Showing papers in "Molecular Crystals and Liquid Crystals in 1983"
TL;DR: In this article, the authors summarize the current understanding of the high-speed, bistable, threshold-sensitive electro-optic effects obtained in planar structures using surface interactions to suppress the spontaneous director helix characteristic of the bulk ferroelectric liquid crystal.
Abstract: The strong linear coupling of the director ň to electric field E in ferroelectric liquid crystals can be utilized to perform high-speed electro-optic switching suitable for device applications. In this article we summarize the current understanding of the high-speed, bistable, threshold-sensitive electro-optic effects obtained in planar structures using surface interactions to suppress the spontaneous director helix characteristic of the bulk ferroelectric liquid crystal.
228 citations
TL;DR: More than 35 different methods for creating surface alignment have been reported using both organic and inorganic films as well as various mechanical treatments as discussed by the authors, and many of these methods are reviewed and categorized.
Abstract: Ever since Mauguin described the fabrication of liquid crystal cells by rubbing glass plates with paper to obtain uniform homogeneous alignment, scientists have been attempting to study and understand the mechanism of anchoring and the subsequent alignment of these materials on various substrates. More than 35 different methods for creating surface alignment have been reported using both organic and inorganic films as well as various mechanical treatments. In this paper, many of these methods are reviewed and categorized. The mechanism of surface anchoring involves not one but several mechanisms. The nature of the surface material, the liquid crystal structure, and the past history of the surface, all play major roles in determining the mechanism for a specific technique.
137 citations
TL;DR: The mesomorphic behavior of octa (dodecyloxymethyl) phthalocyanine was studied with DSC, optical microscopy, and X-ray diffraction.
Abstract: The mesomorphic behavior of octa (dodecyloxymethyl) phthalocyanine was studied with DSC, optical microscopy, and X-ray diffraction. Two discotic mesophases were observed as a function of temperature. Their structure corresponds to the piling up of the flat molecules in columns which are laterally assembled according to a two-dimensional hexagonal lattice (D = 31.2 A). The repeat distance of the molecules along the columns was found to be of about 4.5 A. The low-temperature discotic phase showed an extra sharp reflection at 20.5 A, indicating a further ordering of the molecules.
113 citations
TL;DR: In this article, a simplified model of ±2π twist disclination pairs is proposed which describes the unwinding of the Sm C∗ structure under the external electric field, and critical fields for switching the helical Sm C ∗ structure, as well as the unwound structure are estimated.
Abstract: The mechanism of a field induced transition from helical Sm C∗ to Sm C structure in a DOBAMBC liquid crystal situated between two glass plates has been studied by optical methods. The important role of a regular system of twist disclination lines (dechiralization lines) in unwinding the helical structure by electric field has been revealed. A simplified model of ±2π twist disclination pairs is proposed which describes the unwinding of the Sm C∗ structure. Under the external electric field the pairs of ±2π twist disclinations move and annihilate each other and thus effectively unwind the helical structure of the sample. Critical fields for switching the helical Sm C∗ structure, as well as the unwound structure, are estimated.
110 citations
TL;DR: In this paper, the relative static permittivity of octylcyanobiphenyl (8CB) in the smectic A, the nematic and the isotropic phases between 22°C and 140°C is reported.
Abstract: Measurements of the relative static permittivity e of octylcyanobiphenyl (8CB) in the smectic A, the nematic and the isotropic phases between 22°C and 140°C are reported. The resolution of the measurements was better than 0.01% and the temperature stability was better than 0.01 °C. Detailed measurements have been carried out near the AN and NI transitions. For the AN transition. no discontinuity in e|| or e| was observed, which is consistent with the second-order nature of this transition in 8CB. From the dielectric anisotropy in the N-phase, a critical exponent β ≃ 0.25 was obtained for the temperature dependence of the order parameter. This value of β is in support of the hypothesis of quasi-tricriticality for this transition. In the isotropic phase of 8CB, a pretransitional anomalous maximum in e was observed near T N1- The same effect was also measured for two other materials with cyano-end groups (undecylcyanobiphenyl and pentylcyanophenylcyclohexane). For two compounds without a cyano-end g...
