Effect of the layer charge on the interaction of porphyrin dyes in layered silicates dispersions

Interaction between tetracationic porphyrin, 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin (TMPyP), and layered silicates in aqueous dispersions was studied using absorption, steady-state and time-resolved fluorescence spectroscopies. The charge density of silicates increases in order synthetic laponite (LAP)<Kunipia F montmorillonite (KF)<synthetic fluorohectorite (FHT). Interpretations of the spectra of layered silicate-porphyrin (LSP) systems considered models of dye adsorption on clay mineral colloid particles, analyzing phenomena occurring in similar systems such as structural changes of TMPyP and the formation of dye molecular assemblies. Structural changes of TMPyP, including flattening of the porphyrin molecule, do not fully explain all the spectral observations. One should mention variations of the Q-bands and fluorescence spectra in dependence on the layer charge. The molecular association of the TMPyP molecules is expected to occur to a certain extent in dependence on the layer charge of a clay mineral template. H-aggregates were not observed in any system. Only FHT colloids induced the formation of at least two components with significantly different spectral properties.     

Thermally induced variations in the conformational composition and spatial orientation of molecular components of a dicarbocyanine dye layer

The effect of heating on the spatial orientation and concentration of the components of dicarbocyanine dye layers on a glass substrate is studied experimentally. Layers of two types differing in the spatial orientation angles of all their components (monomeric all-trans and β-mono-cis isomers, dimers, and J aggregates) are considered. It is shown that storing of samples at temperatures of 150–200°C causes partial thermal destruction but does not change the absorption spectra of the molecular components. Heating of the layer of the first type changes neither the orientation nor the relative concentration of the components. Heating of the layer of the second type leads to irreversible changes in the orientation angles of all the molecular components and causes the β-mono-cis isomer and the dimer to transform into the all-trans isomer and the J aggregate. The dependences of the orientation angle on the heating time have the form of saturating functions. The rate of variation of the orientation angle and its limiting value in the saturation region increase with increasing temperature of heating. At high temperatures, the layer of the second type transforms completely into the layer with the first type of spatial orientation. A mechanism of the changes in the angles of the spatial orientation of the layer components, which includes the stages of thermal isomerization and reorientation of each molecular component, as well as rearrangement of its environment, is proposed. Energetic and kinetic parameters of all the stages of layer reconstruction satisfying the experimental results obtained in the region from 150 to 230°C are determined.     

Microstructural Evolution and Its Effect on Mechanical Properties of Isotactic Polypropylene by Shear Plastic Deformation at Elevated Temperatures

Isotactic polypropylene (iPP) was plastically shear deformed by equal channel angular extrusion (ECAE) at extrusion temperatures varied from 45 to 125°C (25 mm/min). The evolutions of morphology and crystal orientation were studied by reflected optical microscopy (ROM), scanning electron microscopy (SEM), and X-ray diffraction. It was found that the original spherulites were deformed into nearly ellipsoids with their long axis tilted at an angle away from the flow direction. Azimuthal scanning results revealed that two preferred crystal orientations were formed after ECAE. The crystal plasticity was activated by increasing the extrusion temperature, followed by fast rotation of crystallites toward the shear direction. The thermal mechanical analysis (TMA) indicated that low extrusion temperature was favorable to fix the molecular orientation. The iPP samples processed at the investigated temperatures displayed a significant increase in the impact strength, especially for those extruded at 45°C and 65°C. The tensile results revealed a greater elongation at break in the samples deformed at low temperatures (45°C and 65°C) but not in those deformed at high temperatures (85°C or above).     

