Order guest-host effect

Guest-host effect Orientational ordering of a solute molecule by a liquid crystal solvent. 

When solute molecules are dissolved in liquid crystal, the molecular interactions between the solute and the partially ordered liquid crystal molecules result in some degree of orientational ordering being imparted to the solute molecules. This is the guest-host effect. 

It has been shown that moderate laser powers may be used to induce textural changes in both nematic and smectic polymer systems. However, in order to achieve laser writing on an acceptable timescale with low pulse energies, the polymer should be doped with a dye, as in the guest-host effect, to increase the absorption at the wavelength of the writing laser. It has been demonstrated that laser writing may be... 

A combination of two dyes (with positive and negative dichroism) has been used [177] for color switching in the guest-host effect. The degree of dye order was 5dye = 0.677 and 0.754 for anthraquinone D /D > 1) and tetrazine (T) /D ) dyes, respectively. High values of color contrast were thus achieved on electrooptical switching. 

Coles et al. were the first to investigate the dye guest host effect in a FLC polymer (60). The high-polarization polyacrylate 14 [31] (see above), containing 4% of a blue azo dye (M 483 from Mitsui Toatsu Chemical, Inc.X gave the absorption spectra displayed in Figure 41. From the absorptioo parallel and perpendicular to the direction of molecular orientation (diiector). an order parameter of 0 J7,... 

The results of studying the optical properties (birefringence, IR and UV dichroism), x-ray, spectroscopy, NMR, and EPR (with specially introduced paramagnetic probes) methods are usually used for estimating the order parameter [40]. The so-called guest-host effect is a widely used method (cf. Chapter 8). 

The use of the guest-host effect not only permits controlling the optical properties of dyed polymer films but also makes it possible to measure the S order parameters of the liquid crystal. Measurement of the order paramet is usually done by either analyzing the dichroic ratio of plane-orient films with... 

At time t = 0, a dc field is applied it produces an electric field-induced Pockels effect (EFIPE), which is solely due to a third-order effect Eq) in the case of the copolymer because the molecules are not oriented by the dc field alone at room temperature, but which also contains a part due to the rotation, in a polar manner, of free chromophores in the guest-host system (induced The value of x is measured from the modulations of ATR... 

Stahelin, M., Walsh, C. A., Borland, D. M., Miller, R. D., Twieg, R. J., and Volksen, W. Orientational decay in poled 2nd-order nonlinear-optical guest-host polymers Temperature dependence and effects of poling geometry. J. Appl. Phys. vol. 73 (no. 12), 15 [une 1993, p. 8471-8479. 

On the other hand, liquid crystalline polymers applied to optical information storage has attracted great attention. The liquid crystalline polymer is applied mainly in terms of the thermo-optical effect. The backbone of liquid crystalline polymer can be polysiloxane, polyacrylate, or polyesters. In order to enhance the absorption coefficient for the writing laser beam, the dyes may be either dissolved into the liquid crystalline polymer in the guest-host model or attached to the backbone of the liquid crystalline polymer to form a copolymer. The nematic, cholesteric and smectic liquid crystalline polymers are all be able to be utilized in optical information storage. 

JT/3 is the contribution of the chiral guest to the HTP in the case of an isotropic orientational distribution of the guest in the anisotropic guest-host phase. Contributions to the coordinates of W introduced by other traceless tensors are canceled in the trace of Wy. From (3.20) with IF = 0, the equation of Nordio et al. [31] can be obtained, whereas with W W = 0 and (l/v )(lf22 ii) = 0 ihe approximation of de Gennes follows. In (3.19) and (3.20) the dependence on the variation of the host order is only indirectly taken into account as in the presentation of Nordio et al. The temperature dependence of the host order—especially for the isotropic W/3—is partially neglected. Experimental experience shows that there is no drastic effect. 

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