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21Author    T. Brückert, D. Büsing, A. Würflinger, S. UrbanRequires cookie*
 Abstract    h e r m a l A n a ly s is (D T A) a n d D ie le c tr ic S tu d ie s o f 4 -(tra n s -4 -H e p ty l-C y c lo h e x y l) -b e n z o n itr ile (7 P C H) u n d e r H ig h P r e s s u r e With the aid of DTA the phase diagram of 4-(trans-4-heptyl-cyclohexyl)-benzonitrile, 7PCH, was redetermined. Dielectric studies on the static and complex permittivity have been performed on 7PCH in the pressure range 0.1 -220 MPa, the frequency range 1 kHz-13 MHz and the temperature range 290-380 K. For the slow relaxation process in the nematic phase, characterized by the relaxa­ tion time Tjj , we have calculated the activation volume, A* V u, of about 80 to 60 cm3/mol (decreasing with increasing temperature), and the activation enthalpy, A *Hn, of approximately 70 kJ/mol. The isochoric activation energy, A* Un, amounts to about 36 kJ/mol. The pressure dependence of A * Hu is less pronounced compared with previous findings for 5PCH and 7CB. Estimates of t 0 (extrapo­ lated from the relaxation time in the isotropic phase) allow the calculation of the retardation factor gu = Tn/t0 that is analysed in terms of theories of Martin-Meier-Saupe and Coffey in order to evalu­ ate the nematic potential q. Using data for the order parameter 5 from NMR studies it was possible to determine the strength of the interaction potential in the nematic phase and to check the relation q~S which is valid at p = const., but not at V= const. The results are compared with recent findings for other homologous series. 
  Reference    Z. Naturforsch. 50a, 977—983 (1995); received August 25 1995 
  Published    1995 
  Keywords    Dielectric Relaxation, High Pressure, Liquid Crystals, Activation Parameters, Phase Transitions 
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 TEI-XML for    default:Reihe_A/50/ZNA-1995-50a-0977.pdf 
 Identifier    ZNA-1995-50a-0977 
 Volume    50 
22Author    Phineus Markwick, Stanislaw Urban, Albert WürflingerRequires cookie*
 Title    High Pressure Dielectric Studies of 8CB in the Isotropic, Nematic, and Smectic A Phases  
 Abstract    The static and complex permittivity of 4-n-octyl-4'-cyanobiphenyl (8CB) has been measured for the isotropic, nematic and smectic A phases as functions of temperature and pressure. The ranges of 297 -361 K, 0.1 -220 MPa, and 0.1 -13 MHz, were covered. Only the parallel component of the complex permittivity, £*(/) = e'(f) — ie"(f), was measured. The relaxation times T||(p, T) as well as ris(p, T) were analysed at constant temperature, pressure and volumes yielding the activation volume, A ¥ V(T), activation enthalpy A^H(p), and activation energy lyU(V), respectively. All activation parameters calculated for the smectic A phase of 8CB are smaller than those obtained for the nematic phase. The activation energy constitutes approximately half of the activation enthalpy value in all three phases studied. The pressure study allowed to calculate the pressure dependence of the retardation factor g\\(p, T), from which the nematic potential q(p,T) can be derived. Using the relationships between g\\ and q/RT proposed by Kalmykov and Coffey, the order parameter (Piip, T)) was calculated as a function of pressure. 
  Reference    Z. Naturforsch. 54a, 275—280 (1999); received March 13 1999 
  Published    1999 
  Keywords    Liquid Crystals, 8CB, High Pressure, Dielectric, Thermodynamics, Order Parameter 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0275.pdf 
 Identifier    ZNA-1999-54a-0275 
 Volume    54 
23Author    Reiner Memmer, Folkert JanssenRequires cookie*
 Title    Computer Simulation of Chiral Liquid Crystal Phases IX. Chiral Induction in Guest-host Systems - Calculation of the Helical Twisting Power  
 Abstract    The chiral induction in liquid crystalline phases was studied by Monte Carlo simulation of the chiral Lebwohl-Lasher model. Binary guest-host systems composed of achiral and chiral molecules as well as of different chiral molecules were investigated in dependence on the composition. A cholesteric phase was induced by dissolving a small fraction of chiral molecules in a nematic phase. For dilute solutions the equilibrium pitch was found to be a linear function of the chiral dopant concentration. Independent of system size effects the application of self-determined boundary conditions enabled the determination of the symmetry adapted quantities for the chiral induction, the helical twisting power (HTP) and the achiral helical twisting power (AHTP). Additionally, a different orientational behaviour of enantiomer-ic dopants in the chiral surroundings of a cholesteric host phase has been determined. 
