Smectic Liquid Crystal Phases Research Articles

Molecular and Segmental Orientational Order in a Smectic Mesophase of a Thermotropic Ionic Liquid Crystal

We investigate conformational dynamics in the smectic A phase formed by the mesogenic ionic liquid 1-tetradecyl-3-methylimidazolium nitrate. Solid-state high-resolution 13C nuclear magnetic resonance (NMR) spectra are recorded in the sample with the mesophase director aligned in the magnetic field of the NMR spectrometer. The applied NMR method, proton encoded local field spectroscopy, delivers heteronuclear dipolar couplings of each 13C spin to its 1H neighbours. From the analysis of the dipolar couplings, orientational order parameters of the C–H bonds along the hydrocarbon chain were determined. The estimated value of the molecular order parameter S is significantly lower compared to that in smectic phases of conventional non-ionic liquid crystals.

Effects of monoclinic symmetry on the properties of biaxial liquid crystals.

Tilted smectic liquid crystal phases such as the smectic-C phase seen in calamitic liquid crystals are usually treated using the assumption of biaxial orthorhombic symmetry. However, the smectic-C phase has monoclinic symmetry, thereby allowing disassociation of the principal optic and dielectric axes based on symmetry and invariance principles. This is demonstrated here by comparing optical and dielectric measurements for two materials with highly first-order direct transitions from nematic to smectic-C phases. The results show a high difference between the orientations of the principal axes sets, which is interpreted as the existence of two distinct cone angles for optical and dielectric frequencies. Both materials exhibit an increasing degree of monoclinic behavior with decreasing temperature. Due to fast switching speeds, ferroelectric smectic-C* materials are important for fast modulators and LCoS devices, where the dielectric biaxiality influences device operation.

Curvatures of smectic liquid crystals and their applications

ABSTRACTCurvature is an important concept for understanding layering structures in soft matters, ranging from complex macromolecular self-assembled structures to simple lipid bilayers. Among the various kinds of soft matters, smectic liquid crystal (LC) phases have been widely studied because of their periodic featured curvatures under various external forces. Generally, their curvatures are on the micron-scale due to the bulk elasticity of smectic LC materials. In this review, a combination of sublimation and recondensation of smectic LC materials generates a variety of curvatures at the nanometer scale, which cannot be achieved by self-assembly under thermal equilibrium conditions. In particular, we have focused on the change of curvatures in focal conic domains under non-equilibrium conditions, in which negative and zero Gaussian curvatures in the micron-scale transform to positive Gaussian curvatures in the micron- and nanometer scales. Finally, the review closes with applications using such non-equilibrium self-assembly of smectics.

Adsorption and selective properties of 4-{4-[4(S)-2-methyl-1-butoxybenzoyloxy]phenyldiazenyl}benzaldehyde in gas–mesophase chromatography

Adsorption of 16 organic compounds from the gas phase by 4-{4-[4(S)-2-methyl-1-butoxybenzoyloxy]phenyldiazenyl}benzaldehyde was studied by gas chromatography. It was shown by means of differential scanning calorimetry that 4-{4-[4(S)-2-methyl-1-butoxybenzoyloxy]phenyldiazenyl]benzaldehyde is an enantiotropic polymorphic mesogen and forms smectic and nematic liquid crystal phases. Electron-donor isomers of methylpyridine and dimethylpyridine, isomers of weakly polar xylenes and cresols, and enantiomers of 2,3-butanediol and terpene hydrocarbons, capable of various types of intermolecular interactions with mesogenic aldehyde, were selected as adsorbates. Specific retention volumes of adsorbates and criteria for their separation were calculated. The effect of temperature and chemical nature of the adsorbates on their adsorption redistribution in the gas–liquid crystal system is discussed. It was found experimentally that the adsorbent based on 4-{4-[4(S)-2-methyl-1-butoxybenzoyloxy]phenyldiazeny}lbenzaldehyde exhibits high selectivity for close-boiling organic compounds of various nature and good efficiency and productivity in their separation.

1PA42 ベント型分子液晶における強誘電性 : 反強誘電性の拮抗とキラリティ

1PA42 ベント型分子液晶における強誘電性 : 反強誘電性の拮抗とキラリティ

Tuning Coulombic interactions to stabilize nematic and smectic ionic liquid crystal phases in mixtures of charged soft ellipsoids and spheres.

