Properties Of Liquid Crystalline Materials Research Articles

Survey of Applicable Methods for Determining Viscoelastic Effects in Ferroelectric and Antiferroelectric Chiral Liquid Crystals.

Viscosity, elasticity, and viscoelastic properties are one of the most fundamental properties of liquid crystalline materials; the main problem in determining these properties is the multitude of physical parameters needed to determine the values of elasticity and viscosity constants. In this paper, a number of different measurement methods for the complete characterization of viscoelastic properties for smectic liquid crystalline materials and their mixtures are analyzed, both theoretically and experimentally. The way in which viscoelastic material constants are determined depends mainly on the application/purpose of the materials under study. The subject of this work was to review the methods used to determine viscoelastic effects in ferroelectric and antiferroelectric chiral liquid crystals, their mixtures, composite materials, and even in dielectric systems, which would bear the hallmark of a universal method allowing the application of sufficiently low electric fields. In the case of chiral liquid crystals with ferroelectric and antiferroelectric phases and their subphases, the following assumption applies: fulfilment of Hooke's law (in the case of elastic coefficients) and preservation of laminar flow (in the case of viscosity coefficients).

Clustering triggered emissive liquid crystalline template for dual mode upconverted and downconverted circularly polarized luminescence.

Liquid crystalline materials have attracted significant attention in chiroptical research due to their ability to form long range ordered helical superstructures. Research focus has been on exploiting the unique properties of liquid crystalline materials to demonstrate highly dissymmetric circularly polarised luminescent (CPL) systems. In this study, we present a thermally driven, facile approach to fabricate CPL-active materials utilizing cholesteryl benzoate as the active substrate. Cholesteryl benzoate, a well-known thermotropic liquid crystal, has been found to manifest intriguing optical characteristics upon subjecting to repeated heating-cooling cycles. Despite the absence of conventional fluorescent moieties, the material exhibited luminescence through aggregation induced clustering triggered emission mechanism. Systematic investigations revealed excitation-dependent CPL for solid cholesteryl benzoate films when subjected to multiple thermal cycles. The excited state chiroptical investigation performed after multiple thermal cycles showed a luminescence anisotropy (glum) of 8 × 10-2, which is a high value for simple organic molecules. Moreover, upon co-assembly with lanthanide-based upconversion nanophosphors (UCNPs), the hybrid system demonstrated upconverted circularly polarised luminescence (UC-CPL). Benefiting from the ability to endow upconversion nanoparticles of various sizes, fabrication of UCNP-ChB hybrid nanocomposites exhibiting multicoloured upconversion CPL was demonstrated. These findings highlight the potential of liquid crystalline materials for diverse applications, including 3D optical displays and anticounterfeiting technologies.

Synthesis of New Liquid-Crystalline Compounds Based on Terminal Benzyloxy Group: Characterization, DFT and Mesomorphic Properties.

The effect of the terminal benzyloxy group on the mesomorphic properties of liquid crystalline materials developed from rod-like Schiff base has been described. For this objective, a novel Schiff base liquid crystal family, specifically new series of Schiff base liquid crystals, namely, (E)-4-(alkyloxy)-N-(4-(benzyloxy)benzylidene)aniline, In, are prepared and investigated in detail. The length of the terminal alkyloxy chain (n) varies amongst the compounds in the series. Where n varies between 6, 8 and 16 carbons. At the other end of the compounds, benzyloxy moiety was attached. The molecular structures of all synthesized compounds were established using different spectroscopic techniques. The molecular self-assembly was explored using differential scanning calorimetry (DSC) and polarized optical microscope (POM). Depending on the length of the terminal alkyloxy chain, only one type of SmA phase with different stability was observed. The previously reported para-substituted systems and the present investigated compounds were compared and discussed. The calculated quantum chemical parameters were computationally correlated using the DFT method via the B3LYP 6-311G(d,p) basis set. The theoretical computations revealed that the length of the alkyl side chain influences the zero-point energy, reactivity and other estimated thermodynamic parameters of benzoyloxy/azomethine derivatives. Furthermore, the FMO energy analysis shows that molecule I16 have higher HOMO energies than the other compounds, and I6 has a much lower LUMO level than the rest.

Calorimetry of phase transitions in liquid crystal 8CB under shear flow.

A differential scanning calorimeter equipped with a shearing system (shear rate of  < 400 s-1) was developed to elucidate the thermodynamic properties of liquid crystalline phase transitions under shear flow. An analytical method was proposed to accurately estimate the heat flow caused by shear friction to evaluate the transition entropies. The phase transitions of 4'-n-octyl-4-cyano-biphenyl (8CB) under shear flow were investigated using the developed calorimeter. Although several shear-induced transitions for 8CB have been reported in the past using viscosity and small-angle X-ray scattering (SAXS) measurements, only the nematic-isotropic (N-I) and smectic-A-nematic (SA-N) transitions were detected as heat flow peaks. The N-I transition temperature was almost independent of the shear rate. The SA-N transition temperature was also independent of the shear rate, but the transition peak was broadened by applying shear flow. For both transitions, the transition entropies were independent of the shear rate. These results suggest that the thermodynamic properties were not considerably changed by shearing because the molecular alignments in the domains were not substantially changed, whereas shearing changed the LC domain directions, which can be detected by viscosity and SAXS measurements.

