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Showing papers on "Liquid crystal published in 1987"


Patent
20 Nov 1987
TL;DR: In this article, the authors defined the following conditions for a Ferroelectric liquid crystal mixture containing at least one compound of the general formula I: if n is 0 or 1, X is a single covalent bond and X has a C-C double bond, then R and R are each as defined in Claim 1, at least R having a double bond.
Abstract: Ferroelectric liquid crystal mixture containing at least one compound of the general formula … … where n is 0 or 1, X is a single covalent bond, -COO- or -OOC-, X is a single covalent bond, -COO-, -OOC-, -CH2CH2-, -OCH2- or -CH2O-, the rings A , A and A are each independently of the others unsubstituted or cyano-, halogen- or lower alkyl-substituted 1,4-phenylene or one of the rings may also be pyrimidine-2,5-diyl or pyrazine-2,5-diyl and/or when n is 1 one of the rings may also be trans-1,4-cyclohexylene or trans-m-dioxane-2,5-diyl, with the proviso that one of the rings present is pyrimidine-2,5-diyl or pyrazine-2,5-diyl if a further ring is trans-1,4-cyclohexylene or, if n is 0 and X is a single covalent bond, R and R are each as defined in Claim 1, at least R having a C-C double bond,… and novel compounds of the formula I.

673 citations


Journal ArticleDOI
TL;DR: The concept of mesophase polymers was introduced by as discussed by the authors, where the chains are sufficiently rigid to remain mutually aligned in the liquid phase although the perfect positional periodicity of a crystal is no longer present.
Abstract: Not much more than a decade ago, the plastics industry viewed itself as a mature branch of the heavy chemical industry. Its raison d'etre was the mass production of four or five main-line polymers, and profits were equated to tonnage output, plant efficiency, and clever downstream processing such as film blowing. The chemistry was essentially simple and the monomer, of course, cheap. There was, however, a spark of new thinking. A trend was developing toward the design and manufacture of more complex, more expensive polymers, with special properties which could command a special price. Such products would sell advanced scientific know-how, not just engineering expertise which could all too easily be exported to the major oil producers in the form of a polymer plant. Designing particular molecules to achieve desired properties is now a major theme of polymer producers. There is a move toward increasing the aromatic content of polymer backbones to achieve greater levels of chemical and thermal stability, while the development of new cross-linking systems remains as chemically intensive as ever. It is, however, the introduction of liquid crystalline polymers which, above all, has exploited the principles of molecular design, while at the same time challenging our understanding in a new area of polymer science. A polymer is “liquid crystalline” where the chains are sufficiently rigid to remain mutually aligned in the liquid phase although the perfect positional periodicity of a crystal is no longer present. In other words there is a long-range orientational order without long-range positional order (Figure 1). Structurally, therefore, the phase is intermediate between a crystal and a liquid leading to the use of the term mesophase . Where the liquid crystalline phase forms on melting the polymer, it is known as thermotropic , but where it is achieved by solvent addition it is called Inotropic. Increasing temperature, or solvent concentration, will eventually lead to the reversion of the liquid crystal phase to the normal isotropic polymer melt.

619 citations


Journal ArticleDOI
TL;DR: In this article, the buffing process orients the polymer's molecular chains in a manner similar to cold drawing of bulk polymer samples, and the formation of a liquid-crystal phase on the crystalline, oriented polymer surface is analogous to the epitaxial growth of conventional solid crystals.
Abstract: Smetic and nematic liquid‐crystal materials can be homogeneously aligned by buffed thin films of appropriate polymers. We propose that the buffing process orients the polymer’s molecular chains in a manner similar to cold drawing of bulk polymer samples. Experimental verification of this theory is obtained by measuring buffing‐induced birefringence in thin films of various polymers coated on glass. Further experiments establish that the oriented state of the polymer chains, and not scratching or grooving of the surface, is necessary to produce alignment. Alignment is found to occur when the polymer is both oriented and crystalline. A picture of alignment is presented in which the formation of a liquid‐crystal phase on the crystalline,oriented polymer surface is analogous to the epitaxial growth of conventional solid crystals.

