Soluble dyes defined

An emulsion may be defined as a mixture of particles of one liquid with some second liquid. The two common types of emulsions are oil-in-water (O/W) and water-in-oil (W/0), where the term oil is used to denote the water-insoluble fiuid. These two types are illustrated in Fig. XIV-1, where it is clear that the majority or outer phase is continuous, whereas the minority or inner phase is not. These two emulsion types are distinguished by their ability to disperse oil or water-soluble dyes, their dilution with oil or water, and their conductivity (O/W emulsions have much higher conductivity than do W/0 ones see Ref. 1 for reviews). 

As a special case, the interactions of soluble dyes with uniform inorganic particles is considered here, with emphasis on the preparation of well defined pigments. 

As discussed earlier, the use of an indicator to determine the CMC can be applied to aqueous as well as non-aqueous systems. Rhodamine B, for example, can be added to detect reversed micelles at very low surfactant concentrations. The transition from monomers to micelles can then be followed by the depolarization of the fluorescence. Another method involving the use of a dye is dye solubilization. For non-aqueous systems, a water-soluble dye should be used, for example, Eosin Y or Merocyanin 540. As soon as the first aggregates form, the solubilized dye can be measured by its UV-Vis absorbance. This method yields satisfactory results for some surfactants. However, sometimes the solubilization of such a dye is so high that the micellar structure is affected by the dye. If the solubilization is weaker, the dye taken up by the micelles is often insufficient to produce a reasonable signal. Especially when the CMC is very low, the pseudo-phase volume fraction of the micellar phase at concentrations just above the CMC is far too low to solubilize a significant amount of dye. This makes it difficult to define a clear CMC and requires the evaluation of different water-soluble dyes. It should be mentioned that as with aqueous... 

Dyes, on the other hand, ate colored substances which ate soluble or go into solution during the appHcation process and impart color by selective absorption of light. In contrast to dyes, whose coloristic properties ate almost exclusively defined by their chemical stmcture, the properties of pigments also depend on the physical characteristics of its particles. 

A defining characteristic of dyes is the abiUty to dissolve in a given medium. Dissolution leaves no particles to refract or scatter light and thus a dye solution is transparent. A distinct advantage of a soluble-type stain is this transparency and brightness afforded by use of various dye types. SolubiUty is increased by agitation or heat, or a combination of the two. 

For practical reasons the different solubility can be used as a basis for a classification of solvent dyes, although there is no strict differentiation. Chemical constitution is defined here as a structure which meets the corresponding solvent requirements. 

The C.I. Constitution number is given in this paper as a guide to references for synthesis in the Colour Index. Any duplication of these syntheses should be attempted only under the supervision of an experienced chemist who is aware of the latest ecological, toxicological, and safety requirements. These requirements must be constantly observed even if attention is not explicidy drawn to them. A further point to note is that dye chemists often write the free sulfonic acid form, even if they have obtained a salt. The reason is that the dyes are often not completely neutral or may not be a defined salt. This commonly arises when potassium or sodium salts are involved, and therefore the free sulfonic acid formula is frequentiy used as a general term. A sulfonate salt does not influence the color as such, but water solubility is affected. Consequently, for pigments the cation is always given in the chemical formula. 

In addition to the light-harvesting property, this host-guest complex also exhibits a high photocytotoxicity. Its IC50 value, defined as the dye concentration required to kill 50% of the cells, for HT29 human colon adenocarcinoma cells is only 0.09 p,M, which is comparable with that of 113 itself formulated with Cremophor EL (0.15 p,M). The complexation with 93 (M = 2H) enhances the water solubility of 113 and therefore can prevent the use of Cremophor EL, which may cause serious hypersensitivity reactions. 

Colorants are typically defined as pigments and dyes that, when added to plastics, define a specific color. The subject of colorants has been discussed in numerous books and papers. However, in the context of this chapter, a dye is defined as a substance that is soluble in the resin system and produces color only by the absorption of light and no scattering of light. Pigments are not soluble in the resin system and therefore must be mixed into the resin by one of many dispersion processes. Factors such as pigment particle size and ease of mixing or dispersion directly influence their... 

A definition for plastics dyes that has evolved in practical use is somewhat more useful than traditional ones namely, a dyestuff is a dyestuff when used in a given polymer because it is soluble in the polymer. In contrast, pigments are therefore defined as not being soluble in the polymer being colored. 

In addition to the terms defined in Table 1.9, empirical polarity scales have been developed based on solvatochroism. The most common solvatochromic dye used in these experiments is Reichardt s betaine dye (Figure 1.8). The UV-Vis spectrum of a solvatochromic dye changes in different solvents. In some cases, the dyes are modified to increase solubility for experiments in lower polarity media or alternative solvents. 

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