Three-layer piezoelectrets from fluorinated ethylene-propylene (FEP) copolymer films

A process for preparing three-layer piezoelectrets from fluorinated ethylene-propylene (FEP) copolymer films is introduced. Samples are made from commercial FEP films by means of laser cutting, laser bonding, electrode evaporation, and high-field poling. The observed dielectric-resonance spectra demonstrate the piezoelectricity of the FEP sandwiches. Piezoelectric d ₃₃ coefficients up to a few hundred pC/N are achieved. Charging at elevated temperatures can increase the thermal stability of the piezoelectrets. Isothermal experiments for approximately 15 min demonstrate that samples charged at 140°C keep their piezoelectric activity up to at least 120°C and retain 70% of their initial d ₃₃ even at 130°C. Acoustical measurements show a relatively flat frequency response in the range between 300 Hz and 20 kHz.     

Chemical bond formation during laser bonding of Teflon FEP and titanium

Teflon^® FEP (fluorinated ethylene propylene) is resistant to most chemical solvents, is heat sealable and has low moisture uptake, which make this polymer attractive as a packaging materials for electronics and implantable devices. Teflon^® FEP/Ti microjoints were fabricated by using focused infrared laser irradiation. Teflon^® FEP/Ti interfaces were studied by using X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS). The XPS results give evidence for the formation of Ti-F bonds in the interfacial region. The AES and SEM-EDS results show that the chemical bond formation occurs only in the actual bond area. No evidence for chemical bond formation was found in the heat affected zone surrounding the laser bonds.     

面向空耦电声换能器应用的高性能FEP/PTFE复合膜压电驻极体

压电驻极体(也称为铁电驻极体)是一类具有强压电效应的微孔结构驻极体材料,具有柔韧、低密度、低特性声阻抗等特征,是制备柔性空气耦合声电换能器的理想材料.针对器件对高灵敏度和高温工作环境的应用需求,本文报道高性能氟化乙丙烯/聚四氟乙烯(FEP/PTFE)复合膜压电驻极体的制备和性能表征.研究结果表明, FEP/PTFE膜的特性声阻抗为0.02 MRayl (1 Rayl=10 Pa·s/m);在小压强范围内的准静态压电电荷系数d₃₃可高达800 pC/N,且具有良好的压强特性.基于FEP/PTFE复合膜压电驻极体的麦克风的灵敏度最高可达6.4 mV/Pa@1 kHz,远高于文献报道的相同结构的压电驻极体麦克风的灵敏度,且具有平坦的频响曲线.对于直径为20 mm的超声波发射器,当驱动电压V_p为600 V时,样品中轴线上距离器件表面100 mm处, 40—80 kHz频率范围内产生的超声波的声压级为80—90 dB (参考声压为20μPa).基于FEP/PTFE复合膜压电驻极体的声电换能器的热稳定性显著优于聚丙烯(PP)压电驻极体声电换能器:在125...     

Electron beam induced conductivity in ‘PET’ and ‘FEP’

Electron Beam Induced Conductivity (EBIC), classified into EBIC (bulk) and EBIC (surface) have been measured in PET and FEP respectively. The peculiar oscillatory nature of the induced gain versus beam energy variations is explained in terms of the spatial distributions of the trapping centres near the surface of the polymers.     

Constant hole schubweg in Teflon FEP (fluorinated ethylene propylene copolymer)

The hole schubweg (distance travelled between deep trapping events) in Teflon FEP (fluorinated ethylene propylene copolymer) is determined by measuring the mean depth of charge injected from the polymer surface, with various fields applied to the sample. It is found that the mean-depth of the injected charge after deep trapping is independent of the electrical field strength from 0.04 to 0.4 MV/cm. The lower value of 0.04 MV/cm is determined by the sensitivity of the method.     

