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In a frustrated binary-mixture system of ferroelectric and antiferroelectric liquid crystals, where the border line between SmC * A and SmC * in the temperature-concentration phase diagram runs almost parallel to the ordinate temperature axis, we have found a continuous change between them close to the critical concentration. The continuity has been confirmed as an intrinsic property in the bulk by observing almost perfect bell-shaped Bragg reflection bands due to the helicoidal director structure. The temperature variation of peak wavelength of the half-pitch band and, in particular, the characteristic disappearance of the full-pitch band apparently within the SmC * temperature region have been simulated with a change in the ratio of ferroelectric and antiferroelectric orderings. The observed continuous change has been described by the entropy effect in the 1D Ising model with the synclinic and anticlinic orderings as spins.

Comparative x-ray and dielectric measurements have been made on a liquid crystal exhibiting a smectic-A-chiral-smectic-C (smectic-C*) transition in bulk and confined geometries. It is observed that confining the material in Anopore membranes having 200-nm pore size leads to the following features: (1) the temperature dependence of the x-ray layer spacing shows a qualitatively different behavior, (2) in the smectic-A phase the soft mode relaxation frequency increases by a factor of 2.5, and (3) in the smectic-C* phase the relaxation frequency of the Goldstone mode increases dramatically by as much as 400 times, perhaps owing to a partial unwinding of the helix by the surface induced field.

Results of the experimental study on different antiferroelectric liquid crystal (AFLC) materials are presented using a number of techniques such as the optical birefringence, electro-optics and the measurements of optical thickness of free-standing films. Despite differences in the molecular structures of the various AFLC materials studied, these are found to exhibit a de Vries type of smecticA (SmA) properties in a temperature range higher than SmC. This correlation leads to the conclusion that these two classes of liquid crystals are related to each other. Furthermore, we suggest that these arise from the same physical mechanism, namely the existence of the weak synclinic (or reduced anticlinic) correlations between the neighbouring molecular tilt directions.

We draw several electric-field-temperature (E-T ) phase diagrams with electric-field-induced birefringence contours in the nOHFBBB1M7 (n = 10) and nOTBBB1M7 (n = 11) (C11) mixture system by changing the C11 concentration carefully; some of the mixtures show the unusual extraordinary phase sequence where subphases with the four-, five-, and six-layer superlattice structures emerge above the smectic-C * main phase. We try to understand the results in terms of two complementary models that have so far been proposed: the phenomenological Landau model of phase transitions by Dolganov et al. (2003)]. The observed E-T phase diagram can be well reproduced by the phenomenological model. An emergence of the subphase with the four-layer superlattice structure above smectic-C * is also understandable in terms of the partially molecular model. We discuss the pros and cons of the two models as well.

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We have constructed the E-T phase diagrams by drawing the field-induced birefringence contours in the prototype MHPOCBC and MHPOOCBC binary mixture system. The obtained subphase evolution in the diagrams clearly indicate that there exist some additional biaxial subphases other than the ordinary ones with three-and four-layer superstructures, and that the field-induced deformation of uniaxial SmC Ã a in MHPOCBC occurs quite differently in the high and low temperature regions. We have discussed the origin and structures of the additional subphases and different types of the field-induced deformations in terms of the extended Emelyanenko-Osipov model together with the Devil's staircase character of field-induced unwinding process of the SmC Ã a short-pitch helical structure published by Yamashita et al. in these Proceedings.