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.     

Infrared study of polyethylene oriented in molten state by flow in a die

In this work PTFE sheets irradiated with γ rays at 150°C and 200°C were studied using x-ray photoelectron spectroscopy (XPS). The main structural changes in PTFE due to radiation are the formation of CF₃ and CF groups. An irradiation temperature dependence of the relative content of the three kinds of groups in irradiated PTFE was observed. The CF₃ groups, especially when irradiation is carried out a lower temperatures, can defluorinate in the same manner as previosly reported for CF₂ groups. The CF groups, on the other hand, are observed to increase with increasing írradiation dose and irradiation temperature; the latter was explained as due to an increase in branching structures.     

Effects of γ rays irradiation on structure and property of TiO2 thin films

TiO₂ thin films were deposited on a glass substrate by the radio frequency magnetron sputtering method, and annealed for 2 h at temperatures of 550°C. Then, ⁶⁰Co γ rays with different doses were used to irradiate the resulting TiO₂ thin films. The surface features of films before and after irradiation were observed by scanning electron microscope (SEM). Simultaneously, the crystal structure and optical properties of films before and after irradiation were studied by X-ray diffraction (XRD), UV–VIS transmission spectrum and Photoluminescence (PL) spectrum, respectively. The SEM analysis shows that the film is smooth with tiny particles on the film surface, and non-crystallization trend was clear after irradiated with γ rays. The XRD results indicated that the structure of the film at the room temperature mainly exists in the form of amorphous and mixed crystal at a sputtering power of 200 W, and non-crystallinity was more obvious after irradiation. Obvious difference can be found for the transmissibility of the irradiated and pre irradiation TiO₂ films by the UV-VIS spectra. The color becomes light yellow, and the new absorption edge also appeared at about 430 nm. PL spectra and photocatalysis experiments indicate that the photocatalysis degradation rate of the TiO₂ films on methylthionine chloride solution irradiated with the maximum dose can be increased to 90%.     

Different responses of several kinds of copolymerized polyimide films to ultraviolet irradiation

The surfaces of three kinds of copolymerized polyimide films were irradiated by ultraviolet (UV) light. The chemical composition changes of the films after irradiation were investigated by X-ray photoelectron spectroscopy (XPS), while their topographical changes were studied by atomic force microscopy (AFM). Besides, the surface topographical variation induced changes in friction behavior were recorded on a DF·PM unidirectional friction and wear test rig in a ball on block contact configuration. It was found that photodegradation took place, which induced the chain scission of the polyimide molecules and formation of low molecular weight oxidized material (LMWOM). Due to different photostability of the three kinds of polyimide, different chemical composition changes and forms of “LMWOM” were observed. Also, different friction behavior variations of the three kinds of polyimide films were recorded. It is thought that the polyimide film of PI (PPA + PMDA) with rod-like structures might have stronger photo-resistance, whose form of “LMWOM” was “nodules” and whose friction coefficient increased at 2 h of irradiation possibly due to cross-linking. In the case of PI (OPA + PMDA) and PI (MPA + PMDA) films, they mainly underwent photodegradation, which might soften the surfaces and increased the friction coefficients with increasing irradiation time.     

60Co的γ辐照对SB的自由体积和微结构的影响的PALS和FT-IR的研究

利用正电子湮没技术和傅里叶红外分析研究手段，基于Eldrup的自由体积孔经典模型，分别研究了⁶⁰Co的γ辐照剂量对聚苯乙烯-丁二烯二嵌段共聚物(SB)的自由体积和微结构变化的影响，并关联两种测试结果，确定了⁶⁰Co的γ辐照对SB的辐照交联和降解模型.而后用热重分析(TGA)研究了辐照前后的SB的热稳定，给出了自由体积参数变化与热稳定的关联. 关键词： 正电子湮没技术 正电子素 嵌段共聚物 γ辐射     

γ射线与N离子辐照类金刚石薄膜的机理研究

对类金刚石 (以下简称 DLC)薄膜受 γ射线与 N离子辐照的结果进行了比较 .通过 Raman光谱分析得出 :γ射线辐照造成薄膜中 SP3C— H和 SP2C— H键的减少及 SP3C— C键的增加 ,与此同时氢原子结合成氢分子 ,并从膜中释出 ,薄膜的类金刚石特征更加明显.当辐照剂量达1 0×104Gy时 ,SP3C—H键减少了约 5 0 % .N离子辐照使 DLC薄膜中 SP3C— C键、SP2 C—H键及 SP3C—H键的含量均变少 ,并伴随着氢分子的释出 ,直接导致 DLC薄膜的进一步石墨化,其对 SP3C—H及 SP2C— H键的破坏程度远大于γ射线 .两者在辐照机理上截然不同.The results of the diamond like carbon films(the following is called for short DLC film) irradiated by γ rays and N ion were reported. It showed that SP 3C—H and SP 2C—H bonds were decreased, and SP 3C—C bonds were increased by γ ray irradiation, and induced hydrogen recombination with H 2 molecules, and subsequently released from the surface of the films. When the γ ray irradiation dose reached 10×104Gy, the numbers of SP3C—H bonds were decreased by about 50%...     

