聚丙烯孔洞型铁电驻极体薄膜的压电性研究

利用准静态法和激光干涉法测量正、逆压电d33系数,研究了经压力膨化处理的聚丙烯孔洞型铁电驻极体薄膜压电系数的压强和频率特性及其热稳定性.结果表明,聚丙烯薄膜经压力膨化处理后,其压电性能改善的原因是:压力膨化处理既能有效地降低孔洞膜的弹性模量Y,又能增强其储电能力.聚丙烯孔洞膜的压电d33系数在激励信号压强为0.2～4kPa的范围内基本保持恒定,但当其值高于4kPa时,d33系数出现了明显的下降.聚丙烯孔洞膜的压电d33系数随频率上升而下降(即从0.001Hz时的1200pC/N降低到其机械共振频率附近时的350pC/N),是与材料的弹性模量Y随频率的上升而增加直接相关.对不同工艺参数制备的样品,其机械共振频率位于150～400kHz范围内.实验结果还表明:聚丙烯孔洞膜的压电d33系数的热稳定性与非孔洞型聚丙烯驻极体薄膜的电荷储存热稳定性相近.     

经二次膨化工艺优化的孔洞结构聚丙烯薄膜的压电性

报道了提高孔洞结构压电驻极体膜压电活性的新方法。该方法是在对已膨化处理的压电驻极体薄膜再进行一次膨化处理,通过调节薄膜的力学性能来进一步优化材料的压电活性。结果表明,将聚丙烯（PP）压电驻极体薄膜进行二次膨化处理后,其压电活性比一次膨化的PP薄膜提高约40％。这是因为薄膜在真空蒸镀电极过程中导致的厚度减小能够通过二次膨化工艺得到恢复,而厚度的增加可以有效地降低材料的杨氏模量,从而使薄膜的压电系数d33增加;两次膨化温度对压电系数d33均有影响,并且相互联系;通过选择合理的一次和二次膨化工艺参数（例如100℃和45℃）能够获得稳定的高压电系数压电驻极体膜。     

单层及多层PP蜂窝膜驻极体的压电性

经压力膨化处理后,以正逆压电系数d33测量研究了一种经无栅电晕充电的国产商用聚丙烯蜂窝膜(cellular PP,商品名PQ50)驻极体的压电性.经过优化工艺参数压力膨化处理后的PQ50蜂窝膜呈现600pC/N以上的准静态压电系数,这一量值约为PVDF相关系数的40倍.而通过将单层PQ50蜂窝膜驻极体粘贴形成合理的多层结构,得到的复合膜系压电系数d33高达2010pC/N,约为PZT压电陶瓷相应系数的3倍.从而为拓宽这类新一代的非极性孔洞聚合物压电功能膜应用领域,推动其应用进程提供了一定的理论和技术依据.     

化学改性对气体压力膨化孔洞聚丙烯膜的压电热稳定性和机电性能的影响

通过压电d33系数等温衰减测量、热刺激放电（TSD）技术及介电谐振谱分析，研究了孔洞PP原膜及其化学改性膜在经历相同的压力膨化和热处理工艺后的压电热稳定性和机电性能。对比性地研究了90℃膨化和RT膨化对孔洞PP膜压电热稳定性和机电性能的影响。结果表明：化学改性及热膨化工艺改善了孔洞PP膜的压电热稳定性和机电性能，且90℃膨化改性膜比RT膨化改性膜具有更好的压电热稳定性和机电性能。     

压力膨化处理和充电方法对PP蜂窝膜压电性的影响

以压力膨化技术处理改性商用SHD50型聚丙烯蜂窝膜(PP Cellular),它们的压电 d33 系数可达193pC/N,比未经处理的样品提高了约 2 个数量级。利用点电晕充电,接触法充电和动态压电 d33系数测量研究了上述2种不同充电方法对 SHD50 膜压电性的影响。     

聚丙烯孔洞驻极体薄膜的突出压电活性及其应用研究

聚丙烯(PP)孔洞膜可呈现高达1000pC/N的准静态压电d33系数,是久负盛名的铁电聚合物PVDF相应系数的50倍以上,可和压电陶瓷相媲美.基于国内外最新研究成果,综述了PP孔洞膜的制备技术、极化方法、压电活性以及可能的应用前景.     

