Showing papers in "Molecular Crystals and Liquid Crystals in 1980"
TL;DR: In this article, a nematic liquid crystal, pentyl-cyano-biphenyl (5CB), was studied in two different flow situations: Poiseuille flow and torsional shear flow, in both cases with and without the simultaneous application of an electric field.
Abstract: A nematic liquid crystal, pentyl-cyano-biphenyl (5CB) is studied in two different flow situations: Poiseuille flow and torsional shear flow, in both cases with and without the simultaneous application of an electric field. The Poiseuille flow set-up gives an accurate determination of the Miesowicz viscosity ηc and a less precise estimation of ηb. With ηc known it is possible to separately determine the elastic constants K 11 and K 33 and the viscous coefficients α2, α3, and thereby γ1, γ2 from the torsional shear flow experiment. Using the data we have also been able to calculate the actual director profile in the liquid crystal as a function of applied shear and electric field. Curves are given of K 11, K 33, K 11/K 33, α2, α3, γ1, γ2, γ1/γ2, ηb and ηc for 5CB as a function of temperature through the whole nematic range from 22.0 °C to 35.1 °C. After the completion of our manuscript we have noticed the recent article by J. Wahl, Z. Natur-forsch. 34a, 818 (1979). Wahl discusses shear flow in the ...
155 citations
TL;DR: In this article, the shear dependence of structures of polyγ-benzyl-lglutamate PBLG in m-cresol was examined in a polarizing microscope using a specially constructed shearing stage and stroboscopic illumination.
Abstract: The shear dependence of structures of liquid crystalline solutions of Poly-γ-benzyl-l-glutamate PBLG in m-cresol was examined in a polarizing microscope using a specially constructed shearing stage and stroboscopic illumination. Three different textures were observed depending on shear rate. The shear rates at which the texture changes occurred correlated well with the changes in sign of the first normal stress difference reported earlier.1,2 The region of negative first normal stress difference corresponded to a texture consisting of striations perpendicular to shear. The transverse striations were also observed to develop over a period of seconds or minutes after cessation of shear at rates within the first positive region of N 1, These striations could be fixed in a dried film by using a volatile helicogenic solvent (1,4-dioxane). A speculative model is proposed to account for the rheological observations in Refs.1,2 and the rheo-optical observations reported herein.
132 citations
TL;DR: In this paper, the same authors showed that CH2Cl2(1), (2), (3), (4), (5) and (6) compounds of stoichiometry (pe)2(PF6)1.1 × 0.6 THF, (pe(2(AsF6),1.5×0.5 THF), and (pe3(SbF6)2× 0.75 CH2CL2) have been obtained as crystalline samples by electrochemical deposition from CH 2Cl2 [(1, (2
Abstract: Compounds of stoichiometry (pe)2(PF6)1.1 × 0.8CH2Cl2(1) (pe = perylene), (pe)2(AsF6)1.1 × 0.7 CH2Cl2 (2), (pe)2(PF6)1.4 × 0.6 THF (3), (pe)2(AsF6)1.5 × 0.5 THF (4) and (pe)3(SbF6)2 × 0.75 CH2Cl2 (5) have been obtained as crystalline samples by electrochemical deposition from CH2Cl2 [(1), (2) and (5)] or from THF [(3) and (4)] solutions of perylene, containing the appropriate counterion. The three compounds (1)-(3) crystallize in isomorphous orthorhombic lattices. (1) forms black needles: space group Pnmn with a = 4.285 A, b = 12.915 A and c = 14.033 A, z = 1. (2) gives black needles, orthorhombic space group Pnmn with a = 4.294 A, b = 13.077 A, and c = 14.132 A, z = 1. The structures of (1) and (2) were solved by direct methods and refined by least squares to final R = 0.148 and R = 0.088 based on 476 and 322 observed reflections. The perylene forms segregated stacks in direction of the a-axis with interplanar distances of 3.40 A and an angle of 37.7° between the bc-plane and the perylene. The ch...
96 citations
TL;DR: In this paper, the phase transitions were confirmed by microscopic and calorimetric (Perkin Elmer DSC 2) measurements in some homologous series and the phase transition was shown to be stable.
Abstract: This preliminary publication will give information on the phase transitions which we confirmed by microscopic and calorimetric (Perkin Elmer DSC 2) measurements in some homologous series.
89 citations
TL;DR: In this article, it was shown that a porphyrin compound, uro-porphyrin I octa-n-dodecyl ester, which has a flat, octagonally shaped molecular structure can also exhibit a discotic phase.
