Leslie light scattering

Because of the difficulty with which polymeric nematic monodomains are prepared, there are few measurements of Leslie viscosities and Frank constants for LCPs reported in the literature. The most complete data sets are for PBG solutions, reported by Lee and Meyer (1990), who dissolved the polymer in a mixed solvent of 18% dioxane and 82% dichloromethane with a few percent added dimethylformamide. Some of these data, measured by light scattering and by the response of the nematic director to an applied magnetic field, are shown in Figs. 11-19 and 11-20 and in Table 11-1. While the twist constant has a value of around K2 0.6 x 10 dyn, which is believed to be roughly independent of concentration and molecular weight, the splay and bend constants ATj and K3 are sensitive to concentration and molecular weight. 

Few other sets of viscosities exist for polymeric nematics. Yang and Shine (1993) obtained three of the Leslie viscosities for monodomains of poly(n-hexyl isocyanate) (PHIC) from rheological measurements in the presence of an electric field, and they obtained values reasonably consistent with the predictions of the Kuzuu-Doi expressions. From monodomains of the polyion PBZT, poly(l,4-phenylene-2,6-benzobisthiazole) in methane sulfonic acid, some of the Leslie-Ericksen parameters have been extracted via light-scattering and magnetic-field-reorientation studies (Berry 198S Srinivasarao and... 

The Orsay Liquid Crystal Group [28] determined a model of director modes of fluctuation based on the hydrodynamic description of nematic phases by Leslie [29] and Ericksen [30]. This approach developed the subject of dynamic light scattering in liquid crystals, and allows viscoelastic ratios to be deduced from light scattering data. For singly scattered light from a material, the time... 

In smectic C materials, the relative twist of the planes is uncoupled to the layer thickness, giving rise to strong, nematic-like scattering [106]. There are relatively few light scattering studies of either achiral or chiral SmC phases, despite the technological importance of the ferroelectric SmC phase. This is in part due to the few discussions of the elastic theories of these phases, and in particular descriptions that include dynamic behaviour. Indeed it is only relatively recently that Leslie et al. [107] de-... 

Some of the Leslie coefficients can easily be determined by light scattering, while others, such as o, are virtually unacces-sible. 

As the transmission curve of a liquid crystal display during the switching process depends on all the Leslie coefficients due to backflow effects, it is possible to determine the coefficients from the transmission curve. In analogy to light scattering, the coefficients are obtained with different accuracies [38, 39]. The investigation of torsional shear flow in a liquid crystal [31-35] allows the determination of quantities from which some Leslie coefficients can be determined, if one shear viscosity coefficient is known. 

There are other reports on the study of pretransitional dynamics in polymeric and lyotropic nematics. Quantitative measurements of ratios of Frank elastic constants and Leslie viscosities in the pretransitional range of poly-y-benzyl-glutamate polymeric nematic are reported by Taratuta et al. [85]. McClymer and Keyes [86-88] report light scattering studies of pretransitional dynamics of potassium laurate-decanol-D20 system. An interesting study of a magnetic-field induced I N phase transition in a colloidal suspension is reported by Tang and Fraden [89]. 

F. M. Leslie, C. M. Waters, Light scattering from nematic liquid crystal in the presence of an electric field. Mol. Cryst. Liq. Cryst. 1985, 123, 101-117. 

Galerne, Martinand, Durand and Veyssie [100] have measured some of the smectic viscosities for the SmC liquid crystal DOBCP at 103°C. Prom the experimental data, Leslie and Gill [178] deduced that, in the context of light scattering, in terms... 

Several methods have been developed to evaluate the Leslie viscosity coefficients described in detail in [18, 28, 31]. These methods include the inelastic scattering of light [60, 93], pulse [94], and rotating [95] magnetic fields, attenuation of the ultrasound shear wave [96], etc. The results obtained by different methods for such important coefficients as rotational viscosity agree fairly well with each other [78], Fig. 2.25. The simplest and most useful methods for measuring 71-values are based on the dynamics... 

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