Showing papers on "Liquid crystal published in 1998"

The Structure and Rheology of Complex Fluids

Abstract: Part I: Fundamentals 1. Introduction to Complex Fluids 1.3 Rheological Measurements and Properties 1.4 Kinematics and Stress 1.5 Flow, Slip, and Yield 1.6 Structural Probes of Complex Fluids 1.7 Computational Methods 1.8 The Stress Tensor 1.9 Summary 2. Basic Forces 2.1 Intoduction 2.3 Van der Waals Interactions 2.4 Electrostatic Interactions 2.5 Hydrogen-Bonding, Hydrophobic, and Other Interactions 2.6 Summary Part II: Polymers, Glassy Liquids, and Polymer Gels 3. Polymers 3.1 Introduction 3.2 Equilibrium Properties 3.3 Intrinsic Viscosity and Overlap Concentration 3.4 Elementary Molecular Theories 3.5 Linear Viscoelasticity and Time-Temperature Superposition 3.6 The Rheology of Dilute Polymer Solutions 3.7 The Rheology of Entangled Polymers 3.8 Summary 4. Glassy Liquids 4.1 Introduction 4.2 Phenomenology of the Glass Transition 4.3 Free-Volume Theories 4.4 Entropy Theories 4.5 Nonlinear Relaxation and Aging 4.6 Mode-Coupling Theory and Colloidal Hard-Sphere Glasses 4.7 Analog Models 4.8 Rheology of Glassy Liquids 4.9 Summary 5. Polymer Gels 5.1 Introduction 5.2 Gelation Theoies 5.3 Rheology of Chemical Gels and Near-Gels 5.4 Rheology of Physical Gels 5.5 Summary Part III: Suspensions 6. Particulate Suspensions 6.1 Introduction 6.2 Hard, and Slightly Deformable Spheres 6.3 Nonspherical Particles 6.4 Electrically Charged Particles 6.5 Particles in Viscoelastic Liquids: "Filled Melts" 6.6 Summary 7. Particulate Gels 7.1 Introduction 7.2 Particle Interactions in Suspensions 7.3 Rheology of Particulate Gels 7.4 Summary 8. Electro- and Magneto-Responsive Suspensions 8.1 Introduction 8.2 Electrorheological Fluids 8.3 Magnetorheological Fluids 8.4 Ferrofluids 8.5 Summary 9. Foams, Emulsions, and Blends 9.1 Introduction 9.2 Emulsion Preparation 9.3 Rheology of Emulsions and Immiscible Blends 9.4 Structure and Coarsening of Foams 9.5 Rheology of Foams 9.6 Summary Part IV: Liquid Crystals and Self-Assembling Fluids 10. Liquid Crystals 10.1 Introduction 10.2 Nematics 10.3 Cholesterics: Chiral Nemantics 10.4 Smectics 10.5 Summary 11. Liquid Crystalline Polymers 11.1 Introduction 11.2 Molecular Characteristics of Liquid Crystalline Polymers 11.3 Flow Properties of Nematic LCP's 11.4 Molecular Dynamics of Polymeric Nematics 11.5 Molecular Theory for the Rheology of Polymeric Nematics 11.6 Summary 12. Surfactant Solutions 12.1 Introduction 12.2 Methods of Predicting Microstructures 12.3 Disordered Micellar Solutions 12.4 Surfactant Liquid Crystals 12.5 Summary 13. Block Copolymers 13.1 Introduction 13.2 Thermodynamics of Block Copolymers 13.3 Rheology and Shear-Aligning of Block Copolymers 13.4 Summary Appendix: Momentum-Balance Equations in the Absence of Inertia

Effect of microcrystallite preparation conditions on the formation of colloid crystals of cellulose

Abstract: Stable colloidal suspensions of cellulose microcrystallites may be prepared from filter paper by sulfuric acid hydrolysis. Above a critical concentration, the suspensions form a chiral nematic ordered phase, or ‘colloid crystal’. The preparation conditions govern the properties of the individual cellulose microcrystallites, and hence the liquid crystalline phase separation of the cellulose suspensions. The particle properties and the phase separation of the suspensions were strongly dependent on the hydrolysis temperature and time, and on the intensity of the ultrasonic irradiation used to disperse the particles. The particle size of the microcrystallites was characterized with transmission electron microscopy and photon correlation spectroscopy. The surface charge was determined by conductometric titration. It was possible to fractionate the microcrystallites by size using the partitioning between isotropic and liquid crystalline phases; the longer microcrystallites migrate to the liquid crystalline phase

