Color Displays with Gel-Glass Dispersed Liquid Crystals

Liquid crystal microdroplets trapped into silica gel-glasses by sol-gel processes may be used for display applications. Gel-glass dispersed liquid crystals (GDLC) are switched between opaque and transparent states by applying external AC-voltage signals; no polarizers are required. The feasibility of applying these materials to colored displays has been explored. A comparative study of different dyes for GDLC color displays, which were either embedded in the sol-gel matrix or dissolved in the liquid crystal microdroplets is presented.     

Properties and production of F-doped silica glass

Fluorine-doped silica glass is an optical material with high transmission in the vacuum ultraviolet region, specifically at 157 nm. This feature, along with low thermal expansion and ease of polishing make it the material of choice for the photomask substrate for the 157 nm lithography node. We report the synthesis of fluorine-doped silica glass using various dopants. Characterization of the glasses was achieved by measuring vacuum UV and IR spectra and by refractive index measurements. Transmission and refractive index are both found to depend on fluorine concentration.     

Doped colloidal photonic crystal structure with refractive index chirping to the [111] crystallographic axis

A three-dimensionally ordered array of close-packed colloidal spheres, a photonic crystal structure in which the refractive index of the medium interstitial lattice in a colloidal crystal spatially changes in the [111] crystallographic axis, is demonstrated. The colloidal photonic crystal structure with refractive index chirping was produced by infiltration of a monomer and organic dopants with a high refractive index into a silica opal, followed by interfacial gel polymerization. The resulting photonic crystal structure has a gradually varying stop band at each different (111) plane in the face-centered cubic (fcc) crystal structure at a normal incidence. This novel structure exhibited optical characteristics that have band-gap broadening by the superposition of stop bands at each plane of the crystal with different dielectric functions. Moreover, the refractive index perturbation in the [111] fcc opal also showed a defect state within a pseudo-photonic band gap. This new type of photonic crystal structure should be useful for the band-gap engineering of photonic-band-gap materials.     

New ferroelectric liquid crystals with a trifluoromethyl group

New chiral dopants, possessing a trifluoromethyl group, have been synthesized. These dopants have different polar groups, located between the chiral centre and the diphenylacetylene core. The polar part is chosen from ester, methylene ether and ether linkages. Each new chiral dopant was mixed with a non-chiral liquid crystal mixture or a ferroelectric liquid crystal mixture, and their transition temperatures and electrooptic properties measured. The largest spontaneous polarization, 4·1 nC cm^-2, was obtained at 25°C for the ferroelectric liquid crystal mixture in which the dopant, with a methylene ether linkage, was incorporated. Molecular orbital calculations (MNDO method) for the dopants show that the calculated dipole moments are correlated with the measured spontaneous polarization, and the calculated results explain the experimental results quite well. In addition, it has been found that the conformation of the chiral part is an important factor which affects the magnitude of spontaneous polarization.     

Organic Polymer-Silica Gel Hybrid: A Precursor of Highly Porous Silica Gel

In this article I describe two of our discoveries. The first is the preparation of a transparent solid material composed of an organic polymer and silica gel. A novel material called a “hybrid” has successfully been prepared by the sol-gel reaction of ethyl orthosilicate in the presence of an organic polymer consisting of repeating units having an N-alkylamide group. The molecular-level dispersion of the organic polymer in the framework of silica gel has been established, which is due to the hydrogen-bond interaction between the organic polymer and silanol group of silica gel. The second discovery is the preparation of porous silica gel, which has been achieved by calcination of the organic polymer-silica gel hybrid at 600°C. Pore sizes ranging from 10 to 20 Å have been attained. A method of controlling pore size has been proposed.     

New ferroelectric liquid crystals with a trifluoromethyl group

Abstract

New chiral dopants, possessing a trifluoromethyl group, have been synthesized. These dopants have different polar groups, located between the chiral centre and the diphenylacetylene core. The polar part is chosen from ester, methylene ether and ether linkages. Each new chiral dopant was mixed with a non-chiral liquid crystal mixture or a ferroelectric liquid crystal mixture, and their transition temperatures and electrooptic properties measured. The largest spontaneous polarization, 4·1 nC cm^?2, was obtained at 25°C for the ferroelectric liquid crystal mixture in which the dopant, with a methylene ether linkage, was incorporated. Molecular orbital calculations (MNDO method) for the dopants show that the calculated dipole moments are correlated with the measured spontaneous polarization, and the calculated results explain the experimental results quite well. In addition, it has been found that the conformation of the chiral part is an important factor which affects the magnitude of spontaneous polarization.     

