纳米Ag离子制备出具有核-壳结构的Ag镶嵌BaTiO₃@PDA-Ag颗粒。以介电聚合物聚偏氟乙烯-六氟丙烯（P（VDF-HFP））为基体,采用溶液流延法制备了BaTiO₃@PDA-Ag/P（VDF-HFP）复合材料厚膜。利用FTIR和XPS验证了BaTiO₃@PDA-Ag/P（VDF-HFP）复合材料结构和形貌,并用宽频介电频谱仪和铁电测试仪分别比较了PDA包覆前后的不同BaTiO₃含量的BaTiO₃@PDA-Ag/P（VDF-HFP）复合膜在低电场下的介电性能和高电场下的电极化性能。结果表明,BaTiO₃@PDA-Ag质量分数为20wt%的BaTiO₃@PDA-Ag/P（VDF-HFP）复合膜在10 Hz下介电常数（ε_r）达到了25,介电损耗（tanδ）仅为0.1,在175 M·Vm-1电场下电极化强度（D_m）为6.2 μC·cm-2,200 M·Vm-1时储能密度（U_e）达到了6.9 J·cm-3,高于其它界面未处理复合膜。以上结果可为此类介电复合材料界面结构处理和电性能研究提供参考。      

纳米二氧化硅颗粒对PVDF超滤膜凝胶过程和结构的影响

以PDVF(聚偏氟乙烯)超滤膜为研究对象,通过凝胶动力学常数K、产生沉淀的聚合物层厚度的平方x2和凝胶时间t之间的关系、絮凝值的变化来反映SiO2颗粒对膜凝胶速率和膜结构的影响,并用膜凝胶动力学观测装置观察并记录成膜过程.实验结果表明,在铸膜液中添加纳米二氧化硅颗粒可以使聚偏氟乙烯超滤膜的凝胶速率减小,形成的膜更加致密.     

新型压电热电功能材料——汽相沉积法聚脲薄膜

1.前言1969年,日本小林理研公司的河合平司博士第一次发现了聚偏氟乙烯(PVDF)的压电性(物质当发生形变或受到应力时就会产生电极化,相反,当受到电场作用时就会产生形变和应力的一种性质)。自那以后,关于合成高分子压电性、热电性(物质随温度变化而极化程度也发生变化的一种性质)的研究很快就在世界上盛行起来。表1列出了有关压电性、热电性高分子研究的主要进展情况。     

电致变色器件关键材料凝胶聚合物电解质研究进展

凝胶聚合物电解质是构成电致变色器件(ECD)的关键材料,其在器件中作为电极间的传导介质,为电致变色反应提供补偿离子。利用不同基体材料制备的凝胶聚合物电解质对提高电致变色器件性能具有重要影响。综述了聚环氧乙烷(PEO)、聚丙烯腈(PAN)、聚甲基丙烯酸甲酯(PMMA)、聚偏氟乙烯(PVDF)、聚偏氟乙烯-六氟丙烯(PVDF-HFP)、聚乙烯醇缩丁醛(PVB)及生物材料作为凝胶电解质聚合物基体的导电机理。阐述了它们作为电致变色器件电解质层对离子电导率、透光度、电致变色性能的影响。最后对凝胶聚合物电解质未来发展趋势进行了展望。     

热极化和电晕极化铁电PVDF薄膜的成分和结构

用高分辨率X-射线光电子能谱（XPS）研究了热极化和电晕极化的PVDF薄膜的成分和结构的变化。结果表明：PVDF薄膜的热极化和电晕极化反应过程和机理不同。在热极化过程中.高温强电场作用使PVDF薄膜产生了少量的F^-自由基,继而产生HF,形成了新C=C键：怛是,在电晕极化过程中荷能粒子使PVDF产生了H^＋自由基。热极...     