Electronic liquid-crystal phases of a doped Mott insulator

Abstract: The character of the ground state of an antiferromagnetic insulator is fundamentally altered following addition of even a small amount of charge1. The added charge is concentrated into domain walls across which a π phase shift in the spin correlations of the host material is induced. In two dimensions, these domain walls are ‘stripes’ which can be insulating2,3 or conducting4,5,6 — that is, metallic ‘rivers’ with their own low-energy degrees of freedom. However, in arrays of one-dimensional metals, which occur in materials such as organic conductors7, interactions between stripes typically drive a transition to an insulating ordered charge-density-wave (CDW) state at low temperatures. Here it is shown that such a transition is eliminated if the zero-point energy of transverse stripe fluctuations is sufficiently large compared tothe CDW coupling between stripes. As a consequence, there should exist electronic quantum liquid-crystal phases, which constitute new states of matter, and which can be either high-temperature superconductors or two-dimensional anisotropic ‘metallic’ non-Fermi liquids. Neutron scattering and other experiments in the copper oxide superconductor La1.6−xNd0.4SrxCuO4 already provide evidence for the existence of these phases in at least one class of materials.

Electro-optic characteristics and switching principle of a nematic liquid crystal cell controlled by fringe-field switching

Abstract: We have fabricated a nematic liquid crystal cell associated with a homogeneously aligned to twisted transition of a liquid crystal director. In the absence of an electric field, the liquid crystal molecule is homogeneously aligned under the crossed polarizers, and thus the cell appears to be black. When a fringe field induced by interdigital electrodes is applied, liquid crystal molecules rotate in plane even above electrodes and thus the cell transmits light. The device exhibits a high transmittance ratio as well as a wide viewing angle, which solves a long standing problem of low transmittance existing in the conventional in-plane switching mode. We show that the distance between electrodes smaller than the width of an electrode and cell gap is required for generating fringe field with applied voltage and rotating molecules above electrodes. We also investigate the mechanism of fringe-field switching and dependence of electro-optic effect on different cell conditions and dielectric anisotropy of liquid ...

Ionic liquid crystals: hexafluorophosphate salts

Abstract: A series of novel hexafluorophosphate salts, based on N,N′-dialkylimidazolium and substituted N-alkylpyridinium cations, display liquid crystalline behaviour at temperatures above their melting point. The temperature range over which liquid crystalline behaviour is observed increases markedly with increasing alkyl chain length. Alkyl substitution at the 3- and 4-positions on the pyridinium ring results in a decrease in the melting point compared with the equivalent unsubstituted salt, but also leads to a large decrease in the tendency towards liquid crystalline behaviour (or mesogenicity). The salts prepared are fully characterised using a wide variety of techniques, including NMR and IR spectroscopy, DSC, and single crystal X-ray diffraction in the case of 1-dodecyl-3-methylimidazolium hexafluorophosphate. The effect of preparing mixtures containing different proportions of two cations is also reported.

Topological defects and interactions in nematic emulsions

Abstract: Inverse nematic emulsions, in which surfactant-coated water droplets are dispersed in a nematic host fluid, have distinctive properties that set them apart from dispersions of two isotropic fluids or of nematic droplets in an isotropic fluid. We present a comprehensive theoretical study of the distortions produced in the nematic host by the dispersed droplets and of solvent-mediated dipolar interactions between droplets that lead to their experimentally observed chaining. A single droplet in a nematic host acts like a macroscopic hedgehog defect. Global boundary conditions force the nucleation of compensating topological defects in the nematic host. Using variational techniques, we show that in the lowest energy configuration, a single water droplet draws a single hedgehog out of the nematic host to form a tightly bound dipole. Configurations in which the water droplet is encircled by a disclination ring have higher energy. The droplet dipole induces distortions in the nematic host that lead to an effective dipole-dipole interaction between droplets, and hence to chaining.

Spinodal dewetting in liquid crystal and liquid metal films

Abstract: Theory predicts that dewetting of a homogeneous liquid film from a solid surface may proceed via unstable surface waves on the liquid. This phenomenon, usually termed spinodal dewetting, has been sought after in many systems. Observations in liquid crystal and liquid metal films showed that, as expected, the emerging structures were similar to those found for spinodal decomposition in mixtures. Certain differences, however, could be attributed to peculiarities of the wetting forces in these two dissimilar systems, thereby demonstrating the role of nonlinearities inherent in the wetting forces.

