环氧树脂高温分子链松弛与玻璃化转变特性

环氧树脂是电力设备中广泛应用的一种绝缘材料, 其介电性能受到分子链运动特性的影响. 本文制备了直径为50 mm、厚度为1 mm的环氧树脂试样, 采用差示扫描量热仪和宽频介电谱仪测试了环氧树脂的玻璃化转变温度和介电特性. 实验结果表明, 环氧树脂的玻璃化转变温度为105 ℃, 在玻璃化转变温度以上, 高频段出现了由分子链段运动造成的松弛过程, 低频段出现了由载流子在材料中迁移造成的直流电导过程. 发现环氧树脂不同尺寸分子链段的松弛时间不同, 其松弛时间分布较宽, 计算得到了分子链段在不同温度下的松弛时间分布特性. 分子链松弛峰频率和直流电导随温度的变化关系服从Vogel-Tammann-Fulcher公式. 拟合实验结果得到分子链松弛峰频率和直流电导的Vogel温度和强度系数. 由Vogel温度计算得到了与差示扫描量热测试结果一致的玻璃化转变温度, 约为102 ℃. 结果表明玻璃化转变温度以上环氧树脂的自由体积增大, 分子链段有足够的空间来响应外电场从而产生分子链松弛极化, 载流子有足够的能量在材料中迁移形成电导.     

VDF（52）／TrFE（48）铁电共聚物的非晶介电弛豫

用液氮淬火和热处理方法制得结晶度相差较大的铁电共聚物ＶＤＦ（５２）／ＴｒＦＥ（４８）试样。介导弛豫研究提示室温以下共聚物的频率谱由低频和高频两部分组成。低频部由非晶区被冻结分子链段的微布郎运动贡献。符合ＷＬＦ方程；高频部由晶区分子链段较小尺度的局域运动产生，遵从Ａｒｒｈｅｎｉｕｓ规律。分峰拟合结果得到共聚物的玻璃化转变温度为－２４℃，局域弛豫活化能为４６．１ｋＪ／ｍｏｌ．     

原位红外光谱研究间规聚丙烯介晶相的相转变行为

聚合物的介晶相作为一种介于结晶和无定形之间的有序态结构[1],其相转变行为对于理解结晶过程具有重要的意义。间规聚丙烯(sPP)是一种典型的多晶型聚合物,不同的晶型中分子链采取不同的构象[2]。基于红外光谱对分子链构象的敏感性,本工作采用原位红外光谱研究了sPP介晶相在连续升温过程中的微观结构变化。通过对拉伸后的sPP薄膜进行应力松弛得到了高介晶相含量的sPP薄膜。红外光谱研究结果表明,介晶相在升温过程中经历了多次相转变过程。在20~40℃之间,介晶相和少量结晶完善程度低的formⅡ晶体发生部分熔融;在40~90℃范围内,未熔融的介晶相转变为formⅠ/Ⅱ,且在70~90℃之间,还存在formⅠ/Ⅱ的完善和无定形相向formⅠ/Ⅱ的转变,即无定形相的冷结晶过程。当温度高于90℃时,formⅠ/Ⅱ开始发生熔融。     

尼龙6在高压退火中的晶体生长

 利用六面顶压机制备了高压退火的尼龙6样品,通过宽角X射线衍射（WAXD）、差示扫描量热（DSC）和红外光谱等手段,探索了高压退火对尼龙6结晶度以及晶体结构的变化。研究发现,在高压退火过程中尼龙6分子链段运动受到压力的限制,材料中晶体的形成主要依靠转氨基反应实现。     

典型高分子材料的固体核磁共振研究

本论文通过固体核磁共振（NMR）谱及动力学参量的测量,并结合X-射线衍射技术和DSC测量等研究了两种典型高分子材料的相结构、链的运动以及相与相之间的关系.  乙烯-醋酸乙烯共聚物( EVA) 是最主要的乙烯共聚物之一. 研究发现,EVA的相组成非常复杂,共有5个不同的组分. 除了PE中所观察到的常规单斜晶相和刚性的正交晶相外,我们发现还存在第三个晶相分量－运动性较强的晶相（SOCP,可能是转动相）. 它不仅拥有自己的熔点,而且它的化学位移和分子运动性不同于刚性正交晶相（LOCP）. 另一方面,非晶相也由两种不同的分量组成：运动受限的各相异性的非晶界面相和高度可动的橡胶型的非晶相. 我们进一步详细研究了EVA中的晶区链动力学和非晶区的低温冻结行为. 实验发现,在正交晶相中,高分子链以180° flip-flop方式运动,同时伴随沿链方向的平移型跳跃运动,并引起正交晶相和非晶相之间的长程链扩散,通过NOE的测量证实了这种相间链扩散的存在,并进一步通过实验证实这种相间链扩散是一种受限扩散而不是自由扩散. 同时非晶相的两个组分具有不同的低温冻结行为：当温度低于-弛豫转变温度时,橡胶型的非晶相中的长程分子运动被冻结,但仍存在分子的局域运动;而界面非晶在低温时冻结成一种有序取向结构,并用质子自旋扩散实验证实该有序结构与正交晶相相邻近.  少量纳米级片层状粘土分散在聚合物中就可赋予材料许多优异的性能,我们用固体NMR技术对EVA/REC复合材料的结构和其中粘土的分散性质进行研究,发现上述复合材料中所形成的晶体类型不仅依赖于各组分的性质还依赖于所形成的复合材料的类型.  偏氟乙烯/三氟乙烯共聚物（P（VDF-TrFE））是最主要的铁电高聚物之一. 我们利用变温固体¹⁹F MAS NMR 谱及弛豫数据的测量详细研究了电子辐照对P(VDF-TrFE)共聚物的分子结构、构型、运动性以及相变等的影响. 发现,电子辐照不仅改变了分子链段的构型和运动性,同时也改变了局部分子化学结构. 电子辐照促使铁电相向顺电相(或者非晶相)转变,与此同时诱发了富含VDF和含-TrFE链段从全反式的构型到混合的反式-旁式构型的转变. 电子辐照加剧顺电区域中的分子运动而在高温熔融态中(>100 ℃）,分子的运动反而受限.     

