Displays: antiferroelectric liquid crystals

Pretransitional Effect in Antiferroelectric Liquid Crystal Displays.679... 

Antiferroelectric liquid crystal displays (AFLCDs) have been relevant to flat panel displays since the discovery of AFLCs. Their characteristic features can be summarized as follows ... 

There are two review commentaries about the antiferroelectric phase, one by Fukuda et al. in 1994 [77] and one by Takezoe et al. in 2010 [78]. There is a sense of maturity in this field both theoretically and experimentally. Also, the interest in other secondary phases seems to be endless. Apphcations for antiferroelectric phases are made in the field of fast switching displays, such as V-shaped switching displays, 45° orthoconic antiferroelectric liquid crystal displays, and so on. Even though speed is a great feature, research with the aim of display applications is declining. 

As witli tlie nematic phase, a chiral version of tlie smectic C phase has been observed and is denoted SniC. In tliis phase, tlie director rotates around tlie cone generated by tlie tilt angle [9,32]. This phase is helielectric, i.e. tlie spontaneous polarization induced by dipolar ordering (transverse to tlie molecular long axis) rotates around a helix. However, if tlie helix is unwound by external forces such as surface interactions, or electric fields or by compensating tlie pitch in a mixture, so tliat it becomes infinite, tlie phase becomes ferroelectric. This is tlie basis of ferroelectric liquid crystal displays (section C2.2.4.4). If tliere is an alternation in polarization direction between layers tlie phase can be ferrielectric or antiferroelectric. A smectic A phase foniied by chiral molecules is sometimes denoted SiiiA, altliough, due to the untilted symmetry of tlie phase, it is not itself chiral. This notation is strictly incorrect because tlie asterisk should be used to indicate the chirality of tlie phase and not tliat of tlie constituent molecules. 

In conclusion of this chapter it should be stated that bistable and tristable switching of ferro- and antiferroelectric liquid crystals is very fast and provides long memory states. The latter allows one to design displays without semiconductor... 

Matsumoto, T., Fukuda, A., Johno, M., Motoyama, Y., Yui, T., Setnnun, A.-S., Yamashita, M. A novel pnrpcrty caused by frustration between ferroelectricity and antiferroelectricity and its application to liquid crystal displays Ferroelectricity and V-shape switching. J. Mater. Chem. 9, 2051-2080 (1999)... 

Liquid Crystals (Family Number Tl). Ferroelectric and antiferroelectric liquid crystals are very useful as fast display elements. 

So far, four display modes have been proposed in ferroelectric and antiferroelectric display applications, as shown in Figure 9.34. A bistable switching in surface stabilized ferroelectric liquid crystals (SSFLCs) has been manufactured as a passive matrix liquid crystal display (PM-LCD). The counterpart of AFLC is a tristable switching, which is also a promising candidate for PM-LCD. In addition to these PM-LCDs, active matrix displays (AM-LCDs) are also proposed in FLC and AFLC materials, i.e., deformed helix FLCD (DHFLC) and V-shaped LCD (VLCD). In this section, PM-AFLCD and AM-VLCD will be described. 

The existence or nonexistence of mirror symmetry plays an important role in nature. The lack of mirror symmetry, called chirality, can be found in systems of all length scales, from elementary particles to macroscopic systems. Due to the collective behavior of the molecules in liquid crystals, molecular chirality has a particularly remarkable influence on the macroscopic physical properties of these systems. Probably, even the flrst observations of thermotropic liquid crystals by Planer (1861) and Reinitzer (1888) were due to the conspicuous selective reflection of the helical structure that occurs in chiral liquid crystals. Many physical properties of liquid crystals depend on chirality, e.g., certain linear and nonlinear optical properties, the occurrence of ferro-, ferri-, antiferro- and piezo-electric behavior, the electroclinic effect, and even the appearance of new phases. In addition, the majority of optical applications of liquid crystals is due to chiral structures, namely the ther-mochromic effect of cholesteric liquid crystals, the rotation of the plane of polarization in twisted nematic liquid crystal displays, and the ferroelectric and antiferroelectric switching of smectic liquid crystals. 

The applications of liquid crystals have unquestionably added incentive to the quest for new liquid crystal materials with superior properties such as viscosity, elastic constants, transition temperatures, and stability. In recent years this has catalyzed work on chiral materials as dopants for ferroelectric displays and for antiferroelectric materials with structures avoiding the number of potentially labile ester groups that were present in the original materials in which... 

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