Optical Amplification of Ligand-Receptor Binding Using Liquid Crystals

Abstract: Liquid crystals (LCs) were used to amplify and transduce receptor-mediated binding of proteins at surfaces into optical outputs. Spontaneously organized surfaces were designed so that protein molecules, upon binding to ligands hosted on these surfaces, triggered changes in the orientations of 1- to 20-micrometer-thick films of supported LCs, thus corresponding to a reorientation of ∼10 5 to 10 6 mesogens per protein. Binding-induced changes in the intensity of light transmitted through the LC were easily seen with the naked eye and could be further amplified by using surfaces designed so that protein-ligand recognition causes twisted nematic LCs to untwist. This approach to the detection of ligand-receptor binding does not require labeling of the analyte, does not require the use of electroanalytical apparatus, provides a spatial resolution of micrometers, and is sufficiently simple that it may find use in biochemical assays and imaging of spatially resolved chemical libraries.

Non-conventional liquid crystals—the importance of micro-segregation for self-organisation

Abstract: Selected examples of recently synthesised non-conventional liquid crystals are highlighted. These are cyclic and open chain oligoamides, molecules containing tetrahedral or octahedral central cores, dendrimers, polyhydroxy amphiphiles, taper shaped molecules, liquid crystals with perfluorinated or oligosiloxane segments, rod-coil molecules as well as special types of polycatenar and laterally branched calamitic molecules. Their mesomorphic properties are discussed as a consequence of incompatibility, micro-segregation and space filling. The analysis is based on the general concept of amphiphilicity, which describes any chemical or structural contrast within a molecule, such as hydrophilic/lipophilic, polar/non-polar, hydrocarbon/fluorocarbon, oligosiloxane/hydrocarbon or rigid/flexible. These non-conventional liquid crystals will be regarded as block molecules. Depending on the degree of chemical and structural difference and the size of the different building blocks micro-segregation can occur with formation of lamellar, columnar or spheroidal aggregates which organise to smectic, columnar and cubic mesophases. The striking analogies between the polymorphism of thermotropic and lyotropic liquid crystals and block-copolymers are pointed out.

Inverted and multiple nematic emulsions

Abstract: We investigate experimentally the structures that form when small colloidal particles are suspended in a nematic solvent. These structures are anisotropic, and their formation is driven by interactions arising from the orientational elasticity of the nematic solvent. By using inverted and multiple nematic emulsions composed of water droplets dispersed in a thermotropic liquid crystal, we identify the nature of these interactions, and demonstrate that they can be controlled by the anchoring of the liquid crystal molecules at the surfaces of the droplets. When the anchoring is normal, the droplets form linear chains, suggesting a long-range dipole-dipole attraction between the particles. By contrast, the interactions are repulsive at short range, and prevent contact of the droplets, thereby stabilizing them against coalescence. When the anchoring is planar, the droplets generate distortions that have a quadrupolar character. The resultant elastic interactions lead to more compact, but still anisotropic, clusters.

Vertically-aligned (VA) liquid crystal display device

Abstract: A vertically alignment mode liquid crystal display device having an improved viewing angle characteristic is disclosed. The disclosed liquid crystal display device uses a liquid crystal having a negative anisotropic dielectric constant, and orientations of the liquid crystal are vertical to substrates when no voltage being applied, almost horizontal when a predetermined voltage is applied, and oblique when an intermediate voltage is applied. At least one of the substrates includes a structure as domain regulating means, and inclined surfaces of the structure operate as a trigger to regulate azimuths of the oblique orientations of the liquid crystal when the intermediate voltage is applied.

Helical Polyacetylene Synthesized with a Chiral Nematic Reaction Field

Abstract: Helical polyacetylene was synthesized under an asymmetric reaction field consisting of chiral nematic (N*) liquid crystals (LCs). The chiral nematic LC was prepared by adding a chiroptical binaphthol derivative as a chiral dopant to a mixture of two nematic LCs. Acetylene polymerizations were carried out using the catalyst titanium tetra-n-butoxide-triethylaluminum dissolved in the chiral nematic LC solvent. The polyacetylene film was shown by scanning electron microscopy to consist of clockwise or counterclockwise helical structure of fibrils. A Cotton effect was observed in the region of the pi --> pi* transition of the polyacetylene chain in circular dichroism spectra. The high electrical conductivities of approximately 1500 to 1800 siemens per centimeter after iodine doping and the chiral helicity of these films may be exploited in electromagnetic and optical applications.