  Reference    Z. Naturforsch. 54a, 747—754 (1999); received October 29 1999 
  Published    1999 
  Keywords    Chirality, Liquid Crystals, Computer Simulation, Induced Cholesteric Phases, Helical Twisting Power 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0747.pdf 
 Identifier    ZNA-1999-54a-0747 
 Volume    54 
24Author    DurgaPrasad OjhaRequires cookie*
 Title    Molecular Ordering in Liquid Crystalline EMBAC. A Quantum Mechanical Study  
 Abstract    Molecular ordering in a liquid crystal, ethyl 4-(4'-methoxybenzylidene amino) cinnamate (EMBAC) has been studied by intermolecular interaction energy calculations. The CNDO/2 method has been employed to compute the atomic charge and atomic dipole at each atomic centre. The modified Rayleigh-Schrödinger perturbation theory along with the multicentered-multipole expansion method have been employed to evaluate the long-range intermolecular interactions, while a '6-exp' potential function has been assumed for the short-range interactions. On the basis of stacking, in-plane, and terminal interac-tion energy calculations all possible geometrical arrangements of a molecular pair have been considered, and the most favourable configuration of the pair has been obtained. Molecular parameters like total ener-gy, binding energy and total dipole moment have been given. Results are discussed in the light of those obtained for the nematogens 4-(4'-ethoxyphenylazo) phenyl valerate (EPPV) and 4,4'-di-n-propoxy-azoxybenzene (DPAB). An attempt is made to explain the liquid crystalline behavior of these liquid crys-tals and thereby develop a molecular model for liquid crystallinity. 
  Reference    Z. Naturforsch. 55a, 923—928 (2000); received September 28 2000 
  Published    2000 
  Keywords    Liquid Crystal, Multicentered-multipole, CNDO/2 Method, Intermolecular Interactions, EMBAC 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0923.pdf 
 Identifier    ZNA-2000-55a-0923 
 Volume    55 
25Author    A. K. Urbatov, P. Janik, A. D. Ro, Zd-R Zo Sk, S.J R Zo Sk, M. Paluch, P. M. Alik, J. Z. Io Ło, J. JaRequires cookie*
 Title    Universal Scaling of Alpha Relaxation in Complex Liquids  
 Abstract    A plot is given, showing the result of a scaling analysis of dielectric loss curves containing, apart from low molecular glass former data (glycerol, dibutyl phtalate), also loss curves of the following liquid crystalline materials, mostly in the iso­ tropic phase: 4-(2-methylbutyl)-4'cyanobiphenyl (5*CB, supercooled isotropic phase), 4-cyano-4-n-alkyl biphenyls (nematogens 5CB and 8CB, isotropic phase), 4-(4-cyano-4-butylcyclohexyl)-4'-octylbiphenyl (laterally substituted nema-togen, isotropic phase), and 4-n-alkyl-4'-isothiocyanatobiphe-nyl (5 and 10 BT, isotropic and SmE phases). The plot applies the scaling formula originally proposed for glassforming, super­ cooled liquids [Dendzik et al.7]. The result supports the recent suggestion that dielectric relaxation in the isotropic phase of nematogens may show some features typical for "glassy" mate­ rials. 
