测定极化聚合物膜的二阶非线性光学系数的新方法──偏振红外光谱法

本文报道在一维刚性取向气体模型基础上用偏振红外光谱测出的极化膜的取向度估算其二阶非线性光学系数α值的方法。方法表明,在目前采用的各种极化方法所能达到的极化效率范围内,取向因子可表示为     

FOURIER TRANSFORM INFRARED STUDY OF FRACTIONATED AROMATIC POLYESTERS

Infrared spectra at different temperatures have been studied for fractions ofa liquid crystal tormmg aromatic polyester. The molecular interactions in different phases and their changes duringthe transitions were discussed. Abrupt frequency shift was found for bands of groups both in mesogens and flexible spacers during fusion and isotropization transitions. It may imply that both the mesogens and the flexible spacers are included in the same crystalline phase and give their contributions to the formation of the mesophase. The splitting into doublet of the C—O stretching vibrations was observed for both the aromatic and aliphatic esters and was attributed to the existence of local regions for ester groups different in ordering. The more ordered regions do not disappear completely even in the isotropic liquid phase.     

Palladium nanoparticles as catalysts for reduction of Cr(VI) and Suzuki coupling reaction

Herein, six kinds of PdNPs (including icosahedron, sphere, spindle, cube, rod, and wire) were synthesized via simple methods. The catalytic activities were investigated by the reduction reaction of Cr(VI) and Suzuki coupling reaction. Chemically synthesized morphologies of the six catalysis were characterized by transmission electron microscopy, field emission scanning electron microscopy, and X-ray diffraction, etc. Pd icosahedron shows a better catalytic property than other PdNPs with a rate constants 0.42 min^?1 for the reduction of Cr(VI). Moreover, the electrocatalyst shows that Pd icosahedron possesses a bigger surface area of 8.56 m²/g than other nanoparticles, which is attributed to the better catalyst. The Pd icosahedron possesses a better catalytic property, attributing to the abundant exposed {111} facets with high activity on Pd icosahedron. The catalytic activities are closely related to the surface area with the following order: icosahedrons ≥ sphere > rod > spindle > cube > wire. The Pd icosahedron catalyst represents a strong activity for Suzuki coupling reaction as well, outweighting is 80%. The results reveal that Pd icosahedron acts as an efficient catalyst compared to other PdNPs (wire, rod, sphere, spindle, and cube).     

Rubbing‐induced molecular alignment and its relaxation in polystyrene thin films

Rubbing‐induced molecular alignment and its relaxation in polystyrene (PS) thin films are studied with optical birefringence. A novel relaxation of the alignment is observed that is distinctly different from the known relaxation processes of PS. First, it is not the Kohlrausch–Williams–Watts type but instead is characterized by two single exponentials plus a temperature‐dependent constant. At temperatures several degrees or more below the glass‐transition temperature (T_g), the relaxation time falls between that of the α and β relaxations. Second, the decay time constants are the same within 40% for PS with weight‐average molecular weights (M_w's) of 13,700–550,000 Da at temperatures well below the sample T_g's, indicating that the molecular relaxations involved are mostly local within the entanglement distance. Nonetheless, the temperature at which the rubbing‐induced molecular alignment disappears (T₀) exhibits a strong M_w dependence and closely approximates the T_g of the sample. Furthermore, T₀ depends notably on the thickness of the polymer in much the same way as previously found for the T_g of supported PS films. This suggests that the α process becomes dominant near T_g. Preliminary spectroscopic studies in the mid‐infrared range show a significant degree of bending of the phenyl ring toward the sample surface, with the C? C bond connecting the phenyl ring and the main chain tends to lie along the rubbing direction, which indicates that the relaxation is connected with the reorientation of this C? C bond. We exclude the observed relaxation, as predominantly a near‐surface one, because detailed studies on the effects of rubbing conditions on the degree of molecular alignment indicate that the alignment is not local to the polymer–air surface. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2906–2914, 2001     

An Attenuated Total Reflection FT‐IR Spectroscopic Study of Polyamide 6/Clay Nanocomposite Fibers

Summary: An attenuated total reflection FT‐IR spectroscopic study of the hydrogen bonding, molecular orientation, and crystalline phase transitions in polyamide 6 (PA6)/clay nanocomposite (PA6CN) fibers is proposed. The nanoscale dispersed clay layers lowered the degree of order of hydrogen bonding, affected little the hydrogen bonding strength, and increased the degree of orientation of both γ crystalline and overall domains. A partial γ to α phase transition appeared with time.

Schematic representation of the attenuated total reflection FT‐IR dichroism measurements.     

