Retardation factor, nematics

Figure 3. Retardation factor gj = T as function of the nematic potential barrier parameter cr = q/RT according to Meier et al, Eq. (26) (broken line), and Coffey et a 146 150 gq 27) (dashed line) and exact solution (solid line). (Reprinted with kind permission from the authors and the editor of Liq. Crystals.)...

Figure 23. Comparison of the retardation factors gj and corresponding nematic potential q values obtained for 5PCH at different conditions. [Crosses, Meier-Saupe Eq. (26) other symbols, Coffey et al. Eq. (27).]...

Having retardation factors, one can calculate the nematic potential q using equations derived originally by Meier and Saupe [Eq. (26)] or by Coffey and co-workers [Eq. (27), Fig. 3j. With the aid of Eq. (26) the nematic potential has been calculated as a function of temperature and pressure for various nematics. " For nCB compounds the q values vary between 3kJ/mol near T, point and 6kJ/mol near the... 

It is possible to extend the Debye theory of dipole relaxation to include the aligning action of this nematic potential and to show how the retardation factor g depends on the nematic order [39]. 

In the study of dielectric relaxation, temperature is an important variable, and it is observed that relaxation times decrease as the temperature increases. In Debye s model for the rotational diffusion of dipoles, the temperature dependence of the relaxation is determined by the diffusion constant or microscopic viscosity. For liquid crystals the nematic ordering potential contributes to rotational relaxation, and the temperature dependence of the order parameter influences the retardation factors. If rotational diffusion is an activated process, then it is appropriate to use an Arrhenius equation for the relaxation times ... 

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