水在金属氧化物表面的吸附与解离

水(H2O)由H原子和O原子组成.地球上有大量的水,若能找到一种经济、实用的方法将H2O解离生成H2和O2,则在新能源的开发和应用方面,意义深远.水在固体表面的吸附现象极为普遍,在某些金属或金属氧化物表面,H2O被吸附并解离成OH-和H+.文章以有序氧化镁(MgO(100))薄膜和Pd/MgO(100)体系为例,在超高真空条件下,用光电子能谱和高分辨电子能量损失谱方法,研究了水在它们表面的吸附与解离.研究结果表明,H2O在MgO(100)表面可以被部分解离,而H2O在Pd/MgO(100)表面的解离与Pd的含量有关.了解水与固体表面的相互作用机理还需要做更多的基础研究工作.     

层状二硫化钼研究进展

近年来,层状二硫化钼由于其特殊的类石墨烯结构和独特的物理化学性质已成为国内外研究的热点.本文综述了层状二硫化钼的物理结构、价带结构和光学性质;介绍了制备方法,包括生长制备和剥离制备.生长制备的原料包括四硫代钼酸铵((NH4)_2MoS_4)、钼(Mo)和三氧化钼(MoO_3)等.剥离制备包括微机械剥离、液相超声法、锂离子插层法和电化学锂离子插层法等.归纳了层状二硫化钼在场效应晶体管、传感器和存储方面的应用,展望了层状二硫化钼的研究前景.     

聚合温度及铁电液晶有序度对单体转化率的影响

采用琉醇和丙烯酸的混合物作为反应单体,利用红外光谱仪检测反应前后单体的C=C双键吸收峰的变化,研究了温度对单体转化率的影响。制备了单体含量为10%的聚合物稳定铁电液晶器件,研究了铁电液晶有序度对单体的影响。实验表明:随着温度的增加单体的转化率增加,随着铁电液晶有序度的增加单体的转化率增加;在铁电液晶中单体的转化率主要受有序度的影响;制备聚合物稳定铁电液晶器件最佳的聚合条件为近晶A相(SmA)下聚合。     

三元杂多阴离子层状化合物的合成、表征及催化活性

用离子交换法合成了具有Keggin结构的三元杂多阴离子层状化合物LDH-K8[MnCu(H2O)W11O39],LDH-K8[MnFe(H2O)W11O39],LDH-K8[MnCo(H2O)W11O39]和LDH-K8[MnZn(H2O)W11O39],并用XRD、IR、UV对其进行了表征。结果表明:杂多阴离子进入水滑石层间后,仍保留了其Keggin结构。利用层状化合物催化合成乙酸正丁酯考察其催化活性,结果表明:层状化合物在酯化反应中显示优良的催化性能。     

层状钙钛矿钴氧化物Y1-xGdxBaCo2O5中稀土离子半径对电荷有序转变的影响

研究了层状钙钛矿钴氧化物Y1-xGdxBaCo2O5(x=0,0.25,0.5,0.75,1)的结构和输运性质,结果显示它们具有相似的相变行为,从而证明GdBaCo2O5与YBaCo2O5一样,也存在电荷有序转变.结果还表明电荷有序转变温度随稀土离子半径增加而上升.     

混合排列向列相液晶薄盒中–1/2向错引起的有序重构的扩散

基于Landau-de Gennes理论, 利用松弛迭代法, 研究了混合排列向列相液晶薄盒中–1/2向错引起的有序重构的扩散现象, 给出了–1/2向错的核结构、双轴性结构, 以及盒厚减小时有序重构的扩散. 当盒厚小于15ξ时, 随着盒厚的减小, 向错范围和有序重构区域沿基板方向迅速扩散; 当盒厚减小到临界厚度10ξ时, 有序重构的范围扩散到整个液晶盒中, 以向错中心所对应的平面为界, 指向矢一部分垂面排列, 另一部分沿面排列. 本文的研究对拓扑缺陷对向列相液晶中的亚微米胶体粒子的调节作用具有一定的理论指导意义. 关键词： 混合排列向列相液晶薄盒 –1/2向错 有序重构扩散 松弛迭代法     