Nuclear Overhauser Effect Spectroscopy (NOESY) and 3JHH Coupling Measurements in the Determination of the Conformation of the Sesquiterpene Antimalarial Arteether in Solution

The twisting of the A-, B-, and D- rings of β-arteether were determined from dihedral angles derived from ³J_HH coupling constants and a Karplus-type equation that takes into account heteroatom substitution. The angles obtained by NMR were also compared to the angles obtained by molecular modeling and to those obtained from the methyoxyl analog (artemether) using x-ray crystallography. The NMR results showed that the A-ring was a relatively undistorted chair conformation with the 14-methyl group in an equatorial position. The NMR data indicated that the B-ring was very distorted and the D-ring was twisted outward because of the steric interactions with the ethoxy group. Two-dimensional NOESY data was used to measure selected proton-proton distances for arteether in solution and these distances were also compared to those obtained by molecular modeling and from the x-ray data for artemether. The NOESY data also indicated that the conformation of the A-ring was fairly normal, the B-ring was twisted, and the ethoxy group was in an extended conformation (C₁₁-C₁₂-O-C₁₆=+170°, and C₁₂-O-C₁₆-C₁₇=+169°)     

Effect of annealing on the structure and morphology of nylon 6 fibers

Changes in the structure of nylon 6 fibers annealed in dry and wet atmospheres were studied by small-and wide-angle x-ray diffraction. In the presence of water or saturated steam, fibers can be annealed to the same strucutral state at temperatures 70°C lower than in dry atmosphere. This is due to the enhanced mobility of the molecular segments in the amorphous region, a mechanism which is also known to lower the T_g by the same amount. Upon annealing under unconstrained conditions, lamellar spacing, crystallite size in the equatorial plane, crystalline as well as fiber density, and the chain-axis repeat increase with annealing-temperature; whereas crystalline orientation and the Van der Waals separation of the hydrogen-bonded sheets decrease. The monoclinic angle 8 remains constant at 66.7° (σ = 0.3°) and might depend on the starting fiber rather than on the treatment of the fiber. Most of these changes occur above a critical temperature of 170°C if dry, or 100°C if wet; rate of crystallization is also the highest under these conditions in nylon. The effect of these changes on such fiber properties as dyeing and the role of micro voids in dye diffusion and in dye uptake are discussed. Surface premelting and the accompanying changes in the surface structure of the lamellae, selective melting, and more importantly, the longitudinal motion of the nylon 6 chains and the resulting folding of interfibrillar extended amorphous chains are invoked to explain the shrinkage of the fiber, disorientation of the crystallites, increase in crystalline perfection, and the increase in lamellar spacing.     

Optimization of detection device geometry for NIR spectroscopy using a three-layered model of stone fruit

The influences of detection device geometry and fiber optic parameters on near infrared spectroscopy measurements were assessed using stone fruit models based on Monte Carlo simulation. The stone fruit was modeled as concentric spherical layered tissues including the skin, the flesh and the core. The choices of the detection angle, the diameter of the detection fiber, the numerical aperture, and the height of the probe were discussed. Receiving diffuse reflectance signals at detection angles in the range of 35°–50° and normalizing the detection signals by the collection area and the solid acceptance angle prior to use are suggested. Fiber probes with diameters D = 0.06 cm or 0.1 cm, NA = 0.20 or 0.30, and height h ≤ 0.8 cm are preferred. The probe deflection angle should be limited to within ±5° to guarantee measurement accuracy.     

Fluorescence properties of the dye-intercalated smectite

The fluorescence properties of the dye Rhodamine 590 and Rhodamine 640 intercalated into montmorillonite were studied. All of the intercalation reactions were accomplished in an ethanol solution which contained the corresponding quality of Rhodamine. The TG-DTA and the X-ray diffraction data showed that the immobilization of Rhodamine depended on the amount of ethanol incorporated in the interlayer space of montmorillonite. The 14.8 Å basal spacing of products indicated a conformation of Rhodamine with the xanthene nucleus and the phenyl group positioned parallel and perpendicular to the silicate layer, respectively. Also, the infrared pleochromism, which supported the proposed orientation of the phenyl group, was observed at 1250 and 712 cm⁻¹. The main fluorescence bands of both products were observed near 600 nm when excited by the 514.5 nm line of an argon ion laser. The results indicated that the mesomeric structure determined the fluorescence behavior, which was little different for the two products owing to the environment of the interlayer. These data are briefly discussed relative to the reaction conditions utilized for the synthesis of products. Also, the results support the idea that the products have a high potential for use as a host for a tunable laser.     

