Home About us Contact
|
Home About us Contact | ||
|
|
||
Liquid Crystals (liquid + crystal)
Kinds of Liquid Crystals Terms modified by Liquid Crystals Selected AbstractsA Stimuli-Responsive, Photoluminescent, Anthracene-Based Liquid Crystal: Emission Color Determined by Thermal and Mechanical ProcessesADVANCED FUNCTIONAL MATERIALS, Issue 12 2009Yoshimitsu Sagara Abstract Here, a photoluminescent liquid crystal that exhibits a change of emission color on the metastable,stable phase transition induced by external stimuli is prepared. A 2,6-diethynylanthracene derivative with amide groups and dendritic side chains exhibits a columnar phase on slow cooling from the isotropic phase and shows blue emission in this columnar phase. In contrast, a cubic phase is obtained by rapid cooling from the isotropic phase. In the cubic phase, the 2,6-diethynylanthracene cores form excimers, resulting in yellow emission. While the columnar phase is a stable liquid-crystalline (LC) phase, the cubic phase is a metastable LC phase. It is found that a change of the photoluminescent color from yellow to blue is observed on the cubic-columnar phase transition induced by heating or mechanical shearing for this 2,6-diethynylanthracene derivative in the cubic phase. This change of photoluminescent color is ascribed to the inhibition of excimer formation on the metastable,stable LC phase transition. [source] Piezoelectric and Electric-Field-Induced Properties of a Ferroelectric Bent-Core Liquid CrystalADVANCED MATERIALS, Issue 37 2009Antal Jákli A new adamantane bent-core liquid crystal exhibiting a metastable ferroelectric phase with large polarization is synthesized and characterized. The material shows reversible switching between a birefringent (opaque) and an optically isotropic (clear) state. In the clear state, the observed piezoelectric constant is comparable to those of commercial solid-state piezotransducers. [source] Nanorod-Driven Orientational Control of Liquid Crystal for Polarization-Tailored Electro-Optic DevicesADVANCED MATERIALS, Issue 9 2009Somobrata Acharya Dispersion of ultranarrow ZnS nanorods of molecular dimensions encapsulated by a fluid-like soft organic layer in the nematic liquid crystal (LC ZLI-4792) results in a novel soft-matter-type blend with previously unachieved electro-optic properties. The local ordering of the nanorods significantly affects the global ordering of the blend, allowing a more rapid response. [source] Synergistic Ordering of Side-Group Liquid Crystal Polymer and Small Molecule Liquid Crystal: Order and Phase Behavior of Nematic Polymer Solutions,MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 19-20 2007Neal R. Scruggs Abstract Addition of a small-molecule liquid crystal (5CB) to a cyanobiphenyl-based side-group liquid crystal polymer (SGLCP) stabilizes nematic order, increasing the isotropization temperature (TNI) more than 15,°C. Despite synergistic ordering at high concentration, small amounts of polymer destabilize nematic order. Even though TNI(SGLCP) is 27,°C greater than TNI(5CB), 2H NMR shows that the order parameter of the SGLCP is less than that of 5CB at concentrations for which monodomains were accessible (,10 wt.-%). The results imply that nematic order is frustrated in the bulk polymer and addition of small molecule LC relaxes this frustration by allowing greater configurational freedom. Conversely, adding small amounts of polymer to the bulk 5CB introduces frustration, resulting in the strong asymmetry of the phase diagram. [source] UV Polymerisation of Surfactants Adsorbed at the Nematic Liquid Crystal,Water Interface Produces an Optical ResponseCHEMPHYSCHEM, Issue 17 2009Paul D. I. Fletcher Prof. Abstract We have investigated the changes in crossed polariser optical textures produced by adsorption and UV polymerisation of a range of polymerisable surfactants at the interface between a nematic liquid crystal and water. Similar to non-polymerisable surfactants, the adsorption of polymerisable surfactants with sufficiently long hydrophobic tail groups produces a transition from planar to homeotropic anchoring. UV polymerisation of surfactants with a polymerisable group located