Bowlic and Polar Liquid Crystal Polymers

Bowlic liquid crystals are made up of polar molecules. Both main-chain and side-chain bowlic polymers are possible. Exactly solvable discrete models describing the phases and conformations of these bowlic and other polar liquid crystal polymers are presented. For the ideal one-dimensional case the model is equivalent to the 1D Ising model. Susceptibility and other properties are calculated. Wave propagation and solitons in these polar polymers are discussed. Possible highly conducting and high T_c superconducting liquid crystal polymers are proposed.     

Liquid crystal–gold nanoparticle composites

Nanoparticles (NPs) have emerged as extremely promising materials to alter and improve the properties of liquid crystals (LCs) used, for example, in device applications. In this paper, we summarise recent work from our lab that aims to provide a fundamental understanding of structure–property and composition–property relationships governing LC–NP interactions, which may point to new directions for major improvements in the efficiency of LCs used in display applications. A variety of LC hosts (phases) doped with surface-functionalised gold NPs have been systematically studied ranging from one-dimensionally ordered nematic over two-dimensionally ordered smectic to three-dimensionally ordered columnar phases. Significant progress with respect to LC–NP interactions was made for NP-doped nematic phases. Here, the observation of an unusual texture for Au NP-doped nematic LCs, that is, the formation of birefringent stripe textures and the induction of homeotropic alignment of the nematic LC similar to chiral finger (or fingerprint) textures, provided the basis for numerous experimental studies using Au NPs with different core sizes and surface functionalities.     

Biphenyl-based liquid crystal precursors with alkanoate and hydroxyl group

We synthesized a series of 4′-hydroxy-[1,1′-biphenyl]-4-yl alkanoate with a potentially reactive functional hydroxyl group as a LC precursor, which facilitates reaction with other chemical groups to tailor biphenyl-based liquid crystals (LCs) for specific applications. Several liquid crystalline materials were also synthesized based on these LC precursors to show high probability to generate various potential LCs. With increasing chain length, the melting point decreased and R_f (retardation factor: migration distance of substance ÷ migration distance of solvent front) of the synthesized LC precursor increased. This LC precursor series provides a useful first synthesis step to design tunable biphenyl/ester-based LCs.     

Synthesis of four liquid crystals and study of alkyl chain effect on the nematic range for application in GC

Four liquid crystals (LCs) compounds which contain the 1,3,4-oxadiazole group were synthesized and characterized with spectroscopic techniques (IR, ¹H- and ¹³C NMR), their thermal properties were analyzed by the Differential Scanning Calorimetry (DSC) and the polarizing microscope (POM). A comparative study of the mesomorphic properties of these LCs and three other compounds which have already been used as a stationary phase in gas chromatography (GC) was carried out. These compounds have the same main nucleus. LCs V1, LC1, LC2 and LC3 gave a nematic (N) phase to the heating, LCs V2 and V3 recorded smectic A (SmA) and N phases. However, the range (N) has disappeared in V4.     

Active and Passive LC Based Polarization Elements

Passive and active polarization elements were created by surface and bulk photo-alignment of LCs, reactive LCs, photo-sensitive LCP and photo-curable monomer/LC composites. The use of different photo­sensitive liquid crystalline materials for the development of highly anisotropic elements with high spatial resolution and stability or, alternatively, fast switch ability will be discussed. Photo-active and voltage tunable polarization and diffraction elements are presented. For active micro-optic application a photo-addressed patterned retarder was created. Electrically switchable diffraction gratings were generated by interference exposure of photo-curable LC composites at room temperature characterized by droplet free morphology. These polarization sensitive diffraction elements are characterized be excellent optical properties and low switching times.     

The Role of Host Molecules in the Crystalline Inclusion Compounds: Hexamethylenebis(trimethylammonium) dications as guest species

ABSTRACT

This report demonstrates hybrid homeotropic alignment of liquid crystals (LCs) using a self-assembled molecular (SAM) layer. 4-(4-Hep-tylphenyl)benzoic acid forms a SAM layer through hydrogen bonding with indium-tin oxide (ITO) substrate, and the LCs were aligned vertically without a polyimide (PI) layer on one side of substrate. The proposed hybrid structure featured a more stable homeotropic alignment than the LC device (LCD) with only half of a PI layer, and showed electro-optical characteristics similar to conventional LCDs with full PI layers. The SAM layer showed stable alignment and fast response in the LC cell by a simple doping method.     

Synthesis and powder X-ray diffraction of new Schiff-base liquid crystal

Liquid crystals (LCs) are soft materials that combine the fluidity of disordered liquids and the long-range orientational or positional order of crystalline solids, along one or two directions of space. A search for better stationary phases, including highly selective ones, is an important trend in chromatography development. Among the stationary phases under investigation are LC stationary phases that have been recently generated much interest. A variety of isomeric molecules were separated with high accuracy. Successfully, X-ray scattering is widely used to investigate and characterise the microscopic structure of most LCs. In this paper, a new liquid crystalline material that can be used potentially as stationary phase in gas chromatography was synthesised and characterised by means of nuclear magnetic resonance (NMR), infrared (IR) spectra, elemental analysis and X-ray diffraction.     