Investigation of the role of the projectile-target orientation angles on the evaporation residue production

The measured yield of evaporation residues in reactions with massive nuclei have been well reproduced by using the partial fusion and quasifission cross sections obtained in the dinuclear-system model. The influence of the orientation angles of the projectile- and target-nucleus symmetry axes relative to the beam direction on the production of the evaporation residues is investigated for the ⁴⁸Ca + ¹⁵⁴Sm reaction as a function of the beam energy. At the low beam energies only the orientation angles close to αP = 30° (projectile) and αP = 0°–15° (target) can contribute to the formation of evaporation residues. At large beam energies (about E _c.m. = 140–180 MeV) the collisions at all values of orientation angles αP and α _T of reactants can contribute to the evaporation residue cross section which ranges between 10–100 mb, while at E _c.m. > 185 MeV the evaporation residue cross section ranges between 0.1–1 mb because the fission barrier for the compound nucleus decreases by increasing its excitation energy and angular momentum.     

Effect of interfacial interaction on the structure and rheological properties of polyamide-6/clay nanocomposites

A series of polyamide-6 (PA6)/layered silicate (clay) nanocomposites were prepared via direct melt compounding using a conventional single screw extruder, and then the effect of interfacial interaction on the characteristic internal structure and rheological properties of PA6/clay nanocomposites was investigated. XRD diffractograms indicated a large extent of exfoliation of the layered silicate entering into a strong interaction with PA6. The formation of such morphology was further supported by TEM images. In addition, various rheological properties were interpreted in conjunction with morphological characteristics depending on interfacial interaction between PA6 and the layered silicate.     

Energie- und Winkelverteilung sekundärer Photonen bei der Wechselwirkung eines 6,2 GeV-Gammastrahls mit komplexen Kernen

The energy spectra of secondary photons from the interaction of a 6.2 GeV bremsstrahlung beam with targets of H₂, Be, C, Al and Cu are measured for laboratory angles from 35° to 120°. All spectra exhibit an exponential decrease of the photon yield with increasing momentum. Difference measurements with energies of the bremsstrahlung beam from 3.5 to 6.2 GeV for a center of mass angle of 90° are compared with the thermodynamical model of Fermi and the reaction temperature is determined to be 83MeV±8%. The results agree approximately with the measurements of p-Be-collisions at small laboratory angles.     

正二十四烷烃石蜡/膨胀石墨（EG）复合相变材料分子动力学模拟

相变材料(PCMs)在相变时的恒温、高能量密度等特性,经常应用于设备的热管理,但是PCMs导热系数低的缺点影响了其使用范围.本文采用分子动力学方法,模拟了在正二十四烷烃石蜡PCMs中添加不同结构(层状、交叉状)的膨胀石墨(EG)之后构成的复合PCMs的物性.文章通过径向分布函数(RDF)、声子态密度(PDOS)、比热容和导热系数这四个指标,分析了夹角为0°的层状结构,夹角为45°、90°的交叉状EG添加物对于石蜡热物性的影响. EG(0°、45°、90°)添加使得石蜡的原子分布在不同程度上变得更加均匀、紧密,使得石蜡的比热容有所增加.同时,两种类型的添加物提高了石蜡的PDOS,提高了导热系数.其中,EG(90°)添加物对于石蜡导热系数的提升最为明显,石蜡/EG(0°、45°、90°)模型中EG的含量分别为33.63 wt%、30.86 wt%和23.20 wt%,相比于的石蜡的导热系数分别提升了417.1%、345.7%和522.9%. EG的添加能够提高石蜡的导热系数,不同结构的EG对石蜡导热系数的影响有着较大的区别.     

High CEC generation and surface modification in mica and vermiculite minerals

Montmorillonite layered silicate has been commonly used to reinforce polymer matrices. Due to its swelling in water, organic modification of the mineral surface is easily achieved which makes the surface compatible with polymers. Other minerals like mica and vermiculite though can also lead to high aspect ratio platelets in nanocomposites, but they do not swell in water owing to much stronger electrostatic forces of attraction holding their platelets together (layer charge density >0.5?eq?·?mol^?1 in comparison with 0.25–0.5?eq?·?mol^?1 for montmorillonite). In current study, milling, delamination and cation exchange processing of mica and vermiculite minerals has been reported to explore their potential as reinforcement materials. Wet grinding and subsequent sieving of the coarse minerals led to fine-sized particles suitable to perform chemical delamination in water. The delamination process resulted in Li-mica and Na-vermiculite with enhanced access to the interlayer cations, thus, higher CEC. Successful surface modification of the delaminated minerals with alkyl ammonium ions could be achieved which resulted in significant enhancements in their basal plane spacing. Peak degradation temperatures of 260°C were measured for C18 and 2C18 modified vermiculite, whereas 300°C and 275°C were observed respectively for C18 and 2C18 modified mica minerals which make them suitable for compounding with polymers at high temperature.     