in the hydrophobic tail region changes the anchoring from homeotropic back to planar. Polymerisation in the hydrophilic headgroup region does not produce an optical transition. We demonstrate that these systems can be used to "write with light" in the interfaces and that they form the basis of a UV sensor device in which the optical response is visible to the naked eye. [source] Self-Organization of Dipolar 4,4,-Disubstituted 2,2,-Bipyridine Metal Complexes into Luminescent Lamellar Liquid CrystalsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2003Daniela Pucci Abstract Mononuclear cis -dichloro complexes, [LnMCl2], with different metal centres (PtII, NiII, and ZnII) and a series of palladium and platinum derivatives, [L2MX2], in which chloride groups are replaced with iodide, bromide, and azide ligands, have been synthesized from 4,4,-disubstituted-2,2,-bipyridines. Upon complexation of these non-mesogenic ligands, the peculiar structural arrangement, characterized by intermolecular associations of the new derivatives, induces mesomorphism in most [L2MX2] complexes, confirming the importance of coordination chemistry in metal-mediated formation of liquid crystals. Single crystal X-ray structures have been determined for dihexadecyl 2,2,-bipyridyl-4,4,-dicarboxylatopalladium and -zinc dichloride derivatives. Both the metal centres and the ancillary ligands have been varied to use dipole coupling as a tool to control molecular architecture: thermal, as well as spectroscopic properties, depend strongly upon molecular dipolar interactions. Tunable red and blue emitters based on PdII and PtII, both in solution and in the solid state, have been obtained. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] A Convenient Synthetic Route to Tetrahydropyran-Based Liquid CrystalsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 15 2006Peer Kirsch Abstract The tetrahydropyran moiety has been identified as a highly advantageous addition to the toolbox for the design of nematic liquid crystals for LCD applications. A new synthetic procedure based on the Lewis acid catalysed ring opening of oxetanes by lithium iminoenolates followed by reductive dehydroxylation of the resulting hemiketal provides a convenient preparative access to this class of materials.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Towards Efficient Dispersion of Carbon Nanotubes in Thermotropic Liquid CrystalsADVANCED FUNCTIONAL MATERIALS, Issue 19 2010Stefan Schymura Abstract Motivated by numerous recent reports indicating attractive properties of composite materials of carbon nanotubes (CNTs) and liquid crystals (LCs) and a lack of research aimed at optimizing such composites, the process of dispersing CNTs in thermotropic LCs is systematically studied. LC hosts can perform comparably or even better than the best known organic solvents for CNTs such as N -methyl pyrrolidone (NMP), provided that the dispersion process and choice of LC material are optimized. The chemical structure of the molecules in the LC is very important; variations in core as well as in terminal alkyl chain influence the result. Several observations moreover indicate that the anisotropic nematic phase, aligning the nanotubes in the matrix, per se stabilizes the dispersion compared to a host that is isotropic and thus yields random tube orientation. The chemical and physical phenomena governing the preparation of the dispersion and its stability are identified, taking into account enthalpic, entropic, as well as kinetic factors. This allows a guideline on how to best design and prepare CNT,LC composites to be sketched, following which tailored development of new LCs may take the advanced functional material that CNT,LC composites comprise to the stage of commercial application. [source] Photoswitchable Gas Permeation Membranes Based on Liquid CrystalsADVANCED FUNCTIONAL MATERIALS, Issue 17 2010Eric G, owacki Abstract We have fabricated switchable gas permeation membranes in which a photoswitchable low-molecular-weight liquid crystalline (LC) material acts as the active element. Liquid crystal mixtures are doped with mesogenic azo dyes and infused into commercially available