Liquid Crystal Region Research Articles

Modeling the reflection from cholesteric liquid crystals using modal analysis and mode matching

The reflection and transmission spectra from right-handed cholesteric liquid crystals are computed in the visible region for a linearly, circularly, or elliptically polarized incident plane wave at oblique incidence. The liquid crystal cell is sandwiched between dielectric layers of certain thickness and refractive index. The underlined formulation is based on a modal analysis of the governing field expressions in the dielectric and liquid-crystal regions. A representative matrix system is obtained after enforcing the continuity of the tangential electric and magnetic fields at the material interfaces. Solution of the governing matrix system results in the reflectance and transmittance for a given wavelength. Numerical results for both normal and oblique incidence were obtained and compared with data published in the literature. The underlined formulation is effective, accurate, robust, versatile, and computationally efficient.

Calculation of spectral shifts in UV–visible region and photo stability of thermotropic liquid crystals: Solvent and alkyl chain length effects

The calculation of spectral shifts in UV–Visible region, and photo stability of thermotropic liquid crystals p-n-Alkoxy cinnamic acid (nOCAC) with n=2, 4, 6, and 8 have been systematically investigated using the CNDO/S+CI, and INDO/S+CI methods. These methods have been employed to calculate/ analyze the geometric structures, absorbance measurements, spectral shifts in UV–Visible region, and photo stability of the nOCAC molecules. The electronic transitions, absorption wavelength, HOMO, and LUMO energies have been reported. Further, photo stability of the molecules has been discussed in the light of absorption wavelength, and electronic transition oscillator strength (f). The effect of different solvent media and alkyl chain length on these factors has also been discussed. It has been observed that the HOMO, LUMO, and energy gap are independent for the chosen solvents. In the present article, an attempt has been made for a new insight on photo stability of liquid crystals by maintaining their conductivity. Further, these absorption spectra will provide valuable data base for future computational studies, and the other experimental investigations.

Synthesis and characterisation of side chain liquid crystal copolymers containing sulfonic acid groups

A series of novel side chain liquid crystal copolymers, the poly[10-(4-methoxy-4′-oxy-azobenzene) decyl methacrylate]–co-poly[2-acrylamido-2-methyl-1-propanesulfonic acid]s (10-MeOAzB/AMPS-x/y) have been synthesised by free radical copolymerisation. The mol fraction of the sulfonic acid-based group, AMPS, has been varied over a broad range of composition in the copolymers, and these have been characterised using differential scanning calorimetry (DSC), polarised light microscopy (PLM), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray diffraction (XRD). The liquid crystal homopolymer and copolymers containing up to 0.54 mol fraction AMPS-based units, all exhibit a smectic A phase, while at higher mol fraction AMPS-based groups, liquid crystallinity is extinguished and the copolymers are amorphous. The local packing arrangements within the smectic A phase varies with composition attributed, in part, to phase separation between acid rich domains and liquid crystal regions. The dependence of the transitional properties on copolymer composition may be interpreted in terms of the packing efficiency of the mesogenic side chains and hydrogen bonding between the sulfonic acid groups, as a consequence of increasing the concentration of acid-based groups.

Shape-Dependent Oriented Trapping and Scaffolding of Plasmonic Nanoparticles by Topological Defects for Self-Assembly of Colloidal Dimers in Liquid Crystals

We demonstrate scaffolding of plasmonic nanoparticles by topological defects induced by colloidal microspheres to match their surface boundary conditions with a uniform far-field alignment in a liquid crystal host. Displacing energetically costly liquid crystal regions of reduced order, anisotropic nanoparticles with concave or convex shapes not only stably localize in defects but also self-orient with respect to the microsphere surface. Using laser tweezers, we manipulate the ensuing nanoparticle-microsphere colloidal dimers, probing the strength of elastic binding and demonstrating self-assembly of hierarchical colloidal superstructures such as chains and arrays.

Programmed size-selected permeation of ssDNA into ZnS mesoporous hollow spheres

The permeability of liquid crystal templated ZnS mesoporous hollow spheres is programmed and investigated with molecular probes. Pore size programming was achieved by swelling of the hydrophobic regions of the lyotropic liquid crystal used to template the mesoporous shell. Small angle X-ray scattering and transmission electron microscopy confirm that the mesopore diameter can be tuned between 2.5 and 4.1 nm. Predictions of the mesopore permeability of ssDNA from Flory scaling theory inspire the selection of fluorescently tagged ssDNA probes. Short ssDNA strands were found to easily penetrate the mesoporous shell, while large strands were excluded. Intermediate length ssDNA strands were able to penetrate shells with 4.1 nm mesopores, while being sterically excluded from 2.5 nm mesopores.

