Dichroic ratio linear

Using this strategy, constmction of multilayer films of - O. fim thickness by self-assembly of methyl 23-ttichlorosilyltticosanoate (MTST) on siUcon substrates has been demonstrated (Fig. 9) (165). The linear relationship between the film thickness and the layer number showed a slope of 3.5 nm /layer. Filipsometry data, absorbance intensities, and dichroic ratios for the multilayers all suggest that the samples were composed of distinct monolayers. However, ir data indicated that there maybe more tilting or disordering of the alkyl chains in the seven-layer sample than for the monolayer samples. 

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... 

Fig. 22(b) shows polarized visible absorption spectra of mixed LB films of MS-C2o binary and MS-C20-AL18 ternary systems prepared by using an aqueous subphase containing Cd2+ ions, where the ratio in the mixed system is [MS] [C20] [AL18] = l 2 x (x — 0 and 1) [77-84]. The thick and thin lines in Fig. 22(b) refer to the spectra, Atl and A , measured by linearly polarized light with the electric vector parallel and perpendicular to the dipping direction of the substrate, respectively. For x = 0, a sharp absorption peak is observed at 590 nm, which is red-shifted from the MS monomer peak at around 540 nm. The dichroic ratio R of the 590 nm band is R> 1, where R is defined as A /A . For x= 1.0, on the other hand, a sharp blue-shifted band with R< 1 appears at 505 nm. Fig. 22(c) refers to the cases of the corresponding binary and ternary systems fabricated under the subphase without the Cd2+ ions [84], Unlike the results in Fig. 22(b), remarkably red- and blue-shifted bands are not observed... 

The azulenes (184 and 185) also shown in Table 3.23 are red liquid crystalline dyes with a negative dichroic ratio. The compound 184 exhibits a low order parameter, probably due to its strongly non-linear shape. However, the longer, thinner compound 185 results in the formation of an unidentified... 

Fig. 26 Dichroic ratios in absorption (R) as a function of Mn as measured at 380 nm. The open squares correspond to the samples annealed at 80 °C for 10 minutes and the solid squares those at 180 °C for 18 h. A dotted line shows M, the Nem-Hex transition point of PF2/6. An inset shows the region of an exponential drop between Mn = 104-105 g/mol and a linear fit. Reprinted with permission from [55]. (2005) by the American Chemical Society...

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. 

Polarized (linear dichroic) spectroscopy of vitamin D3 (28) and its p-N,N-dimethylaminobenzoate, the 10,19-dihydro-derivative (29), and simple model compounds of analogous structure [e.g. (30)], lead to smaller dichroic ratios than would be expected for rod-like molecules in a fully extended s-trans conformation. These observations are interpreted as evidence of considerable oscillation about the 6,7-single bond, which in the extreme case of elevated temperature is necessary for the thermal vitamin provitamin inter con version. 

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 ... 

Fig. 13. Dichroic ratio v. tb aw ratio for various infra-red bands of linear polyethylene drawn at 6(FC. Frequencies in wavenumbers are indicated for each curve. (Q), slowly cooled Marlex 6050 (9), quenched Mar lex 6050 (A), slowly cooled Marlex 6002 (A), quenched Marlex 6002 (from Glenz and Peterlirt ).

Glenz and Peterlin " have made an extensive study of the dichroic properties of linear polyethylene drawn at 60°C to draw ratios between S and 25. Figure 13 shows the dichroic ratios determined from the bands... 

A final remark will concern the "glassy liquid crystal". All the textures observed for both linear and comb-like polymers in the nematic gi atggcag eagily e quenched and supercooled to room temperature 99999 Both the homeotropic alignment ggd tjie planar one remain fixed in the glassy state on cooling . From the dichroic ratio of the bands in the IR spectra of... 

First, the ratio is constructed from the spectra at each rotation angle a or tilt angle / with the help of the linear correlation analysis (K. Fahmy, personal communication) A(a)/A(o=0) [A(/ )/A(/ =0)]. The ratio of each transition moment as a function of the angle a or can thus be obtained. This theoretical function can be calculated with the help of the Jones Formalism (4) and this function is necessary for fitting the ratios at o=90 and 0=90 degrees to obtain the dichroic ratio Ax/Ay and Ay/Az. Finally the normalized absorption axes can be determined. 

For oriented single crystals there will generally be a difference in the absorption between two linearly polarized IR beams that are mutually orthogonal and orthogonal to the direction of propagations. The dichroic ratio is defined as... 

Fig. 12. Examples of 3 guest-host azo dyes. The linear structure of these molecules assures a high dichroic ratio.

Note that /// and I are perpendicular and parallel to the main chain, respectively. The aligned films exhibit a linear dichroism in the fluorescence band around 550 nm due to the uniaxially aligned polythiophene chain, giving a dichroic ratio (/ ////) of 3.8. The iodine-doped aligned Aims exhibited an anisotropy of about 8 in electrical conductivity, although the absolute value of the conductivity was very low, e.g. of the order of 10 -10 Scm ... 

Ultimate dichroic ratio Dynamic infrared linear dichroism Observation period Time... 

The molecular anisotropy also manifests itself in a variety of spectroscopic techniques. Dichroism, the difference in absorption coefficients of linearly polarized light measured in orthogonal directions, is another phenomenon wherein one can extract average molecular orientational order present in the nematic phase. The dichroic ratio D = A Ax (see Chapter 7), the ratio of the intensities of the absorption band of a characteristic transition measured with the polarized incident radiation parallel to n, A, relative to that with it perpendicular to n. Ax, is given by... 

Figure 7.6 Dichroic ratio D vs. draw ratio for cold drawn linear polyethylene [I]...

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