track-etched membranes with regular cylindrical pores (0.40 to 10.0 ,m). Tunability of mass transfer can be achieved through a combination of (1) LC/mesogenic dye composition, (2) surface-induced alignment, and (3) reversible photoinduced LC-isotropic transitions. Photo-induced isothermal phase changes in the imbibed material afford large and fully reversible changes in the permeability of the membrane to nitrogen. Both the LC and photogenerated isotropic states demonstrate a linear permeability/pressure relationship, but they show significant differences in their permeability coefficients. Liquid crystal compositions can be chosen such that the LC phase is more permeable than the isotropic,or vice versa , and can be further tuned by surface alignment. Permeability switching response times are 5 s, with alternating UV and >420-nm radiation at an intensity of 2 mW/cm2 being sufficient for complete and reversible switching. Thermal and kinetic properties of the confined LC materials are evaluated and correlated with the observed permeation properties. We demonstrate for the first time reversible permeation control of a membrane with light irradiation. [source] Planar Alignment of Columnar Discotic Liquid Crystals by Isotropic Phase Dewetting on Chemically Patterned SurfacesADVANCED FUNCTIONAL MATERIALS, Issue 6 2010Jonathan P. Bramble Abstract A novel method of creating planar aligned columnar discotic liquid crystals (cDLCs) on surfaces, which also gives control over the azimuthal angle, is presented. Surfaces are chemically patterned with stripes via microcontact printing of organothiol self-assembled monolayers (SAMs) on gold, or via deep UV patterning of organosilane SAMs on silicon. These are then used to isolate long droplets of cDLCs by dewetting in the isotropic phase. Upon cooling from the isotropic into the hexagonal columnar phase, polarizing microscopy reveals that the cDLC aligns in a planar orientation. Results for three triphenylene derivatives (HAT-6, HHTT, H7T) and for a phthalocyanine derivative (8H2Pc) are presented. H7T and HAT-6 are found to align with the director perpendicular to the stripe direction, but HHTT and 8H2Pc align parallel to the stripe direction. This relatively simple new method for creating planar aligned columnar phases of DLCs gives control over the azimuthal angle: a condition required for organic field-effect transistor applications of cDLCs. [source] Phototunable Azobenzene Cholesteric Liquid Crystals with 2000 nm RangeADVANCED FUNCTIONAL MATERIALS, Issue 21 2009Timothy J. White Abstract Phototuning of more than 2000,nm is demonstrated in an azobenzene-based cholesteric liquid crystal (azo-CLC) consisting of a high-helical-twisting-power, axially chiral bis(azo) molecule (QL76). Phototuning range and rate are compared as a function of chiral dopant concentration, light intensity, and thickness. CLCs composed of QL76 maintain the CLC phase regardless of intensity or duration of exposure. The time necessary for the complete restoration of the original spectral properties (position, bandwidth, baseline transmission, and reflectivity) of QL76-based CLC is dramatically reduced from days to a few minutes by polymer stabilization of the CLC helix. [source] Controlling Light Emission in Luminescent Solar Concentrators Through Use of Dye Molecules Aligned in a Planar Manner by Liquid CrystalsADVANCED FUNCTIONAL MATERIALS, Issue 17 2009Paul P. C. Verbunt Abstract A luminescent solar concentrator (LSC) is a potential low-cost enhancement of the standard large-area silicon photovoltaic panels for the generation of electricity from sunlight. In this work, guest,host systems are investigated using anisotropic fluorescent dyes and liquid crystal mesogens to control the direction of emitted light in the LSC. It is determined that up to 30% more light is emitted from the edge of an LSC waveguide with planar dye alignment parallel to the alignment direction than from any edge of an LSC with no alignment (isotropic). The aligned samples continue to show dichroic performance after additions of both edge mirrors and rear scattering layer. [source] Phototunable Microlens Array Based on Polymer