Superlattice structures observed in the extraordinary phase sequence and analyzed by the phenomenological Landau model and the partially molecular model

Abstract

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. [ P. V. Dolganov et al. Phys. Rev. E 86 020701 (2012)] and the partially molecular Emelyanenko-Osipov model [ A. V. Emelyanenko and M. A. Osipov Phys. Rev. E 68 051703 (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.