Synthesis and thermal behavior of gem-dinitro valerylated polystyrene

Commercial polystyrene has been chemically modified with 4,4-dinitro valeryl chloride by use of Friedel–Crafts acylation reaction in the presence of anhydrous aluminum chloride in a mixture of 1,2-dichloroethane and nitrobenzene. The modified polystyrene containing –COCH₂CH₂C(NO₂)₂CH₃ fragments in side phenyl rings, named gem-dinitro valerylated polystyrene (GDN-PS), was characterized by an Ubbelohde’s viscometer, FTIR, and ¹H NMR spectroscopy. Simultaneous thermogravimetry–differential thermal analysis and differential scanning calorimetry (DSC) have been used to study thermal behavior of the polymer. The results of TG analysis revealed that the main thermal degradation for the GDN-PS occurs during two temperature ranges of 200–300 and 300–430 °C. The DTA curve of GDN-PS is showing a visible exothermic peak at 253.8 °C corresponding to the decomposition of gem-dinitro valeryl groups. The decomposition kinetic of the gem-dinitro groups for GDN-PS with degree of substitution (DS) 11 % was studied by non-isothermal DSC under various heating rates. Kinetic parameters such as activation energy and frequency factor for thermal decomposition of GDN-PS with DS 11 % were evaluated via the ASTM E698 and two isoconversional methods.     

The Shackling Effect in Cyclic Azobenzene Liquid Crystal

We demonstrate here a novel method for the design of liquid crystals (LCs) via the cyclization of mesogens by flexible chains. For two azobenzene-4,4′-dicarboxylate derivatives, the cyclic dimer, cyclic bis(tetraethylene glycol azobenzene-4,4′-dicarboxylate) (CBTAD), shows LC properties with smectic A phase, while its linear counterpart, bis(2-(2′-hydroxyethyloxy)ethyl azobenzene-4,4′-dicarboxylate (BHAD), has no LC phase. The difference is ascribed to the shackling effect from the cyclic topology, which leads to the much smaller entropy change during phase transitions and increases the isotropic temperature greatly for cyclics. In addition, the trans-to-cis isomerization of azobenzene groups under UV-light is also limited in CBTAD. With the reversible isomerization of azobenzene groups, CBTAD showed interesting isothermal phase transition behaviors, where the LC phase disappeared upon photoirradiation of 365 nm UV-light, and recovered when the UV-light was off. Combined with the smectic LC nature, a novel UV-light tuned visible light regulator was designed, by simply placing CBTAD in two glass plates. The scattered phase of smectic LC was utilized as the “OFF” state for light passage, while the UV-light induced isotropic phase was utilized as the “ON” state. The shackling effect outlined here should be applicable for the design of cyclic LC oligomers/polymers with special properties.

     

Impact of the flexibility of pillar linkers on the structure and CO_2 adsorption property of ‘‘pillar-layered' MOFs

A new metal–organic framework {[Zn_2(bpta)(bpy-ee)(H_2O)_2]·x solve}_n(1)(H_4bpta = biphenyl-2,20,6,60-tetracarboxylic acid and bpy-ee = 1,2-bis(4-pyridyl)ethylene) has been obtained under hydrothermal condition, and structurally characterized by single-crystal X-ray diffraction. Complex 1 reveals a threedimensional(3D) ‘‘pillar-layered' framework with non-flexible linker, in which some different structure characters can be found compared to that of some related other ‘‘pillar-layered' MOFs based on flexible pillar linkers. It demonstrates the impact of the flexibility of pillar linker on the final structure in this system. In addition, the selective CO_2 adsorption performance of 1 was also investigated.     

新水溶性卟啉季铵盐的合成及与锌的显色反应研究

合成了-种新型水溶性卟啶卟啉季铵盐即溴化5-[(4-N-芐基)吡啶基]10,15,20-(4-N-吡啶基)卟啉,研究了该试剂与锌的显色反应.在pH2.5的邻苯二甲酸氢钾-盐酸缓冲溶液中,形成了配位比为1:1的配合物,基最大吸收波长λ=424nm,表现摩尔吸光系数ε=2.03×105L·mol-1·cm-1.在0-1.2μg/10mL范围内吸光度与锌质量浓度关系符合比耳定律,该法灵敏度高、选择性好.本法应用于环境水试样中痕量锌离子的分析,结果令人满意.     

