Anchoring zenithal

Fig. 4.9. Scattering geometry for measurements of (a) azimuthal and (b) zenithal anchoring coefficient, n is the director, i and / the polarisations of the incoming and outgoing beams, and fei and fcf the corresponding wave vectors.

A comment should be added on the rotational viscosity of the sample in the experiment. It can easily be shown that in the case of azimuthal anchoring measurements, the viscosity entering the analysis equals the rotational viscosity 71. When measuring the zenithal anchoring coefficient, the effective viscosity has to be corrected according to the scattering geometry. However, in first approximation the pure splay mode viscosity is sufficient. 

Fig. 4.12. (a) Temperature dependence of azimuthal Wtp dots) and zenithal Wo (squares) anchoring coefficients for nematic 5CB on rubbed Nylon with Tni being the transition temperature into the isotropic phase (b) A comparison of the ratios of the two anchoring coefficients W jW p (circles) with the ratio of the corresponding Frank elastic constants KijK2 [Q5](solid line) [64]. 

In contrast to other bistable nematic modes the surface state of the director does not change in zenithal bistable mode devices, which gives them an important robustness. In other words, while the device is bistable, the director state at the ZBD surface is monostable. This feature gives a smaller temperature dependence than other modes utilizing weak anchoring and multiple surface states. Among the many similarities with FLC devices there is also the fact that the stable states are polarized, i.e. they have a non-zero polarization in bulk. Therefore we anticipate problems with im-... 

Here we consider only homeotropic grating surface alignment. A zenithal bistable device surface can also be realized with planar surface anchoring on the grating surface. ... 

The zenithal anchoring is often called polar, but this word is misleading because polar anchoring is related to polar director L as given by Eq. (10.13). Thus, the Rapini form corresponds to the sine-squared shape potential well for any director deviation (3 (89 or 8cp ) from the easy direction (9, cPq) ... 

In the Rapini approximation, the zenithal and azimuthal anchoring energies are defined for the director n in terms of angles a and p ... 

Vilfan, M., Mertelj, A., and Copic, M. (2002). Dynamic light scattering measurements of azimuthal and zenithal anchoring of nematic liquid crystals, Phys. Rev. E 65 041712(1-7). 

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