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Recent measurements of the elastic constants in lyotropic chromonic liquid crystals (LCLCs) have revealed an anomalously small twist elastic constant compared to the splay and bend constants. Interestingly, measurements of the elastic constants in the micellar lyotropic liquid crystals (LLCs) that are formed by surfactants, by far the most ubiquitous and studied class of LLCs, are extremely rare and report only the ratios of elastic constants and do not include the twist elastic constant. By means of light scattering, this study presents absolute values of the elastic constants and their corresponding viscosities for the nematic phase of a standard LLC composed of disk-shaped micelles. Very different elastic moduli are found. While the splay elastic constant is in the typical range of 1.5 pN as is true in general for thermotropic nematics, the twist elastic constant is found to be one order of magnitude smaller (0.30 pN) and almost two orders of magnitude smaller than the bend elastic constant (21 pN). These results demonstrate that a small twist elastic constant is not restricted to the special case of LCLCs, but is true for LLCs in general. The reason for this extremely small twist elastic constant very likely originates with the flexibility of the assemblies that are the building blocks of both micellar and chromonic lyotropic liquid crystals. [ABSTRACT FROM AUTHOR]

In some liquid crystal (LC) mixtures of bent-core host molecules that form helical nanofilaments (HNFs) and chiral, rod-shaped molecular guests, the spontaneous chirality of the HNFs is not influenced by the guest handedness. In other mixtures, the filaments become homochiral, responding to the handedness of the guest. We show that the important distinction between these two behaviours is the solubility of the guest material in the HNF phase. In our experiments, chiral LC mesogens doped into the HNF phase result in an enantiomeric imbalance and sometimes change the phase sequence on cooling from the isotropic melt. [ABSTRACT FROM PUBLISHER]

The chiral carbosilane-terminated liquid crystal 2-[(2S,3S)-2,3-difluorohexyloxy]-5-[4-(12,12,14,14,16,16-hexamethyl-12,14,16-trisilaheptadecyloxy)phenyl]pyrimidine (QL32-6) undergoes a smectic A*-smectic C* phase transition with a maximum layer contraction of only 0.2%. It exhibits an electroclinic effect (ECE) comparable to that reported for the ‘de Vries-like’ liquid crystal 8422[2F3] and shows no appreciable optical stripe defects due to horizontal chevron formation. [ABSTRACT FROM AUTHOR]

Lyotropic nematic and cholesteric liquid crystalline phases were produced using the racemic amphiphiles, potassiumN-dodecanoyl-DL-alaninate (DL-KDDA) andDL-serinate (DL-KDDS) and theirl-enantiomers, potassiumN-dodecanoyl-L-alaninate (L-KDDA) andL-serinate (l-KDDS), respectively. The different racemic nematic and cholesteric phases were characterised by a polarising light microscope. In order to calculate the helical twisting powers (htp) of the cholesteric phases, their pitches were determined as a function of concentrations of theL-enantiomers. The results showed that theL-KDDA system had a higher helical twisting power than theL-KDDS system. Small-angle X-ray scattering (saxs) techniques were performed for determination of the structural differences between the racemic micelles and the chiral micelles of the racemic and intrinsic cholesteric phases, respectively. Saxs results showed that the intrinsic cholesteric micelles are more compact than their corresponding racemic micelles. These results were interpreted in terms of the different molecular arrangements of the chiral amphiphiles in micelles compared to the amphiphiles in racemic micelles. According to our experimental results and the results on induced cholesteric phases in the literature, we proposed that there must be (1) a crucial distance and (2) a critical micelle size in order to obtain chiral induction, supporting some theoretical studies reported in the literature. In addition, we also showed that chiral induction does not take place completely as was suggested by pairwise interaction or sterical interaction models in the literature, but through anisotropic chiral interactions via distorted micelles for which a crucial distance between the micelles and a critical micelle size are required. [ABSTRACT FROM AUTHOR]

A lyotropic analogue of the ferroelectric smectic C* phase has been found. The lyotropic smectic C* phase shows macroscopic chirality effects, such as a helical ground state and polarity‐dependent electrooptic switching, thus indicating the presence of a spontaneous electric polarization. The helicity implies communication of the chiral director twist across the achiral solvent layers separating adjacent layers of the chiral mesogens. [ABSTRACT FROM AUTHOR]

A liquid crystalline compound with the azo group in the molecular core and three lactic acid units in the chiral chain (n = 3) was synthesised and its mesomorphic properties established. Spontaneous polarisation and tilt angle were determined in the ferroelectric and antiferroelectric smectic C phases. Dielectric spectroscopy in the frequency range of 1 Hz-10 MHz was performed within the temperature range of smectic phases showing the characteristic modes in each phase. Small-angle X-ray diffraction was performed and temperature dependences of layer spacing value calculated. Comparison with previously studied compounds with one (n = 1) and two lactate units (n = 2) is presented to establish the effect of lactate unit number on the liquid crystalline properties. [ABSTRACT FROM AUTHOR]

Using a discrete model for the synclinic SmC* and the anticlinic SmCa* phases we give a theoretical explanation for the fact that the helix twisting sense reverses at a transition between these phases (direct transition or via the so-called chiral smectic C ‘subphases’) and we derive an explicit expression for the helical pitch in the SmCa* phase. As the theory shows and as we also demonstrate experimentally, the reversal is of a different nature from helix inversions within a single phase, where the inversion is always coupled to a pitch divergence. At a clinicity change the common behaviour is instead pitch-shortening on approaching the phase transition and the associated helix twisting sense reversal. The phenomenon may be put to use in smart mixing in order to control the helix pitch, either for achieving long pitch for surface-stabilized ferroelectric and antiferroelectric liquid crystal displays; or a very short pitch, in the case of devices utilizing the deformed helix mode. [ABSTRACT FROM AUTHOR]