λ-Shaped mesogens based on chalconyl ester core having variable side chain: Synthesis and characterisation

In present study, we have synthesized two newly chalconyl-ester core LCs having variable side chain and fixed disubstituted butoxy group at another terminal end. All this compounds were well characterized by elemental analysis, FT-IR, ¹H NMR. The mesomorphic properties of these compounds were observed by optical polarized light microscopy (POM) and also confirmed by using differential scanning calorimetry (DSC) and X-ray diffraction pattern (XRD). Detailed XRD investigation endorses the presence of the nematic phase in higher angle region and SmC phase in lower angle region. In addition, it is found that all the prepared materials display enantiotropic LCs phases except first four members in series-1 and first member in series-2. Thermal stability of SmC and nematic phase of series-1 is higher as compare to series-2. To get more insights, the DFT based HOMO, LUMO studies are carried out which supports intramolecular charge transfer interactions and stability in this class of mesogens.     

Molecular orientation and dielectric anisotropy properties of 4-cyano-4′-n-heptylbiphenyl-TiO2 liquid crystal composite

The molecular orientation and the dielectric anisotropy of the nematic liquid crystal (LC) 4-cyano-4′-n-heptylbiphenyl (7CB) and of TiO₂-doped 7CB have been investigated. The dielectric properties of the LCs exhibit a relaxation peak that shifts to lower frequencies with increasing voltages. The relaxation frequencies of 7CB and 7CB/TiO₂ liquid crystals were calculated and found to decrease as the bias voltage increases. This is attributed to molecular reorientation. The dielectric anisotropy of the LCs changes from the positive type to negative type and the static electric permittivity and dielectric anisotropy values were found to be lower for the 7CB/TiO₂ system.     

Specific features of electromechanical conversion in various liquid crystalline phases

Electromechanical effect in various liquid crystalline phases—nematic, smectic A, and smectic C—is studied. It is shown that a liquid crystal (LC) sample in the nematic phase does not differ from an electromechanical converter containing an isotropic dielectric and exhibits no features characteristic of LCs at electromechanical conversion. A phenomenon similar to the piezoelectric effect may occur in ferroelectric LCs due to their biaxiality.     

Acoustic Waves and Supramolecular Structures in Liquid Crystals

Crystallography Reports - The achievements in the study of the supramolecular structures arising in liquid crystals (LCs) under acoustic waves, which was started by the work of Professor А.P....     

Modal liquid crystal lenses

Abstract

When considering the possibility of commercially viable applications for discotic liquid crystals it is worth noting that in the case of calamitic liquid crystals some 80 to 90 years elapsed between their discovery in 1888 and their first application in displays. Since discotic mesophases were only discovered in 1977 [ll, it is not surprising that the first applications are yet to be realized.     

Electro-Optical Properties in Polymer-Stabilized Blue Phase of n-OCB Homologue Chiral Nematic Liquid Crystal Mixtures

In this study, the chemical structures and physical property dependencies of the electro-optical properties were investigated in polymer-stabilized blue phase (BP) using the four kinds of 4-n-alkyloxy-4′-cyanobiphenyl (n-OCB) homologue chiral nematic LCs. It was confirmed that the optical response time and Kerr coefficient in polymer-stabilized BP was varied with the molecular parity as determined by the alkyl chain length of the n-OCB homologue chiral nematic LC mixtures.     

Imaging of bacteria using chromonic liquid crystals

We explored adsorption isotherms of Escherichia coli (E.coli) and Salmonella over the poly-L-lysine (PLL) coated glass surface. The detection of the adsorbed bacteria was explored using 14 wt% di-sodium-chromo-glycate (DSCG) solution in water and 5CB. The textures of the optical cells made up of LCs and the adsorbed bacteria over PLL-coated glass substrate were obtained by using a polarized microscope in the transmission mode under crossed polars. We found that DSCG solution exhibits a dark spot on the adsorbed E.coli and Salmonella. In contrast to DSCG solution, 5CB did not show any dark spot.     

All‐aromatic liquid crystal thermosets: New high‐performance materials for structural applications

Over the past two decades, there has been an increasing interest in all‐aromatic crosslinked liquid crystal (LC) systems for structural, electronics and coatings applications. In this paper we will give a brief overview of our work on oligomeric liquid crystals end‐capped with phenylethynyl reactive end‐groups. All reactive oligomers were synthesized using standard melt‐condensation techniques and the final products form homogeneous nematic melts over a wide temperature range (220–400?°C). The reactive LC oligomers could be cured at elevated temperatures (310–400?°C) to form true rigid‐rod nematic networks. As will be demonstrated, this oligomer approach allows us to design all‐aromatic nematic networks with a variety of favorable physical, mechanical and processing characteristics. Depending on the backbone chemistry, and end‐group concentration, we can access liquid crystal thermosets with Tg’s between 110–280?°C and storage moduli (E') of 2‐5 GPa. The oligomeric nature of our reactive LCs results in excellent melt processing characteristics (|η*| ? 1?Pa.s at 100?rad.s^?1) and allows for the processing of complex structures such as fiber‐reinforced composites. Based on our current results we are convinced that reactive all‐aromatic liquid crystals can be interesting alternatives over existing high‐performance polymers such as polyarylether ketones (PEEK and PEKK) polyphenylenesulfide (PPS) and polyetherimides (PEIs).     