Highly birefringent nematic and chiral nematic liquid crystals

We report a simple interference method to determine the dispersion of the extraordinary refractive index and birefringence of highly conjugated and coloured nematic liquid crystals used as light-emitting materials in organic electroluminescent devices. The measurements are made in the nematic glass phase at room temperature. The birefringence is highly dispersive and values up to 1.1 are obtained. Chiral groups are incorporated into the end chains giving a chiral nematic liquid crystal with a very wide stopband in the visible region. The Berreman matrix method is used to simulate transmission through the chiral nematic liquid crystal cell using the refractive index parameters obtained experimentally. Excellent agreement between theory and experiment is found.     

Photochromic reverse mode polymer dispersed liquid crystals

Control of light intensity and colour are two of the major features required in the realization of smart windows. We designed a bi‐functional polymer dispersed liquid crystal (PDLC) film in order to satisfy such requirements, i.e. it is able both to modulate the optical transmission, if an external electric field is applied, and to change colour if exposed to sunlight. A monomer/liquid crystal mixture was doped with a small amount of photochromic material and homeotropically aligned by means of rough surfaces. A transparent and pale pink coloured film was achieved after photopolymerization. Such a film changes colour upon exposure for some seconds to sunlight or ultraviolet radiation in a persistent but reversible manner. In addition, the film appears transparent without the application of an electric field (OFF state) and becomes opaque on application of a driving voltage of about 75?V (ON state), and thus the film operates in reverse mode with respect to conventional PDLCs.     

Thermal tuning band gap in cholesteric liquid crystals

The phase of a liquid crystal (LC) changing from a nematic phase to a cholesteric (Ch) mesophase is achieved by adding different ratios of chiral dopants S811. By studying the transmission spectrum, we are able to measure the helical pitch in cholesteric phase. The pitch in the mixtures of nematic E7 and chiral dopants S811 as a function of the concentration of the dopant and temperature is investigated. The sensitivity of the selective reflection notch of the cholesteric phase to the thermal tuning depends strongly on the ratios of the chiral dopants. It reveals that the influence of temperature is more profound for those cholesteric liquid crystals (CLCs) which exhibit smectic A (SmA) at lower temperatures. When fitted using Keating's formula, the helical pitch calculated from our experimental results lies on the predicted curve. Optimised ratios of the mixture CLCs for the optimised reflection band with the specified wavelength ranging from 467 nm to 2123 nm are suggested.     

Photochromic reverse mode polymer dispersed liquid crystals

Control of light intensity and colour are two of the major features required in the realization of smart windows. We designed a bi-functional polymer dispersed liquid crystal (PDLC) film in order to satisfy such requirements, i.e. it is able both to modulate the optical transmission, if an external electric field is applied, and to change colour if exposed to sunlight. A monomer/liquid crystal mixture was doped with a small amount of photochromic material and homeotropically aligned by means of rough surfaces. A transparent and pale pink coloured film was achieved after photopolymerization. Such a film changes colour upon exposure for some seconds to sunlight or ultraviolet radiation in a persistent but reversible manner. In addition, the film appears transparent without the application of an electric field (OFF state) and becomes opaque on application of a driving voltage of about 75 V (ON state), and thus the film operates in reverse mode with respect to conventional PDLCs.     

Highly birefringent nematic and chiral nematic liquid crystals

We report a simple interference method to determine the dispersion of the extraordinary refractive index and birefringence of highly conjugated and coloured nematic liquid crystals used as light‐emitting materials in organic electroluminescent devices. The measurements are made in the nematic glass phase at room temperature. The birefringence is highly dispersive and values up to 1.1 are obtained. Chiral groups are incorporated into the end chains giving a chiral nematic liquid crystal with a very wide stopband in the visible region. The Berreman matrix method is used to simulate transmission through the chiral nematic liquid crystal cell using the refractive index parameters obtained experimentally. Excellent agreement between theory and experiment is found.     

