Dyes physical attraction

Recently, a series of chemical substances called functional dyes have attracted considerable attention. Because such dyes have long conjugated pi-electron systems and in many cases possess intramolecular charge transfer structures, functional dyes are expected to show interesting optical and electronic properties. Among functional dyes, phthalocyanine compounds have been extensively investigated because of their excellent physical, chemical and coloristic properties, as mentioned above. For example, about 1000 related US patents, published from 1990 onwards, are retrievable from the World Patent Index data base of Derwent, and more than 30 % of these are classified in such non-colorant applications as electrophotography, catalysis, and infrared radiation absorption. 

The insoluble, hydrophobic disperse dyes readily dye nylon, and because their mode of attraction is completely nonionic they are completely insensitive to chemical variations and pH. Small molecular-sized disperse dyes (ca mol wt 400) show very high rates of diffusion and excellent migration properties and they are insensitive to physical variations in the nylon. As the molecular size of disperse dyes increases they show increasing sensitivity to physical variation. 

Up until 1977, the non-covalent polymeric assemblies found in biological membranes rarely attracted any interest in supramolecular organic chemistry. Pure phospholipids and glycolipids were only synthesized for biophysical chemists who required pure preparations of uniform vesicles, in order to investigate phase transitions, membrane stability and leakiness, and some other physical properties. Only very few attempts were made to deviate from natural membrane lipids and to develop defined artificial membrane systems. In 1977, T. Kunitake published a paper on A Totally Synthetic Bilayer Membrane in which didodecyl dimethylammonium bromide was shown to form stable vesicles. This opened the way to simple and modifiable membrane structures. Since then, organic chemists have prepared numerous monolayer and bilayer membrane structures with hitherto unknown properties and coupled them with redox-active dyes, porous domains and chiral surfaces. Recently, fluid bilayers found in spherical vesicles have also been complemented by crystalline mono-... 

Paper chromatography is an analytical technique that uses paper as a medium to separate the different dye components dissolved in a mixture. In this process, the mixture to be separated is placed on a piece of chromatography paper. A solvent is then allowed to soak up into the paper. As the solvent travels across the paper, some of the components of the mixture are carried with it. Particles of the same component group together. The components that are most soluble and least attracted to the paper travel farther than others. A color band is created and the different components can be seen separated on the paper. The success of chromatography hinges on the slight difference in the physical properties of the individual components. 

Historically the first commercially successful synthetic fibre was Nylon 66. At the time when it appeared on the market its dyeing presented many difficulties. The fibre is hydrophobic and, therefore, not very attractive to water-soluble dyes. In the early stages of manufacture the polymer was liable to vary from batch to batch, both in physical properties and with regard to the number of amino end groups. This caused variations in affinity for dyes producing barry effects, unless great care was taken to keep each batch separate. 

The initial attraction between the fibre and the anionic dye is polar but when the molecule is attached to the site non-polar forces come into play. Because of this dual attachment the wet fastness is significantly better than that of the disperse dyes where only physical forces are involved. The anionic dyes, however, are more sensitive to variations in the chemical constitution of the polyamide and also they are of higher molecular weight than the disperse dyes and therefore may give rise to levelling difficulties and yield barre dyeings. 

At first reverse phase sorbents were prepared by impregnating the support with long-chain hydrocarbons such as paraffins and silicone oils to give packings of defined composition with the stationary phase held to the support by purely physical forces of attraction [53]. These materials though of use for the analysis of lipophilic substances, fats and waxes, steroids and fat soluble vitamins and dyes were unsatisfactory as the stationary phase can be washed off by the eluant which consequently lowers the capacity and effectiveness of the partition separation. 

Fluorescent semiconductor nanocrystals (CdSe, CdTe, PbSe, and others), otherwise included in the term quantum dots (QDs), have attracted much attention in various research fields for more than 20 yeais owing to their chemical and physical properties, which differ markedly fi om those of the bulk solid (quantum size effect). Quantum dots have size-tuneable light emission (usually with a narrow emission band), bright luminescence (high quantum yield), long stability (photobleaching resistance), and broad absorption spectra for simultaneous excitation of multiple fluorescence colors compared with classical organic fluorescent dyes. 

The chemical and physical characteristics of plasmas and lasers make them an environmentally attractive option for surface treatment in the textile industry. Since the 1970s, lasers have been used for such textile applications as cutting and printing and, since the mid-1980s, plasmas have started to be used in the industry to oxidize fibre surfaces for improved dyeing. 

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