多孔聚四氟乙烯/氟代乙烯丙烯共聚物复合驻极体材料的压电效应研究

采用高温熔融和电晕充电方法制备了由聚四氟乙烯/氟代乙烯丙烯共聚物复合而成的空间电荷驻极体压电膜.借助准静态压电系数测量，研究了制备工艺对复合膜压电活性的影响.根据Kacprzyk等提出的复合驻极体膜的压电模型，结合等温表面电位衰减和压电系数衰减测量结果，讨论了驻极体复合膜系统中的压电性产生机制.结果表明，压电效应的大小不仅取决于俘获在材料中的电荷密度的大小，还与被俘获电荷在材料中的存在形式和分布有关. 关键词： 空间电荷驻极体 压电效应 聚合物复合膜     

PMMA and FEP surface modifications induced with EUV pulses in two selected wavelength ranges

Surface modification of PMMA and FEP polymers using extreme ultraviolet (EUV) in two spectral ranges was investigated. A laser-plasma EUV source based on a double stream gas puff target equipped with an Au coated ellipsoidal collector was used for the experiment. The spectrum of the focused radiation from Kr plasma consisted of a narrow feature with a maximum at 10 nm and a long-wavelength tail up to 70 nm. Al and Zr filters were employed for the selection of radiation from these two spectral regions. The radiation fluences in the two cases were comparable. Polymer samples were mounted in the focal plane of the EUV collector and irradiated for 1–2 min with a 10 Hz repetition rate. Weak ablation accompanied by creation of micro- and nanostructures of different kinds was obtained in both cases. Significant differences in the surface structures after irradiation of PMMA and FEP in these two spectral regions were revealed.     

PTFE、FEP涂层表面CaCO3污垢特性的实验研究

实验室里进行了PTFE与FEP表面CaCO3污垢的对比实验.采用直接称重法获得污垢生长曲线,研究了在不同流速、温度、浓度条件下PTFE和FEP两种表面污垢特性.实验结果表明:在相同流速、浓度和温度条件下,FEP比PTFE有更好的阻垢性能;溶液流速、温度和浓度对CaCO3污垢沉积有较大影响:增大溶液流速、降低溶液的温度和浓度都会使这两种材料表面的污垢渐近值减小.     

关于室温高温中FEP驻极体热稳定性的研究

本文通过实验对负极化FEP驻极体的热稳定性进行比较研究。从而得出室温高温两种极化方法下FEP驻极体寿命的研究。     

Physical foaming of fluorinated ethylene-propylene (FEP) copolymers in supercritical carbon dioxide: single-film fluoropolymer piezoelectrets

Cellular polymer foams with significant piezoelectric activity were prepared from fluorinated ethylene-propylene (FEP) copolymers. The required void structure is obtained by saturation of FEP films with supercritical carbon dioxide and a subsequent heat treatment for controlled inflation. After bipolar electric charging of the voids and evaporation of electrodes, the FEP films show piezoelectric d₃₃ coefficients up to 50 pC/N. The present physical foaming process generates cellular fluoropolymer piezoelectret films with usually only one single void across the film thickness. PACS 81.05.Rm; 77.65.-j; 77.84.Jd; 61.41.+e     

毫米级栅型电场分布FEP薄膜驻极体的制备及其电荷存储性能研究

采用电晕注极和热注极技术, 在厚度为25 μm的氟化乙丙烯共聚物(FEP)表面制备了宽度为2 mm和3 mm的具有栅型电场分布的驻极体, 研究了注极温度和电极宽度对其电荷存储性能的影响. 样品注极后经150天的存储, 栅型电场分布变得清晰而有规律, 覆盖铝电极区电位已衰减至接近零, 未覆盖铝电极区仍保持高电位; 对电极宽度为2 mm和3 mm的样品, 覆盖铝电极区与未覆盖铝电极区的表面电位差分别为110 V和130 V(电场强度差分别为44 kV/cm和52 kV/cm). 表面电位跟踪测试结果表明: 电晕注极样品初始表面电位高于热注极样品; 在相同的注极方法下, 注极温度越高初始表面电位越高, 电极宽度越小初始表面电位越低. 依据电晕注极和热注极原理对实验结果的分析表明, FEP和金属铝在电荷存储性能上的差异是FEP表面蒸镀铝电极后能获得栅型电场分布的原因所在.     