By mixing a bistereogenic antiferroelectric liquid crystal (AFLC) compound, exhibiting only the SmQ and SmCa mesophases, with the achiral N-SmC liquid crystal HOAB we could induce all three AFLC SmC-type subphases, SmCα, SmCβ and SmCγ. This seems to be in contradiction with two recent postulations regarding the subphase stability, one of which suggests that the subphases appear as a result of strong chiral interactions, the other that these phases require high smectic order something one would generally not expect in mixtures. We have studied the helical pitch, optical tilt angle, spontaneous polarization and the x-ray diffraction due to the smectic layering, as a function of mixing ratio in order to better understand the relation between phase sequence and mixture composition. The smectic layer spacing shows a strongly non-linear behavior suggesting that the basic structure of the pure AFLC substance is retained up to a HOAB content of about 75%. [ABSTRACT FROM AUTHOR]

Only six years ago, the first clear-cut example of a ferroelectric, lyotropic liquid crystal was discovered. Since then, ongoing investigations in this new research field provided numerous instances of the missing pieces to complete the formerly blank picture of the lyotropic smectic C* (SmC*) phase. In this review we wanted to combine these new results and put them into a wider historical and scientific context. We start by giving an introduction about characteristic features of the well-known thermotropic SmC* phase and why it is so difficult to find a lyotropic equivalent of this fascinating phase. After discussing early examples of achiral lyotropic and swollen SmC phases, we recap the discovery of the first lyotropic SmC* phase. The molecular features necessary for its formation and its properties are analyzed. We place special emphasis on discussing the long-range orientational order of the tilt direction and the corresponding chirality effects. By comparing these exceptional features with thermotropic and swollen SmC* phases, we aim to improve not only the understanding of the lyotropic SmC* phase, but also of the relationship between thermotropic and lyotropic systems in general. [ABSTRACT FROM AUTHOR]

In thermotropic chiral Sm-A* phases, an electric field along the smectic layers breaks the D∞ symmetry of the Sm-A* phase and induces a tilt of the liquid crystal director. This so-called electroclinic effect (ECE) was first reported by Garoff and Meyer in 1977 and attracted substantial scientific and technological interest due to its linear and submicrosecond electro-optic response [S. Garoff and R. B. Meyer, Phys. Rev. A 19, 338 (1979)]. We now report the observation of an ECE in the pretransitional regime from a lyotropic chiral lamellar L*α phase into a lyo-Sm-C* phase, the lyotropic analog to the thermotropic Sm-C* phase which was recently discovered by Bruckner et al. [Angew. Chem. Int. Ed. 52, 8934 (2013)]. We further show that the observed ECE has all signatures of its thermotropic counterpart, namely (i) the effect is chiral in nature and vanishes in the racemic Lα phase, (ii) the effect is essentially linear in the sign and magnitude of the electric field, and (iii) the magnitude of the effect diverges hyperbolically as the temperature approaches the critical temperature of the second order tilting transition. Specific deviations between the ECEs in chiral lamellar and chiral smectic phases are related to the internal field screening effect of electric double layers formed by inevitable ionic impurities in lyotropic phases. [ABSTRACT FROM AUTHOR]

Recently, the emergence of spontaneous reflection-symmetry-broken configurations in achiral chromonic liquid crystals confined in cylindrical capillaries with homeotropic anchoring at the cylinder walls was reported, namely, the so-called twisted-escaped radial (TER) and twisted planar polar (TPP) configurations. This new example of spontaneous reflection symmetry breaking in liquid crystals was attributed to the twist elastic modulus, which is known to be unusually small in comparison to the splay and bend moduli in the case of chromonic liquid crystals. We now report the experimental observation of reflection symmetry breaking in cylindrical capillaries in the case of a classical, achiral, and nonchromonic lyotropic liquid crystal forming a nematic phase of disklike micelles orienting homeotropically at the capillary walls. We observed the same chiral TER configuration, as well as a nonplanar twisted polar (TP) configuration. The TP configuration is characterized by two half-unit so-called twist disclinations, where the director twist around the line defects drives the formation of a double helix of the disclinations along the axis of the capillary. Additionally, there is a transverse twist between the two disclination lines with the same handedness as the axial twist. Similarities with and differences from the case of chromonic liquid crystals are discussed; in particular, we examine the conditions under which spontaneous reflection symmetry breaking occurs in the nonchromonic system. It seems that the chiral TER configuration can be stabilized by the presence of point defects. [ABSTRACT FROM AUTHOR]

Nematic liquid crystals (NLCs) form helical macroscopic structures through chiral induction when doped with chiral species. We describe a very simple, though highly sensitive method for determination of handedness and pitch of the induced twist in the case of very weak twisting powers of such chiral dopants. A tiny droptypically less than 10 nLof the chiral doped NLC is placed on a plate promoting a uniform planar surface anchoring of the liquid crystal director. At the curved NLC-air interface the anchoring is homeotropic and in the sessile droplets we get a locally twisted hybrid director structure with a disclination line extending across the droplet. The configuration of the disclination line (S-like or backwards S-like) reveals the sign of twisting power and extremely large pitch values in the range of 10 mm can easily be measured. We demonstrate the method using the standard NLC 4-cyano-4′-pentylbiphenyl (5CB), weakly doped with the chiral material 2-hydroxy-2-phenylacetic acid (mandelic acid). [ABSTRACT FROM AUTHOR]