Electrically switchable mirrors and optical components made from liquid-crystal gels

Abstract: In liquid-crystal (LC) display devices, patterned electrodes are used to effect switching of molecular orientation within a pixel element, and thin layers of a material (typically a polymer) at the surfaces of the cell plates induce the liquid-crystal molecules to revert to their original orientation after the electric field is switched off1. Because of their periodic variation in refractive index, cholesteric LC phases (which have a helical variation in orientation) reflect light at a wavelength determined by the helical pitch2,3, and so can potentially be used in switchable optical devices such as shutters, reflectors and notch- and band-pass filters. But orientation layers are unable to restore the initial orientation in cholesteric phases. They can instead be given an internal ‘memory’ of their initial orientation by creating an anisotropic polymer network within the system using in situ photopolymerization4. Here we show that such crosslinked cholesteric gels can be used to produce fast electrically switchable reflectors with narrow- to broad-band widths (the latter having a silvery mirror-like appearance). By photopolymerizing in a patterned manner, we can make image recordings in the gels which become visible on application of an electric field. These patterned gels offer the prospect of making optical components such as lenses and gratings by holographic recording.

Measurement of Residual Dipolar Couplings of Macromolecules Aligned in the Nematic Phase of a Colloidal Suspension of Rod-Shaped Viruses

Abstract: Residual dipolar couplings provide long-range structural restraints for NMR structure determination of macromolecules1 that are not accessible by most other NMR observables, which are dependent on close spatial proximity of atoms.2 Thus, dipolar couplings provide restraints for defining the relative orientation of structural elements where the information content provided by the NOE restraints is insufficient, either due to the lack of NOEs or to the accumulation of errors over long distances.2 In addition, the use of various different dipolar couplings (e.g., DNH, DNC′, DHNC′, DCH, DCRC′) along the protein backbone narrowly restricts the backbone torsion angles.3 The measurement of residual dipolar couplings requires that the macromolecule of interest be weakly aligned in the magnetic field. Alignment can be induced in a number of ways including the magnetic field itself4 or the use of a liquid crystalline medium.5 In general, alignment arising from the former is very small and cannot be exploited on a routine basis.2,4 Moderate degrees of alignment, while retaining the resolution, sensitivity, and simplicity obtained in the isotropic phase, can be obtained by dissolving macromolecules in a very dilute liquid crystalline phase6 of lipid bicelles.7 For biological macromolecules, the liquid crystalline medium must possess a number of key features; it has to be miscible with water, it should not bind to the macromolecule of interest, it should be stable at dilute concentrations over long periods of time, and it should only induce moderate degrees of alignment. While the bicelles have been successfully applied in a number of cases,3,6 there are instances where the protein, possibly due to the presence of surface hydrophobic patches, adversely affects the stability of the bicelle, leading to phase separation of its components.8 In addition, the bicelles are thermotropic, adopting a liquid crystalline phase over a narrow range of temperatures, and are only stable over a limited pH range due to acidand base-catalyzed hydrolysis of ester bonds.6 In this paper, we show that the nematic phase of a colloidal suspension of rod-shaped viruses provides an alternative to bicelles. Suspensions of charged, rod-shaped viruses, such as the filamentous baceriophage fd and tobacco mosaic virus (TMV), are known to undergo an isotropic-nematic phase transition at relatively low concentrations.9 Figure 1 displays the residual onebond N-H (DNH) dipolar couplings for a ∼0.5 mM solution of streptococcal protein G (56 residues)10 in colloidal suspensions of ∼28 mg/mL fd and ∼50 mg/mL TMV.11 The values of DNH range from +15 to -15 Hz in the case of the fd suspension and +10 to -10 Hz in the case of the TMV suspension. The general expression for the residual dipolar coupling DAB(θ,φ) between two directly coupled nuclei A and B is given by Da{(3cos θ 1) + /2R(sin θ cos2φ)}where Da and Dr in units of hertz are the axial and rhombic components of the * To whom correspondence should be addressed. E-mail: G.M.C., clore@speck.niddk.nih.gov. A.M.G., gronenborn@vger.niddk.nih.gov. Tel.: (301) 496-0782. Fax: (301) 496-0825. (1) Tjandra, N.; Omichinski, J. G.; Gronenborn, A. M.; Clore, G. M.; Bax, A. Nat. Struct. Biol. 1997, 4, 732-738. (2) Clore, G. M.; Gronenborn, A. M. Nat. Struct. Biol. 1997, 4, 849-853. (3) (a) Bewley, C. A.; Kustafson, K. R.; Boyd, M. R., Covell, D. G.; Bax, A.; Clore, G. M.; Gronenborn, A. M. Nat. Struct. Biol. 1998, 5, 571-578. (b) Cai, M.; Huang, Y.; Zheng, R.; Wei, S. Q.; Ghirlando, R.; Lee, M. S.; Craigie, R.; Gronenborn, A. M.; Clore, G. M. Nat. Struct. Biol. 1998, 5, 903909. (4) Bothner-By, A. A. In Encyclopedia of Nuclear Magnetic Resonance; Grant, D. M., Harris, R. K., Eds.; Wiley: Chichester, 1996; pp 2932-2938. (5) Emsley, J. W.; Lindon, J. C. NMR spectroscopy using Liquid Crystal SolVents; Peregamon Press: New York, 1975. (6) (a) Tjandra, A.; Bax, A. Science 1997, 278, 1111-1114. (b) Cornilescu, G.; Marquardt, J. L.; Ottiger, M.; Bax, A. J. Am. Chem. Soc. 1998, 120, 68366837. (c) Ramirez, B. E.; Bax, A. J. Am. Chem. Soc. 1998, 120, 9106-9107. (7) Sanders, C. R.; Hare, B. J.; Howard, K. P.; Prestegard, J. H. Prog. Nucl. Magn. Reson. Spectrosc. 1994, 26, 421-444. (8) Examples at the NIH where the bicelles have proved to be unstable include enzyme I, the enzyme I-HPR complex, the N-terminal domain of HIV-1 integrase coordinated to cadmium, SIV gp41 (G.M.C. and A.M.G., unpublished data), the VR domain of a T-cell inhibitor (J. S. Hu and A. Bax, personal communication), and HIV protease (D. Torchia, personal communication). (9) (a) Fraden, S.; Maret, G.; Caspar, D. L. D.; Meyer, R. B. Phys. ReV. Lett. 1989, 63, 2068-2071. (b) Tang, J.; Fraden, S. Liq. Cryst. 1995, 4, 459467. (10) Protein G (Gronenborn, A. M.; Filpula, D. R.; Essig, N. Z.; Achari, A.; Whitlow, M., Wingfield, P. T.; Clore, G. M. Science 1991, 253, 657661) in a colloidal suspension of fd was prepared by adding the protein to a dilute (∼1-5 mg/mL) solution of fd in the appropriate buffer, followed by concentration to ∼0.5 mM protein and ∼25-28 mg/mL fd. Protein G in a colloidal suspension of TMV was prepared by adding a stock solution of TMV (210 mg/mL) in water to a protein solution in buffer to yield ∼0.5 mM in protein and ∼50 mg/mL TMV. Over a period of about 6 h, the TMV solution separated into a lower birefringent nematic phase and an upper isotropic phase. The upper isotropic phase was removed, and only the nematic phase was employed for NMR. As the pH of the solution approaches the pI of the virus particles (∼4.2 for fd and ∼3 for TMV), precipitation occurs. Once precipitation of fd has occurred, birefringence cannot be recovered, and the suspension remains isotropic, even though the fd particles can be resolubilized by raising the pH. Thus, solutions of fd should not be taken to pH values below 5.0. At this time, we have also employed suspensions of fd phage successfully for both enzyme I and the enzyme I-HPr complex, where previously a variety of lipid bicelles had proved to be unstable. Figure 1. Plot of DNH measured at 750 MHz versus residue number for the protein G domain (∼0.5 mM) dissolved in the nematic phase of a colloidal suspension of fd (∼28 mg/mL) and TMV (∼50 mg/mL) at 20 °C in 50 mM sodium phosphate buffer pH 5.4. The secondary structure and a ribbon diagram of protein G10 are shown below the figure, together with the axes for the alignment tensor obtained in the nematic phase of fd (top) and DMPC/DHPC bicelles (bottom). 10571 J. Am. Chem. Soc. 1998, 120, 10571-10572

