New developments in millimeter wave spectroscopy

In the past few years millimeter and submillimeter wave spectroscopy has been the backbone for modern molecular line astronomy. The detection of unstable and high-temperature molecular species in the interstellar environment has stimulated the development of methods of detecting molecular ions, radicals and unstable molecules in the laboratory by means of millimeter wave technology. Some of the recent experimental advances as well as the developments which have occurred in the analysis of high resolution rotational and vibrational spectra with regard to understanding molecular dynamics will be discussed.     

The millimeter wave spectrum of iodoethyne,HCCI

The rotational spectrum of iodoethyne, HCCI, has been observed in the frequency range from 105 to 305 GHz. A sensitive spectrometer system employing source modulation, a harmonic generator millimeter wave source and a liquid helium cooled InSb-detector has been used. The rotational constants and nuclear quadrupole coupling parameters of HCCI have been obtained for the ground state and the first and second excited vibrational states of ν₄. The rotational spectrum of the 2ν₅ state has also been identified. The very weak spectrum shows unusual relative intensities which are interpreted by assuming a dipole moment change with ν₄ excitation of 0.07 D. The ground state dipole moment is then estimated to be 0.020(10) D.     

Liquid crystal bridges

The liquid crystalline material octylcyanobiphenyl was studied in the form of bridges spanning the space between two solid supports in an immiscible water bath. In the nematic phase the bridge collapses above a certain length-to-diameter ratio, consistent with the behaviour of ordinary Newtonian liquid bridges. The smectic A phase, however, exhibited the formation of very long, stable columns as a consequence of its non-Newtonian behaviour.     

Electric field induced birefringence in a ferroelectric liquid crystal

We have measured the d.c. electric field dependence of the birefringence and conoscopic images for the smectic C* phase of a partially racemized ferroelectric chiral smectic liquid crystal CE-8. The experiments were performed using 50mu m thick homeotropic cells with lateral electrodes which created a d.c. electric field parallel to the smectic layers. The observed field induced birefringence shows a characteristic step-like behaviour which is due to the stepby-step unwinding of the helical structure in a sample with finite dimensions along the helical axis. In conoscopic observations we observe that these steps are associated with moving disclination lines that traverse the sample in the direction of the smectic layers. The observed electric field dependence of the birefringence is discussed in terms of the soliton-like unwinding of helical smectic structures and compared with the predictions of the Landau theory. A qualitatively good agreement is obtained.     

Liquid crystal mixtures for potential infrared applications

Liquid crystals (LCs) with diazo linkages have high dielectric and optical anisotropy. Two newly synthesized liquid crystalline compounds were dissolved in room temperature LC hosts, E7 and PTTP-24/36, to assess their properties. It was found that these mixtures have higher birefringence, larger dielectric anisotropy, and better elastic properties than the hosts. Satisfactory viscoelastic coefficients were also obtained for these mixtures, showing that they are promising LC materials for applications in the near IR region.     

Liquid crystal mixtures for potential infrared applications

Liquid crystals (LCs) with diazo linkages have high dielectric and optical anisotropy. Two newly synthesized liquid crystalline compounds were dissolved in room temperature LC hosts, E7 and PTTP-24/36, to assess their properties. It was found that these mixtures have higher birefringence, larger dielectric anisotropy, and better elastic properties than the hosts. Satisfactory viscoelastic coefficients were also obtained for these mixtures, showing that they are promising LC materials for applications in the near IR region.     

High birefringence and high resistivity isothiocyanate-based nematic liquid crystal mixtures

The molecular structures and physical properties of several single- and double-fluorinated isothiocyanatotolane, isothiocyanatocyclohexyltolane, and isothiocyanatoterphenyl compounds are reported. Two eutectic mixtures comprising these compounds are formulated and their properties evaluated. These mixtures exhibit a high birefringence, relatively low viscosity, high resistivity, and good photo and thermal stabilities. Potential applications of these mixtures for spatial light modulators, optical phased arrays, and high speed photonics are discussed.     

Liquid crystal polymer optics

In this paper we give a concise overview of various optical applications of Liquid Crystalline side‐chain polymers. The possibility to tune the LC structure and phase‐diagrams, as well as the availability of methods to create specific structures in the director field, allows materials to be developed for data‐storage media and as optical compensation films for LC display applications.     

