Showing papers in "Molecular Crystals and Liquid Crystals in 1982"
IBM1
TL;DR: In this article, optical spectroscopy studies of both the electrochemically oxidized and the neutral polymer suggest the presence of highly mobile spins, consistent with the α,α' bonding in these polymers.
Abstract: Oxidized and neutral films of polypyrrole have been prepared electrochemically in the absence of oxygen and water. The neutral films are insulating and can be readily oxidized by chemical oxidizing agents to give films of greater conductivity than can be achieved by electrochemical oxidation. Optical spectroscopy provides evidence for the similarity of the polymeric carbonium ion produced by both types of oxidation. NMR studies are consistent with the α,α’ bonding in these polymers; they also show the expected downfield shifts relative to the neutral polymer on both chemical and electrochemical oxidation. ESR studies of both the electrochemically oxidized and the neutral polymer suggest the presence of highly mobile spins.
390 citations
TL;DR: In this paper, the absolute values of the elastic constants and order parameters of several cyanobiphenyls were calculated using the Freedericksz threshold fields and refractive indices.
Abstract: We present revised absolute values of the elastic constants and order parameters of several cyanobiphenyls. The calculations make use of our earlier measurements of Freedericksz threshold fields and refractive indices, and corrected values of normalizing constants, particularly in respect of the anisotropy of magnetic susceptibility. The new values agree well with some recent measurements.
215 citations
IBM1
TL;DR: In this paper, the electrochemical and conducting properties of polypyrrole conducting films are modified by substituting substitutents into the cationic pyrrole polymer or by varying the accompanying anion.
Abstract: Conducting films of polypyrrole can be modified by introducing substitutents into the cationic pyrrole polymer or by varying the accompanying anion. The electrochemical route for the preparation of these films is particularly convenient for making these modifications since the variations are made in the selection of the monomer or the electrolyte. This eliminates the need for subsequent chemical treatments of the film. As expected, the electrochemical and conducting properties of the film are changed by these chemical modifications.
200 citations
TL;DR: In this article, low threshold nematic mixtures are presented exhibiting very low dielectric crossover frequencies fc ≃ 1 kHz at 20°C and unusually large, low- as well as high-frequency anisotropies.
Abstract: Novel low threshold nematic mixtures are presented exhibiting very low dielectric crossover frequencies fc ≃ 1 kHz at 20°C and unusually large, low- as well as high-frequency dielectric anisotropie...
116 citations
TL;DR: X-ray diffuse scattering experiments on the superconducting salts (TMTSF)2X with X = PF6, AsF6, and ClO4 reveal no charge density wave instability, in contrast with the poorly conducting (TMTTF)2PF6 salt as mentioned in this paper.
Abstract: X-ray diffuse scattering experiments on the superconducting salts (TMTSF)2X with X = PF6, AsF6 and ClO4 reveal no charge density wave instability, in contrast with the poorly conducting (TMTTF)2PF6 salt. New structural phase transitions coinciding with conductivity anomalies are found in (TMTSF)2NO3, (TMTSF)2ReO4, and (TMTTF)2ClO4. It is suggested that they correspond to order-disorder transitions involving the non-centrosymmetric counter ions. Relationships between these structural instabilities and superconductivity are also discussed.
105 citations
TL;DR: Doi's theory for the dynamics of rod-like polymers in concentrated solutions was extended to include the effect of a molecular field as discussed by the authors, and the resulting expression for the stress tensor is defined.
Abstract: Doi's molecular theory for the dynamics of rod-like polymers in concentrated solutions is here extended to include the effect of a molecular field. The resulting expression for the stress tensor is...
88 citations
TL;DR: The crystal growth of black phosphorus (B.P.) and its electrical properties have been studied at high pressures and high temperatures as discussed by the authors, where a wedge type cubic anvil high pressure apparatus was used in the present experiments.
Abstract: The crystal growth of black phosphorus(B.P.) and its electrical properties have been studied at high pressures and high temperatures. A wedge type cubic anvil high pressure apparatus was used in the present experiments. From the measurement of the electrical resistance the melting points of B.P. have determined at high pressures. When B.P. is melted in the carbon furnace and slowly cools at 2.3 GPa, the large single crystals have often been grown. The size of the largest one is 4 mm in diameter and 5 mm in length. The anisotropic resistivity within the layers(ac-plane) has been observed. The resistivities along the a-, c- and b(perpendicular to the layer)-axes were about 0.1, ∼1 and 102∼103 Ωcm, respectively at atmospheric pressure. The resistivity along the a-axis was insensitive to pressure; on the other hand, the resistivities along the c- and b- axes decreased rapidly with increasing pressure at room temperature. The resistivity along the b-axis was about two orders of magnitudes larger than ...
