Chevron texture forms

In case of strong planar and azimuthal anchoring when the director is fixed at the surfaces, typically a so-called chevron texture forms, where the layers have a kink in the middle of cells. The formation of the chevron layer structure leads to defects, where regions of opposite kink directions meet. 

On the other hand, in the cell with a stripe-shaped texture formed by applying a 15 V im , 10 Hz AC voltage at the transition from SmA phase to SmC phase, the realization of excellent bistability was confirmed even with a short pitch length and a large spontaneous polarization. For this kind of cell, the structure of horizontal chevrons as shown in Fig. 6.3.21 is proposed. 

Figure 35. A model of chevron textures (the chevrons are viewed from the top) showing alternating angular and rounded contours, at both the slide and the coverslip level. Prismatic domains d and d are filled with antiparallel conical sheets, in continuity along the generators r, s, t and u. Parabolic contours M, N and P join and form angles along the lines L at the coverslip level C, and similarly arcs M, N and P join and form angles along the lines L at the slide level S.

Transitions with the participation of liquid crystals sometimes show characteristic phenomena. If a nematic modification turns to a smectic A or smectic C phase, transient stripes in the form of a myelinic texture (also called chevron texture or striated texture) are often visible. Typically for the polyester prepared from di-w-propyl-/ -terphenyl-4,4" carboxylate and tetramethylene glycol, the nematic phase separates from the isotropic liquid on cooling in droplets which coalesce and form large domains. Cooling of the threaded-schlieren texture produces a transition to the smectic A phase this change is characterized by transition phenomena, mostly stripes, which broaden into larger areas ( transition bars ). 

The stripe-shaped texture parallel to the rubbing direction is observed due to the formation of periodic undulation of the layer structure (Fig. 6.3.19). In the case that a strong AC voltage is applied, the chevron structure is deformed into the bookshelf structure and the strain occurs. The strain is relaxed by the rotation of the layer direction [55] which forms the periodic layer undulation. 

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