605 citations


Journal ArticleDOI
TL;DR: In this article, the relationship between the molecular hyperpolarizability and the macroscopic susceptibility is presented, and the susceptibility is seen to depend on the microscopic order parameters commonly associated with liquid crystals and is discussed in the limits of one-dimensional molecules and poled polymer glasses.
Abstract: Liquid crystals and polymer glasses can be formed into orientationally ordered materials by raising the temperature of the material to a temperature at which molecular motion is greatly enhanced, applying an external aligning field, and then cooling with the field applied. The resulting material exhibits second-order nonlinear-optical effects. In this paper, the relationship between the molecular hyperpolarizability and the macroscopic susceptibility is presented. The susceptibility is seen to depend on the microscopic order parameters commonly associated with liquid crystals and is discussed in the limits of one-dimensional molecules and poled polymer glasses. Agreement is found between the theory and second-harmonic-generation measurements of polymer glasses. Results of electro-optic measurements are compared with second-harmonic-generation measurements that suggest that the electro-optic effect is mostly electronic in origin.

491 citations


Book
01 Jan 1987
TL;DR: In this article, the authors classify liquid crystal phases in relation to molecular structure materials requirements for Nematic and Chiral Nematic Electro-optical Displays Materials Requirements for Smectic Liquid Crystal Displays Cholesteric Materials for Surface Thermography Liquid Crystal Polymers.
Abstract: Classification of Liquid Crystal Phases Liquid Crystal Behaviour in Relation to Molecular Structure Materials Requirements for Nematic and Chiral Nematic Electro-optical Displays Materials Requirements for Smectic Liquid Crystal Displays Cholesteric Materials for Surface Thermography Liquid Crystal Polymers.

479 citations


Journal ArticleDOI
TL;DR: The core structure of half-integer wedge disclinations in nematic liquid crystals has been investigated within the Landau-de Gennes theory, by solution of the appropriate Euler-Lagrange equations.
Abstract: The core structure of half-integer wedge disclinations in nematic liquid crystals has been investigated within the Landau-de Gennes theory, by solution of the appropriate Euler-Lagrange equations. Close to the nematic-isotropic transition the energy density exhibits a domain-wall-like structure around the core which disappears at low temperatures. The inner core does not consist of isotropic fluid, and the core is heavily biaxial at all temperatures.

295 citations


Journal ArticleDOI
TL;DR: Rotation du directeur sous l'effet d'un champ electrique applique perpendiculairement a l'axe helicoidale isabelle âtre un effet electrooptique lineaire flexoelectrique.
Abstract: A linear electro-optic effect in a cholesteric liquid crystal is described and attributed to the flexoelectric effect. An electric field applied perpendicular to the helix axis rotates the director about an axis parallel to the field. This produces a periodic splay-bend pattern in the helix, which couples flexoelectrically to the field.

289 citations



Journal ArticleDOI
TL;DR: In this article, the extrusion, fiber spinning, compression, and injection molding of blends of polycarbonate and two thermotropic liquid crystal polymers based on wholly aromatic copolyesters have been studied.
Abstract: Rheological properties, extrusion, fiber spinning, compression, and injection molding of blends of polycarbonate and two thermotropic liquid crystal polymers based on wholly aromatic copolyesters have been studied. Blends were prepared using an internal Banbury mixer and static Koch mixer. Based upon differential scanning calorimetry and dynamic mechanical measurements, these blends have been shown to be incompatible in the entire range of concentrations. During extrusion and injection molding at high strain rates, it has been observed that thermotropic liquid crystal polymer at concentrations 2.5, 5, and 10 percent by weight in situ forms high modulus and high strength fibers within the polycarbonate matrix leading to self-reinforced polymer composites. The tensile strength of the composite containing 10 percent of liquid crystal polymer exceeds that of the pure components. In addition, anisotropy of properties of the injection molded parts has been found to substantially reduce in a comparison with that of liquid crystal polymer. The processing conditions and technique for the production of self-reinforced polymer composite during processing of the blends have been identified. This has been done by measurements of mechanical properties, direct observation of morphology, and by theoretical calculation using simplified composite theory for the unidirectional continuous fiber-reinforced composites. At the high concentrations, 25 and 50 percent by weight, thermotropic liquid crystal polymer forms large spherical droplets inside polycarbonate leading to highly brittle material. This is in distinction from the fibrous, high modulus tough composites formed at the lower concentrations.