Liquid crystal biosensor for detecting ischemia modified albumin

Research on Chemical Intermediates - Ischemia modified albumin detection has great significance in early diagnosis and treatment of myocardial ischemia. In this study, anti-IMA was immobilized on...     

Liquid crystal compound anti-ice surface

In some cold areas/regions, ice accumulation is harmful to aircrafts, highways and power lines. To overcome this challenge, many researchers have focused on developing anti-icing surfaces. In this paper, liquid crystal compound Cholest-5-en-3-ol(3β)-4-(2-propenyloxy)benzoate was synthesised, and a liquid crystal surface (LC surface) is prepared by heating the liquid crystal compound to 250°C and then cooling it. We determined ice-phobic properties of LC surface using differential scanning calorimetry (DSC) and polarised optical microscope (POM). A phenomenon that the freezing of water droplet on the LC surface is delayed was found. Compared with the two measurement methods, we obtained similar result that water freezing temperature was delayed nearly by 8°C on average on the LC surface. A process of ice/frost formation is observed using POM. The results displayed that the glass wafer without LC was covered completely by ice/frost, whereas on the LC surface at the same temperature no ice/frost was formed. Characteristics of LC surface were observed by field emission scanning electron microscope (FESEM) and Fourier transform infrared (FT-IR) imaging system. We suggest that the reason behind anti-ice surface is related to surface molecules and this is an important factor which may have an effect on anti-icing property.     

Liquid crystal dimers and oligomers

A liquid crystal dimer is composed of molecules containing two mesogenic groups linked via a flexible spacer. Initial interest in these materials stemmed from their ability to act as model compounds for semi-flexible main chain liquid crystal polymers but are now of fundamental interest in their own right because their behaviour is significantly different to that of conventional low molar mass liquid crystals. Recently research has begun to focus also on higher monodisperse oligomers such as trimers and tetramers consisting of molecules containing either three or four mesogenic units, respectively, linked via flexible spacers. In this review the most recent developments in our understanding of structure–property relationships in liquid crystal dimers and higher oligomers is discussed.     

Liquid crystal chemistry and poetry

This paper comments on a recent article “Revolutionary poetry and liquid crystal chemistry: Herman Gorter, Ada Prins and the interface between literature and science” by Hub Zwart (Foundations of Chemistry, published online: 10 July 2020), in which the author explores the influence of the liquid crystal research of Ada Prins on the epic poem Pan written by her long-time lover Herman Gorter. The present paper reviews the basic science of liquid crystals and explains the connections between the work of Prins and its influence on the poem. Other examples of the use of “liquid crystal” as a literary device are identified from renaissance poetry, and the uses of the metaphor in these poems are analysed from a scientific perspective. From these examples it is suggested that creative concepts from poetry may contain elements of substance that appear in hitherto unrecognised scientific realities.

     

Optically compensated double-layer electrically controlled birefringence liquid crystal display with wide-viewing-angle cone

An electrically controlled birefringence liquid crystal display has a problem over narrow viewing angle. To solve this problem, the authors proposed a double-layer electrically controlled birefringence liquid crystal display with a wide-viewing-angle cone under an applied voltage. In this device, each liquid crystal layer compensates the variation of retardation as a function of viewing angle. However, the optical compensation occurs only when certain voltages are applied. The objective of this paper is to propose a novel film compensated double-layer electrically controlled birefringence liquid crystal display that has a wide cone of view in any state. This device is based on the concept of compensation of retardation.     

Liquid crystal effects on bacterial viability

The primary objective of this research was to test the hypothesis that lyotropic chromonic liquid crystals (neutral grey, red 14, blue 27, cromolyn) are not toxic to bacteria as compared with surfactant‐based lyotropic (CPCl and CsPFO) or thermotropic (5CB and E7) liquid crystals. Biocompatibility of most liquid crystals is currently unknown and is required for the development of systems interfacing liquid crystals and biological systems. Potential liquid crystal toxicity was evaluated by two methods. The first examined bacterial survival measured by bacterial growth over 24 hours, after exposure to various liquid crystals. The second toxicity method evaluated liquid crystal effects on bacterial membrane permeability using two fluorescent dyes. Three different types of bacteria were evaluated to assess bacterial structure differences with respect to liquid crystal toxicity. The results of this study indicate that lyotropic chromonic liquid crystals are not toxic to bacteria, whereas thermotropic and surfactant‐based lyotropic liquid crystals are toxic to one or more forms of bacteria. We conclude that lyotropic chromonic liquid crystals may be the preferred material in designing liquid crystal‐based systems that interact with biological systems, especially in the use of liquid crystal‐based biosensors.     