Abstract: A number of materials which exhibit the relatively new discotic phase have recently been discovered. All of the materials known which show this type of phase have molecular structures that are flat and hexagonal in shape. In this current work, we have shown that a porphyrin compound, uro-porphyrin I octa-n-dodecyl ester, which has a flat, octagonally shaped molecular structure can also exhibit a discotic phase. This is the first report of the discotic liquid crystal phase being exhibited by porphyrin compounds.
78 citations
TL;DR: In this article, the effect of chromophore aggregation on the photoconductivity of dye-sensitized Langmuir films has been examined employing three derivatives of a surface-active merocyanine with a rhodanine nucleus.
Abstract: The effect of chromophore aggregation upon the photoconductivity in the dye-sensitized Langmuir films has been examined employing three derivatives of a surface-active merocyanine with a rhodanine nucleus. The values of the lateral component Δσt and the anisotropy ratio Δσ∥/Δσ⊥ for the case with a strongly developed aggregate are found to be more than a decade larger than those for no or incomplete aggregation.
72 citations
TL;DR: In this paper, the fluorescence spectrum of 4-cyanobiphenyl, 4-cyclane-4'-propyloxybipenyl, four-cyano-4'nophenyl and four-cyclano-nopinioned polycyclic biphenyl has been analyzed as a function of solvent polarity and solute concentration.
Abstract: The fluorescence spectrum of 4-cyanobiphenyl, 4-cyano-4'-propyloxybiphenyl, 4-cyano-4'-octylbiphenyl and 4-cyano-4'-octyloxybiphenyl has been analyzed as a function of solvent polarity and solute concentration. The fluorescence originates from the planar 1 L a state polarized along the long axis of the molecule. A red shift of the emission and loss of vibrational structure is observed by increasing the solvent polarity in fluid solution but these effects are absent in glassy ethanol at 77°K. This red shift has been assigned to an orientation relaxation process of the solvent cage in the electric field of the excited solute that has a higher dipole moment than the ground state. Excimers are formed in concentrated solutions.
69 citations
TL;DR: Pleochroic anthraquinone dyes have been prepared with order parameters of up to 0.70 when dissolved in liquid crystals as mentioned in this paper and showed significantly higher stability than most other high order parameter azo-dyes.
Abstract: Pleochroic anthraquinone dyes have been prepared with order parameters of up to 0.70 when dissolved in liquid crystals. Over 100 dyes have been synthesised, in which a variety of substituents have been incorporated into the 1,4, and 5 positions on the anthraquinone nucleus, affording red, purple, blue and green dyes. Several dyes showed significantly higher stability than most other high order parameter azo-dyes. Some dyes showed solubility and order parameter sufficiently high to allow their employment in liquid crystal displays.
66 citations
IBM1
TL;DR: In this article, a rational synthesis of transition metal dithiene complexes with mesophorphic properties is reported, in which the Ni and Pt congerers have no mesomorphic properties at all.
Abstract: A rational synthesis of transition metal dithiene complexes with mesophorphic properties is reported. In addition to the nickel complexes described earlier, we have now obtained the Pd and Pt congerers. While the Ni and Pt complexes show, depending on the length of the para-n-alkyl chains, smectic or nematic mesophases, the Pd complexes have no mesomorphic properties at all. We suggest that the reason for the absence of a mesophase in the Pd complexes is caused by the formation of dimers.
62 citations
TL;DR: The isotypic crystal form for the smectogenic p-n-alkoxybenzoic acids has been determined by room-temperature single-crystal x-ray diffraction analyses for the acids having 7, 8, 9, and 10 carbon atoms in the alkyl chain this paper.
Abstract: The isotypic crystal form for the smectogenic p-n-alkoxybenzoic acids has been determined by room-temperature single-crystal x-ray diffraction analyses for the acids having 7, 8, 9, and 10 carbon atoms in the alkyl chain. The molecules are present in the crystals as centrosymmetric hydrogen-bonded dimers. The alkyl chains adopt an all-trans extended conformation but a gauche-relation of the ether oxygen and C(γ) about the C(α)-C(β) bond of the chains imparts a markedly non-linear and non-planar conformation to the molecules. With these chain lengths, adoption of this conformation makes possible an imbricated stratified layer structure in which the alkyl chains and the central aromatic nuclei are segregated into separate close-packed strata. Antiparallel interdigitation of chains in adjacent layers gives a 2:1 ratio of chains to nuclei in the strata. Evidence is presented that the molecules in the smectic mesophase probably retain the conformation found in the crystal and it is shown that the chan...
59 citations
TL;DR: The behavior of cellulose acetate was studied in over 30 solvents and it was found that the concentration C* at which the anisotropic phase appears, is dependent on the nature of the solvent as mentioned in this paper.