228 citations


Journal ArticleDOI
TL;DR: Polymerisation radicalaire dans le THF de l'acrylate de bis [(methoxy-4 benzoyl) oxy] benzyle is described in this paper.
Abstract: Polymerisation radicalaire dans le THF de l'acrylate de bis [(methoxy-4 benzoyl) oxy] benzyle

225 citations


Book
01 Jan 1987
TL;DR: In this article, the authors studied the properties of low-molecular-weight liquid-crystalline polymers and showed that the formation and properties of these polymers are related with their properties.
Abstract: 1 Structure of Comb-Shaped Polymers.- 1.1. Early Studies.- 1.2. The Amorphous State.- 1.3. The Crystalline State of Isotactic Poly(l-alkyl ethylene)s, Poly(l-alkyl ethylene oxide)s, and Poly(alkyl aldehyde)s.- 1.4. The Rotational-Crystalline State.- 1.4.1. Hexagonal Packing.- 1.4.2. d Spacings. Single- and Two-Layer Packing of the Side Chains.- 1.4.3. Heats of Fusion, Length of Crystallizable Sequences of Units, and Convergence Temperature.- 1.5. Crystallization of Comb-Shaped Copolymers.- 1.6. Supermolecular Structure.- References.- 2 Molecular Mobility in Comb-Shaped Polymers.- 2.1. Effect of the Phase State on the Relaxation Properties.- 2.1.1. Polyethylene and Isotactic Poly(l-alkyl ethylene)s.- 2.1.2. Amorphous Comb-Shaped Polymers.- 2.1.3. Crystalline Comb-Shaped Polymers.- 2.1.4. Concluding Comments.- 2.2. Rheological Properties of Comb-Shaped Poly(alkyl acrylate)s and Poly(l-alkyl ethylene)s.- References.- 3 Comb-Shaped Macromolecules in Solutions and Intramolecular Interactions.- 3.1. Optical Anisotropy.- 3.2. Conformational State and Intramolecular Mobility.- 3.3. Unperturbed Dimensions of the Macromolecules.- 3.4. Gel Formation in Solutions of Comb-Shaped Polymers.- References.- 4 Thermotropic Liquid-Crystalline Polymers.- 4.1. General Information on the Formation and Structure of Low-Molecular-Weight Liquid Crystals.- 4.2. The Liquid-Crystalline State in Linear Polymers.- 4.3. Synthesis of Liquid-Crystalline Polymers with Mesogenic Side Groups and Some Features of the Formation of Mesophases.- 4.4. Comb-Shaped Liquid-Crystalline Polymers.- 4.5. Features of the Properties of Thermotropic Liquid-Crystalline Polymers Correlated with Their Macromolecular Nature.- 4.6. Theory of the Liquid-Crystalline Ordering of Melts of Linear and Branched Macromolecules with Mesogenic Groups in the Main and Side Chains.- 4.7. Mechanisms of the Formation and Properties of the Smectic, Nematic, and Cholesteric Mesophases of Liquid-Crystalline Polymers with Mesogenic Side Groups.- 4.7.1. Smectic Mesophases.- 4.7.1.1. Chemical Structure and Thermal Properties.- 4.7.1.2. Structure of Smectic Mesophases.- 4.7.1.2.a. SA Mesophases.- 4.7.1.2.b. SB, SE, and SF Mesophases and Other Types of Structures with Translationally Ordered Groups in Layers.- 4.7.1.2.c. SC Mesophases.- 4.7.1.3. Some General Comments on the Structure of Smectic Polymers.- 4.7.2. Nematic Mesophase.- 4.7.3. Comparison of Some Properties of Smectic and Nematic Liquid-Crystalline Polymers.- 4.7.3.1. Homopolymers.- 4.7.3.1.a. The Order Parameter.- 4.7.3.1.b. Rheological Properties.- 4.7.3.1.c. Molecular Mobility in the Solid State.- 4.7.3.2. Copolymers.- 4.7.3.2.a. Copolymers of Mesogenic and Nonmesogenic Monomers.- 4.7.3.2.b. Copolymers of Two Mesogenic Monomers.- 4.7.4. The Cholesteric Mesophase.- 4.7.4.1. Optical Properties.- 4.7.4.2. The Structure of Cholesteric Polymers.- 4.8. Behavior of Liquid-Crystalline Polymers in Electrical and Magnetic Fields.- 4.8.1. Orientational Effects.- 4.8.1.1. The Concept of Electro- and Magnetooptical Effects in Low- Molecular -Weight Liquid Crystals..- 4.8.1.2. Comb-Shaped Liquid-Crystalline Polymers.- 4.8.1.2.a. The Fredericks Transition (S Effect).- 4.8.1.2.b. Orientation in a Magnetic Field.- 4.8.1.2.c. The "Guest-Host" Effect.- 4.8.1.2.d. Optical Recording of Information (Thermal Addressing).- 4.8.1.2.e. The Structural Transition Induced by an Electric Field.- 4.8.2. Electrohydrodynamic Effects.- 4.9. Behavior of Liquid-Crystalline Polymers with Mesogenic Side Groups in Dilute Solutions.- References.

