Hydrolytic degradation of carbohydrate-based polyamides of the AABB type derived from l-arabinose and d-xylose

The hydrolytic degradation of a series of aregic carbohydrate-based polyamides derived from l-arabinose and d-xylose is described. These polyamides are those that are fully sugar-based (PA-SuSu), those derived from aldaric acids and polyalkylene diamines (PA-mSu), and those derived from diamine sugars and polyalkylene dicarboxylic acids (PA-Sun). Their physical properties and crystal structures depend on their constitution and the configuration of the carbohydrate-based moiety. The feasibility of the hydrolysis of these polyamides was, in general, related with such structural properties. Thus, the fully sugar-based PA-SuSu were amorphous, water-soluble materials, and were hydrolysed in water at 70 °C. PA-mSu were crystalline and more resistant to hydrolysis — they were degraded at pH 2 and 70 °C [T_g(s) 60-90 °C]. PA-Sun were amorphous and highly hygroscopic materials — they were hydrolysed in water at 37 °C [T_g(s) 25-40 °C].     

MgO负载Fe基催化剂选择性合成单/双/多壁碳纳米管

通过浸渍及水热处理获得MgO负载的Fe基催化剂,并将其用于化学气相沉积过程裂解甲烷获得碳纳米管.结果表明,单/双/多壁碳纳米管可选择性地生长在Fe负载量不同的Fe/MgO催化剂上.当Fe负载量仅为0.5%时,铁原子在载体表面烧结为0.8～1.2nm的铁颗粒,碳在这种小颗粒上以表面扩散为主,导致单壁碳纳米管形成,并且单壁碳纳米管的选择性高达90%.当Fe负载量提高到3%时,铁原子聚集成约2.0nm的颗粒,在化学气相沉积中生长碳纳米管时,碳在Fe催化剂颗粒中的体相扩散的贡献增大,在表相扩散和体相扩散的共同作用下,双壁碳纳米管的选择性显著增高.当进一步增加Fe负载量时,铁原子烧结形成1～8nm的颗粒,经过化学气相沉积,在催化剂上生长了单、双、多壁碳纳米管.随着Fe在MgO载体上负载量的增加,管径、管壁数以及半导体管的含量都增加.本研究提供了一种适合大批量选择性生长单/双/多壁碳纳米管的方法.     

含四硫富瓦烯结构单元的酞菁和四氮杂卟啉衍生物的研究概况

综述了含四硫富瓦烯(TTF)结构单元的酞菁和四氮杂卟啉衍生物的合成、光物理和电化学性质以及聚集和自组装性能的研究概况.     

Dynamic adhesion behavior of micrometer-scale particles flowing over patchy surfaces with nanoscale electrostatic heterogeneity

The dynamic adhesion behavior of micrometer-scale silica particles is investigated numerically for a low Reynolds number shear flow over a planar collecting wall with randomly distributed electrostatic heterogeneity at the 10-nanometer scale. The hydrodynamic forces and torques on a particle are coupled to spatially varying colloidal interactions between the particle and wall. Contact and frictional forces are included in the force and torque balances to capture particle skipping, rolling, and arrest. These dynamic adhesion signatures are consistent with experimental results and are reminiscent of motion signatures observed in cell adhesion under flowing conditions, although for the synthetic system the particle–wall interactions are controlled by colloidal forces rather than physical bonds between cells and a functionalized surface. As the fraction of the surface (Θ) covered by the cationic patches is increased from zero, particle behavior sequentially transitions from no contact with the surface to skipping, rolling, and arrest, with the threshold patch density for adhesion (Θ_crit) always greater than zero and in quantitative agreement with experimental results. The ionic strength of the flowing solution determines the extent of the electrostatic interactions and can be used to tune selectively the dynamic adhesion behavior by modulating two competing effects. The extent of electrostatic interactions in the plane of the wall, or electrostatic zone of influence, governs the importance of spatial fluctuations in the cationic patch density and thus determines if flowing particles contact the wall. The distance these interactions extend into solution normal to the wall determines the strength of the particle–wall attraction, which governs the transition from skipping and rolling to arrest. The influence of Θ, particle size, Debye length, and shear rate is quantified through the construction of adhesion regime diagrams, which delineate the regions in parameter space that give rise to different dynamic adhesion signatures and illustrate selective adhesion based on particle size or curvature. The results of this study are suggestive of novel ways to control particle–wall interactions using randomly distributed surface heterogeneity.     