Incorporation of Photoluminescent Polarizers into Liquid Crystal Displays

Abstract: Liquid crystal displays, the dominant flat panel display technology, are limited in brightness and energy efficiency because of the use of absorbing polarizers and color filters. Liquid crystal-based photoluminescent display devices have been fabricated that use thin, polarized photoluminescent layers that have highly anisotropic absorption or emission. These layers both polarize light and generate bright color. This approach can simplify device design and substantially increase device brightness, contrast, efficiency, and (in specific configurations) viewing angle.

Characterization of magnetically oriented phospholipid micelles for measurement of dipolar couplings in macromolecules.

Abstract: Weak alignment of solute molecules with the magnetic field can be achieved in a dilute liquid crystalline medium, consisting of an aqueous mixture of dimyristoyl-phosphatidylcholine (DMPC) and dihexanoyl-phosphatidylcholine (DHPC). For a certain range of molar ratios, DMPC and DHPC can form large, disc-shaped particles, commonly referred to as bicelles (Sanders and Schwonek, 1992), which cooperatively align in the magnetic field and induce a small degree of alignment on asymmetrically shaped solute molecules. As a result, dipolar couplings between pairs of 1H, 13C or 15N nuclei are no longer averaged to zero by rotational diffusion and they can be readily measured, providing valuable structural information. The stability of these liquid crystals and the degree of alignment of the solute molecules depend strongly on experimental variables such as the DMPC:DHPC ratio and concentration, the preparation protocol of the DMPC/DHPC mixtures, as well as salt, temperature, and pH. The lower temperature limit for which the liquid crystalline phase is stable can be reduced to 20 degrees C by using a ternary mixture of DHPC, DMPC, and 1-myristoyl-2-myristoleoyl-sn-glycero-3-phosphocholine, or a binary mixture of DHPC and ditridecanoyl-phosphatidylcholine. These issues are discussed, with an emphasis on the use of the medium for obtaining weak alignment of biological macromolecules.