TRANSMISSION THROUGH TWISTED CLAD LIQUID CRYSTAL OPTICAL FIBERS

The paper presents an analytical investigation of three- layer twisted clad liquid crystal flber in respect of its power propagation characteristics. The flber under consideration has dielectric non- magnetic materials in its core and inner clad sections, whereas the outermost clad is made of radially anisotropic liquid crystal material. Twist in the flber is introduced in the form of superflne helical turns at the interface of the core and the inner clad regions with specifled values of pitch angle. Results demonstrate large conflnement of optical power in the outermost liquid crystal section. Further, the angle of twist is seen to have its pronounced efiect on controlling the ∞ow of power as it exhibits the ability of governing the propagation characteristics of the medium. The observed propagation feature is attributed to the radial anisotropy of the liquid crystal outer region as well as the amount of twist introduced, and attracts useful applications of such complex flber structures in evanescent fleld optical sensing and other coupling devices primarily used in integrated optics.

Polarization separation of light beams at the interface of two mesophases

The features of reflection of the linearly polarized light beams at the interface between two regions of a nematic liquid crystal (LC) with the orthogonal director orientation have been analyzed. The relationship between light beam propagation in a LC material and polarization of laser radiation has been established. Rotation of the polarization plane of a light beam has been found for the radiation introduced through the free surface “LC—air” deformed due to the capillarity effect. The total internal reflection effect has been demonstrated experimentally together with the possibility for special separation of the orthogonally polarized light beams at the interface of two mesophases.

Solubilization and rheology of the system ascorbic acid-water-polysorbate 80: temperature effects.

Abstract Changes induced by temperature in the relative position and extent of the isotropic and liquid crystal phases present in the ascorbic acid-water-polysorbate 80 system have been recorded. Increases in temperature reduce the size of the liquid crystal phase. This phase is pseudoplastic, but a small central region also shows thixotropic hysteresis loops. On recycling, most systems show Newtonian behaviour. In the isotropic regions, an increase in temperature results in a fall in log of viscosity proportionate to 1/Tabs, but in the liquid crystal region an increase in temperature may cause a similar fall or, because of a change in the relative position of the system within the liquid crystal region, an increase.

Pseudo-ternary phase diagrams of lecithin-based microemulsions: influence of monoalkylphosphates.

The formation of macroscopically homogeneous, stable, fluid, optically transparent, isotropic solutions (microemulsions) was delineated, at 25 degrees C, for systems containing water, soybean lecithin, sodium monoalkylphosphate (hexyl or ocytl), alcohol and isopropyl myristate. Six straight or branched alcohols (1-butanol, 2-butanol, isobutanol, 1-pentanol, 2-pentanol, 3-pentanol) were investigated as co-surfactants. A constant lecithin/alcohol mixing ratio was used, while the aqueous phase consisted of a solution of alkylphosphates at different concentrations. An increase of the microemulsion domain was seen by increasing the concentration of the alkylphosphate. With 0.2m hexylphosphate, as aqueous phase, the microemulsion domain consisted of a single, region, that, in the presence of butylic alcohols, spanded the greater portion of the phase diagram. In the presence of amyl alcohols the area of this region was much smaller. With 0.2 m octylphosphate the realm of existence of the microemulsions, except for 1-pentanol, consisted of two regions separated by a liquid-crystal region. With all the alcohols examined, the liquid-crystal phase solubilized a larger amount of oil in the presence of octylphosphate than in the presence of hexylphosphate. The stability ranges of microemulsions in systems containing soybean, lecithin, alcohol, water, and isopropyl myristate can be greatly increased by using a second hydrophobic amphiphile, such as hexylphosphate, to adjust the hydrophilic-lipophilic balance or the spontaneous peaking properties of lecithin-alcohol systems.

Solubility and viscosity relations in the system ascorbic acid--water--polysorbate 80.