86 citations
TL;DR: In this article, the refractive indices and densities of six liquid crystals (two alkylcyanobiphenyls, three alkoxycyclaneobipenyls and one mixture of two alkylancyanogenobiphensyls) have been reported as a function of temperature.
Abstract: The refractive indices and densities of six liquid crystals—two alkylcyanobiphenyls, three alkoxycyanobiphenyls and one mixture of two alkylcyanobiphenyls have been reported as a function of temperature. The effective polarizabilities αeand αo in the nematic phase calculated using the methods due to Neugebauer, Vuks and Saupe and Maier, are found to be appreciably different, though the order parameter S evaluated with those values of (αe - αo) are in good agreement. The preference of one method over the other two is discussed.
72 citations
IBM1
TL;DR: In this article, it was shown that polyazulene has a 1,3-linked azulene unit structure, and that the reaction mechanism involves dimerization of radical cations and depr...
Abstract: Electrochemical oxidation of azulene in acetonitrile containing an appropriate electrolyte yields thick, electrically conducting polymeric films. Free-standing films of polyazulene peeled off a platinum electrode have electrical conductivities [sgrave]=10−2 to 1/Ω·cm, depending on the counter-anion, with perchlorate or tetrafluoroborate giving the highest values. Similar polymers are obtained from benzenoid or heterocyclic aromatic monomers, for example, pyrene, triphenylene or carbazole. These polymers resemble the better known polypyrrole. Spectroscopic evidence shows that the polymer consist of aromatic units, and elemental analysis reveals incorporation of counter-anions from the electrolyte; for polyazulene, one per 4 monomeric units. The consequences of alkyl substituents upon the tendency of the monomer to polymerize reveal that the hypothetical structure of polyazulene is best represented by 1,3-linked azulene units. The reaction mechanism involves dimerization of radical cations and depr...
70 citations
TL;DR: In this article, an adiabatic scanning calorimeter has been used in a calorimetric investigation of alkyl-cyanobiphenyl (nCB) liquid crystals.
Abstract: An adiabatic scanning calorimeter has been used in a calorimetric investigation of alkyl-cyanobiphenyl (nCB) liquid crystals. Measurements near solid to smectic (KA), smectic A to nematic (AN) and nematic to isotropic (NI) or smectic A to isotropic (AI) phase transitions have been carried out for scanning rates as low as a few μKs−1. Results for the temperature dependence of the heat capacity as well as for the enthalpy (including latent heats) have been obtained for 8CB, 9CB, 10CB and 11CB. Latent heat values are reported for the different KA, NI and AI transitions. For the two compounds 8CB and 9CB, which show a AN transition, it was found that, within the resolution of the experiments, these transitions are second-order. The anomalous heat capacity observed near the AN transition is much larger for 9CB than for 8CB. The critical exponent α obtained from power law fits to the heat capacity data is 0.31 ± 0.03 for 8CB and 0.50 ± 0.05 for 9CB. It is suggested that the AN transition in 9CB must be...
70 citations
TL;DR: In this article, a mixture of 1,4-phenylene and trans-1,4 cyclohexylene rings was used for short switching times of electro-optical displays at −40°C.
Abstract: Mixtures of broad nematic temperature ranges that permit acceptably short switching times of electro-optical displays at −40°C can be composed of compounds of relatively low polarity and high transition temperatures from the nematic to the isotropic state (T NI. Structures combining 1,4-phenylene and trans-1,4-cyclohexylene rings are particularly suited for this purpose.
61 citations
TL;DR: In this article, the authors compared liquid crystalline-side chain copolymers with analogous liquid-crystalline mixtures and showed that the polymers can be homogenously oriented by surface effects such as low molar mass mixtures.
Abstract: Liquid crystalline-side chain copolymers are compared with analogous liquid crystalline mixtures. The polymers can be homogenously oriented by surface effects such as low molar mass mixtures. These...
58 citations
TL;DR: In this article, the blue phases of two cholesteric systems were studied under the influence of an electric field, and the wavelength of maximum absorption due to the selective reflection of circularly polarized light of both blue phase I (BP I) and blue phase II (BP II) turns out to be shifted to longer wavelengths with increasing electric field.