Enhanced electrical properties of multiwalled carbon nanotube/poly(vinylidenefluoride) films through a rolling process

Poly(vinylidene fluoride) (PVDF) films containing multiwalled carbon nanotubes (MWCNTs) were prepared by solution casting method, followed by a rolling process. With the presence of MWCNTs (up to 0.3 wt%), the influence of rolling process on the crystal structure and the electrical properties of PVDF was studied. It is shown that rolling can induce phase transition as well as increase in the crystallinity of PVDF, leading to enhancement of ferroelectric and dielectric properties. In addition, MWCNTs may promote the phase transition of PVDF, while impeding the increase of crystallinity during the rolling process. With a higher breakdown field and a lower coercive electric field in comparison with the original films, the rolled films can be efficiently poled to obtain good piezoelectricity. Moreover, with the presence of MWCNTs, electric field-induced changes in crystallinity can be obviously observed in the poled MWCNTs/PVDF films. With the highest crystallinity of β-phase, the rolled films containing 0.075 wt% MWCNTs possess the highest piezoelectric coefficient d₃₃ of ~33 pC/N while that of pure PVDF films is only ~22 pC/N.     

Epitaxially Grown Ferroelectric PVDF‐TrFE Film on Shape‐Tailored Semiconducting Rubrene Single Crystal

Epitaxial crystallization of thin poly(vinylidene fluoride‐co‐trifluoroethylene) (PVDF‐TrFE) films is important for the full utilization of their ferroelectric properties. Epitaxy can offer a route for maximizing the degree of crystallinity with the effective orientation of the crystals with respect to the electric field. Despite various approaches for the epitaxial control of the crystalline structure of PVDF‐TrFE, its epitaxy on a semiconductor is yet to be accomplished. Herein, the epitaxial growth of PVDF‐TrFE crystals on a single‐crystalline organic semiconductor rubrene grown via physical vapor deposition is presented. The epitaxy results in polymer crystals globally ordered with specific crystal orientations dictated by the epitaxial relation between the polymer and rubrene crystal. The lattice matching between the c‐axis of PVDF‐TrFE crystals and the (210) plane of orthorhombic rubrene crystals develops two degenerate crystal orientations of the PVDF‐TrFE crystalline lamellae aligned nearly perpendicular to each other. Thin PVDF‐TrFE films with epitaxially grown crystals are incorporated into metal/ferroelectric polymer/metal and metal/ferroelectric polymer/semiconductor/metal capacitors, which exhibit excellent nonvolatile polarization and capacitance behavior, respectively. Furthermore, combined with a printing technique for micropatterning rubrene single crystals, the epitaxy of a PVDF‐TrFE film is formed selectively on the patterned rubrene with characteristic epitaxial crystal orientation over a large area.     

A low-temperature pyroelectric study of PVDF thick films

Pyroelectric coefficient measurements were made at various temperatures for poled and unpoled samples of PVDF films. Samples were produced using the spin-coating technique onto glass substrates. Experiments were made using the quasi-static technique. PVDF samples were poled at various electric field strengths and the relation between poling field strength and the pyroelectric coefficient was investigated. The effect of the poling temperature was also studied. The maximum pyroelectric coefficient was obtained for a poling temperature of 340 K and for a poling field strength of . Dielectric permitivity and dielectric loss measurements were also performed in the 125–375 K temperature range.     

X-ray photoelectron spectroscopy characterization of the interface between Ag electrode and PVDF film treated by electric poling

Interface changes induced by electric poling treatment between an Ag electrode deposited by vacuum thermal evaporation and a polymer thin film have been investigated. The polymer film poly (vinylidene fluoride) (PVDF), a fluoropolymer of repeat unit (–CH₂–CF₂–) was treated under electric poling at high temperature of 90°C. The characterization was accomplished using X-ray photoelectron spectroscopy (XPS) as a primary tool. The results indicate that the piezoelectricity of PVDF thin films and adhesion force between polymer thin film and metallic electrode are improved by electric poling and chemical bond joint.     

Study of electrical polarization hysteresis in ferroelectric polyvinylidene fluoride films

Electric properties of polyvinylidene (PVDF) films fabricated using the Langmuir-Schaefer method have been studied. Films of different thickness were deposited on silicon substrates and analyzed using several techniques. X-ray diffraction (XRD) data showed that PVDF films crystallize at an annealing temperature above 130 °C. Polarization versus electric field (PE) ferroelectric measurements was done for samples prepared with electrodes. PE measurements show that the coercivity of the films increases as the maximum applied electric field increases. The coercivity dependence on the frequency of the applied electric field can be fitted as f^0.6. The results also show that the coercivity decreases with increasing the thickness of PVDF film due to the pinning effect.     

