Stability of Antiferroelectricity and Causes for its Appearance in SmC_α ^* and SmC_A ^* Phases of a Chiral Smectic Liquid Crystal, MHPOBC

Abstract

The smectic layer thickness and the switching behavior in MHPOBC have been studied as a function of temperature; SmCα * is a tilted phase and is antiferroelectric at least in the higher-temperature region but becomes ferrielectric with decreasing temperature. The gradual appearance of ferrielectric characteristics in SmCα * suggests the emergence of the Devil's staircase. To explain the antiferroelectricity in SmCα * and SmCA *, two types of molecular interactions are proposed: one is the interaction between the spontaneous polarizations in the neighboring layers which is effective in SmCα *, and the other is the pairing of transverse dipole moments responsible for the antiferroelectricity in SmCA *.

Polymer stabilization of the smectic C-alpha* liquid crystal phase—Over tenfold thermal stabilization by confining networks of photo-polymerized reactive mesogens

“…12 The most reliable and direct indicator to establish the existence of the SmC a * phase is the current reversal method. 13 The current reversal response to an applied triangular electric field is two polarization reversal peaks indicative of an antiferroelectric system. One of the two peaks increases in intensity with decreasing temperature, while the other peak decreases, implying ferrielectric-like character.…”

The Structure and Properties of Antiferroelectric Liquid Crystals

“…The stable existence of ferrielectric phases of the first group has been found experimentally [18,19,23,72], and their molecular structures are determined (at least on the basis of the Ising and ANNNI models). The second group of the ferrielectric phases, which has been observed rather recently in the temperature range between antiferroelectric AF and ferroelectric SmC* phases [24,38,40,73], reveals some unusual properties, and their stability and structure are still under investigation. There does not appear to be any available direct method for the identification of molecular structures of ferrielectric phases.…”

“…As stated, the structure of these phases is model dependent. The situation is even more unclear for new ferrielectric phases, such as FIL and FIH [ 18,19,23,72]; FiLC [38,40], FIl and F12 [46]; and sprl, spr2, spr3 [24]. The names of these phases are related to their position in the temperature scale rather than to their molecular structure.…”

Electro-optical properties of an orthoconic liquid crystal mixture (W-182) and its molecular dynamics

“…9 These subphases such as SmC ␣ * , SmC ␤ * , and SmC ␥ * can exhibit polarization between those of antiferroelectric and ferroelectric phases and often have a very complex electro-optic signature. At high temperatures, antiferroelectric nature was observed, though it actually behaves with a ferrielectric nature due to the emergence of the devil's staircase, 10 and the SmC ␥ * phase behaves with a ferrielectric nature. Although SmC ␤ * , in most cases, shows a similar behavior to the ferroelectric phase ͑SmC * ͒, 9,10 the dielectric and the electroclinic measurements indicate that the SmC ␤ * phase is different from the SmC * phase and is actually ferrielectric in nature.…”