Study of a new homologous series of liquid crystals: Isopropyl-p-(p/-n-alkoxy cinnamoyloxy) cinnamates

A new homologous series: isopropyl-p-[p^/-n-alkoxy cinnamoyloxy] cinnamates was synthesized and studied with a view to understanding and establishing the relation between liquid crystal property and molecular structure. Twelve homologues were synthesized. Methyl to butyl homologues are not liquid crystals, while pentyl, hexyl, heptyl, octyl, decyl, dodecyl, tetradecyl, and hexadecyl derivatives are enantiotropic liquid crystal in nature with nematogenic character. Smectogenic character is totally absent. A phase diagram is obtained by plotting a graph of transition temperatures versus number of carbon atoms is n-alkyl chain of left n-alkoxy terminal end group. Solid-isotropic or solid-nematic transition curve rises steeply from methyl to propyl derivatives and falls to pentyl homologue through butyl homologue, and follows a zigzag path of rising and falling values as the series is ascended. Nematic–isotropic transition curve shows descending tendency as series is ascended in a normal manner with exhibition of odd-even effect. Smectic mesophase does not appear even in the monotropic condition. Phase transition temperatures are determined by hot stage polarizing microscope. Analytical data support the structure of molecules. Texture of nematic mesophase is of threaded type. Mesomorphic properties are compared with structurally similar homologous series.     

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.     

Temperature dependence of the density of some liquid crystals in the alkyl cyanobiphenyl series

Experimental results for the temperature dependence of the density of propyl – cyanobiphenyl (3CB), butyl – cyanobiphenyl (4CB) and hexyl – cyanobiphenyl (6CB) are presented. The results are compared with previous results for temperature dependence of other members of the alkyl cyanobiphenyl series (nCB). The deviation of the density from linear temperature dependence is discussed in terms of the recently discovered corresponding rule for nematic liquid crystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Direct structural observation of the alignment and elongation in lyotropic chromonic liquid crystals under shear flow

The structural characterization of the orientation and elongation under shear flow in Lyotropic Chromonic Liquid Crystals (LCLCs) molecules, Sunset Yellow FCF (SSY), was performed by in situ rheological small/wide angle X-ray scattering (Rheo-SAXS/WAXS). The X-ray measurement results clearly demonstrated that the stacked aggregates were oriented and elongated to the shear direction under shear flow. Further shear rate increase caused the enhancement in the orientation and elongation with the inter-aggregate distance constant, and then the structural change decreased implying the onset of the orientation saturation at high shear rates.     

Fabrication of a fast-switching liquid crystal device using reactive self-assembled polyimide alignment layer

ABSTRACT

We proposed a new vertical alignment method for simultaneously improving the alignment force and electro-optical properties. The key point of the new method is the self-assembly of the reactive monomer via hydrogen bonding with the polyimide alignment layer and the formation of pre-tilt using the reactive monomer on an alignment layer. Through the self-assembly of the reactive monomer and the generation of the pre-tilt, it is possible to obtain a higher alignment force and a fast response time. As a result, through a simple additional step, we can fabricate a fast-switching liquid crystal device using a reactive self-assembled alignment layer.     

Blue phase liquid crystals stabilized by graphene oxide modified with aminoalkyl group

In the present work, the graphene oxide/blue phase liquid crystal composites and long aminoalkyl chains functionalized graphene/blue phase liquid crystal composites were prepared by doping the additives into a blue phase exhibiting liquid crystal host. It is found that the blue phase temperature range could be widened by dispersing a small amount of functionalized graphene. It suggests that anisotropic two-dimensional flake nanoparticles may be of great usefulness for stabilizing blue phases.     

Evolution of the growth interface in liquid phase diffusion growth of bulk SiGe single crystals

The article presents a study for the evolution of growth interface in crystal growth by Liquid Phase Diffusion (LPD). Specific LPD experiments were designed to grow compositionally graded, germanium‐rich Si_xGe_1‐x single crystals of 25 mm in diameter with various thicknesses. Measured interface shapes show the evolution of the growth interface. Silicon compositions were measured by the Energy Dispersive X‐ray analysis (EDX) in the growth and radial directions. The study shows the feasibility of extracting the desired seeds of uniform composition from LPD grown crystals, for subsequent use in other epitaxial growth processes. © 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

Synthesis,characterization and structural phase transition studies in trismethylammonium pentachloro barium dihydrate single crystals