溶剂对辐射变色膜吸收剂量的影响

本实验室分别选用无水乙醇和丙酮溶液为溶剂制成两种类型的辐射变色膜, 并对这两种辐射变色膜进行了60Co γ射线与紫外线辐照, 研究不同溶剂对辐射变色膜吸收剂量的影响。实验发现, 60Co γ射线与紫外线辐照后, 使用丙酮作溶剂的辐射变色膜变色效果比无水乙醇的更加明显。在相同的辐照剂量下, 使用丙酮作为溶剂的变色膜比用无水乙醇的光谱吸收峰(680 nm)值平均高65.5%。γ射线辐照时, 用丙酮作为溶剂的辐射变色膜变色的辐照剂量下限为0.5 Gy, 而用无水乙醇做为溶剂的为1 Gy; 紫外辐照时, 用丙酮为溶剂的辐射变色膜吸收峰处吸收剂量的线性响应区间为0～6×100 μJ/cm2, 而用无水乙醇做为溶剂的为0～36×100 μJ/cm2。     

Higher stabilities of positive and negative charge on tetrafluoroethylene–hexafluoropropylene copolymer (FEP) electrets treated with titanium-tetrachloride vapor

Tetrafluoroethylene–hexafluoropropylene copolymer (FEP) films were treated with titanium-tetrachloride vapor in a molecular-layer deposition process. As a result of the surface treatment, significant improvements of the thermal and temporal charge stability were observed. Charge-decay measurements revealed enhancements of the half-value temperatures and the relaxation times of positively charged FEP electrets by at least 120 °C and two orders of magnitude, respectively. Beyond previous publications on fluoropolymer electrets with surface modification, we here report enhanced charge stabilities of the FEP films charged in negative as well as in positive corona discharges. Even though the improvement for negatively charged FEP films is moderate (half-value temperature about 20 °C higher), our experiments show that the asymmetry in positive and negative charge stability that is typical for FEP electrets can be overcome by means of chemical surface treatments. The results are discussed in the context of the formation of modified surface layers with enhanced charge-trapping properties.     

The use of positron annihilation Doppler broadening spectroscopy in the characterization of radiochromic dosimetry films

The positron annihilation Doppler broadening (PADB) spectroscopy has been employed to probe the defects and structural changes of various types of materials. In this work, an investigation was carried out for the first time to use PADB spectroscopy in probing the γ irradiated radiochromic films. The GafChromic MD–55 and HD–V2 radiochromic films irradiated with absorbed doses ranges of 0–80 and 0–2000 Gy, respectively, were subjected to Doppler broadening measurements employing a HPGe γ–ray spectrometer. The Doppler broadening line–shape parameters (S and W) of 511 keV annihilation radiations were discussed in terms of the polymerization degree of the active components of these dosimetry films. The S- and W-parameters were found to be dependent on the active component structures of both films. A reasonable correlation was also found between the values of the S–parameter and the optical density of these radiochromic films. In addition, the Doppler broadening line–shape parameters were successfully used to provide explanation of the observed nonlinearity of these films at the end of their dynamic dose ranges. The results demonstrate the applicability of the PADB technique to probe the physical and chemical changes occurred in the active layer of the studied radiochromic films during the solid–state polymerization reaction caused by γ irradiation of different absorbed doses.     

Study of near surface layer of graphite produced by nitrogen ion bombardment at high doses

To study the modified surface layers of graphites and deposited films of sputtered material, the dependences of sputtering yield Y , and ion-electron emission coefficient γ on ion incidence angle and target temperature under high dose 30 keV N⁺ ₂ ion irradiation have been measured. In the angular range θ=0-80° Y and γ increase approximately as inverse cosθ, Y of POCO-AXF-5Q are 1.5 times larger than of MPG-LT. The dependences of γ (T) manifests a step-like behaviour typical for the radiation induced phase transitions. EPR analysis shows that at near room temperatures the point electron defects are typical of carbon and the defects due to carbon atoms interacting with 14 N nuclei. At elevated temperatures (≥ 300°C) there are the defects typical of graphite-like structures. The films deposited on glass collectors shows for cold targets only the defects typical of carbon, for the heated graphites - also the defects associated with C-¹⁴N nuclei interaction.     