可聚合型溶致液晶单体3,4,5-三(11-十一烷氧丙烯酰氧基)苯甲酸钠的自组装及紫外光固化性能

以3,4,5-三羟基苯甲酸为原料,依次经过酯化、醚化、酰氯化和钠盐化四步反应合成一种可聚合型溶致液晶单体3,4,5-三(11-十一烷氧丙烯酰氧基)苯甲酸钠,并对其结构进行了傅里叶变换红外与1H核磁表征. 在室温下研究了该单体在水中的自组装行为,组装体结构通过偏光显微镜与X射线衍射仪进行表征. 研究表明,单体与水比例为80:20时可自组装为层状(La)相,92:8时组装为反六方(H_II)相,这与临界堆积参数的理论计算相吻合,表明单体浓度是影响组装体结构的重要因素. 在组装的基础上研究了含不同光引发剂的溶致液晶体系的双键转化率及固化后组装体结构的保留. 经实时红外表征及溶胶-凝胶法的验证发现在光强为30 mW/cm²的365 nm下曝光30 min,含引发剂Darocur2959的溶致液晶体系双键转化率可达78%. 聚合之后La相与H_II相的纳米结构都得到了保留.     

液晶聚合物/柔性链聚合物共混体系相分离形态

利用元胞动力学方法在二维情况下对浓度、取向序参量的含时Ginzberg Landau方程进行数值求解 ,研究了液晶聚合物 /柔性链聚合物共混体系的相分离动力学 ,考察了浓度、取向有序过程的耦合对相分离形态的影响 .结果表明 ,此耦合作用对相分离的时间进程以及相分离图样的空间排布都有影响 .液晶聚合物的取向有序相当于增加了两组分间的不相容性而促进两相分离 ;两个序参量在热力学方面的耦合使液晶聚合物趋向于沿着界面方向取向 ,而动力学方面的耦合使液晶聚合物分子沿着其取向方向扩散 ,相分离图样的空间排布由这两种效应共同决定 .通过极化率张量的定义用数值方法模拟得到了相分离体系的小角光散射图样 ,结果表明 ,散射强度分布具有方位角依赖性 ,它是由浓度、取向序参量的空间变化共同决定的 .     

同步辐射X光小角衍射法研究尿素对磷脂相变的影响

报道用差示扫描量热和同步辐射X光衍射方法研究尿素对二油酰磷脂酰乙醇胺(DOPE)相变的影响.结果表明尿素在任何所研究的浓度下均能稳定层状液晶相而不是反六角相和层状凝胶相,DOPE多重膜的重复间距随尿素浓度的增加而增大.磷脂表面和尿素之间形成氢键或者尿素破坏有序水结构的Hofmeister效应可能是影响DOPE相行为的原因.此外,鼠尾胶原蛋白的X射线小角衍射图谱可以作为小角衍射仪校准与标定的标准.     

偶氮苯介晶基元取向方式对其取向稳定性影响

根据取向透射率变化研究了偶氮苯侧链液晶聚合物在不同光照功率条件下的取向,用锥光干涉法表征了侧链介晶基元的取向方向,并研究了升温对取向膜的稳定性影响.实验结果表明介晶基元的取向速度和取向度都随光照时间和光照功率增加而增加;超过一定阈值功率(20 mW/cm2)时,随着光照时间延长薄膜的透射率(取向度)反而降低.高功率光照...     

Lamellar phenylene-bridged hybrid silicones

The acid-hydrolysis of a bismethyldiethoxysilylated para-phenylene-bridged derivative, (EtO)₂MeSi(CH₂)₃NHCONH(C₆H₄)NHCONH(CH₂)₃SiMe(OEt)₂, with urea groups has been performed in pure aqueous medium. The scanning electron microscopy (SEM) analysis of the resulting insoluble solid revealed plate-like forms. A lamellar structure was determined from the powder X-ray diffraction (PXRD) studies with a sharp peak at 21.1 Å. The solid state CP-MAS NMR spectra (²⁹Si and ¹³C) of the bridged siloxane hybrid exhibit a moderately condensed material with complete preservation of the Si–C bonds throughout the hybrid network.     