  Reference    Z. Naturforsch. 56a, 893—894 (2001); received September 21 2001 
  Published    2001 
  Keywords    Complex Liquids Supercooled Liquids, Liquid Crystals, Dielectric Loss Curves, Universality 
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 TEI-XML for    default:Reihe_A/56/ZNA-2001-56a-0893_n.pdf 
 Identifier    ZNA-2001-56a-0893_n 
 Volume    56 
26Author    MagedA. OsmanRequires cookie*
 Title    Synthesis of Low Melting Liquid Crystalline N-(4-n-Alkylbenzilidene)-4'-n-aIkylanilines  
 Abstract    The synthesis of a number of dialkylbenzilidene anilines is described. Mesomorphic phases are found at or below room temperature. An efficient method for the preparation of the 4-n-alkylanilines and their benzilidene derivatives is described. 
  Reference    (Z. Naturforsch. 31b, 801—804 [1976]; received February 18 1976) 
  Published    1976 
  Keywords    Liquid Crystals, Schiff Bases, Dialkylbenzilidene Anilines, p-n-Alkylanilines, Mesophases 
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 TEI-XML for    default:Reihe_B/31/ZNB-1976-31b-0801.pdf 
 Identifier    ZNB-1976-31b-0801 
 Volume    31 
27Author    Andreas Eckert, Bernd Kohne, Klaus PraefckeRequires cookie*
 Title    Flüssigkristalline Kohlenhydratdithioacetale * * Liquid Crystalline Carbohydrate Dithioacetals*  
 Abstract    Aus Anlaß der vor 100 Jahren vom Botaniker F. Reinitzer [1] und dem Physiker O. Lehmann [2] begonnenen Flüssigkristallforschung [3] Various S,S-dialkyl acetals of hexanal and numerous aldoses, tripodal in structure, have been synthesized, characterized and investigated by optical microscopy and D. S. C. Most of these geminal dithioacetals show a complicated melting behaviour and are thermotropic liquid crystal-line, exhibiting only one smectic-like phase of identical type. This mesophase is not miscible with the S Ad -Phase of other amphiphilic sugar-based liquid crystals. As shown in a homologues series of D-glucose S.S-dialkylacetal derivatives clearing points are rising as function of growing number n of carbon atoms in their S-alkyl chains. With constant n given a similar trend is observed by varying the length of the polar, hydrophilic sugar units. Regarding stereochemistry the dithioderivatives 5 and 12 of the pentose or hexose series, respectively, with a configuration related to that of D-mannose exhibit relatively the most stable mesophase. However, the most stable mesophase of all investigated sugar dithioderivatives is exhibited by the heptose S.S-dialkylacetal 13. Surprisingly, derivative 10 of L-rhamnose (6-desoxy-L-mannose) — the terminal hydroxyl group in the sugar chain of mannose is missing! -showed to be non-mesomorphic, demonstrating that a terminal hydroxyl group of these sugar derivatives seems to be essential for exhibiting a mesophase. On the other hand, as shown with the dithioderivative 9 of 2-desoxy-D-glucose in comparison to the derivative 8e and 12 of D-glucose or D-mannose, respectively, their clearing points seem to be less, although differently effected if an internal hydroxyl group — for instance here at C-2 — has been stripped off. Melting behaviour as well as thermomesogenic properties of the presented amphiphilic carbo-hydrate liquid crystals in relationship to their molecular structure are discussed in detail. 
  Reference    Z. Naturforsch. 43b, 878—888 (1988); eingegangen am 22. Dezember 1987 
  Published    1988 
  Keywords    Aldoses, Liquid Crystals, Mesophases Sugar SS-Dialkyl Acetals, Tripodal Amphiphiles 
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 TEI-XML for    default:Reihe_B/43/ZNB-1988-43b-0878.pdf 
 Identifier    ZNB-1988-43b-0878 
 Volume    43 
28Author    V.Salas Reyes3, C. AguilerabRequires cookie*
 Title    Synthesis and Characterization of Copper(II) and Nickel(II) Complexes Derived from «-Substituted Malondialdehydes  
 Abstract    The synthesis and characterization of two series of novel bis(4'-alkyloxyphenyl)m alondi-aldehydes of copper(II) and nickel(II), (R=C"H2"+1, n = 9, 10, 11, 12) from 2-(4'-hydroxy-phenyl)-3-dimethylamino acrolein is described. 