Dispersed Liquid CrystalsADVANCED FUNCTIONAL MATERIALS, Issue 7 2009Gui-Rong Xiong Abstract A microfluidic system is designed to fabricate polymer dispersed liquid crystal microspheres, whose shape, surface smoothness, and size are controlled. A microlens array (MLA) is constructed by the assembly of the monodispersed microspheres. In the MLA, each microsphere acts as a separate imaging unit. As the liquid crystal (LC) used is a mixed liquid crystal that contain photoresponsive 4-butyl-4-methoxyazobenzene, the imaging capability and light transportation of the MLA can be reversibly controlled by light irradiation. [source] Liquid-Crystalline Nanostructures: , -Conjugated Oligothiophene-Based Polycatenar Liquid Crystals: Self-Organization and Photoconductive, Luminescent, and Redox Properties (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 3 2009Mater. Polycatenar , -conjugated oligothiophenes tethering multiple flexible chains can be used as electro-, photo-, and redox-active materials, as reported by Takashi Kato, Takuma Yasuda, and co-workers on page 411. Various functional liquid-crystalline assemblies including smectic, columnar, and micellar cubic nanostructures can be constructed by polycatenar oligothiophenes. This simple and versatile design strategy would be useful for further development of new functional , -conjugated materials. [source] , -Conjugated Oligothiophene-Based Polycatenar Liquid Crystals: Self-Organization and Photoconductive, Luminescent, and Redox PropertiesADVANCED FUNCTIONAL MATERIALS, Issue 3 2009Takuma Yasuda Abstract A series of liquid-crystalline (LC) ,- -conjugated oligothiophenes bearing three or two alkoxy chains at their extremities has been designed and synthesized. These polycatenar oligothiophenes form various LC nanostructures including smectic, columnar, and micellar cubic phases. These properties depend on the number and length of the terminal alkoxy chains. The hole mobilities for the oligothiophenes have been measured. The layered smectic and columnar structures are capable of transporting holes, leading to mobilities of up to 0.01,cm2 V,1 s,1. The columnar LC assemblies have also been explored to produce linearly polarized light-emission. Fine red polarized fluorescence is observed from a uniaxially aligned film of the oligothiophenes. The redox properties of the oligothiophenes both in solutions and in films have been examined. The oligothiophenes exhibit electrochromism upon applying an oxidative potential. The present design strategy is useful for fabricating a variety of functional electro-active molecular assemblies. [source] One- and Two-Dimensionally Structured Polymer Networks in Liquid Crystals for Switchable Diffractive Optical Applications,ADVANCED FUNCTIONAL MATERIALS, Issue 12 2004P. Kossyrev Abstract We have created one- and two-dimensionally structured polymer networks dispersed in a liquid-crystal solvent using a holographic exposure technique. These structures have potential for electrically switchable, reverse-mode, polarization selective and non-selective diffractive optical elements. Using a simple phenomenological model to describe our diffraction measurements in conjunction with microscopic studies, we are able to estimate the structured polymer wall thickness as a function of monomer concentration. [source] Photogeneration of High Pretilt Angles of Nematic Liquid Crystals by Non-Polarized Light Irradiation of Azobenzene-Containing Polymer Films,ADVANCED FUNCTIONAL MATERIALS, Issue 3 2004S. Furumi Abstract A vertical-alignment (VA) cell of nematic liquid crystals (LCs) was prepared using photoirradiated thin films of a poly(methacrylate) with mesogenic moieties of 4-trifluoromethoxyazobenzene as the side chains. Optical anisotropy was generated by oblique irradiation of the azobenzene-containing polymer films with non-polarized UV light, followed by annealing treatment to enhance the photodichroism, which displayed thermal stability. The combination of oblique exposure to non-polarized UV light and subsequent annealing treatment brought about high pretilt angles of nematic LCs so that a photoaligned VA LC cell was fabricated. The photopatterned LC