短脉冲激光打靶用溅射防护薄膜的光学性质

针对短脉冲激光打靶用溅射防护聚合物薄膜做了初步研究。研究了氟化乙丙共聚物(FEP)、全氟烷氧基共聚物和乙烯-四氟乙烯共聚物三种厚度均为25μm的聚合物薄膜的透过率,结果表明FEP薄膜在355nm处光透过率达93%,有望用于激光打靶的溅射防护。进一步对FEP聚合物薄膜的波前畸变、激光损伤阈值进行了研究,结果表明φ80mm的聚合物薄膜在632.8nm处的透射波前畸变的峰谷值(PV值)为波长的1.006倍;在采用输出波长355nm,脉冲宽度9.3ns的Nd:YAG激光为照射光源波长处,薄膜零损伤概率时的最高激光能量密度为10.35J/cm2,100%损伤概率时的最低激光能量密度为11.48J/cm2。     

Influence of ion-irradiation parameters on defect formation in silicon films

It is shown that unlike bulk silicon, for which amorphization is observed at an irradiation dose of 5 × 10¹⁶ ion/cm², thin silicon films on sapphire are amorphized at lower critical doses (10¹⁵ ion/cm²). An undamaged surface layer remains when the silicon films are irradiated with Si⁺ ion beams. Its thickness depends on the current density of the incident beam. Rutherford backscattering studies show that annealing at 950°C improves the crystallinity of the irradiated silicon film. Annealing of the films at 1100°C leads to mixing of the silicon-sapphire interface.     

Observation of grain growth in swift heavy ion irradiated NiO thin films

NiO thin films grown on Si(100) substrates by electron beam evaporation, were sintered at 500 °C and 700 °C. The films were irradiated with 120 MeV Au⁹⁺ ions. Irradiation had different effects depending upon the initial microstructure of the films. Irradiation of the films at a fluence of 3 × 10¹¹ ions cm⁻² leads to grain growth for the films sintered at 500 °C and grain fragmentation for the films sintered at 700 °C. At still higher fluences of irradiation, grain size in 500 °C sintered film decreased, but the same improved in 700 °C sintered film. Associated with the grain size, texturing of the films was also shown to undergo significant modifications under irradiation.     

γ射线辐照对a-SiC:H薄膜结构与特性的影响

 采用射频（13.56 MHz）反应溅射方法制备a-SiC:H 薄膜，并将其在空气中进行高能γ射线(平均为1.25 MeV)辐照，5个样品的吸收剂量分别为0，2×10⁴，4×10⁴，6×10⁴，8×10⁴ Gy。采用拉曼及红外光谱对薄膜的结构进行表征,得到了其结构与特性的变化规律。研究与分析表明：随样品吸收剂量的增加，陷入空穴中的电子会被激发，a-SiC:H薄膜中的SiC成份增加，电阻率变小，数量级为105Ω·cm；薄膜存在结晶化的趋势,其主要原因在于由Si－O－Si键断裂而产生的Si取代膜中C－C键中的C而形成晶态SiC，在此过程中出现了Si－O－Si键及a-SiC:H的减少，晶态SiC的增加。经γ射线辐照后薄膜的氢含量降低，折射率从5.19增大到5.53，辐照后薄膜的透过率均低于原膜的透过率。在500~2 300 cm^-1(对应波长为20.00~5.29 μm)波段内，a-SiC:H薄膜存在一定的增透作用。     

High energy electron irradiation effects on polystyrene films

The effect of an 8 MeV electron-beam on the structural, optical and dielectric properties of polystyrene films has been investigated respectively by means of Fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible (UV–VIS) spectroscopy and electrical impedance (LCR) analysis over a radiation dose in the range of 50–250 kGy using a Microtron accelerator. The FTIR spectral analysis shows no change in the overall structure of the irradiated polystyrene films, except a minor change in the intensity of a few peaks in the FTIR spectrum, indicating that polystyrene is resistant to electron-beam irradiation over the range of radiation doses investigated. The optical band gap analysis using the UV–VIS absorption spectra of the polystyrene shows a small decrease in the optical band gap (E _g) and the activation energy with an increase in electron doses. Further, the dielectric measurements over a frequency range of 100 Hz to 1 MHz for the electron-beam-irradiated polystyrene films show that both the dielectric constant and the dielectric loss increase with an increase in electron radiation dose, which may be ascribed to the formation of defect sites in the band gap of polystyrene as a consequence of molecular chain scission in the polymer films upon irradiation.     