Lamellar pattern formation in small-world media

Numerical and analytical techniques are used to investigate the effects of quenched disorder of small-world networks on the phase ordering dynamics of lamellar patterns as modeled by the Swift-Hohenberg equation. Morphologies for small and large values of the network randomness are quite different. It is found that addition of shortcuts to an underlying regular lattice makes the growth of domains evolving from random initial conditions much slower at late times. As the randomness increases, the evolution is eventually frozen.     

Application of Lamellar Clustering Theory to Isotactic Polypropylene and Direct Observation of Lamellar Cluster Morphology by Electron Microscopy

In this work the lamellar cluster model was found to be applicable to the explanation of the mechanical yield behavior in polypropylene materials. According to the lamellar clustering theory, a spherulite is composed of radiating arms, each arm is composed of lamellar clusters, and each lamellar cluster is an aggregate of structural units of the cluster, including several crystalline lamellae and amorphous layers. The intercluster links capable of supporting external force play a role in the destruction of lamellar clusters at the yield point. These morphological features were directly confirmed from TEM observation on two-dimensional polypropylene spherulites that were crystallized from mixtures of isotactic polypropylene and atactic polypropylene, with the latter being removed later by a solvent. In addition, the structural parameters, such as the distance between intercrystalline links and the lamellar cluster thickness, which were determined by applying the mechanical yielding data to the lamellar cluster theory, were confirmed to be in agreement with the quantitative estimations from the TEM images of the polypropylene spherulites.     

Lamellar phase coexistence induced by electrostatic interactions

Membranes containing highly charged biomolecules can have a minimal free-energy state at small separations that originates in the strongly correlated electrostatic interactions mediated by counterions. This phenomenon can lead to a condensed, lamellar phase of charged membranes that coexists in thermodynamic equilibrium with a very dilute membrane phase. Although the dilute phase is mostly water, entropy dictates that this phase must contain some membranes and counterions. Thus, electrostatics alone can give rise to the coexistence of a condensed and an unbound lamellar phase. We use numerical simulations to predict the nature of this coexistence when the charge density of the membrane is large, for the case of multivalent counterions and for a membrane charge that is characteristic of biomolecules. We also investigate the effects of counterion size and salt on the two coexisting phases. With increasing salt concentration, we predict that electrostatic screening by salt can destroy the phase separation.     

On Perpendicular and Tilted Chains in Lamellar Crystals

Chain tilt and surface disorder were investigated in end-deuterated long n-alkane C₁₂D₂₅C₁₉₂H₃₈₄C₁₂HD₂₄ crystallized from solution and in n-alkane C₁₆₂H₃₂₆ crystallized from melt. Small-angle X-ray scattering and infrared spectroscopy were employed. Extended-chain crystals of C₁₂D₂₅C₁₉₂H₃₈₄C₁₂HD₂₄ as-grown from solution have the molecular axis perpendicular to the lamellar surface, but when heated, around 90°C, they start tilting relative to the layer normal. The tilt increases gradually to reach 35° just below the melting point. C₁₆₂H₃₂₆ crystallized from the melt at small supercoolings has chains tilted at 35° at the outset, as found previously for all melt-crystallized long alkanes and polyethylene. However, for the first time in long alkanes, it is found that when molten C₁₆₂H₃₂₆ is supercooled to ΔT≥10 K, crystals with perpendicular chains form. At still larger ΔT, the chains are once-folded, with a mixed population of tilted and perpendicular chain crystals. The use of Davydov splitting of the CH₂ and CD₂ bending vibration of the end-labelled alkane C₁₂D₂₅C₁₉₂H₃₈₄C₁₂HD₂₄ allows independent IR probing of molecular disorder at the deuterated surface and in the hydrogenous crystal interior. The initially small CD₂ splitting and the presence of an additional singlet component indicate a rough surface in as-grown crystals, with considerable longitudinal interchain disorder. It is estimated that about 10% of chains are displaced by up to a dozen C-atoms. The increase in splitting and decrease in absorbance of the singlet, which occur on annealing at progressively higher temperatures, are evidence of steady improvement in translational surface order, occurring simultaneously with increasing chain tilt angle. From the above evidence, it is concluded that the absence of tilt in as-grown crystals is not the result of high surface order, as in the case of shorter odd n-alkanes, but rather of a high frozen-in longitudinal disorder with chain ends or folds protruding out of or sunken beneath the crystal surface. It is also concluded that chain tilt only becomes necessary as the crystal surface becomes translationally more ordered and the crystal–amorphous interface sharpens. The effect of chain tilt on the Davydov splitting is addressed briefly.     

