Antiferroelectric smectics

Figure 8.16 Illustration of symmetry of Soto Bustamante-Blinov achiral antiferroelectric smectic LC with finite number of layers. Such systems can be studied using DRLM technique with thin freely suspended smectic films, (a) With even number of bilayers, film has local C2 symmetry, and therefore no net electric polarization, (b) With odd number of bilayers, film has local Cnv symmetry and is therefore polar, with net spontaneous electric polarization in plane of layers.

FIGURE 43. Structures of the ferroelectric and antiferroelectric smectic C phases in their unwound states... 

Gorecka E, Nakata M, Mieczkowski J, Takanishi Y, Ishikawa K, Watanabe J, Takezoe H, Eichhorm SH, Swager TM (2000) Induced antiferroelectric smectic-CA phase by doping ferroelectric-C phase with bent-shaped molecules. Phys Rev Lett 85 2526-2529... 

An antiferroelectric smectic phase has been identified recently. The structure is expected to have an interlayer herringbone arrangement. 

M. Cepic and B. Zeks, Flexoelectricity and piezoelectricity The reason for the rich variety of phases in antiferroelectric smectic liquid crystals, Phys. Rev. Lett. 87(8), 085501/1-4, (2001). 

Keith, C. Dantlgraber, G. Reddy, R. A. Baumeister, U. Tschierske, C. Ferroelectric and antiferroelectric smectic and columnar liquid crystalline phases formed by sily-lated and non-silylated molecules with fluorinated bent cores. Chem. Mater. 2007, 19, 694-710. 

Pociecha, D. Araoka, R Ishikawa, K. Takezoe, H. Guo, L. Gomola, K. An optically uniaxial antiferroelectric smectic phase in asymmetrical bent-core compounds containing a 3-aminophenol central unit J. Mater. Chem. 2010, 20, 7944. 

Boemelburg, J., Heppke, G., and Hollidt, J., Evidence for an antiferroelectric smectic phase in a chiral side-chain polymer, Makromol. Chem. Rapid Commun., 12, 483-488 (1991). 

Figure 8. Comparison of the local structures of the ferroelectric, ferrielectric, and antiferroelectric smectic C phases.

A sub-phase of the smectic C phase also exists which is called (for the moment) the alternating smectic C (SmCai,) phase [55-57]. This phase was originally discovered by Levelut et al. [55] and given the code letter smectic O. However, the chiral version of this phase was labelled as being an antiferroelectric smectic C phase by Fuku-da [58], and it is this descriptor that is in current, general use. Consequently, the achiral modification of the antiferroelectric phase requires a matching code letter, and therefore, for the present we have opted to use smectic C i, as this term best describes the structure of the phase in relation to the antiferroelectric label. 

Table 18. Structures of typical antiferroelectric smectic SmC compounds.

Keith C, Reddy RA, Tschitaske C (2005) The first example of a liquid crystalline side-chain polymer with bent-cme mesogenic units ferroelectric switching and spontaneous achiral symmetry breaking in an achiral polymer. Chem Commun 7 871-873 Keith C, Dantlgraber G, Amaranatha Reddy R, Baumeister U, Tschierske C (2007) Ferroelectric and antiferroelectric smectic and columnar liquid crystalline phases framed by silylated and non-silylated molecules with ilurainated bent Cotes. Chtan Mater 19 694-710... 

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