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71.
高分子共混体系相分离动力学研究已取得了很大的进展。Cahn理论可很好地描述相分离初期过程,de Gennes的蛇行理论可较好地描述相分离初期大分子扩散。在相分离后期,人们已经发现动力学参量的标度行为,但实验结果不一,标度成因尚不十分清楚。本文研究了聚甲基丙烯酸甲酯(PMMA)/聚醋酸乙烯酯(PVAc)共混体系相分离后期过程。分析了结构函数的标度行为,初步讨论了相凝聚特征。 相似文献
72.
Hong‐Ze Gao Zhong‐Min Su Chun‐Sheng Qin Ri‐Gen Mo Yu‐He Kan 《International journal of quantum chemistry》2004,97(6):992-1001
Bis(2‐methyl‐8‐quinolinolato)aluminum(III) hydroxide complex (AlMq2OH) is used in organic light‐emitting diodes (OLEDs) as an electron transport material and emitting layer. By means of ab initio Hartree–Fock (HF) and density functional theory (DFT) B3LYP methods, the structure of AlMq2OH was optimized. The frontier molecular orbital characteristics and energy levels of AlMq2OH have been analyzed systematically to study the electronic transition mechanism in AlMq2OH. For comparison and calibration, bis(8‐quinolinolato)aluminum(III) hydroxide complex (Alq2OH) has also been examined with these methods using the same basis sets. The lowest singlet excited state (S1) of AlMq2OH has been studied by the singles configuration interaction (CIS) method and time‐dependent DFT (TD‐DFT) using a hybrid functional, B3‐LYP, and the 6‐31G* basis set. The lowest singlet electronic transition (S0 → S1) of AlMq2OH is π → π* electronic transitions and primarily localized on the different quinolate ligands. The emission of AlMq2OH is due to the electron transitions from a phenoxide donor to a pyridyl acceptor from another quinolate ligand including C → C and O → N transference. Two possible electron transfer pathways are presented, one by carbon, oxygen, and nitrogen atoms and the other via metal cation Al3+. The comparison between the CIS‐optimized excited‐state structure with the HF ground‐state structure indicates that the geometric shift is mainly confined to the one quinolate and these changes can be easily understood in terms of the nodal patterns of the highest occupied and lowest unoccupied molecular orbitals. On the basis of the CIS‐optimized structure of the excited state, TD‐B3‐LYP calculations predict an emission wavelength of 499.78 nm. An absorption wavelength at 380.79 nm on the optimized structure of B3LYP/6‐31G* was predicted. They are comparable to AlMq2OH 485 and 390 nm observed experimentally for photoluminescence and UV‐vis absorption spectra of AlMq2OH solid thin film on quartz, respectively. Lending theoretical corroboration to recent experimental observations and supposition, the reasons for the blue‐shift of AlMq2OH were revealed. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004 相似文献
73.
A method for direct de termination of total in organic arsenic (III+V), arsenic (III) and dimethylarsinate (DMA) in sea water was developed by combining continuous‐flow selective hydride generation and inductively coupled plasma mass spectrometry (ICP‐MS) is presented. The principle underlying selective hydride generation is based on proper control of the reaction conditions for achieving separation of the respective arsenic species. The effects of pH and composition of reaction media on mutual interference between the arsenic species were investigated in detail. The results indicate that the appropriate media for the selective determination of total in organic arsenic, DMA and As(III) are 6 M HNO3, acetate buffer at pH = 4.63 and citrate buffer at pH = 6.54, respectively. The concentrations of total inorganic arsenic species, As(III+V), and As(III) were respectively deter mined and that of As(V) was obtained by the difference between them. As to the concentration of DMA, it was obtained after correction from the interference caused by As(III) and As(V). By following the established procedure, the detection lim its (as based on 3‐sigma criterion) for As(III+V), As(III) and DMA were 0.050, 0.009, and 0.002 ng/mL, respectively. There liability of the pro posed method was evaluated in terms of precision and spike addition. The results indicated that the precision of better than 3% and spike recovery of 95 to 105% for all the arsenic species tested in the natural sea water samples can be obtained. 相似文献
74.
用循环伏安法和电位阶跃法研究了LiCl-KCl-NaCl熔盐体系中碳的阴极还原机理。在钨、铂、不锈钢等微电极上得到的伏安图表明碳的还原是由CO_3~(2-)离子经一步电化学反应实现的,电极反应速度控制步骤为CO_3~(2-)离子向阴极的扩散过程,还原过程具有反应物吸附特征。碳在W、Pt、不锈钢电极上析出电位分别为-2.05V、-1.745V和-1.90V(均相对于Ag/AgCl参比电极)。 相似文献
75.