温度和湿度对聚四氟乙烯多孔驻极体膜压电活性稳定性的影响

研究了具有开放性孔洞的聚四氟乙烯(voided polytetrafluoroethylene,PTFE)多孔膜和PP蜂窝膜(polypropylene cellular)的驻极体行为和压电活性的温度效应。研究结果指出：和PP蜂窝膜驻极体相比．PTFE多孔膜驻极体呈现出突出的电荷储存和压电活性的温度稳定性;研究了这类稳定性的驻极体和材料的结构根源。PTFE多孔薄膜驻板体这种压电活性的温度稳定性主要依赖于这类驻极体材料电荷储存及材料的本征性能(如力学性质等)的温度稳定性。实验结果还说明：PTFE多孔膜突出的压电系数温度稳定性使它大大扩展了以包括PP在内的空间电荷型多孔膜研制的压电功能元器件的耐温要求。本文还讨论了环境因素(如相对湿度)对这类功能膜压电活性的影响,分析了环境湿度对压电活性影响的结构根源。     

微孔结构氟聚合物铁电驻极体的制备及其热稳定性研究

描述了一种微孔结构氟聚合物铁电驻极体的制备方法，利用准静态方法测量了该功能膜的压电系数如，并通过等温衰减和热刺激放电电流谱的测量研究了凼，的热稳定性。结果表明，这类氟聚合物铁电驻极体膜的准静态压电系数d33与热压时间有关；与聚丙烯（PP）压电驻极体膜相比较，氟聚合物压电驻极体膜不但具有更高的压电活性，而且呈现更优良的热稳定性。     

FEP和多孔PTFE复合膜铁电驻极体的压电性及电荷动态特性

报道了将致密的FEP和多孔PTFE交互层叠在一起，采用热粘合的方法制备出具有孔洞结构的聚合物复合膜，然后经电晕极化处理使该复合膜成为铁电驻极体。最后用准静态方法测量该铁电复合膜的压电系数d33，并通过热刺激电流放电（TSD）电流谱和等温衰减研究了FEP和多孔PTFE复合膜铁电驻极体的电荷动态特性。结果表明：该复合膜的压电系数d33可达200～500pC/N，在0～12kPa的压强范围内呈现出良好的线性，并且在90℃下老化160min后仍保持在原来的43％且趋于稳定；FEP和多孔PTFE复合膜铁电驻极体电荷在热激发脱阱后复合途径主要有2种：一种是沿着固体介质的表面迁移与异性电荷复合，另一种是穿过固体介质层与异性电荷复合。在低温区（7512附近）前者占优，高温区（120℃附近）后者占优。     

多孔PTFE/P(VDF-HFP)复合膜的驻极体性质

通过栅控恒压负电晕充电、等温表面电位衰减测量、热刺激放电(Thermally Stimulated Discharge,TSD)电流谱分析、电荷TSD和压电d33系数测量等方法,首次研究了将旋涂在基片上的含一定溶剂的聚偏氟乙烯和六氟丙烯共聚物(P(VDF-HFP))薄膜与多孔聚四氟乙烯薄膜均匀压合形成的多孔PTFE/P(VDF-HFP)双层复合膜系的驻极体性质.从多孔PTFE面充电的双层膜具有较从P(VDF-HFP)面充电优异的多的电荷热稳定性.使用介电谐振谱测量的双层膜的压电d33系数(31pC/N)是传统的铁电聚合物材料PVDF相应值(15 pC/N)的2倍左右.     

Piezoelectricity of single- and multi-layer cellular polypropylene film electrets

The piezoelectricity of a pressure-treated cellular polypropylene (PP) (commercially available, trade name PQ50) film electret was studied by the measurement of direct- and inverse-piezoelectric d₃₃ coefficient. The sample expanded with optimal parameters has a quasi-static piezoelectric d₃₃ coefficient of more than 600 pC/N, which is about 40 times as high as that of polyvinylidene fluoride (PVDF). In addition, the hybrid multi-layer system, which properly combines single-layer cellular PP film electrets, shows a quasi-static piezoelectric sensitivity of as high as 2010 pC/N. This is around three times higher than that of well-known lead zirconate titanate (PZT) ceramics. The results are theoretically and technically helpful to promote the application of cellular PP film electrets.     

