Chevron layer structure tilt angle

The origin of the chevron layer structure is explained by the discrepancy between the layer spacing of the SmC phase and that of the high temperature phase, which is usually the SmA phase. The layer spacing in the SmA phase, dA is fixed at the surfaces, and it decreases to do in the SmC phase because the molecules decline at the tilt angle Q from the smectic layer normal as shown in Fig. 5.1.6. This figure leads to a simple relation,... 

The chevron layer structures of several SSFLCs from various FLC materials exhibiting different optical molecular tilt angles have been precisely investigated, and a correlation between the layer tilt angle of the chevron structure and the optical molecular tilt angle was confirmed. 

Figure 5.1.21 shows the coordinate systems of the director in the chevron layer structure, where n is the director, c is the c-director, and p is the spontaneous polarization vector. It is assumed that the tilt angle 9 and the layer tilt angle S are constant, and the azimuthal angle depends only on the cell thickness, direction Y. The director is expressed as... 

Another reason for this is the complexity of molecular orientation in FLC devices. FLC devices have layered structures, three surfaces (that is, two substrate surfaces and a chevron interface), tilt angles, spontaneous polarization, etc. These features lead to more complex phenomena such as layer leaning, twisted orientations, low shock stability, layer rotation, etc. 

Figure 92. The shrinkage in smectic layer thickness due to the molecular tilt 0(T) in the SmC phase results in a folding instablity of the layer structure ( chevrons ). Even if the fold can he made to go everywhere in the same direction (in the figure to the right) to avoid invasive zigzag defect structures, the switching angle is now less than 2 9, which lowers brightness and contrast.

Polymers which form smectic and nematic phases are easily oriented in the nematic phase, the mesogenic groups are positioned along the axis of orientation, and the nematic-smectic transition is then possible in the oriented sample (fiber). If the mesogenic groups in the smectic phase formed are tilted toward the layer, then a chevron-like structure is formed, where the smectic layers form a certain angle with the axis of the fiber [55]. 

One of the important aligning techniques, which allows us to avoid zigzag defects between two adjacent smectic layers bent in opposite directions (chevrons), remains the oblique evaporation of silicon monoxide [141-144] (Fig. 7.25). Zig-zag defects are avoided by the promotion [25] of only one possible bend or tilt of the smectic layers due to a specific oblique director orientation at the boundaries (Fig. 7.25). Samples with the antiparallel evaporation direction contain uniformly tilted layers. Those with parallel directions exhibit the chevron structure of tilted layers free of zig-zag defects. Reference [135] shows that in the case of parallel evaporation the variation of the evaporation angle results in different chevron bend angles. 

In Fig. 6.3.19, the structure of the stripe-shaped texture is shown. The width of the stripe becomes equal to the cell gap and the layer rotation angle becomes equal to chevron angle [68]. In certain conditions the tilted bookshelf structure can also be realized in this the width of the stripe becomes twice that of the cell gap [54]. 

A special case of tilted layers is the chevron structure, for which the tilt makes a kink either symmetrically in the middle or un-symmetrically closer to one of the surfaces. The chevron structure means that two values +5 and -5 appear in the sample. As can be seen from Eqs. (389) and (390), the angle 5 only appears as a quadratic dependence, hence the relations are also valid in the chevron case. Solving for the principal values in the chevron or tilted layers case, we obtain... 

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