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Showing papers in "Molecular Crystals and Liquid Crystals in 1985"


Journal ArticleDOI
TL;DR: In this paper, the qulnoid-benzenoid-diimine form is doped by dilute aqueous protonic acids to the metallic regime to give the corresponding iminium salt.
Abstract: “Polyaniline” has been synthesized in various forms both chemically and electrochemically in aqueous media. The qulnoid-benzenoid-diimine form, an insulator, is doped by dilute aqueous protonic acids to the metallic regime ([sgrave] = 5 ohm−1cm−1; compressed pellet) to give the corresponding iminium salt. This represents a new type of p-doping phenomenon in a conducting polymer. Both these forms are stable in the presence of air and/or water. The doping process is reversed by treatment with aqueous alkali. Cyclic voltammetry studies in an aqueous electrolyte show excellent reversibility between selected reduced and oxidized forms of polyaniline.

798 citations


Journal ArticleDOI
TL;DR: In this paper, the quinoid-benzenoid-diimine form of polyaniline was used as an anode in conjunction with a Pb02 cathode in an aqueous 0.5M Pb(BF4)2 electrolyte.
Abstract: The quinoid-benzenoid-diimine form, (=(C6H4)=N-(C6H4)-N=)x of “polyaniline” shows excellent cathode characteristics including recyclability when used in conjunction with a zinc anode in an aqueous electrolyte of (l. 0M ZnCl2 + 0. 5M NH4Cl) having a pH of ∼ 4. The reduced form of this material, (-(C6H4)-N(H)-(C6H4)-N(H)-)x can be used as an anode in conjunction with a Pb02 cathode in an aqueous 0.5M Pb(BF4)2 electrolyte.

453 citations


Journal ArticleDOI
TL;DR: The polyaniline (PANI) is an interesting material because it can be a very stable electronic conductive polymer as discussed by the authors and it shows several electrochemical redox systems which have to be elucidated.
Abstract: The polyaniline (PANI) is an interesting material because it can be a very stable electronic conductive polymer. It shows several electrochemical redox systems which have to be elucidated. For the application as battery material, it is the polymer probably which has the larger charge density (Ah/kg).

248 citations


Journal ArticleDOI
TL;DR: Highly conducting poly(p-phenylene vinylene), PPV, has been obtained via pyrolysis of the soluble precursor polymer derived from p-xylylene bis(diethyl sulfonium bromide) which is processed to film as discussed by the authors.
Abstract: Highly conducting poly(p-phenylene vinylene), PPV, has been obtained via pyrolysis of the soluble precursor polymer derived from p-xylylene bis(diethyl sulfonium bromide) which is processed to film...

194 citations


Journal ArticleDOI
Paul R. Gerber1
TL;DR: In this article, a system which shows a relatively large blue-phase range is investigated, and the response times are a few tens of microseconds below 10°C. But due to the small value of the cholesteric pitch, the blue phase shows no Bragg-reflections in visible light.
Abstract: A system which shows a relatively large blue-phase range is investigated. Owing to the small value of the cholesteric pitch the blue-phase shows no Bragg-reflections in visible light. Nevertheless, electric-field induced birefringence shows quite large values. The response times are a few tens of microseconds below 10°C. Crude estimates of the effects lead to values reasonably close to the experimental ones. Zero voltage birefringence effects are encountered, field induced and slowly decaying at higher temperatures and surface induced at lower temperatures where a uniaxial phase appears to be stable.

183 citations


Journal ArticleDOI
TL;DR: In this article, a layered anisotropic conducting structure is described for an amphiphilic TCNQ salt, and the LB technique is used for the extraction of the conducting structure.
Abstract: A layered anisotropic conducting structure is described. The LB technique is used for an amphiphilic TCNQ salt.

163 citations


Journal ArticleDOI
TL;DR: In this article, the evidence for the presence of the pyrrole moiety in electrochemically prepared polypyrrole is reviewed together with structural and IR data obtained for the crystalline dimer and trimer of pyrdrugs.
Abstract: The evidence for the presence of the pyrrole moiety in electro-chemically prepared polypyrrole is reviewed together with structural and IR data obtained for the crystalline dimer and trimer of pyrrole. The modification of the mechanical properties of polypyrrole by formation of graft copolymers with polystyrene, by polymerization of the pyrrole monomer within the matrix of a swellable polymer film and by polymerization of the pyrrole on vitreous carbon electrodes is described.