Abstract: The blue phases of two cholesteric systems are studied under the influence of an electric field The wavelength of maximum absorption due to the selective reflection of circularly polarized light of both blue phase I (BP I) and blue phase II (BP II) turns out to be shifted to longer wavelengths with increasing electric field In addition to that, a phase transition from BP II to BP I is observed for one of the systems used Under favorable conditions, brilliant color changes from blue to red are observed in the reflected light
TL;DR: Propionic, n-butyric, isobutyric and phthalic acid esters of (hydroxypropyl)cellulose were prepared and characterized in this paper.
Abstract: Propionic, n-butyric, isobutyric and phthalic acid esters of (hydroxypropyl)cellulose were prepared and characterized. The aliphatic esters were readily formed by reacting (hydroxypropyl)cellulose with the corresponding acid chloride at room temperature. The phthalic acid ester was formed by reacting phthalic anhydride with (hydroxypropyl)cellulose in pyridine at 45°C. The bulk aliphatic esters exhibit cholesteric reflection in the visible range of the spectrum. The wavelength of the reflection peak maximum, Λo, was measured spec-trophotometrically at different temperatures. Plots of Λo reached zero (i.e. the cholesteric pitch became infinite) at temperatures close to the anisotropic-isotropic phase transition temperatures. The latter temperatures were determined experimentally by polarizing micros-copy and differential scanning calorimetry, and were in the range 165°C ± 10°C for all cellulose derivatives studied in this work. The optical rotatory dispersion (ORD) and circular dichroism (CD) of t...
TL;DR: In this paper, thermomicroscopic analysis of 4-cyano-4'-n-propylbiphenyl (CB 3) revealed solid crystalline polymorphism.
Abstract: DSC and thermomicroscopic analysis of 4-cyano-4'-n-propylbiphenyl (CB 3) revealed solid crystalline polymorphism. Thus the compound exhibits two solid phases subsequent to appropriate thermal treatment. The melting points are KI: 338.4 (5) K and KII: 326.3(3) K. The enthalpies of fusion for KI and KII are 19.9(5) kJ/mol and 16.7(7) kJ/mol, respectively. The compound also possesses a monotropic nematic phase, its clearing point being 303.3(2) K and ΔH N-I = 0.3(2) kJ/mol. The crystals of the higher melting modification are monoclinic, with a = 6.259 (3) A, b = 19.1216 (9) A, c = 11.0473 (5) A and β = 103.39 (2) °. The space group is P21/c. For 1014 nonzero reflections, R = 0.051, R w = 0.042. The dihedral angle between the phenyl rings was found to be 42.8°.
TL;DR: In this paper, a measurement of the specific heat of DOBAMBC is presented, and it is shown that a Landau expansion of the free energy density with a sixth-order term is adequate to describe the measurement.
Abstract: A measurement of the specific heat of DOBAMBC is presented, and it is shown that a Landau expansion of the free-energy density with a sixth-order term is adequate to describe the measurement. The coefficients in the Landau expansion are estimated from this measurement. The dependence of the tilt angle on applied electric and magnetic fields is discussed for both smectic-C and chiral (ferroelectric) smectic-C liquid crystals. Numerical estimates of the Landau coefficients are used to show that the effect of external forces on the tilt angle is negligible except when being less than approximately 0.2 K from the transition to the smectic-A phase. The effect on the smectic-C-smectic-A phase-transition temperature is also discussed. Boundary effects can also affect the tilt angle, and an expression for the penetration depth of a boundary-induced disturbance is calculated. For thin, planar samples, a coupling between the two boundaries can induce a transition to the smectic-A phase. It is demonstrated ...
TL;DR: In this paper, measurements of electric permittivities and elastic constants for various terminally cyano substituted nematics and their mixtures with terminally dialkyl substituted nematogens are reported, and it is suggested that these results can be attributed to the reduced anti-parallel local ordering observed in the mixtures.
Abstract: Measurements of electric permittivities and elastic constants for various terminally cyano substituted nematics and their mixtures with terminally dialkyl substituted nematogens are reported. The mixtures showed a considerably reduced ratio of the bend to splay elastic constants (k 33/k 11) compared with the pure p-cyano substituted nematics. Also the large diversity in k 33/k 11 observed for the p-cyano substituted nematics was found to converge upon dilution. It is suggested that these results can be attributed to the reduced anti-parallel local ordering observed in the mixtures.
