Alignment hybrid twisted nematic

These orientations are classified into two groups. The directors of the liquid crystal molecules in the Homogeneous, Tilted and Homeotropic cases are aligned in one fixed direction, while, the director of the liquid crystal molecules in the Splay, Twist, Bend, Hybrid and Super-twisted nematic cases are not fixed in one direction. In the latter orientations, the liquid crystals are under stress. 

Besides these two standard cell alignments, there are many other variations such as hybrid, twisted, supertwisted, fingerprint, multidomain vertically aligned, etc. Industrial processing of these nematic cells, as well as the transparent conductive coating of the cell windows for electro-optical device applications, is understandably more elaborate. 

The flexoelectric distortion in Hybrid Aligned Nematic (HAN) configuration was studied [190, 191]. In HAN cells the director is homeotropic on one of the substrates and homogeneous on the other. The measme-ments of transmitted intensity in HAN samples allow us to evaluate for MBBA both a nematic anchoring energy W for the homeotropic orientation VF 6 X 10 erg/cm and the sum of the flexoelectric moduli 11 + 33 —4.5 X 10 dyn / [191]- In an electric field normal to the initial director plane, the flexoelectric effect results in the appearance of twist deformation, observed by the rotation of linearly polarized light [190]. 

Several types of spontaneous periodic director pattern yield information about elastic coefficients. Static stripe textures, as described by Lonberg and Meyer [45], appear in polymer nematics if the twist/splay ratio below the critical value of 0.303. Calculations of director fields and the influence of elastic constants and external fields on the appearance of these periodic patterns have been performed by several authors (e.g. [49-51]). In nematic cells with different anchoring conditions at the upper and lower cell plates (hybrid cells), other types of striped texture appear these are similar in nature, but involve different director deformations and elastic coefficients. For a description of various types of static periodic texture and their relationship to elastic coefficients see, for example, Lavren-tovich and Pergamenshchik [52]. In thin hybrid aligned films, a critical thickness is observed below which the director align-... 

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