Electrochemical and photochemical reduction of a series of azobenzene dyes in protic and aprotic solvents

The electrochemical and photochemical reduction in ethanol of a series of azobenzene dyes containing tertiary amine groups has been investigated. It has been shown that the two mechanisms are of parallel importance and an explanation suggested using quantum chemical calculations (AM1, DFT). The solvation of these dyes in protic (methanol) and aprotic (dimethylformamide) solvents has also been studied and the effect of solvation on their electrochemical and photochemical reduction is discussed.     

Intercalation of cationic azobenzene derivatives in a synthetic mica and their photoresponse

Four types of cationic azobenzene derivatives (Azds) having quaternary ammonium functional group at the 4-position (“single-hand”) or at the 4 and 4′-positions (“double-hand”) were synthesized and intercalated in a synthetic mica, Li taeniolite (LiTN), by ion exchange to obtain photoresponsive complexes. Powder X-ray results suggested that the long axis of molecules was at an angle of 58–62° from the mica layer for the single-hand series and at about 24° for the double-hand series. Photoresponse by ultraviolet (UV) irradiation with λ=365 nm and visible light (VIS) with λ=436 nm was monitored by the change in d(001), the basal spacing. Each Azd/TN complex showed different types of behavior toward UV/VIS irradiation. Complexes of a double-hand azo derivative showed a basal-spacing contraction of 0.7% under UV irradiation, but recovered their initial length under VIS irradiation, or by standing in the dark. Another complex presented a nonreversible change in basal spacing of 4%. This contraction under UV irradiation was attributed to trans-to-cis isomerization of the azobenzene moiety in guests, although the complex interlayer-space environment may have caused a different response after contraction.     

The facile synthesis and optical nonlinearity of hyperbranched polyaspartimides with azobenzene dyes

A series of thermally stable nonlinear optical hyperbranched polyaspartimides were synthesized via the Michael addition reaction of a fluorine-containing trimaleimide, 1,1-tris[4-(4-maleimide-2-trifluoromethyl-phenoxy)-phenyl]ethane and two respective azobenzene dyes, namely bis(4-aminophenyl(4-(4-nitrophenyl)-diazenyl)phenyl)-amine and 2,4-diamino-4′-(4-nitrophenyl-diazenyl)-azobenzene, using p-toluenesulfonic acid as catalyst. The incorporation of fluorine-rich components within the hyperbranched polymers increased solubility in organic solvents and reduced optical loss. Owing to the three-dimensional, void-rich, topological structure of the highly branched polymers, the spatial separation of the dyes endows the polymers with a favorable site isolation effect, which thereby negates chromophoric aggregation. Using in situ contact poling, electro-optical coefficients, r₃₃ of 6.5–14.7 pm V^?1 and temporal stability at 80 °C were obtained. Both the dynamic thermal and temporal stabilities of the hyperbranched polyaspartimides were superior to those of their linear analogues.     

Polymerization of acrylonitrile in the presence of vinylsulphone dyes

Information regarding the effect of vinylsulphone dyes on the kinetics of polymerization of acrylonitrile is presented in detail. Some of the physical properties of the products, polyacrylonitrile/vinylsulphone dye copolymers, are discussed, although the subject of their thorough characterization is reserved for a later publication. Considerable detail is given concerning the experimental procedures, to ensure ease of understanding of the techniques involved. ⁶⁰Co γ rays were employed as the polymerization initiator whilst the effect of γ radiation on the chromophore was noted, where relevant.     

X-ray and molecular modelling studies of 4-[N-alkylamino]azobenzene dyes

4-[N,N-Bisalkyl]amino-2′-chloro-4′-nitroazobenzenes were recrystallized from acetone in either triclinic or monoclinic cells with the space group P-1 or P2₁/c. The asymmetric unit cell of dyes having at least one N-cyanoethyl group contained two molecules that were symmetrically unequivalent. The aromatic rings in the azobenzene skeleton were essentially planar with respect to the plane of the azo group, although the C6–C1–N1–N2 torsion angle was 13.2° when the N,N-dicyanoethyl group was employed. X-ray studies were used as a basis for assessing the utility of nonlocal DFT calculations in predicting the equilibrium molecular geometry and solvatochromic properties of the compounds using MM3/ZINDO-S and the COSMO Solvation Model. Although B3LYP and PBE energy functionals were comparable in predicting bond lengths, PBE was slightly better than B3LYP in predicting torsion angles. Furthermore, the dipolarity/polarizability index (π¹) was the preferred solvent parameter for predicting the effects of solvents on λ_max.     

Polymers from acrylonitrile polymerized in the presence of vinylsulphone dyes

The properties of a series of ‘copolymers’ of acrylonitrile and various vinylsulphone dyes are discussed. Information relating to molecular size, the nature of the linkage between the chromophore and the backbone and the reactivity ratios of the two ‘monomers’ is given. These reactivity ratios are calculated from extinction coefficients on the assumption that there is no appreciable breakdown of the chromophore during polymerization. Factors governing the role of the dye in the polymerization process are considered in some detail. Thermal analysis techniques have been used to investigate the thermal stability of the products of polymerization. The thermograms have been used to assess the potential of these materials as pigments and to study the nature of their decomposition.     