Laser-induced periodic surface structures formed on the sidewalls of microholes trepanned by a femtosecond laser

Laser-induced periodic surface structures (LIPSSs) were observed on the sidewalls of 300-μm-diameter holes trepanned on cemented tungsten carbide using femtosecond laser pulses at a wavelength of 800 nm. For a circularly polarized beam, LIPSSs were formed at a period of 300 nm and oriented perpendicularly to the plane of incidence on the sidewalls. For a linearly polarized beam, LIPSS formation was dependent on the relative angle α between the polarization direction and the plane of incidence. For relative angles α from 0° to 70° and from 110° to 180°, LIPSS spacing was 300 nm. However, there were two types of LIPSSs coexisting from 70° to 110°. One had a spacing of 120 nm and the other had a spacing that varied from 500 to 760 nm. It was found that the orientation angle of LIPSSs measured between the LIPSS orientation and the plane of incidence had a nonlinear dependence on α. To understand this dependence, a model was proposed in which LIPSSs are assumed to align perpendicularly to the direction of the absorbed electric field lying in the tangent plane of the sidewall of a drilled hole. The calculated results from this model showed good agreement with the experimental results.     

Effects of draw-down ratio and annealing treatment on structure formation in extruded strands of a thermotropic liquid crystalline copolyester

The molecular orientation, thermal behavior, and crystal lattice structure in extruded strands of a thermotropic liquid crystalline polymer (LCP) were studied with wide-angle x-ray diffraction (WAXD) and differential scanning calorimetry (DSC). The purpose of this work is to elucidate the effects of draw-down ratio and annealing treatment on the structure development in the LCP strands. The crystal orientation function markedly increased with increasing draw-down ratio, but the increase of orientation function saturated at higher draw-down ratio. Annealing treatment below 250°C slightly increased the degree of orientation, whereas the molecular orientation was relaxed by annealing at 270°C. In addition, the thermal properties and crystal lattice structure were sensitive to the annealing treatment. The change of DSC curves with annealing temperature suggested that the initial crystalline texture of as-extruded samples was reorganized into a more ordered structure by the annealing treatment. Draw-down ratio had some effects on the thermal properties. The molecular orientation facilitated the crystallization during annealing.     

Delbrück scattering of 9 MeV photons from tantalum

The differential elastic scattering cross section of 9.0 MeV photons by ¹⁸¹Ta has been measured at angles between 25° and 140° and a good agreement was obtained between the measured and predicted values at θ = 35–90°. In calculating the theoretical cross sections the coherent scattering contributions of nuclear Thomson (NT), nuclear resonance (NR) and Delbrück (D) amplitudes were included while that of Rayleigh (R) scattering was excluded. The D-amplitudes were taken from a recent calculation by Mork and Papatzacos. Evidence for the contribution of the real D-amplitude is obtained.     

多层奥氏体钢中超声相控阵辐射声场分析

针对一维线性超声相控阵透过楔块,在多层不同晶轴取向的奥氏体钢中的声场辐射问题,结合高斯声束等效点源模型以及基于时间最小原理的射线追踪法,给出了各层介质中透射声场的计算方法。将奥氏体钢近似为横向各向同性介质,计算了相控阵透过楔块,在晶轴取向为0°的奥氏体钢中的无延时纵波声场,计算结果与COMSOL仿真结果相吻合,从而验证了所用方法的正确性。通过加入不同的延迟法则,仿真计算了三层含有不同晶轴取向(0°,30°,100°)的奥氏体钢中的纵波声场,实现了相控阵声场的偏转与聚焦,分析了偏转声场与聚焦声场的传播特性。仿真结果表明,不同的晶轴取向将导致不同的声束偏转以及聚焦效果。通过延迟激励各阵元,虽然可以控制声束偏转或聚焦到预定位置,但是晶轴取向仍会对声束宽度以及幅值产生一定的影响。     

