Dichroism dichroic ratio

It was found that In D decays linearly with time [where D is the dichroic ratio defined in Eq. (2)]. The time constant for the decay of the dichroism, r, is plotted vs temperature-1 in Fig. 25. It was shown (Stavola et al., 1988b) that the time constant, r, for a single H jump from one BC site adjacent to the B to another given by r=4r. From the fit to the data shown in Fig. 25 the following expression for the time constant for a single H jump was obtained ... 

Further, planar orientation of PPV chains in the film plane was demonstrated from the linear dichroism dichroic ratio Ap/As decreased from 2.1 to 1.2 when the incident angle of polarized light increased from 0° to 45°, where Ap and As... 

The linear dichroism measurement demonstrated that MOPPV chains formed the planar orientation chains in the LB films dichroic ratio Ap/As... 

Dichroic dyes of positive and negative dichroism are required for various configurations of the Heilmeier and Zanoni as well as the White and Taylor GH-LCDs with positive and negative contrast. They should be chemically, photochemically and electrochemically stable, as well as exhibit a high order parameter, a high dichroic ratio and good solubility in the host nematic matrix. 

In 1958, Beer et al. re-examined the infrared dichroism situation and remeasured the dichroic ratio for several of the peptide bands in collagen. On the basis of studies on model compounds, they calculated the directions of the transition moments for the principal bands in the peptide link and, using the atomic coordinates for various proposed collagen models, the inclination of these transition moment vectors to the fiber axis. Since Beer (1956) had shown that the dichroism of a partially oriented polymer may be considered equivalent to that of a sample containing fully aligned and completely random portions, a disorientation parameter (/) characteristic of the degree of order of the sample could be calculated for each band. The spread of the values obtained for this parameter, which is characteristic of the sample only and not of the bands used to determine it,... 

IR dichroism of proteins, dichroic ratios and bond angles discussed critically. 

Another quantity that characterizes optical anisotropy is the dichroic ratio Aj /Aj a frequently used alternative definition of the reduced linear dichroism is LD = (Ay - Aj )/(A + Aj ). In isotropic (randomly oriented) samples, there is nothing to distinguish physically between the laboratory X and y directions, so that such samples exhibit zero linear dichroism (A = A Hence, static linear dichroism studies are applicable only to oriented samples. 

Another use of infrared spectroscopy employs linearly polarized infrared radiation to determine information about oriented samples, an experiment that has been termed infrared dichroism. The absorbance will be a maximum when the electric field vector and the dipole moment vector are in the same direction, and the absorbance will be zero when the two are perpendicular. Only uniaxial orientation will be considered because this situation is normally found in the literature. R, the dichroic ratio, is defined as follows ... 

Some indications of the influence of ionic azobenzene derivative structure (Fig. 2.7) and polyelectrolyte can be deduced from a number of azobenzene derivative studied (Ziegler et al., 2002). All studied LbL films (24 layers) exhibited only out-of-plane orientation. Only for anionic-derivative Z1 (indicated in Fig. 2.7) and only with PDADMAC, dichroic ratio of 2 was observed. In the layers of Zl, but with PEI as polyelectrolyte, photoorientation and photoisomerization are totally restrieted by strong aggregation. The high value of dichroism of PDADMAC/Zl layers should be caused by the hexamethylene spacer of Zl, which results in higher mobility necessary for the orientation process. Cationic Z2-Z5 were all manufactured into LbL films using the same polyelectrolyte PSS, and maximum value of 1.4 (dichroie ratio) was found. 

Carbonate tons and Enamel. Elliott (1965) has used polarized infrared absorption spectra to study longitudinal sections of human tooth enamel in order to determine whether carbonate ions can substitute for hydroxyl ions in the enamel. His conclusion was that carbonate ions substitute to a very limited extent for hydroxyl ions. The evidence consisted of certain bands in the infrared spectra of enamel (Fig. 19.12) which coincide with those of the synthetic apatite in which this substitution is known to have taken place (Fig. 19.13). In a hydroxyapatite that had been reacted with carbon dioxide at 1000°C, carbonate ion had absorption bands at 878, 1463, and 1528cm , and the hydroxyapatite 3570 cm band (OH ) had disappeared (Fig. 19.13). Elliott examined enamel which had been heated at 1000°C in carbon dioxide and measured the dichroism of the out-of-plane deformations at the 879 cm" mode (Fig 19.14). From the dichroic ratio he was able to calculate that the plane of the carbonate ion is nearly parallel to the c-axis of the apatite. Elliott et al. (1948) have given the dichroic ratio applicable to this case as... 

General quantitative relations between observed dichroic ratios and structural orientation functions have been considered by several authors. These include Fraser,Beer, Patterson and Ward, Stein, Chappel, Kawai and Stein, and Nomura et al More recently, Flory and Abe, and also Nagai, have carried out statistical calculations relating specifically to the stress-dichroism coefficients of amorphous polymer networks. Some results of these calculations will be summarised below. First, however, it is informative to derive some general relationships between the dichroic ratio and appropriate orientation functions. 

IR spectroscopy is very useful for the assessment of chain orientation. Recent excellent reviews on the subject have been given by Bower and Maddams [19] and Koenig [20]. The measurement of IR dichroism requires the use of IR radiation with polarization parallel to and perpendicular to a selected reference direction. The fundamental principle underlying the dichroism is that the absorbance A is proportional to the square of the cosine of the angle between the transition moment vector and the electrical field vector. The IR radiation is strongly absorbed when the electric vector of the light and the transition moment vector are parallel. No absorption of the IR radiation occurs however if the two vectors are perpendicular to each other. The dichroic ratio R is defined as... 

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