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Nematic Liquid Crystal (nematic + liquid_crystal)
Selected AbstractsUV 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] 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] Cover Picture: Bistable Nematic Liquid Crystals with Self-Assembled Fibers (Adv. Mater.ADVANCED MATERIALS, Issue 6 20056/2005) Abstract The cover shows a recording process using nematic liquid crystal alignment. On p.,692, Kato and co-workers report that reversibly bistable states have been achieved for nematic liquid crystals incorporating a small amount of self-assembled fibers. Homeotropic monodomains and non-aligned multidomains can be fixed and switched by thermal treatment in electric fields. The technique is applied to the formation of rewritable light scattering patterns, as shown on the cover. [source] Synthesis of Novel Chiral Ionic Liquids and Their Phase Behavior in Mixtures with Smectic and Nematic Liquid Crystals.CHEMINFORM, Issue 14 2005Martin Tosoni No abstract is available for this article. [source] Ferroelectric Response and Induced Biaxiality in the Nematic Phase of Bent-Core MesogensADVANCED FUNCTIONAL MATERIALS, Issue 16 2009Oriano Francescangeli Abstract The still undiscovered fluid ferroelectric nematic phase is expected to exhibit a much faster and easier response to an external electric field compared to conventional ferroelectric smectic liquid crystals; therefore, the discovery of such a phase could open new avenues in electro-optic device technology. Here, experimental evidence of a ferroelectric response to a switching electric field in a low molar mass nematic liquid crystal is reported and connected with field-induced biaxiality. The fluid is made of bent-core polar molecules and is nematic over a range of 120,°C. Combining repolarization current measurements, electro-optical characterizations, X-ray diffraction and computer simulations, ferroelectric switching is demonstrated and it is concluded that the response is due to field-induced reorganization of polar cybotactic groups within the nematic phase. This work represents significant progress toward the realization of ferroelectric fluids that can be aligned at command with a simple electric field. [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] 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] 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] 1,1,1-Trichloro-3-(1-phenethylamino-ethylidene)- pentane-2,4-dione,synthesis, spectroscopic, theoretical and structural elucidationJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 12 2007Tsonko M. Kolev Abstract 1,1,1-Trichloro-3-(1-phenethylamino-ethylidene)-pentane-2,4-dione is spectroscopically and structurally elucidated by means of linear-polarized IR spectroscopy (IR-LD) of oriented solids as a colloidal suspension in nematic liquid crystal. Structural information and IR-spectroscopic assignment are supported by quantum chemical calculations at MP2 and B3LYP level of theory and 6-311++G** basis set. The geometry is characterized with an inramolecular hydrogen bond of NH,OC with length of 2.526,Å and a NHO angle of 140.5(1)°. The NHC(CH3)CCCO(CH3) fragment is nearly flat with a maximal deviation of total planarity of 10.4°. Copyright © 2007 John Wiley & Sons, Ltd. [source] Vertically aligned polypyrrole drawing a fingerprint array prepared by electrochemical polymerization in chiral nematic electrolyteJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2006Hiromasa Goto A new electrochemical polymerization method for preparing vertically aligned polypyrrole drawing a fingerprint array was developed. Polymerization of Py in the chiral nematic liquid crystal (N*-LC) produces vertical alignment of the fibril structure. Here, the N*-LC plays a role of a molecular vessel. The fibril can grow with forming vertically aligned fibril structure along the fingerprint texture of N*-LC by electrochemical polymerization process. [source] Sign inversion of the optical torque on the nematic director enhanced by anthraquinone dye dopants stable to the light actionLASER PHYSICS LETTERS, Issue 11 2006V. Ya. Abstract By analyzing the total and on-axis transmittance of the laser beam we studied the enhanced light-induced director reorientation (Jánossy effect) in a nematic liquid crystal doped with anthraquinone dye molecules that do not have photoinduced conformational transformations. The obtained dependence on the angle between the light polarization E and the initial director n0 shows: first order director reorientation (DR) transition with hysteresis for E , n0; second order reversible DR transition with the extremely low threshold intensity for E , n0; sign inversion of the nonlinear refractive index and DR in the intermediate geometry. The data suggest a presence of two different kinds of dipoles in the system: those absorbing light and those giving rise to the nonlinear