ELECTROCLINIC PROPERTIES

The electroclinic properties of this complex are an induced tilt angle of 12° close to the Sa -Sc transition, with a value of 4° near the Sa-I transition but with a shorter response time of only 25 ms. 

Chiellini, E., Galli, G., Lagerwall, S. T., and Komitov, L., Electroclinic properties of chiral smectic A liquid crystalline polymers and block copolymers, Macromoi. Svmp., 96, 79-94 (1995). 

Relation Between Ferroelectric and Electroclinic Properties and Molecular Chirality Chiral-Racemic Studies... 

As mentioned in the introduction, chiral compounds can exhibit chiral mesophases and these are important due to the important physical properties that they may exhibit, including thermochroism, ferroelectric and electroclinic effects [15], In 1975, Meyer predicted the existence of a spontaneous polarization (Pg) in chiral, tilted smectic phases [86], and the existence of such polar order within a liquid crystal phase has important implications both scientifically and industrially [19]. The asymmetry associated with the chirality may also produce a beneficial lowering of transition temperatures. 

This is a chiral smectic A with symmetry Dqo. Its properties are similar to those of the achiral SmA. However, close to the transition to the smectic C phase, the chiral smectic A phase shows interesting pretransitional phenomena in the dielectric and electrooptical effects (the so-caUed soft dielectric mode and electroclinic effect). They will be discussed in Chapter 13. 

Shashidhar R, Naciri J, Ratna BR (2000) Large electroclinic effect and associated properties of chiral smectic a liquid crystals. In Prigogine I, Rice SA and Vij JK (eds) Advances in chemical physics, vol 113, John Wiley Sons, Inc., Hoboken, NJ, USA. pp 51-76. doi 10.1002/9780470141724.ch2... 

Similar effects can be described for other phases. The smectic A phase of chiral compounds may show electroclinic effect (Effect (a)) or can be transferred to the TGBa phase (Effect (c)). The smectic C phase of chiral compounds may have hehcal ordering (Effect (b)), but can have polar ferroelectric properties (Effect (a)) even without helical structures. Further, a TGBc phase or a Sd phase might be induced (Effect (c)). 

Smectic Liquid Crystals Ferroelectric Properties and Electroclinic Effect... 

Essentially, the structural features described above apply to both non-chiral and chiral compounds. However, the presence of chiral molecules in smectic- and C phases results in additional properties and structures not present in phases of nonchiral substances. These are the ferroelectric properties and the electroclinic effect, which will be discussed in detail in Sections 8.3 and 8.4, and the helical structure in the smectic-C phase. 

By mixing a chiral liquid-crystal compound with its optical antipode, systems possessing arbitrary values of the enantiomeric excess can be designed. If a chiral compound shows smectic-C and smectic- I phases, the racemate, i.e., the 1 1 mixture of the two antipodes, also exhibits these phases but the ferroelectric properties of the smectic-C phase and the electroclinic effect in the smectic- phase are lost. This offers the unique possibility to study a given system with and without ferroelectridty or with a variable markedness of its ferroelectric properties. 

The ferroelectric properties of the chiral smectic-C phase and the electroclinic effect of the smectic- phase appeared as a result of the symmetry breaking caused by the presence of chiral molecules. One can think of smectic phases in which nonchiral molecules arrange themselves in a polar order [86], and it seems that such phases were recently observed, indeed experimentally. The molecules which establish these phases are not chiral but possess a bent core resembling a bow- or banana-like shape [87] a second class of nonchiral liquid crystals showing polar ordering consists of certain polymer-monomer mixtures [88],... 

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. 

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