Pigment crystal structure

After development, the textile is rinsed and subjected to careful afterwash in which excess dye lake is removed from the fiber surface. Otherwise, it severely impairs the rubbing-fastness of the dyeing. In addition, through the change in pigment crystal structure occurring during aftertreatment, a stable final shade is achieved with enhanced fastness. ... 

Vaterite is thermodynamically most unstable in the three crystal structures. Vaterite, however, is expected to be used in various purposes, because it has some features such as high specific surface area, high solubility, high dispersion, and small specific gravity compared with the other two crystal systems. Spherical vaterite crystals have already been reported in the presence of divalent cations [33], a surfactant [bis(2-ethylhexyl)sodium sulfate (AOT)] [32], poly(styrene-sulfonate) [34], poly(vinylalcohol) [13], and double-hydrophilic block copolymers [31]. The control of the particle size of spherical vaterite should be important for application as pigments, fillers and dentifrice. 

C. I. Pigment Red 183 (214), which range in shades from yellow to bluish-red and brown and exhibit excellent fastness properties. Their good stability to light and heat and their insolubility is attributed to extensive intermolecular association as a result of hydrogen bonding and dipolar forces in the crystal structure, as illustrated in Figure 9.3. 

Figure 9.3 Intermolecular association in the crystal structure of a benzimidazolone azo pigment...

The crystal structure of the OCP from Arthrospira maxima has been solved to 2.1 A resolution (Kerfeld et al. 2003). It is composed of two domains and the carotenoid, 3 -hydroxyechinenone, spans both. The carotenoid is almost completely buried within the protein only 3.4% of the pigment surface is accessible to solvent (see Figure 1.3a). The OCP is a dimer in solution the intermolecular interactions are largely mediated by hydrogen bonding among the N-terminal 30 amino acids, as shown in Figure 1.3b... 

Prescott M, Ling M, Beddoe T, Oakley AJ, Dove S, Hoegh-Guldherg O, Devenish RJ, Rossjohn J (2003) The 2.2 A crystal structure of a pocilloporin pigment reveals a nonplanar chromophore conformation. Structure 11 275-284... 

A white pigment for rubbers and plastics characterised by high tinctorial power, fastness to light, and chemical stability. Titanium dioxide pigments are made in two crystal forms, mtile and anatase, which differ in crystal structure and crystal size. 

Inorganic pigments, 29 375-417 black pigments, 29 408-410 chemical properties of, 29 377-378 classification of, 29 402 colored pigments, 29 397-408 crystal structure of, 29 377-378 durability of, 29 382-384 environmental aspects of, 29 413-415 lead- and cadmium-containing, 29 414-415... 

The methods used to convert these vat dyes into a suitable physical form (and in some cases, crystal structure) for use as pigments have been carefully guarded industrial secrets, revealed only in patents. The general principles are clear, however. One method is to reduce the vat dye in the usual manner to bring it into solution and then to re-precipitate it under very carefully controlled conditions. The other is to subject the dye to a fine grinding operation. Whichever approach is used, the aim is to reduce the mean particle size to below 1 J,m (1000 nm). 

In the manufacture of quinacridone pigments only the first and last of the four routes outlined have been operated commercially. Synthesis is followed by the milling processes necessary to give products with the crystal structure and particle size required for their use as pigments. 

Naturally occurring iron oxide pigments are widely distributed geographically and can be found in a wide range of colours from black to reds and yellows, depending on composition and crystal structure. Ochres of many kinds and from different sources were often used in oil... 

Substitution patterns, especially that of the diazotized aromatic amine, determine the color of a pigment to some extent but empirical data do not lead to unambiguous conclusions as to the exact influence of a particular substituent on the shade. The problem is intricate, since the substitution pattern also has a bearing on the size and orientation of a pigment molecule and therefore on its crystal structure, including all the interactions associated with it. 

An overview of the effect of crystal structure on color application properties of organic pigments was published [7]. 

Fig. 1 The complete crystal structures of pigment 4 (R H) and its derivative (R OCH3) as derived from three dimensional X-ray diffraction analysis. The molecules are shown both as single units (above) and within the crystal lattice (below), seen perpendicular to the molecular plane.

The thermodynamic stability is a feature unique to each of the individual crystal structures of a chemical compound. Transforming an unstable modification into a stable one may require a certain amount of activation energy, but the process always offers an ultimate energetic advantage. Energy levels may vary considerably between pigments and even between crystal modifications. 

This section will discuss some important concepts from coloristic practice and the optical properties of pigmented systems. Space considerations permit a treatment of only the most vital concepts. The reader must consult the literature for further details and accounts of special problems [1], A review on the effect of crystal structure on color application properties was published [2],... 

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