小角x射线散射结晶聚合物结构的研究

利用结晶聚合物的“三相结构”模型计算了结晶聚合物的一维电子密度相关函数,结论是三相模型的片层厚度和不变量与两相结构的意义不同.利用计算结果分析了一批样品的结构参量,发现用Ruland方法得到的结晶过渡层的厚度与用一维电子密度相关函数的结果是一致的.用Bragg定律求出的结晶聚合物的长周期与相关函数法长周期相差很多.这是因为两种分析结晶过渡层厚度的方法都是以样品电子密度的不均匀区为基础的,本质是一致的.但是Bragg法的长周期与相关函数法的长周期代表的范围不同 关键词： 小角x射线散射 结晶聚合物 三相结构 相关函数     

小角x射线散射结晶聚合物过渡层厚度的测定

由于结晶聚合物中的过渡层是弥散的，而修正的Porod定律是解决这种问题的有效方法之一. 把相关函数法和Porod定律法求结晶聚合物的过渡层厚度进行了比较，它们的计算结果是一致的. 关键词： 小角x射线散射 结晶聚合物 过渡层厚度 相关函数法 Porod定律     

基于长周期光栅的有机聚合物高速电光调制器

结合长周期光栅的特性和有机聚合物的优点,首次提出了一种新型的基于长周期光栅的有机聚合物高速电光调制器结构。应用多层光波导理论,分析计算了聚合物折射系数变化与长周期光栅谐振波长的关系。在此基础上进行了模拟实验,结果表明理论分析与实验基本一致。     

(111)择优取向的Pb(Zr0.52Ti0.48)O3铁电薄膜的制备及研究

选用不同浓度的Pb(Zr0.52Ti0.48)O3溶胶,用Sol-gel法在Pt/Ti/SiO2/Si基片上沉积一层厚度不同的Pb(Zr0.52Ti0.48)O3(PZT52)过渡层,经400℃烘烤、550℃退火等程序后,再用Sol-gel法在PZT52过渡层上沉积Pb(Zr0.52Ti0.48)O3薄膜.XRD分析表明,有PZT52过渡层的Pb(Zr0.52Ti0.48)O3薄膜具有(111)择优取向的钙钛矿结构,且随着过渡层厚度的增加,Pb(Zr0.52Ti0.48)O3薄膜的(111)择优取向程度越高.SEM分析表明,当PZT52过渡层的厚度达到14nm以上,Pb(Zr0.52Ti0.48)O3薄膜结晶程度得到明显改善,平均晶粒尺寸大大增加.介电、铁电性能测试表明,与没有过渡层的Pb(Zr0.52Ti0.48)O3薄膜相比,有PZT52过渡层的Pb(Zr0.52Ti0.48)O3薄膜具有较大的介电常数和剩余极化强度,而介电损耗则较小.     

一种近似计算金属多层膜界面过渡层厚度的方法

在用小角射线衍射研究离子束溅射法制备的多层膜基本结构时,提出了一个可以计算界面过渡层厚度公式。由实验曲线和文中提出公式得到过渡层厚度,并与用实验曲线和理论曲线进行拟合所得值进行了对比,结果表明这两种方法得到的过渡层厚度基本一致。     

基于长周期光栅的有机聚合物高速电光调制器

TN761 2004064380 基于长周期光栅的有机聚合物高速电光调制器=A novel electro-optic polymer modulator based on long period fiber gratings[刊,中]/董小伟(北京交通大学光波技术研究所.北京(100044)),裴丽…∥光学技术.—2004,30(3).—289-291,295 结合长周期光栅的特性和有机聚合物的优点,首次提出了一种新型的基于长周期光栅的有机聚合物高速电光调制器结构。应用多层光波导理论,分析计算了聚合     

镀高折射率纳米膜的长周期光纤光栅特性研究

针对镀高折射率纳米膜的长周期光栅,建立了传感理论模型,研究了长周期光栅的谐振波长与纳米膜厚度及外界折射率的关系,给出不同纳米膜厚度下长周期光栅不同包层模式重组特性.研究发现,当长周期光栅外面镀上一层沿角向均匀分布的纳米膜时,随着膜厚变化会出现包层模分布的明显调制;适当选择镀膜参数和外界介质折射率,最低次包层模式HE1,2会成为镀膜层中的导模,其他的包层模式将会发生模式转换现象;对于较低次包层模式(如HE1.6),在模式转换的时候存在两步转换,而高次的包层模只有一步转换(如HE1.14).同时给出了包层模式转换对外界折射率响应的关系:当膜层厚度增加时,长周期光栅模式转换现象移至低折射率区域.     

