Thermotropic Liquid Crystal Materials Research Articles

Prolonged memory effect in smectic A phase of a thermotropic liquid crystal material

The long-duration memory effect in thermotropic liquid crystal (LC) materials has long been a topic of substantial interest and numerous pioneering works. Although the idea of exploring the memory effect had been started from the nematic (N) phase of LC itself, but due to its very short duration, it was soon shifted to the other LC phases such as ferroelectric LC (FLC) or their derivatives and composites. Therefore, we demonstrate here the prolonged memory effect in a smectic A (SmA) phase of a pristine thermotropic LC material namely 4-octyl-4′-cyanobiphenyl (8CB). The memory effect has also been investigated in the N phase to estimate its duration as compared to the SmA phase. To examine the memory effect, firstly, we measured the dielectric permittivity using the dielectric spectroscopic technique with and without 40 V DC biasing. Furthermore, these results have been confirmed by means of optical textures recorded through a polarizing optical microscope. Moreover, we have also observed the removal and retrieval of two stable states by sequent application of heat and DC biasing to examine the cyclability of the LC compound under testing. We anticipate that our results will definitely bridge the gap that occurred in the advancement of emerging futuristic LC-based memory devices.

Enhancement of electro-optical properties and phase transition temperature of thermotropic liquid crystal 5CB by doping with 4-n-pentylbenzoic acid

ABSTRACT Liquid crystalline materials that have been used in the display industry need to have a wide temperature-range nematic phase while remaining functioning in different climate conditions. In this work, a new binary mixture of thermotropic liquid crystal materials, particularly the nematic phase, has been studied. A widely used material 5CB (4-Cyano-4’−pentyl biphenyl), exhibiting nematics phase, and PA (4-Phenylbenzoic acid) were preferred. Mixtures of different concentrations of 5CB-PA were prepared and investigated using dielectric spectroscopy, phase transition and electro-optical responses techniques. It was found that not only was an improvement to the dielectric anisotropic achieved but also the nematic temperature range extended from 35 ºC to just above 50°C by adding 10 wt.%. On the other hand, the threshold voltage is increased by 10% for the same sample. In addition, elastic constants and response time showed similar behaviours upon increasing the loading concentration of PA, whereas the visco-elastic coefficient significantly declined. All the estimated values for the pure 5CB are in good agreement with the literature. This improvement in the operating temperature range is unique and suggests that the doping can lead to cheap and mass production of a stable liquid crystalline material for their application in the display industry.

Kretschmann-Based Optical Sensor via Thermally Tunable Refractive Index

This study discusses whether the prism used in a Kretschmann-based surface plasmon sensor can be fabricated from a thermotropic liquid crystal (TLC) material. The refractive index of the TLC prism can be thermally tuned to match the excitation requirements for the surface plasmon modes along the metal–TLC interface of the proposed sensing platform. The TLC material was chemically prepared in vitro and was thermally and optically characterized. The measurements reported a wide mesophase temperature range ΔT (~35 °C) and a relatively high clearing temperature TC (~84 °C) which constitutes a stable thermal control for the TLC optical parameters. The experimentally measured refractive indices of the TLC material reflect a linear change in line with the temperatures at several selected wavelengths in the visible region. A design of the surface plasmon sensor was proposed, which provided a linear response to the investigated analytes refractive index. This work highlights the importance of employing TLC material in designs compatible with detecting refractive index changes by thermal tuning and presents refractive index interrogation as an alternative method for exciting surface plasmon modes.

Preparation of Luminescent Thermotropic Liquid Crystal from Benzodiathiazole Derivatives.

Luminescent liquid crystal materials (LLCMs) have been a hot research topic in the field of fluorescent materials. In this study, we successfully designed and synthesized an intense fluorescence thermotropic liquid crystal material with a fluorescence quantum yield (Φ) of 0.26 in the solid state. Moreover, the alkyl chain attached to the terminus of the chromophore was able to promote the stability of electrochemical and thermal properties, which was beneficial to the device fabrication reproducibility and stability of the device performance.