电子与太阳电磁射线综合辐照对Teflon FEP/Al光学性能的影响

 在30keV的电子、质子单独辐照及电子与太阳电磁射线综合辐照作用下，对Teflon FEP/Al第二表面镜光学性能的演化进行了研究。试验结果表明，在相同辐照通量与能量乘积的情况下，电子与质子单独辐照后Teflon FEP/Al涂层材料的太阳吸收比变化相同，故可用电子与太阳电磁射线综合辐照简化地面模拟加速试验。Teflon FEP/Al光学性能退化动力学曲线可描述成加速系数与辐照时间乘积（称为当量辐照时间）的指数函数形式。在当量辐照时间相同的情况下，太阳吸收比的变化与加速系数无关。     

Permeation of gases through modified polymer films III. Gas permeability and separation characteristics of gamma-irradiated teflon FEP copolymer films

A study has been made of the diffusion, solubility, and separation of nitrogen and methane gases at temperatures ranging from 15° to 50°C in a series of Teflon FEP copolymer films which were irradiated by γ rays in air and under vacuum. The irradiated films were subjected to postirradiation treatment temperatures above and below the glass I transition temperature of the copolymer. The effect of radiation on crystallinity and cross-linking was examined by density, thermal, and tensile strength measurements. Diffusion and permeability coefficients of both gases decreased with irradiation dose but solubility coefficients were not greatly affected. Nitrogen-methane separation factors for vacuum-irradiated films increased with irradiation dose, but little change was observed for the air-irradiated films. Chain scission appeared to be the predominant reaction in air-irradiated films whereas both cross-linking and chain scission occurred in vacuum-irradiated films depending on post-irradiation heat-treatment conditions. The permselectivity of the Teflon FEP films was increased by γ irradiation but this was achieved at the expense of the permeation rate.     

Theoretical study of keto–enol tautomerism by quantum mechanical calculations (the QM/MC/FEP method)

In this study, the tautomeric equilibrium between the keto and enol forms has been studied for five typical ketones and aldehydes: i‐butanal, acetaldehyde, acetone, acetylacetone, and dimedone. The level of theory used in the gas‐phase calculation was Becke, three‐parameter, Lee–Yang–Parr/6‐311G(d,p)//Becke, three‐parameter, Lee–Yang–Parr/6‐31G(d). The free energies of solvation were included in the calculation by using the free‐energy perturbation method based on Monte Carlo simulation, that is, the quantum mechanical/Monte Carlo/free‐energy perturbation method. Three different models, incorporating no‐water, one‐water, and two‐waters, were adopted. The results showed that in the gas phase the addition of water molecules to the reaction mechanism caused the activation barriers (ΔG^?_gas) to decrease by half relative to the water‐free mechanism, but there was no effect on the relative difference in free energy, ΔG_gas. The solvation effects (ΔG_sol), based on quantum mechanical/Monte Carlo/free‐energy perturbation calculations, were added to those of the gas‐phase results of the one‐water and two‐waters models. The two‐waters model produced values that were very consistent with the experimental data for all of the tautomers. The differences in the relative Gibbs free energy (ΔG_rxn) were less than 1.0 kcal mol^–1. In summary, the inclusion of solvent molecules in gas‐phase calculations plays a very important role in producing results consistent with experimental data. Copyright © 2012 John Wiley & Sons, Ltd.     

Neutron irradiation effects on A1GaN//GaN high electron mobility transistors

AlGaN/GaN high electron mobility transistors(HEMTs) were exposed to 1 MeV neutron irradiation at a neutron fluence of 1 × 10 15 cm 2.The dc characteristics of the devices,such as the drain saturation current and the maximum transconductance,decreased after neutron irradiation.The gate leakage currents increased obviously after neutron irradiation.However,the rf characteristics,such as the cut-off frequency and the maximum frequency,were hardly affected by neutron irradiation.The AlGaN/GaN heterojunctions have been employed for the better understanding of the degradation mechanism.It is shown in the Hall measurements and capacitance-voltage tests that the mobility and concentration of two-dimensional electron gas(2DEG) decreased after neutron irradiation.There was no evidence of the full-width at half-maximum of X-ray diffraction(XRD) rocking curve changing after irradiation,so the dislocation was not influenced by neutron irradiation.It is concluded that the point defects induced in AlGaN and GaN by neutron irradiation are the dominant mechanisms responsible for performance degradations of AlGaN/GaN HEMT devices.     

