Zenithal bistable device: Comparison of modeling and experiment

Competing alignments of nematic liquid crystals on square-patterned substrates

“…In each of these, the bistability pertains between one state with a continuous director arrangement and a second containing orientational defects that are pinned in some way by the substrate inhomogeneity. This suggests that the key length scale for achieving bistability here is the size and periodicity of the patterning, a conjecture which is supported by the success of mesoscopic modeling approaches in both accessing the bistable states and relating, semiquantitatively, switching fields to geometrical parameters [7,8].…”

Beam-splitter switches based on zenithal bistable liquid-crystal gratings

“…In the case of ZB structures, it has been shown that the two stable states correspond to a high-tilt, vertical aligned nematic (VAN), and a low-tilt, hybrid aligned nematic (HAN) configuration [9,12,14,19]. The latter is characterized by the presence of two point defects, which lead to point singularities when the LC problem is treated by the classical Frank continuum model that represents the nematic director via a unit vector whose spatial variations describe the LC distortions.…”

“…1. We consider two cases: sinusoidal and triangular gratings, both of which have been shown to support the VAN and HAN states [12,19]. The grating and the superstratum are made of a polymer material.…”

“…In a different approach, it has been demonstrated that certain LC geometries that involve periodical grating structures in one or two dimensions can be bistable, meaning that there are two equilibrium stable states corresponding to different molecular orientation profiles [9][10][11][12][13][14][15][16][17][18][19][20][21]. Such geometries allow for the design of devices with zero power consumption, except when switching between the two states is required.…”

“…Such geometries allow for the design of devices with zero power consumption, except when switching between the two states is required. This concept has been exploited in the development of passively addressed displays for image storing, based on the zenithal bistable (ZB) device, one of the most extensively investigated LC bistable structures [9,[11][12][13][14]18,19]. In this configuration, the LC is confined in a cell formed between a flat top surface and a bottom grating structure, both of which are typically treated so as to provide homeotropic (perpendicular) molecular alignment.…”