SmCsPA antiferroelectric phases

This interpretation of the properties exhibited by the major EO-active phases of NOBOW and the rest of the classic banana mesogens posits the existence of four supermolecular diastereomers, at least two of which, the antiferroelectric phases SmCsPA and ShiCaPa, must exist as separate wells on the... 

Fig. 13.29 Bent-shape molecules form polar smectic layers in the polar plane xz with polarization (a). Upon cooling, the molecules can spontaneously acquire a tilt forward or back within the tilt plane yz. The stack of the layers may be either synclinic SmCs or anticlinic SmCA (b). Additionally, depending on the direction of polarization P both the synclinic and anticlinic structure may have uniform (ferroelectric Pp) or alternating (antiferroelectric P ) distribution of polarization within the stack. In the field absence there are four stractures marked by symbols below. Note that the leftmost structure is chiral SmC and rightmost structure is also chiral because, for any pair of neighbours, the directions of the tilt and polarization change together leaving the same handedness of the vector triple. In the electric field, the phase transitions fixjm chiral SmCAPA <> chiral SmCsPp and from racemic SmCsPA to racemic SmCAPp structures are possible (shown by ark arrows)...

In a stack of subsequent layers the tilt may be constant (synclinic structure) or alternating (anticlinic structure). Both synclinic and anticlinic multilayer stacks can further be subdivided into ferroelectric and antiferroelectric structures. The molecular projections (Mito the tilt plane 7y are shown in Fig. 13.29b. In ferroelectric (symbol F) phases spmitaneous polarization has the same direction in each layer (synclinic chiral SmCsPp and anticlinic achiral SmCAPp phases). In the antiferroelectric (symbol A) phases the direction of polarization alternates (achiral synclinic SmCsPA and chiral anticlinic SmCAPA phases). In fact we have a conglomerate of chiral and achiral phases both in either synclinic or anticlinic form. 

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