On the polymerization of styrene in the presence of vinyl sulfone dyes

An azo dye derived from vinyl sulfone has been prepared having the following formula: A study has been made of the copolymerization of styrene with the above dye in the presence of benzoyl peroxide as an initiator. The colored polymers thus obtained preserve their shade even after repeated precipitation, because the dye is directly bound to the polymer chain. The polymerization has been studied in the temperature interval of 60–80°C, and the activation energy of the process has been determined. The effect of the amount of dye on the polymerization process has been investigated, and the proportion of dye chemically bound to the polymer has been determined spectrophotometrically. The effect of the dye on the molecular weight, correspondingly on [η] and the polydispersity of the colored polymers, has also been studied.     

The synthesis and structural study of two benzothiazolyl azo dyes: X-ray crystallographic and computational study of azo–hydrazone tautomerism

The synthesis, FT-IR, ¹H and ¹³C NMR characterisation, as well as crystal and molecular structure determined by single-crystal X-ray diffraction data, of two azo dyes derived from 6-aminobenzothiazole: 6-[(4-N,N-dimethylaminophenyl)diazenyl]benzothiazole and 6-[(2-hydroxy-1-naphthyl)diazenyl]benzothiazole are reported. Both dyes are essentially planar with the exclusion of methyl groups in 6-[(4-N,N-dimethylaminophenyl)diazenyl]benzothiazole, which exibits 100% E-configuration in terms of orientation of the substituents about the central azo linkage. Single-crystal X-ray study of 6-[(2-hydroxy-1-naphthyl)diazenyl]benzothiazole was undertaken to established whether the hydrazone or azo tautomer was present in the solid state as well as any potential shift in tautomeric equilibrium imparted by temperature variation (296 and 100 K). Density functional theory calculations revealed that the hydrazone tautomer was more stable than the azo tautomer and that the tautomeric equilibrium was shifted towards the hydrazone form at lower temperature.     

Synthesis and characterization of liquid crystalline copolysiloxanes containing azobenzene dyes and 1,3-dioxane based mesogenic side groups

Summary The synthesis and characterization of nine side-chain liquid crystalline copolysiloxanes containing trans-5-(n-undecanyl)-2-(4-cyanophenyl)-1,3-dioxane and 4-(alkanyloxyphenylazo)benzonitrile side groups are presented. The azobenzene dye contents in the copolymers range from about 5 to 20 wt.-%. The nature of the mesophase exhibited by the copolysiloxanes depends very much on the dye concentration. Three copolysiloxanes which contain about 5 wt.-% azobenzene dye, display a smectic A phase while the other six copolysiloxanes which contain more then 10 wt.-% azobenzene dye, exhibit a nematic phase. All the obtained copolysiloxanes show a very low glass transition temperature and a very wide temperature range of mesophase.     

Developments in the chemistry of reactive dyes and their application processes

This review describes the immense impact of reactive dyes on the textile industry. Their use on cellulosic fibres is especially important, but their growing popularity on polyamide substrates is notable. Detailed information is given about developments both in the chemistry of reactive systems and in the chemical technology involved in their application to a variety of fibre types. It is also pointed out that further research is necessary to improve dye–fibre fixation efficiency, especially when dyeing full shades on cellulosic fibres. This work is necessary to address the current environmental problem of colour in dyehouse effluent. The potential solutions reviewed include multifunctional reactive dyes, cationic reactive dyes, and cellulose fibre modification.     

Adhesion of air bubbles to a fluorite surface in the presence of oleate species

Measurements of the detachment force of air bubbles from a surface of fluorite covered with an oleate film immersed in an aqueous sodium oleate solution or water were carried out. The contact angles for the systems fluorite/oleate film-drop of aqueous sodium oleate solution-air, fluorite/oleate film-air bubble-aqueous sodium oleate solution, and fluorite/oleate film-air bubble-water were also measured. The detachment forces were also calculated from the measured contact angles. It was found that the adhesion of air bubbles to the fluorite surface increased considerably in the presence of an oleate film on the fluorite surface, but decreased if the oleate film was at the water-air interface. Good agreement between the theoretically calculated and the measured values of the detachment force for the system fluorite/oleate film-air bubble-sodium oleate aqueous solution when the concentration of this latter solution was in the range 0 to 87.1 mg/dm³ was also found, but for concentrations over 87.1 mg/dm³ the calculated values of the detachment force were higher than the measured values. The calculations and measurements indicate that the most favourable condition for the adhesion of air bubbles to fluorite grains is the presence of a chemisorbed film of oleate without surface precipitation of calcium oleate salt at low concentrations of oleate species in water.     