噁唑体系激发态质子转移和失活的理论研究

利用高精度的CASSCF和MS-CASPT2电子结构计算方法系统地研究了2-(2'-羟基苯基)-4-甲基噁唑的光物理和光化学机理. 在CASSCF级别,首先优化得到势能面极小结构和圆锥交叉结构,及激发态质子转移、异构化、和失活的极小能量路径. 然后用MS-CASPT2方法对所有得到的结构和能量路径进行单点能量校正,我们发现在含有OH…N氢键的构象异构体中,激发态质子转移基本上是一个无垒的过程;在含OH…O 氢键的构象异构体中,激发态质子转移被抑制了. 此外,找到两个能量较低的酮式S₁/S₀圆锥交叉结构,使得激发态质子转移生成的S₁酮式结构可以很快失活到达基态. 但是,醇式S₁/S₀圆锥交叉结构能量较高,抑制了S₁醇式结构的激发态失活.     

平行线偏光激发CPT共振方案实验研究

目前的相干布居囚禁(CPT)原子钟和CPT磁场计中普遍采用圆偏振光方案 (σ⁺-σ⁺)实现CPT共振, 该方案对原子的利用率较低. 为了提高原子的利用率, 本文实验研究了通过平行线偏振相干双色光与⁸⁷Rb原子作用实现CPT共振的方案(lin//lin). 与σ⁺-σ⁺方案相比较, lin//lin方案消除了极化暗态, 获得更多工作原子. 在相同的实验条件下, 开展对比实验研究获得了信噪比为σ⁺-σ⁺方案2倍, 微分线型信号的中心斜率为σ⁺-σ⁺方案1.65倍的CPT共振信号. 研究结果表明该方案是实现低功耗原子钟、磁场计等设备的理想候选.     

Improving performance of 750-Mb//s visible light commun- ication system using adaptive Nyquist windowing

We propose a configuration of a wavelength division multiplexing （WDM）-visible light communication （VLC） system using orthogonal frequency division multiplexing （OFDM） modulation and an adaptive Nyquist windowing of the OFDM signal in the receiver. Based on this configuration, we demonstrate a 750-Mb/s WDM-VLC transmission based on RGB light-emitting diode （LED） with a distance of 70 cm. The measured bit error rate （BER） for all channels are under the pre-forwaxd error correction limit of 3,8 × 10-3. The BER performances of all the channels of the proposed WDM-VLC system show considerable improvement compared with those of the system without Nvauist windowing.     

1，8-二羟基-2-萘甲醛激发态双质子转移反应的MS-CASPT2//CASSCF研究

激发态双质子转移反应长期困扰着理论和实验科学家并成为了一个悬而未决的热点问题. 本文利用完全活化空间自洽场方法及其二阶微扰理论(MS-CASPT2//CASSCF)系统地研究了典型体系1,8-二羟基-2-萘甲醛(DHNA)的激发态双质子转移反应以及相关的激发态弛豫过程. 在MS-CASPT2//CASSCF水平下,本文优化了三个能量相近但结构不同的S₁态互变异构体,即S1-ENOL、S1-KETO-1和S1-KETO-2,以及两个关键的S₁/S₀锥形交叉点结构,即S1S0-KETO-1和S1S0-KETO-2. 其中,两个极小点S1-KETO-1和S1-KETO-2与实验上观测到的双荧光发射现象密切相关. 本文还利用MS-CASPT2//CASSCF方法计算了双质子转移反应的二维势能面以及从极小点到交叉点结构的线性内插路径;相应计算结果证实了DHNA体系具有分步的激发态双质子转移机制. 具体来说,从S1-ENOL到S1-KETO-1的第一个质子转移过程是无能垒的,而从S1-KETO-1到S1-KETO-2的第二个质子转移过程则需要克服一个大约6.0 kcal/mol的能垒. 此外,由于从S1-KETO-1 (S1-KETO-2)到S1S0-KETO-1 (S1S0-KETO-2)的线性内插路径显示DHNA体系需要翻越一个约为12.0 kcal/mol的能垒,因此DHNA体系将在S₁态上停留一段时间并发生双荧光发射现象. 当然,S₁/S₀锥形交叉点也会促使DHNA体系从S₁态内转换到S₀态,而这会一定程度上降低DHNA体系发射荧光的效率. 可以通过限制C5-C8-C9-O10二面角旋转来降低体系的内转换效率,进而提高DHNA体系的发光效率. 本工作不仅有助于理解激发态双质子转移机制,还有助于设计具有优异发光性能的新型分子材料.