Dry Thermotropic Glycolipid Self-Assembly:A Review

Also recognized as carbohydrate liquid crystals, glycolipids are amphiphiles whose basic unit comprises of a sugar group attached to an alkyl chain. Glycolipids are amphitropic, which means these materials form liquid crystal self-assemblies when dry (thermotropic) as well as when dissolved in solvents (lyotropic/surfactants) such as water. Many glycolipids are also naturally derived since these can be found in cell membranes. Their membrane and surfactant functions are largely understood through their lyotropic properties. While glycolipids are expected to play major roles as eco-friendly surfactants in the global surfactant market, their usefulness as thermotropic liquid crystal material is, to date, unknown, due to relatively lack of research performed and data reported in the literature. Understandably since glycolipids are hygroscopic with many hydroxy groups, removing the last trace water is very challenging. In recent time, with careful lyophilization and more consistent characterization technique, some researchers have attempted serious studies into "dry" or anhydrous glycolipids. Motivated by possible developments of novel thermotropic applications, some results from these studies also provide surprising new understanding to support conventional wisdom of the lyotropic systems. Here we review the dry state of glycosides, a family of glycolipids whose sugar headgroup is linked to the lipid chain via a glycosidic oxygen linker. The structure property relationship of both linear and anhydrous Guerbet glycosides will be examined. In particular, how the variation of sugar stereochemistry (e.g. anomer vs. epimer), the chain length and chain branching affect the formation of thermotropic liquid crystals phases, which not only located under equilibrium but also far from equilibrium conditions (glassy phase) are scrutinized. The dry glycolipid assembly has been subjected to electric and magnetic fields and the results show interesting behaviors including a possible transient current generation.

Molecular structural flexibility dependence of mesomorphism through ortho-substituted bromo group

ABSTRACTA novel series of liquid crystal (LC) materials of Schiff's bases viz. RO-C6H4‒CH˭CH‒COO‒C6H4‒N˭CH‒C6H4‒Br (ortho) is synthesized and studied with a views to understanding and establishing the effect of molecular structure on liquid crystal properties and to provide novel thermotropic LC material to the scientific and technological community of research interest. The novel series consists of thirteen members (C1 to C8, C10, C12, C14, C16 & C18). All the members of a series are enantiotropic liquid crystals. Smectic (C10‒C18) and nematic (C1‒C18) property commence from C10 and C1 homologue respectively. Transition temperatures and the textures of homologues were determined using a polarizing optical microscope (POM) equipped with a heating stage. Transition curves Cr-M, Sm-N and N-I of a phase diagram behaved in normal manner. Odd–even effect is absent for Sm-N transition curve, but it is present for N-I curve. Sm-N transition curve is extrapolated to C8 and C6 nonsmectogenic homologues to determine and predict their latent ability for exhibition of smectic property. Analytical and spectral data confirms the molecular structures of homologues. Thermal stabilities of smectic and nematic are 85.4°C and 130.1°C °C whose upper and lower total mesophase length vary from 58.0°C to 06.0°C at the C10 and C1 = C5 = C6 homologue, respectively. Textures of nematic phase are threaded or Schlieren and smectic phase are of type A or C. LC properties of present novel series are compared with structurally series known series. Thus, present novel series is predominantly nematogenic and partly smectogenic with middle ordered melting type and considerable total mesophase length range.

Metal-centered polyoxometalates encapsulated by surfactant resulting in the thermotropic liquid crystal materials

Waugh- and Silverton-type polyoxometalates (POMs) K3(NH4)3[MnMo9O32] and H8[CeMo12O42] are enwrapped by dioctadecyldimethylammonium (DODA+) forming the surfactant-encapsulated POMs (SEPs) (DODA)6[MnMo9O32]·16H2O (DODA-MnMo9) and (DODA)8[CeMo12O42]·9H2O (DODA-CeMo12), which exhibit typical thermotropic liquid-crystalline properties. Here, the Waugh- and Silverton-type polyoxoanions centered by metal cation were firstly introduced into liquid crystal materials. The chemical composition of these SEP complexes was determined by IR spectra, elemental analysis and TG analysis. Also, the polarized optical microscopy, differential scanning calorimetry (DSC), variable temperature X-ray diffraction (VT-XRD) and transmission electron microscopes (TEM) were performed to characterize their liquid-crystalline behavior.