Field-induced effect in the <111>-oriented 0.70Pb(Mg1/3Nb2/3)O3–0.30PbTiO3 single crystals

Temperature-dependent dielectric constant, X-ray diffraction(XRD), thermally stimulated discharging current (TSDC) and polarization hysteresis loops for <111>-oriented 0.70Pb(Mg_1/3Nb_2/3)O₃–0.30PbTiO₃ crystals after poling under different fields were measured. Comparing with unpoled sample during heating, except that there is a transition from the state of normal ferroelectric rhombohedral (macro-domain) to the state of relaxor ferroelectric rhombohedral (micro-domain) for the poled samples, it was found that no other phase transition was induced by poling fields. XRD showed that after poling the piezoelectric elongation of the unit cell occurred along the polar direction. It was suggested that an extra peak in the T–ε curve of poled sample around 105 °C is not only caused by a macro–micro domain transition but also caused by the depolarization process of 180° and 71° domain switching simultaneously.     

Dielectric response of polymer relaxors

Dielectric response of vinylidene fluoride type ferroelectric polymers is dominated by that of segmental motions in the amorphous phase in temperature range 200–300 K and contributions related to the local mode and ferroelectric–paraelectric transition in the crystalline phase of the polymer at higher temperatures. Diffuse and frequency-dependent dielectric anomaly observed in fast electron irradiated polyvinylidene fluoride-trifluoroethylene P(VDF/TrFE) has been related to relaxor-like behavior induced in the semicrystalline ferroelectric copolymers. As random field and the response of polar nanosize clusters determine the relaxor behavior the effects of disorder and fast electron irradiation (below and above T _C) on the three contributions to the dielectric response of PVDF, P(VDF/TrFE)(75/25) and P(VDF/TrFE)(50/50) are shown. The processes involved in radiation-induced functionalization of PVDF-type polymers are discussed on the basis of results of ESR, IR and Raman spectroscopy studies.     

Electric Field Effects on the Thermodynamics of Multiferroic Chains

The thermodynamic properties of the helical spins with a magnetoelectric coupling are studied theoretically using Monte Carlo simulations. It is shown that the spin?Cspin correlations are affected by thermal fluctuations and by an electric field. Results for the temperature-dependence of the ferroelectric polarization and for the electric susceptibility are presented and analyzed with a focus on the multiferroic phase transition.     

Synergy-Compensation Effect of Ferroelectric Polarization and Cationic Vacancy Collaboratively Promoting CO2 Photoreduction

Photocatalytic CO₂ reduction is severely limited by the rapid recombination of photo-generated charges and insufficient reactive sites. Creating electric field and defects are effective strategies to inhibit charge recombination and enrich catalytic sites, respectively. Herein, a coupled strategy of ferroelectric poling and cationic vacancy is developed to achieve high-performance CO₂ photoreduction on ferroelectric Bi₂MoO₆, and their interesting synergy-compensation relationship is first disclosed. Corona poling increases the remnant polarization of Bi₂MoO₆ to enhance the intrinsic electric field for promoting charge separation, while it decreases the CO₂ adsorption. The introduced Mo vacancy (V_Mo) facilitates the adsorption and activation of CO₂, and surface charge separation by creating local electric field. Unfortunately, V_Mo largely reduces the remnant polarization intensity. Coupling poling and V_Mo not only integrate their advantages, resulting in an approximately sevenfold increased surface charge transfer efficiency, but also compensate for their shortcomings, for example, V_Mo largely alleviates the negative effects of ferroelectric poling on CO₂ adsorption. In the absence of co-catalyst or sacrificial agent, the poled Bi₂MoO₆ with V_Mo exhibits a superior CO₂-to-CO evolution rate of 19.75 µmol g⁻¹ h⁻¹, ≈8.4 times higher than the Bi₂MoO₆ nanosheets. This work provides new ideas for exploring the role of polarization and defects in photocatalysis.