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Showing papers on "Liquid crystal published in 2002"


Journal ArticleDOI
TL;DR: This work shows the stabilization of blue phases over a temperature range of more than 60 K including room temperature (260–326 K), and demonstrates an electro-optical switching with a response time of the order of 10−4 s for the stabilized blue phases at room temperature.
Abstract: Blue phases are types of liquid crystal phases that appear in a temperature range between a chiral nematic phase and an isotropic liquid phase. Because blue phases have a three-dimensional cubic structure with lattice periods of several hundred nanometres, they exhibit selective Bragg reflections in the range of visible light corresponding to the cubic lattice. From the viewpoint of applications, although blue phases are of interest for fast light modulators or tunable photonic crystals, the very narrow temperature range, usually less than a few kelvin, within which blue phases exist has always been a problem. Here we show the stabilization of blue phases over a temperature range of more than 60 K including room temperature (260–326 K). Furthermore, we demonstrate an electro-optical switching with a response time of the order of 10−4 s for the stabilized blue phases at room temperature.

1,876 citations


Journal ArticleDOI
03 May 2002-Science
TL;DR: A liquid crystal system was used for the fabrication of a highly ordered composite material from genetically engineered M13 bacteriophage and zinc sulfide nanocrystals, which spontaneously evolved a self-supporting hybrid film material.
Abstract: A liquid crystal system was used for the fabrication of a highly ordered composite material from genetically engineered M13 bacteriophage and zinc sulfide (ZnS) nanocrystals. The bacteriophage, which formed the basis of the self-ordering system, were selected to have a specific recognition moiety for ZnS crystal surfaces. The bacteriophage were coupled with ZnS solution precursors and spontaneously evolved a self-supporting hybrid film material that was ordered at the nanoscale and at the micrometer scale into approximately 72-micrometer domains, which were continuous over a centimeter length scale. In addition, suspensions were prepared in which the lyotropic liquid crystalline phase behavior of the hybrid material was controlled by solvent concentration and by the use of a magnetic field.

975 citations


Journal ArticleDOI
Takashi Kato1
29 Mar 2002-Science
TL;DR: In this paper, phase segregation and self-assembly are used to enhance anisotropic properties such as ionic conductivity in liquid crystalline materials, such as hydrogen bonding and ionic interactions.
Abstract: Additional functionality can be incorporated into liquid crystalline materials by using phase segregation and self-assembly. Intermolecular interactions such as hydrogen bonding and ionic interactions play key roles in the formation of these complex structures. One-, two-, and three-dimensional phase-segregated structures on various scales of length are formed by self-assembly of a variety of partially incompatible molecules. Such structures can enhance anisotropic properties such as ionic conductivity.

800 citations


Journal ArticleDOI
TL;DR: In this article, the authors have fabricated organic thin-film transistor (OTFT)-driven active matrix liquid crystal displays on flexible polymeric substrates using a low-temperature process.
Abstract: We have fabricated organic thin-film transistor (OTFT)-driven active matrix liquid crystal displays on flexible polymeric substrates. These small displays have 16×16 pixel polymer-dispersed liquid crystal arrays addressed by pentacene active layer OTFTs. The displays were fabricated using a low-temperature process (<110 °C) on flexible polyethylene naphthalate film and are operated as reflective active matrix displays.

792 citations


Journal ArticleDOI
TL;DR: The first observations of lasing in three-dimensional photonic crystals, in the cholesteric blue phase II are reported, showing that distributed feedback is realized in three dimensions, resulting in almost diffraction-limited lasing with significantly lower thresholds than in one dimension.
Abstract: Photonic-bandgap materials, with periodicity in one, two or three dimensions, offer control of spontaneous emission and photon localization. Low-threshold lasing has been demonstrated in two-dimensional photonic-bandgap materials, both with distributed feedback and defect modes. Liquid crystals with chiral constituents exhibit mesophases with modulated ground states. Helical cholesterics are one-dimensional, whereas blue phases are three-dimensional self-assembled photonic-bandgap structures. Although mirrorless lasing was predicted and observed in one-dimensional helical cholesteric materials and chiral ferroelectric smectic materials, it is of great interest to probe light confinement in three dimensions. Here, we report the first observations of lasing in three-dimensional photonic crystals, in the cholesteric blue phase II. Our results show that distributed feedback is realized in three dimensions, resulting in almost diffraction-limited lasing with significantly lower thresholds than in one dimension. In addition to mirrorless lasing, these self-assembled soft photonic-bandgap materials may also be useful for waveguiding, switching and sensing applications.