150 citations


Journal ArticleDOI
TL;DR: In this article, the authors found that polyaniline (4oSN) exhibits a low energy absorption edge beginning near 1800 cm−1 (ca: 0.22 eV).
Abstract: Polyaniline, (4oSN) is found to exhibit a low energy absorption edge beginning near 1800 cm−1 (ca: 0.22 eV), and a strong anion-induced absorption from about 800 to 1200 cm−1. Electrical conductivity has an activation energy of 0.05 (15%) eV consistent with an anion-induced energy gap of about 0.1 eV.

142 citations


Journal ArticleDOI
TL;DR: In this article, the metal-insulator transition upon pH variation has been investigated in polyaniline samples equilibrated at different pH levels, and it has been shown that the metal insulator becomes metal-conductivity, thermoelectric power, spin concentration and spin dynamics changes with pH variation.
Abstract: Conductivity, thermoelectric power, spin concentration and spin dynamics has been measured in polyaniline samples equilibrated at different pH. Data provide evidence for Metal-Insulator transition upon pH variation.

140 citations


Journal ArticleDOI
TL;DR: The first ambient pressure organic superconductors based on sulfur compounds have been obtained and investigated in (BEDT-TTP)-I system in this paper, where the first superconductivity was obtained using a superconducting superconductor with sulfur compounds.
Abstract: The first ambient-pressure organic super-conductors based on sulfur compounds have been obtained and investigated in (BEDT-TTP)-I system.

138 citations


Journal ArticleDOI
TL;DR: In this article, the quinoid-benzenoid-diimine form of polyaniline is doped by dilute aqueous protonic acids to the metallic regime to give the corresponding iminium salt.
Abstract: “Polyaniline” has been synthesized in various forms both chemically and electrochemically in aqueous media. The quinoid-benzenoid-diimine form, an insulator, is doped by dilute aqueous protonic acids to the metallic regime ([sgrave] ∼ 5 ohm−1cm−1; compressed pellet) to give the corresponding iminium salt. The polymer is not oxidized during the doping process. This represents a new type of p-doping phenomenon in a conducting polymer. Both these forms of polyaniline are stable in the presence of air and/ or water. The doping process is reversed by treatment with aqueous alkali. The mechanism by which doping occurs is discussed.

Journal ArticleDOI
TL;DR: In this paper, binary phase diagrams are presented for mixtures of CHBT or DBT with compounds with the isothiocyanato terminal group, showing that CHBT and DBT yield with the latter simple eutectics.
Abstract: The synthesis is described and the mesomorphic properties have been tested for two homologous series of compounds with the isothiocyanato (-NCS) terminal group: 4-(trans-4′-n-alkylcyclohexyl)isothiocyanatobenzenes (CHBT—formula 1) and 5-trans-n-alkyl-2-(4′-isothiocyanatophenyl)-1,3-dioxans (DBT—formula 2). CHBT are nematics, and reveal low viscosity and low melting points, DBT are A1 smectics. In this work, binary phase diagrams are presented for mixtures of CHBT or DBT with compounds with the —CN terminal group. CHBT and DBT yield with the latter simple eutectics. Moreover, DBT when mixed with A d smectics at an appropriate smectic layer spacing ratio, yield nematic mixtures. The suitability of CHBT as components of display mixtures is postulated.

Journal ArticleDOI
TL;DR: In this paper, the effect of lateral substituents on the type and thermodynamic stability of the mesophases shown by terminally polar and nonpolar rod-like mesogens is described.
Abstract: The effect of lateral substituents on the type and thermodynamic stability of the mesophases shown by terminally polar and nonpolar rod-like mesogens is described. Lateral substituents both sterically force the interacting molecules apart and also hinder the packing of the molecules in a layered structure, thus suppressing smectic order and favouring the nematic phase. The nematic → isotropic transition temperature, νm decreases with increasing van der Waals volume, Vw of the lateral substituent, irrespective of its dipole moment, due to the increase in intermolecular distance r. The relationship between νm and Vw is non-linear because the repulsive and attractive forces are different functions of r. The depression in νni depends not only on Vw of the substituent, but also on its position and on the structure of the rigid core. In aromatic nitriles, lateral substituents with + M effect in an ortho position with respect to the terminal cyano group, hinder the molecular association and therefore, l...