Dye-activated hybrid organic/inorganic mesostructured titania waveguides

A room-temperature synthesis route for the fabrication of a new type of hybrid organic/inorganic mesostructured material based on titania instead of silica as the inorganic component has been developed. This approach enables facile processing of the titania/block copolymer surfactant precursor solution into optically activated, transparent, and crack-free fibers and planar waveguides with adjustable thickness. Stabilization of the structures occurs upon solvent evaporation by formation of a solid, glasslike material without heat treatment. These dye-activated, high refractive index, titania-based composites show efficient waveguiding and mirrorless lasing at low thresholds without the need of an ultralow refractive index support layer.     

Refractive index increase of acrylate‐based polymers by adding soluble aromatic guest‐molecules

This work presents the influence of dopants on viscosity in an uncured liquid state as well as on refractive index, Abbe number, optical loss, and glass transition temperature of different polymer compositions. The base material consists of Genomer 2263, a bisphenol, an epoxy diacrylate as matrix polymer, and benzyl methacrylate as comonomer. As dopants, the soluble aromatic guest‐molecules 9‐bromophenantrene and 9‐vinylcarbazole are investigated. The viscosity can be adjusted by different mixtures of the matrix polymer and comonomer from 3000 down to 4 mPa sec. Depending on the type and content of the dopants, the refractive index, Abbe number, and the glass transition temperature can be adjusted. The refractive indices increase linear at 589 nm and 20°C from 1.572 to 1.638 by doping, with Abbe numbers between 20 and 30. At this wavelength, the optical losses were determined to be around 2 dB · cm^?1. The glass transition temperature can be tailored between 50 and 98°C. A way to use high amounts of optical dopants is presented, which opens up the way for different shaping technologies like inkjet printing of optical components. Copyright © 2016 John Wiley & Sons, Ltd.     

Electrically-induced optical storage effects in smectic polysiloxanes A variable transmission device

Changes in the optical transmission induced by electric fields have been studied in a smectic side-chain polysiloxane liquid crystal. The transmission varied from effectively zero, for a highly scattering (opaque) texture, to total, for a homeotropic texture, on increasing the applied voltage across the material. The field-induced textures were durably stored in the smectic phase, enabling the order parameter of the side groups to be studied by dielectric relaxation measurements. For the highly transparent texture, a side group order parameter of 0-92 has been observed.     

Chirality-induced phase transitions in some liquid crystalline binary mixtures

Novel binary mixtures have been prepared between an optically active antiferroelectric liquid crystal, (S)-4-(1-methylheptyloxycarbonyl)phenyl 4'-octyloxy-biphenyl-4-carboxylate, and an optically active twin liquid crystal, (R)-3-methyladipic acid bis[4-(5-octyl-2-(pyrimidinyl)phenyl] ester, and the liquid crystalline properties investigated. The stability of each liquid crystal phase was found to decrease by mixing these two liquid crystalline materials. Furthermore, a phase diagram between these compounds showed a clear discontinuity in phase sequences. These results indicate that the liquid crystal phases are different in nature between these materials. The mixture consisting of the antiferroelectric material (40 per cent) and the twin material (60 per cent) shows an unusual liquid crystal phase, where the texture is similar to that reported for the twist grain boundary (TGB) phase. Related binary mixtures have been prepared between optically active or racemic materials, where the chirality of the system is expected to be altered systematically. The TGB phase was found to be induced only in the mixture between the optically active materials. Two kinds of effect on the appearance of the TGB phase, i.e. a strong helical structure induced by the optically active twin liquid crystal and a decrease of the smectic layer strength achieved by mixing between two types of liquid crystalline materials, are discussed.     