We have investigated the effect of electrostatic interactions in mixtures of soft ellipsoids and spheres based on the well-known Gay-Berne (GB) and Lennard-Jones (LJ) potential, respectively. These model systems, in their original version, that is without any electrostatic charge, have been thoroughly investigated in the literature both as pure components and mixtures. In particular, mixtures of particles of different shapes, such as spheres and ellipsoids, tend to phase separate because of the excluded volume effects. Common ionic liquid crystals, based on imidazolium or other quaternary ammonium salts, are usually composed of roughly elongated (although flexible) cations and roughly spherical anions, that is, particles with a similar shape such as the GB and LJ models. Therefore, in this work, we present the results of molecular dynamics simulations of mixtures of positively charged GB and negatively charged LJ particles as models of ionic liquid crystals. Interestingly, by modulating the charge of the particles it is possible to stabilize isotropic, nematic, smectic and crystalline ionic phases. The relative weight of Coulomb (a radial, therefore isotropic interaction) and van der Waals (an anisotropic interaction) contributions is a key parameter to tune the stability of various mesophases.

Examination of molecular packing in orthogonal smectic liquid crystal phases: a guide for molecular design of functional smectic phases.

The reported layer spacings (dsmectic) of six homologues of mesogens exhibiting orthogonal smectic phases (SmE, SmB, and SmA phases) are reexamined. The slopes of the linear dependences on chain length (n, the number of carbon atoms in the hydrocarbon chain) are clearly categorized into two groups: 1.9 Å (CH2)-1 and 1.4 Å (CH2)-1. It is clarified that in the former the molecules take a rod-like form (rod-form; category-I), whereas in the latter the molecules are bent around the connection between the core and chain moieties (bent-form; category-II). The average relative positions of adjacent molecules within the smectic structures are deduced from the intercept of the linear functions of dsmectic against n. The relation between and the features of molecules belonging to the two categories are discussed for molecular design of functional smectic liquid crystals.

A Family of Amphiphilic Cyclodextrin Liquid Crystals Governed by Dipole-Dipole Interactions.

A novel family of amphiphilic cyclodextrin(CD)-based liquid crystals that bear O-acetylated oligoethylene glycol chains at the secondary face is reported. Unlike most of the previously reported liquid crystals (LC) based on chemically modified CDs, which depend on H-bonding as the primary intermolecular forces, the present CD derivatives self-assemble into highly ordered smectic liquid crystal phases via the weaker dipole-dipole intermolecular interactions. The obtained materials are found to display much improved properties such as improved thermostability, reduced clearing temperatures, and better fluidity. The present work opens up new possibilities to design CD-based LC materials.

Transitional subphases near the electric-field-induced phase transition to the ferroelectric phase in Se-containing chiral smectic liquid crystals observed by resonant x-ray scattering.

Resonant x-ray scattering experiments revealed transitional subphases near the electric-field-induced phase transition of a Se-containing chiral liquid crystal in a planar aligned cell geometry. In the lower-temperature range (Sm-C_{A}^{*} and three-layer periodicity Sm-C_{γ}^{*} phases), the six-layer periodicity subphase appeared with increasing electric field during the field-induced transition from Sm-C_{γ}^{*} to Sm-C^{*}. In the higher-temperature range [four-layer periodicity antiferroelectric (AF) phase], the peak positions of the three-layer satellites shifted to those of the four-layer satellites and then the satellites corresponding to the five- through seven-layer periodicity appeared in sequence. Near the AF to Sm-C_{α}^{*} phase transition temperature, the layer periodicity increased with applied field. The molecular configurations of the subphases near the field-induced transition are discussed based on the Ising, distorted clock, and perfect clock models.

Soft ellipsoid potential for biaxial molecules

A soft ellipsoid contact pair potential model for biaxial molecules is proposed considering the configuration dependent energy anisotropy explicitly alongwith their geometrical aspects. Analytic expressions of forces and torques for this coarse-grained potential are provided to make it convenient for molecular dynamics simulation study. Additionally, some molecular dynamics simulations are performed to generate biaxial smectic and nematic liquid crystal phases.

Controlling the volatility of the written optical state in electrochromic DNA liquid crystals.

