The spectroscopic behaviour of J-aggregates of cyanine dyes without long chains incorporated in the monolayer assemblies

Cyanine dyes without long alkyl chains can be incorporated into composite monolayers with stearic acid at the air-water interface. In the composite monolayer of a 1:1 mixture of dye I (5,5′-dichloro-3,3′,9-triethylthiacarbocyanine chloride) and stearic acid on the water surface, two J-bands were observed, depending on the surface pressure. In the case of dye II (5,5′-dichloro-3,3′-diethyl-9-phehylthiacarbocyanine chloride) the J-aggregate was more stable than those of dye I.

The composite monolayers including the dyes can be transferred onto a solid support, retaining the J-aggregate between stearic acid layers. When the temperature was raised above 55°C, the J-band decreased very rapidly with a simultaneous increase in dimer and monomer bands. These spectral changes can be repeated with good reversibility. The correlation between the absorption spectra and the formation of J-aggregates for dyes I and II is discussed.     

Growth and coarsening of g. p. Zones in Al- Zn alloys

The structural changes during the precipitation of G. P. zones in Al-Zn binary alloys have been investigated by means of anin situ small-angle scattering technique using synchrotron radiation. Defining a specific time, normalized by the half-completion time, the time-dependent evolution of the precipitation process can be divided into three periods, independent of alloy composition and quench-ing conditions. The structural and kinetic features of the first two periods have been analyzed in detail. The first stage represents a growing process of clusters with diffuse interface into the well-defined G. P. zones. The average size of these clusters increases, and the density decreases. The second stage corresponds to the Ostwald ripening process. This mechanism is described by utilizing a modified Lifshitz-Slyozov-Wagner theory.     

Stereoselective Hydrolysis of Amino Acid Esters Catalyzed by β-Cyclodextrin-L(or D)-histidine Compounds

The catalytic activity of β-cyclodextrin-L(or D)-histidine compounds, β-CD-D-His(e) ( 2a ), β-CD-L-His(e) ( 2b ), and β-CD-D-D-His(a) ( 2c ), for the stereoselective hydrolysis of N-acyl-amino acid esters ( 3a-f ) was examined at 25° C (pH 7.90). The ability of 2a-c to bind the ester substrate into the cyclodextrin cavity and to attack the bound substrate by the nucleophilic imidazolyl group of the histidine moiety resulted in extremely high activity for those catalysts. However, the stereoselection of the enantiomeric esters during the inclusion of the substrate by 2a-c was found to be opposite, in terms of chiral specificity, to that during the esterolysis of 2a-c in the molecular cavity: that is, the stereoselective activity of 2a-c is very small. The catalytic activities of 2a-c are also influenced by the structural differences in 3a-f , which result in the different modes of substrate inclusion by the catalyst through hydrophobic forces.     

Large-field (> 20 × 25 mm) replication by EUV lithography

A two-aspherical-mirror system designed for large-area, high-resolution pattern replication has been developed. In order to expand the exposure area to 20 mm × 25 mm, new critical-illumination optics and a scanning mask stage synchronized with the wafer stage were developed. These improvements enabled the reduction of patterns in a large exposure field.     

Preparation of anti-oil stained membrane by grafting polyethylene glycol macromer onto polysulfone membrane

In this study, anti-oil stained ultrafiltration membrane was prepared by grafting a polyethylene glycol diacrylate macromer onto a plasma-activated polysulfone membrane. The macromer formed a hydrate layer which prevented oil in emulsion from directly contacting the membrane surface, thus preventing the oil from staining the membrane. © 1994 John Wiley & Sons, Inc.     

Chain extenders for polyesters. I. Addition-type chain extenders reactive with carboxyl end groups of polyesters

Effective chain extenders for linear polyesters were investigated among some bis-heterocycles, which were capable of coupling carboxyl terminals of the polyesters through addition reaction. Consequently, 2,2′-bis(2-oxazoline), 2,2′-bis(5,6-dihydro-4H-1,3-oxazine) and N,N′-hexamethylenebis(carbamoyl-2- oxazoline) were found to be the most effective chain extenders. Starting from a poly(ethylene terephthalate) (PET) having intrinsic viscosity ([η]) of 0.66 and carboxyl content (CV) of 46 eq/10⁶ g, one could obtain polyesters with [η] of above 1.0 and CV of below 5 eq/10⁶ g in the presence of the chain extenders. Typical reaction condition for the coupling of PET was heating PET under atmospheric nitrogen above its melting temperature with 0.5 mol % of a chain extenders only for several minutes. Bis-2-thiazolines showed no effect under the condition investigated, while in case of bis-2-imidazolines definite degradation was observed. Bis-N-acylaziridines and bisiminocarbonates resulted in some gell formation, indicative of side reactions.     