Abstract: The behavior of cellulose acetate was studied in over 30 solvents. It was found that the concentration C* at which the anisotropic phase appears, is dependent on the nature of the solvent....
TL;DR: In this paper, the authors proposed a new model for disodium cromoglycate (DSCG) phases, where the M phase consists of square hollow cylinders of DSCG packed in a hexagonal array in a water continuum, and the N phase is a nematic array of the same hollow cylinders but separated by so much water that although the local parallelism is retained, the hexagonal ordering is lost.
Abstract: New models are proposed for the two lyotropic liquid crystal phases of the anti-asthmatic drug, disodium cromoglycate (DSCG). It is suggested that the M phase consists of square hollow cylinders of DSCG packed in a hexagonal array in a water continuum. Each hollow cylinder consists of a stack of rings of four DSCG molecules and is filled with water. The N phase, which occurs at higher dilution, is pictured as a nematic array of the same hollow cylinders but separated by so much water that although the local parallelism is retained, the hexagonal ordering is lost.
TL;DR: The second singlet-singlet absorption system of naphthalene (1 B 2u) has been examined in diverse host media at low temperature as mentioned in this paper, and the structure admits to a direct quantitative analysis by means of extended Herzberg-Teller theory and provides coupling terms within such a framework.
Abstract: The second singlet-singlet absorption system of naphthalene (1 B 2u) has been examined in diverse host media at low temperature. Naphthalene substituted in durene and p-xylene crystals reveals hundreds of narrow lines (w 1/2 ∼2 cm−1) within the first 1500 cm−1 of 1 B 2u, Although the same gross band contours occur in all mixed crystal systems studied, each provided unique internal structure; also each deuterium isotope of naphthalene has a unique internal line pattern. This complexity is shown to derive from resonant vibronic interference between the 1 B 2u, electronic configuration and the underlying 1 B 3u vibronic manifold. It is a clear demonstration of the detailed interactions responsible for radiationless processes in such systems. The structure admits to a direct quantitative analysis by means of extended Herzberg-Teller theory and provides coupling terms within such a framework.
TL;DR: In this article, the optical nonlinearity of a nematic liquid crystal (NLC) was considered and the strongest effect was due to the local turn of the NLC director.
Abstract: The optical non-linearity of a nematic liquid crystal (NLC) is considered. The strongest effect studied is due to the local turn of NLC director. The possibility of wavefront conjugation by four-wave interaction in a NLC is considered. Strong effects of self-focusing in a NLC due to the orientational mechanism of non-linearity are predicted.
TL;DR: In this paper, x-ray diffraction by nematic and smectic liquid crystals is critically examined in terms of the data available and the structural models and molecular theories that have been proposed to explain it.
Abstract: Following a very brief historical review, x-ray diffraction by nematic and smectic liquid crystals is critically examined in terms of the data available and the structural models and molecular theories that have been proposed to explain it. Studiesof TBBA are used to illustrate some of the principal mesophases that have been distinguished. Other types of liquid crystals and their phase transitions are also briefly reviewed. This analysis shows that careful experimental work is still needed to decide the kinds of models that best describe the various types of mesophases that have been shown to exist.
TL;DR: The heat capacity of benzene-hexa-n-hexanoate, C6(OCOC5H11)6, with a purity of 99.98 mole per cent has been measured between 13 and 393 K as discussed by the authors.
Abstract: The heat capacity of benzene-hexa-n-hexanoate, C6(OCOC5H11)6, with a purity of 99.98 mole per cent has been measured between 13 and 393 K. Four phase transitions were found at 251.58 (Phase IV → II...
TL;DR: In this paper, the principal molecular polarizabilities (αe and αo) for the samples have been calculated using Neugebauer's relation and the necessary density measurements have been made by us.
Abstract: Refractive indices of bis-(4′-n-alkyloxy benzal)-2-chloro-1,4 phenylene diamine (alkyl = hexyl, octyl and decyl), RO-TN-101 and RO-CE-154 have been measured over the whole nematic ranges for different wave lengths. A prism method has been employed for these measurements. The samples were aligned by surface rubbing and by the application of magnetic field. For all the samples, the refractive index for the extra-ordinary ray (ne ) decreases and that for the ordinary ray (no) increases with increasing temperature. At the nematic isotropic transition there is a discontinuity in the refractive indices values. The principal molecular polarizabilities (αe and αo) for the samples have been calculated using Neugebauer's relation. The necessary density measurements have been made by us. The anisotropy of the molecular polarizabilities was calculated using Haller's extrapolation method. The orientational order parameters were calculated at different temperatures for the samples using principal polarizabilit...