Journal ArticleDOI
TL;DR: In this article, the authors describe a new class of light control films consisting of submicron liquid crystal droplets dispersed in ultraviolct-cured polymer matrices, which can respond optically to both applied electric fields and temperature changes.
Abstract: This paper describes a new class of light control films consisting of submicron liquid crystal droplets dispersed in ultraviolct-cured polymer matrices. These films, which can respond optically to both applied electric fields and temperature changes, are potentially useful for displays and light shutters. The optical performance of these films depends on a variety of structural, electro-optical and thermal properties. This report describes scanning electron microscope studies of film structure, measurements of voltage dependent film transmittance and light scattering, and calorimetric studies which indicate that microdroplet formation in the films occurs as a result of phase separation which takes place during the cure process.

Journal ArticleDOI
TL;DR: The phase diagram of a system of hard parallel spherocylinders with length-to-width ratios L/D between 0 and ∞ is investigated by Monte Carlo simulation, finding a stable smectic phase formed at densities well below the thermodynamic melting point.
Abstract: The phase diagram of a system of hard parallel spherocylinders with length-to-width ratios L/D between 0 and ∞ is investigated by Monte Carlo simulation. In addition to a low-density nematic phase and a high-density crystalline phase, two phases with partial translational order are observed, viz., a smectic phase and a columnar phase. By computing the absolute free energy of all phases, their range of stability and coexistence points are determined. For L/D ratios exceeding 0.5, a stable smectic phase is formed at densities well below the thermodynamic melting point. The nematic-to-smectic transition appears to be continuous. A columnar phase is only observed for L/D>3 at densities intermediate between the smectic and crystalline phases. The smectic-to-columnar transition is first order for L/D≤5. In the limit L/D→∞ this transition becomes continuous.


Book
01 Jan 1987
TL;DR: In this article, transition moments techniques of alignment and measurement of uniaxial alignment processes of rank two processes reducible to rank two process of rank four examples of applications are presented.
Abstract: Introduction and theoretical background transition moments techniques of alignment and measurement quantitative aspects of uniaxial alignment processes of rank two processes reducible to rank two processes of rank four examples of applications appendix 1 - molecular symmetry and elemental group theory appendix 2 - Cartesian tensors and polarized intensities appendix 3 - Mueller-Stokes formulation for description of the interaction between polarized light and anisotropic samples subject index compound index.

Patent
17 Feb 1987
TL;DR: In this article, an electrically controlled birefringence effect and processes for the production of the cell and a uniaxial medium or material of negative optical anistropy usable therein are described.
Abstract: Liquid crystal cell using the electrically controlled birefringence effect and processes for the production of the cell and a uniaxial medium or material of negative optical anistropy usable therein. The cell can comprise two crossed rectilinear polarizers, two glass plates provided with transparent electrodes and placed between said polarizers, a liquid crystal layer between the plates and, between a plate and a polarizer, a layer of a negative uniaxial thermoplastic polymer having its extraordinary axis perpendicular to the plates. This layer can be obtained by heating the polymer up to the isotropic state, under a uniform presure on the polarizers, cooling and eliminating the pressure. Application to the production of data display devices.