Degradation of maleic acid in a wet air oxidation environment in the presence and absence of a platinum catalyst

Over a temperature range of 415–478 K, the catalytic and non-catalytic degradation of an aqueous solution of maleic acid (0.03 M) has been studied both in the presence of oxygen and under an inert atmosphere (nitrogen). These reactions were first-order for maleic acid. The non-catalytic oxidation reaction was zero-order in oxygen over a partial pressure range of 0.4–1.4 MPa. The apparent activation energies for the non-catalytic removal of maleic acid under both a nitrogen (66.7 kJ mol⁻¹) and an air (131.5 kJ mol⁻¹) environment have been calculated. The use of 0.5 wt.% platinum on γ-alumina catalyst significantly enhanced the degradation rate of maleic acid. A kinetic expression was developed accounting for both homogeneous and heterogeneous routes in maleic acid elimination. Although maleic acid removal was zero-order for oxygen concentration, the presence of oxygen is shown to result in significant chemical oxygen demand (COD) removal in both the catalytic and the non-catalytic process. Finally, the stability of a platinum catalyst has been tested for eight consecutive runs without any noticeable loss in catalyst activity.     

A kinetic study on the dissolution of disperse dyes in the presence of intensifying additives

The kinetics controlling the water solubility of a disperse dye in the presence of the intensifiers polyethyleneglycol, caprolactam and combination of both were investigated. An exponential rate equation was found to describe the dissolution process. It was established that the additives increase the rate of dissolution.     

Synthesis of novel fluorescent styryl dyes based on the imidazo[1,2-a]pyridinium chromophore and their spectral-fluorescent properties in the presence of nucleic acids and proteins

The imidazo[1,2-a]pyridinium heterocyclic system was used to prepare styryl dyes. Improved synthetic methods were proposed for the parent imidazo[1,2-a]pyridines and their corresponding quaternary salts. The standard method for preparing styrylcyanines was modified for the synthesis of the target imidazo[1,2-a]pyridinium dyes. Spectral-luminescent properties of the obtained dyes in free state and in the presence of nucleic acids, BSA, and BSA/detergent system were studied. 7-[2-(4-Dihexylaminophenyl)-1-ethenyl]-2-(2,4-dimethoxyphenyl)-1-ethylimidazo[1,2-a]pyridin-1-ium iodide (SIP-8) containing C₆ aliphatic tails and 2,4-methoxy substituents in the 2-phenyl ring exhibited specificity to BSA.     

苯并二呋喃酮类分散染料的合成及近期发展

本文介绍了苯并二呋喃酮类分散染料的类型、合成方法及最近几年来的发展状况。     

Methods for calculating the evaporation heats of hydrocarbons and their mixtures in a wide temperature range

Studies of liquid–vapor phase transitions allowed us to determine the thermodynamically substantiated scales for constructing a generalized temperature dependence of evaporation heats for individual hydrocarbons and their binary mixtures.     

Studies on the performance of a hydrocyclone and modeling for flow characterization in presence and absence of air core

Hydrocyclones are getting more and more interest from various industries. They are widely used to separate particulates from liquid at high throughput because of their advantages like simple structure, low cost, large capacity and small volume, require little way of maintenance and support structure. Modeling of complex and multiphase flow behavior inside the hydrocyclone is done usually with the help of computational fluid dynamic study. Current study involves experimental investigation of separation performance characteristics of the hydrocyclone using new design parameters. For experimental purpose, a new hydrocyclone was designed with insertion of solid rod, at central portion of conical section of hydrocyclone, inside the hydrocyclone . By which air core could be eliminated effectively and hydrocyclone performance is improved. This effect may be observed due to reduction of radial and axial components of velocity and turbulence in the area near the entrance of the vortex finder. Therefore, the flow field characteristics inside the hydrocyclone with no air core become more suitable for separation. Also the effect of flow rate, vortex finder depths, air core and particle interaction were studied experimentally. A new arrangement was suggested to eliminate the air core formed inside the hydrocyclone. In this case, effect of diameter and height of solid rod inserted inside the hydrocyclone with changing total inlet flow rate was studied experimentally. Three-dimensional geometry and meshing of hydrocyclone is created in Gambit, preprocessor of commercial software—Fluent, for hydrodynamic study.     

含空气蒸汽冷凝传热特性数值模拟

根据已有的传热传质关系式,通过CFD软件在控制方程中加载控制方程源项,建立了含空气蒸汽冷凝的数值计算模型,运用此模型对两种实验的共10组工况进行了数值计算。结果表明,计算模型对两组实验在压力、温度、空气含量以及冷凝传热系数的预测方面均有较高的准确度;潜热传热系数及显热传热系数都随着空气含量的升高而减小;在空气质量分数低于50%的工况下,潜热换热是冷凝传热的主导因素;局部潜热传热系数沿传热管高度方向从下至上呈递减趋势,而局部显热传热系数则呈现相反变化。