Crystal structure and vapor pressure of a copper(II) complex with 2,2,6,6-tetramethyl-4-fluoroheptane-3,5-dione

Synthesis and single crystal X-ray diffraction study were carried out for copper(II) 2,2,6,6-tetramethyl-4-fluoroheptane-3,5-dionate (Bruker AXS P4 automated diffractometer, MoK _α radiation). Crystal data for C₂₂H₃₆CuF₂O₄: a = 5.9165(4) Å, b = 10.2787(7) Å, c = 10.5223(8) Å, α = 81.383(3)°, β = 76.106(3)°, γ = 83.778(3)°, space group P $\bar 1$ , V = 612.42(7) ų, Z = 1, d _x = 1.264 g/cm³. The structure is molecular; the copper atom has a square plane coordination formed by the oxygen atoms of two β-diketonate ligands; the average Cu-O distance is 1.895 Å, ∠O-Cu-O 92.5°. Only van der Waals interactions are realized between the molecules in the structure. The temperature dependences of the saturated vapor pressure were studied by the mass transfer technique, and the standard thermodynamic parameters of sublimation were derived for the complex, ΔH _subl ⁰ = 115.6 ± 1.1 kJ/mol, ΔS _subl ⁰ = 204.9 ± 2.5 J/mol·K.     

Building an oxidation reactor in Taiwan: From volatile organic compounds to secondary organic aerosols

Large amounts of volatile organic compounds (VOCs) are emitted into the atmosphere from both human and natural sources. A significant portion of VOCs would be oxidized via their reactions with atmospheric oxidants like OH, NO₃, ozone, etc. The products of the oxidation reactions are often of low volatility and may condense to form secondary organic aerosols (SOA). To study the effect of VOC oxidation in aerosol formation, we are building an oxidation flow reactor system, which consists of (1) a 22-l aluminum chamber, (2) an ozone source with an ozone detector, (3) a UV-C (254 nm) lamp, (4) a photoionization detector to measure the effective VOC concentration, (5) various flow/concentration controlling apparatuses, and (6) a scanning mobility particle sizer to monitor the generated particles. Under the conditions of high UV and ozone levels, the oxidation process can be speeded up by orders of magnitude in this reactor. We hope to use this reactor: (i) to learn the “potential” mass of SOA that can be formed from a given VOC source like a traffic or industry site; (ii) to trace back the SOA source by utilizing the shortened reaction times; (iii) to learn the trends from VOC to SOA.     

High-pressure infrared spectroscopy of ionic liquids mixed with Tween 80

In this study, the possibility of using Tween 80 to disturb the microstructures of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF₄) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF₆) was investigated under high pressures. The imidazolioum C H absorptions of pure ionic liquids (ILs) are significantly blue-shifted under high pressures. However, mild changes in imidazolioum C H stretching frequencies were observed for IL/Tween 80 mixtures. Tween 80 may hinder cations of ILs to form network structures with anions under high pressures via pressure-enhanced cation-Tween 80 interactions. Based on the experimental results, Tween 80-[BMIM]PF₆ interactions are more effective in disturbing the local structure of imidazolium C H than Tween 80-[BMIM]BF₄ interactions.     

氟化氢溶液无电沉积法制备W掺杂Ag树枝晶

应用无电沉积在氟化氢溶液制备W掺杂Ag树枝晶,样品由XPS,XRD,SEM和TEM表征,结果表明在Ag-W二元体系中,Ag的生长起主导作用,不受钨酸根离子而改变。提出W元素的掺杂方式,即W元素的掺杂是在银的沉积过程中通过化学吸附—钨酸根二聚体的氧原子与银原子的化学作用力而实现的。循环伏安法用于检测银氧间的化学键能的强弱。     

Effects of rubber type on the curing and physical properties of silica filled rubber compounds

As environmental regulations are getting stricter, tire industries for automobiles have shown much interest in substituting silica for conventional carbon black partially or entirely. To take full advantage of silica as fillers for rubbers, it is essential to find a reasonable rubber system that shows an excellent performance with silica reinforcement. Therefore, in this study, several different rubber compounds comprising the same amount of silica were prepared with several different rubber systems, respectively. The processability, curing characteristics, and mechanical and viscoelastic properties of the rubber compounds were investigated to analyze the performance of the rubber compounds as tire tread materials. Among the rubber compounds studied, SBR1721 compound comprising natural rubber (NR) and styrene butadiene rubber (SBR) with high styrene content was considered the most appropriate for application to tire tread materials. Copyright © 2008 John Wiley & Sons, Ltd.