Single top production associated with a neutral scalar at LHC in topcolor-assisted technicolor

The topcolor-assisted technicolor(TC2)model predicts a number of neutral SCalars like the top-pion (π0t)and the top-Higgs(h0t).These scalar8 have flavor-changing neutral-current(FCNC)top quark couphngs,among which the top-charm transition couplings may be sizable.Such FCNC couplings induce single top productions associated with a neutral scalar at the CERN Large Hadron Collider(LHC)through the parton processes cg→tπ0t and cg→th0t.In this paper we examine these productions and find their production rates can exceed the 3σ sensitivity of the LHC in a large part of parameter space.Since in the Standard Model and the minimal supersymmetric model such rare productions have unobservably small production rates at the LHC.these rare processes will serve as a good probe for the TC2 model.     

Ultrasensitive and selective colorimetric detection of thiourea using silver nanoprobes

A novel colorimetric thiourea (TU) sensor was developed utilizing citrate modified silver nanoparticles (AgNPs). The introduction of TU reduced the overall surface charges of the AgNPs, resulting in aggregation of AgNPs and a colorimetric response correlating with the concentration of TU. The detection of TU could be realized within 2 min, with an ultralow detection limit of 0.8 nM by the absorption method. In addition, the AgNPs sensor also showed good selectivity in the presence of potential interfering compounds. Since common steps such as modification and separation could be successfully avoided, the sensor developed here could provide a simple, cost-effective yet rapid and sensitive measurement tool for TU detection, and may provide new opportunities in the development of sensors for food safety and environmental monitoring in the future.     

硼烯和碱土金属硼化物二维纳米材料的制备、结构、物性及应用研究

随着石墨烯研究的兴起,二维纳米材料得以迅速发展.在众多的二维纳米材料中,硼烯和碱土金属硼化物二维材料由于具有高费米速度、高杨氏模量、高透光性、高延展性、高度的各向异性、大的泊松比和高的化学稳定性等独特的性质,成为研究人员关注的焦点.本文侧重介绍目前硼烯和碱土金属硼化物二维纳米材料的制备工艺、结构、物性和应用情况.首先总结了目前硼烯的主要结构构型和制备及掺杂工艺;其次介绍了碱土金属硼化物二维纳米材料的理论结构构型和可能的制备路线;最后对硼烯和二维碱土金属硼化物纳米材料的物理特性进行归纳总结,同时预测它们未来最可能实现应用的领域.     

“Oxidative etching-aggregation” of silver nanoparticles by melamine and electron acceptors: An innovative route toward ultrasensitive and versatile functional colorimetric sensors

An innovative and versatile functional colorimetric sensor for melamine (MA) and H₂O₂ was developed with simplicity, excellent selectivity and ultrasensitivity. The detection mechanism was based on the “oxidative etching-aggregation” of silver nanoparticles (AgNPs) by the cooperation effect of MA and electron acceptors such as H₂O₂, ozone or Fe(NO₃)₃. The detection limits of this method for MA could reach as low as 0.08 nM, 0.16 nM and 3 nM when H₂O₂, ozone or Fe(NO₃)₃ was used as an electron acceptor, respectively. When using H₂O₂ as a typical electron acceptor, the method enabled the detection of H₂O₂ with a detection limit of 0.2 nM. This proposed method offered a new way to design MA and H₂O₂ sensors and might be easily extended to detect other nucleophilic reagents and electron acceptors based on colorimetric sensors.     

Detailed Characteristics of Expansion Velocity of Si from Laser Ablated SiC

Optical emission of plasma is used to investigate the characteristics of dynamics distribution in the plume gen- erated by ablation of a SiC sample using Nd：YAG laser. The plume expansion dynamics is characterized by time-of-flight measurement. We find that the profiles of Si （I） （390.55 nm） split into two components and the Si （1I） （634. 71 nm） spectra show two distinct expansion dynamics regions. The time-of-flight measurement of Si（ll） （634. 71 nm） under different laser irradianee conditions, from 0.236 G W/cm^2 to 1.667 G W/cm^2, are presented and discussed.     

新型光谱曲线特征参数与水稻叶绿素含量间的关系研究

利用高光谱信息检测作物叶绿素含量信息是田间作物长势诊断的重要研究内容。利用水稻光谱和叶绿素含量田间实测数据,从作物叶绿素含量不同,光谱曲线峰谷波形有高矮胖瘦形态变化的观点出发,提出光谱曲线峰谷波形中特征边的上升、下降速率以及组成峰谷波形两边的夹角等新型特征量,利用归一化光谱信息,分析了这些变量与水稻叶绿素含量间的相关关系。研究结果显示:(1)可见光波段范围520～740nm之间的归一化光谱反射率与叶绿素含量间呈良好的负相关关系;(2)绿峰反射光谱曲线特征边的变化速率及绿峰两边的夹角等变量与水稻叶绿素含量具有较好的相关性,表明利用这些新型变量开展叶绿素含量高光谱无损监测成为可能,这将为利用高光谱信息开展作物长势与营养诊断提供新的思路和方法。