refractive index. (© 2006 by Astro, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] A relaxed model and its homogenization for nematic liquid crystals in composite materialsMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 10 2004Quan Shen Abstract We analyse a model for equilibrium configurations of composite systems of nematic liquid crystal with polymer inclusions, in the presence of an external magnetic field. We assume that the system has a periodic structure, and consider the relaxed problem on the unit length constraint of the nematic director field. The relaxation of the Oseen,Frank energy functional is carried out by including bulk as well as surface energy penalty terms, rendering the problem fully non-linear. We employ two-scale convergence methods to obtain effective configurations of the system, as the size of the polymeric inclusions tends to zero. We discuss the minimizers of the effective energies for, both, the constrained as well as the unconstrained models. Copyright © 2004 John Wiley & Sons, Ltd. [source] Short wavelength light reflecting films from side-chain liquid crystal homopolymers with chiral spacersPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 9 2001J. M. G. Cowie Abstract A series of acrylate monomers with alkoxy tails of varying lengths are synthesised and polymerised. The butoxy analogue had a stable enantiotropic cholesteric liquid crystalline phase which formed a grandjean texture when prepared as a thin film between glass slides. The polymer was mixed with a low molar mass nematic liquid crystal in various proportions and the pitch of the chiral nematic phases were determined using a cano-wedge cell technique. The polymer prepared from (S)-2-(4-butoxyphenyl-4,-benzoyloxy)-1-methyl ethyl acrylate had a pitch length of 113,nm which indicates that the polymer film could be employed in optical devices requiring selective reflection of light with short wavelengths in the region of 170,nm. Copyright © 2001 John Wiley & Sons, Ltd. [source] Helical polyacetylene,Origins and synthesisTHE CHEMICAL RECORD, Issue 6 2008Kazuo Akagi Abstract We present the origins and synthesis of helical polyacetylene (H-PA) by focusing on its peculiar spiral morphology. Interfacial polymerization of acetylene was carried out in an asymmetric reaction field consisting of chiral nematic liquid crystal (N*-LC) and Ziegler,Natta catalyst. As the N*-LC is composed of nematic liquid crystal and a chiral compound such as a binaphthyl derivative with either the R - or S -configuration, the screw directions of the polyacetylene chain and fibril bundle,and even the spiral morphology,are rigorously controlled by the chirality of the selected compound. Interestingly, the screw directions of the fibril and the bundle in H-PA were found to be opposite to that of N*-LC. It is worthwhile to emphasize that the hierarchical spiral morphology involving the primary to higher order structure is generated in a synthetic polymer such as polyacetylene by using N*-LC as an asymmetric polymerization solvent. © 2008 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 8: 395,406; 2008: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.20163 [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] 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] Design of Biomolecular Interfaces Using Liquid Crystals Containing Oligomeric Ethylene GlycolADVANCED FUNCTIONAL MATERIALS, Issue 13 2010Zhongqiang Yang Abstract An investigation of nematic liquid crystals (LCs) formed from miscible mixtures of 4-cyano-4,-pentylbiphenyl (5CB) and 2-(2-[2-{2-(2,3-difluoro-4-{4-(4- trans -pentylcyclohexyl)-phenyl-phenoxy)ethoxy}ethoxy]ethoxy)ethanol (EG4-LC) is reported, the latter being a mesogen with a tetra(ethylene glycol) tail. Quantitative characterization of the ordering of this LC mixture at biologically relevant aqueous interfaces reveals that addition of EG4-LC (1%,5% by weight) to 5CB causes a continuous transition in the ordering of the LC from a planar (pure 5CB) to a perpendicular (homeotropic) orientation. The homeotropic ordering is also seen in aqueous dispersions of micrometer-sized droplets of the LC mixture, which exhibit enhanced stability against coalescence. These observations and others, all of which suggest partitioning of the EG4-LC from the bulk of the LC to its aqueous interface, are complemented by measurements of the adsorption of bovine serum albumin to the aqueous,LC interface. Overall, the results demonstrate a general and facile approach to the design of LCs with interfaces that present biologically relevant chemical functional groups, assume well-defined orientations at aqueous interfaces, and lower non-specific protein adsorption. The bulk of the LC serves as a reservoir of EG4-LC, thus permitting easy preparation of these interfaces and the potential for spontaneous repair of the EG4-decorated interfaces during contact with biological