  Reference    Z. Naturforsch. 50b, 205 (1995); received September 28 1994 
  Published    1995 
  Keywords    M alondialdehyde, Acroleins, Formylation, M etallom esogen, Liquid Crystal 
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 TEI-XML for    default:Reihe_B/50/ZNB-1995-50b-0205.pdf 
 Identifier    ZNB-1995-50b-0205 
 Volume    50 
29Author    V. I. StepanovRequires cookie*
 Title    Comment on the Osipov-Terentjev Calculation of the Viscosity of Liquid Crystals  
 Abstract    The calculation of the viscosity of liquid crystals based on the rotational diffusion approximation recently reported by Osipov and Terentjev [1 a] is critically examined. It is shown that the main result of their treatment -the evaluation of the activational exponent -arises from the neglect of the second derivative of the distribution function with respect to the azimuthal angle in the Fokker-Planck equation. The correct asymptotic formula for the rotational viscosity coefficient is derived. 
  Reference    Z. Naturforsch. 47a, 625—626 (1992); received August 8 1991 
  Published    1992 
  Keywords    Liquid crystal, Viscosity coefficient, Rotational diffusion, Fokker-Planck equation, Energy barrier 
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 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0625_n.pdf 
 Identifier    ZNA-1992-47a-0625_n 
 Volume    47 
30Author    C. Forte, M. Geppi, C. A. VeraciniRequires cookie*
 Title    Study of the Molecular Dynamics from Deuterium Zeeman and Quadrupolar NMR Relaxation of 4,4'-di-n-Heptylazoxybenzene in the Nematic and Smectic A Phases  
 Abstract    The deuterium spin-lattice (T1Z) and quadrupolar (r iQ) relaxation times of the liquid crystal 4,4'-Heptyl-azoxybenzene (HAB), deuterated on the aromatic rings and the first methylene group of the chains, have been measured by means of the Jeener-Broekaert pulse sequence at two different frequencies (10 and 46.04 M Hz) and throughout the nematic and the smectic A phase. By applying suitable models, we have determined rotational and reorientational diffusion coefficients and evalu­ ated the contribution of the different m otions (internal, molecular and collective) to the relaxation. In particular we have found a non negligible contribution from order director fluctuations. A comparison between the Tlz and Ti Q measurements performed by means of Jeener-Broekaert and Wimperis pulse sequences is also shown. 
  Reference    Z. Naturforsch. 49a, 311 (1994); received August 16 1993 
  Published    1994 
  Keywords    Liquid crystal, Deuterium N M R, M olecular dynamics, Deuterium relaxation, Director fluctuation 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-0311.pdf 
 Identifier    ZNA-1994-49a-0311 
 Volume    49 
31Author    Stanislaw Urban, Albert Wiirflinger3Requires cookie*
 Title    DTA and Dielectric Studies under Pressure of a Smectogen Substance with a Strong Perpendicular Dipole Moment  
 Abstract    The phase diagram of a substance with two CN groups attached to the benzene ring at lateral posi­ tions (CNCN) has been obtained with differential thermal analysis (DTA). The pressure range of the smectic A phase is limited, resulting in a triple point (Cr, SA, L) at 135 MPa and 371 K. However, the SA-phase exists also above the triple point as a metastable phase. The transverse relaxation times rx were obtained from the dielectric spectra measured for several isotherms as a function of pressure with­ in the SA-phase of CNCN. The activation volume, A#Vj_ = RT (d In = (52 ± 3) cm3/mol is larg­ er than A Vj|, recently derived from the pressure dependence of the longitudinal relaxation times for other substances in the SA-phase. It is concluded that due to steric hindrances made by the cyano groups the molecular rotations around the long axes become strongly slowed down by pressure and the smec­ tic phase disappears 