Design and construction of a thermotropic liquid crystal material based on high-nuclear transition-metal cluster-containing polyoxometalates

DODA+ was used as a surfactant to react with polyoxoanion [Ni9(OH)3(H2O)6(HPO4)2(PW9O34)3]16−, resulting in an organic–inorganic hybrid complex SEP-1, the first liquid crystal materials based on high-nuclear transition-metal cluster-substituted polyoxoanions.

Preparation and characterization of liquid crystalline polyurethane‐imide modified epoxy resin composites

Liquid crystalline polyurethane‐imide (PUI) was synthesized from polyethyleneglycol, toluene diisocyarate, and pyromellitic dianhydride by solution polymerization and characterized by FTIR spectrum. The liquid crystal properties of PUI were verified by differential scanning calorimetry, polarizing microscope (POM), and X‐ray diffraction. PUI is a longitudinal liquid crystal with LC sequences in the backbone along the main‐chain direction. PUI was used to blend with epoxy resin(ER) as a modifier. The mechanical properties, thermal property, and morphology of PUI/ER composites were investigated. It was found that PUI was a kind of thermotropic liquid crystal material within a wide range of temperature. Remarkable improvement in strength and toughness of ER/PUI composites was achieved by the blending of PUI with epoxy in appropriate proportions. The maximum for bending strain and bending strength of the composite reached the level of 10.65% and 178 MPa, respectively when the mass fraction of PUI was 15 wt%. The mechanical behaviors of the PUI/ER were consistent with morphology analysis of the fracture surfaces of PUI/ER composites from SEM. POLYM. ENG. SCI., 54:1704–1711, 2014. © 2013 Society of Plastics Engineers

Optical Measurements of Thermotropic Liquid Crystals

In this work, an experimental approach was used for measuring birefringence of thermotropic liquid crystal materials at different wavelengths in the visible region by using speckle interferometry. Also the values of the refractive indices were measured for these thermotropic liquid crystal materials in isotropic and liquid crystal phases at different wave-lengths. Temperature dependency of the refractive indices for each LC sample at certain wavelengths was investigated in the isotropic and in LC phases.

Ionically Self-Assembled Clustomesogen with Switchable Magnetic/Luminescence Properties Containing [Re6Se8(CN)6]n−(n= 3, 4) Anionic Clusters

Octahedral anionic rhenium clusters are obtained by high-temperature solid-state chemistry synthesis as single crystals or powders within which their charge is counter balanced by alkali cations. The ceramic-like behavior of the solid-state Re6 based inorganic compound limits strongly their use in functional devices. We present herein a facile route to introduce these anionic clusters in a self-organized hybrid organic–inorganic material. By replacing alkali countercations by mesogenic organic ones, polarized optical microscopy (POM), DSC, X-ray, magnetic, fluorescence, and cyclic voltammetry techniques confirm that a lyotropic and thermotropic liquid crystal material, able to switch reversibly from a bright red NIR luminescent form to a magnetic green-colored one, is obtained.

Optical measurements of mixture thermotropic liquid crystals

In this work, a new experimental approach was used for measuring birefringence of mixture thermotropic liquid crystal materials at different wavelengths in the visible region. Also the values of the refractive indices were measured for these mixture thermotropic liquid crystals in isotropic and liquid crystal phase at different wavelengths.

Vinamidines and vinamidinium salts. New thermotropic liquid crystals

Abstract Following studies concerning mesomorphic heteroaromatic salts (pyrylium, thiopyrylium, dithiolium), we present here new thermotropic liquid crystal materials based on 1,5diazapentadienium (vinamidinium) salts and on the pseudocyclic vinamidine system (1,5-diazapentadiene). The mesomorphic properties of these systems have been studied by microscopic observations, DSC and X-ray diffraction.