Microstructure and Ion Exchange in Stearic Acid Langmuir-Blodgett Films Studied by Fourier Transform Infrared-Attenuated Total Reflection Spectroscopy

Fourier transform infrared-attenuated total reflection (FTIR-ATR) spectra have been recorded of 11-layer Langmuir-Blodgett (LB) films of stearic acid deposited at various surface pressures (0.1, 15, and 35 mN/m), and the molecular orientation angles were evaluated quantitatively, which supplied insight into the molecular order with the alkyl chains tightly packed like crystal in the LB films deposited at the zero and higher surface pressures. These experimental results indicate that, in the Langmuir film as the precursor of LB films, stearic acid molecules self-aggregate to form two-dimensional crystalline domains already even at the zero surface pressure, which results in the inhomogeneity of monolayer. The analysis of dependence of nu(C=O) intensity on the surface pressure, surface density, and subphase temperature leads to the conclusion that the defects in LB films originate from the Langmuir film and be conserved upon deposition. Annealing below 50 degrees C and cooling could improve the monolayer homogeneity, and thus a defect-free or low-defect LB films can be deposited. Furthermore, ion exchange conducted in the LB films, on the other hand, confirms the existence of structure defects in LB films of stearic acid. The polar plane microstructure, lateral transport along the polar planes and the coordination types of stearic acid/cation system may be the rate-limiting process. The results have implication on the possible uses of stearic acid LB films as ion-exchange materials or sensors. Copyright 2001 Academic Press.     

六甲基环三硅氧烷非平衡聚合的研究

六甲基环三硅氧烷(D_3)在为催化剂,二甲亚砜为促进剂的情况下聚合,得到了分子量分布窄且没有大环体的聚二甲基硅氧烷。本文指出了反应溶液中溶解的氧会降低催化剂的活性。在除去了溶液中的氧以后,聚合反应速度大为加快,D_3转化率几乎达100％,而且得到的聚合物是活性高分子,可以继续进行聚合。同时还研究了在除氧以后D_3非平衡聚合反应的特点。     

Single Atom Alloy Preparation and Applications in Heterogeneous Catalysis

There have been remarkable progresses in manipulating heterogeneous catalysts' nanostructures in the past decade. The concept of single atom alloy (SAA) was firstly proposed in 2012 when researchers successfully stabilized single Pd atoms on the Cu(111) surface. However, earlier work in 2009, which focused on replacing one Au atom with a Pd atom in thiolate protected Au₂₅ nanoclusters, could also be considered as the pioneer work of single atom alloy. Both kinds of single atom alloys exhibited the potential of maximum utilization of scarce elements and attractive catalytic performances. The well‐defined structures of SAA catalysts make accurate modeling possible, which further realizes the rational design of single atom alloy catalysts. In this review, we summarize the research trajectory of single atom alloys as well as recent achievements in this field. We also introduce several commonly adopted characterization methods for SAA catalysts such as scanning tunneling microscopy (STM), temperature programmed reaction (TPR), extended X‐ray absorption fine structure (EXAFS) spectra, matrix assisted laser desorption/ionization mass spectrum (MALDI‐MS) and differential pulse voltammetry (DPV). Through discussing recent progresses in SAA catalysts, we propose that future researches in this filed should be focused on exploring new kinds of metal nanocrystals and controlling the nanostructure of SAA even more precisely.     

Phase separation in the formation of hollow particles by suspension polymerization for divinylbenzene/toluene droplets dissolving polystyrene

Phase-separation behavior within polymerizing divinylbenzene/toluene droplet dissolving polystyrenes (PS) was investigated to clarify the formation mechanism of the hollow polymer particles by suspension polymerization. No hollow particles were obtained at a low content of low-molecular-weight PS where phase separation occurred at high conversion. On the other hand, hollow particles were obtained at a high content of high-molecular-weight PS where phase separation occurred at low conversion. The phase separation in an early stage of the polymerization, which was promoted by the presence of PS and cross-links of polydivinylbenzene, was a key factor for the formation of the hollow structure.     