TL;DR: In this paper, the phase separation of mesogen-nonmesogen mixture was studied with particular emphasis on the effects of boundary conditions imposed at container walls such as rubbed polyvinylalcohol (PVA) film, obliquely evaporated SiO film, free surface, etc.
Abstract: The phase separation of a mesogen-nonmesogen mixture was studied with particular emphasis on the effects of boundary conditions imposed at container walls such as rubbed polyvinylalcohol (PVA) film, obliquely evaporated SiO film, free surface, etc. Microscopic observations revealed that the equilibrium shapes of a nematic or isotropic liquid formed on a substrate in the temperature range of isotropic-nematic coexistence vanes greatly depending on the nature of the substrate. Typically the contact angle of a nematic liquid formed at the isotropic-substrate interface is 0° on a rubbed PVA film and at the free surface, and is nearly 180° on an Sio film. The connection between the substrate induced ordering and the contact angle is discussed.
TL;DR: A review of the state of knowledge of the blue phase of cholesteric liquid crystals can be found in this article, where the authors show the significance of blue phase studies to other problems in condensed matter research.
Abstract: Experimental studies of the blue phase of cholesteric liquid crystals have revealed two cubic phases (BPI and BPII) and a possible amorphous “fog” phase (BPIII). In addition, a number of theoretical models have been proposed which arrive at these structures from the point of view of a Landau theory, a lattice of disclinations, or as an ordered emulsion. We review the present state of knowledge of the blue phase and show the significance of blue phase studies to other problems in condensed matter research.
TL;DR: Petroleum heavy residual oil, coal-tar, coal liquefaction products and the like, being a mixcture of heavy hydrocarbons, are used as the industrial resources of cawrbon materials which are not likely to be replaced easily as discussed by the authors.
Abstract: Petroleum heavy residual oil, coal-tar, coal-liquefaction products and the like, being a mixcture of heavy hydrocarbons, are used as the industrial resources of cawrbon materials which are not likely to be replaced easily.
TL;DR: In this paper, the state of the art of molecular theories of nematic mesophases is reviewed, with particular emphasis on the basic assumptions and approximations, the relative strengths and weaknesses, and the most fruitful applications of each of them.
Abstract: In this paper, the current state of the art of molecular theories of nematic mesophases is reviewed. For this purpose, the many theories of nematogens which have been proposed are grouped into two classes: (1) the Maier-Saupe theory and its extensions and variants, which assume that nematic long-range order is primarily due to anisotropic intermolecular attractions and (2) the hard-rod and van der Waals theories, which assume that nematic order results primarily from excluded volume effects. These two types of theories are discussed in turn, with particular emphasis on the basic assumptions and approximations, the relative strengths and weaknesses, and the most fruitful applications of each of them. Finally, prospects for improving and extending current molecular theories are examined briefly.
TL;DR: In this paper, the debye relaxation time τ characterizing the hindered rotation of polar nematic molecules around their short axes is much more affected by molecular structural factors than by their rotational viscosity γ1.
Abstract: Four novel liquid crystal classes are presented, namely bi-, tri-, and tetracyclic ethanes, pyridazines, and tetracyclic chloro-diesters. Each class exhibits distinct physical characteristics, such as low viscosities η − 12 cP, low elastic ratios k33/k11 ∼ 1, large mesomorphic ranges −40°C. 250°C, large negative dielectric anisotropies δ e − 9 and/or low dielectric relaxation frequencies f e ∼ 1 kHz. It is shown that the dielectric Debye relaxation time τ characterizing the hindered rotation of polar nematic molecules around their short axes is much more affected by molecular structural factors than by their rotational viscosity γ1. The material and electro-optical properties of mixtures for twisted nematic and guest-host LCDs comprising the new compounds are presented. The mixtures cover a wide range of applications such as high contrast, fast and multiplexable automotive TN-LCDs; positive and negative contrast guest-host LCDs; high-information density matrix, and dual-frequency addressable LCDs.
TL;DR: In this paper, the molecular properties of mesogenic molecules having a terminal cyano group and a terminal n-pentyl-X-cyano chain were measured, and the relative nematic stabilities of the mesogens and their physical properties were discussed in terms of their measured molecular properties.