512 citations



Journal ArticleDOI
TL;DR: In this paper, single and multiwalled carbon nanotubes dispersed in nematic liquid crystal (LC) solvents are found to be orientationally ordered by the nematic matrix, and procedures for the preparation of monolayer and multilayer nanotube films with organization controlled using well-established methods of LC alignment, including grooved surfaces, magnetic fields, and patterned electrodes.
Abstract: Single- and multiwalled carbon nanotubes dispersed in nematic liquid crystal (LC) solvents are found to be orientationally ordered by the nematic matrix. Procedures are demonstrated for the preparation of monolayer and multilayer nanotube films with organization controlled using well-established methods of LC alignment, including grooved surfaces, magnetic fields, and patterned electrodes. LC alignment should be possible with other nanometer-sized building blocks, offering a general route for controlled assembly of organized nanomaterials and devices.

473 citations


Journal ArticleDOI
17 Oct 2002-Nature
TL;DR: This work shows that the attachment of five aromatic groups to one pentagon of a C60 fullerene molecule yields deeply conical molecules that stack into polar columnar assemblies, which should be applicable to other molecules and yield a range of new polar liquid crystalline materials.
Abstract: Polar liquid crystalline materials can be used in optical and electronic applications, and recent interest has turned to formation strategies that exploit the shape of polar molecules and their interactions to direct molecular alignment. For example, banana-shaped molecules align their molecular bent within smectic layers, whereas conical molecules should form polar columnar assemblies. However, the flatness of the conical molecules used until now and their ability to flip have limited the success of this approach to making polar liquid crystalline materials. Here we show that the attachment of five aromatic groups to one pentagon of a C(60) fullerene molecule yields deeply conical molecules that stack into polar columnar assemblies. The stacking is driven by attractive interactions between the spherical fullerene moiety and the hollow cone formed by the five aromatic side groups of a neighbouring molecule in the same column. This packing pattern is maintained when we extend the aromatic groups by attaching flexible aliphatic chains, which yields compounds with thermotropic and lyotropic liquid crystalline properties. In contrast, the previously reported fullerene-containing liquid crystals all exhibit thermotropic properties only, and none of them contains the fullerene moiety as a functional part of its mesogen units. Our design strategy should be applicable to other molecules and yield a range of new polar liquid crystalline materials.

353 citations


Journal ArticleDOI
TL;DR: The interaction between spatial optical solitons in undoped nematic liquid crystals is governed by reorientational nonlinearity with a significant nonlocality, and a scalar model accounts for the main features that were experimentally observed.
Abstract: The interaction between spatial optical solitons in undoped nematic liquid crystals is governed by reorientational nonlinearity with a significant nonlocality. We demonstrate several cases of interactions, including crossing, interlacing, and merging of spatial solitons in voltage-biased liquid-crystal cells. A scalar model accounts for the main features that were experimentally observed.

327 citations


Journal ArticleDOI
TL;DR: A range of monodomain nematic liquid-crystal elastomers containing differing proportions of photoisomerizable mesogenic moieties, which turn from a rodlike to a kinked shape upon ultraviolet (uv) irradiation, was studied and theoretical analysis gives a good quantitative agreement with experiment.
Abstract: A range of monodomain nematic liquid-crystal elastomers containing differing proportions of photoisomerizable mesogenic moieties, which turn from a rodlike to a kinked shape upon ultraviolet (uv) irradiation, was studied. Depending on the proportion and positional role of the photosensitive groups in the crosslinked polymer network, different types and magnitudes of response were found. The principle consequence of such photoisomerization is the destabilization of the nematic phase, whose order parameter depends on temperature in a near-critical fashion. Accordingly, the effect of uv irradiation is dramatically enhanced near the critical temperature, with the associated reduction in the nematic order parameter manifesting as a change in the macroscopic shape of the elastomer samples, producing a large uniaxial contraction. Theoretical analysis of this phenomenon gives a good quantitative agreement with experiment.