Mechanical properties of laser-pressure-welded joint between dissimilar galvannealed steel and pure aluminium

Dissimilar metal joints of Zn-coated Galvannealed steel (GA steel) and commercially available pure aluminium (A1050) sheets were produced by changing the laser power and the roller pressure by the laser pressure welding method. By this method, the YAG laser beam was irradiated into a flare groove made by these dissimilar metal sheets. In addition, the laser beam was scanned at various frequencies and patterns through the fθ lens using two-dimensional scanning mirrors. Then the sheets were pressed by the pressure rolls to be joined.

The compound layers in the weld interface were observed by an optical microscope and the layer thicknesses were measured. The thicknesses ranged from 7 to 20 μm. The mechanical properties of the welded joints were evaluated by the tensile-shear test and peel test. In the tensile-shear test, the strengths of the joints produced under the most welding conditions were so high that the fracture occurred through the base aluminium sheet. In the peel test of the specimens subjected to a laser beam of 1200–1400 W power under roller pressure of 2.94 kN, the specimen fracture took place in the base aluminium sheet. Even if the compound layer was thick, high joint strength was obtained. On the other hand, the specimen fractured in the weld interface at a laser power of 1500 W. The results of X-ray diffraction on the peel test specimen surface identified that the intermetallic compound on the GA steel side was Fe₂Al₅Zn_0.4. Moreover, the aluminium parts adhering to the GA steel side were confirmed. These results suggest that the fracture in the peel test occurred between the compound layer and A1050 and partly in the base aluminium. A micro-Vickers hardness test was performed to examine the hardness distribution in the compound layer. The hardness values near A1050 and GA steel were about 100 and 470 Hv, respectively, which suggests that the compound layer should not necessarily consist of brittle intermetallic compounds. It is therefore concluded that laser pressure welding could produce high strength joints of GA steel and A1050 dissimilar materials.     

Mechanochemistry of Syringylglycerol-β-Guaiacyl Ether and Its Similarity to the Conventional Bleaching of Mechanical Pulps

Syringylalcohol (1), α-methyl syringylalcohol (2), 3, 4, 5-trime-thoxyphenyl methylcarbinol (3) were dispersed onto filter paper pulp or linter pulp, and treated, respectively, with a ceramic ball mill (CBM) or a vibration ball mill (VBM-1 or -2) under air for 1h. Mechanical treatment of VBM-2, having the more rigid surface of linter pulp, furnished the p-carbonylphenols (5), (6), and 3, 5-dimethoxy-p-benzoquinone (7). Mechanical treatments of syringylgl-ycerol-β-guaiacyl ether (4) with CBM, VBM, and a laboratory refiner provided α-(2-methoxyphenoxy)-β-hydroxypropiosyringone (8) in the highest yield and a less yield of p-quinone derivative (7) and others as shown in TABLE 2 and FIGURE 3. When treated the resultant mixture with alkaline H₂0₂, the chromophore (III) can be decomposed, but remarkable amounts of the leucochromophre (IV) are produced as shown in FIGURE 4.     

Novel Poly(N‐isopropylacrylamide)‐graft‐poly(vinylidene fluoride) Copolymers for Temperature‐Sensitive Microfiltration Membranes

In the present work, we report on the synthesis and characterization of poly(vinylidene fluoride) (PVDF) with N‐isopropylacrylamide (NIPAAM) polymer side chains from molecular graft copolymerization in solution. The copolymer can be readily cast into temperature‐sensitive microfiltration (MF) membranes by the phase inversion technique. The copolymer approach to membrane fabrication allows a much better control of the physicochemical nature of the membrane pores through the variation in graft concentration, membrane casting temperature and concentration of the membrane casting solution.

     

Corrosion behaviour of mild steel in chloride solutions with Na2HPO4 additive and the development of antifreeze

ABSTRACT

Chloride salts can prevent roads from freezing in cold regions, together with severe corrosion on steel constructions. To develop an ecological and low-corrosive antifreeze, di-sodium hydrogenphosphate (Na₂HPO₄) was chosen as the additive into chloride salts. The addition of Na₂HPO₄ into either of the antifreezes of natural salt (N/S), NaCl, CaCl₂ or MgCl₂ can suppress the corrosion reaction of mild steel in the 3.0% antifreeze solution. Moreover, the addition of CaCl₂ or MgCl₂ into the antifreeze containing NaCl and 2.0% Na₂HPO₄ significantly decreased the corrosion rate. According to polarisation and XPS analyses, it is evident that the obtained low corrosion rates on mild steel are related to the suppressed cathodic and anodic reactions and the formation of a protective film containing Fe, P, O, Ca or Mg.

This paper is part of a supplementary issue from the 17th Asia-Pacific Corrosion Control Conference (APCCC-17).