New chlorine‐substituted liquid crystals possessing frustrated TGB_A and SmQ phases

Abstract

Several series of chlorine-substituted rod-like liquid crystalline compounds have been synthesised containing a different number of lactate units in the chiral chain. Sequences of phases and phase transition temperatures were determined by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction studies. Depending on the molecule structure, the materials possess a rich variety of mesophases, i.e. the paraelectric chiral smectic A (SmA*), ferroelectric chiral smectic C (SmC*) and antiferroelectric smectic C (SmC A *) phases. Additionally, some compounds with one and two lactate groups exhibit the frustrated antiferroelectric twist grain boundary (TGB A ) and smectic Q (SmQ) phases, respectively. The existence of the SmQ phase ordered in two directions was confirmed by X-ray diffraction on a non-oriented sample. The effects of the non-chiral chain length and number of the chiral lactate groups on the mesomorphic properties, spontaneous polarisation, spontaneous tilt angle and complex permittivity have been studied and discussed.

Spontaneous polarization and dielectric relaxation dynamics of ferroelectric liquid crystals derived from 2(S)-[2(S)-ethylhexyolxy] propionic acid and its (S, R)-diastereomer

“…According to Ref. [33], this variation might be caused by the increase of helical pitch when temperature is decreasing. Regarding samples A and B whose core structures contain a biphenyl ring, the variation with temperature and the magnitude on the dielectric strength ε Δ and relaxation frequency f r are similar for both samples as shown in Fig.…”

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

“…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.…”

Spontaneous Polarization and Dielectric Relaxation Dynamics of Two Novel Diastereomeric Ferroelectric Liquid Crystals

“…As seen in Fig. 5, for both samples, it is worth noting that a jump variation at the temperature dependence of ∆ε 1 occurred in the phase transition from the SmC * phase to the SmCγ * -like phase when cooling due to a strong contribution of the SmCγ * -like phase, which is associated to a strong contribution of the ferrielectric Goldstone mode [31]. Moreover, despite the jump variation, the relaxation frequency f rj decreased with decrease of temperature, which was as reported in the SmCγ * phase in Ref.…”