Electric Field Induced Walls in the Bend Geometry of a Nematic Liquid Crystal

Abstract

A homeotropically aligned nematic is subjected to the action of an ac electric field applied in the sample plane. With progressively increasing electric voltage, walls move away from the electrodes, approach each other and merge. A subsequent decrease of voltage to zero causes the reverse process to occur except for hysteresis. The hysteresis width is employed to estimate the adhesion surface energy density of the walls; the surface energy density is of the same order as the anisotropy in surface tension of nematics. The wall thickness diminishes with increasing voltage. This shows that the observed walls are similar to those produced by magnetic fields. The walls exhibit curvature in the sample plane, the undulation in a wall being regular at sufficiently elevated frequencies (f). The walls are decorated along their length by a zigzag defect pattern which is being reported in the bend Freedericksz geometry for the first time. Some of the observations are explained qualitatively.

Key Words:

• Nematic
• electric field
• bend geometry
• zigzag disclinations
• alignment inversion walls
• Freedericksz transition