In-situ studies of electron field emission of single carbon nanotubes inside the TEM

Electron field emission characteristics of individual multi-walled carbon nanotubes (MWCNTs) were investigated in situ inside the transmission electron microscope (TEM). For a single MWCNT it was found that while field-emission can hardly occur from the side of the nanotube, a curved nanotube may result in finite side emission and the best emission geometry is the top emission geometry. Current-voltage (I-V) measurements made at different vacuum conditions and voltage sweeps emphasize the importance of the adsorbates on the electron field emission of MWCNTs. For a contaminated MWCNT, although the field emission current was reduced, the stability of its emission was improved. A current of up to several tens of μA was observed for a single MWCNT, but it was found that long time emission usually results in drastic structure damage that may lead to sudden emission failure.     

新型层状表面相锆基固体酸催化酯化反应研究

将所研制的层状表面相锆基固体酸催化剂用于一元、二元醇醋酸酯和其他羧酸酯类产品的合成 ,考察了其催化性能。研究发现 :层状表面相锆基固体酸催化剂对所考察的酯化反应具有很好的普遍适用性 ,但其酯化率与醇的性质和结构密切有关。催化反应动力学研究表明乙酸与丁醇、戊醇、己醇的酯化反应均为二级反应 ,且反应活化能均较低 ,分别为 47 4kJ/mol、2 3 3kJ/mol和 19 8kJ/mo     

Effect of temperature on polymer migration II: Concentration equation

Polymer migration is a generally well-known phenomenon in a flow field, and it has been verified that the sources of such phenomena are nonhomogeneity of the flow, concentration effects and hydrodynamic interactions between the polymer molecules. In addition, temperature effects were found to be another source of polymer migration. The Langevin equation for a polymer molecule was first derived from single chain dynamics using a kinetic theory for the bead-spring elastic harmonic dumbbell model, as described in part I (reference [1]). In this paper the diffusion equation and concentration profile of the polymer molecules induced by a temperature gradient are obtained from the Fokker-Planck equation. A new differential operator is also introduced to calculate the concentration profile. From the concentration equation obtained in the general flow geometry, we find that in dilute polymer solution there are significant effects on the polymer migration not only due to the nonhomogeneity of the flow field but also due to temperature gradients.     

Dependence of properties of liquid crystalline aromatic copolyesters on monomer sequence-copolyesters derived from terephthalic acid, 2,7-naphthalenediol and p-hydroxybenzoic acid

Summary An aromatic copolyester with the ordered sequence of terephthalic acid (TA)-p-hydroxybenzoic acid (HB)-2,7-naphthalenediol (ND)-p-hydroxybenzoic acid (HB) was prepared and its properties were compared with those of the corresponding random copolyester having the same overall monomer composition. Thermal and crystallizing properties of the two polymers are quite different. The former exhibits significantly higher glass transition and melting temperatures than the latter. The former's degree of crystallinity also is much higher than the latter's. Both polymers are thermotropic and form nematic melts.     

可降解聚丙烯发泡塑料初探

开发可降解聚丙烯(PP)发泡制品具有广阔的发展前景。PP自身的化学结构特点使其具有比其它聚烯烃和PS更优异的降解性能。在PP中添加各种光降解剂,或引入光敏基团可以促进PP的光降解性;将其与天然高分子或各种可降解塑料混合也可以有效促进PP的生物降解;将降解和发泡的配方和工艺合理结合以获得光降解性、生物降解性或光 生物双降解的发泡PP制品是完全可能的。     

功能性建筑涂料照亮市场

功能性建筑涂料除了具备普通建筑涂料的装饰作用外，还能起到某种功能性作用。随着国民经济的快速发展，其应用也越来越普遍，可以预期，功能性建筑涂料的实用性，拓宽建筑涂料的应用范围。本文作者庚晋介绍了几种功能性建筑涂料的特点、主要用途、最新研究动态、施工方法、市场前景等。     

Preparation,characterization, and adsorption properties for metal ions of a novel chelating resin containing sulfoxide and diethylene glycol

A novel chelating resin containing sulfoxide and diethylene glycol, poly{4‐vinylbenzyl‐[2‐2‐(hydroxyethyl)ethoxyl]sulfoxide} (PVESO) was synthesized using chloromethylated polystyrene (PS‐Cl) as material. Its structure was characterized by elemental analysis, infrared spectra, and scanning electron microscopy (SEM). The adsorption capacities of the resin for Hg²⁺, Ag⁺, Cu²⁺, Zn²⁺, and Pb²⁺ at various pH values were determined. The maximum adsorption capacities for Hg²⁺ and Ag⁺ were 1.56 and 0.75 mmol g^?1 respectively. The resin had high selectivity for Hg²⁺ and Ag⁺ over the pH range 1.0–7.0. The adsorption capacities for Hg²⁺ and Ag⁺ under competitive condition were also determined by batch experiment method. In addition, the adsorption kinetics of the resin towards Hg²⁺ at different temperatures was also investigated. The results showed that the adsorption rate was governed by film diffusion at 20°C and 25°C, by particle diffusion at 30°C and 35°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 6054–6059, 2006     

Propylene epoxidation in a microreactor with electric heating

Gas phase propylene epoxidation on gold catalysts has attracted wide attention from industry and academia due to its high selectivity. However, it suffers from low propylene conversion and rapid catalyst deactivation. Experiments showed that propylene conversion could be increased by raising H₂, O₂, or C₃H₆ concentration in the feed, but the feed compositions were within the explosion limit. It was also shown that the activity of the used catalyst could be fully recovered, but the regeneration temperature was 280 °C, much higher than that for reaction. Therefore a microchannel reactor was devised to suppress explosion and was constructed with Fecralloy, to raise the temperature rapidly for catalyst regeneration by electric heating. In two minutes the temperature of the reactor could be raised from 50 to 300 °C. Catalysts were coated on the alloy belt by dip coating, and the performance of the reactor was evaluated under different operating conditions. Results showed that in the microreactor the overall reaction rate was controlled mainly by the intrinsic reaction rate, and also influenced by film diffusion to a certain extent. The deactivated catalyst was regenerated in the microchannel reactor and the activity was fully recovered.     

Blends of chlorinated isotactic polypropylene with poly(ethylene-co-vinyl acetate) I. Effect of component polymers composition on the blend miscibility

Chlorinated isotactic polypropylenes (CPP) having various chlorine contents were blended with poly(ethylene-co-vinyl acetate)s (EVA) having various vinyl acetate (VA) contents. The blends were made by casting films from dilute THF solutions and miscibility of the blends was identified by single glass transition temperature, which was confirmed by DSC and dynamic mechanical measurements. Based on the miscibility data from a large number of CPP/EVA combinations, a miscibility map was depicted where CO equivalent weight (CO-EQW) of EVA was plotted against chlorine equivalent weight (Cl-EQW) of CPP. Though an attractive interaction between CPP and EVA could be detected in all the miscible and immiscible blend pairs, miscibility of the CPP/EVA blends could solely be observed in a relatively narrow range of Cl-EQW ca. 65–100 and CO-EQW ca. 170–230.     

硫醇自组装膜的电化学研究进展

综述了在金电极上硫醇自组装膜的电化学表征方法，性质和应用，介绍了自组装膜上的电子传递机理，并进行了简要的展望。