Unique effect of an electric field on a new liquid crystalline lactic acid derivative

Abstract

A new chiral lactic acid derivative is presented, exhibiting a frustrated liquid crystalline phase, namely the orthogonal twist grain boundary TGBA phase in a broad temperature interval. A unique effect is observed that the applied electric field reversibly transforms the planar TGBA texture to the homeotropic one, homogeneously dark in crossed polarizers. The transformation is analogous to the Frederiks transition known in nematics, in which switching under electric field is driven by the positive dielectric anisotropy. A similar effect is established also in the SmA phase of the racemic mixture, where the field induced transformation is irreversible. A positive dielectric anisotropy in both the chiral compound and the racemic mixture is detected up to the frequency of about 10 kHz, above this frequency the anisotropy is negative. The unusual behavior of the TGBA phase under the electric field can be explained by the specific packing of molecules within the smectic layers, resulting in a relatively high layer compressibility which lowers the energy of the structural defects and thus facilitates the structure transformation. The perfectly dark state of the studied compounds, induced by the electric field, either stable or reversible, is appealing for specific applications. The change of the sign of the dielectric anisotropy, known in nematics as the dual frequency effect, might be important for photonics such as adaptive or diffractive optics.

Ultra-short helix pitch and spiral ordering in cholesteric liquid crystal revealed by resonant soft X-ray scattering

“…Contrary to this, the studied compound EZL10/10 represents a rather simple molecular structure (Scheme 1), with a lactate in the chiral chain. In our previous research it was proved that lactate unit as a source of chirality is very efficient as was demonstrated by frequent presence of blue and twist-grain boundary phases [36][37][38]. In comparison with low pitch cholesterics studied by soft X-ray resonant scattering earlier [23,39], herein we present a simple molecular structure those pitch length can be easily varied by admixture of opposite enantiomer to get a series of structures with tailored pitches.…”

Frustrated smectic liquid crystalline phases in lactic acid derivatives

“…In such a case the growth of filaments can be observed in crossed polarizers in a dark background (see Figure 7). [16,20] Recently, we have analysed the formation of filaments and supposed that finite blocks of developing TGBA structure are separated by dislocation loops having screw and edge components. [21] Screw components of the dislocation loops form twist grain boundaries between the blocks in filaments and edge components form incoherent grain boundaries between a block and surrounding SmA layers.…”

“…Quite unusual optical effect under applied electric field has been established in TGBA phase with a lactic acid derivative denoted as PHB. [20] The applied d.c. electric field transforms the planar (coloured) texture to the homeotropic one, homogeneously dark in crossed polarizers. In that case the transformation was realized due to interaction of the field with positive dielectric anisotropy of molecules.…”

How mobile phase composition and column temperature affect enantiomer elution order of liquid crystals on amylose tris(3‐chloro‐5‐methylphenylcarbamate) as chiral selector

“…The values of ΔΔH 0 and ΔΔS 0 obtained from slope and intercept of linear trends from such experimental set can be plotted against each other to obtain the plot of entropyenthalpy compensation (EEC) of chiral discrimination, which can reveal how small variations in chromatographic conditions or solute structure reflect on the enantioseparation mechanism [26]. [11,[28][29][30][31][32][33][34]. The compounds were characterized by nuclear magnetic resonance and their purity (achiral impurities) was evaluated by HPLC.…”

“…Deionized water was prepared on Milli-Q water purification system purchased from Millipore (Bedford, MA). Both the racemic mixtures and the S enantiomers of studied LCs were synthesized at the Institute of Physics of the Czech Academy of Sciences [11,[28][29][30][31][32][33][34]. The compounds were characterized by nuclear magnetic resonance and their purity (achiral impurities) was evaluated by HPLC.…”