Diffractive pigment

The phenomena of light interference can also be produced using difiraction technology. Diffractive pigments are manufactured by vacuum deposition on a specially patterned surface [49, 50]. 

By controlling the particle diemnsions and the surface microstructure, diffractive pigments generate the appearance of multiple, bright rainbow-producing 

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The latest category of special-effect pigments is diffractive pigments, in which interference is produced by diffraction technology. These pigments are produced by vacuum deposition on specially patterned surfaces. 

Mica [12001 -26-2]—Cl Pigment White 20, Cl No. 77019. A white powder obtained from the naturally occurring mineral muscovite mica, consisting predominantly of a potassium aluminum siHcate, [1327-44-2] H2KAl2(Si0 2- Mica may be identified and semiquantitatively determined by its characteristic x-ray diffraction pattern and by its optical properties. 

X-Ray diffraction analysis of phthaleine and sulfophthaleine pigments 97YZ764. 

Applications The general applications of XRD comprise routine phase identification, quantitative analysis, compositional studies of crystalline solid compounds, texture and residual stress analysis, high-and low-temperature studies, low-angle analysis, films, etc. Single-crystal X-ray diffraction has been used for detailed structural analysis of many pure polymer additives (antioxidants, flame retardants, plasticisers, fillers, pigments and dyes, etc.) and for conformational analysis. A variety of analytical techniques are used to identify and classify different crystal polymorphs, notably XRD, microscopy, DSC, FTIR and NIRS. A comprehensive review of the analytical techniques employed for the analysis of polymorphs has been compiled [324]. The Rietveld method has been used to model a mineral-filled PPS compound [325]. 

The influence of mixed coupling on the properties of Cl Pigment Yellow 12 has been studied recently [12]. Carboxy- or sulpho- substituted derivatives of acetoacetanilide were evaluated as co-coupling components and analysis revealed that the state of the crystal and the particle size were changed and new diffraction peaks were observed. When these modified pigments were treated with a fatty amine such as stearylamine, the hydrocarbon chains enclosed the anionic groups in the co-coupler so that properties such as flowability, wettability and dispersibility in nonpolar solvents were greatly improved. 

Organic pigments have been reviewed [118]. X-ray powder diffraction data of many organic colorants have been collected and discussed [119]. 

Questions about such interactions could only be resolved by knowledge of the exact geometry of the atoms of a pigment molecule in its unit cell and the relative position of each individual molecule within the crystal lattice. This is elucidated through three dimensional X-ray diffraction analysis of single crystals [8]. 

Considering the fact that the X-ray diffraction pattern of a crystal depends on its lattice structure, pigment powders can be analyzed with a Debye-Scherrer diffraction camera to establish a correlation between X-ray diffraction and crystal modification. It is synthetically not possible to produce a defined crystal modification of a new pigment. Attempts to modify the preparative procedure or to apply different aftertreatment may result in a pigment of two or more crystalline forms, different not only in lattice structure, but also in color and performance. 

Comparative three dimensional X-ray diffraction studies have been carried out on a red and a brown representative of the Naphthol AS pigment series, differing only by the presence or absence of one methoxy group in the anilide function of the coupling component (4). 

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 crystallinity of organic pigment powders makes X-ray diffraction analysis the single most important technique to determine crystal modifications. The reflexions that are recorded at various angles from the direction of the incident beam are a function of the unit cell dimensions and are expected to reflect the symmetry and the geometry of the crystal lattice. The intensity of the reflected beam, on the other hand, is largely controlled by the content of the unit cell in other words, since it is indicative of the structural amplitudes and parameters and the electron density distribution, it provides the basis for true structural determination [32],... 

Any crystal modification is practically fingerprinted by its X-ray diffraction spectrum. Another factor determined by the same instrumentation is isomorphism in chemically different pigments, which is associated with almost equal diffraction angles and X-ray intensities in both experiments. It is also important to ensure that the intensity of the incident beam is approximately the same for both measurements. 

X-ray diffraction of pigment powder lends itself to the determination of pigment crystallinity. It is thus possible not only to determine the chemical configuration of a crystalline compound, but also the lattice system of the crystal through the diffraction pattern, in other words, the crystal quality size of crystallites, structural defects (Fig. 18). 

Since the properties of organic pigments are closely related to the quality of their crystals, X-ray diffraction provides the instrumentation that is necessary to monitor those properties during synthesis and, even more important, during finishing. 

Scanning electron microscopy makes it possible to trace the time curve of blooming on the surface of a plasticized PVC sample [43]. Pigment Yellow 1 develops detectable surface crystals within a period of only a few horns, and the area is densely covered within a day (Fig. 26 a and b). Even a small space may be sufficient for a pigment to develop a variety of apparently different crystalline forms (Fig. 27), although only one crystal modification appears by X-ray diffraction... 

Table 5 Changes in the crystallite size of some polycyclic pigments in coatings or plastics coloration as a result of heat exposure (calculated from the X-ray diffraction spectra).

The comparative X-ray diffraction analysis of Pigment Yellow 1, 11710 with P.Y.6 revealed also an almost planar structure of the molecule in its 2-oxohydra-zone form [4],... 

Adsorption of e.g. rosin (abietic acid) at the pigment surface may - depending on the concentration of the rosin - reduce or accelerate the crystal growth. The presence of an excess amount of rosin during the production of diarylide yellow pigments of the Pigment Yellow 13 type affords an additional crystal modification, which can be identified by X-ray diffraction spectroscopy [4],... 

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