Liquid crystal effects on bacterial viability

The primary objective of this research was to test the hypothesis that lyotropic chromonic liquid crystals (neutral grey, red 14, blue 27, cromolyn) are not toxic to bacteria as compared with surfactant-based lyotropic (CPCl and CsPFO) or thermotropic (5CB and E7) liquid crystals. Biocompatibility of most liquid crystals is currently unknown and is required for the development of systems interfacing liquid crystals and biological systems. Potential liquid crystal toxicity was evaluated by two methods. The first examined bacterial survival measured by bacterial growth over 24 hours, after exposure to various liquid crystals. The second toxicity method evaluated liquid crystal effects on bacterial membrane permeability using two fluorescent dyes. Three different types of bacteria were evaluated to assess bacterial structure differences with respect to liquid crystal toxicity. The results of this study indicate that lyotropic chromonic liquid crystals are not toxic to bacteria, whereas thermotropic and surfactant-based lyotropic liquid crystals are toxic to one or more forms of bacteria. We conclude that lyotropic chromonic liquid crystals may be the preferred material in designing liquid crystal-based systems that interact with biological systems, especially in the use of liquid crystal-based biosensors.     

Liquid crystal parameters through image analysis

A technique which combines image analysis and polarising optical microscope (POM) is a useful tool for the physical investigation of discotic liquid crystals, such as hexabutoxytriphenylene and hexahexyloxytriphenylene. This investigation includes the phase transitions, optical properties and order parameter as a function of temperature. Textures of discotic liquid crystals are captured as a function of temperature using POM. These microscopic textures are analysed using MATLAB software to compute statistical parameters, Legendre moments, optical parameters and order parameters of discotic liquid crystal samples. Compared with other techniques in the literature, the proposed methodology is a reliable and very simple technique for the physical investigation of liquid crystals.     

Liquid crystal phases in confined geometries

ABSTRACT

The orientation control of liquid crystal (LC) phases is essential for fundamental studies as well as practical applications. Surface treatment and topographic confinement have emerged as two of the most effective tools to control ordering and orientation of various types of LC phases. This review is intended to give an overview of the LC phases controlled in confined geometries at micro- and nanometre scales, in which the orientation control methods and the effective analytical techniques will be covered. Finally, the review closes with the applications using such confined LC phases.     

Liquid crystal nanoparticles prepared as miniemulsions

Liquid crystal nanoparticles using the low molecular weight liquid crystal E7 are prepared by a miniemulsion approach with a droplet size between 180 and 630 nm. The sizes of liquid crystal droplets prepared in this work are one of the smallest sizes ever reported for liquid crystals, and they are considerably dependent on the type and amount of the surfactant used, as well as on the amount of hexadecane. Furthermore, the behavior of a liquid crystal confined to small droplets is investigated. DSC measurements reveal a large shift in the nematic-isotropic phase transition temperature. Further investigations on liquid crystal droplets are carried out using AFM measurements showing that these particles have an order of the liquid crystal molecules within the droplets. Light scattering measurements yield the temperature dependence of the anisotropy and the temporal stability of the droplets. An effect of the director fluctuations within the droplets on dynamic depolarized scattering was found.     

Liquid crystal polymers from swallow-tailed mesogens

Swallow-tailed compounds containing an acetylenic unit have been synthesized. Only those compounds with a three ring structure exhibited liquid-crystalline phases. The platinum catalysed addition of these monomers to compounds containing Si-H groups was used to synthesize polymeric materials. Only those polymers with the tetramethyldisiloxane unit showed mesophases. The synthesis, characterization, and phase behaviour are described.