HS-6顶空进样器的性能考察及其应用

考察了连接在Sigmal气相色谱仪上的HS-6顶空分析器的性能,特别注意考察了样品的体积,平衡所需时间和分流比等对保留时间和峰高的影响,研究结果还表明增加样品的加热温度和稀释样品的浓度会改善测定的灵敏度,文章还给出了一系列不同类型样品的应用结果,包括香烟、茶叶、啤酒、中药等。     

分析裂化气中0.5ppm～1%含量的杂质烃

本文介绍了一种分析裂化气中杂质烃的方法。所建分析系统由填充玻璃毛细管柱和填充预柱各一根、阀和FID各一个组成。采用一次进样、外标法定量,约30分钟即可完成测定裂化气中低至0.5ppm含量的痕量C_2～C_4炔和二烯。方法适用围范至少是0.5ppm～1%。当样品含量为1～5 ppm时,相对标准偏差小于50%。     

手性酰胺聚硅氧烷固定相的制备与气相色谱性能

以L-苯丙氨酸,L-缬氨酸为手性源,合成了二种含末端烯基,具有刚性苯基链节的新型手性酰胺单体;并通过硅氢加成方法将其接枝到含氢硅油上,制备了两种新型手性酰胺聚硅氧烷固定相.这一新方法具有简单易行,各步产率较高的优点,所制备的手性固定相具有较好的毛细管柱色谱性能.手性拆分能力和耐温性.     

二苄亚砜硝酸钕的晶体结构

二苄亚砜硝酸钕Nd(NO_3)_3·[(C_6H_5CH_2)_2S0]属三斜晶系,P1空间群,晶胞参数:a=9.835(2),b=12.445(2),c=19.971(5)A,α=104.13(2)°,β=90.34(2)°γ=74.96(1)°Z=2。晶体结构用重原子法解出,经最小二乘修正后R因子为0.031。钕离子由九个氧配位,形成稍歪扭的三帽三方棱柱配位多面体,其中一个三角面由三个二苄亚砜(DBSO)提供的氧形成,其他氧原子则由硝酸根提供。平均Nd-O(DBSO)=2.379A,Nd-O(NO_3)=2.536A。     

等温气液平衡盐效应的研究——有机溶剂-水-无机盐体系

本文报导了甲醇-水-氯化锂、乙醇-水-氯化锂、丙酮-水-氯化锂和丙酮-水-碳酸钾体系在298.15 K时的等温气液平衡数据, 以及用三参数Margules公式的关联结果。提出了由等温气液平衡数据计算混合溶剂中盐的溶剂化数的理论公式。     

Preparation and electrochemistry of azobenzene self-assembled monolayers on gold--long range tunneling and end-group hydrogen bonding effect

A series of thiol-functionalied azobenzene derivatives (RAzoCnSH: R=H for n=3-6, abbreviated as AzoCnSH; R=CH(3)CONH for n=4, abbreviated as aaAzoC4SH) on gold electrodes were prepared and their self-assembly and electrochemical properties were studied by cyclic voltammetry. They all formed uniform and reproducible self-assembled monolayers (SAMs) on gold and showed well-behaved voltammetric responses in aqueous solution. Both the length of the alkyl chain spacer and the H-bonding of the end acetamino group had effects on the stability and the electrochemical kinetics of the SAMs, and the effect of the H-bonding was dominant. The surface coverage of the SAMs (AzoCnSH) is gradually increased with an increase of the alkyl chain spacer length, whereas the presence of the terminal acetamino group leads to a greater increase of the surface coverage. At a low scan rate, voltammetric responses corresponding to an irreversible two-electron, two-proton reduction/oxidation of the trans-azobenzene redox center were obtained in the range of +300 mV and -800 mV, which exhibited very large peak-to-peak splitting. At a high scan rate of 500 mV/s, two steps of reversible one-electron, one-proton reduction/oxidation corresponding to the cis-isomer in azobenzene-thiol SAMs (n is odd) was clearly observed between +300 and -200 mV. The apparent electron-transfer rate is decreased with increasing distance between the azobenzene redox center and the gold electrode. The existence of the end acetamino group which restricted the conformational change during the redox process also led to a decrease of the standard rate constant, and this restriction effect is more predominant than the distance effect.