Sol–gel preparation of antireflective coatings at 351 nm with different thickness and improved moisture-resistance

Antireflective (AR) coatings at 351 nm with different thickness were designed and prepared by sol–gel process using tetraethylorthosilicate as precursor and ammonia as catalyst. The parameters of these coatings, including film thickness and refractive index, were calculated by optical formula and the coatings were prepared accordingly. Sol dilution method was used to adjust the film thickness. The wavelengths of maximum transmission measured by UV–Vis spectrophotometer, were used to monitor the film thickness. It was found that AR coatings with higher thickness possess better abrasion-resistance. Hydroxyl terminated polydimethylsiloxane (PDMS) was added into pure silica sol to improve both the abrasion-resistance and moisture-resistance of AR coating.     

具有负泊松比效应的2D碳纳米结构设计及其性能的理论计算研究

本文利用第一性原理PBE密度泛函理论计算的方法设计了一种由炔基链、吡啶环及少量氢原子组成的具有内凹六边形结构单元的新型理想二维碳纳米结构,并对其平面内负泊松比效应等力学性能和光学性能与电子结构进行了预测.计算表明,该2D材料具有较好的结构稳定性和特殊的力学性能.当将该2D结构在面内(bc面)沿c方向压缩时,其在b方向收缩;当沿c方向拉伸时,其在b方向伸长,即该2D结构同样具有期望的负泊松比效应.材料的泊松比为-3.26;将该2D结构沿b方向拉伸时,c方向将随之伸长;沿b方向压缩时,c方向将随之收缩.沿b方向拉伸或压缩时,泊松比约为-1.951.即该2D材料在面内具有非常显著的负泊松比效应.此外,该2D材料表现出半导体材料的电子结构特征和良好的光反射和折射性能.希望本工作能为具有本征负泊松比效应和优良电子与光学功能的理想二维碳纳米材料的开发提供一种理想的结构设计策略.     

Strain induced topological transitions in twisted double bilayer graphene

We theoretically study the band structures and the valley Chern numbers of the AB–AB and AB–BA stacked twisted double bilayer graphene under heterostrain effect. In the absence of heterostrain, due to the constrains by the spatial symmetries, the central two flat bands of the AB–AB are topological trivial bands, while in the AB–BA they have a finite Chern number. The heterostrain breaks all the point group symmetries and the constrains are lifted, hence the topological properties of the two arrangements can be tuned by different strain magnitudes ϵ and directions ϕ. The heterostrain has dissimilar impacts on the Chern numbers of the AB–AB and AB–BA, owing to their different band gaps, and these gaps can be modified by a vertical electric field. Our results show that the topological transitions for both arrangements occur in the ϵ range of 0.1%–0.4%, which can be realized in the graphene-based sample.     

Effect of Hydrogen on Dislocation Nucleation and Motion:Nanoindentation Experiment and Discrete Dislocation Dynamics Simulation

The hydrogen effect on the nucleation and motion of dislocations in single-crystal bcc Fe with(110)surface was investigated by both nanoindentation experiments ...     

Synthesis and fluorescence properties of 7-hydroxy-3-(2-pyridyl)coumarin derivatives

Three coumarin derivatives, 7-hydroxy-3-(2-pyridyl)coumarin (HPC), 7-(4-(5-(4-tert-butylphenyl)-1,3,4-oxadiazol-2-yl)benzyloxy)-3-(2-pyridyl)coumarin (Ox-PC), and 7-(4-(9H-carbazol-9-yl)butoxy)-3-(2-pyridyl)coumarin (Cz-PC), were synthesized and characterized by elemental analysis, ¹H NMR, FT-IR, and UV?Cvis absorption spectra. The fluorescence behaviors of the compounds in methanol solutions and solid states were investigated. HPC exhibits weak green emission, whereas Cz-PC and Ox-PC show strong blue emissions in dilute solutions.     

Sol–gel preparation of double-layer tri-wavelength antireflective coating

Double-layer tri-wavelength antireflective (AR) coating effective simultaneously at 351, 527 and 1,053?nm has been designed and prepared by the sol?Cgel process. The refractive index and film thickness of bottom layer and up layer are 1.27 and 113?nm, and 1.17 and 245?nm, respectively. The bottom layer with refractive index of 1.27 was prepared from a mixture of acid-catalyzed and base-catalyzed silica sols, and the up layer with refractive index of 1.17 was prepared from polypropylene oxide modified silica sol. It was found that the addition of polypropylene oxide into the sol significantly decreased the refractive index and increased the hydrophobicity of the AR coating. The obtained tri-wavelength AR coating gives very high transmittance of 99.7, 99.1 and 98.0?% at 351, 527 and 1,053?nm, simultaneously.     