TL;DR: Some homologous 4n-Alkyloxy-benzoyloxy]-benzylidene-4′-cyanoanilines are presented in this paper.
Abstract: Some homologous 4[4-n-Alkyloxy-benzoyloxy]-benzylidene-4′-cyanoanilines are presented. Three of them exhibit a reentrant nematic phase. For the decyloxy compound the variant of polymorphism Nre SC SA N is. was found.
TL;DR: In this article, a new type of thermotropic soluble cholesteric polymer is described, which contains nematogenic moieties separated by flexible spacers with an asymmetric center in the backbone, giving spontaneously characteristic Grandjean texture when heated above its transition temperature between slide and cover slip.
Abstract: The synthesis of a new type of thermotropic soluble cholesteric polymer is described. The polymer contains nematogenic moieties separated by flexible spacers with an asymmetric center in the backbone. The polymer gives spontaneously characteristic Grandjean texturers when heated above its transition temperature between slide and cover slip. Selective reflection of light in the visible (λ ∼ 5000–5600A) occurs for a co-polymer containing ppl-azoxyphenol/dodecanedioic acid and (+)3-methyladipic acid units.
TL;DR: In this paper, the thermal dependence of the flexoelectric coefficient in the nematic phase of several compounds is investigated and it is found that the dependence varies essentially like the angular order parameter S. All these observations are consistent with the quadrupolar interpretation, but also define cases in which the dipolar contribution shows up.
Abstract: We report on an experimental investigation of the thermal dependence of the flexoelectric coefficient in the nematic phase of several compounds. It is found to vary essentially like the angular order parameter S. For the first time a symmetric compound (pp' hexyloxytolan) is shown to exhibit a “regular” flexoelectric behavior. All these observations are consistent with the quadrupolar interpretation, but we also define cases in which the dipolar contribution shows up. Nous communiquons des resultats concernant la dependance thermique du coefficient flexo-electrique dans la phase nematique de plusieurs composes. Nous trouvons qu'il varie essentielle-ment comme le parametre d'ordre angulaire S. Nous montrons aussi, pour la premiere fois, qu'un compose symetrique (le pp' hexyloxytolane) a une activite flexoelectrique “normale”. Ces observations sont compatibles avec l'interpretation quadrupolaire du phenomene, mais nous definissons aussi des cas dans lesquels il est possible de mettre en evidence la...
TL;DR: In this article, the surface plasmon technique is employed to measure the refractive indices and to probe the nematic-isotropic phase transition of 4-cyano-4′-n-pentylbiphenyl.
Abstract: The surface plasmon technique is employed to measure the refractive indices and to probe the nematic-isotropic phase transition of 4-cyano-4′-n-pentylbiphenyl. Coexistence of isotropic and nematic phases in a 60 mK range and a hysteresis effect of the phase transition have been observed. A diffuse droplet model is used to estimate the supercooling and superheating range.
TL;DR: In this article, the relationship between molecular alignments, surface tension (γL) of nematic liquid crystals and critical surface tension of surfaces is examined for various surface structures using thirteen types of alkoxysilanes RSi(OCnH2n+1)3.
Abstract: The relationship between molecular alignments, surface tension (γL) of nematic liquid crystals and critical surface tension (γC) of surfaces are examined for various surface structures using thirteen types of alkoxysilanes RSi(OCnH2n+1)3. As the results, Creagh's conception that the perpendicular alignments are induced when γ C γ γ L was found to be not necessarily correct. Moreover, Porte's theory which gave the theoretical basis to Creagh's conception was examined, and it is clarified that the prerequisite for the theory is not generally realized.
TL;DR: The order parameters of a number of azo- and anthraquinonoid dyes dissolved in a eutectic liquid crystal mixture composed of derivatives of 4-cyanobiphenyl- and 4-cyclano-p-terphenyl (Type E7, B.D.H. Chemicals Ltd.) have been determined spectrometrically as discussed by the authors.
Abstract: The order parameters of a number of azo- and anthraquinonoid dyes dissolved in a eutectic liquid crystal mixture composed of derivatives of 4-cyanobiphenyl- and 4-cyano-p-terphenyl (Type E7, B.D.H. Chemicals Ltd.) have been determined spectrometrically. Orientation was achieved using rubbed polyvinyl alcohol coated cells. A good correlation was found between order parameter and molecular structure, allowing order parameters to be predicted for other dyes based on the monazo-chromophore. Azo-dyes exhibited a marked red shift relative to the colour of the dye in slightly polar isotropic solvents, whereas anthraquinonoid dyes showed little change. The results are interpreted in terms of charge transfer perturbations arising from dipole-interactions between guest and host molecules.
