Narrow Results

An unidentified mesophase D_x of bis(octakisdodecyloxyphthalocyaninato)lutetium(III) reported by us in 1997 was reinvestigated by temperature-dependent X-ray diffraction and temperature-dependent electronic spectra of the thin film. The D_x phase was thus established as a novel type of D_ro (P2₁/a) mesophase in which two different stacking distances h_t and h_f exist. It was also revealed that the step-up increase of electroconductivity is attributable to the step-up enlargement of π-π overlap of Pc macrocycles according to the phase transitions crystal → D_ro (P2₁/a) → D_ho. This is strongly related to delocalization of the radical electron.

Density functional (DF) theory is used to study confined two-dimensional molecular fluids. The approximate DF used here is based upon a functional Taylor series expansion of the excess grand potential about the density of a uniform molecular liquid. This formalism is applied to obtain the density profiles of the hard-ellipse fluid confined between two parallel hard walls. The required direct correlation function is obtained using Percus–Yevick and hypernetted chain approximations for low- and high-number density, respectively. Both the restricted orientation model and the extension of this model are used. Generally, we obtained that the number density of the hard ellipses with the major axes parallel to the wall is larger near the walls than the other directions. To check the results, we show that for isotropic hard-ellipse fluids the average number density in the middle of the wall is almost equal to the bulk density and as we expect the average number density of the ellipses at the wall is nearly equal to the amount of the reduced pressure, βP. We also perform Monte Carlo simulation and find reasonable agreement with our results.

The anisotropic intermolecular forces responsible for the orientational ordering in liquid crystals are probed by comparing Monte Carlo (MC) simulations with experimental nuclear magnetic resonance (NMR) results for solutes in nematic liquid crystals. In a special liquid crystal mixture where all long-range interactions are assumed to be minimized, the models for short-range interactions which best fit NMR experimental solute order parameters also best fit solute order parameters from MC simulations of hard ellipsoids. This is taken as an indication that in this special mixture the intermolecular potential is dominated by short-range forces. However, for liquid crystals where long-range interactions are important, simulations of hard ellipsoids with point quadrupoles cannot reproduce even the gross effects observed with experimental NMR data.

Atomistic molecular dynamics simulations have been used, apparently for the first time, to investigate the anchoring behavior of a liquid crystal at the interface with an amorphous polymer. The simulations studied a system consisting of the nematogen 5CB at the surface of amorphous polyethylene, and used the simple Dreiding II force field. The simulations indicate a preference for nonplanar anchoring. Two distinct microscopic paths have been identified by which the liquid crystal changes orientation at the surface. In one case, only one or a few of the 5CB molecules are rotating at any particular time. In the other case, a substantial fraction of the molecules rotate simultaneously.

Inspired by condensed matter physics we propose a new, asymmetric, family of cosmic strings. These strings present a conical curvature singularity plus a surrounding region of alternating positive and negative curvature as the azimuthal angle is changed. Their sources include both positive and negative mass density regions.

In this work, the effect of thin films on the orientational, thermotropic and optical properties and on the peculiarities of the nematic–isotropic liquid phase transition has been carried out.

The planar textures of MBBA+EBBA eutectic mixture on the surfaces coated with Al₂O₃ and ZrO₂ thin films have been obtained. The optical and thermodynamical parameters of the obtained, oriented textures have been determined. The effect of thin films on the temperature width of heterophase region and on the nematic–isotropic liquid phase transition temperatures has been investigated. The shift of the phase transition temperatures and the change of the temperature width of the heterophase region have been revealed.

For the analysis of peculiarities of the nematic–isotropic liquid phase transition and the heterophase regions of this transition, the mean field theory has been used.

In this work, effect of thickness of the liquid crystalline layer on the morphologic, thermotropic and thermodynamical properties of the nematic–isotropic liquid and isotropic liquid–nematic phase transitions in Shiff based liquid crystals has been investigated.

The shift of temperatures of the nematic–isotropic liquid and isotropic liquid–nematic phase transitions to the lower temperatures and the widening of linear and temperature widths of the heterophase regions of these phase transitions by the increase in the thickness of liquid crystalline layer have been found.

