Color-shifting effects

It has been found that for flaky pigment particles suitable for strong color-shifting effects, a symmetrical arrangement of the layers is necessary. A minimum of five layers and, for some optical purposes, even more may be required. The need... 

Figure 12.7.2 Layering patterns of absorber (partially reflected)/dielectric (low re-fractive)/reflector (inner reflector)/dielectric/absorber used to create the optical effect of color-shifting ink.

Nacreous and interference pigments are used as colorants or part of color formulations for all applications where traditional pigments are used, but where additional color depth, brilliance, iridescence, color shift (flop), and other spectacular effects are desired [5.253]. Mica-based pigments dominate their combination of pearl and interference effects, brilliance, stability, and weather resistance is unsurpassed. Furthermore, they are non-toxic [5.221],... 

Compared to the formulation of Judd, our use of simple color shifts is much more elegant. A temporal effect is introduced when we assume that the local averaging, as described in Chapter 10, takes a finite amount of time. It takes some time until the process converges. Of course, intermediate results can still be obtained at any point in time. The computed output color would then depend on outdated information about local space average color, which is stored in the parallel network. This would explain why afterimages occur when the focus of fixation is suddenly moved to a different location. 

The electronegativities of the substituents are an important determinant of the shift, but the greater variety of the substances reveals a second effect due to the dn-pn overlap between the substituents and the silicon. Studies of the origin of the color showed that the more electrons at the silicon, the greater the bond strength of the silicon-silicon bonds and the greater the color shift. 

Quantum size effects famous examples are the color shift upon size reduction of semiconductor nanoparticles like CdSe [14-16], and the surface plasmon resonance of metallic nanoparticles like gold [17, 18]. 

Elementary chlorine, bromine, and iodine dissolve in many organic solvents, and the variations in the colors among the iodine solutions in various solvents have been a matter of interest to many workers. (Both bromine solutions and solutions of iodine monochloride show analogous variations, but the effect for iodine is by far the most striking.) In completely nonbasic solvents (for example, CCU and CS2) iodine appears violet, the same color as its vapor but as the basicity of the solvent increases, the iodine color shifts toward orange or brown, presumably because the electronic excitation responsible for the iodine color is made more difficult by approach of electron-rich reagents. As the basicity of the solvent increases, the iodine-to-iodine bond weakens in the organic base, pyridine (reaction c, below), many of the I—I bonds are broken, wrhereas... 

Color shift is another important issue for liquid crystal displays. In an IPS mode, yellowish color shift occurs at the = 45° azimuthal angle and bluish color shift occurs at = -45° due to the phase retardation difference. To suppress color shift, a chevron-shaped electrode similar to a two-domain structure has been proposed [34,35] Each pixel is divided into two domains, where the LC directors face in opposite directions and the color shift is compensated effectively. 

Another way to use the technique is to fix the colloid onto the distance layer s surface. If the height of distance layer itself is changed specifically via. an enzymatic assay shrinking or swelling the distance layer, for example, a color shift is observed. By this, the presence of an enzyme substrate or a reactive chemical is transduced by the system into an optical signal. The effect of moderate to high analyte concentrations can be observed with the naked eye. Applications and details of this technique are discussed below. 

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