二乙基二烯丙基氯化铵均聚及其与丙烯酰胺或丙烯酸共聚动力学研究

采用膨胀计法研究了以过硫酸铵为引发剂,二乙基二烯丙基氯化铵(DEDAAC)在水溶液中的均聚及其与丙烯酰胺(AM)和丙烯酸(AA)共聚动力学,测定了相应的聚合表观活化能;采用元素分析法测定了DEDAAC分别与AM和AA在低转化率下共聚物的组成,并采用氯离子选择性电极法测定了DEDAAC-AM共聚物中的氯离子含量,按Kelen-Tudos方法求得了相应的竞聚率.结果表明,DEDAAC均聚速率方程为RP=k[M]0.99[I]0.76,表观活化能Ea=77.00kJ/mol,说明链终止为单基终止和双基终止并存,引发过程与单体浓度无关;DEDAAC与AM在摩尔比为4∶1时,共聚动力学方程为RP=[M]2.53[I]0.90,表观活化能Ea=67.06kJ/mol,单体竞聚率为rDE=0.31±0.02、rAM=5.27±0.53;DEDAAC与AA在摩尔比为4∶1时,共聚动力学方程为RP=k[M]2.94[I]0.83,表观活化能Ea=70.07kJ/mol,竞聚率为rDE=0.28±0.03、rAA=5.15±0.28;DEDAAC与AM和AA等共聚为非理想共聚,得到的产物均为无规共聚物.     

Volumetric Properties of Binary Mixtures of Isomeric Butanols and C8 Solvents at 298.15 K

Excess molar volumes, V _m ^E, over the whole composition range for binary mixtures of 1-butanol, 2-butanol, and 2-methyl-2-propanol + 1-octanol, or 2-octanol, or di-n-butyl ether, or n-hexylacetate were determined at 298.15 K from density measurements carried out with a vibrating-tube densimeter. Small V _m ^E values, both positive and negative, are displayed by mixtures containing 1- or 2-octanol, whereas positive and larger values are always found for mixtures containing dibutyl ether and hexylacetate. These results can be justified in terms of H-bonding interactions and/or steric hindrance due to the branched alkyl chains. Partial molar volumes at infinite dilution of the isomeric butanols in the C8 compounds were also calculated from the apparent molar volumes in dilute solution. The solute-solvent interactions and the effects of the local organisation of the solvent around the butanol molecules were discussed using the void and cavity volumes as different estimates of the intrinsic volume of the molecules. The volumetric behavior of butanols seems to be determined by the solute-solvent interactions rather than packaging effects.     

Synthesis and properties of the double perovskites La2NiVO6, La2CoVO6, and La2CoTiO6

The double perovskites La₂CoVO₆, La₂CoTiO₆, and La₂NiVO₆, are described. Rietveld fitting of neutron and powder X-ray diffraction data show La₂NiVO₆ and La₂CoVO₆ to have a disordered arrangement of B-cations whereas La₂CoTiO₆ shows ordering of the B-cations (with ∼5% Co/Ti inversion). Curie-Weiss fits to the linear region of the 1/χ plots reveal Weiss temperatures of −107, −34.8, and 16.3 K for La₂CoVO₆, La₂CoTiO₆, and La₂NiVO₆, respectively, and magnetic transitions are observed. La₂CoTiO₆ prepared by our method differs from material prepared by lower-temperature routes. A simple antiferromagnetic spin model is consistent with the data for La₂CoTiO₆. These compounds are semiconductors with bandgaps of 0.41 (La₂CoVO₆), 1.02 (La₂CoTiO₆) and 0.45 eV (La₂NiVO₆).     

多色蓝在核酸分子上的Langmuir聚集吸附

用微相吸附-光谱修正（MPASC）新技术研究核酸与多色蓝(PCB)探针分子间的相互作用，分析核酸分子内双静电膜的形成与Langmuir吸附的关联性.通过pH 7.24的介质核酸-PCB反应的光谱研究，测定了结合产物的物理化学参数：结合比1PCB:2DNA-PCB、1PCB:3RNA-PCB, 平衡常数KDNA-PCB=5.42×104， KRNA-PCB=2.82×104,摩尔吸收系数ε(DNA-PCB, 625 nm)=5.65×103（mo1－1•L ）•cm－1， ε(RNA-PCB, 625 nm)=3.85×103 （mol－1•L）•cm－1.结果表明， RNA分子仅形成约60％双螺旋结构链，核酸双螺旋每一周期的负静电沟最大聚集10个PCB分子.该吸附反应用于核酸样品测定，结果良好.     