Preparation and Structural Properties of Liquid Crystalline Materials and its Transition Metals Complexes

Preparation and Structural Properties of Liquid Crystalline Materials and its Transition Metals Complexes

Liquid crystalline material exhibiting multiple phase transitions: morphologic properties and optical transmission

Morphologic and thermo-optical properties of liquid crystalline material exhibiting multiple phase transitions were investigated in this work. Investigations were carried out for both the direct (by heating) and the reverse (by cooling) phase transitions. Thermo-morphologic properties of the heterophase regions of phase transitions were investigated. Temperature dependences of the optical transmission were studied, the mean optical density of crystalline state, smectic C, smectic A and nematic mesophases was estimated, temperature widths of the heterophase regions ofcrystal↔smectic C,smectic C↔smectic A,smectic A↔nematicandnematic↔isotropic liquidphase transitions were determined with high accuracy.

Dipolar Aggregation and the Static Dielectric Permittivity of Some Liquid Crystalline Materials

In the paper, we show how some modifications in the chemical structure of mesogenic molecules can lead to an essential increase of the dielectric permittivity of liquid crystalline material due to the reduced molecular ability to the antiparallel dipolar aggregation. As an example, the static permittivities of two nematogenic homologous series, CnH2n+1PhPhCN and CnH2n+1PhCOOPhCN, are analyzed. However, the structural modifications of mesogenic molecules lead often to unfavorable changes in some important physical properties of liquid crystalline material, as a shift in the clearing temperature, for example, or can lead even to a disappearance of the mesophase. This paper presents such an event observed for the compound composed of C5H11PhPh(CH3)CN molecules, the methyl derivatives of C5H11PhPhCN molecules, which form a well-known nematic liquid crystal.

Quantum dots as liquid crystal dopants

Liquid crystal nanoscience, a field exploring the mutually beneficial combination of the unique properties of nanoscale materials and fluid, yet ordered liquid crystalline phases, is increasingly focusing on semiconductor quantum dots. In one major research thrust, the anisotropic properties of the liquid crystal host are sought to facilitate the assembly of quantum dots into arrays, in another, both size- and shape-dependent optical and electronic properties of quantum dots are used to manipulate optical, electro-optical and alignment properties of liquid crystalline materials. This feature article reviews recent accomplishments and new insights in this fascinating area of soft matter nanocomposites including work from our laboratory on a series of CdSe and CdTe quantum dots as additives in nematic liquid crystal hosts.

Photorefractive properties of new liquid crystals in the near-infrared range

This work focuses on the definition of optical anisotropy of liquid crystals in the near-infrared range. The main goal of this paper was to measure the photorefractive properties of new liquid crystal materials with high refractive index in the near-infrared range such as 1294-1b, which has a relatively high anisotropy of the refractive index in the optical range with Δn having a value of more than 0.35. Optical anisotropy in the near-infrared range of well-known liquid crystals such as 5CB and 6CHBT as described in different papers was used to test the measuring method. The measured refractive indexes were similar to the refractive indexes published in the literature. Depending on the literature, the data state that the diffraction efficiency is dependent upon the temperature and the polarisation of the read-beam. Interesting applications of liquid crystals in the near-infrared range are also discussed. In this work the methodology for the measurement of liquid crystals in the near-infrared spectrum is described in some detail. The main aim of the work presented is due to the demand for new materials that will meet the requirements for the telecommunications industry, which uses a third window transmission (with a wavelength of 1.55 μm). There are many indications that materials which may be applicable in these areas may be liquid crystals. The properties of liquid crystalline materials in this band are particularly interesting because of their possible applications. Already, liquid crystals are used for switches and modulators for waves in the near-infrared range.

Synthesis of rod-like bis-ester liquid crystals and their influence on photoelectric properties of liquid crystalline materials

Six novel rod-like magnetic liquid crystals have been prepared, in which trans-bicyclohexyl or trans-cyclohexylphenyl and biphenylcarboxylic acid phenyl ester mesogenic cores with n-propyl and n-pentyl substituents were terminated by 4-hydroxyl-TEMPO (TEMPO = 2,2,6,6-tetramethylpiperidine-1-oxy). Their structures were confirmed by elemental analysis, IR and MS. Determined by SQUID, EPR, DSC and HS-POM (heat stage polarizing optical microscope), the six compounds all have both magnetic and liquid crystalline properties; their temperature ranges of mesophase were from 16.0 to 24.8 °C, and the magnetic liquid crystal molecules could obviously improve the response sensitivity of liquid crystal materials.

