Adsorption enthalpy and desorption enthalpy during displacement of adsorbate to solvent in a liquid-solid system

The adsorption heat of the stoichiometric displacement process for the adsorption of a solute in a liquid-solid system was investigated. On the basis of the SDM-A and the rule of the additivity of energy, an expression which describes the dependence of the adsorption enthalpy on the nature and concentration of the solute, and on the solvent and adsorbent, was derived. The adsorption heat determined for the solute with the traditional method can be divided into two independent fractions, relating to the adsorption of the solute and to the desorption of the solvent. Experimental data on both isotherms from the literatures and precise calorimetry were used to test the adsorption heat and its fractions computed quantitatively via the equations presented in this study, and a satisfactory degree of conformity between them was obtained. Supported by the Natural Science Foundation of Shaanxi Province in China.     

A facile approach to surface graft vinyl acetate onto polyolefin articles

A facile and environment friendly approach was developed to graft vinyl acetate (VAc) onto plastic articles in an aqueous solution using tert‐butyl alcohol (TBA) as a compatiblizer and benzoyl peroxide (BPO) as an initiator. In a novel setup, excessive monomer suspended in a water phase, VAc could be conveniently grafted on the model substrate of low‐density polyethylene (LDPE) film and the graft percentage (GP) could be developed up to 7.3%. Reaction temperature could increase GP significantly, while adding monomer over a critical volume did not influence GP. By adding some paradioxybenzene, i.e. 0.06–0.08% in VAc phase, homopolymer PVAc could be avoided practically, while graft polymerization proceeded favorably in aqueous solutions. It was proved by attenuated total reflection‐infrared (ATR‐IR) spectroscopy that grafted VAc was located mainly at the surface of the LDPE film and hydrophilic nature of both grafted and alcoholyzed films were improved via contact angle measurements. Copyright © 2004 John Wiley & Sons, Ltd.     

Evolution of the geometrical and electronic structures of Gan(n=2-26) clusters: a density-functional theory study

Density-functional theory with generalized gradient approximation for the exchange-correlation potential has been used to calculate the lowest-energy geometries and electronic structure of neutral gallium clusters containing up to 26 atoms. Harmonic vibrational frequency analysis is undertaken to assure that the lowest-energy geometries are real local minima. With increasing cluster size, we find that the gallium clusters tend to adopt compact structures. The structures comprise triangular units that connect each other with different dihedral angles. The lowest-energy structure can be obtained by capping an atom on the structure of smaller one. The capping site occurs at a site where interactions with more atoms are available. The binding energy evolves monotonically with size, but Ga(8), Ga(14), and Ga(20) exhibit particularly higher stability. Except Ga(2) and Ga(4), all even-numbered gallium clusters we studied are closed-shell singlet states with a substantial highest occupied and lowest unoccupied molecular orbitals gap. The odd-numbered clusters are open shell with a small gap. The size dependence of cluster's ionization potentials and electron affinities is discussed and compared with available experiment.     

Measuring trihalomethane concentrations in water using supported capillary membrane sampling-gas chromatography

The objective of this study was to develop and evaluate a supported capillary membrane sampling-gas chromatography method for the analysis of trihalomethanes (THMs) in drinking water. The effects of experimental parameters, such as flow rate of carrier gas, water temperature, ionic strengths of solutions and transfer line temperature on the system performance were investigated. The results of method detection limit and accuracy and precision studies are reported.     

Isolation, characterization, and theoretical study of La2@C78

A new metallofullerene, La2@C78, has been synthesized by DC arc discharge method, isolated by high-performance liquid chromatography, and characterized by laser desorption time-of-flight mass spectrometry, UV-vis-NIR absorption, differential pulse voltammetry, 13C NMR spectroscopy, and theoretical calculations. The La2@C78/CS2 solution is dark violet and presents several characteristic absorption features at 647, 561, 533, and 386 nm, with an onset around 1000 nm. With respect to empty D3-C78, the capability of La2@C78 as an electron acceptor or donor is stronger. Addition of 1,1,2,2-tetrakis(2,4,6-trimethylphenyl)-1,2-disirane to La2@C78 photochemically, as well as thermally, affords bis- and mono-adducts. Theoretical studies and 13C NMR spectroscopic analysis of La2@C78 indicate that it possesses a D3h-C78 cage (78:5).     

聚苯乙烯稀溶液的小角激光弹性和准弹性光散射

随着激光技术的发展,近年来出现了与散射光频加宽相应的光子相干光谱即准弹性光散射。于是,利用光散射(也称弹性光散射)法不仅能获得高聚物的各种物性参数如分子量(?),第二维利系数A_2和均方旋转半径(),而且还能得到大分子在溶液中的动态参数,即扩散系数D_0。由D_0求得流体力学半径R_H。本文只涉及小角度准弹性光散射(1°<θ<7°)对稀溶液范围的平动扩散系数的测定。与文献比较,表明方法是成功的。