Alignment instability caused by anchoring of the in-plane directors to the rubbing direction in the V-shaped switching

Abstract

In order to investigate the molecular alignment in the smectic liquid crystals showing the V-shaped switching behavior, two types of the liquid crystal cells, a sandwiched cell and an open cell, were prepared. Homogeneous alignment with the smectic layer normal formed at y12³ with respect to the rubbing direction r is obtained in the Sm-A phase in both cells. However, in the open cell, the director n is rotated towards r when the Sm-A sample is cooled into the tilted Sm-X* phase. In addition, its maximum rotation angle is y12³. In this con®guration, the molecules lie along r. Meanwhile, the sandwiched cell with the one-side rubbing treatment exhibits the averaged optical axis almost parallel to the layer normal in the Sm-X* phase. In this paper, a simple small-twisted state in the thin sandwiched cell is suggested to account for the experimental results.

Surface molecular alignment by in-plane anchoring in the cell showing the V-shaped switching

“…8 In SmA phase, the smectic layer normal l deviates at an angle of ϳ12°from the rubbing axis r, rather similar to the behavior in a sandwich cell. However, in SmX* phase, the director n becomes parallel to r in an open cell.…”

“…However, the strong in-plane anchoring by the rubbing treatment restrains all the molecules along r below 2-3°C from a SmA -SmX* phase transition. 8 On the other hand, the molecules near the unrubbed surface tend to be rotated in the opposite direction with respect to l due to polar anchoring. Finally the molecules are twisted along the cell thickness between such two different surface alignments.…”

“…Considering an apparent tilt angle of ϳ35°, it is very clear that the direction of P on the surface is closer to ϭ /2 than to 0 or , contrary to Clark et al's early predictions. 7,8 And, the small twisted state along the cell thickness has been investigated in the sandwich cell on the basis of this alignment. That is, the apparently uniform-like molecular alignment is due to this small twisted state along the cell thickness.…”

“…1͑a͔͒ is one of the major areas of current interest in the field of chiral smectic liquid crystals. [1][2][3][4][5][6][7][8] The reason for interest in them lies in their promise of realizing new types of liquid crystal displays ͑LCDs͒. 9 Since the discovery of V-shaped switching, random 1,2 and the collective models 5,6 were proposed to explain its switching mechanism.…”

“…[2][3][4]8 We used two polyimides, RN1199 and RN1266 ͑Nissan Chemical Industries, Ltd.͒, as the aligning material. They were spin coated on glass substrates with an ITO coating.…”