87 citations
TL;DR: In this article, the authors describe a nematic liquid crystalline phase of negative diamagnetic anisotropy which readily orients in a magnetic field, and the phase transition temper...
Abstract: Disodium cromoglycate in water (~10-15% by weight) forms a nematic liquid crystalline phase of negative diamagnetic anisotropy which readily orients in a magnetic field. The phase transition temper...
80 citations
TL;DR: In this article, the spontaneous electrochemical undoping of polyacetylene, which occurs when appropriate combinations and configurations of (CH)x are employed, permits the fabrication of lightweight rechargeable batteries having large energy and large power densities.
Abstract: Polyacetylene, (CH)x, can be controllably doped p-type (oxidized) or n-type (reduced) by simple electrochemical procedures. Cyclic voltammetry studies on freestanding films of cis-(CH)x show that (CH)x can be reversibly oxidized at ~+3.6V vs. Li and reversibly reduced at ~+1.4V vs. Li. The spontaneous electrochemical “undoping” of p- and/or n-doped (CH)x, which occurs when appropriate combinations and configurations of (CH)x are employed, permits (CH)x to be used in the fabrication of lightweight rechargeable batteries having large energy and large power densities. Cis-(CH)x can be readily isomerized to the trans-isomer by electrochemical p-doping followed by electrochemical reduction to (CH)x.
75 citations
TL;DR: In this article, the electron donor DBTTF and its charge transfer salts with the acceptors TCNQ and 2,5-TCNQF2 were reported, and the crystal structures for the three systems are as follows: (a) neutral DBT...
Abstract: Crystal structures for the electron donor DBTTF and its charge-transfer salts with the acceptors TCNQ and 2,5-TCNQF2 are reported. Crystal data for the three systems are as follows: (a) neutral DBT...
71 citations
TL;DR: In this article, the synthesis and characterization of palladium (II) complexes with liquid crystal azobenzene ligands was reported, having a [sgrave] metal-carbon bond and a metal-metal chloro bridge, display ordered mesophases.
Abstract: The synthesis and characterization of palladium (II) complexes with liquid crystal azobenzene ligands is reported. The new organometallic compounds, having a [sgrave] metal-carbon bond and a metal-metal chloro bridge, display ordered mesophases. The temperatures of the K-N phase transition, in the region of 200°C, are some 130° higher than those for the related free ligands.
TL;DR: In this article, PPS, a melt and solution processible poly(p-phenylene sulfide), can be made highly conducting by doping with strong electron acceptors such as ASF5.
Abstract: Poly(p-phenylene sulfide), PPS, a melt and solution processible polymer, can be made highly conducting by doping with strong electron acceptors such as ASF5. Virgin PPS is an insulator with a relat...
TL;DR: In this article, measurements of the anisotropy of the critical field in (TMTSF)2X superconductors are presented, and the results show that the a axis Hc2 is Pauli limited based on a Tc near 1K. The large energy gap obtained from tunneling data is therefore thermodynamically untenable.
Abstract: Measurements of the anisotropy of the critical field in (TMTSF)2X superconductors are presented. The results show that the a axis Hc2 is Pauli limited based on a Tc near 1K. The large energy gap obtained from tunneling data is therefore thermodynamically untenable in terms of the present critical field studies and the superconductivity is singlet rather than triplet. Moreover, we find that low levels of irradiation induced defects eliminate the superconductivity in the ClO4 and PF6 salts and leave the thermopower of the ClO4 salt below 100K unchanged. These results are incompatible with the proposal for 1D superconducting fluctuations below 40K. A discussion of the arguments for and against the occurance of superconducting fluctuations in the (TMTSF)2X salts is given with emphasis on the role of interchain interactions and other possible interpretations of the tunneling data.
TL;DR: The MBRA series (4'-0- (2-methyl)-butyl resorcylidene-4-alkylanilines, 1) has been extended by MBRA 4 and 12, both showing low-temperature smectic phases as discussed by the authors.