Interfacial Defects and Lamellar Decomposition in Titanium Aluminides

The interfacial defect content of lamellar interfaces in Ti aluminide alloys has been evaluated by HREM and the data analysed using the Topological Theory of Interfacial Defects. It has been found that the defects observed are all perfect interfacial disconnections, and that the lamellar decomposition is diffusion-controlled. An analysis of the diffusive fluxes required for disconnection motion has been used to reconcile the apparent discrepancy between this conclusion and the martensitic crystallography exhibited by the TiAl lamellae. Moreover, this analysis has been used to explain why disconnections with Burgers vectors b = 1/3〈211〉 have been observed in these interfaces.     

非晶态异质结构a-Si:H/a-SiNx:H和a-Si:H,a-SiNx:H薄膜的应力研究

实验发现在一定Si—H键浓度下,相对于平坦的硅衬底而言,在其上沉积的a-Si:H薄膜具有压缩应力,a-SiN_x:H薄膜具有伸张应力。当a-Si:H和a-SiN_x:H层厚度比近似于1:2时,硅衬底上生长的a-Si:H/a-SiN_x:H/c-Si样品,弯曲最小,并能保持很长时间。文中还给出了应力随退火变化的情况,并对实验结果进行了讨论。 关键词：     

Lamellar phase of stacked two-dimensional rafts of actin filaments

We examined liquid crystalline phases of the cytoskeletal polyelectrolyte filamentous (F-)actin in the presence of multivalent counterions. As a function of increasing ion concentration, the F-actin rods in either an isotropic or a nematic phase will transform into a new and unexpected lamellar phase of cross-linked rafts (L(XR) phase), before condensing into a bundled phase of parallel, close-packed rods. This behavior is generic for alkali earth divalent ions Mg2+, Ca2+, Sr2+, and Ba2+, and the structural transitions are achieved without any architecture-specific actin-binding linker proteins.     

Lamellar structure and nanomechanical properties of quasicrystalline Al-Cu-Fe alloys

The kinetics of structural phase transformations in quasicrystal-forming Al-Cu-Fe alloys with compositions in the region of stability of the icosahedral (i) phase has been investigated. It has been shown that, depending on the development of metastable transformations i → pentagonal phases P1 and P2, a homogeneous lamellar structure (i + P1 + P2) or a polygrain i-phase is formed in the alloys. The P-h diagrams obtained upon nanoindentation, atomic force microscopy, and scanning electron microscopy of indentations have demonstrated signs of elasto-plastic deformation of the alloys with lamellar and polygrain icosahedral structures. It has been found that, in contrast to the polygrain icosahedral alloys with a normal size effect of nanoindentation, the alloys with a lamellar structure are characterized by a nonmonotonic dependence of the hardness (H) on the maximum load (P _max) and exhibit the effect of strain hardening in the range of loads 50 mN ≤ P _max < 500 mN. The strain hardening is considered as the result of resistance exerted by boundaries of the lamellar structure to the development of plastic deformation.     

a-Si:H/a-SiNx:H超晶格的掺杂效应

采用带有可转动掩板的沉积系统,合成出一类新的a-Si:H/掺杂a-SiN_x:H超晶格。样品中各子层厚度及a-SiN_x:H子层中N/Si比固定,仅改变掺杂浓度。结果发现:此类超晶格中的费密能级可以通过a-SiN_x:H层中的掺杂来控制,即a-Si:H/a-SiN_x:H超晶格可以从n型转变为p型,依赖于a-SiN_x:H子层中B的掺杂比。然而,a-SiN_x:H子层中P的掺杂对a-Si:H/a-SiN_x:H超晶格传输特性影响并不大。 关键词：