The effect of thickness of liquid crystalline layer on morphologic, thermotropic and thermodynamical properties of liquid crystals under investigations is connected with change of interaction energy between liquid crystalline molecules and reference surfaces.

A new series of thermotropic polyurethanes containing biphenyl units was synthesized by polyaddition reaction of diisocyanates such as 2,6-tolylene diisocyanate, 2,5-tolylene diisocyanate, 2,4-tolylene diisocyanate, and 1,4-phenylene diisocyanate, with 4,4□-bis(9-hydroxynonoxy)biphenyl (BP9). Structures of the monomer and the corresponding polymers were identified using FT-IR and ¹H NMR spectroscopic methods. BP9 exhibited a smectic type mesophase, however, nematic phase was found for all synthesized liquid crystalline polyurethanes except for 1,4-phenylene diisocyanate/BP9 based polyurethane. Their phase transition temperatures and thermal stability were investigated by differential scanning calorimetry (DSC), optical polarizing microscopy, and X-ray scattering. The infrared study indicated that the hydrogen bonding among urethane linkages attributed to the mesomorphism. Thermal gravimetric analysis (TGA) of synthesized polyurethanes showed that no weight loss of the polymers observed up to 280°C.

We describe two different systems, the first one based on a magnetorheological elastomer and the second one on magnetic particles inside a liquid crystal. In both system we manage to have chain structures with particles that are not in contact. The effect of the gap between particles on the viscoelastic properties are studied. We show in particular how in magnetorheological elastomers, the energy dissipation is closely related to the creation and the motion of cavities in the gap between the particles. In liquid crystal chaining of particles can occur without applying a magnetic field. This happens if the anchoring of liquid crystal on the surface of the particles is homeotropic. We demonstrate how the combination of elastic defects and of a magnetic field allow to obtain microscopic springs made of a pair of magnetic spheres.

Depending on the properties of photonic band gap materials, a novel photonic crystal fiber (PCF), formed by lithium niobate and liquid crystal, has been studied numerically. Dispersion relationships and transmission spectra of the PCF are calculated by methods of the full-vector modal and the finite difference time domain, respectively. The parameter-dependent dispersion and transmission of the PCF have been found. It is shown that the design of the novel photonic crystal fiber could be supported by the theoretical analysis in the paper.

Superfluidity in fermionic systems originates from pairing of fermions, and Bose condensation of these Cooper pairs. The Cooper pairs are usually made of fermions of different species; thus the most favorable situation for pairing and superfluidity is when the two species of fermions that form pairs have the same density. This paper studies the possible superfluid states when the two pairing species have different densities, and show that the resultant states have remarkable similarities to the phases of liquid crystals. This enables us to provide a unified description of the possible pairing phases and understand the phase transitions among them.

In the present work, we report the blue phase (BP) in a binary mixture of cholesteryl nonanoate (CN) and N-(4-ethoxybenzylidene)-4-butylaniline (EBBA). The mixture exhibits BP over a temperature range of 2.3 K at optimum composition (50:50) of liquid crystals (LCs). The effect of silica nanoparticles (SNPs) doping on thermal stability of BPs has also been demonstrated and nearly 6 K wide BP temperature range was achieved at 0.5 wt.% of SNPs. A porous type texture was also observed during the BP formation process in the doped samples.

The temperature and pressure dependence of the static dielectric permittivity in the isotropic phase of the isotropic to cholesteric phase transition is calculated using Landau–de Gennes’s fluctuation theory, allowing spatial variation of the orientational order parameter. A comparison is made with experimental data available in the isotropic phase of the isotropic to cholesteric phase transition.