高压下尼龙1010-单壁碳纳米管复合材料的结晶行为

 采用XKY-6×1200MN型六面顶压机,在不同温度、压力条件下处理30 min后制备了尼龙1010(PA1010)-单壁碳纳米管（SWCNT）复合材料的高压结晶样品,通过X射线衍射（XRD）、差热分析仪（DSC）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）,研究了高压处理样品的结晶行为、结构变化及形貌特征。结果表明：在1.0~2.5 GPa压力下,属于高压熔体结晶;在3.0和4.5 GPa压力下属于高压退火处理;高压结晶或高压退火均有助于聚合物片层晶体的增厚,并且高压熔体结晶的增厚效果优于高压退火处理。XRD结果表明,PA1010的三斜晶型在高压处理后保持不变,高压熔体结晶或高压退火都可以使(100)晶面和(010)晶面间距减小,即高压处理致使聚合物分子链紧密堆积。DSC结果表明：在高压熔体结晶过程中,升高压力和温度可以得到片层厚度较大的PA1010晶体;在2.0 GPa、350 ℃下获得的高压结晶样品的熔点和结晶度最高,分别达到208.5 ℃和64.6%。SEM和TEM结果表明：与常压结晶样品相比,高压结晶样品内部出现c轴厚度超过150 μm的大尺寸晶体;SWCNT与PA1010基体之间形成相互穿插的网络结构,刚性的SWCNT作为高压成核剂促进PA1010晶体生长和增厚。     

有机电致发光器件中由缓冲层薄膜诱导产生的空穴传输层薄膜的结晶化

有机薄膜层的结晶是有机电致发光器件衰减的主要机理之一。研究发现以CaPe做为缓冲层时比没有缓冲层时NPB薄膜更容易结晶,CuPc对NPB薄膜具有诱导结晶作用。通过原子力显微镜(AFM)以及宽角X射线衍射(WAXRD)详细研究了不同厚度、不同颗粒大小的缓冲层CuPc薄膜对空穴传输层NPB薄膜的结晶诱导作用。这个发现为以下结论提供了证据,以CuPc薄膜做为缓冲层的OLED器件的长期衰减可部分归结于由缓冲层CuPc引起的空穴传输层NPB薄膜的结晶。     

金刚石膜的厚度及背表面过渡层对热导率的影响

 采用微波等离子体化学气相沉积（MWPCVD）方法制备金刚石膜，研究了金刚石膜的厚度以及生长初期的SiC过渡层对其热导率的影响，给出了膜厚和背表面SiC过渡层减薄厚度与金刚石膜热导率的关系。     

半晶态聚合物的分子动力学模拟

采用粗粒化聚乙烯醇模型,应用分子动力学方法模拟熔融态聚合物经过缓慢冷却、局部结晶形成半晶态聚合物的过程.静态结构因子的演变显示出在结晶初期小角散射强度的增大先于布拉格峰的出现,这与小角/大角X射线散射实验现象相一致.模拟得到的半晶态聚合物呈现为折叠链构成的晶区与非晶区交杂在一起的结构形态,与缨状微束结构模型相一致.研究发现在不同的冷却阶段具有不同的有序结构形成机制.从结晶温度到玻璃化温度的凝固过程中,存在分子链的伸展和伸直分子链之间平行排列两种形式的结构转变;而在玻璃化温度之后,材料的活性只允许调整伸直分子链之间的相对排列位置.     