Single crystals of trismethylammonium pentachlorobarium dihydrate were grown by slow evaporation method at ambient temperature. The crystals were characterized through powder XRD, thermal, infrared and NMR spectral studies. While the powder XRD pattern confirms the crystallinity of the title compound, the TG indicates the removal of occluded and adsorbed water molecules from the crystal when it is heated up to 86 °C. The TG study also confirms the presence of two water molecules of crystallization which are dehydrated on heating the crystal between 107 °C and 150 °C. The anhydrous compound is found to be stable at least up to 900 °C. The DTA curve shows two endothermic dips corresponding to weight losses observed in the TG curve. The low temperature DSC study shows thermal anomalies during the heating and cooling cycles indicating both first and second order phase transitions. The high temperature DSC shows the stepwise dehydration indicating phase transitions at temperatures 103 °C and 145 °C. The characteristic vibrational frequencies due to methylammonium ion, BaCl₅ and other groups are assigned based on FTIR spectra. The NMR spectrum confirms the presence of protons of the methyl group and water of crystallization in the compound. In this paper, an attempt is also made to understand the effect of methyl group on the phase transitions of the compound in comparison with a closely related compound, trisammoniumpentachloro barium dihydrate. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phase transitions from density and order parameter from polarisabilities in symmetric dimeric liquid crystals

As a part of our systematic studies on liquid crystal dimers, we present in this article the nature of phase transitions across isotropic–nematic and nematic–smectic-A exhibited by DLCs, α,ω-bis-(4-n-alkylaniline benzylidene-4?-oxy) alkanes. Further, the orientational order parameter in the nematic phase of these DLCs are estimated from the molecular polarisabilities calculated using the experimental refractive indices and density results. The molecular polarisabilities α_e and α_o are obtained for the compounds using the above results for both Vuks and Neugebauer local field models applicable to nematic liquid crystal. α_e and α_o calculated in this way are used to obtain Δα. The polarisability anisotropy in the perfect order (absolute K) is calculated semi-empirically using the δ-function model developed by Lippincott et al. and molecular vibration method. The values of polarisability anisotropy for both local electric field models differ significantly. No criterion is known to decide which value is correct. To avoid the determination of uncertain α and Δα values considering different local field models, a simple procedure developed by Kuczynski et al. was used for evaluation of S, based solely on birefringence δn = (n_e-n_o) and this value of S is compared with those obtained from field models.     

Temperature dependence of lattice parameters of SBN single crystals in the vicinity of their structural phase transitions

Changes of lattice parameters of Sr_xBa_1‒xNb₂O₆ (0.35 < x < 0.72) solid solution single crystals were measured as a function of temperature. The X‐ray Bond’ method was used to carry out very precise measurements of the lattice parameters. Fine correlations between values of the lattice parameter and the Sr concentration in the solid solution of Sr_xBa_1‒xNb₂O₆ single crystals are found. A conventional analysis of lattice parameter data in terms of spontaneous strain and strain/order parameter coupling shows that a normal structural phase transition does occur. While the ferroelectric system (SBN26) displays a nearly tricritical behavior, β ≈ 0.20, the relaxor one (SBN61) complies with the two‐dimensional Ising‐model‐like criticality, β ≈ 0.17.     

Playing with nanosegregation in discotic crown ethers: from molecular design to OFETs,nanofibers and luminescent materials

Discotic liquid crystals are promising materials for electronic device applications. Combining extended π-systems with crown ethers may further open access to functional supramolecular hybrid materials. In the present publication, we briefly summarise recent literature developments and focus in a second part on our work in the field of discotic crown ethers. The crown ether derivatives are conveniently accessible by convergent syntheses which allow a high degree of variation with respect to side chains, mesogenic unit, size and symmetry of the crown core, metal complexation and counterion. This set of compounds provides a basis for systematic structure–property relationship investigations. Numerous experimental studies identified factors being crucial for mesophase stabilisation and geometry and furthermore led to novel room-temperature crown ether mesogens. The latter were obtained by congestion of the mesogenic units and even introduction of peripheral δ-methyl branched side chains. The formation of molybdenum clustomesogens and their application as luminescent hybrid materials is also described.     