  Reference    Z. Naturforsch. 56a, 489—4 (2001); received April 23 2001 
  Published    2001 
  Keywords    Liquid Crystals, Smectic A, DTA, Phase Diagram, Dielectric Relaxation, High Pressure 
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 TEI-XML for    default:Reihe_A/56/ZNA-2001-56a-0489.pdf 
 Identifier    ZNA-2001-56a-0489 
 Volume    56 
32Author    MagedA. Osman, M. A. OsmanRequires cookie*
 Title    Nematic Liquid Crystals with High Positive Dielectric Anisotropy * Nematic Liquid Crystals 1093 *>-®-CH-N-©-CN  
 Abstract    Alkylamino-and formyl alkylamino-cyano Schiff's base, biphenyl and phenylbenzoate liquid crystals were synthesized. The mesomorphic behaviour of these compounds is described. The introduction of the formyl group in the higher homologues lead to the disappearance of the mesophase. The alkylamino and formylalkylamino substituents are strong electron donating groups and lead to nematic phases with remarkably high positive dielectric anisotropy. Interest in electrooptical displays based on the twisted nematic effect [1] has lead to a growing demand for nematic liquid crystals with positive dielectric anisotropy. Non-polar or almost non-polar nematic compounds of the type 1 were found to possess a very small positive dielectric anisotropy (As = 0.05-0.5) [5-7], X =-CH= N-|21 , -C00-131,—N=N— |4| 1 Nematic phases of the Schiff's base and phenyl-benzoate type with larger A a were synthesized by A. Boiler [8, 9] through replacement of one of the alkyl groups by the cyano group which possess a larger dipole moment (—4 D). The remaining alkyl group on the other end of the molecule, which has a dipole moment of -f-0.3 D, was not changed. Recently, G. Gray [10] and R. Eidenschink [11] prepared analogous nematic phases of the biphenyl and phenyl cyclohexane types. All these compounds have A e values from 8 to 20 [12-14] which allow an operating voltage of 3 volts for a twisted nematic display. Since the threshold voltage and, correspond-ingly, the operating voltage is proportional to \J11A e, it is clear that new nematic liquid crystals with larger dielectric anisotropics are required if the operating voltage is to be substantially reduced. This can be achieved by replacing the remaining alkyl group with an electron donating substituent having a stronger dipole moment along the molecu-lar axis. The first attempt along this line was made by introducing the dimethylamino group (-(-1.6 D) * Reprint requests to Dr. M. A. Osman. 0340-5087/79/0800-1092/$ 01.00/0 at the other end of the benzyliden-aminobenzo-nitrile molecule, but this gave an isotropic com-pound melting at 183 °C [15]. The disappearance of the liquid crystalline properties is probably due to the high melting point of this compound and to the bulkiness of the dimethylamino group which lowers its clearing point. The aim of this work is to introduce the less bulky monoalkylamino group in molecules of type 1 and to study the effect of this substitution on their mesomorphic behaviour and on the magni-tude of the dielectric anisotropy. Results and Discussion N-(4-Methylaminobenzylidene)-4'-aminobenzo-nitrile (2) was prepared by condensing 4-methyl-aminobenzaldehyde with 4-aminobenzonitrile in bulk [16]. CH3HN-^)-cho+H2N-<Q>-CN-^CH3HN-Q>-CH-N^Q>-CN z The aldehyde was prepared by the Vilsmeier re-action [17]. 2"c> ~HjC :N CN H0 ~ H 3 CHN <> CHO Compound 2 melted at 163.1 °C and showed a monotropic nematic phase clearing at 138.0 °C. This confirmed that the disappearance of the meso-phase in the dimethylamino derivative was caused by the bulkiness of this group. However, the melting point of compound 2 is too high for practical applications and for conveniently measuring the dielectric anisotropy. The higher homologues of alkylaminobenzaldehyde and their Schiff's bases were therefore prepared in an attempt to lower the melting point. It seemed also of interest to 