Abstract The solubility of ascorbic acid in dispersions of polysorbate 80 has been examined. Over a large region of the solubility range liquid crystal exists, bounded by isotropic liquid phases. Excess solubilizate separates out as crystalline material. The rheological properties are complex. Within the isotropic phases the viscosity is Newtonian, but as soon as liquid crystal is produced pseudoplastic or thixotropic flow occurs. In the centre of the liquid crystal region, there were concentrations exhibiting a “yield” value followed by relaxation before the usual thixotropic loop.

ON THE TAPERED OPTICAL FIBERS WITH RADIALLY ANISOTROPIC LIQUID CRYSTAL CLAD

The paper presents an analytical investigation of a tapered core optical flber of which the outermost section is loaded with radially anisotropic liquid crystal. The analyses are dealt with transverse modes supported in the flber structure followed by the relative distribution of power in the difierent flber sections. Preliminary dispersion characteristics of the guide are also illustrated. The results demonstrate that the TE modes transport very large amount of power in the outermost liquid crystal region | the criteria much useful for flber optic sensing and fleld coupling devices.

On the transmission by liquid crystal tapered optical fibers

A three-layer liquid crystal tapered optical fiber (LCTF) is investigated with the emphasis on the power confinements by the low order TE and TM modes sustained in the different sections of LCTF. The outermost clad section is considered to be made of liquid crystal with radial anisotropy whereas the core and the inner clad are dielectric regions. Rigorous field expressions in the different LCTF sections are deduced, and the plots of power confinement factors (or the relative distributions) are ultimately made considering different fiber dimensions. The results reveal that the TE modes confine maximum amount of power in the outermost liquid crystal region, which is attributed to the radial anisotropy of the section. Such features of LCTFs attract their usefulness in the area of field coupling devices and optical sensing where evanescent field technique is primarily implemented.

Double Self Quotient Image Based Image Flattening for Defect Detection in Thin Film Transistor Liquid Crystal Display Panel

This paper presents the results of using self quotient image (SQI) to flatten the background region of a thin film transistor liquid crystal display image. To overcome an inherent shortcoming of SQI method, namely the halo effect in thin film transistor liquid crystal display images, double SQI method is introduced. Experimental results demonstrate that SQI can be used effectively to eliminate a non-uniformity of the background region in a test image.

TE MODE PROPAGATION THROUGH TAPERED CORE LIQUID CRYSTAL OPTICAL FIBERS

An analysis is presented of a three-layer tapered core liquid crystal optical flber (TLCF) having the outermost clad section made of radially anisotropic liquid crystal. TE mode propagation through TLCF is demonstrated with maximum distribution of power in the liquid crystal section under the situation that the TLCF core and the inner clad regions are constructed of homogeneous and isotropic dielectric materials. Such a propagation feature is attributed to the radial anisotropy of the liquid crystal outer region, and attracts useful applications of TLCFs in evanescent fleld optical sensing and other coupling devices primarily used in integrated optics.

Phase Behavior and Structure Properties of the Sodium Dodecyl Sulfate (SDS)/Brij 30/Water System

The phase behavior of the sodium dodecyl sulfate (SDS)/Brij 30/H2O system is shown by a phase diagram. The system can form micelle, reverse micelle, anisotropic lamellar, and hexagonal liquid crystal regions. The rheological behavior of the viscoselastic solution follows the Maxwell model at lower shear frequencies and deviates from it at higher shear frequencies in the oscillatory frequency sweeping experiment, which is the typical property of wormlike micelles entangled to form a transient network. In addition, the results are evaluated by dynamic light scattering and freeze-fracture images, which are consistent with the rheological behavior.

Phase Behavior of Engkabang Fat with Nonionic Surfactants

Abstract Phase behavior of engkabang fat was determined through the construction of ternary phase diagrams using nonionic surfactants. Several phase regions appeared in the ternary phase diagrams such as isotropic, homogenous, liquid crystal, two phase and three phase regions. The increase of hydrophilic-lipophilic balance (HLB) values of the nonionic surfactants used gave larger isotropic and homogenous region in the ternary phase diagrams. The combination of engkabang fat:Solubilisant Gamma (2:1) in the ternary phases diagram gave an even larger isotropic and homogenous regions as well as the formation of liquid crystal region.