Journal ArticleDOI
TL;DR: In this article, high molecular weight films, fibers and foams of poly(p-phenylene vinylene), (PPV) have been prepared via a water soluble polyelectrolyte precursor.
Abstract: High molecular weight films, fibers and foams of poly(p-phenylene vinylene), (PPV), have been prepared via a water soluble polyelectrolyte precursor. p-Type chemical doping of these materials with ASF5 and H2SO4 leads to high conductivity and to high electrical anisotropy in oriented films and fibers. n-Doping with sodium naphthalide is also possible giving a semiconducting material. PPV synthesis, processing, and conductivity results are reported.

Journal ArticleDOI
TL;DR: The progression of phases which evolve during the alkali metal doping of polyacetylene and poly(p-phenylene) is examined in this article using newly developed structure concepts, crystal packing analysis, and diffraction and electrochemical data.
Abstract: The progression of phases which evolve during the alkali metal doping of polyacetylene and poly(p-phenylene) is examined using newly developed structure concepts, crystal packing analysis, and diffraction and electrochemical data. At least for alkali metals larger than Li+, at dopant concentrations above a few percent the alkali metal ions aggregate in columns within the host polymer lattice. Structural variations result for polyacetylene both from the degree these columns are filled and the chain-to-column ratio. More limited phase variation results for poly(p-phenylene), where 2,3, and 4 chain/column structures are observed, but the metal-metal spacing within the columns is fixed. Structural models are presented for the 2 chain/column complex of poly(p-phenylene) and the 3 chain/column complexes of K and Rb doped trans polyacetylene.

Journal ArticleDOI
TL;DR: In this article, a number of laterally fluorinated terphenyls of structure (I) have been synthesized, with the lateral fluoro-substituent in the central benzene ring.
Abstract: A number of laterally fluorinated 4,4″-di-n-alkyl-, 4,4″-di-n-alkoxy- and 4-n-alkyl-4″-n-alkoxy-l,r:4′,1″-terphenyls of structure (I) have been synthesised, with the lateral fluoro-substituent in the central benzene ring. The nematic and smectic thermal stabilities for all three series of compounds, have been examined. A typical example is (I), X = n–C5 HU, Y = n–C3 H7, C–N 50°C and N–I 140.6°C. For the 4,4″-di-n-alkyl-1,1′:4′,1″-terphenyls, the position of the lateral fluoro-substituent with respect to the longest n-alkyl chain is found to be important in determining the smectic behaviour of this class of compound. By using a combination of optical microscopy, X-ray diffraction and miscibility studies, the complex smectic behaviour of the higher homologues of this series has also been investigated. A comparison of the liquid crystal behaviour of the laterally fluorinated ter-phenyls of structure (I) with their non-fluorinated analogues is also given. A selected number of these compounds, have be...

Journal ArticleDOI
TL;DR: In this paper, the authors review the various kinds of information that can be obtained from x-ray diffraction studies and present specific examples from the literature of determinations of each of them.
Abstract: The paper first reviews briefly the various kinds of information that can be obtained from x-ray diffraction studies. Next, specific examples are given from the literature of determinations of each...

Journal ArticleDOI
TL;DR: In this paper, the relationship between the twisting power and the molecular structure of the dopant and neraatic solvent is discussed, and the mechanism of induction seems to be connected to the transfer of chirality from the solute to the solvent via chiral conformations of the latter.
Abstract: The relationship between the twisting power (β) and the molecular structure of the dopant and neraatic solvent are discussed. High values of β are observed whenever two (or more) planar or quasi-planar moieties, chirally distorted one with respect to the other, are present in the dopant. For high twisting powers, the mechanism of induction seems to be connected to the transfer of chirality from the solute to the solvent via chiral conformations of the latter. Sterochemical and analytical applications are briefly discussed.