Liquid crystals are widely used in displays for portable electronic information display. To broaden their scope for other applications like smart windows and tags, new material properties such as polarizer-free operation and tunable memory of a written state become important. Here, we describe an anhydrous nanoDNA–surfactant thermotropic liquid crystal system, which exhibits distinctive electrically controlled optical absorption, and temperature-dependent memory. In the liquid crystal isotropic phase, electric field-induced colouration and bleaching have a switching time of seconds. Upon transition to the smectic liquid crystal phase, optical memory of the written state is observed for many hours without applied voltage. The reorientation of the DNA–surfactant lamellar layers plays an important role in preventing colour decay. Thereby, the volatility of optoelectronic state can be controlled simply by changing the phase of the material. This research may pave the way for developing a new generation of DNA-based, phase-modulated, photoelectronic devices.

The topology of dislocations in smectic liquid crystals

The order parameter of the smectic liquid crystal phase is the same as that of a superfluid or superconductor, namely a complex scalar field. We show that the essential difference in boundary conditions between these systems leads to a markedly different topological structure of the defects. Screw and edge defects can be distinguished topologically. This implies an invariant on an edge dislocation loop so that smectic defects can be topologically linked not unlike defects in ordered systems with non-Abelian fundamental groups.

Smectic-A and Hexatic-B Liquid Crystal Phases of Sanidic Alkyl-Substituted Dibenzo[fg,op]naphthacenes

Despite longstanding interest in liquid crystalline compounds with simple rod- or disc-like shapes (calamitics or discotics), very few examples of the analogous board-shaped, or "sanidic", liquid crystals exist. A new series of alkyl-substituted dibenzo[fg,op]naphthacenes have been prepared by planarization of o-phenylene precursors through dehydrohalogenation. Their photophysical properties have been studied in dichloromethane. Liquid crystal phase behavior was characterized by polarized optical microscopy, differential scanning calorimetry, and X-ray diffraction. All of the compounds exhibit monotropic liquid crystal phases on cooling from the isotropic phase. The compounds with shorter alkyl (pentyl and heptyl) chains exhibit the uniaxial smectic-A phase analogous to that of simple calamitic mesogens. The compounds with longer alkyl (nonyl, undecyl, and tridecyl) chains exhibit a new smectic liquid crystal phase featuring short-range positional order with an apparent rectangular lattice in the smectic layers, that is, an orthogonal biaxial hexatic-B. The molecular arrangement in this phase likely corresponds to a distorted herringbone packing of the board-shaped structures. Further, the compound with nonyl chains exhibits an underlying smectic-B phase. DFT calculations show that the cores of the mesogens are twisted into C2-symmetric saddle-shaped geometries because of steric interactions along their rims. The liquid crystal phases and their structures are discussed in the context of the compounds' board-like shapes and intercore interactions.

Intercalated soft-crystalline mesophase exhibited by an unsymmetrical twist-bend nematogen

A number of new states of matter have been reported in recent years for liquid crystal dimers, most notably the twist-bend nematic phase which exhibits spontaneous breaking of symmetry through the emergence of chiral structures in an achiral fluid. In this communication we report on an unsymmetrical liquid crystal dimer that exhibits a transition from the spontaneously chiral twist-bend nematic phase into a novel smectic liquid crystal phase.

Induced smectic phases of stoichiometric liquid crystal mixtures.

We revealed the detailed structures of induced smectic liquid crystal (LC) phases composed of a binary mixture of charge-transfer (CT) LC substances. Although neither of the constituents had highly ordered smectic phases, the mixture exhibited smectic-E (SmE) or smectic-B (SmB) phases when mixed at ratios of 1 : 1 and 2 : 3, respectively. The results of polarized optical microscopy, differential scanning calorimetry, X-ray diffraction, and infrared spectroscopy indicated that the induced smectic phases were stabilized by an exquisite balance between the CT interactions, dipolar interactions, and excluded volume effects. We proposed a possible model for the molecular arrangements in the SmE and SmB phases, which consistently explained the experimental results including the stoichiometric ratios.

Molecular dynamics of anhydrous glycolipid self-assembly in lamellar and hexagonal phases.