systems. [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] 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] Cover Picture: Bistable Nematic Liquid Crystals with Self-Assembled Fibers (Adv. Mater.ADVANCED MATERIALS, Issue 6 20056/2005) Abstract The cover shows a recording process using nematic liquid crystal alignment. On p.,692, Kato and co-workers report that reversibly bistable states have been achieved for nematic liquid crystals incorporating a small amount of self-assembled fibers. Homeotropic monodomains and non-aligned multidomains can be fixed and switched by thermal treatment in electric fields. The technique is applied to the formation of rewritable light scattering patterns, as shown on the cover. [source] Organosoluble and transparent polyimides derived from alicyclic dianhydride and aromatic diaminesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2002J. G. Liu Abstract Organosoluble polyimides were synthesized with the alicyclic dianhydride 1,8-dimethylbicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride and aromatic diamines. The polyimides possessed good solubility both in strong dipolar solvents and in common solvents; the thermal decomposition temperature of the polyimides exceeded 420 °C. Strong and flexible films of the polyimides, with the cutoff of ultraviolet,visible absorption lower than 310,320 nm, exhibited good features as the alignment layers for nematic liquid crystals with pretilt angles of 1.5,2.9°. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 110,119, 2002 [source] Global weak solution to the flow of liquid crystals systemMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 17 2009Fei Jiang Abstract In this paper, we study a simplified system for the flow of nematic liquid crystals in a bounded domain in the three-dimensional space. We derive the basic energy law which enables us to prove the global existence of the weak solutions under the condition that the initial density belongs to L,(,) for any . Especially, we also obtain that the weak solutions satisfy the energy inequality in integral or differential form. Copyright © 2009 John Wiley & Sons, Ltd. [source] A relaxed model and its homogenization for nematic liquid crystals in composite materialsMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 10 2004Quan Shen Abstract We analyse a model for equilibrium configurations of composite systems of nematic liquid crystal with polymer inclusions, in the presence of an external magnetic field. We assume that the system has a periodic structure, and consider the relaxed problem on the unit length constraint of the nematic director field. The relaxation of the Oseen,Frank energy functional is carried out by including bulk as well as surface energy penalty terms, rendering the problem fully non-linear. We employ two-scale convergence methods to obtain effective configurations of the system, as the size of the polymeric inclusions tends to zero. We discuss the minimizers of the effective energies for, both, the constrained as well as the unconstrained models. Copyright © 2004 John Wiley & Sons, Ltd. [source] Angle-resolved Mueller polarimeter using a microscope objectivePHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2008S. Ben Hatit Abstract A new Mueller polarimeter based on liquid crystals and a microscope objective is presented for the characterization of diffraction gratings in a conical diffraction mounting. Fast measurements of complete Mueller matrices over a range of polar angles , (0,60°) and azimuthal angles , (0,360°) are achieved without mechanical movements. The polarization states generator and analyzer are based on nematic liquid crystals. The angular range is achieved through focalization of light over the measured sample with a microscope objective of high numerical aperture and imaging of the objective's back Fourier plane on a CCD. Results on isotropic samples and diffraction gratings are shown. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Photochromic composites based on porous stretched polyethylene filled by nematic liquid crystal mixturesPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 2 2010Alexey Bobrovsky Abstract A number of the novel photochromic polyethylene (PE)-based liquid crystal composites were prepared and studied. The oriented stretched porous polyethylene films were used as the polymer matrices. Commercial liquid crystals doped with new photochromic compounds were introduced into PE films and photo-optical properties of the obtained composites were investigated. It was shown that a director of nematic liquid crystals is highly oriented along the stretching axis of PE films resulting in noticeable linear dichroism of the PE composite films. New approaches for reversible or irreversible image recording on PE LC composites by UV irradiation were demonstrated. Copyright © 2009 John Wiley & Sons, Ltd. [source] | ||||||||||||||||