本文提出平行催化体系的对位叠式循环方波伏安法,并对共作了系统的研究,推导了这一方法的催化电流理论方程,并用验验证这理论的正确性,得到其各脉冲电流皆为同方向,对位叠式循环催化电流相当于将电流叠加4次,而波形不受方波幅度大小的影响,因而灵敏度和分辨率有较大提高,优于其它方波伏安法。 相似文献
76.
近年来亚硝酸甲酯分子(CHa0NO)的光解动力学研究十分活跃{‘5],主要集中在紫外激光的单光子解离的机理,光解过程的矢量相关性质和光解产物的态分布.CH30NO分子的解离能D。(CH30-NO)=174kJ·mol‘,若单从能量上看,人<689。的光就能使其解离,但人>400urn的光解离研究还未见报导.*H30*0分子在人>40onm的强激光场下是充电离还是先解离,是单光子解离还是多光子解离,以及通过哪个电子态解离都不清楚.时间飞行质谱不仅具有质量分辨率高、范围宽,而且响应快,因此适合做光解光电离过程初生态产物的探测.特别是时间飞… 相似文献
77.
Cα-Tetrasubstituted α-amino acids are ubiquitous and unique structural units in bioactive natural products and pharmaceutical compounds. The asymmetric synthesis of these molecules has attracted a lot of attention, but a more efficient method is still greatly desired. Here we describe the first sequential four-step acylation reaction for the efficient synthesis of chiral Cα-tetrasubstituted α-amino acid derivatives from simple N-acylated amino acids via an auto-tandem catalysis using a single nucleophilic catalyst. The synthetic efficiency is improved via a direct enantioselective C-acylation; the methodology affords the corresponding Cα-tetrasubstituted α-amino acid derivatives with excellent enantioselectivities (up to 99% ee). This step-economic, one-pot, and auto-tandem strategy provides facile access to important chiral building blocks, such as peptides, serines, and oxazolines, which are often used in medicinal and synthetic chemistry.The first four-step sequential reaction for the synthesis of Cα-tetrasubstituted chiral α-amino acid derivatives via auto-tandem catalysis has been developed. 相似文献
78.
J. Říkovská A. Machová W. D. Hamilton J. Dupák Chan Chen Mo M. Finger N. A. Lebedev B. S. Neganov V. N. Pavlov A. F. Shchus 《Czechoslovak Journal of Physics》1979,29(6):620-639
The anisotropy of the angular distribution of gamma-rays from the decay of156Tb, oriented in a gadolinium matrix at low temperatures, has been measured at the angles of 0 and π/2 with respect to the applied magnetic field direction in the range of temperatures from 14·6 to 68·4 mK. The temperature dependence of anisotropy was measured for the first time. The parameters of hyperfine magnetic dipole and electric quadrupole splittings have been determined and the values of the magnetic dipole moment ¦Μ156¦=(9·6±1·3)×10?27 J/T and the electric quadrupole momentQ 156=(2·9±0·9)×10?28 m2 of the156Tb ground state have been calculated. Multipole mixing ratios andB(E2) branching ratios of many gamma-ray transitions occurring in156Gd have been found and the results have been discussed in terms of the rotational-vibration and pairing-plus-quadrupole models. 相似文献
79.
80.
微结构演化对镁合金材料力学性能有着显著的影响,为了揭示镁合金宏观塑性各向异性特性与非均匀孪生变形的关系,开展了不同路径下的单轴加载试验以及采用含滑移、孪生机制的晶体塑性本构模型对试验条件下的镁合金变形行为进行数值模拟研究.文中本构模型描述了滑移与孪生变形机制以及晶格转动的机制,同时研究采用三维微结构代表性有限元模型,其包含晶粒尺寸、晶向和晶界倾角等微结构参数.研究结果表明,轧制镁合金具有强烈的宏观塑性各向异性行为,并对这种镁合金塑性各向异性行为的模拟结果以及多晶织构的模拟演化结果与试验测量进行对比,结果都基本吻合.对孪生非均匀变形模拟分析表明,镁合金宏观塑性各向异性行为与滑移、孪生变形机制的不同启动组合紧密相关,同时多晶体内应力的非均匀分布受到孪生变形的严重影响.而不同晶粒尺寸的晶粒所发生的孪生变形有比较大的差异,造成孪晶变体在晶粒内的分布极不均匀.该研究可为通过微结构的合理配置来设计和控制材料的力学性能提供理论依据. 相似文献