The molecular dynamics of a synthetic branched chain glycolipid, 2-decyl-tetradecyl-β-d-maltoside (C14-10G2), in the dry assemblage of smectic and columnar liquid crystal phases has been studied by dielectric spectroscopy as a function of frequency and temperature during the cooling process. Strong relaxation modes were observed corresponding to the tilted smectic and columnar phases, respectively. At low frequency (∼900 Hz to 1 kHz) in the smectic phase, Process I* was observed due to the tilted sugar bilayer structure. The process continued in the columnar phase (Process I) with an abrupt dynamic change due to phase transition in the frequency range of ∼1.3 kHz to 22 kHz. An additional process (Process II) was observed in the columnar phase with a broader relaxation in the frequency range of ∼10 Hz to 1 kHz. A bias field dependence study was performed in the columnar phase and we found that the relaxation strength rapidly decreased with increased applied dc bias field. This relaxation originates from a collective motion of polar groups within the columns. The results of dielectric spectroscopy were supported by a molecular dynamics simulation study to identify the origin of the relaxation processes, which could be related to the chirality and hydrogen bonds of the sugar lipid.

FT-IR Study on Liquid Crystal Phase Transitions of Thermotropic Hydrogen-Bonded Cubic Mesogenes, 1,2-Bis(4'-n-alkoxybenzoyl)hydrazines (BABH-n) and 4'-n-Alkoxy-3'-nitrobiphenyl-4-carboxlic acid (ANBC-n): Spectroscopic Evidence for Quasibinary Picture Model.

Changes in intermolecular interactions and molecular geometry for two kinds of thermotropic cubic mesogenes, 4'-n-alkoxy-3'-nitrobiphenyl-4-carboxlic acid (denoted as ANBC-n, where n represents the number of carbon atoms in the alkoxy group) and 1,2-bis(4'-n-alkoxybenzoyl)hydrazines (BABH-n), at liquid crystal (LC) phase transitions were revealed utilizing the frequency shifts in Fourier transform infrared (FT-IR) bands as a guide. The ANBC-n and BABH-n form two kinds of bicontinuous cubic (Cub(bi)), Ia3d and Im3m types, and smectic LC phases depending on the length of the alkyl chain and temperature. In the present work, two kinds of phase transitions, i.e., smectic C ↔ Ia3d-Cub(bi) phase transition for the ANBC-16 and BABH-9 and Ia3d-Cub(bi) ↔ Im3m-Cub(bi) phase transition for the BABH-13 and BABH-16, were examined, and the experimental result was compared to the entropy changes predicted by the quasibinary picture model. In this model, it is postulated that the basic units in the BABH-n and ANBC-n, i.e., the "chain" and "core", would contribute to the phase transition entropy in different ways. A conclusion of the FT-IR result shows the adequacy of this model for the behavior of the alkyl chain. On the other hand, the FT-IR result suggested that entropy changes for the "core" predicted by this model are not directly related to changes in the intermolecular interactions between the aromatic cores of the LC molecules at the phase transitions.

Synthesis and some features of phase behavior of chiral p-alkoxyphenyl glycerol ethers

A series of (S)-3-(4-alkoxyphenoxy)propane-1,2-diols was prepared with the enantiomeric excess 86–92% by Sharpless asymmetric dihydroxylation of 1-alkoxy-4-allyloxybenzenes with an AD-mix-β mixture. R-Enantiomers with enantiomeric excess 97–99% and racemic samples were obtained by reaction of sodium p-substituted phenolates with (R)- and rac-3-chloropropane-1,2-diol. The phase behavior of racemates and scalemates in the produced homolog series of glycerol aryl ethers with hydrocarbon substituents of various length was examined by means of thermomicroscopy. The higher memberes of the homolog series of both racemic and scalemic diols undergo at heating an enantiotropic phase transition to a smectic liquid crystal phase.

Multistep hierarchical self-assembly of chiral nanopore arrays.

A series of simple hierarchical self-assembly steps achieve self-organization from the centimeter to the subnanometer-length scales in the form of square-centimeter arrays of linear nanopores, each one having a single chiral helical nanofilament of large internal surface area and interfacial interactions based on chiral crystalline molecular arrangements.

ChemInform Abstract: Orientation Control over Bent‐core Smectic Liquid Crystal Phases

AbstractReview: 84 refs.