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1Author    Hanka Moryson, Danuta Bauman, Wojciech Hilczer, Stanislaw HoffmannRequires cookie*
 Title    Molecular Orientation in Uniaxial Liquid Crystal Phases as Studied by Electron Paramagnetic Resonance  
 Abstract    The electron paramagnetic resonance spectra of 3/3-doxyl-5a:-cholestane dissolved in five liquid crystals have been recorded as a function of temperature in the isotropic and mesogenic phases. From these spectra the order parameter (P2) has been determined. The results have been com-pared with the data obtained from the optical birefringence measurements and from the polarized absorption spectra of the dichroic dye dissolved in liquid crystal host. 
  Reference    Z. Naturforsch. 54a, 299—304 (1999); received March 31 1999 
  Published    1999 
  Keywords    Liquid Crystal, EPR, Order Parameter 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0299.pdf 
 Identifier    ZNA-1999-54a-0299 
 Volume    54 
2Author    K. H. Schweikert, F. NoackRequires cookie*
 Title      
 Abstract    The frequency dependence of the longitudinal proton spin relaxation time Tx was measured by field-cycling and standard NMR techniques in the nematic, smectic and reentrant nematic mesophases of the reentrant liquid crystal 6OCB-8OCB. The results clearly demonstrate that, in contrast to conclusions reported in the literature, the underlying relaxation mechanisms are the same for the nematic and reentrant nematic order, but different in the nematic and smectic phase. In particular, at low frequencies the nematic and reentrant samples reveal a square-root dispersion profile (T, ~ v1 2) characteristic for nematic director fluctuations, whereas the smectic samples show a dissimilar and only very narrow dispersion step. It can be attributed to a linear relaxation time increase (Tx ~ v1) expected for smectic-type order fluctuations. The experimental data are described and discussed in terms of four molecular processes, namely nematic or smectic order fluctuations, self-diffusion, rotational motions, and a resonant proton nitrogen coupling. 
  Reference    Z. Naturforsch. 44a, 597 (1989); received April 19 1989 
  Published    1989 
  Keywords    Spin relaxation Field-cycling, Liquid crystals, Reentrant nematic 
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 TEI-XML for    default:Reihe_A/44/ZNA-1989-44a-0597.pdf 
 Identifier    ZNA-1989-44a-0597 
 Volume    44 
3Author    V. Vill, J. ThiemRequires cookie*
 Title    Flüssigkristalle mit monosubstituierten alicyclischen und heteroalicyclischen Ringen Liquid Crystals Derived from Mono-Substituted Alicyclic and Heteroalicyclic Rings  
 Abstract    Twenty two liquid crystalline mono-substituted cyclopentanes and cyclohexanes including their oxygen analogues were prepard and studied. Smectic phases with clearing temperatures 5^80 °C were observed, and these do not differ considerably between the esters of the more flexible five-mem-bered ring derivatives and those of the conformationally more rigid six-membered rings. In case of the latter, decreasing clearing points ar observed with increasing ratios of the axial conformation (static conformational effect). Altogether rather low clearing points are observed, which may be interpreted by a dynamic conformational effect owing to which fast ring inversion causes the compounds to appear in a bulkier shape, and this results in a disadvantageous packing in the mesophase. 
  Reference    Z. Naturforsch. 45a, 1345—1348 (1990); eingegangen am 21. Oktober 1990 
  Published    1990 
  Keywords    Alicyclic rings, Liquid crystals, Conformation, Oxygen heterocycles 
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 TEI-XML for    default:Reihe_A/45/ZNA-1990-45a-1345.pdf 
 Identifier    ZNA-1990-45a-1345 
 Volume    45 
4Author    S. U. Rban, T. Briickert, A. W. ÜrflingerRequires cookie*
 Title    Dielectric Studies on Liquid Crystals under High Pressure: VI. Low Frequency Relaxation Process in the Nematic and Smectic A Phase of 4-n-Octyl-4'-Cyanobiphenyl (8 CB)  
 Abstract    Dielectric relaxation studies of 4-n-octyl-4'-cyanobiphenyl (8 CB) were performed in the pressure range 0 .1 -1 2 0 M Pa, the frequency range 1 k H z -1 3 M Hz and the temperature range 2 9 5-331 K. The dielectric behaviour of 8C B in the nematic phase is similar to that of 5CB, 6C B and 7CB. In particular, the activation enthalpy decreases with increasing pressure and the activation volume decreases with increasing temperature in the nematic phase. In the smectic A phase of 8CB both these parameters are markedly lower and show opposite pressure and temperature dependencies. We tentatively interpret these effects as a result of breaking of the dipole-dipole correlations which manifests itself differently in these liquid crystalline phases. 
  Reference    Z. Naturforsch. 49a, 552 (1994); received March 5 1994 
  Published    1994 
  Keywords    Dielectric relaxation, High pressure, Liquid crystals, Activation quantities 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-0552.pdf 
 Identifier    ZNA-1994-49a-0552 
 Volume    49 
5Author    I. D. Ierking1, F. G. Ießelm Ann1, P. Zugenm, H. R2, H. Z. Aschke2, W. Kuczynski3Requires cookie*
 Title    The Origin of the Helical Twist Inversion in Single Component Cholesteric Liquid Crystals  
 Abstract    The cholesteric twist inversion by temperature variation o f a single com ponent thermotropic liquid crystalline system was experimentally investigated and is explained by the partial twisting power model, evaluating the temperature dependent pitch o f five different configurations of a benzoic acid biphenyl ester with two chiral centers. The temperature dependence o f the twisting power and the cholesteric pitch for several stereoisomeric com pounds can in first approximation be predicted by the partial twisting powers of the individual chiral centers determined from the partially racemic configurations. 