Enhanced Ordering of Liquid Crystalline Suspensions of Cellulose Microfibrils: A Small Angle Neutron Scattering Study

Abstract: Small angle neutron scattering, SANS, was used to characterize the enhanced ordering induced by magnetic and shear alignment of chiral nematic liquid crystals of cellulose microfibrils in aqueous suspension. In a ∼2 T magnetic field the chiral nematic phase exhibits a uniform orientation over an entire 10 mL sample. SANS data confirmed that the cholesteric axis of this phase aligns along the magnetic field with implications that the distance between microfibrils is shorter along the cholesteric axis than perpendicular to it. This is consistent with the hypothesis that cellulose microfibrils are helically twisted rods. Under shear flow, the alignment of microfibrils changes from chiral nematic to nematic with relative order increasing with increasing shear rate. The axial ratio (length/width) is the key parameter in determining the relative order achieved and in determining the relaxation behavior after shear ceases.

Topological defects in dispersed words and worlds around liquid crystals, or liquid crystal drops

Abstract: The structure of dispersed liquid crystal droplets elasticity, surface tension, and surface anchoring. For sufficiently large droplets with radius R K / W a, where K is the bulk elastic constant and W a is the anchoring coefficient, the surface terms prevail. As a result, the equilibrium states of large droplets contain topologically stable defects. Application of topological theorems to and hedgehogs is reviewed. is controlled by a balance of the bulk defect structures, e.g. monopoles, boojums

Formation of Nematic Liquid Crystals in Suspensions of Hard Colloidal Platelets

Abstract: A novel model system of hard colloidal platelets was observed to phase-separate into an isotropic and a liquid crystalline phase. Polarization microscopy revealed that the liquid crystalline phase was of nematic origin. With such orientational ordering in suspensions of platelike particles already being predicted in the 1940s by Onsager's theory and corroborated more recently by computer simulations, a direct comparison with experimental observations has now become possible. Furthermore, the apparently unhindered formation of a macroscopic nematic phase in a suspension of hard platelets sheds new light on the issue of gelation instead of nematic phase formation in suspensions of clay platelets.

Supramolecular Liquid Crystals. Self-Assembly of a Trimeric Supramolecular Disk and Its Self-Organization into a Columnar Discotic Mesophase

Abstract: 6,7-Bis(alkyloxy)-2,3-dihydrophthalazine-1,4-diones self-assemble into lactim−lactam trimeric disks in solution as demonstrated by SEC and NMR. With suitable substituents, as in Phthal8, Phthal12, and Phthal16, these disks self-organize into a thermotropic, columnar, discotic phase. The disubstituted phthalhydrazide unit thus represents a general motif for the recognition-induced generation of supramolecular, discotic liquid crystals by self-assembly.