This paper reports the tunable transmission properties of asymmetric one-dimensional periodic structure (1DPS) composed of SiO₂ and anisotropic metamaterial (AMM) layers with defect of liquid crystal (LC) sandwiched by two SiO₂ layers, i.e., (SiO${}_2|$AMM)${}^3|$SiO${}_2|$LC$|$SiO${}_2|$(SiO${}_2|$AMM)³ using the transfer matrix method (TMM). We have studied the optical properties of the periodic structure (SiO${}_2|$AMM)³$|$SiO${}_2|$LC$|$SiO${}_2|$(SiO${}_2|$AMM)³ with a different incident angle of the electromagnetic wave for particular director angle of LC molecules. The tunability of the transmission property of the considered 1DPS shows that the transmittance depends upon the orientation of LC molecules. Such an asymmetric periodic structure (1DPS) composed of SiO₂ and AMM with a defect of LC sandwiched by two SiO₂ layers, (SiO₂$|$AMM)${}^3|$SiO${}_2|$LC$|$SiO${}_2|$(SiO${}_2|$AMM)³, may be used as a tunable optical filter and bi-stable device.

Liquid crystal (LC) research in China started during the Cultural Revolution years in the late 1960s. It was motivated partly by the potential application in liquid-crystal display (LCD) digital television (TV) and movies, deemed good for the government’s political propaganda agenda. The large-screen LCD TV/ movie project was initiated and done at the Tsinghua University, Beijing, which became successful in 1976 with prototypes built. Although it never reached the commercial stage, the research achievement was world-leading then. Here, the history of this project and other LC research at the Tsinghua University in the 1970s and 1980s are described for the first time, with appropriate historical backgrounds provided. Tsinghua’s significant contributions in basic LC research and a description of the founding and workings of the Chinese Liquid Crystal Society are also included. Finally, lessons drawn from this piece of science history are presented.

In this work, the effect of thin films on the thermotropic and thermo-optical properties and peculiarities of the phase transitions between the smectic A and isotropic liquid have been investigated. Peculiarities of the heterophase regions of the straight smectic A-isotropic liquid and reverse isotropic liquid-smectic A phase transitions have been studied.

Change of morphologic properties of the heterophase regions, shift of the phase transition temperatures and the change of temperature widths of these heterophase regions under thin film influence have been observed.

We examined the electrical and optical properties of a new material containing polymer–clay nano-composite dispersed in a nematic liquid. The clay (Cloisite-type) was modified by copolymerization of maleic anhydride and divinyl benzene, using azobisisobutytironitrile as the initiator. The final polymer–clay nano-composite has an intercalated structure according to XRD patterns. We measured the thermally stimulated depolarization currents and determined the activation energies. Simultaneously we measured the optical transmission and we studied the influence of the previously applied polarizing electric fields.

We investigate energetically favorable configurations of point disclinations in nematic films having a bump geometry. Gradual expansion in the bump width Δ gives rise to a sudden shift in the stable position of the disclinations from the top to the skirt of the bump. The positional shift observed across a threshold Δ^th obeys a power law function of |Δ - Δ^th|, indicating a new class of continuous phase transition that governs the defect configuration in curved nematic films.

Photonic crystals (PCs) with infiltrating liquid crystals (LCs) have many potential applications because of their ability to continuously modulate the band-gaps. Using the plane-wave expansion method (PWM), we simulate the band-gap distribution of 2D honeycomb lattice PC with different pillar structures (circle, hexagonal and square pillar) and with different filling ratios, considering both when the LC is used as filling pillar material and semiconductors (Si, Ge) are used in the substrate, and when the semiconductors (Si, Ge) are pillar material and the LC is the substrate. Results show that unlike LC-based triangle lattice PC, optimized honeycomb lattice PC has the ability to generate absolute photonic band-gaps for fabricating optical switches. We provide optimization parameters for LC infiltrating honeycomb lattice PC structure based on simulation results and analysis.

The shear-sensitive liquid crystal coating (SSLCC) technique is investigated in the high-speed jet flow of a micro-wind-tunnel. An approach to measure surface shear stress vector distribution using the SSLCC technique is established, where six synchronous cameras are used to record the coating color at different circumferential view angles. Spatial wall shear stress vector distributions on the test surface are obtained at different velocities. The results are encouraging and demonstrate the great potential of the SSLCC technique in high-speed wind-tunnel measurement.