Conventional Smectics

Note 4 The tilt direction varies in a random manner from layer to layer in conventional smectic C mesophases. However it can alternate from layer to layer, as in an antiferro-electric chiral smectic C mesophase (see Definition 5.9, Note 7) and in the smectic C mesophase formed by certain liquid crystal dimers with an odd-number of carbon atoms in the spacers. The recommended symbol for this type of mesophase is SmCa. 

Aside from exhibiting a rich range of conventional smectic phases, members of the m.OnO.m family also exhibit novel modulated hexatic phases [155] in which the tilted hexatic smectic monolayers have a periodic modulation in their smectic structure, analogous to the Sm C ribbon phase. Two such phases have been identified and have been termed the Sml and Sm2 phases. The Sml phase is exhibited by members of the m.OnO.m family with... 

The conventional smectic A phase, formed by chiral molecules and be-... 

The chiral smectic C phase is formed by optically active molecules which, in their racemic form, give rise to the conventional smectic C phase. The local symmetry of the C phase (C2) is polar since the plane of the molecular tilt (see Fig. 1.2(c)) is no longer a mirror plane. Thus, the spontaneous polarization is allowed which is directed along the C2-axis (-h and — directions are possible). 

The orthogonal arrangement of the disc-like molecules in the columns of and D id phases makes these phases uniaxial, while the tilted phases (Drd and Doh.d and Dt) are optically biaxial. There are two additional columnar phases labeled as and that have not yet been classified. The columnar phases were discovered before the observation of a nematic phase for disc-like molecules. Both chiral nematic phases and the re-entrant behavior have now been observed in discotics. The phase diagram and molecular structure of a typical discotic liquid crystal are shown in Fig. 1.11. Finally, it is noted that another classification scheme for the discotic mesophases has been used [1.26], which is based on the notation used for the conventional smectics. 

SmAi is a conventional smectic A phase where the molecules have random head-to-tail orientations ... 

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