  Reference    Z. Naturforsch. 34b, 1092—1095 (1979); received March 23 1979 
  Published    1979 
  Keywords    Liquid Crystals, Nematic Phases, High Positive Dielectric Anisotropy, Alkylamino-cyano-biphenyls, Alkylamino-cyano-phenylbenzoates 
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 TEI-XML for    default:Reihe_B/34/ZNB-1979-34b-1092.pdf 
 Identifier    ZNB-1979-34b-1092 
 Volume    34 
33Author    Jan Böm, G. Erd, Heppke, A. Ndreas RanftRequires cookie*
 Title    Synthese und ferroelektrische Eigenschaften chiraler Ester von 2,5-Diphenylpyrimidinen mit a-Fluorcarbonsäuren Synthesis and Ferroelectric Properties of 2,5-Diphenylpyrimidines with Different a-Fluorocarboxylic Acids  
 Abstract    Chiral esters of 2-[4-/?-hexylphenyl]-5-[4-hydroxyphenyl]pyrimidine and 2-[4-w-hexyloxy-phenyl]-5-[4-hydroxyphenyl]pyrimidine with four different a-fluorocarboxylic acids have been synthesized. The spontaneous polarization and the tilt angles in the smectic C* phase were m easured as a function of tem perature. All compounds exhibit wide range smectic C* phases, the highest values of the spontaneous polarization being about 400 nC/cm: . Additionally the spon­ taneous polarization in a higher ordered smectic phase was determ ined, the values ranging up to about 600 nC/cm2. The spontaneous polarization/tilt angle ratio strongly increases with decreasing tem perature. 
  Reference    Z. Naturforsch. 44b, 1127—1131 (1989); eingegangen am 6. März 1989 
  Published    1989 
  Keywords    Liquid Crystals, Smectic Liquid Crystals, Ferroelectric Properties, Chiral cc-Fluorocarboxylic Acid E sters, 2, 5-Diphenylpyrim idines 
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 TEI-XML for    default:Reihe_B/44/ZNB-1989-44b-1127.pdf 
 Identifier    ZNB-1989-44b-1127 
 Volume    44 
34Author    B. KirsteRequires cookie*
 Title    EPR and ENDO R Investigations of a Cholestane Spin Probe in Liquid Crystals  
 Abstract    A detailed EN D O R study o f anisotropic proton hyperfine shifts in the nitroxide spin probe 3-doxylcholestane (CSL) in liquid-crystalline solution is described. The data are interpreted by means o f theoretically calculated proton hyperfine tensors (M cConnell-Strathdee-Derbyshire treatment), providing an independent check o f the ordering matrix. The orientational order and the dynamic behavior o f the nematic and smectic phases o f the liquid crystals (40,6), (50,6), and 8CB are investigated by EPR using CSL and phenalenyl as spin probes. 
  Reference    Z. Naturforsch. 42a, 1296—1304 (1987); received August 8 1987 
  Published    1987 
  Keywords    EPR, EN D O R, liquid crystal, order parameters, sm ectic phase 
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 TEI-XML for    default:Reihe_A/42/ZNA-1987-42a-1296.pdf 
 Identifier    ZNA-1987-42a-1296 
 Volume    42 
35Author    Bernd Kohne, Klaus Praefcke, Werner Stephan, Peter NürnbergRequires cookie*
 Title    Discotische Flüssigkristalle: Beziehung zwischen Molekülstruktur und discogenen Eigenschaften scheibenförmiger Verbindungen, /iic/rf-flüssigkristalline Ester des //ryo-Inosits und des Mytilits [ 1 , 2 ] Discotic Liquid Crystals: Relation between Molecular Structure and Discogenic Properties of Disc-shaped Compounds, Non-liquid Crystalline Esters of m yo -Inositol and Mytilitol [1,2]  
  Reference    Z. Naturforsch. 40b, 981 (1985); eingegangen am 25. März 1985 
  Published    1985 
  Keywords    Cyclitols, D erivatives o f Natural Products, C yclohexane D erivatives, Liquid Crystals, Cores o f D iscogenic Com pounds 
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 TEI-XML for    default:Reihe_B/40/ZNB-1985-40b-0981.pdf 
 Identifier    ZNB-1985-40b-0981 
 Volume    40