Journal ArticleDOI
TL;DR: In this article, the effects of substituting a phenyl ring by a cyclohexyl ring, as well as of a -CN group by an -NCS group have been analyzed.
Abstract: Temperature dependences of density, refractive indices, and dielectric constants have been measured for mesogenic compounds of as for some of their cyano-analogues: and . The effects of substituting a phenyl ring by a cyclohexyl ring, as well as of a –CN group by an –NCS group have been analyzed. The results lead to the following conclusions: (i) the above exchange of rings leads to mesogens the long molecular axes of which do not coincide with the axes of the terminal groups, –CN or –NCS; (ii) antiparallel correlation of molecular dipoles found for cyano-mesogens does not occur in the case of isothiocyanato-mesogens.

Journal ArticleDOI
TL;DR: In this article, an adiabatic scanning calorimeter was used to investigate the temperature dependence of the enthalpy and the heat capacity near the smectic A to nematic (N) phase transition in mixtures of alkylcyanobiphenyl (nCB) liquid crystals.
Abstract: An adiabatic scanning calorimeter has been used to investigate the temperature dependence of the enthalpy and the heat capacity near the smectic A (A) to nematic (N) phase transition in mixtures of alkylcyanobiphenyl (nCB) liquid crystals. Mixtures of 8CB + 10 CB with small N-ranges undergo first-order transitions, but mixtures with large N-ranges exhibit continuous ones. A tricritical point could be located for the 10CB mole fraction of 0.3135. For a nearly tricritical mixture, a critical exponent α = 0.50 ± 0.02 has been observed. For mixtures with continuous AN transitions it is seen that this specific heat exponent α decreases with the width of the nematic range.

Journal ArticleDOI
TL;DR: The effect of fluorine substitution into a mesogenic system depends critically on the manner in which it is introduced as discussed by the authors, and lateral fluorination is particularly interesting for the strong suppression of smectic phase stability which can result.
Abstract: The effect of fluorine substitution into a mesogenic system depends critically on the manner in which it is introduced. The relative stabilities of smectic and nematic phases may be inverted by altering the site of substitution, and lateral fluorination is particularly interesting for the strong suppression of smectic phase stability which can result. This effect has been applied to hydrocarbon mesogens to obtain new series of wide range, room temperature nematics of low viscosity and moderately high birefringence. These properties are readily conferred on mixtures, and the technical utility of fluorinated LC's is illustrated by reference to wide nematic range, fast switching mixtures having high birefringence, and suitable for static or multiplex drive.

Journal ArticleDOI
TL;DR: In this paper, a tenside anion "doped", highly conducting polypyrroles (PPY) have been grown electrochemically from aqueous electrolytes.
Abstract: Tenside anion “doped”, highly conducting polypyrroles (PPY) have been grown electrochemical-ly from aqueous electrolytes The influence of the electrolysis parameters on the conductivity have been investigated The X-ray diffraction patterns allow to derive a structural model

Journal ArticleDOI
TL;DR: The elastic constants k11, k22, k33, the bulk and rotational viscosities, the birefringence, the static dielectric and electro-optical properties in TN-LCDs of new, positive dielectrics and electro...
Abstract: The elastic constants k11, k22, k33 , the bulk and rotational viscosities, the birefringence, the static dielectric and electro-optical properties in TN-LCDs of new, positive dielectric and electro...

Journal ArticleDOI
TL;DR: The synthesis and properties of a range of liquid crystalline side chain polysiloxanes are described in this paper, and the effects of changes in chemical structure, such as lateral substitution, on the properties of these materials are discussed, and comparisons are made with similar structural changes in low molar mass materials.
Abstract: The synthesis and properties of a range of liquid crystalline side chain polysiloxanes are described. The effects of changes in chemical structure, such as lateral substitution, on the properties of these materials are discussed, and comparisons are made with the effects of similar structural changes in low molar mass materials. By selecting suitable side chains for homopolymers and copolymers, room temperature smectic, nematic and cholesteric (chiral nematic) polysiloxanes of positive dielectric anisotropy have been prepared, including the first example of a nematic siloxane homopolymer containing a cyano-group.