黄芪异黄酮类化合物抗氧化活性的密度泛函理论研究

本文采用密度泛函理论中的B3LYP方法在6-311G(d,p)水平上对黄芪中的四种异黄酮类化合物毛蕊异黄酮、毛蕊异黄酮苷、芒柄花素、芒柄花苷进行了优化计算,从四个分子的几何结构、酚羟基氢原子上的NBO电荷、酚羟基解离能、HOMO和LUMO能级以及其能级差△E(LUMO-HOMO)等方面分析了四种黄芪异黄酮类化合物清除自由基的活性.C3.位的酚羟基为毛蕊异黄酮苷元及其苷分子的最大可能活性位点,C7位酚羟基也具有一定的活性,可以增加分子本身的抗氧化活性,C7位酚羟基为芒柄花素分子的活性位点.C3,位或C7位上酚羟基氢原子带正电荷越大、酚羟基的解离能越小、△E(LUMO-HOMO)越小、HOMO能级相对越高分子的抗氧化活性越高.糖苷取代C7位酚羟基上的H原子,可以提高HOMO、LUMO的轨道能级,但是分子失去了7位酚羟基,从而降低了毛蕊异黄酮苷分子的抗氧化活性.结果表明,四种黄芪异黄酮类化合物的抗氧化能力大小为:毛蕊异黄酮＞毛蕊异黄酮苷＞芒柄花素＞＞芒柄花苷.对芒柄花素和羟基自由基反应的过渡态进行了计算研究.     

Sensitive, rapid and easy analysis of three catecholamine metabolites in human urine and serum by liquid chromatography tandem mass spectrometry

A sensitive and easy analytical method for catecholamine metabolites including 4-hydroxy-3-methoxyphenylglycol sulfate (HMPG sulfate), vanillylmandelic acid (VMA) and homovanillic acid (HVA) determination was developed based on liquid chromatography-tandem mass spectrometry in a negative multiple reaction monitoring mode. The analytes were rapidly separated on a reversed-phase Waters Xbridge C18 column (150 × 2.1 mm i.d.) with the mobile phase of 15% (v/v) acetonitrile containing 2 mM ammonium formate and 85% (v/v) formic acid solution (0.05%, v/v). Mass spectrometric conditions, such as characteristic fragmentations and quantification ion transitions, both with chromatographic conditions including separation column type and mobile phase composition, were systematically investigated to get optimal sensitivity and specificity. The limits of detection were in the range of 0.03-0.7 ng/mL for the targets. Recovery rates of spiked urine samples with three different concentration levels (low, middle and high) were above 86% with precisions less than 5.7%. For serum analysis, acetonitrile chosen both as protein precipitation reagent and extraction solvent facilitates to reduce matrix effects. Recovery rates of spiked serum sample were in the range of 90.6% to 111.1% for three targets. The intra-day and inter-day precisions were satisfactory less than 8.7%. This proposed method was successfully applied to determine HMPG sulfate, HVA and VMA present in human urine and serum.     

Probing the interactions between chlorpheniramine and 2:1 phyllosilicates

Interactions between chlorpheniramine (CP), an antihistamine drug used to treat allergy, and 2:1 phyllosilicates were studied under batch kinetic and different solution conditions to investigate the effect of charge density of the substrates on CP removal from solution. The CP removal by Na-montmorillonite was instantaneous, with a very large rate constant and a fast rate, reaching a capacity of 0.64 mmol/g, compared to its cation exchange capacity of 0.85 mmol_c/g. In contrast, CP removal by talc was 10 times lower at 0.06 mmol/g. Stoichiometric desorption of exchangeable cations accompanying CP removal by Na-montmorillonite confirmed cation exchange as the dominant interaction mechanism. Solution pH had a minimal effect on CP removal by Na-montmorillonite until pH 11. On the contrary, a slight increase in CP removal by talc was observed as the solution pH increased, due to increased negative charges on the pH-dependent surfaces of talc. Interactions between CP and Na-montmorillonite occurred on both external and interlayer sites, resulting in a d-spacing expansion from 12.5 Å to 15.2 Å. In contrast, interactions between CP and talc were only limited to the external surfaces. It was the charge density that ultimately controlled the amount of CP removal by 2:1 phyllosilicates. Thus, montmorillonite offers a superior option for the removal of cationic drugs from aqueous solution.     

Polyacrylonitrile fiber mat supported solid acid catalyst for acetalization

Abstract  

A novel polyacrylonitrile hybrid fiber mat supported solid acid catalyst was prepared by electrospinning, and its catalytic activities were carefully investigated through acetalization reactions. The results showed that this hybrid fiber mat exhibits high activity for the reactions, with average yields over 95%. Besides having catalytic activities similar to the solid acid, the heterogeneous solid acid/polyacrylonitrile mat can be reused in six runs without significant loss of catalytic activities. The large size of the hybrid fiber mat greatly facilitates recovery of the catalyst from the reaction mixture. The high and stable catalytic activities of the hybrid fiber mat hold great potential for green chemical processes and preparation of membrane reactors in the future.