Thermotropic and optical behaviour of new PDLC systems based on a polysulfone matrix and a cyanoazomethine liquid crystal

The thermotropic and optical characterisations of a novel polymer dispersed liquid crystal (PDLC) system based on polysulfone UDEL P-1700 as polymer matrix and a low molecular weight liquid crystal compound containing a mesogenic azomethine core and a cyano-substituent were investigated. The PDLC samples were prepared by solvent-induced phase separation (SIPS) and thermally induced phase separation (TIPS) methods using various compositions in the two components. Information on the morphology and phase structure was obtained by polarising optical microscopy, differential scanning calorimetry and X-ray diffraction measurements. PDLC systems with well-defined droplets were obtained for the composite with medium content of liquid crystal compound. The optical characterisation of these materials was performed by analysing their UV–visible absorption and photoluminescence emission as a function of the liquid crystal aggregation degree.     

超细磁性钴粉的制备及磁性能

在室温条件下,水溶液中以聚乙烯吡咯烷酮K30(PVP)作为分散剂,水合联氨为还原剂,制备超细磁性钴粉。用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、能谱仪(EDS)和振动样品磁强计(VSM)对其进行表征。结果显示:超细磁性钴粉为蠕虫状微球,粒径约为0.8μm,晶型为面心立方(FCC)和六方密堆积(HCP)结构,饱和磁化强度为25.6 emu·g^-1,矫顽力为499.2 Oe(1 Oe=79.5775 A·m^-1,测试温度为298.15 K)。     

纳米三氧化钨的制备、表征及对六硝基六氮杂异伍兹烷热分解的影响

采用水热法通过控制前躯体钨酸钠的加入量和反应时间制备了长方体形纳米WO₃,利用X射线粉末衍射(XRD)、透射电镜(TEM)、扫描电镜及能量散射光谱仪(SEM-EDS)对样品进行表征。并运用差示扫描量热法(DSC)研究纳米WO₃对六硝基六氮杂异伍兹烷(CL-20)热分解特性的影响。结果表明:与单组分CL-20相比,纳米WO₃的加入使复合物WO₃/CL-20的热分解峰温降低2.95℃,活化能减小7.74 kJ·mol^-1,因此纳米WO₃能够加速CL-20的热分解。     

Determination of perfluorinated compounds in environmental water samples by high-performance liquid chromatography-electrospray tandem mass spectrometry using surfactant-coated Fe3O4 magnetic nanoparticles as adsorbents

A novel method was developed for solid-phase extraction (SPE) of perfluorinated compounds (PFCs) from environmental water samples using cetyltrimethylammonium bromide (CTAB) coated Fe₃O₄ nanoparticles (Fe₃O₄ NPs) as an adsorbent. The magnetic nanosized adsorbent has a large surface area and superparamagnetic properties. This gives it a high extraction capacity and allows for convenient isolation by a magnetic field. Compared with other SPE methods and our previous work on PFCs, this method exhibited a fairly good analytical performance and required a small amount of sorbent (50 mg) and short pretreatment times (30 min) for 800 mL environmental water samples. Seven PFCs, including perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), perfluoroundecanoic acid (PFUnDA), perfluorododecanoic acid (PFDoDA), and perfluorotetradecanoic acid (PFTA), extracted by the optimized method were determined by high-performance liquid chromatography-electrospray tandem mass spectrometry (HPLC/ESI-MS/MS). A concentration factor of 1600 was achieved when extracting 800 mL of several environmental water samples. Detection limits obtained for PFOA, PFOS, PFNA, PFDA, PFUnDA, PFDoDA and PFTA were 0.14, 0.022, 0.31, 0.23, 0.11, 0.16, 0.091 ng/L, respectively. The relative standard deviations of recoveries ranged from 1 to 8%, indicating good method precision.     

颗粒聚合体碰撞破损的细观力学仿真研究

粉末和颗粒材料常常以聚合体(agglomerate,还可译成结块, 聚团等)的形式存在.无论是自然环境中还是工业处理过程中, 微小颗粒聚合体碰撞破损是一常见物理现象.近十几年来, 对颗粒聚合体碰撞研究在试验和数值模拟方面均取得了很大的进展.特别是利用颗粒离散元方法, 结合经典接触力学理论, 对微米颗粒聚合体碰撞破损的细观力学机理进行的研究, 取得了很多重要成果.基本形成了较为完善的模拟分析方法, 提出了许多新概念, 形成了目前适于分析研究的专用分析程序.本文介绍了目前国际上颗粒聚合体碰撞破损模拟研究的一般方法和理论, 总结了现有的主要研究内容及成果, 并提出一些研究展望.      

SURFACE EFFECT ON NANOSIZED VOID GROWTH IN A RIGID-PERFECTLY PLASTIC MATERIAL

The influence of the surface effect on the nanosized spherical void growth in a rigidperfectly plastic material is analyzed and the mechanism of the nanosized void growth with high triaxiality is given. Based on the Rice and Tracey model for a macro void growth, the present model is proposed to account for the nanosized void growth under a uniform remote strain rate field with consideration on the surface effect. It is concluded that the surface effect yields an evident resistant influence on the nanosized void growth. That is, this influence decays as the void radius increases. With high triaxiality, the nanosized void growth is divided into two stages： the initial stage and the mature stage. At the first stage, the void grows slowly and the influence of surface effect is relatively weak, whereas at the second stage, the influence is significant and the void grows drastically.     

Particle size of powders under hydrothermal conditions

Various non‐oxide (CuI, AgI, AgCl, PbS, CuS and ZnS) and oxide (ZnO, TiO₂, SnO₂, CeO₂ and ZrO₂) powders were prepared under hydrothermal conditions to investigate the effects of temperature, pH and precursors on the particle size of powders. It was found that the particle sizes of PbS, CuS and ZnS powders were much smaller than that of CuI, AgI and AgCl powders prepared under the same conditions. The particle sizes of TiO₂, SnO₂, CeO₂ and ZrO₂ powders are much smaller than that of ZnO powders prepared under the same conditions. It is concluded that the solution conditions have a certain effect on the particle size of powders under the hydrothermal conditions. The particle size of powders increased with the rising of temperature. Additional factors affecting the particle size were uncovered through studying the nucleation mechanism. The particle size was mainly related to the Madelung constant and the electric charge number of ions. Powders with smaller particle size resulted from systems that possessed the larger Madelung constant and ionic charge number. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure and magnetism of manganese‐doped ZnO powder samples

The magnetic and structural properties of manganese‐doped ZnO powder samples prepared by a solid state method are reported. Magnetization measurements indicate ferromagnetic behavior, with hysteresis observed in the M vs. H behavior at 300 K. Coercive fields were <100 Oe at 300 K. Temperature‐dependent magnetization measurements showed evidence for ordering temperatures of >300 K. However, the results show that ferromagnetism originates from the doped matrix rather than any type of magnetic cluster and the ferromagnetism is due to the defects and/or oxygen vacancies confined to the surface of the grains. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)