Abstract: Condensation of chiral S-4-(6-methyl)octyloxy-2-hydroxybenzaldehyde (S-4-0- (6-methyl)octylresorcylaldehyde) with 4-alkylanilines (the MORA series, 3) gives low-melting Schiff bases showing chiral smectic C phases at or slightly above room temperature. The previously known MBRA series (4'-0- (2-methyl)-butyl- resorcylidene-4-alkylanilines, 1) has been extended by MBRA 4 and 12, both showing low-temperature smectic phases. Bis (S, S-4'-(2-methylbutyloxy-2-hydroxybenzylidene)-2-chloro-1,4-phenylene-diamine shows a cholesteric blue phase between 174 and 175 °C.
TL;DR: In this paper, an experimental investigation of the electronic properties of the conducting cation radical salts (TMTSF)2X, has shown how the development of superconductivity at low temperature is affected by the...
Abstract: An experimental investigation of the electronic properties of the conducting cation radical salts (TMTSF)2X, has shown how the development of superconductivity at low temperature is affected by the...
TL;DR: The development of order on the surface of the liquid crystal 5 CB as the temperature is lowered to approach the isotropic-nematic phase temperature T c is strikingly shown by measurement of the surface ellipticity as mentioned in this paper.
Abstract: The development of order on the surface of the liquid crystal 5 CB as the temperature is lowered to approach the isotropic-nematic phase temperature T c is strikingly shown by measurement of the surface ellipticity. The total excess surface order varies as In (T–Tc) which is consistent with expectations based upon the simple Landau free energy-gradient term model.
TL;DR: Inelastic light scattering experiments with tunable lasers give unique information on the morphology and excitations in undoped polyacetylene. as discussed by the authors reviewed the characteristics of these spectra and the current state of their interpretation.
Abstract: Inelastic light scattering experiments with tunable lasers give unique information on the morphology and excitations in undoped polyacetylene. The characteristics of these spectra and the current state of their interpretation are reviewed here. In the case of trans (CH)x, the model relating the Raman and absorption profiles to an inhomogeneous distribution of conjugation lengths is described and quantitative implications presented. New results reported include the following: measurements and analysis of Raman profiles indicating the large contribution from short conjugation lengths in trans (CH)X; the lack of direct evidence for photogenerated solitons in recent two-beam Raman spectra (there may be evidence for soliton formation in the excited state linewidth, however); and the markedly different resonance Raman behavior and photoluminescence in cis (CH)X and short segments of trans (CH)X.
TL;DR: In this paper, the authors have determined phase diagrams for cholesteryl propionate mixed with various nematics and a chiral nematic mixed with cyanohexyloxybiphenyl (6OCB).
Abstract: We have determined phase diagrams (using the light microscope) and pitch (using a wedge geometry) for cholesteryl propionate mixed with various nematics and a chiral nematic mixed with cyanohexyloxybiphenyl (6OCB). We have succeeded in untwisting both blue phases, BPI and BPII of the latter mixture in an electric field. We find that with increasing field, BPI transforms to a cholesteric whereas BPII transforms to a nematic before aligning in the field. Furthermore, the voltage to align the blue phases is not very different from that in the cholesteric phase despite the fact that the pitch is quite different in each case. Our model is that blue phases are triggered by the appearance of submicroscopic isotropic regions in the cholesteric. These regions necessitate nematic boundary conditions at the isotropic interface. Because cholesterics and nematics are thermodynamically the same phase (they are completely miscible), a cholesteric-isotropic emulsion occurs to minimize the loss in twist energy. T...
TL;DR: In this paper, the angle-dependent pair interactions are assumed to be of second-rank form, and a simple theory of rod/plate liquid-crystal mixtures is presented.
Abstract: We present a simple theory of rod/plate liquid-crystal mixtures in which the angle-dependent pair interactions are assumed to be of second-rank form. Calculations are reported for varying relative anisotropies of the “rods” and “plates”. Temperature vs. mole-fraction phase diagrams show successive isotropic (I) → uniaxial ( U) and U → biaxial ( B) transitions which are first- and second-order, respectively. For each pair of species there exists a special composition ( x rod*) for which cooling of the isotropic phase leads directly (and continuously) to a biaxial liquid. As X rod approaches X rod* from either side, the first-orderness of the I → U transition (i.e. discontinuities in volume, order parameter, etc.) becomes vanishingly small. Furthermore the transition temperature of the rod-(plate-) solvent is found to be depressed when “doped” by not-too-anisotropic plates (rods) and elevated when doped by sufficiently anisotropic plates (rods). These behaviors are explained in terms of simple excl...