静态随机存储器单粒子效应的角度影响研究

利用兰州重离子加速器加速的高能离子研究了入射角度对IDT71256的单粒子翻转截面和多位翻转比例的影响.研究表明：在大角度掠射轰击下单粒子翻转截面的增大包括了多位翻转的贡献；离子在器件敏感层中沉积的能量及其横向分布是影响多位翻转的两个重要参数，IDT71256发生三位以上多位翻转的比例随着离子入射角度的增大而增加. 关键词： 静态存储器 单粒子翻转 多位翻转 沉积能量 横向分布     

Turbulent convective heat transfer in an inclined tube filled with sodium

Turbulent free convection of liquid sodium in a straight thermally insulated tube with a length equal to 20 diameters and with end heat exchangers ensuring a fixed temperature drop is investigated experimentally. The experiments are performed for a fixed Rayleigh number Ra = 2.4 × 10⁶ and various angles of inclination of the tube relative to the vertical. A strong dependence of the power transferred along the tube on the angle of inclination is revealed: the Nusselt number in the angular range under investigation changes by an order of magnitude with a maximum at the angle of 65° with the vertical. The characteristics of large-scale circulation and turbulent temperature pulsations show that convective heat transfer is mainly determined by the velocity of large-scale circulation of sodium. Turbulent pulsations are maximal for small angles of inclination (α = 20°–30°) and reduce the heat flux along the channel, although in the limit of small angles (vertical tube), there is no large-scale circulation, and the convective heat flux, which is an order of magnitude larger than the molecular heat flux, is ensured only by small scale (turbulent) flow.     

Ultra Fine Layered Silicate Synthesis from Synthetic Silicate Raw Material

This paper reports the results of experiments on ultra fine layered silicates Na-fluorotaeniolite and Na-fluorotetrasilicic mica synthesis in the melts prepared from reaction blends based on synthetic silicate raw material, namely synthetic magnesium silicate dihydrate (MSDH, MgO·SiO₂·2H₂O). The MSDH–Na₂SiF₆–LiF, MSDH–Na₂SiF₆–MgF₂ and MSDH–Na₂SiF₆–NaF blends, whose compositions are close to the stoichiometry of the Na-fluorotaeniolite (NaMg₂Li[Si₄O₁₀]F₂) and Na-fluorotetrasilicic mica (NaMg_2.5[Si₄O₁₀]F₂) were studied in the temperature range 1080–1225°C. Magnesium silicate dihydrate, the phase composition of synthesis products and layered silicates (Na-fluorotaeniolite and Na-fluorotetrasilicic mica) were examined using the crystal optical, X-ray diffraction at room and high temperatures, differential thermal and chemical analyses. It has been shown that studied blends possessed a high reactivity, owing to which the layered silicates were synthesized at lower temperatures (～180–300°C) and the duration of the synthesis was shortened severalfold. The maximal yield of the Na-fluorotetrasilicic mica was observed in the reaction blend with the Na₂SiF₆ and NaF as halogen-containing compounds. The specific effects of MSDH on the physicochemical processes proceeded during heat treatment of the reaction blends were described.     

离轴三反射望远镜遮光罩设计与杂光分析

分析了离轴三反射望远镜的杂散光特性,给出了遮光罩设计的基本原则并进行了初步的设计.根据系统所要探测到的极限星等,通过计算得到了望远镜光学系统的点源透射比所必需满足的条件;在Tracepro杂光分析软件中建模,在方位角为0°、45°、90°、135°和180°时分别对0.1°～80°之间共15个离轴角度进行了光线追迹,通过计算得到了系统的PST曲线.结果表明,系统PST整体上是下降的且在离轴角30°以后接近指标要求,但在方位角0°和180°时,PST曲线在个别角度有突增的现象,通过光线追迹数据,得到了主要的杂光传输路径,提出了对遮光罩的修改方案并对其进行了修改.最后对改进后的系统重新进行了仿真分析.仿真结果表明,系统的杂光抑制能力达到了指标要求.