P(St-co-MAA)乳液体系对CaCO3结晶的调控

大量研究表明, 有机/无机界面上的相互作用[1]是控制无机结晶的晶型、形貌、粒径等特征的决定因素. 本文利用乳液聚合方法合成了在诱导无机矿化后依然保持较为刚性界面的、能与无机离子作用的微球, 并在乳液中进行碳酸钙结晶实验, 用XRD, FTIR和SEM等手段对结晶进行了表征.     

Effects of Self—coiling of Organic Molecules on Intramolecular Exciplex Formation and Fluoresscence Quenching in DX—H2O Solvent System

Effects of self-coiling of organic molecules on intramolecular exciplex formation of compound I,in which the carbazole chromophore and terephthalic acid methylester acceptor group are linked by one (CH2)10 chain,and the decrease of the fluorescence intensities of compounds Ⅱ，Ⅲ，and Ⅳ,in which the carbazole chromophore and 3,5-dinitrobenzoate are connected by one aliphatic chain of (CH2)10 (Ⅱ），（CH2）12（Ⅲ）,or (CH2)4(Ⅳ）,have been studied in the dioxane (DX)-H2O binary system.The results show that self-coiling of organic molecules in DX-H2O facilitates intramolecular exciplex formation of I and induces the decrease of fluorescence intensities of Ⅱ,bacause of the proximity effect brought about by selfcoiling of organic molecules under hydrophobic-lipophilic interaction(HLI) between the excited carbazole chromophore and the acceptor.Since the similar effects are observed even when the concentration of the probes are less than their CAgCs(critical aggregate concentrations )in the DX-H2O mixture with the same φ values,formation of the intermolecular exciplex has been excluded.The effects are found to be strongly depended on φ values,indication that they are mainly driven by HLI.The properties of the acceptors can also affect the intramolecular exciplex formation.With terephthalic acid methylester moiety as the acceptor,the carbazole chromophore exhibits the fluorescence spectra of the exciplex,while with 3,5-dinitrobenzoate moiety as the acceptor,only the fluorescence spectra of excited carbazolyl chromophore are observed.     

A new gas chromatographic stationary phase: Polysiloxane with β-cyclodextrin side chain for the separation of chiral and positional isomers

Summary A new stationary phase [bikis(2,6-di-O-pentyl-3-O-hex-6-enyl)-pentakis(2,6-di-O-pentyl-3-O-methyl)-β-CD-polysiloxane] was synthesized and successfully applied in GC for the separation of chiral and achiral isomers. It possesses high column efficiency and exhibits excellent separation ability for disubstituted benzenes. Some typical enantiomers and optical isomers are well separated. The separation behavior of this new phase is characterized and discussed.     

Study on the thermal stability of a chiral stationary phase coated on capillaries for GC

A chiral stationary phase prepared by bonding L -valine-t-butylamide to XE-60 has been coated on glass and metal capillaries. The performances of the chiral glass and metal columns were equivalent to those of commercial fused silica capillary columns. The thermal stability of the glass column was examined up to 280°C. It was found that no appreciable change in separation factor (α value) was observed up to 230°C. The α values gradually decreased between 240 and 260°C, and enantiomer separation was no longer achieved at 280°C. It was concluded that the allowable upper limit temperature of the chiral stationary phase is between 230 and 240°C in the isothermal mode, and ca 260°C in temperature-programmed mode.     

Quo Vadis total reflection X-ray fluorescence?

The multielement trace analytical method ‘total reflection X-ray fluorescence’ (TXRF) has become a successfully established method in the semiconductor industry, particularly, in the ultra trace element analysis of silicon wafer surfaces. TXRF applications can fulfill general industrial requirements on daily routine of monitoring wafer cleanliness up to 300 mm diameter under cleanroom conditions. Nowadays, TXRF and hyphenated TXRF methods such as ‘vapor phase decomposition (VPD)-TXRF’, i.e. TXRF with a preceding surface and acid digestion and preconcentration procedure, are automated routine techniques (‘wafer surface preparation system’, WSPS). A linear range from 10⁸ to 10¹⁴ [atoms/cm²] for some elements is regularly controlled. Instrument uptime is higher than 90%. The method is not tedious and can automatically be operated for 24 h/7 days. Elements such as S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Br, Sn, Sb, Ba and Pb are included in the software for standard peak search. The detection limits of recovered elements are between 1×10¹¹ and 1×10⁷ [atoms/cm²] depending upon X-ray excitation energy and the element of interest. For the determination of low Z elements, i.e. Na, Al and Mg, TXRF has also been extended but its implementation for routine analysis needs further research. At present, VPD-TXRF determination of light elements is viable in a range of 10⁹ [atoms/cm²]. Novel detectors such as silicon drift detectors (SDD) with an active area of 5 mm², 10 mm² or 20 mm², respectively, and multi-array detectors forming up to 70 mm² are commercially available. The first SDD with 100 mm² (!) area and integrated backside FET is working under laboratory conditions. Applications of and comparison with ICP-MS, HR-ICP-MS and SR-TXRF, an extension of TXRF capabilities with an extremely powerful energy source, are also reported.     