TL;DR: In this article, strongly oriented poly-crystalline samples of polyesters containing mesogenic moieties and flexible spacers in the main chain have been produced by slowly cooling the molten samples in magnetic fields of up to 16 Tesla.
Abstract: Strongly oriented poly-crystalline samples of polyesters containing mesogenic moieties and flexible spacers in the main chain have been produced by slowly cooling the molten samples in magnetic fields of up to 16 Tesla. This simple method appears to be successful for those polymers forming a “true” nematic phase over an extended range of temperatures. Cholesteric polymers are not oriented. Mesogenic polymers (such as SEB-5, SUC-5, and SEB-7) which pass only through a state of partial parallel ordering of chain segments before cystallizing cannot be oriented macroscopically. In these samples crystallization may interfere with the chain alignment in the magnetic field. In contrast to low molecular weight liquid crystals, the isotropic-liquid crystalline transition of the polyesters investigated has a strong thermal hysteresis.
TL;DR: In this paper, the results of ab initio SCF LCAO crystal orbital calculations are presented for pure and doped polyacetylenes, polydiacetylene backbones, stacked TCNQ and TTF columns and for linear chains of (SNI)X.
Abstract: Results of ab initio SCF LCAO crystal orbital calculations are presented for pure and doped polyacetylenes, polydiacetylene backbones, stacked TCNQ and TTF columns and for linear chains of (SNI)X. ...
TL;DR: In this article, the design constraints for the formulation of good organic conductors and a brief review of the synthesis of heterocyclic selenium π-donors such as TMTSF and the zero pr
Abstract: Following an examination of the design constraints for the formulation of good organic conductors and a brief review of the synthesis of heterocyclic selenium π-donors such as TMTSF and the zero pr...
TL;DR: In this paper, the splitting of the D2O signal in the nematic range was reported for mixtures of D2Os and DSCG varying in the molar ratio D2 O/DSCG from 120 to 260.
Abstract: Disodium cromoglycate (DSCG) in mixtures with water forms a nematic state of high water concentration with cylindrical aggregates. Samples prepared with D2O were studied by deuteron magnetic resonance. The splitting of the D2O signal in the nematic range is reported for mixtures of D2O and DSCG varying in the molar ratio D2O/DSCG from 120 to 260 and for mixtures containing NaCl with molar ratios D2O/DSCG of 167 and 207 and NaCl/DSCG of 0.5 and 2. The splitting in the nematic range increases with decreasing temperature. At corresponding temperatures and for a given NaCl concentration the splitting is approximately inversely proportional to the D2O concentration. The addition of NaCl increases the temperature stability of the nematic range and reduces the temperature dependence of the splitting. It indicates that the addition of salt leads to stiffer aggregates.
TL;DR: In this article, a mechanism for the formation of the polymeric complexes was proposed according to the KOVACIC polycondenzation reaction of aromatic hydrocarbons, which is stable materials due to the strong electron donating property of the thiophene system.
Abstract: Poly (2,5-thiophenediyl) (2) reacts with AsF5 in a gas phase reaction yielding Poly (2,5-thiophenediyl) complexes with cationic centers and AsF6 counterions (1). Polymeric complexes of the same structure are formed by gas phase reactions of AsF5 with thiophene (3) and 2,2-bithienyl (4) via an oxidative poly-condenzation reaction. Treatment of the polymeric complexes 1 with aqueous ammonia yields 2. These complexes are stable materials due to the strong electron donating property of the thiophene system. They may be handled without any special precaution. They have electrical conductivities as high as 0.02 Ω−1 cm−1 (activation energy: E = 0.04eV). A possible mechanism for the formation of the polymeric complexes 1 is proposed according to the KOVACIC polycondenzation reaction of aromatic hydrocarbons.
TL;DR: In this article, a review of the influence of macromolecular architecture on the electronic structure of polymers is presented, and the density of valence electron states (DOVS) based on the CNDO/S3 molecular orbital model is applied to demonstrate the occurrence of short chain segments in mixed cis-trans polyacetylene.