Microdeformational behavior of oriented semicrystalline polymers

A new experimental approach to the evaluation of microdeformational properties on the supermolecular level of highly oriented semicrystalline polymer is proposed. It is based on small-angle x-ray scattering measurements in situ during elastic and plastic tensile deformation of oriented samples along the orientation axes. The main idea of this approach consists of consideration of the competition of two processes occurring in uniaxial deformation: (1) intrafibrillar deformation of long periods; (2) mutual interfibrillar slip. A quantitative experimental criterion of inhomogeneity of intrafibrillar deformation is introduced. The combination of inhomogeneous fibril deformation and interfibrillar slip can explain all kinds of relationships between micro- (long period) and macrodeformations. The proposed approach was tested for several highly oriented polymer films and fibers.     

Crystalline and relaxation properties of ethylene copolymer films inserted between two steel sheets

The relaxation and crystalline properties of ethylene vinyl acetate (EVA) co-polymers inserted in steel/polymer/steel assemblies were studied. To investigate the properties of the interfacial region, polymers of different thickness inserted in the assemblies were analyzed. The studied EVA copolymers are semicrystalline polymers. The relaxation properties of the amorphous phase were investigated by dynamic mechanical measurements performed on the steel/polymer/steel assemblies, and the crystalline properties were studied by differential scanning calorimetry (DSC). The results indicate that, for low polymer thicknesses, the mobility of the amorphous phase is significantly reduced. Significant changes in the crystalline organization also were observed when the polymer thickness decreased, with the presence of more numerous disorganized crystals for thin EVA layers. These crystals can act as physical ties that reduce the mobility of the neighboring amorphous chains. These results indicate the formation of an interphase layer of reduced mobility.     

Deviations from liquidlike behavior in molten polymer films at interfaces

We have performed x-ray specular and diffuse scattering on liquid polymer films and analyzed the spectra as a function of film thickness and molecular weight. The results show that films whose molecular weight is close to the entanglement length behave as simple liquids except that the shortest wavelength is determined by the radius of gyration (R(g)) rather than the monomer-monomer distance. When the molecular weight is higher than the entanglement length, the strong deviations from liquidlike behavior are observed. We find that the long wavelength cutoff vector, q(l,c), scales with film thickness, d as d(-1.1+/-0.1) rather than the usual d(-2) expected for simple liquids. If we assume that these deviations are due to surface pinning of the polymer chains, then our results are consistent with the formalism developed by Fredrickson et al. to explain the capillary wave spectrum that can propagate in a polymer brush.     

DETERMINATION OF CRYSTALLINE LAMELLAR THICKNESS IN POLY(ETHYLENE TEREPHTHALATE) USING SMALL-ANGLE X-RAY SCATTERING AND TRANSMISSION ELECTRON MICROSCOPY*

The crystalline lamellar thickness of semicrystalline poly(ethylene terephthalate) (PET) was evaluated using small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) techniques. Both SAXS onedimensional (1D) correlation function and interface distribution function analyses were utilized to determine the crystalline lamellar thickness. The two-dimensional fast Fourier transformation (2D-FFT) of the TEM image and the Gaussian-like lamellar thickness distribution determined from the TEM image were also performed. Results indicate that the larger value of the two correlation lengths calculated from the SAXS analysis should be assigned to the crystalline lamellar thickness in PET. Discussions and comparison among different methods for characterizing the lamellar thickness of semicrystalline polymers are made.

     

预取向半晶态高分子片晶结构形成微观机理及其应力-应变响应特性的分子动力学模拟

通过分子动力学模拟方法对不同预取向聚乙烯醇熔体(polyvinyl alcohol,PVA)形成的半晶态高分子熔体形成核结晶及拉伸过程中的应力-应变响应特性进行了系统地研究.模拟结果显示预取向度高的PVA熔体对应更快的成核动力学.通过追踪全trans伸直链长度(dtt)、成核原子维诺体积(V)和中心对称参数(S)等序参量在不同取向度熔体下的等温成核与结晶演化过程,给出了PVA熔体成核路径及形成半晶态的分子构象;通过对形成的半晶态高分子结构进一步分析,发现随着熔体取向度的增加,晶体和无定型对应的取向度也会增加,但是当应变剪切大于5时,其对应的结晶度、晶体和无定型取向度不再发生变化;通过对无定型区链结构的定义与分析,可知取向度越高的熔体对应越高的Tie链数目,随着熔体取向度的增加,Loop链的数目也会减小;通过恒速拉伸应力测试可知,所形成半晶态高分子结构力学响应会随着取向度及Tie链数增加而增加,当取向及Tie链数目相同时,应力-应变曲线形状大小也基本保持一致.     