309 citations


Journal ArticleDOI
14 Nov 2002-Nature
TL;DR: This work has demonstrated how bistability can be robustly engineered into a nematic LC device, by patterning a substrate with an orientational chequerboard pattern that enforces orthogonal LC alignment in neighbouring square domains, and extended this symmetry approach to obtain a tristable surface-aligned nematicLC.
Abstract: It has long been appreciated that liquid-crystal (LC) devices in which the LC molecules adopt multiple stable orientations could drastically reduce the power consumption required for high-information-content displays. But for the commonly used nematic LCs, which are intrinsically uniaxial in symmetry, no industrially feasible multi-stable LC device has been realized1,2,3,4,5,6,7. Recently we demonstrated how bistability can be robustly engineered into a nematic LC device, by patterning a substrate with an orientational chequerboard pattern that enforces orthogonal LC alignment in neighbouring square domains8,9. As a result of the four-fold symmetry of the pattern, the two diagonal axes of the chequerboard become equally stable macroscopic orientations. Here we extend this symmetry approach to obtain a tristable surface-aligned nematic LC. A microscopic pattern exhibiting six-fold symmetry is inscribed on a polyimide surface using the stylus of an atomic force microscope. The hexagonal symmetry of the microscopic orientational domains in turn gives rise to three stable macroscopic LC orientations, which are mutually switchable by an in-plane electric field. The resulting switching mode is surface driven, and hence should be compatible with demanding flexible display applications.

Journal ArticleDOI
TL;DR: In this article, the authors proposed to use anisotropic nano-sized objects to allow micron-scale colloids to link or functionalize with a four-fold valence, similar to the sp3 hybridized chemical bonds associated with, e.g., carbon, silicon and germanium.
Abstract: We propose coating spherical particles or droplets with anisotropic nano-sized objects to allow micron-scale colloids to link or functionalize with a four-fold valence, similar to the sp3 hybridized chemical bonds associated with, e.g., carbon, silicon and germanium. Candidates for such coatings include triblock copolymers, gemini lipids, metallic or semiconducting nanorods and conventional liquid crystal compounds. We estimate the size of the relevant nematic Frank constants, discuss how to obtain other valences and analyze the thermal distortions of ground state configurations of defects on the sphere.

Journal ArticleDOI
TL;DR: In this paper, the authors proposed a 4-fold valence for anisotropic nanosized objects, similar to the sp3 hybridized chemical bonds associated with carbon, silicon, and germanium.
Abstract: We propose coating spherical particles or droplets with anisotropic nanosized objects to allow micron-scale colloids to link or functionalize with a 4-fold valence, similar to the sp3 hybridized chemical bonds associated with, e.g., carbon, silicon, and germanium. Candidates for such coatings include triblock copolymers, gemini lipids, metallic or semiconducting nanorods, and conventional liquid crystal compounds. We estimate the size of the relevant nematic Frank constants, discuss how to obtain other valences and analyze the thermal distortions of ground-state configurations of defects on the sphere.

Journal ArticleDOI
TL;DR: In this paper, the formation of liquid crystalline phases of CdSe semiconductor nanorods has been studied and shown to have great importance for both application and fundamental study.
Abstract: Rodlike molecules form liquid crystalline phases with orientational order and positional disorder. The great majority of materials in which liquid crystalline phases have been observed are comprised of organic molecules or polymers, even though there has been continuing and growing interest in inorganic liquid crystals. Recent advances in the control of the sizes and shapes of inorganic nanocrystals allow for the formation of a broad class of new inorganic liquid crystals. Here we show the formation of liquid crystalline phases of CdSe semiconductor nanorods. These new liquid crystalline phases may have great importance for both application and fundamental study.