Journal ArticleDOI
TL;DR: In this article, the angle of maximum transmission through a film in the presence of an applied field was investigated and the optical response of these materials as a function of applied field is also shown to be dependent on the ratio np/no as is the contrast exhibited by information displays.
Abstract: The refractive index of the polymer np is adjusted relative to the ordinary refractive index of dispersed droplets of nematic liquid crystal no to regulate the angle of maximum transmission through a film in the presence of an applied field. Maximum transmission occurs at normal incidence when np≤no with the breadth of the angle of view being largest at np=no. When np>no, maximum transmission is peaked at an angle away from normal incidence, the value of the angle depending upon the ratio np/no. Angular discriminating filters are therefore possible with these films. The optical response of these materials as a function of applied field is also shown to be dependent on the ratio np/no as is the contrast exhibited by information displays. Methods for measuring the scattering cross section of a nematic droplet are also described.

Journal ArticleDOI
TL;DR: In this article, a liquid-crystal electro-optic modulating device similar to the surface-stabilized ferroelectric liquid crystal device is described, but instead of using a tilted smectic phase like the C* phase, it utilizes the above-lying, nonferroelectric A phase, taking advantage of the electroclinic effect.
Abstract: A new liquid‐crystal electro‐optic modulating device similar to the surface‐stabilized ferroelectric liquid‐crystal device is described. It uses the same kind of ferroelectric chiral smectics and the same geometry as that device (thin sample in the ‘‘bookshelf ’’ layer arrangement) but instead of using a tilted smectic phase like the C* phase, it utilizes the above‐lying, nonferroelectric A phase, taking advantage of the electroclinic effect. The achievable optical intensity modulation that can be detected through the full range of the A phase is considerably lower than for the surface‐stabilized device, but the response is much faster. Furthermore, the response is strictly linear with respect to the applied electric field. The device concept is thus appropriate for modulator rather than for display applications. We describe the underlying physics and present measurements of induced tilt angle, of light modulation depth, and of rise time.

Journal ArticleDOI
TL;DR: In this article, a generalized Landau-de-Gennes elastic free energy of liquid crystals, in powers of a symmetric and traceless tensor order parameter, polarization field, of external fields and all respective derivatives, is constructed.
Abstract: Using angular momentum representation a method is proposed that allows the systematic construction of a generalized Landau-de Gennes elastic free energy of liquid crystals, in powers of a symmetric and traceless tensor order parameter, polarization field, of external fields and all respective derivatives. By this method all linearly independent elastic invariants and surface terms are constructed for nematics and cholesterics up to fourth order terms. In particular it is shown that up to fourth order in the tensor order parameter there are nineteen bulk elastic constants and four surface terms in the free energy of a general, biaxial nematic. In addition, the stability of this expansion is studied in detail. Some special cases of the elastic free energy of liquid crystals, already discussed in the literature, are reexamined and discrepancies with our results are emphasized. Finally, a thermo-dynamically correct way of establishing contact between the generalized de Gennes elastic free energy and ...

Journal ArticleDOI
TL;DR: In this paper, a thermodynamic model for ternary systems consisting of ionic surfactant-long-chain alcohol-water was presented, and the phase equilibria were determined by deriving explicit expressions for the chemical potentials of the three components and using the criterion that they should be equal for phases in equilibrium.
Abstract: A thermodynamic model is presented for ternary systems consisting of ionic surfactant-long-chain alcohol-water. The important contributions to the model free energy are (i) an electrostatic term; (ii) a free energy term; (iii) four entropy terms; (iv) constraints imposed by molecular packing restrictions; and (v) a hydration force. The free energy expressions are developed for (spherical) micellar solutions, normal hexagonal liquid crystals, lamellar liquid crystals, reversed hexagonal liquid crystals, and inverted (spherical) micellar solutions. For all these types of phases the aggregate geometries are optimized and the relative stabilities are determined. The phase equilibria are determined by deriving explicit expressions for the chemical potentials of the three components and using the criterion that they should be equal for phases in equilibrium. The model gives a nearly quantitative description of the equilibria in the test system potassium decanoate-octanol-water. The general conclusions are (i) at high ratios of ionic surfactant to alcohol the dominating factor is the electrostatics, with an additional effect from the fact that the alcohol decreases the free energy of the polar-apolar interface; (ii) the stability of the inverted micellar system is greatly influenced by the entropy of mixing between the palisade layer and the bulk alcohol medium; (iii) atmore » low water contents one has to invoke the occurrence of a hydration force.« less