Optical spectra of Yb and Yb–Nd interaction in Cs2NaNd0,4Yb0,6Cl6

Interaction between octahedrally coordinated Nd³⁺ and Yd³⁺ in Cs₂NaNd_0,4Yb_0,6Cl₆ reduces the Nd³⁺ luminescence lifetime by roughly two orders of magnitude with respect to that found in Cs₂NaNdCl_{6– · –} Analysis of low temperature absorption and emission spectra reveals that the nonradiative Nd³⁺–Yb³⁺ energy transfer has to be assisted by lattice phonon emission, nevertheless the rate of the transfer is high in the 4–300 K temperature region and attains 5.8×10⁵s^-1 at room temperature. A phase transition of Cs₂NaNd_0,4Yb_0,6Cl₆ between 12 and 13 K is evidenced by abrupt change of both the spectra and lifetimes of Yb³⁺. Reduction of Yb³⁺ lifetime from 5.3 ms to 150 μs is at the transition from low symmetry phase to high symmetry phase is supposed to be associated with a three ion interaction which occurs in ordered lattice and disappears in low temperature disordered structure.     

The effects of substituent size and molecular weight on the liquid crystalline properties of poly(2-alkyl-1,4-phenylene terephthalate)s

A series of low molecular weight, thermotropic poly(2-alkyl-1,4-phenylene terephthalate)s was prepared by the solution polycondensation reaction of terephthaloyl chloride and alkylhydroquinones containing n-alkyl substituents of increasing size from methyl to dodecyl. Samples of the low molecular weight polymers so obtained were also further polycondensed in the solid state to obtain high molecular weight polymers. The liquid crystalline phase behaviors and textures were determined, and the effects of polymer structure and molecular weight on these properties are discussed. All of the polymers obtained formed thermotropic, nematic mesophases, which were less stable for the lower molecular weight polymers, as expected, than were the mesophases formed by the higher molecular weight polymers. © 1994 John Wiley & Sons, Inc.     

Unusual peak defocusing in capillary GC on hexakis(2,6-diO-pentyl-3-O-acetyl)-α-cyclodextrin stationary phase

An unusual peak defocusing effect influencing chromatographic performance over a limited range of elution temperatures is described for hexakis(2,6-di-O-pentyl-3-O-acetyl)-α-cyclodextrin stationary phase. Since this phenomenon is likely to be dependent on minor details of the cyclodextrin molecule, full assignment of the ¹H- and ¹³C-NMR-spectra are given.     

2-溴丙酸气相热消除反应的机理

用密度泛函（DFT）方法,在B3LYP/6-31G**水平上对2-溴丙酸气相消除反应机理进行了研究.计算表明,反应主要是通过半极化五元环结构过渡态进行的,羧基上的氢原子协助溴原子离去,羧基氧原子帮助稳定过渡态.在B3LYP/6-311＋＋G(3df,3pd)水平上对B3LYP/6-31G**优化的几何构型进行了单点能计算,计算所得反应的速度控制步骤的活化能为189.461 kJ•mol－1,偏离实验值((180.3±3.4) kJ•mol－1)5.08％.     

A MORPHOLOGICAL STUDY OF POLY（DIVINYLBENZENE-co-ACRYLIC ACID） IN CROSSLINKING PRECIPITATION POLYMERIZATION

Divinylbenzene-80 （DVB-80） and polar monomer acrylic acid （AA） having hydrogen bonding at a total monomer loading of 5 vol% were precipitated-copolymerized in a variety of organic solvents with 2,2＇-azobis（isobutyronitrile） （AIBN） as initiator. The experiments were investigated from a two-dimensional matrix, i.e., the actual crosslinking degree of DVB varying from 0 to 80% and the solvent composition varying from 0 to 100% of toluene mixture with acetonitrile, when the mixture of acetonitrile and toluene was used as the reaction solvent. Under various reaction conditions, six distinct morphologies including soluble polymers, swellable microgels, coagulum, irregular microparticles, and nano-/micrometer microspheres were formed and the structures of these polymer architectures were described. A morphological map was utilized to discuss the effects of both crosslinking degree of DVB and composition of solvent on the transitions between morphology domains. The results demonstrated that the microspheres are formed by an internal contraction due to the marginal solvency of the continuous phase and the crosslinking of the polymer network through the covalent bonding from DVB as well as the interchain hydrogen-bonding between the carboxylic acid units.