Abstract: The molecular properties of polarizability, polarizability anisotropy and dipole moment have been measured for a series of mesogenic molecules having a terminal cyano group and a terminal n-pentyl chain. Molecules investigated were of the form n-pentyl-X-cyano, where X was biphenyl, cyclohexyl-phenyl, phenyl-cyclohexyl, bicyclohexyl and bicyclo-octyl-phenyl. Measured polarizabilities were compared with bond additivity calculations for the molecules having different alkyl chain conformations. The relative nematic stabilities of the mesogens and their physical properties are discussed in terms of their measured molecular properties.
TL;DR: The crystal and molecular structures of three homologous trans, trans-4'-alkylbicyclohexyl-4-carbonitriles with the following alkyl groups are described in this article.
Abstract: The crystal and molecular structures of three homologous trans, trans-4'-alkylbicyclohexyl-4-carbonitriles (Cyclohexylcyclohexanes, CCHs) with the following alkyl groups: propyl (CCH3); pentyl (CCH5); heptyl (CCH7) are described All three compounds exhibit liquid crystalline phases at higher temperatures Both cyclohexyl rings assume the chair conformation and the alkyl groups adopt the trans-conformation In the crystalline state two kinds of layer structure are discussed In the first type, the long axes of the molecules are tilted to the normal of the layer In the second kind of structure, the longest molecular axis lies within the layer The role of the cyano dipoles is discussed In CCH3 a dipole-dipole interaction in the crystal is indicated The packing in the solid crystalline states of the three compounds is compared with the known models, derived from X-ray data, for the liquid crystalline state
TL;DR: The first thermotropic transition metal complexes discogens are bis(p-n-alkylbenzoyl)methanato copper (II) including one derivative possessing two sorts of side chains as mentioned in this paper.
Abstract: The series of the first thermotropic transition metal complexes discogens is completed: bis(p-n-alkylbenzoyl)methanato copper (II) including one derivative possessing two sorts of side chains. The symmetrical and unsymmetrical members of this series exhibit the same very organized discophase. The intermediates for the synthesis, the bis(p-n-alkylbenzoyl)methanes with two identical or different side chains, containing more than 18 carbon atoms exhibit the same very organized optically biaxial and positive smectic phase. The existence of another smectic phase stable at lower temperatures is established for a symmetrical term of this series.
TL;DR: In this article, the synthesis and properties of the l-(trans-4′-n-alkylcyclohexyl)-2-(4”-cyanophenyl)ethanes are described.
Abstract: The synthesis and some important properties of the l-(trans-4′-n-alkylcyclohexyl)-2-(4”-cyanophenyl)ethanes—where n-alkyl = C 1 to C 7—are described. These stable low melting materials have excellent properties comparable in many ways with those of the PCH materials wherein the cyclohexyl and phenyl rings are directly linked. The properties of the new series of materials, which we propose should be called the PECH compounds, are further elaborated in a companion paper by Raynes, et al, also presented at the Bangalore conference. In that paper it is made clear that the PECH materials have in fact higher order parameters and give superior order parameters for dissolved dyes compared with the PCH materials. The PECH compounds are therefore significant new nematogens to be considered for use in both twisted nematic and cholesteric-nematic dyed phase change displays.
TL;DR: In this paper, positive dielectric anisotropy liquid crystals are studied in cylindrical pores in a 10 μm thick polymer membrane of diameters 0.2-12μm.
Abstract: Positive dielectric anisotropy liquid crystals are studied in cylindrical pores in a 10 μm thick polymer membrane of diameters 0.2-12μm. Transition temperature depressions increase with decreasing pore size. Singularities of strength 1 are observed in the center of the pores, accompanied by some strength ½ singularities. By applying a voltage across the membrane, the S = 1 singularities are shown to be “escaped” singularities. S = +½ singularities show a critical destruction at a characteristic voltage.
TL;DR: The state-of-the-art in the liquid crystal display field is described in this paper, where major effects and their applications are discussed, and the state of the art is presented.
Abstract: This paper is a reveiw of thmore sinigicant developments in the liquid crystal display field during the last fifteen years. Major effects and their applications are discussed, and the state-of-the-art is presented.