Ferroelectric Phenomena in Crystals: Physical Foundations

Abstract: 1. General Characteristics of Structural Phase Transitions in Crystals.- 1.1 First- and Second-Order Structural Phase Transitions.- 1.2 Structural Phase Transitions of Displacive and Order-Disorder Types.- 1.3 The Domain Structure.- 1.4 Ferroelectric Phase Transitions.- 1.5 Basic Types of Ferroelectric Crystals.- 2. Phenomenological Theory of Second-Order Structural Transitions in Crystals.- 2.1 The Incomplete Thermodynamic Potential.- 2.2 Structural Phase Transitions Described by a One-Component Order Parameter.- 2.3 Structural Phase Transitions Described by Two- and Three-Component Order Parameters.- 3. Proper Ferroelectrics: Anomalies of Physical Properties in Phase Transitions.- 3.1 Anomalies of Thermal and Electrical Properties (One-Component Order Parameter).- 3.2 Anomalies of Electrical Properties (Multicomponent Order Parameter).- 3.3 First-Order Phase Transitions Close to Second-Order Transitions.- 3.4 The Tricritical Point.- 4. Dielectric Anomalies in Structural Nonferroelectric and Improper Ferroelectric Phase Transitions.- 4.1 Nonferroelectric Phase Transitions: Dielectric Anomalies.- 4.2 Improper Ferroelectric Phase Transitions: Dielectric Anomalies.- 5. Anomalies of Elastic and Electromechanical Characteristics of Crystals in Second-Order Phase Transitions.- 5.1 One-Component Order Parameter: Elastic Properties of an Isotropic Liquid.- 5.2 One-Component Order Parameter: Elastic Properties of an Anisotropic Crystal.- 5.3 Ferroelectric-Ferroelastics: One-Component Order Parameter with Transformation Properties of the Component of a Second-Rank Tensor and the Polar Vector.- 5.4 Temperature Dependences of "Morphic" Moduli of Elasticity.- 5.5 Two-Component Order Parameter: Elastic Properties of Crystals.- 5.6 Piezoelectric Effect and Electrostriction in the Case of One-Component Order Parameter and Centrosymmetric Paraelectric Phase.- 5.7 Piezoelectric Effect in the Case of One-Component Order Parameter and Noncentrosymmetric Paraelectric Phase.- 6. Fluctuations of the Order Parameter in Phenomenological Theory.- 6.1 Spatially Inhomogeneous Fluctuations of the Order Parameter in the Incomplete Thermodynamic Potential.- 6.2 Applicability of Landau Theory to Nonferroelectric Structural Phase Transitions.- 6.3 Applicability of Landau Theory to Phase Transitions in Uniaxial Ferroelectrics.- 6.4 Fluctuational Phenomena in Ferroelectric-Ferroelastics and in Phase Transitions in Multiaxial Ferroelectrics.- 7. Structural Phase Transitions in the Single-Ion Model.- 7.1 Problems of the Microscopic Theory.- 7.2 The Single-Ion Model of a Diatomic Crystal.- 7.3 Phase Transitions of Displacive and Order-Disorder Types in the Single-Ion Model.- 7.4 Applicability of the Landau Theory to Phase Transitions of Displacive and Order-Disorder Types.- 8. Statistical Theory of Ferroelectric Phase Transitions of the Order-Disorder Type.- 8.1 The Hamiltonian of a Uniaxial Ferroelectric with an Order-Disorder Phase Transition.- 8.2 The Free Energy of an Order-Disorder Crystal in the Self-Consistent Molecular Field Approximation.- 8.3 Tunneling Effects in Hydrogen-Containing Ferroelectrics.- 8.4 The Cluster Approximation: Crystals of the KH2P04 Group.- 9. Dynamics of Displacive and Order-Disorder Phase Transitions.- 9.1 The Equation of Motion of the Order Parameter.- 9.2 Dynamic Dielectric Constant: Order-Disorder Phase Transitions.- 9.3 Dynamic Dielectric Constant: Displacive Phase Transitions.- 9.4 Microscopic Theory of Dynamic Processes in Displacive Phase Transitions.- 9.5 Microscopic Theory of Dynamic Processes in Order-Disorder Phase Transitions.- 9.6 Dielectric Constant and Soft Mode: The Lyddane-Sachs-Teller Relation.- 10. Domain Structure and Defects.- 10.1 Nucleation of Domains in a Structural Phase Transition.- 10.2 Domain Wall Structure: One-Component Order Parameter.- 10.3 Domain Wall Structure: Two-Component Order Parameter.- 10.4 Motion of the Domain Wall in an Ideal and a Real Crystal.- 10.5 Motion of the Domain Wall: Account of the Discreteness of the Crystal.- 10.6 Domain Walls and Defects.- 10.7 Defects in the Symmetrical Phase.- 10.8 Domains in Proper Ferroelectrics.- 10.9 Domains in Ferroelastics.- 10.10 Domains in Polyaxial Ferroelectrics.- 11. Ferroelectrics with an Incommensurate Phase.- 11.1 Phase Transitions into an Incommensurate Phase.- 11.2 Phenomenological Theory of Phase Transitions into an Incommensurate Phase.- 11.3 Specific Features of Crystal Lattice Vibrations in an Incommensurate Phase.- 11.4 The Incommensurate Phase in a Real Crystal.- 11.5 The Commensurate-Incommensurate Phase Transition: A Special Type of Phase Transition.- 11.6 Evolution of the Structure of the Incommensurate Phase (General Picture).- 11.7 Evolution of the Structure of the Incommensurate Phase (the Continuum Approximation).- 12. Ferroelectric Liquid Crystals.- 12.1 Basic Types of Orientational Ordering in Liquid Crystals.- 12.2 Conditions for Existence of Dipolar Ordering in Liquid Crystals.- 12.3 Phenomenological Theory of Phase Transition SmA* -? SmC*.- 12.4 The Behavior of a Ferroelectric Smectic Liquid Crystal in an External Electric Field.- 13. Crystallochemical Aspects of the Theory of Ferroelectric Phenomena.- 13.1 Calculation of the Constants of the Hamiltonians of Some Crystals.- 13.2 An Approach Based on the Classical Theory of Ionic Crystals.- 14. Recommended Literature.- References.