Journal ArticleDOI
TL;DR: In this article, the most recent developments in the understanding of structure-property relationships in liquid crystal dimers and higher oligomers are discussed, including trimers and tetramers.
Abstract: A liquid crystal dimer is composed of molecules containing two mesogenic groups linked via a flexible spacer. Initial interest in these materials stemmed from their ability to act as model compounds for semi-flexible main chain liquid crystal polymers but are now of fundamental interest in their own right because their behaviour is significantly different to that of conventional low molar mass liquid crystals. Recently research has begun to focus also on higher monodisperse oligomers such as trimers and tetramers consisting of molecules containing either three or four mesogenic units, respectively, linked via flexible spacers. In this review the most recent developments in our understanding of structure–property relationships in liquid crystal dimers and higher oligomers is discussed.

Journal ArticleDOI
30 Aug 2002-Langmuir
TL;DR: In this paper, the spontaneous self-organization of 1-decyl-3methylimidazolium bromide is shown to result in the formation of a liquid-crystalline gel, thus providing a simple means of preparing a supramolecular assembly.
Abstract: Addition of water to 1-decyl-3-methylimidazolium bromide is shown to result in its spontaneous self-organization and the concomitant formation of a liquid-crystalline gel, thus providing a simple means of preparing a supramolecular assembly comprising a room-temperature ionic liquid.

Journal ArticleDOI
27 Jun 2002-Langmuir
TL;DR: In this paper, the authors report an experimental system that permits optical imaging of the reversible adsorption of amphiphiles at stable, planar interfaces formed between aqueous phases and immiscible thermotropic liquid crystals.
Abstract: We report an experimental system that permits optical imaging of the reversible adsorption of amphiphiles at stable, planar interfaces formed between aqueous phases and immiscible thermotropic liquid crystals. Copper grids (hole sizes of 19−292 μm and thicknesses of 18−20 μm) supported on glass surfaces treated using octadecyltrichlorosilane were impregnated with nematic 4-cyano-4‘-pentylbiphenyl (5CB). Films of 5CB confined within the grids were stable (did not dewet the grid) to immersion into either water, aqueous solutions of sodium dodecyl sulfate (SDS), or aqueous solutions of SDS containing NaCl. Whereas the anchoring of 5CB on the copper grid dominated the appearance of the 5CB when using grids with hole sizes of 19 μm, reversible changes in the orientation of the liquid crystal (observed using polarized light) caused by adsorption of SDS at the liquid crystal−aqueous interface were readily observed when using grids with hole sizes larger than 19 μm. With increasing concentrations of SDS in the aq...

Journal ArticleDOI
TL;DR: In this article, a twisted nematic liquid-crystal device (LCD) was fabricated by doping with Pd nanoparticles covered with another kind of liquidcrystal molecules, which exhibited a frequency modulation response to an applied alternative voltage wave form.
Abstract: Palladium nanoparticles covered with liquid-crystal molecules were prepared by UV irradiation of an alcohol solution of palladium(II) acetate in the presence of liquid-crystal molecules. The prepared Pd nanoparticles have an average diameter of 2.5 nm. A twisted nematic (TN) liquid-crystal device (LCD) was fabricated by doping with Pd nanoparticles covered with another kind of nematic liquid-crystal molecules. In this device the sign of the dielectric anisotropy (Δe) of the liquid-crystal molecules, which cover Pd nanoparticles, is opposite to that of nematic liquid-crystal molecules, which work as the host of the device (Δe>0). The TN-LCD cell fabricated in this research exhibits a frequency modulation response to an applied alternative voltage wave form.

