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Sign Inversion of the Spontaneous Polarization in a “de Vries”‐Type Ferroelectric Liquid Crystal
Author(s) -
nenmacher Dorothee,
Lemieux Robert P.,
Osipov Mikhail A.,
Giesselmann Frank
Publication year - 2014
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201301154
Subject(s) - ferroelectricity , liquid crystal , mesogen , binary number , polar , intermolecular force , polarization (electrochemistry) , chemistry , phase transition , condensed matter physics , materials science , molecule , thermodynamics , dielectric , organic chemistry , liquid crystalline , physics , optoelectronics , arithmetic , mathematics , astronomy
Abstract In contrast to common ferroelectric smectic C* liquid crystals, the siloxane‐terminated smectic mesogen E6 is characterized by an unusual temperature variation of the spontaneous polarization. The polarization starts to grow from nearly zero despite the first‐order SmA*‐SmC* transition, and increases faster than linearly over a large temperature interval while the tilt angle rapidly saturates. To study this behavior in more detail, binary mixtures of different concentrations of E6 in the achiral SmC material C8Cl , which has a similar chemical structure, were investigated. Surprisingly, all mixtures show a temperature dependent polarization sign inversion, which shifts towards the SmC*‐SmA* transition with increasing E6 concentration. For the pure E6 the inversion temperature meets the SmA*‐SmC* phase transition temperature. In a second binary mixture with E6 and a conventional material C9 – 2PhP we found out, that the dependence of the inversion temperature on the concentration of E6 changes qualitatively when the nanosegregation is partially destroyed. A molecular theory of the polarization sign inversion in smectics C* with strong polar intermolecular interactions is developed which enables one to explain the concentration dependence of the inversion temperature in both mixtures.