Liquid crystal device having spacers and manufacturing method thereof

Abstract: Disclosed is a liquid crystal light modulating element comprising a pair of substrates and a liquid crystal modulating layer interposed between the substrates. The liquid crystal modulating layer mainly comprises (1) a liquid crystal material for light modulation, (2) a plurality of spacers for maintaining a gap between the substrates, and (3) a plurality of resin structural nodules for supporting and adhering said pair of substrates. The resin structural nodules are arranged within a light modulating region based on a predetermined principle or a predetermined pattern.

Dynamic drive methods and apparatus for a bistable liquid crystal display

Abstract: A flat-panel liquid crystal display (10). The display includes a flat sheet of bistable chiral nematic liquid crystal material activated by a drive circuit that individually controls the display state of multiple picture elements. The driver circuitry activates the liquid crystal domains with various drive schemes which have any number of different phases (300, 312, 318, and 320) to attain various addressing sequence times. At the end of each drive scheme, the texture of the liquid crystal material is allowed to provide either focal conic or twisted planar end states (320) across the two-dimensional array of picture elements. Each drive scheme employs at least a preparation phase (300) and a selection phase (318) to predispose the liquid crystal material to one of the end states.

Optically induced space-charge fields, dc voltage, and extraordinarily large nonlinearity in dye-doped nematic liquid crystals

Abstract: We have observed extraordinarily large optical nonlinearity in Methyl Red–doped nematic liquid-crystal film. Grating diffraction can be generated with an optical intensity as low as 40 µW/cm2, and a refractive-index change coefficient of more than 6 cm2/W is obtained. The effect is attributed to formation of an optically induced dc space-charge field and to the resulting reorientation of the highly birefringent nematic director axis.

Dihexylquaterthiophene, A Two-Dimensional Liquid Crystal-like Organic Semiconductor with High Transport Properties†

Abstract: End-substitution of quaterthiophene with hexyl groups leads to a highly soluble conjugated oligomer, α,ω-dihexylquaterthiophene (DH4T), which has been characterized for its thermal, structural, and...

Modeling the phase behavior of polymer-clay composites

Abstract: To model the phase behavior of polymer-clay composites, we develop a free energy expression for a mixture of polymers and solid, thin disks. The free energy expression is adopted from the Onsager model for the equilibrium behavior of rigid rods. Thus, our theory takes into account the possible nematic ordering of the disks within the polymer matrix. By minimizing this free energy and calculating the chemical potentials, we construct phase diagrams for the polymer-disk mixtures. The findings provide guidelines for tailoring the polymer molecular weight and the volume fraction of the different components to fabricate thermodynamically stable mixtures with the desired morphology.

Liquid-crystalline behavior of rod-coil diblock copolymers

Abstract: The exact mean-field phase behavior of the Semenov–Vasilenko model for rod-coil diblock copolymers is studied by applying self-consistent field techniques. The behavior depends on three quantities: the rod/coil immiscibility χN, the coil volume fraction f, and the ratio ν of the characteristic coil to rod dimensions. When χN≲5, the rods and coils mix producing a nematic phase, and at larger χN, they microphase separate forming a lamellar phase. The nonlamellar phases expected at f≳0.7 are not treated here. The lamellar phase is typically a smectic-C structure with monolayers of tilted rods. A thorough understanding of the model is achieved by closely examining segment distributions and various contributions to the free energy. The tilt angle θ is generally controlled by a competition between rod/coil interfacial tension and stretching of the coils. Lowering f reduces the latter contribution, causing θ→0 and producing a continuous transition to a smectic-A structure. Beyond that, there is a tendency to form structures with the rods arranged in bilayers, but this is strongly suppressed by a large steric penalty. We suggest that small amounts of solvent can greatly alleviate this penalty, and therefore could significantly affect some aspects of the phase behavior.

Liquid crystalline coronene derivatives with extraordinary fluorescence properties

Abstract: Tempering of polystyrene films containing the novel liquid crystalline coronenebis(dicarboximide)s 2, which are formed by an easy route from perylene-3,4;9,10-tetracarboxylic dianhydride (1), leads to a shift of the emission within a few seconds. This could be used for dot-by-dot coloring and thus optical displays. The photoluminescence properties of 2 in the solid matrix are dependent on the nature of the aggregates formed.