cell exhibited electro-optical properties with excellent optical quality when a voltage was applied even after heating at 100,°C for several hours. [source] Synthesis of Novel Chiral Ionic Liquids and Their Phase Behavior in Mixtures with Smectic and Nematic Liquid CrystalsHELVETICA CHIMICA ACTA, Issue 11 2004Martin Tosoni Alkylation of 1-alkyl-1H -imidazoles 2a,f with citronellyl bromide 1b opens access to chiral 1H -imidazolium bromides 3a,f (Scheme,1). A similar strategy yielded the chiral pyridinium ionic liquid 6 (Scheme,2). Dialkylation of 1H -imidazole (7) gave the C2 -symmetric 1,3-dicitronellyl-1H -imidazolium bromide (8) (Scheme,3). Differential scanning calorimetry and optical polarizing microscopy revealed smectic mesophases for 1-citronellyl-3-tetradecy-1H -limidazolium bromide (3e) and 1-citronellylpyridinium bromide (6) (Table). In binary mixtures with smectic and nematic liquid crystals 9 and 10, 1-citronellyl-3-methyl-1H -imidazolium bromide (3a) behaved differently. Increasing quantities of 3a cause a decrease of the smectic-phase width for the mixture 3a/9 (Fig.,3), whereas the phase width of the nematic phase for 3a/10 remained nearly constant (Fig.,4). [source] Composite Holographic Gratings Containing Light-Responsive Liquid Crystals for Visible Bichromatic SwitchingADVANCED MATERIALS, Issue 21 2010Luciano De Sio Polymeric microstructures, produced in a multi-step chemico-physical process, confine and stabilize a well-aligned nematic liquid crystal (NLC) film, which is doped with a high-performance mesogenic azobenzene dye, sensitive in the visible range. [source] Nanoparticle-Dispersed Liquid Crystals Fabricated by Sputter DopingADVANCED MATERIALS, Issue 5 2010Hiroyuki Yoshida A simple and robust method to prepare nanoparticle-dispersed liquid crystals is demonstrated. Highly dispersed gold nanoparticle,liquid crystal suspensions are fabricated by simply sputter doping the gold target on the host liquid crystal (see figure). The existence of the nanoparticles is supported by optical extinction measurements, polarization optical microscopy, and transmission electron microscopy. An improvement in the electro-optic response, namely, a decrease in the threshold voltage, is also demonstrated in twist nematic devices fabricated using the nanoparticle-dispersed liquid crystal. [source] Liquid-Crystal Patterning: Lithographic Alignment of Discotic Liquid Crystals: A New Time,Temperature Integrating Framework (Adv. Mater.ADVANCED MATERIALS, Issue 46 200946/2009) Liquid crystals are a successful example of how the control of self-assembly via chemical design leads to novel applications. Massimiliano Cavallini, Fabio Biscari, and co-workers report on p. 4688 that direct patterning of a continuous metal-free mesogenic phthalocyanine film (discotic LCs) is achieved by spatial control of column orientation using unconventional lithography. These patterned films work as time,temperature integrators at the columnar rectangular,hexagonal transition temperature. [source] Lithographic Alignment of Discotic Liquid Crystals: A New Time,Temperature Integrating FrameworkADVANCED MATERIALS, Issue 46 2009Massimiliano Cavallini Liquid crystals are a successful example of how the control of self-assembly via chemical design leads to novel applications. Direct patterning of a continuous metal-free mesogenic phthalocyanine film (discotick liquid crystals) is shown by the spatial control of columns orientation by unconventional lithography. These patterned films work as time,temperature integrators at a columnar rectangular,hexagonal transition temperature. [source] Photoluminescent Fibers: Anisotropic Self-Assembly of Photoluminescent Oligo(p -Phenylenevinylene) Derivatives in Liquid Crystals: An Effective Strategy for the Macroscopic Alignment of , -Gels (Adv. Mater.ADVANCED MATERIALS, Issue 40 200940/2009) Takashi Kato, Ayyappanpillai Ajayaghosh, and co-workers report on p. 4029 that aligned photoluminescent ,-conjugated fibers are formed through anisotropic self-assembly of oligo(p -phenylenevinylene) gelators in smectic and nematic liquid crystals. The aligned fibers exhibit polarized photoluminescent properties. These