升温在位红外研究物理老化对间规聚苯乙烯结晶行为的影响

通过在位红外光谱测量研究了物理老化对非晶和δ晶型的间规聚苯乙烯（ＳＰＳ）升温结晶过程的影响。发现对于晶样品来说,在物理老化前后,其结晶（即非晶→α晶型）的温度区间变化不大;但对于δ晶型的样品而言其物理老化后的晶型转变（即δ晶型→γ晶型）温度区间是１０４～１２７℃,与未物理老化的晶型转变温度区间９０～１１２℃相比,转变温度升高了约１４℃,这充分说明了物理老化使溶致型的δ晶型更加稳定,其溶剂与晶体的结     

氯化钙对尼龙6无定形转变过程的在位红外研究

采用在位红外分析、X射线衍射方法研究了氯化钙对尼龙 6结晶的影响。结果表明 ,随尼龙 6中氯化钙含量的增加 ,尼龙 6的结晶度逐渐减小直至变为无定形态。由于氢键作用使尼龙 6分子链规整排列产生结晶 ,因此文章通过在位红外光谱方法研究了尼龙 6 /氯化钙复合材料中与氢键相关的胺基、酰胺Ⅰ带和酰胺Ⅱ带随温度及氯化钙含量的变化情况 ,证实了钙离子能通过与尼龙 6分子链上的羰基发生配位作用 ,插入尼龙 6分子链 ,破坏尼龙 6的氢键 ,降低了尼龙 6分子链的规整排列 ,使尼龙 6的结晶度减小 ,最终使尼龙 6由结晶态转变为无定形态     

限域相变对热致变色环氧绝缘材料介电松弛特性的影响

本文研究了热致变色微胶囊环氧绝缘材料的介电松弛特性及机理.结果表明,热致变色微胶囊环氧绝缘材料表现出非单调介电松弛特性,即在58—66℃温度范围内,介电松弛时间随温度升高而逐渐延长,无法通过传统的Arrhenius或Vogel-Fulcher-Tammann方程进行描述.分析认为,该非单调介电松弛特性主要源于微胶囊内限域相变引发的自由体积变化.随着温度的升高,微胶囊有限空间内发生固-液相变,使得微胶囊内的自由体积逐渐减小,限制了偶极子随外电场的定向过程,导致介电松弛时间逐渐延长.采用限域介电松弛模型拟合了热致变色环氧试样的非单调介电松弛特性,并得到了介电松弛活化能.不同微胶囊含量的热致变色试样的介电松弛活化能均处于相同的数量级,表明其非单调介电松弛过程均发生于热致变色微胶囊内,验证了限域相变对非单调介电松弛特性的作用.     

聚偏氟乙烯在不同衬底上的结晶行为研究

利用滴涂法制备聚偏氟乙烯(PVDF)薄膜,分别以载玻片、铜片、聚四氟乙烯(PTEF)为衬底研究衬底、退火时间和退火温度对PVDF薄膜结晶行为的影响。实验表明PVDF在PTEF基体上更容易结晶,这是因为PTEF是非极性基体,PVDF分子链运动在界面不受限制,能够充分地重排,利于晶体的生长;延长退火时间,PVDF分子链能够充分进行重排,形成规整的结构,提高结晶性;同时提高退火温度也有利于PVDF薄膜的结晶。另外,基体作用、退火时间和退火温度不会改变PVDF晶体结构,但会不同程度地影响α和β相的含量。     

极性分子型电流变液导电机理研究

极性分子型电流变液是一种新型的电流变材料.其介电颗粒上吸附极性分子,极性分子在颗粒间强局域电场作用下发生取向是产生巨电流变效应的关键.通过对Ca—Ti—O(CTO)体系极性分子型电流变液电流密度的测量发现,其导电行为遵从Poole-Frenkel效应的规律,这是极性分子型电流变液的重要特征之一.而500 ℃处理过的CTO粉体不含极性分子,所配制的电流变液无巨电流变效应,其电流密度随外电场强度近似地呈线性关系,显示出传统电流变液特性.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.