Journal ArticleDOI
Daan Frenkel1
TL;DR: The existence of hard-core models for liquid crystals is important for two reasons: first, they can be used to test molecular theories for the static and dynamic properties of liquid crystals and secondly, they may provide a starting point for thermodynamic perturbation theories.
Abstract: Liquid crystals are usually not thought of as ‘simple’ liquids. Nevertheless, a surprising number of features of liquid crystals can be reproduced in computer simulations of very simple model systems, viz. hard ellipsoids of revolution and parallel spherocylinders. In particular, depending on the density and the shape of the hard-core particles, stable isotropic, nematic, smectic and crystalline phases are found. The existence of hard-core models for liquid crystals is important for two reasons. First of all, they can be used to test molecular theories for the static and dynamic properties of liquid crystals. And secondly, they may provide a starting point for thermodynamic perturbation theories. These hard-core models exhibit large pre-transitional fluctuations in the vicinity of some of the phase transitions, similar to those observed in real mesogens. Examples are given of the ‘experimental’ consequences of nematic and smectic precursor effects.

Journal ArticleDOI
TL;DR: In this paper, the nematic isotropic phase transition of liquid crystal induced by partial trans-cis photoisomerization of a small amount of 4-butyl-4-methoxyazobenzene mixed with 4-cyano-4′-n-pentylbiphenyl was read out.
Abstract: Over 100 times amplified image recording was achieved by means of reading out nematic isotropic phase transition of liquid crystal induced by partial trans→cis photoisomerization of a small amount(up to 5 mol%) of 4-butyl-4′-methoxyazobenzene mixed with 4-cyano-4′-n-pentylbiphenyl.

Patent
12 Jun 1987
TL;DR: In this article, the gap adjusting materials are held in place between the base plates and have columnar spacers to be welded at one end to the one base plate, and the easy tendency of the gap materials to movement at the time of injecting the liquid crystal is thereby obviated.
Abstract: PURPOSE: To decrease the fluctuations in an internal space by using gap adjusting materials which are held in place between base plates and have columnar spacers to be welded at one end to the one base plate. CONSTITUTION: This liquid crystal cell consists of two sheets of the base plates 1, 1 which face each other, a frame-shaped spacer 6 which forms the internals space between the base plates 1 and 1, the gap adjusting materials which are disposed in the internal space and a liquid crystal 8 which is sealed in the internal space. The gap adjusting materials are held in place between the base plates and have the columnar spacers 5 to be welded at one end to the one base plate. The easy tendency of the gap materials to movement at the time of injecting the liquid crystal is thereby obviated and the liquid crystal cell having the uniform internal cell is obtd. by adhering both faces of the base plates 1 by using a thermoweldable material 5 for the gap materials. COPYRIGHT: (C)1988,JPO&Japio

Journal ArticleDOI
TL;DR: In this paper, a micro-encapsulated chiral nematic thermochromic liquid crystal was applied to the surface of a color display to measure the response of the display to a rapidly increasing surface temperature.
Abstract: A time-varying surface temperature may be measured by a thin film of encapsulated thermochromic liquid crystal applied to the surface. The work reported in this paper has assessed, for engineering purposes, the response of such a film to a rapidly increasing surface temperature. Rates of increase in temperature of greater than 2000 degrees C s-1 were employed in these tests. The experiments show that the delay between the time at which the surfaces reaches the steady-state colour display temperature and the occurrence of the colour display is no more than a few milliseconds. The particular type of film used employed a micro-encapsulated chiral nematic thermochromic liquid crystal which was supplied by BDH and applied to the surface by a screen printing technique to a thickness of approximately 10 mu m. The conduction of heat into the film is analysed, but this would not appear to explain the observed response time of the thermometer.