Acousto-optics of liquid crystals: Yesterday,today, and tomorrow

The most important results of the recent theoretical and experimental studies in the field of acousto-optics of liquid crystals (LCs) in research lines initiated by the pioneering studies of Professor A.P. Kapustin at the Institute of Crystallography of the Russian Academy of Sciences and carried out at the Acoustic Institute of the Russian Academy of Sciences are generalized and analyzed. These lines include the study of the nature of acoustically induced supramolecular structures in nematic liquid crystals (NLCs) and cholesteric liquid crystals (CLCs) and the development of physical bases of practical LC acousto-optics, related to the detection of acoustic signals.     

British Liquid Crystal Society Annual Conference, 1991 Reading,UK

This report describes the physical principles underlying the switching of nematic liquid crystals (LCs) by an electric field in the plane of the substrate. The results have contributed to development of an IPS-mode-TFT-LCD, which is now commercially available and one of the most popular TFT-LCDs with ultra-wide viewing angle characteristics. The report summarizes work in the Glenn Brown prize winning PhD thesis, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo, 152-8551 Japan.     

Photo-Controllable Rotation of Cholesteric Double-Twist Cylinders

Abstract

We fabricated aggregates of cholesteric cylinders coexisting with the isotropic phase and investigated their dynamics under a temperature gradient. Each constituent cylinder possessed the double-twist (DT) structure, and when a heat flux was applied, the whole aggregates rotated as a rigid-body without changing the DT orientation. The angular velocity was proportional to the heat flux and the rotational direction was determined by the molecular chirality and the flux direction. The result suggests that the rigid-body rotation was driven by the thermomechanical cross-correlation in chiral LCs. We also succeeded in switching the rotation by changing the illumination onto the sample.     

VIIIth International Topical Meeting on Optics of Liquid Crystals (OLC'99)

Abstract

Over the past fifteen years the International Topical Conference on Optics of Liquid Crystals (OLC) has provided a stimulating and interdisciplinary forum for the presentation of the best new work in the field of liquid crystals and related materials. The VIIIth International Topical Meeting on Optics of Liquid Crystals was held at the hotel Wyndham Palmas del Mar Resort and Villas in Humacao, Puerto Rico 27 September–1 October 1999. Eighty-five scientists from 17 different countries around the globe (Asia, Europe, North and South America) came to Puerto Rico to present their scientific work and to discuss all the modern aspects of Optics of Liquid Crystals. As a result 21 invited talks, 32 contributed oral presentations and 51 posters were presented. New results at the forefront of research in the optics of liquid crystals were presnted by leading experts in the field. Invited talks given by N. Clark (USA), F. Derrien (France), B. Jerome (Netherlands), R. Kamien (USA), I.-C. Khoo (USA), L. Komitov, (Sweden), T. Lubensky (USA), S. Marino (Japan), I. Musevich (Slovenia), Y. Shen (USA), K. Singer (USA), G. Sinha (USA), H. Skupin (Germany), R. Stannarius (Germany), R. L. Sutherland (USA), B. Taheri (USA), Y. Tabe (Japan), C. Umeton (Italy), D. Weitz (USA), S. Zilker (Germany), and S. Zumer (Slovenia) covered different important topics such as chiral interactions, surface vibrational spectroscopy, time resolved FTIR, holograms in PDLS, lasing in liquid crystals, quadrupolar molecular nonlinear optics, organic photorefractive systems, optical solitons, different aspects of behaviour, properties and applications of chiral smectic liquid crystals, photo-initiated reorientational dynamics, electro-optic effects in LC films, wave generation in two-dimensional LCs and others.     

Studies on dielectric oxide materials containing niobium and tantalum

There are now many advanced materials, which have been discovered with unique dielectric properties having been designed with an eye to specific applications. One of the areas of current interest to the material scientist and solid state chemist is to find new materials suitable for use as dielectric resonators in microwave applications and to tailor its properties. Among them the ABO₃ type perovskite oxides and the AB₂O₆ (columbite/trirutile) type of oxides where B is either Nb or Ta have been pursued vigorously in the recent past. There is a continuous interest to optimise the dielectric properties by suitable doping at the A-site, B-site and the B′ site of the perovskite related A(B_1/3B′_2/3O₃) structure. In addition there is an increasing demand to discover alternate routes of synthesis, which would afford these oxides at much lower temperatures. We discuss our recent results on some of the above materials.