Ion Transport in a Reflective Liquid-Crystal-on-Silicon Microdisplay Cell

A built-in potential exists in the reflective liquid-crystal-on-silicon (LCoS) microdisplay cell due to the work-function difference between the aluminum and indium–tin-oxide electrodes. As a consequence, the flicker is generated unless the dc offset voltage is applied to compensate the built-in potential. In this paper, we present the experimental result that the dc offset voltage changes with time as the display is operated and the ions are generated in the liquid crystal (LC). To understand the experimental result, we simulate the ion motion in the LCoS cell by considering both the drift and diffusion. We discuss how the ion concentration in the LC affects the screening of the internal electric field in the bulk LC region and subsequently the built-in potential in the LCoS cell. We show that for an ion concentration higher than the value required to fully compensate the initial built-in potential, the polarity of the built-in potential is changed due to the high electric field near electrodes. By matching the experimental and simulation results, we predict how the ion concentration in the LC increases as a function of operation time.

Physiochemical Properties of Hydroxy Mixed Ether HMEnSurfactants and their Interaction with Sodium Dodecyl Sulfate SDS

AbstractThis paper is focused on the phase behavior, interaction with anionic surfactant sodium dodecyl sulfate SDS, adsorption and wetting investigations of new hydroxy mixed ether nonionic surfactants HMEn. The phase diagrams of (0.1–100) %wt of HMEn(n-value is the ethoxylation number EO) at the temperature range 20–100°C have shown that the increasing of n-value raises the cloud boundary toward higher temperature. Remarkable result was obtained from the interaction between SDS and HMEB, at which the mixed system exhibits a unique homogeneity and a liquid crystal phase formation. Macroscopically, the liquid crystal region was found when the SDS concentration range between 8 and 24 mM mixed with 10% wt HMEB. The interaction between HMEnand mica was also investigated using atomic force microscopy AFM and a pronounced adsorption of HMEnon mica was observed. Moreover, contact angle results reveal that glass substrate shows strong wettability of HMEnsurfactant solutions compared with polyethylene PE and polymethylmethaacrylate PMMA substrates. This wettability however also decreases with EO number.

Synthesis and thermotropic liquid crystalline properties of heterogemini surfactants containing a quaternary ammonium and a hydroxyl group

A homologous series of novel heterogemini surfactants, ( N , N -dimethyl- N-[3-(alkyloxy)-2-hydroxypropyl]-alkylammonium bromide (referred to as C m OhpNC n ; m, n = 10 , 8; 12, 8; 14, 8; 16, 8; 14, 10; 12, 12 and 10, 14) were synthesized. Their thermotropic phase behavior was investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), infrared spectroscopy (IR) and X-ray diffraction (XRD). All the compounds showed high thermal stability and formed enantiotropic thermotropic smectic A liquid crystals. The mesophase region was sensitive to the overall length ( m + n ) of the two hydrophobic tails and was widened with increasing ( m + n ). When fixing the overall length of the two hydrophobic tails ( m + n = 24 ), the liquid crystal region was affected little by the dissymmetry of the two hydrophobic chains. The combination of IR and XRD results suggested the cis-configuration of the alkyl chain and the alkoxy chain with respect to the extended N–CH 2–CH(OH) skeleton in both crystal lattice and liquid crystal mesophase. The folding of the alkoxy chain at the carbon atom connecting the hydroxyl group led to the hydrogen bonding between the hydroxyl and the Br − counterion, which is beneficial to stabilizing the liquid crystal phase.

Phase Behavior and Shear Alignment in SWNT‐Surfactant Dispersions

The effect of single-walled carbon nanotubes (SWNT) on the phase behavior of the cationic surfactant cetyltrimethylammonium bromide (CTAB) in aqueous solutions is investigated at room temperature. Small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM) are used for characterization of bulk dispersions and nanometrically thin films. Additional carbonaceous additives (fullerenes, multi-walled carbon nanotubes, and carbon black) serve as reference systems. It is found that dispersions of carbonaceous additive (excluding fullerenes) at intermediate surfactant concentrations (below the liquid-crystalline region of the native surfactant) induce demixing and macroscopic phase separation in otherwise homogeneous solutions of CTAB. Two coexisting liquid phases of similar CTAB concentrations are observed, with the carbonaceous species residing within the lower phase. At high CTAB concentrations (liquid-crystal region) the SWNTs are found to incorporate into the ordered lyotropic liquid-crystalline phase while preserving the native d-spacing. Investigation of nanometrically thin films at intermediate surfactant concentrations under external shear reveals shear-induced structure (SIS) in the presence of minute amounts of SWNTs. The effect is found to be exclusive to SWNT and does not occur in dispersions of other carbonaceous additives.