TL;DR: In this paper, the theory of dipole-dipole correlation in nematic liquid crystals is presented and it is shown that different models for the internal field lead to different values for dipole correlation factors.
Abstract: The theory of dipole-dipole correlation in nematic liquid crystals is presented and it is shown that different models for the internal field lead to different values for dipole correlation factors. Results of calculations are presented for three liquid crystals and commented upon. Using the calculated correlation factors and a simplified dielectric theory, predictions are made of the temperature derivatives of the mean permittivity and permittivity anisotropy and compared with experimental values.
TL;DR: The flow aligned viscosities of a series of 4n-alkyl and 4nalkoxy-4′-cyanobiphenyl liquid crystals have been measured over a range of temperatures.
Abstract: The flow aligned viscosities of a series of 4-n-alkyl- and 4-n-alkoxy-4′-cyanobiphenyl liquid crystals have been measured over a range of temperatures. Mixtures of these cyanobiphenyls, some also including a 4-n-alkyl-4″-cyano-p-terphenylh, have been measured and design rules formulated for producing low viscosity mixtures for use in display devices.
TL;DR: In this paper, a two-dimensional ensemble of cylindrically symmetric particles interacting via a weak anisotropic potential using the Monte Carlo technique of computer simulation is studied.
Abstract: We have studied a two-dimensional ensemble of cylindrically symmetric particles interacting via a weak anisotropic potential using the Monte Carlo technique of computer simulation. The calculation is simplified by confining the particles to the sites of a triangular lattice. The internal energy, specific heat, second rank orientational order parameter and second rank orientational pair correlation function were calculated at various temperatures. The variation of the order parameter and pair correlation function shows that the system exhibits a transition from an orientationally disordered to a partially ordered phase. The temperature dependence of the specific heat suggests that the transition is second order or higher. The possibility of the existence of order-disorder transitions in two dimensions is discussed. The results of the simulation are then compared with the predictions of a molecular field theory of orientational phase transitions. As expected the theory is found to be in poor agreem...
IBM1
TL;DR: In this paper, the synthesis and characterization of the first nematic transition metal complex and of smectic complexes of the dithiene type are described, and the first and second nematic metal complexes are synthesized and characterized.
Abstract: The synthesis and characterization of the first nematic transition metal complex and of smectic complexes of the dithiene type are described.
TL;DR: The crystal structures of two nematogens, EOBABN and MOBAPA, have been determined as part of a study of the relations between crystal structure and liquid crystallinity.
Abstract: The crystal structures of two nematogens, p-[(p'-ethoxybenzylidene)aminolbenzonitrile (EOBABN) and p-[(p'-methoxybenzylidene)amino]phenyl acetate (MOBAPA), have been determined as part of a study of the relations between crystal structure and liquid crystallinity. In EOBABN the molecules are arranged in a head-to-tail fashion in rows parallel to the crystal b-axis, with which the molecular long axes make angles of ± 12.5°. This structure is of a common type for nematogens, and could transform to the nematic state by means of a simple displacive transition where the molecules acquire three translational, but at most one rotational, degrees of freedom. In MOBAPA the crystal structure is made up of bimolecular sheets in which the long molecular axes lie in parallel planes normal to the sheet surface, but are inclined to the surface at ± 19°. The director axes of successive sheets lie in the sheet planes, but are mutually perpendicular from one sheet to the next. To proceed to a classical nematic pha...
TL;DR: In this paper, X-ray studies in oriented and not oriented samples of n-pentyl 4-[4-n-dodecyloxybenzylidene-amino] -cinnamate are reported.
Abstract: Results of X-ray studies in oriented and not oriented samples of n-pentyl 4-[4-n-dodecyloxybenzylidene-amino] -cinnamate in the smectic modifications I, C and A respectively are reported. Special emphasis is led to the SI phase, the structure of which is determined to be monoclinic with parameters a=5.04A; b=8.40 A c=37.8 A; s= 106°. An attempt was made to present a model of the packing of the molecules regarding shifts of the molecules, too.
TL;DR: In this paper, a general theory of exciton and electron transport in perfect molecular crystals is discussed and the emphasis is on qualitative results and elucidation of the effect of excitons and phonon bandwidth on the scattering of excITons and on transport.
Abstract: A general theory of exciton (and electron) transport in perfect molecular crystals is discussed. The emphasis is on qualitative results and the elucidation of the effect of exciton and phonon bandwidth on the scattering of excitons and on transport. Various microscopic models are discussed in this light.