Polarization colors

Activated charcoal is ultrafinely divided carbon with lots of places to suck up big, huge, polar, colored impurity molecules. Unfortunately, if you use too much, it ll suck up your product And, if your product was white, or yellow, it ll have a funny gray color from the excess charcoal. Sometimes, the impurities are untouched and only the product gets absorbed. Again, it s a matter of trial and error. Try not to use too much. Suppose you ve got a hot solution of some solid, and the solution is highly colored. Well,... 

Wolman, M., and Bubis, J. J. (1965). The cause of the green polarization color of amyloid stained with Congo red. Histochemie 4, 351-356. 

Mineral fi ber Index of refraction of medi urn Color seen with fiber oriented parallel to polarizer Color seen with fiber oriented perpendicular to polarizer ... 

Polarizing colors are then dependent on two variables the birefringence of the substance and the thickness of the particle. There is a chart showing polarizing colors versus thickness and birefringences called a Michel-Levy chart 2.J]. Thickness is plotted on the ordinate, while polarizing colors are plotted along the abscissa. 

Orthoscopic examination with crossed polars is carried out first of all to determine the isotropism or the anisotropism of a sample. The polarization colors, the defects and variation in molecular orientation, and the orientation pattern or texture of liquid crystals are observed in this examination. With a heating stage the temperature of phase transition is also determined. In addition, with use of a compensator, the determination of vibration directions of the ordinary and extraordinary rays, the determination of relative retardation and birefringence are possible. In this section, the optical basics for orthoscopic observations are briefly outlined. The description of textures frequently observed for polymeric liquid crystals is given in Section 4.1.4. 

Retardation is measured more accurately with compensators, with sample and compensator set at 45° between crossed polars. This alignment is critical, as the superposition of birefringent objects at arbitrary orientations produces extremely complicated effects [70, 71]. The compensator is adjusted until the specimen appears dark. Then the retardation of sample and compensator are equal and opposite, R(net) = 0. If the polarization color change on inserting a compensator shows an increase in retardation, then R(net) > R(specimen), and the compensator is adding its effect to that of the specimen. The... 

Determine the dispersion of birefringence by measurement on a thin sample over a range of wavelengths, then calculate the effect of dispersion on polarization color. 

Polarized light microscopy has shown micrometer-sized domains in the thermotropic LCPs aligned along the fiber axis. The meander of the domains is consistent with their polarization colors (Fig. 5.87, color section). The domains... 

Fig. 5.87 Incomplete extinction in uniaxially oriented TLCP fibers, ribbons and films gives a salt and pepper texture which is seen as individual domains less than 0.5/xm across. The similar polarization colors in polarized light suggest the domains are within the same order, and thus have similar birefringence. 

One of the main tasks in PCS is to obtain the maximum amount of (useful) information from the fluorescence light with reasonable effort and costs. Therefore, as many photons as possible should be detected including their parameters such as polarization, color, detection time, etc. [67]. Improvements have, however, not only been restricted to an improved detection of photons and their parameters, but also implemented new excitation and detection geometries. 

The Michel-Levy chart of these polarization colors [61,62,64] can be used to estimate the retardation of a specimen, within the range 200-1600 nm. For example, first order red is at 575 nm, third order green is at 1250nm. At... 

Polarizers, color filters, and reflectors are usually mounted outside the cell, as dichroic displays do not have very high line reso-... 

In white light, anisotropic structures may appear brightly colored when viewed in crossed (or parallel) polars. These polarization colors or interference colors depend on the retardation (see Section 3.1.7). An estimate of sample retardation can be made from the standard sequence of colors, published as the Michel-Levy chart in many texts [5, 8, 9, 26, 28]. Color can also be used to find the sign of a small retardation when a first-order red plate is inserted as a compensator in white light. Modem devices exist where the polarizing elements are electrically driven and computer controlled. These allow simultaneous measurement of retardation and orientation direction at every point on the image and thus the creation of retardation and orientation maps [29]. 

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