Phase Diagrams of Binary Mixtures of Antiferroelectric and Ferroelectric Compounds with Lactate Units in the Mesogenic Core

Molecular–Statistical Theory for the Description of Re-Entrant Ferroelectric Phase

“…A molecular-statistical approach to the description of the re-entrant ferroelectric phase is derived. We have confirmed the experimental data [5,[7][8][9][10] showing that sufficiently long molecular tails with several transverse electric dipoles near their own chiral centers promote the re-entrant ferroelectric phase observed in lactic acid derivatives [3,4]. If the prime orientational order of the flexible tails is small, the dipoles in the molecular tails can make considerable contribution to the polarization arising spontaneously along the smectic layer normal.…”

“…The re-entrant ferroelectric phase also tends to appear in the mixtures of the ZLL 6/ * and ZLL 8/ * lactic acids [5], and thus, seven chains in the long molecular tail appear to be optimal for the emergence of the re-entrant ferroelectric phase. The existence of the Sm-C * re phase was confirmed by various experimental data, for example, by birefringence [8], calorimetry [3], nuclear magnetic resonance and dielectric spectroscopy [9][10][11] measurements. In the electric field-temperature phase diagram the antiferroelectric smectic phase appears to be isolated, in other words, is surrounded by the ferroelectric smectic phase [8].…”

“…The LC lactic acid derivatives are the unique ferroelectric materials. In particular, they can form the antiferroelectric, hexatic, Sm-X [3,4] and various kinds of re-entrant phases [5]. They also can be used for the synthesis of the side chain polysiloxanes, which are the well-aligned polar polymers [6].…”

Effect of alkyl chains length on properties of ferroelectric liquid crystals with the keto group attached to the molecule core

“…Using the keto group instead of the ether or ester groups for linking the alkyl chain with the molecular core also can lead to substantial increase in the values of spontaneous polarization as it was described by Yoschizawa et al [33] or Petrov [34]. Since that several series of the lactic acid derivatives [9] possessing the keto group as the linkage between the non-chiral chain and molecular core and with one [35,36], two [18,19,23] or three [17] lactate groups have been studied [9,17,37,38]. All these compounds possess the SmA* and SmC* phases over a broad temperature range.…”

“…There are four main advantages of the lactic acid derivatives as a sub-class of chiral LCs that makes them attractive with respect to other materials, i.e. (i) forming of a broad variety of basic LC phases, including the cholesteric N*, paraelectric SmA* [10,11], ferroelectric SmC* [3,8,[12][13][14][15][16], antiferroelectric SmC Ã A [12,[17][18][19][20][21][22][23], polar hexatic phases [9,13,14,19,24] as well as frustrated ones like the twist grain boundary phases, namely TGB Ã A [1][2]7,12] and TGB Ã C [25] or SmQ* phase [12,26] or re-entrant SmA* [27][28][29] and re-entrant SmC* [9,13,24]; (ii) utilization of the lactic unit as a precursor of chiral centre minimizes the cost as the price ratio to the most commonly used chiral precursor material (S)-2-octanol is at least 1:100; (iii) melting points (m.p.) are often reasonable, in the range 30-70 C, and the LC phases can easily be supercooled well below room temperature and (iv) lactic acid-based LCs usually show no ageing, and are highly stable, thermally as well as chemically.…”