Theoretical analysis of the performance of a model supercapacitor consisting of metal oxide nano-particles

The factors influencing the electrochemical behaviour of a supercapacitor have been partly examined in this work. The effects of so-called intrinsic parameters, i.e. exchange current density, unit cell length and double layer (DL) capacitance; as well as the so-called application parameters, i.e. cell current, on the cell potential discharge time have been considered. The contributions of each type of capacitors, DL capacitor and faradaic supercapacitor under various states of operation and material have been analyzed, and the competing (compensating) effects of the two types of capacitors as regards to the discharge and power characteristics manifested by current–potential and energy–power (Ragone plots) are elucidated.     

席夫碱自组装单分子膜的电化学行为

利用自组装技术将席夫碱硫醇衍生物在金表面形成自组装单分子膜,并初步研究了此自组装单分子膜的电化学行为,发现该席夫碱分子在0.1 mol•L－1的KCl溶液中具有电化学不可逆氧化还原行为，且随着自组装时间的增加表观电极反应速率常数值显著减小,最后减小为0,并对此进行了解释.     

A simple adsorption model for ionic surfactants

In the past, few theoretical attempts have been made to describe quantitatively the adsorption of ionic surfactants at liquid interfaces. Well-known adsorption isotherms due to Frumkin or Hill–de Boer cannot respond to the specific electrostatic and geometric properties of the surfactant molecules. Our approach is based on a combination of the Gouy–Chapman theory with a modified Frumkin isotherm. The modification implies that the system is free to choose an optimal head group area and an optimal arrangement of the surfactant molecules in the interface as a function of bulk concentration. Interaction energies between neighbouring adsorbed surfactant molecules and between surfactant and water molecules are taken into consideration. The minimum of the Gibbs free energy of the system is equivalent to a minimal interfacial tension. Thus, the thermodynamically stable isotherm can be obtained as the lower envelope of the family of σ versus ln c isotherms resulting from different choices of the model parameters, including the area per molecule. According to the Gibbs equation, the Γ versus ln c adsorption isotherm is obtained as the derivative of this envelope. By variation of the model parameters, the envelope of the calculated adsorption isotherms can be fitted to experimental data of the interfacial tension versus bulk concentration. A computer program is used to calculate the σ versus c and the Γ versus ln c curves as well as to fit the parameters. Received: 28 October 1999/Accepted: 8 February 2000     

Double pulse laser-induced breakdown spectroscopy of explosives: Initial study towards improved discrimination

Detecting trace explosive residues at standoff distances in real-time is a difficult problem. One method ideally suited for real-time standoff detection is laser-induced breakdown spectroscopy (LIBS). However, atmospheric oxygen and nitrogen contributes to the LIBS signal from the oxygen- and nitrogen-containing explosive compounds, complicating the discrimination of explosives from other organic materials. While bathing the sample in an inert gas will remove atmospheric oxygen and nitrogen interference, it cannot practically be applied for standoff LIBS. Alternatively, we have investigated the potential of double pulse LIBS to improve the discrimination of explosives by diminishing the contribution of atmospheric oxygen and nitrogen to the LIBS signal. These initial studies compare the close-contact (< 1 m) LIBS spectra of explosives using single pulse LIBS in argon with double pulse LIBS in atmosphere. We have demonstrated improved discrimination of an explosive and an organic interferent using double pulse LIBS to reduce the air entrained in the analytical plasma.     

A model for quantitatively describing linear velocity programming in capillary SFC

Summary Linear velocity in capillary SFC is commonly controlled by restricting capillaries. In this paper, a model is described that quantitatively predicts the linear velocity of a supercritical fluid in SFC using tapered or ceramic frittype restrictors. In this model, the flow from the restricting capillary is assumed to be an isentropic expansion. The variation of the linear velocity as a function of pressure, temperature and cross-sectional area of the restricting aperture was predicted by this model. This predictive capability is important to the use of gradient programming in capillary SFC. Finally, the ideal variable restrictor for gradient programming was found to be one that could reversibly increase or decrease the linear velocity independent of the pressure, temperature, and/or density conditions used to create the gradient.     

Study of a Catalytic Mechanism in Additive Differential Pulse Techniques

The new electrochemical double pulse technique, known as additive differential normal pulse voltammetry (ADNPV) when there is no restriction on the duration of both pulses, and additive differential pulse voltammetry (ADPV) when t₂?t₁, has been applied to a pseudo‐first‐order catalytic mechanism. The expressions obtained here are applicable to planar and spherical electrodes, of any radius. This is of great interest since the size of the electrode plays an important role in the preponderating of diffusive and kinetics processes. The signal obtained with this technique presents the same morphological characteristics as the triple pulse technique, double differential pulse voltammetry (DDPV) and is more advantageous than DDPV and than the double pulse one, differential pulse voltammetry (DPV).