Piezoelectricity of single-and multi-layer cellular polypropylene film electrets

The piezoelectricity of a pressure-treated cellular polypropylene (PP) (commercially available, trade name PQ50) film electret was studied by the measurement of direct-and inverse-piezoelectric d ₃₃ coefficient. The sample expanded with optimal parameters has a quasi-static piezoelectric d ₃₃ coefficient of more than 600 pC/N, which is about 40 times as high as that of polyvinylidene fluoride (PVDF). In addition, the hybrid multi-layer system, which properly combines single-layer cellular PP film electrets, shows a quasi-static piezoelectric sensitivity of as high as 2010 pC/N. This is around three times higher than that of well-known lead zirconate titanate (PZT) ceramics. The results are theoretically and technically helpful to promote the application of cellular PP film electrets. Translated from Journal of Functional Materials, 2006, 37(2): 207–209 [译自: 功能材料]     

Dielectric and piezoelectric properties of perovskite materials at cryogenic temperatures

Dielectric and piezoelectric properties of perovskite materials including La modified Pb(Zr, Ti)O3 (PZT's), (Ba, Sr)TiO3 (BST) polycrystalline ceramics and Pb(Zn1/3 Nb2/3)O3-PbTiO3 (PZN-PT) single crystals were investigated for capacitor and actuator applications at cryogenic temperatures. PZTs were compositionally engineered to have decreased Curie temperatures (Tc) by La and Sn doping in order to compensate for the loss of extrinsic contributions to piezoelectricity at cryogenic temperatures. Enhanced extrinsic contributions resulted in piezoelectric coefficients (d33) as high as 250 pC/N at 30 K, superior to that of conventional DOD Type PZT's (d33~100 pC/N). This property enhancement was associated with retuning to the MPB at cryogenic temperatures. 5/95 BST with a dielectric maximum at 57 K was investigated to obtain high electrostrictive properties or E-field induced piezoelectricity. Coupling coefficients (k31) 25% comparable to those of the cryogenic PLZT piezoelectrics were observed at d.c. bias of 1.5 kV/cm and 50 K. Though significantly lower than the room temperature values, PZN-PT rhombohedral single crystals exhibited d33> 500 pC/N at 30 K.     

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.     

弛豫型铁电体在准同型相界的压电性能

ＰＭＮ、ＰＺＮ、ＰＮＮ 等弛豫型铁电体与ＰＴ 形成的固溶体在准同型相界附近具有良好的压电性能。在ＰＭＮ、ＰＺＮ 的单晶材料中,ｋｐ 高达９２ ％ ,ｄ３３ 达到１５００ｐＣ／ Ｎ, 在以ＰＭＮ、ＰＺＮ、ＰＮＮ 为基的陶瓷材料中,ｄ３３ 分别达到６９０ｐＣ／ Ｎ、６８０ｐＣ／Ｎ 和５４０ｐＣ／ Ｎ,Ｑｍ 在１００ 左右。这类材料的共同特点是机电耦合系数和压电系数较大,而品质因数较小,在压电换能器和致动器领域具有很好的应用前景。     

Characterization of piezoelectric films of foamed polyethylene obtained by extrusion

Foamed polyethylene (MDPE) films obtained by extrusion have been characterized by X-ray diffraction, thermogravimetric analysis and tensile tests. The piezoelectric properties have been determined by calculation of piezoelectric constant d₃₃, thermally stimulated depolarized current method and calculation of activation energy depolarization of electrets. It has been found that the crystallinity and internal morphology, including cellular structure, affect the possibility of an effective polarization in order to obtain a piezoelectric material from foamed MDPE. The conditions of processing have a great influence on the piezoelectric properties. The value of piezoelectric constant attains ~18 pC/N and ~75 pC/N for low stress range and diminishes for higher stresses, temperature T_m?~?72 °C and ~82 °C, approximate activation energy attains 2.67 and 3.28 eV, for compacted and non-compacted film, respectively. Because of the simple and cheap method of foaming PE films of piezoelectric properties it is worthy to take care regarding their application for pressure sensors.