Tilt alignment

Note 3 Schlieren textures observed in nematic samples with planar alignment show defect centers with two or four emerging brushes. Schlieren textures in nematic samples with tilted alignments show centers with four brushes centers with two brushes are caused by defect walls. 

An analysis of Eq and of the Clebsch-Gordan coefficients shows that for the appearance of non-zero density matrix elements /mm i at linear polarized excitation it is necessary that the E(different from 0 and 7t/2 see Fig. 5.3. Such excitation geometry implies the creation of tilted alignment (see Fig. 2.3(d)) which is described by alignment components... 

When the Pi cell is used for a display, it requires a compensation film to create the black state. Because of its symmetrical tilt alignment near the substrate, the Pi cell has a biaxial birefringence in the black state. Several approaches were tried to develop a compensation film for the Pi cell. To compensate for the birefringence of the black state by using only one film, biaxiality is required by the film [2]. A combination of an a-plate and c-plate was used [7] to reduce the light leakage in the black state. To compensate for each side of the distributed LC molecules, discotic films were used as the compensation films as shown in Fig. 4.6.4 [4, 5, 8, 9,10]. 

Tilted alignment of MBBA induced by short-chain surfants. Figure 1, G. Porte, Le Journal de Physique, 37, p. 1246 (1976). Reproduced by permission of EDP Sciences. 

Check one more time the TEM alignment, especially pay attention to specimen height, pivot point alignment and beam-tilt alignment. 

In some cases a combination of these techniques has led to a high tilt alignment [3]. 

Figure 8. A positive dielectric anisotropy SmA phase with high tilt alignment showing a 22° layer tilt being electrically driven into a 12° tilt state.

Figure 17 Schematic depiction of a LC brush swollen in a low molecular weight nematic. Competing orienting actions from the brush and the bare surface may result in a tilted alignment. The chemical structure of the sidechain mesogen used in this study is indicated in the inset.

G. Porte and J.P. Jadot, A phase transition-like instability in static samples of twisted nematic liquid crystal when the surfaces induce tilted alignments, J. de Physique, 39, 213-223 (1978). 

Fig. 1.17 For some display devices it is preferable to have a substrate surface treatment which gives a tilted alignment. This drawing shows a smectic A phase with a small tilt, above a glass substrate coated with a conducting layer (usually indium and tin oxide) and an alignment layer giving a small tilt angle...

They correspond to the homogeneous, homeotropic, and tilted alignments using the language of LC optics. The birefringence of the uniaxial material can be positive (rie > rio) or negative ( <, < ng). Thus one can have positive A-plates and negative A-plates, and similarly for the other types. 

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