MonographDOI
01 Jan 2002
TL;DR: In this article, the main types and classification distribution functions and order parameters physical properties of liquid crystals are described, including properties of nematic liquid crystals, elastostatics and nematodynamics.
Abstract: Liquid crystals: main types and classification distribution functions and order parameters physical properties of liquid crystals nematic liquid crystals nematic liquid crystals - elastostatics and nematodynamics smectic liquid crystals liquid crystals of disc-like molecules polymer liquid crystals chiral liquid crystals lyotropic liquid crystals defects and textures in liquid crystals.

Journal ArticleDOI
TL;DR: In this article, the collisional behavior of solitons in a nonlocal medium is exploited to steer a signal in angle and output position, and a power-dependent X junction, AND, and NOR gates are demonstrated.
Abstract: Using mW light beams to generate spatial solitons in nematic liquid crystals, all-optical switching/logic can be performed on a signal launched in the soliton-induced waveguides. Through the collisional behavior of solitons in a nonlocal medium, the signal can be steered in angle and output position. A power-dependent X junction, AND, and NOR gates are demonstrated.

Patent
27 Nov 2002
TL;DR: An improved liquid crystal device and manufacturing method for same are described in this paper, where a pair of substrates, between which a liquid crystal layer is disposed, is joined with pillars inbetween functioning as spacers which are provided of photocurable resin by photolithography.
Abstract: An improved liquid crystal device and manufacturing method for same are described. In the device, a pair of substrates, between which a liquid crystal layer is disposed, is joined with pillars inbetween functioning as spacers which are provided of photocurable resin by photolithography. With this structure, the spacers can be in surface contact with the inside surfaces of the substrates on which electrode arrangement and active devices are formed.

Journal ArticleDOI
TL;DR: In this paper, conductive polyaniline nanowires in emeraldine form can be deposited by potentiodynamic electropolymerization from a reverse hexagonal liquid crystalline phase where one-dimensional aqueous channels can serve as space-confined reactors.
Abstract: Conductive polyaniline nanowires in emeraldine form can be deposited by potentiodynamic electropolymerization from a reverse hexagonal liquid crystalline phase where one-dimensional (1D) aqueous channels can serve as space-confined reactors. Polyaniline nanowire bundles with single-wire diameter of 50–70 nm and length of several microns were obtained from surfactant sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reverse hexagonal liquid crystalline phase. Impedance measurement suggests improved ordering of the reverse hexagonal liquid crystal under external electric field during the electropolymerization process. This enhanced ordering appears essential for the nanowire growth. The nanowires obtained can be easily collected by a simple washing process.


Journal ArticleDOI
TL;DR: In this paper, a concept to electrically control the scattering of light is introduced, which is to embed noble metal nanoparticles in an electro-optical material such as a liquid crystal in order to induce a spectral shift of the particle plasmon resonance by applying an electric field.
Abstract: A concept to electrically control the scattering of light is introduced. The idea is to embed noble metal nanoparticles in an electro-optical material such as a liquid crystal in order to induce a spectral shift of the particle plasmon resonance by applying an electric field. Light scattering experiments on single gold nanoparticles show that spherically shaped nanoparticles become optically spheroidal when covered by an anisotropic liquid crystal. The two particle plasmon resonances of the optically spheroidal gold nanoparticles can be spectrally shifted by up to 50 meV when electric fields of more than 10 kV/cm are applied.

Journal ArticleDOI
TL;DR: In this article, the authors present a recent progress in modeling and simulation of the flow of nematic liquid crystals using the Leslie-Ericksen (LE) theory and the Doi theory.
Abstract: ▪ Abstract Recent progress in modeling and simulation of the flow of nematic liquid crystals is presented. The Leslie-Ericksen (LE) theory has been successful in elucidating the flow of low molar-mass nematics. The theoretical framework for the flow of polymeric nematic liquid crystals is still evolving; extensions of the Doi theory capture qualitative features of the flow of polymeric nematics in simple geometries, but these theories have not been shown to predict texture development in flow. Mesoscopic theories for textured materials based on spatial averaging capture only some qualitative features of nonrectilinear liquid-crystalline polymer flow. Interfacial effects in liquid-crystalline systems have begun to receive attention in the context of interfacial viscoelasticity and the dynamics of dispersed liquid-crystalline polymers in immiscible blends.


