Bistability bistable nematic

The third electro-optical effect using calamitic nematic liquid crystals makes use of a flexoelectric effect manifested by a curved asymmetrical nematic medium. This corresponds to piezoelectricity in crystals. The existence of flexoelectricity in a nematic phase under certain boundary conditions was predicted in the late 1960s and then confirmed experimentally several years later. However, LCDs using this effect, such as bistable nematic displays are only in the development stage and as such they will not be discussed in this monograph. 

E. Lacaze, J.P. Michel, M. Goldmann, M. Gailhanou, M. de Boissieu, M. Alba, Bistable nematic and smectic anchoring in the liquid crystal octylcyanobiphenyl (8CB) adsorbed on a M0S2 single crystal. Phys. Rev. E 69, 041705 (2004)... 

Early Attempts at Bistable Nematic Devices 7.3.1. Nematic displays... 

In contrast to other bistable nematic modes the surface state of the director does not change in zenithal bistable mode devices, which gives them an important robustness. In other words, while the device is bistable, the director state at the ZBD surface is monostable. This feature gives a smaller temperature dependence than other modes utilizing weak anchoring and multiple surface states. Among the many similarities with FLC devices there is also the fact that the stable states are polarized, i.e. they have a non-zero polarization in bulk. Therefore we anticipate problems with im-... 

J. Cheng and G.D. Boyd, Threshold and switching characteristics of a bistable nematic liquid-crystal storage display, Appl. Phys. Lett. 37(12), 1072-1074, (1980). doi 10.1063/1.91881... 

I. Dozov, A. Boissier and T. Laboureau, Nemoptic s bistable nematic liquid-crystal technology - Cholesterics or ferroelectrics are not necessary to make a bistable LCD, and using conventional nematics offers some substantial advantages, Information Display 18(1), 10 13, (2002). 

G.P. Bryan-Brown, C.V. Brown and J.C. Jones, Bistable nematic liquid crystal device, UK Patent GB 2318422 (9 October 1996). 

L.A. Parry-Jones, R.B. Meyer and S.J. Elston, Mechanisms of flexoelectric switching in a zenithally bistable nematic device, J. Appl. Phys. 106(1),... 

C.V. Brown, L. Parry-Jones, S.J. Elston and S.J. Wilkins, Comparison of theoretical and experimental switching curves for a zenithally bistable nematic liquid crystal device. Mol. Cryst. Liq. Cryst. 410(1), 417-425, (2004). doi 10.1080/15421400490433451... 

Joubert, C., Angele, J., Boissier, A., Pecout, B., Forget, S.L., Dozov, I., Stoenescu, D., Lallemand, S., Lagarde, P.M. Reflective bistable nematic displays (BiNem ) fabricated by standard manufacturing equipment. J. SID 11, 17-24 (2003)... 

There are several types of bistable nematic LCDs that have good performance characteristics. They are twisted-untwisted bistable nematic LCD [9-13], zenithal bistable nematic LCD [14,15], surface-induced bistable nematic LCD [16-19], mechanically bistable nematic LCD and bistable STN-LCD [20-24], A bistable nematic material has two bistable states with... 

In LCDs, liquid crystals are usually sandwiched between two substrates. A certain alignment of the liquid crystal at the surface of the substrates is usually necessary in order for a display to operate properly. Bistable nematic liquid crystals can be created by using surface alignment layers. They are divided into two categories zenithal bistable TN and azimuthal TN. 

Figure 10.18 Schematic diagram of the liquid crystal director configurations of the two bistable states of the Z-bistable nematic hquid crystal.

Figure 10.19 Schematic diagram of the azimuhtal bistable nematic liquid crystal.

R. Barberi, M. Giocondo, J. Li and R. Bartolino, Fast bistable nematic display with gray scale, AppL Phys. Lett., 71, 3495 (1997). 

I. Dozov, M. Nobili, and G. Durand, Fast bistable nematic display using monostable surface switching,... 

G. P. Bryan-Brown, M. J. Towler, M. S. Bancroft, and D. G. McDonnell, Bistable nematic alignment using bigratings, Proc. Intnl. Display Research Conf. 94, 209 (1994). 

Obliquely evaporated SiO, which forms a saw-tooth profile at the surface, was first reported by Janning. Similar to the Berremann s model in these cases, the easy axis is determined by the evaporation direction. We note that, in special evaporation directions and SiO thickness ranges, this method could provide bistable anchoring conditions leading to bistable nematic devices." ... 

In addition to the TN and IPS modes in nematic displays, himdreds of other displays methods were invented and tested over the last 30 years. Out of them the bistable nematic development based on surface flexoelectric interactions, the bistable cholesterics displays based on switching between planar and focal conic textures and the polymer dispersed liquid crystal displays found some applications. None of them, however, offer better than a few milliseconds switching time. 

The photoalignment process could be used for the production of new, emerging LCD types such as ferroelectric LCD, bistable nematic LCD, LCD on... 

---