Journal ArticleDOI
Jerry B. Torrance1
TL;DR: In this paper, a simple framework for studying the basic properties of the broad class of organic charge transfer solids is presented and it is shown that many of the differences in behavior of these materials can be explained.
Abstract: This presents a simple framework for studying the basic properties of the broad class of organic charge-transfer solids It is shown that many of the differences in behavior of these materials can

Journal ArticleDOI
TL;DR: A series of phthalocyanine octasubstituted derivatives were studied using optical microscopy and X-ray diffraction as discussed by the authors, some of them were metal-free; the rest contained various metal atoms such as copper, zinc or manganese in the center of the aromatic cores.
Abstract: A series of phthalocyanine octasubstituted derivatives were studied using optical microscopy and X-ray diffraction Some of them were metal-free; the rest contained various metal atoms such as copper, zinc or manganese in the center of the aromatic cores For most of the derivatives, the substituents consisted of eight peripheral decyloxymethyl chains; for one there were six of these plus two cyano groups attached to the same benzene ring; for another, there were short “polyethylene oxide” chains All the samples considered in this work exhibited columnar mesophases with hexagonal packing of the columns, stable in a wide range of temperatures

Journal ArticleDOI
TL;DR: In this paper, it was shown that the Hall voltage is hole-like, its variation versus magnetic field is linear up to 33 kOe, and peaks in magnetoresistance are observed above a threshold field of 41kOe.
Abstract: At 0.1 K, in the normal state, the Hall voltage is hole like, its variation versus magnetic field is linear up to 33 kOe. The measured Hall constant, 4xl0−9 m 3/As, does not vary between 0.1 and 7 K. In a magnetic field higher than 33 kOe, at low temperature, the magneto transport properties are very dependent on the cooling rate, even when a very low concentration of defects is expected. In standard conditions (4 hours from 30 to 4.2 K) electron like quantized Hall voltage and peaks in magnetoresistance are observed above a threshold field of 41 kOe. At the lowest cooling rate (70 hours from 30 to 4.2 K) strong hole like dips appear in the Hall voltage and the threshold field is 33 kOe. These results are understood within a model associating spin density wave phases and fully occupied Landau levels.

Journal ArticleDOI
TL;DR: In this article, the ESR fine structures and magnetic susceptibilities were measured and analyzed to show that the highest spin states were generated as the electronic ground state of the polycarbenes.
Abstract: High-spin polycarbenes (1 and 2) have been designed by using the triplet diphenylcarbene molecule as a repeating unit. The corresponding polydiazo compounds were prepared and photolyzed in 2-methyltetra-hydrofuran matrices and in single crystals of a benzophenone host at cryogenic temperatures. The ESR fine structures and magnetic susceptibilities were measured and analyzed to show that the highest spin states were generated as the electronic ground state of the polycarbenes. Relevance of these results to organic ferromagnets is discussed.

Journal ArticleDOI
TL;DR: In this article, a rotationally invariant form of the Maier-Saupe pseudopotential is generalised to two-component mixtures; the parameters of the theory are the ratios of transition temperatures, number densities and isotropic interaction strengths of the pure components.
Abstract: Molecular field theory is used to determine the temperature-composition phase diagram and component order parameters of binary mixtures of nematic liquid crystals. A rotationally invariant form of the Maier-Saupe pseudopotential is generalised to two-component mixtures; the parameters of the theory are the ratios of transition temperatures, number densities and isotropic interaction strengths of the pure components. The possibility of induced biaxiality and the effects of an external field are discussed. The model predicts a rich variety of phase behaviour. For dissimilar constituents, coexisting nematic-isotropic and nematic-nematic phases are predicted in agreement with experiment and hard particle theories. In general, the order parameters of the two constituents differ in a given phase; changing the sign of the interspecies interaction term in the pseudopotential results in the appearance of a biaxial solution. This biaxial phase is shown to be unstable however, and, on quenching, is expected...

Journal ArticleDOI
TL;DR: In this paper, the importance of various relevant device and material parameters are discussed and optimum conditions for multiplexing at levels over 1 in 100 are found for 3π/2 dye displays.
Abstract: The recently invented 3π/2 dye display offers, for the first time, the prospect of an RMS multiplexed highly complex liquid crystal display with an excellent angle of view. In this paper, the importance of various relevant device and material parameters are discussed and optimum conditions found for multiplexing at levels over 1 in 100.