Modeling analysis of liquid encapsulated Czochralski growth of GaAs and InP crystals

The results of three‐dimensional unsteady modeling of melt turbulent convection with prediction of the crystallization front geometry in liquid encapsulated Czochralski growth of InP bulk crystals and vapor pressure controlled Czochralski growth of GaAs bulk crystals are presented. The three‐dimensional model is combined with axisymmetric calculations of heat and mass transfer in the entire furnace. A comprehensive numerical analysis using various two‐dimensional steady and three‐dimensional unsteady models is also performed to explore their possibilities in predicting the melt/crystal interface geometry. The results obtained with different numerical approaches are analyzed and compared with available experimental data. It has been found that three‐dimensional unsteady consideration of heat and mass transfer in the crystallization zone provides a good reproduction of the solidification front geometry for both GaAs and InP crystal growth.     

Synthesis of liquid crystals based on hydrogen-bonding of 4-(Octyloxy)benzoic acid with 4-alkylbenzoic acids

A molecular recognition process has been used to form new mesogenic molecular structures, where intermolecular hydrogen bonding occurs between 4-(octyloxy)benzoic acid (8BAO) and four 4-alkylbenzoic acids (nBAs, n = 2, 5, 6, 7). The synthesis of these complexes has been attained by resorting to mechanochemistry. The resulting materials have been characterized by polarizing optical thermal microscopy, differential scanning calorimetry, vibrational spectroscopy, X-ray powder diffraction, and ¹H NMR relaxometry. All the elements of the series show the formation of a mesophase. For one of the complexes, its electro-optical properties have also been assessed, resulting comparable to those of other widely used liquid crystals.     

Nuclear magnetic resonance: a powerful tool to study liquid crystals

Nuclear magnetic resonance (NMR) is a spectroscopic technique widely used to investigate materials and soft matter in particular. In this brief review, the main uses of NMR techniques to investigate different aspects of liquid crystals, such as the orientational and dynamic properties, the supramolecular structure and average molecular conformations, are described. In the second part of the paper, the case study of a ‘de Vries’ liquid crystal is reported and the main results obtained by combining different NMR techniques are discussed.     

Effect of reduction/oxidation treatment on blue photorefraction in In:Fe:Cu:LiNbO3 crystals

In:Fe:Cu:LiNbO₃ crystals with reduced/oxidized treatments were prepared by the Czochralski method. The defect structure was analyzed by the UV‐Visible absorption spectra. The blue photorefractive properties, such as the refractive index change, response time, recording sensitivity, dynamic range as well as two‐wave coupling gain coefficient, were also investigated at 488 nm wavelength using the two‐wave coupling experiment. Comparing the as‐grown and oxidized In:Fe:Cu:LiNbO₃ crystals, the reduced sample has the highest recording sensitivity and largest dynamic range. Meanwhile, the high diffraction efficiency is still maintained. Experimental results definitely show that reduction treatment is an effective method to improve the blue photorefractive performance of In:Fe:Cu:LiNbO₃ crystals. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Liquid Crystal Display Research in Japan

The technology development of liquid crystal display started having a remarkable influence on the technology innovation of up-to-date electronic calculator. While a digital display using liquid crystal display has been developed in its earlier stage as the segment type which sets a limit of display to numeric and certain symbols, it is also spent an effort to develop the X - Y matrix type which can display alpha-numeric and moreover kana characters. As a practical application of the X - Y matrix type liquid crystal display, an alpha-numeric type scientific electronic calculator and electronic translator will be reported.

Further, the present status of liquid crystal display applications and trend of R&D in other consumer and industrial electronic industries in Japan will be reported. Finally, activities in the Japanese academic circles will be presented.     

Study on transmission characteristics in photonic crystals with negative effective index of refraction

Transmission spectra from equivalent negative refractive photonic crystals (PCs) composed of a triangular array of air cylinders in a GaAs matrix are studied by finite‐difference time‐domain method in the paper. Mechanism of wave resonance is probed and propagation of optical waves in the PCs is described in terms of effective refraction index and Bloch waves. Our numerical results show that probability of spontaneous radiation would be enhanced extremely under the influence of Bloch resonance waves, stimulated emission and photon tunnel effect, resulting in the optical waves localized greatly in the PCs at particular frequencies. In addition, we find out that the position of transmission peaks, with values far greater than unit, can be controlled by tuning the central frequency of waveguide source. It means that photon current in the PCs also can be controlled to optimize transmission properties of PCs, so as to meet the requirements of novel optical devices based on PCs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)