Characterization of the chemical composition of archaeological glass finds from South-Eastern Bulgaria using PIXE, PIGE and ICP-AES

Using PIXE (proton induced X-ray emission), PIGE (proton induced gamma emission) and ICP-AES (inductively coupled plasma-atomic emission spectroscopy) the concentrations of the 24 elements Al, As, Ba, Br, Ca, Cl, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Pb, Rb, S, Sb, Si, Sn, Sr, Ti, Zn and Zr in 53 archaeological glass samples from South-Eastern Bulgaria, were determined. The glasses are dated from the 1st to 6th century AD. The analytical data showed the samples to be typical soda-lime-silica glass, with natron as flux. A rather broad range of aluminium, titanium and iron impurities was found, with a tendency for more impure glass in the later periods. The decolouring agents were antimony and manganese oxides, with Sb prevailing in earlier, and Mn in later glass.     

NiMn-Based Bimetal–Organic Framework Nanosheets Supported on Multi-Channel Carbon Fibers for Efficient Oxygen Electrocatalysis

Developing noble-metal-free bifunctional oxygen electrocatalysts is of great significance for energy conversion and storage systems. Herein, we have developed a transformation method for growing NiMn-based bimetal–organic framework (NiMn-MOF) nanosheets on multi-channel carbon fibers (MCCF) as a bifunctional oxygen electrocatalyst. Owing to the desired components and architecture, the MCCF/NiMn-MOFs manifest comparable electrocatalytic performance towards oxygen reduction reaction (ORR) with the commercial Pt/C electrocatalyst and superior performance towards oxygen evolution reaction (OER) to the benchmark RuO₂ electrocatalyst. X-ray absorption fine structure (XAFS) spectroscopy and density functional theory (DFT) calculations reveal that the strong synergetic effect of adjacent Ni and Mn nodes within MCCF/NiMn-MOFs effectively promotes the thermodynamic formation of key *O and *OOH intermediates over active NiO₆ centers towards fast ORR and OER kinetics.     

Synthesis of Hydroxyapatite Nanorods under Mild Conditions and Their Drug Release Properties

Hydroxyapatite (HAp) nanorods possess vast potential applications in various fields, and here HAp nanorods with high aspect ratio were synthesized via a convenient two‐stage precipitation‐hydrolysis process at 60°C under atmospheric pressure. The precursor of CaHPO₄ at precipitation stage is well crystallized as nubby morphology with CTAB as surfactant, while CaHPO₄ was dissolved and CTA⁺ stabilized the HAp nuclei during the hydrolysis stage. OH^? ions were absorbed onto the active crystal surface, where Ca²⁺ and PO₄³⁺ reacted with OH^? to make the nuclei grow into larger crystals, and highly crystalline HAp nanorods were obtained by Ostwald ripening. The loaded drug of IBU on the HAp crystals can be 100% released in 24 h. PVP modified HAp nanorods can increase the drug‐loading capacity and release drug faster than pure HAp nanorods. The results indicate that HAp nanorods modified with suitable surfactants are of great use in drug delivery system.     

Facile synthesis of fluorescent carbon dots from shrimp shells and using the carbon dots to detect chromium(VI)

It is important to develop methods to sensitively and selectively determine chromium(VI) because chromium(VI) plays crucial roles in pathological and physiological processes. We developed an easy-to-perform, low-cost, and efficient method for synthesizing carbon dots from shrimp shells by calcining the shells without using any chemical reagents. The as-prepared carbon dots exhibited excitation-dependent fluorescence, with excitation and emission maxima at 350 and 400?nm, respectively. The Carbon dots were found to be excellent fluorescent probes for detecting chromium(VI) using the fluorescence quenching effect. The Carbon dots allowed chromium(VI) to be determined with a high degree of sensitivity. The chromium(VI) detection limit was 0.1?µM, and the relationship between the chromium(VI) concentration and the response was linear up to a chromium(VI) concentration of 70?µM. The method for synthesizing carbon dots is novel and the carbon dots produced offer promise for monitoring chromium(VI) in environmental matrices.     

Synthesis of Copper-Substituted CoS2@CuxS Double-Shelled Nanoboxes by Sequential Ion Exchange for Efficient Sodium Storage

The construction of hybrid architectures for electrode materials has been demonstrated as an efficient strategy to boost sodium-storage properties because of the synergetic effect of each component. However, the fabrication of hybrid nanostructures with a rational structure and desired composition for effective sodium storage is still challenging. In this study, an integrated nanostructure composed of copper-substituted CoS₂@Cu_xS double-shelled nanoboxes (denoted as Cu-CoS₂@Cu_xS DSNBs) was synthesized through a rational metal–organic framework (MOF)-based templating strategy. The unique shell configuration and complex composition endow the Cu-CoS₂@Cu_xS DSNBs with enhanced electrochemical performance in terms of superior rate capability and stable cyclability.