TL;DR: The crystal and molecular structures of two disubstituted biphenylcyclohexanes (BCHs) of the general formula R 6H10C6H4C 6H4X C6H 4X X were determined in this article.
Abstract: The crystal and molecular structures of two disubstituted biphenylcyclohexanes (BCHs) of the general formula R—C6H10C6H4—C6H4—X were determined (BCH5CN, R: C5H11 X: CN; a = 12.671(3), b = 5.567(1), c = 28.695(5) A, β = 97.174(4)°, space group P2 1/c. BCH30, R: C3H7, X: H, a = 6.839(2), b = 8.219(2), c = 31.159(8) A, β = 99.63(1)°, space group P21/c). Crystal data only is given of BCH52, R: C5H11 X: C2H5; a = 17.09(2), b = 6.79(1), c = 37.34(3) A, space group Pbcn Refinement leads to R = 0.089 (BCH5CN) and R = 0.128 (BCH30) respectively. In both compounds, the molecules form layers in the crystalline state. The dihedral angles between the phenyl rings in the biphenyl unit are 2.4° (BCH5CN) and 23.8° (BCH30) respectively. X-ray examinations of the smectic states, and also of some additional BCH-compounds (BCH50, R: C5H11, X: H; BCH54, R: C5H11, X: C4H9; BCH7CN, R: C7H15, X: CN; BCH5NH2, R: C5H11 X: NH2) give monolayered, crystalline smectic B phases for the nonpolar compounds. The compounds contain...
TL;DR: The crystal and molecular structure of 4′- n-butyl-4-cyanobiphenyl (4CB), C17H17N, has been determined at room temperature as discussed by the authors.
Abstract: The crystal and molecular structure of 4′- n-butyl-4-cyanobiphenyl (4CB), C17H17N, has been determined at room temperature. The compound, which exhibits a monotropic nematic phase, crystallizes in the monoclinic space group P21,/ c, a = 12.198, b = 9.204, c = 14.746 A, β = 123.38°, with four molecules in the unit cell. The structure has been refined to R = 0.136 using photographically observed data. The terminal part of the butyl chain is disordered. The 4CB molecules pack in a sheet-like arrangement, with nearest neighbors oriented antiparallel to each other. The angle between the phenyl rings is 40°30′.
TL;DR: In this paper, the effect of an external magnetic field on the orientational order of a nematic liquid crystal has been examined using both Landau-de Gennes and Maier-Saupe theories.
Abstract: The effect of an external magnetic field on the orientational order of a nematic liquid crystal has been examined using both Landau-de Gennes and Maier-Saupe theories. In the Maier-Saupe approach a rotationally invariant form of the pseudo-potential is introduced, which in the absence of an external field leads to three degenerate isomorphic solutions for the order parameter, corresponding to alignment along three principal axes; a similar result is obtainable from the Landau-de Gennes theory. Application of a magnetic field lifts the degeneracy of these solutions, and for materials having a positive diamagnetic susceptibility anisotropy, the uniaxial solution with alignment along the field direction is always energetically favorable. For materials with a negative susceptibility anisotropy, a biaxial solution minimizes the free energy at low temperatures, but on increasing the temperature there is a transition from a biaxial phase to an uniaxial phase. The field dependence of the transition tempe...
TL;DR: In this article, the thermal and dynamic viscoelastic behavior of some thermotropic liquid crystalline polyesters based on α, ω-bis(4-hydroxybenzoyloxy)alkanes and terephthalic acid is reported.
Abstract: The thermal and dynamic viscoelastic behavior of some thermotropic liquid crystalline polyesters based on α, ω-bis(4-hydroxybenzoyloxy)alkanes and terephthalic acid is reported. Original samples obtained by solution polymerization followed by precipitation showed physical and dynamic-mechanical properties typical of semicrystalline polymers. Quenching of the polymers from the LC state gave rise to glass-like mesomorphic modifications that retained a glass transition at considerably higher temperature T 8m than that of the corresponding amorphous material T 8a. However, the formation of a new crystal form with respect to the original sample could not be prevented and the polymers so obtained were in fact partially mesomorphic and partially crystalline materials. All the quenched samples exhibited by dynamic-mechanical and calorimetric analyses a first order solid-solid transition independent of the length of the flexible spacer. Such a phenomenon was interpreted as an order-disorder transition of ...