A colloid of ferroelectric nanoparticles in a cholesteric liquid crystal

The introduction of a minor quantity of ferroelectric nanoparticles into a cholesteric mixture causes a 45% decrease of the driving voltage with both the optical cell quality and the director field in the cell remaining undisturbed. The drop of the driving voltage results from a more than twofold increase of the effective dielectric anisotropy of the nematic matrix, which is the basic component of the cholesteric compound. The results reported clearly show how promising the ferroelectric liquid crystalline (LC) nanocolloids are for various applications. In particular, they offer a unique way for an effective tuning of the dielectric, optical and electro-optic properties of LC materials in a non-synthetic way that is a new direction for the development of advanced anisotropic meso-materials. We suggest that the strong impact of ferroelectric nanoparticles on the properties of the studied chiral nematics is due to the particle's permanent polarization, which produces a giant electric field around it.

Liquid crystalline biopolymers: A new arena for liquid crystal Research

Although discovered almost a century ago, it was until the mid sixties that liquid crystals were just regarded as curious materials that exhibited unusual properties as they melted from a solid to a liquid state of matter. Today liquid crystals (LC) have become the basis of many advanced technologies. They are extensively used in displays of wristwatches, calculators, laptop computers, aircraft and many appliances and have newer applications in flat-panel television, large switchable privacy windows, optical computing and optical devices for communication networks. The future of liquid crystals is envisaged to look even more promising because of their important role in biology and their hitherto not fully discovered potential for applications in food, agriculture, medicine, high performance materials development and other industrial and biotechnological processes. Major classes of biological compounds including lipids, proteins, carbohydrates and nucleic acids all have been found to exist in various liquid crystalline phases in vivo as well as in vitro under well-defined conditions. Their liquid crystalline structure is envisaged to have a very important role in their biological functions and self assembly processes. In order to get a better insight into biological processes at supramolecular level it is very important to have, in depth, knowledge of properties of liquid crystalline materials. This paper gives a brief introduction to liquid crystals and reviews literature on liquid crystalline behaviour of biopolymers both in vitro and in vivo in relation to their implications in the fields of biology, medicine and material science.

Selectivity tuning and molecular modeling of new generation packings for RP HPLC

Retention mechanism, selectivity and physicochemical properties together with theoretical surface simulation experiments of laboratory-synthesized packing materials for high performance liquid chromatography (HPLC) containing cholesterol molecules immobilized on the high quality silica gel were studied. The chromatographic behavior of the three cholesterol-based columns (SG-CHOL, SG-MIX CHOL/AP and SG-10-CHOL) was examined with special regard to retention and selectivity and compared to reference materials: a typical octadecylsilica column (SG-C18) and an alkylamide bonded phase (SG-AP). Temperature investigations (DSC) and molecular modeling simulations didn't bring an expected confirmation of liquid crystalline properties of materials studied. The observed phase transition was attributed to conformation change within the amide bonding.

Optical Anisotropy of Phenylacetylene Homologues

In order to study the relationship between the chemical structures and the optical anisotropic properties of liquid crystalline materials, we synthesized and evaluated phenylacetylene homologoues. The mesomorphic properties and birefringence of the compounds will be presented. The relationship between the calculated anisotropy of polarizability (δ α) and observed optical anisotropy was also investigated. δ n increased with calculated δ α, but some compounds having substituent groups and 1-ring compounds exhibited lower δ n than some compounds which have almost same δ α.

Monte Carlo simulations of a liquid of mesogenic molecules

Monte Carlo computer simulations of a liquid of model anisotropic molecules at various temperatures have been performed for the first time with a system large enough to be representative of a liquid crystalline domain. Although the molecules are not confined to a lattice, the behavior of the simulated system is found to be in surprisingly good agreement with the predictions of the Flory–Ronca–Irvine lattice theory. Our results indicate that reliable computer experiments on the relationships between molecular constitution and properties of liquid crystalline materials are nowadays feasible, provided that the absence of spurious effects related to the system size is carefully checked in each case.

Physical Properties of Liquid Crystalline Materials in Relation to Their Applications

Abstract A short review is given of successively the diamagnetic susceptibility, the refractive index, the dielectric permittivity, the elastic constants and the viscosity coefficients of nematic liquid crystals. Emphasis is on typical results that have been obtained, and the possibilities and problems connected with a molecular interpretation. In particular an attempt is made to distinguish in the macroscopic quantity the influence of the molecular properties involved, of the direct temperature dependence, and of the dependence on the orientational order (indirect temperature dependence).

Liquid crystals and some of their applications

This paper is a brief review of some of the properties and applications of liquid crystals. By studying the references, a reader can gain a more extensive insight into the liquid crystalline state. Classifications of liquid crystalline materials and nomenclature characteristic of the field give the reader a working knowledge of the subject. Polymorphism is one of the common properties of liquid crystalline materials; the subject is covered in the text and summarized in tabular forms. The fundamental properties of liquid crystals are correlated with some of the behaviors and uses of liquid crystals. Optical properties, curvature elastic properties, surface effects, external field effects and hydrodynamics of the liquid crystalline state are discussed as necessary to describe recent practical applications; these include displays, storage of images and other electrooptic devices.