Polarization and piezoelectricity in polymer films with artificial void structure

Laminated polymer-film systems with well-defined void structures were prepared from fluoroethylenepropylene (FEP) and polytetrafluoroethylene (PTFE) layers. First the PTFE films were patterned and then fusion-bonded with the FEP films. The laminates were subjected to either corona or contact charging in order to obtain the desired piezoelectricity. The build-up of the “macro-dipoles” in the laminated films was studied by recording the electric hysteresis loops. The resulting electro-mechanical properties were investigated by means of dielectric resonance spectroscopy (DRS) and direct measurements of the stress-strain relationship. Moreover, the thermal stability of the piezoelectric d ₃₃ coefficient was investigated at elevated temperatures and via thermally stimulated discharge (TSD) current measurements in short circuit. For 150 μm thick laminated films, consisting of one 25 μm thick PTFE layer, two 12.5 μm thick FEP layers, and a void of 100 μm height, the critical voltage necessary for the build-up of the “macro-dipoles” in the inner voids was approximately 1400 V, which agrees with the value calculated from the Paschen Law. A quasi-static piezoelectric d ₃₃ coefficient up to 300 pC/N was observed after corona charging. The mechanical properties of the film systems are highly anisotropic. At room temperature, the Young’s moduli of the laminated film system are around 0.37 MPa in the thickness direction and 274 MPa in the lateral direction, respectively. Using these values, the theoretical shape anisotropy ratio of the void was calculated, which agrees well with experimental observation. Compared with films that do not exhibit structural regularity, the laminates showed improved thermal stability of the d ₃₃ coefficients. The thermal stability of d ₃₃ can be further improved by pre-aging. E.g., the reduction of the d ₃₃ value in the sample pre-aged at 150°C for 5 h was less than 5% after annealing for 30 h at a temperature of 90°C.     

The effects of irradiation temperature and preinjected gases on voids in aluminum

Voids in high purity aluminum irradiated to a fast (E>1 MeV) fluence of 4 × 10²⁰ n/cm² at 125 (0.43T _m) and 150°C (0.45T _m) are fewer in number but very much larger in size than those in material irradiated at 55°C (0.35T _m). Additionally, at 125 and 150°C, the voids adopt a variety of shapes including plates, ribbons, cylinders and more equiaxed polyhedra, and are frequently associated with particles of transmutation-produced silicon. At the higher temperatures voids are larger near grain boundaries than in grain interiors. Injection of hydrogen or helium prior to irradiation causes an increase in the number of voids and a corresponding decrease in size in specimens irradiated at 150°C; 3 at. ppm He is more effective than either 3 or 9 at. ppm H. The gases do not appear to influence swelling.

A commercial purity (99 per cent) aluminum subjected to the same irradiation treatments did not develop voids whether preinjected with gases or not; the visible radiation damage consisted solely of small loops on or near grown-in dislocations.     

Effects of Beta Irradiation,Copolymers, and Blends on the Transformation Rate of Polybutene-1

The beta irradiation of polybutene-1 (PB-1) and its random copolymers with ethylene results in sample degradation without chain cross-linking. The crystal structures of both homopolymer and ethylene copolymers were phase I (I), except that for samples of short time irradiation, after melting, where phase II (II) was also present. The sample crystallinity decreased from 64% to a low of 45% in the irradiated samples for the condition used. The crystal size/perfection of the transformed I was slightly lower than that of parent II. The beta irradiation increased the transformation rate of II → I but to a lower extent than did the amount of ethylene in the copolymers. IR analysis confirmed that electron irradiation resulted in chain scission and a decrease of ?CH₂? and ?CH₃ groups. The mechanical properties decreased with increasing ethylene content and irradiation dose.     

Dielectric dispersion in Langmuir-Blodgett ferroelectric polymer films

The dynamic permittivity of vinylidene fluoride-trifluoroethylene (70:30) copolymer films is measured over wide ranges of frequencies and temperatures. It is revealed that 15-to 45-nm-thick Langmuir-Blodgett films of the vinylidene fluoride-trifluoroethylene copolymer undergo a Debye-type dielectric relaxation. The relaxation time τ increases as the temperature increases and the ferroelectric phase transition is approached. This effect is interpreted as a result of critical slowing down. The influence of gamma irradiation on the dielectric response of Langmuir-Blodgett films consisting of 10 and 30 monolayers is investigated.     

Study of structural,morphological and mechanical properties of PMMA,PVC and their blends

PMMA, PVC and their five blends in different compositions were irradiated by γ -rays of 2 Mrad dose. A comparative study of structural, morphological and mechanical properties of irradiated and non-irradiated samples was carried out. The structural changes that have taken place due to irradiation are seen in the FTIR and X-ray diffraction (XRD) spectra. The ester group is mainly affected in PMMA and the blends. The XRD results have confirmed that the irradiated samples are more amorphous in nature than the non-irradiated ones. The DSC study reveals that some irradiated samples undergo cross-linking, whereas some of them undergo degradation. One of the irradiated blend compositions has become thermally more stable. The SEM study suggests that the irradiated samples have undergone curing. An improvement in the mechanical properties has been observed in some of the irradiated blend compositions.