Sorption of Acid Green 25 on chitosan: Influence of experimental parameters on uptake kinetics and sorption isotherms

Acid Green 25, which is a diazoic dye bearing two sulfonic groups, is efficiently sorbed on chitosan. The protonation of chitosan may explain the electrostatic attraction of this anionic dye and that its optimum pH is close to 3. Preliminary protonation of amine groups (obtained by contact with a sulfuric acid solution) reduced the variation of solution pH following sorbent addition but significantly reduced sorption performance: the maximum sorption capacity of raw chitosan, 525 mg dye/g (0.84 mmol dye/g), was halved by acidic preconditioning. The acidic conditioning also reduced the kinetic rate—the time necessary to reach equilibrium increased up to threefold depending on the experimental conditions. The size of sorbent particles influenced sorption kinetics and equilibrium because of resistance to intraparticle diffusion, but the sorption appeared to occur not only at the surface of the sorbent but also in the intraparticle network of the polymer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1073–1080, 2003     

含两种不同共聚组分改性聚酯的结晶速率

添加己二酸、间苯二甲酸,聚乙二醇对PET进行改性,合成样品。用DSC法研究合成共聚物的等温结晶动力学。结果表明,在所选择的温度范围内,共聚物很好的符合Avrami方程。随温度的升高,共聚物的结晶速度常数K和Avrami指数n逐渐减小,结晶速度G逐渐降低。含2种柔性组分的共聚酯随着一种柔性组分含量的增加,结晶速率G上升;含一种刚性一种柔性组分的共聚酯随刚性组分含量的增加,结晶速率G下降。     

The process window for diamond deposition from the vapor phase with sulfur in the C–H–O feed gas mixtures

Theoretical predictions using a modified radical species ternary diagram for C–H–O system indicate that addition of sulfur expands the C–H–O gas phase compositional window for diamond deposition. Sulfur addition to no-growth domain increases the carbon super-saturation by binding the oxygen and the addition of sulfur to the non-diamond domain reduces the heavy carbon super-saturation by decreasing C_nH_m species concentration in the gas phase. The overall effect of sulfur addition to gas phase mixtures is characterized as that of oxygen addition to the C–H system, i.e. expansion of the compositional window over which diamond can be deposited from the gas phase. In addition, the increasing sulfur concentration to diamond domain feed gases beyond 2000 ppm did not affect the steady state gas phase composition but the quality of diamond was reduced.     

Crystallization of Polymer-Derived Silicon Carbonitride at 1873 K under Nitrogen Overpressure

The chemical stability of an amorphous silicon carbonitride ceramic, having the composition 0.57SiC·0.43Si₃N₄·0.49C is studied as a function of nitrogen overpressure at 1873 K. The ceramic suffers a weight loss at p _N2 < 3.5 bar (1 bar = 100 kPa), does not show a weight change from 3.5 to 11 bar, and gains weight above 11 bar. The structure of the ceramic changes with pressure: it is crystalline from 1 to 6 bar, amorphous at ∼10 bar, and is crystalline above ∼10 bar. The weight-loss transition, at 3.5 bar, is in excellent agreement with the prediction from thermodynamic analysis when the activities of carbon, SiC, and Si₃N₄ are set equal to those of the crystalline forms; this implies that the material crystallizes before decomposition. The amorphous to crystalline transition that occurs at ∼10 bar, and which is accompanied by weight gain, is likely to have taken place by a different mechanism. A nucleation and growth reaction with the atmospheric nitrogen is proposed as the likely mechanism. The supersaturation required to nucleate α-Si₃N₄ crystals is calculated to be 30 kJ/mol.     

双环戊二烯聚合反应热力学和动力学研究

研究了ＤＣＰＤ－ＷＯＣｌ４－ＡｌＥｔ３体系前阶段的反应动力学，采用ＧＣ法分析了不同反应条件下的动力学数据，发现ｌｇ（［ＤＣＰＤ］０／［ＤＣＰＤ］）￣ｔ存在线性关系，说明该体系在前段的聚合反应为一链式反应符合二级反应模型。同时还对该体系聚合反应热力学也进行了研究；对聚合反应的ΔＨｐ、ΔＳｐ、ΔＧｐ进行了讨论。     

高分子材料辐射接枝苯乙烯的研究进展

对各高分子材料辐射接枝苯乙烯的动力学，接枝方法及接枝材料的应用进行了综述，讨论限辐射剂量，剂量率，温度，后效应，溶剂，添加剂和高分子材料厚度及结晶性等方面对接枝反应的影响。     

Non-steady-state model for kinetics of free radical polymerization, 4. Direct thermal initiation

This paper deals with the non-steady-state kinetics of direct thermal initiated polymerization. The initiation is assumed to be a bimolecular reaction of the monomer. The relationship between the radical concentration and the monomer conversion is rigorously derived. In further treatment a few very close approximations are introduced based on the fact that the number of monomer molecules reacting in the initiation step is much less than that consumed in the propagation step for a process producing high polymer, and the value of the rate constant for propagation or chain transfer is much lower than that for chain termination. Expressions for various molecular parameters, such as molecular weight distribution, number-average and weight-average degrees of polymerization, and dispersity, are given. Several numerical examples are provided.     

Significance of fluid regime in biological filtration

A dispersed flow model previously developed to study substrate utilization in unsaturated media was experimentally verified and its practical application was considered. For this purpose, measurements were made using tap water and a synthetic feed solution. The importance of the change in fluid regime as regards to the simultaneous transport and reaction within biological filters were demonstrated. The effect of drop formation and the breakage of liquid jets inside the filters on substrate utilization was also shown.     

氮对纳米硅氮薄膜品化的影响

在电容式耦合等离子体化学气相沉积系统中，用高氢稀释硅烷和氮气为反应气氛制备纳米硅氮（ｎｃ－ＳｉＮｘ：Ｈ）薄膜结果表明：当Ｎ＿２／ＳｉＨ＿４气体流量比（Ｘｎ）从１增加为４时，薄膜的晶态年从５８％降至１４％，晶粒尺寸从１０ｎｍ降至５ｕｍ，Ｎ／Ｓｉ含量比从０．０３增至０．１２．当Ｘｎ≥５，则生成非晶硅氮（ａ－ＳｉＮｘ：Ｈ）薄膜．当Ｘｎ从１增加为１０时，薄膜暗电导率从１０￣（－５）（Ωｃｍ）￣（－１）降至１０￣（－１１）（Ωｃｍ）￣（－１），具有逾渗行为，这与薄膜的晶态率紧密相关．     

环氧油一步合成的反应机理和动力学研究

研究了环氧油一步合成的反应机理和动力学；结合实验结果和理论分析动力学模型，首次提出：在适当的反应条件下，油脂的一步环氧化反应动力学模型可以表示为过氧酸生成反应动力学模型；其实验动力学模型方程为：ｒ０＝ｋ［Ｈ２Ｏ２］（０．９９）［ＨＯＡｃ］（０．９７），其中ｋ与催化剂用量有关。