Abstract: A review of the influence of macromolecular architecture on the electronic structure of polymers is presented. Calculations of the density of valence electron states (DOVS) based on the CNDO/S3 molecular orbital model are presented for polyacetylene, poly(p-phenylene), poly(p-phenylene vinylene), poly(p-phenylene sulfide), poly(2,5-thienylene), poly(1,6 heptadiyne), and poly(p-xylylene). These DOVS are shown to provide good descriptions of measured valence electron photoemission spectra in all cases for which such spectra are available. The model is applied to demonstrate the occurrence of short chain segments in mixed cis-trans polyacetylene. Relationships between macromolecular architecture and characteristic features in the photoemission spectra are demonstrated. In particular, criteria leading to extended pi-electron states are identified.
TL;DR: Deuterium, oxygen-17 and sodium-23 NMR measurements in the mesophase region of the disodiumchromoglycate (DSCG)-Water system are reported in this paper.
Abstract: Deuterium, oxygen-17 and sodium-23 NMR measurements in the mesophase region of the disodiumchromoglycate (DSCG)-Water system are reported. The results indicate that, depending on the temperature and concentration of the DSCG, at least three different mesophases can exist in the system: At temperature below -4°C a relatively highly ordered smectic-like phase exist (phase III) which was not reported previously. Above - 4°C two phases, labeled N and M appear. The dividing line between these two phases is at approximately 18 wt.% DSCG and depends slightly on temperature. Phase N which prevails on the low concentration side of the dividing line, appears to be nematic-like as manifested by the fact that it reorients in a magnetic field, while phase M which appears on the high concentration side of the dividing line seems to be smectic-like. There is no discontinuity in the ordering characteristics of the water solvent in the N-M transition region, suggesting that these two phases have similar ordered s...
TL;DR: In this article, the main chain of the polymers aligns itself in the direction perpendicular to an applied magnetic field, which can be used to detect the lyotropic liquid crystals formed by metal-poly-yne polymers I and II.
Abstract: The lyotropic liquid crystals formed by metal-poly-yne polymers I and II have been directly detected by high resolution P-n.m.r. method which has revealed that the main chain of the polymers aligns itself in the direction perpendicular to an applied magnetic field.
TL;DR: In this paper, nuclear magnetic resonance pulsed-gradient spin-echo measurements are reported for the anisotropic translational diffusion coefficients and their temperature dependence, of methane, monodeuteromethane and chloroform dissolved in several thermotropic liquid crystals exhibiting nematic, smectic A and B phases.
Abstract: Nuclear magnetic resonance pulsed-gradient spin-echo measurements are reported for the anisotropic translational diffusion coefficients and their temperature dependence, of methane, monodeuteromethane and chloroform dissolved in several thermotropic liquid crystals exhibiting nematic, smectic A and smectic B phases. For methane, in those liquid crystals forming only nematic phases, the diffusion parallel to the director (D ⊥) is greater than the perpendicular diffusion (D); the magnitude of the diffusional anisotropy (D ⊥/D ⊥) depends on the nature of the nematic medium. In the nematic phases of smectic-forming materials, D ⊥/D ⊥ < 1. In the smectic A phases, D ⊥/D ⊥ ≪ 1 with a much larger activation energy for D ⊥. In the smectic B phase, D ⊥/D ⊥ ≪ 1 with similar activation energies. Chloroform exhibits similar behavior with deviations in the nematic phases of a polymorphic liquid crystal. A qualitative interpretation of these results is given in terms of several factors which govern the diffusi...
TL;DR: A complete list of mobilities in molecular organic crystals is presented in this paper, which includes many new developments in the field of molecular organic crystal mobilities and includes a list of the most important mobilities.
Abstract: A complete list of mobilities in molecular organic crystals is preseneted. This updates the 1977 list and includes many new developments in the field.
TL;DR: In this paper, the authors report the values of isotropisation enthalpies and entropies of some model compounds, oligomers, and polymers of poly(2,2′-methyl-4,4′-oxyazoxybenzene dodecanedioyl), a thermo-tropic nematic polymer with moderately low transition temperatures and regularly alternating rigid-flexible units in the main chain.
Abstract: We report the values of isotropisation enthalpies and entropies of some model compounds, oligomers, and polymers of poly(2,2′-methyl-4,4′-oxyazoxybenzene dodecanedioyl), a thermo-tropic nematic polymer with moderately low transition temperatures and regularly alternating rigid-flexible units in the main chain. The values of ΔHIN and ΔIN increase rapidly with increasing molecular weight, to reach a plateau at M n > 3,000 g/mole. Results are interpreted in terms of increasing participation of the flexible aliphatic spacer units in the ordering process of the nematic phase. In the polymer, the entire repeating unit is aligned by the nematic potential.