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

摘要

We draw several electric-field–temperature (E-T ) phase diagrams with electric-field-induced birefringencencontours in the nOHFBBB1M7 (n = 10) and nOTBBB1M7 (n = 11) (C11) mixture system by changing thenC11 concentration carefully; some of the mixtures show the unusual extraordinary phase sequence wherensubphases with the four-, five-, and six-layer superlattice structures emerge above the smectic-Cn∗ main phase.nWe try to understand the results in terms of two complementary models that have so far been proposed: thenphenomenological Landau model of phase transitions by Dolganov et al. [P. V. Dolganov et al., Phys. Rev.nE 86, 020701(R) (2012)] and the partially molecular Emelyanenko-Osipov model [A. V. Emelyanenko andnM. A. Osipov, Phys. Rev. E 68, 051703 (2003)]. The observed E-T phase diagram can be well reproduced bynthe phenomenological model. An emergence of the subphase with the four-layer superlattice structure abovensmectic-Cn∗ is also understandable in terms of the partially molecular model.We discuss the pros and cons of thentwo models as well.