Reverse mode operation polymer dispersed liquid crystal with a positive dielectric anisotropy liquid crystal

The development of electrically activated chromogenic materials is important for their potential applications in smart windows. Several previous works have reported on reverse mode operation polymer dispersed liquid crystals (PDLCs) based on negative dielectric anisotropy liquid crystals. They have a transparent OFF state, which turns opaque after the application of a suitable external electric field. Nevertheless, these devices have some limitations such as the use of large amount of expensive liquid crystals with peculiar physical‐chemical properties. In addition, a good matching between the refractive index of liquid crystal and the polymer matrix one is required. The main result of this work is the achievement of reverse mode operation devices prepared with a positive dielectric anisotropy liquid crystal and characterized by a high OFF state transmittance obtained by the onset of high intensity built‐in DC electric fields in a direct mode operation PDLC, which allows the OFF state homeotropic alignment of liquid crystal directors. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

硅胶基质高效液相色谱填料研究进展

高效液相色谱(HPLC)不仅是一种有效的分析分离手段,也是一种重要的高效制备分离技术。色谱柱是HPLC系统的核心,不同性能的填料是HPLC广泛应用的基础。硅胶是开发最早、研究最为深入、应用最为广泛的HPLC固定相基质,其制备方法主要有喷雾干燥法、溶胶-凝胶法、聚合诱导胶体凝聚法及模板法等。近年来,亚2μm小粒径硅胶、核-壳型硅胶、双孔径硅胶、介孔性硅胶、有机杂化硅胶等新型硅胶应用于HPLC并取得了色谱分离技术的飞速发展,例如基于亚2μm填料的超高压液相色谱技术、基于核-壳型填料的快速分离技术、基于杂化硅胶填料的高温液相色谱技术等。硅胶经表面化学键合、聚合物包覆等有机改性可制得先进的大分子限进填料、温敏性填料、手性填料等,大大扩展了HPLC的应用范围。本文对液相色谱用硅胶的制备方法、改性与修饰方法以及硅胶基质固定相的评价方法加以系统综述,概述了新型硅胶在HPLC中的应用进展,并对硅胶基质填料的发展方向与应用前景进行了展望。     

Electrically-induced optical storage effects in smectic polysiloxanes A variable transmission device

Abstract

Changes in the optical transmission induced by electric fields have been studied in a smectic side-chain polysiloxane liquid crystal. The transmission varied from effectively zero, for a highly scattering (opaque) texture, to total, for a homeotropic texture, on increasing the applied voltage across the material. The field-induced textures were durably stored in the smectic phase, enabling the order parameter of the side groups to be studied by dielectric relaxation measurements. For the highly transparent texture, a side group order parameter of 0-92 has been observed.     

Thermo-optic characteristics in transparent glass fabric reinforced composite using inorganic–organic hybrid materials

The thermo-optic characteristics of the transparent glass fabric composite and matrix resin have been investigated. The inorganic–organic hybrid materials modified with sulfur are synthesized as transparent matrix resin with the same refractive index and Abbe number as glass. The optical characteristics of the transparent composite relate to temperature due to the fact that the thermo-optic coefficient (dn/dT) for glass fiber (1.00 × 10⁻⁵K⁻¹) is different to that of inorganic–organic hybrid materials (−1.99 × 10⁻⁴K⁻¹). As the temperature increases, the transparent composite gradually becomes opaque and hazy due to the increased difference in the refractive index between the glass fiber and the matrix. The change in optical characteristics is reversible, meaning that the transparent composites can be used in for various applications in optical devices.     

Optical Application of (Pigmented) Sol-Gel Coatings

The performance of the anti-reflection stack antimony-doped tin oxide/SiO₂ improves considerably if the refractive index of the SiO₂ layer decreases from 1.45 to 1.41 by the introduction of porosity. Porosity can be introduced by the addition of high-boiling co-solvents (or templates e.g. sebacates) to the coating liquid. Fine-tuning of the liquid composition allows the formation of a homogeneous, non-scattering SiO₂ layer with a refractive index of 1.41 and pencil hardness of H7-H8 on large screens (diagonal >1 meter) if a curing temperature of 160°C was used.Another interesting application is the formation of transparent, strongly coloured layers on lamp bulbs. Due to the high operating temperatures, strict requirements are placed on the matrix material and the pigment used. Inorganic pigments have good temperature stability, but their colour saturation is weaker than that of organic pigments, demanding the formation of relatively thick coatings. In order to achieve this, Methyltrimethoxysilane (MTMS) was used as matrix material precursor. Fully transparent, temperature-resistant coatings were developed.