self-assembled liquid-crystalline composites may be applicable to new types of electro-optical and photonic materials. [source] Anisotropic Self-Assembly of Photoluminescent Oligo(p -Phenylenevinylene) Derivatives in Liquid Crystals: An Effective Strategy for the Macroscopic Alignment of , -GelsADVANCED MATERIALS, Issue 40 2009Yuki Hirai Aligned photoluminescent fibers are formed by the self assembly of an oligo-(p-phenylenevinylene) derivative (OPV) in oriented liquid crystals (see figure). The aligned fibers of OPV show polarized yellow emission in the direction of the long axis of fibers. New types of electro-optical and photonic systems can be visualized in the future as the polarized luminescence of these fibers is combined with the dynamic properties of the liquid crystals. [source] Liquid Crystals: Electrically Tuneable Liquid Crystal Photonic Bandgaps (Adv. Mater.ADVANCED MATERIALS, Issue 38-39 200939/2009) On p. 3915, Stephen Morris and co-workers demonstrate broadband wavelength tuning of a photonic bandgap that is electrically driven in a chiral nematic liquid crystal. Remarkably, this tuning is not only broadband but is found to occur without altering the reflection quality of the optical structure. In addition, under certain conditions, the helical structure can be made to exhibit multiple bandgaps across the visible spectrum. [source] SiO2 Nanoparticle Sequestration via Reactive Functionalization in Holographic Polymer-Dispersed Liquid CrystalsADVANCED MATERIALS, Issue 36 2009John D. Busbee Holographic photopolymerization of reactively functionalized silica nanoparticles in polymer/liquid-crystal systems leads to sequestration of the silica nanoparticles in the polymeric domain of holographic polymer-dispersed liquid-crystals Bragg gratings. Excellent dispersion of the nanoparticles maintains the optical properties of the reflection grating without additional scattering while lowering the voltage necessary to switch the state of the grating. [source] Electric-Field-Responsive Lithium-Ion Conductors of Propylenecarbonate-Based Columnar Liquid CrystalsADVANCED MATERIALS, Issue 16 2009Harutoki Shimura One-dimensional lithium-ion conductors responsive to electric fields are prepared by the complexation of a columnar propylenecarbonate-based liquid crystal and lithium triflate. The assemblies are aligned macroscopically by an alternating electric field, and they transport ions along the columnar axes. [source] Exploring Optical Properties of Liquid Crystals for Developing Label-Free and High-Throughput Microfluidic Immunoassays,ADVANCED MATERIALS, Issue 2 2009Chang-Ying Xue The orientational transition of liquid crystals (LCs) is used as a label-free detection mechanism for immunoassays developed in microfluidic systems. LCs only show bright optical textures (visible to the naked eye) in the line-line intersections in which label-free antibodies bind to their surface-immobilized antigens, suggesting the feasibility of using LCs to detect specific antigen-antibody binding events in a high-throughput and multiplexed manner. [source] Bottom-Up Fabrication of Photonic Defect Structures in Cholesteric Liquid Crystals Based on Laser-Assisted Modification of the Helix,ADVANCED MATERIALS, Issue 9 2007H. Yoshida Controlled fabrication of defect structures is performed in cholesteric liquid crystals by a laser-assisted polymerization process that induces a local elongation of the helix (see figure). Low-threshold laser action is observed from the photonic defect-mode observed within the selective reflection band. [source] Homeotropic Alignment of Columnar Liquid Crystals in Open Films by Means of Surface Nanopatterning,ADVANCED MATERIALS, Issue 6 2007I. Gearba Columnar liquid crystals (LCs) are reported to align spontaneously homeotropically,that is, orthogonally to the surface (see figure and inside cover),on a glass surface covered with a layer of poly(tetrafluoroethylene) transferred by friction (rubbing). This strategy for producing macroscopic monodomains of homeotropically aligned LCs may find important applications in the fabrication of LC-based organic solar cells. [source] | ||||||||||||||||||||||||||||||||||