Journal ArticleDOI
TL;DR: It is demonstrated that the LCs or LC mixtures with higher nematic-isotropic phase transition temperatures have higher optimum temperatures and greater potential for improving the figure of merit.
Abstract: This paper describes analyses and confirming experiments on the optimum temperature for fast response in nematic liquid crystal (LC) modulators. It is demonstrated that the LCs or LC mixtures with higher nematic-isotropic phase transition temperatures have higher optimum temperatures and greater potential for improving the figure of merit. Also discussed is the performance of the LC mixture exhibiting optimum temperature at around room temperature.

Journal ArticleDOI
TL;DR: In this article, the surface phases of a nematic liquid in the presence of a smooth substrate are studied using Landau-de Gennes theory, and the alignment of the nematic director is restricted to be either parallel or perpendicular to the substrate, although methods of treating more general structures are indicated.
Abstract: The surface phases of a nematic liquid in the presence of a smooth substrate are studied using Landau--de Gennes theory. The alignment of the nematic director is restricted to be either parallel or perpendicular to the substrate, although methods of treating more general structures are indicated. We describe extensions and a synthesis of earlier studies which obtained analytic solutions of the theory in certain limits, including surface-induced biaxiality, to determine the domains of wetting by planar and homeotropic nematic films as well as by the isotropic phase, as a function of surface-interaction parameters. The relation of wetting to orientational transitions in the surface-induced bulk alignment is discussed. The ``parabolic approximation'' recently introduced in related contexts is used to obtain solutions of the theory in more general circumstances where exact analytic solutions are precluded. It is found that, for realistic values of the ratio of model elastic constants, complete wetting by planar nematic films exhibits ``reentrant'' behavior and does not occur for arbitrarily strong substrate potentials. We argue that this outcome is not an artifact of the parabolic approximation, despite several deficiencies of the method. The relevance to experimental studies of nematic-liquid--substrate interfaces is described.

Journal ArticleDOI
TL;DR: A series of thermotropic poly(1,4-phenylene-2,5-di-nalkoxy terephthalate)s with the length of the n-alkoxy side chains being varied between n = 2 and n = 18 carbon atoms has been examined by optic as mentioned in this paper.
Abstract: A series of thermotropic poly(1,4-phenylene-2,5-di-n-alkoxy terephthalate)s with the length of the n-alkoxy side chains being varied between n = 2 and n = 18 carbon atoms has been examined by optic...

Journal ArticleDOI
TL;DR: In this article, the authors describe light control films consisting of submicron liquid crystal droplets dispersed in epoxy matrices, which can respond optically to both applied electric fields and temperature changes, are potentially useful for displays and light shutters.
Abstract: This paper describes light control films consisting of submicron liquid crystal droplets dispersed in epoxy matrices. These films, which can respond optically to both applied electric fields and temperature changes, are potentially useful for displays and light shutters. The optical performance of these films depends on a variety of structural, electrooptical and thermal properties. This paper describes scanning electron microscope studies of film structure, measurements of voltage dependent film transmittance, contrast ratio and light scattering, and calorimetric studies of the cure process which governs microdroplet formation in the films.

01 Jan 1987
TL;DR: In this article, the structure of the set of singularities of functions of bounded variation is studied and a different method that is used in order to study this basic fact and which is useful to study the finite crystal problem is presented.
Abstract: It will turn out that one necessartly has to understand the structure of the set of singularities of functions of bounded variation. This was first studied by the fundamental work of DeGi orgi [ 16], [3] and H. Federer [7). (see also Vol'pert [ 15], ~:1d Simon [ 12]). In this note we shall explain a different method that we have used in order to study this basic fact and which is useful to study the li~uid crystal problem which we shall explain in Section 2. As a matter of fact we have recovered the well known results mentioned above and furthermore we have obtained new information that we shall be briefly discussing.