Long-range surface plasmon polaritons with subwavelength mode expansion in an asymmetrical system

Long-range surface plasmon polariton (LRSPP) modes in an asymmetrical system, in which the thin metal film is sandwiched between a semi-infinite substrate and a high permittivity polymer film with a finite thickness, are theoretically calculated and analyzed. Due to the high permittivity of the polymer film, at proper polymer film thicknesses, the index-matching condition of the dielectrics at both sides of the metal can be satisfied for supporting LRSPP modes, and the electromagnetic field above the metal can be localized well. It is found that these LRSPP modes have both long propagation lengths and subwavelength mode expansion above the metal at the optimal polymer film thicknesses. Furthermore, the requirements on the refractive index and the thickness of the polymer film to support LRSPP modes at the optimal thicknesses are found to be not critical.     

Insights into molecular chemistry of Chiapas amber using infrared-light microscopy,PIXE/RBS,and sulfur K-edge XANES spectroscopy

Chiapas amber is a natural occurring fossil resin structurally composed of long macromolecule chains with semicrystalline phases associated with both fossil and polymerization process. The most conspicuous characteristic of this fossil polymer is that it preserves ancient organic inclusions. In the present work, PIXE/RBS spectrometry (particle-induced X-ray emission/Rutherford backscattering) were combined with complementary K-edge XANES spectroscopy (X-ray absorption near-edge structure) to identify the amount of sulfur in Chiapas amber. Initially, the amber samples were examined using infrared reflected photomicrography. Amber is transparent to infrared light and so embedded plants and animals are easily visible, showing them in extraordinary detail, as if they were immersed in a water-like solution. The PIXE/RBS data show that the proportion of sulfur in amber is significantly higher than that found in recently formed resins, consistent with the biogeochemical process that transforms the resin into amber during long-term burial in geological deposits. The sulfur K-edge XANES spectra from amber confirm the sulfur abundance and reveal sulfur species in the reduced and intermediate oxidation states in amber. Almost no oxidized sulfur was found, whereas the recent resins show mostly oxidized sulfur fractions. This indicates that labile oxidized sulfur decays during fossilization and resin maturation must occur under conditions of oxygen depletion. The implications of the presence of sulfur in amber for organic preservation is also discussed here. Sulfur compounds work as a polymer additive that promotes intense resin solidification. This restricts the early oxidant-specific biodegradation of the embedded biomatter and, over geological time, provides greater stability against chemical changes.     

Structure of filled linear polyethylene

The structure of linear polyethylene filled with various solid particles (glass beads, silica, kaolin) was examined by using scanning electron microscopy. The mode of attachment of filler particles to semicrystalline polymer was of particular interest. The filler particles were bonded to polymer by polyethylene fibrillar links whose number depended upon the properties of the filler.     

Experimental investigation of the humidity induced change in the conduction mechanism of PEG

Characterization of the electrical properties of covalently linked polyethylene glycol thin films under a changing relative humidity is examined by dc measurements. At low humidity levels, electronic conduction takes place while the absorbed water contributes to this mechanism and increases the current. At around 70% relative humidity, as a result of the water clusters formed, the polymer melts from the semicrystalline form and the current shows a steeper increase. The water vapor condenses and conduction takes an ionic nature. There is a hysteresis between the absorption and desorption of water as the film cannot reach its semicrystalline form in the time interval of desorption. The polymer film could attain its pre-absorption form after annealing. PACS 72.60.+g; 72.80.Le