Journal ArticleDOI
TL;DR: The dependence of the far-field intensity on sample position due to intensity-dependent optical nonlinearities has been analyzed on the basis of the thermal-lens model of Gordon et al. as discussed by the authors.
Abstract: We carried out Z-scan measurements on lyotropic liquid crystals and on lyotropic liquid crystals doped with ferrofluid. In these experiments, the sample is translated through the focal region of a focused Gaussian laser beam. The dependence of the far-field intensity on sample position due to intensity-dependent optical nonlinearities has been analyzed on the basis of the thermal-lens model of Gordon et al. and the Gaussian decomposition analysis of Sheik-Bahae et al. The thermal-lens model is nonlocal in space and time, whereas the Gaussian decomposition is predicated on a strictly local response. We compare the goodness of fit of the predictions of these models to experimental data, and we discuss limitations of these models in describing Z-scan experiments on systems with nonlocal response.

Journal ArticleDOI
TL;DR: In this article, the formation of liquid crystalline phases in concentrated solutions of high aspect ratio (13-18) gold nanorods by polarizing microscopy, transmission electron microscopy and small angle X-ray scattering was observed.
Abstract: Gold nanorods have been prepared in aqueous solution using a seed-mediated growth approach in the presence of surfactant. We observe the formation of liquid crystalline phases in concentrated solutions of high aspect ratio (13–18) gold nanorods by polarizing microscopy, transmission electron microscopy, and small angle X-ray scattering. These phases, which are stable up to 200 °C, exhibit concentration-dependent orientational order.

Journal ArticleDOI
TL;DR: In this article, the phase behavior of achiral banana-shaped molecules was studied by computer simulation and the dependence on temperature of systems of N=1024 rigid banana-shape molecules with bending angle φ =140° has been studied by means of Monte Carlo simulations in the isobaric-isothermal ensemble.
Abstract: The phase behaviour of achiral banana-shaped molecules was studied by computer simulation. The banana-shaped molecules were described by model intermolecular interactions based on the Gay-Berne potential. The characteristic molecular structure was considered by joining two calamitic Gay-Berne particles through a bond to form a biaxial molecule of point symmetry group C 2v with a suitable bending angle. The dependence on temperature of systems of N=1024 rigid banana-shaped molecules with bending angle φ =140° has been studied by means of Monte Carlo simulations in the isobaric-isothermal ensemble (NpT). On cooling an isotropic system, two phase transitions characterized by phase transition enthalpy, entropy and relative volume change have been observed. For the first time by computer simulation of a many-particle system of banana-shaped molecules, at low temperature an untilted smectic phase showing a global phase biaxiality and a spontaneous local polarization in the layers, i.e. a local polar arrangement...

Journal ArticleDOI
TL;DR: In this paper, the rotational diffusion of the azo dye molecules in the field of the polarized light was investigated and the synthesis and properties of azo dyes that can be used for photoaligning liquid crystals (LCs) were investigated.
Abstract: The synthesis and properties of azo dyes that can be used for photoaligning liquid crystals (LCs) have been investigated. The structures and the synthetic procedure for the azo dyes are presented. The photoaligning of azo dyes takes place purely due to the reorientation of the molecular absorption oscillators perpendicular to the UV light polarization. The qualitative model for the phenomenon in terms of the rotational diffusion of the azo dye molecules in the field of the polarized light is discussed. The order parameters S = -0.4 (80% of the maximum absolute value S m = -0.5) were measured from the polarized absorption spectra at the wavelength 372 nm. A temperature stable pretilt angle of 5.3° was obtained by a two-step exposure of the azo dye film using normally incident polarized light followed by oblique non-polarized light. The azimuthal anchoring energy of the photoaligned substrate was Aϕ , 10−4 J m−2, which is the same as the anchoring of the rubbed polyimide (PI) layer. The voltage holding rati...