  Reference    Z. Naturforsch. 49a, 1081—1086 (1994); received August 12 1994 
  Published    1994 
  Keywords    Liquid crystal, Chirality, Cholesteric mesophase, Twist inversion 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-1081.pdf 
 Identifier    ZNA-1994-49a-1081 
 Volume    49 
6Author    Christina Papenfußa, Jozsef Verhásb, Wolfgang MuschikaRequires cookie*
 Title      
 Abstract    A continuum theory of a biaxial nematic phase in liquid crystals is presented. The liquid crys­ talline ordering is described by a field of three unit vectors. Because these are macroscopic directors, the present approach is a generalization of the Ericksen-Leslie theory to biaxial nematics. The applied tools from nonequilibrium thermodynamics are classical Linear Irreversible Thermodynam­ ics and Gyarmati's variational principle. Onsager reci­ procity relations; Gyarmati's variational principle. A S im p lifie d T h e rm o d y n a m ic T h e o r y f o r B ia x ia l N e m a tic s 
  Reference    Z. Naturforsch. 50a, 795—804 (1995); received June 3 1994 
  Published    1995 
  Keywords    Liquid crystals, biaxial nematics, Linear Irreversible Thermodynamics 
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 TEI-XML for    default:Reihe_A/50/ZNA-1995-50a-0795.pdf 
 Identifier    ZNA-1995-50a-0795 
 Volume    50 
7Author    Heidrun Amm, Maren Grigutsch, Ralf StannariusRequires cookie*
 Title    Spatio-temporal Analysis of Electroconvection in Nematics  
 Abstract    We investigate electroconvection in nematic liquid crystals by means of optical microscopy. Time resolved optical images are used to study the director dynamics. For the first time we present instant images in the dielectric regime. A numerical simulation of the optical transmission patterns is performed on the basis of Fermat's principle. In the instant images of dielectric rolls, the periodicity of the observed optical pattern is equal to the wavelength Ao of the convection rolls. The well known low contrast 'stationary' optical texture observed in conventional experiments results from time averaging of these instant images; its wavelength is Ao/2. 
  Reference    Z. Naturforsch. 53a, 117—126 (1998); received December 10 1997 
  Published    1998 
  Keywords    Liquid Crystals, Pattern Formation, Electrohydrodynamic Instability, Optical Microscopy 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0117.pdf 
 Identifier    ZNA-1998-53a-0117 
 Volume    53 
8Author    S. Urban, B. Gestblom, R. Dąbrowski, H. KresseRequires cookie*
 Title    Dielectric Studies of a Substance with Negative Dielectric Anisotropy  
 Abstract    The results of dielectric studies of 6BAP(F) (l-[4-(hexylbicyclo[2,2,2]octyl]-2-(3-fluoro-4-methoxy-phenyl)ethane) in the nematic and isotropic phases are presented. The substance has a negative dielec-tric anisotropy. By applying two experimental techniques, using a network analyzer and time domain spectrometer (TDS), the two main relaxation processes, connected with the molecular reorientation around the short and long axes, respectively, were resolved in the phases studied. The activation bar-riers hindering the motions were obtained. By extrapolation of the longitudinal and transverse relaxa-tion times from the isotropic to the nematic phase the retardation factors, and g x , and the nematic po-tential versus temperature could be calculated. These are discussed together with the order parameter S obtained from the refractive index, and are compared with the predictions of the mean-field theories. 
  Reference    Z. Naturforsch. 53a, 134—140 (1998); received February 20 1998 
  Published    1998 
  Keywords    Liquid Crystals, Dielectric Anisotropy, Dielectric Relaxation, Retardation Factors 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0134.pdf 
 Identifier    ZNA-1998-53a-0134 
 Volume    53 
9Author    A. WiirflingerRequires cookie*
 Title    Nematic Potential and Order Parameter Determined from Dielectric Measurements  
 Abstract    The Maier-Saupe theory is employed in order to calculate order parameters S from the nematic po-tential q. It is found that one of the basic assumptions of the Maier-Saupe theory, q ~S, is approximate-ly fulfilled. The relation between q and S is analysed for various state changes. Previously reported find-ings for 7 PCH that q ~S, not fulfilled along isochoric changes, can be explained by taking into account the pressure and temperature dependences of q. The procedure described in this paper allows to treat experimental data for the nematic potential in a unique way, without being affected by inadequacies of experimentally determined order parameters. 
  Reference    Z. Naturforsch. 53a, 141—144 (1998); received February 11 1998 
  Published    1998 
  Keywords    Liquid Crystals, High Pressure, Nematic Potential, Dielectric Relaxation 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0141.pdf 
 Identifier    ZNA-1998-53a-0141 
 Volume    53 
10Author    Lucia Calucci, Claudia Forte, Marco Geppi, CarloAlberto VeraciniRequires cookie*
 Title    Dynamics of Liquid Crystals by Means of 2 H-NMR: a Comparison between 4,4'-bis(hexyloxy)azoxybenzene and the Derivative Pd(II) Complex AZPAC  
 Abstract    In the present work we report a molecular dynamics investigation of the two mesogens 4,4'-bis(hexyloxy)azoxybenzene (HL) and its Pd(II) acetylacetonate derivative Azpac in their nematic phases. Deuterium Zeeman and quadrupolar spin-lattice relaxation times have been measured at 46.04 MHz on two isotopomers of Azpac (Azpac-d 4 and Azpac-c/ 26 > deuteriated on the aromatic core and on the alkoxy chains, respectively) and on HL-d 4 , an isotopomer of HL partially deuteri-ated on the aromatic core, by means of the Wimperis pulse sequence. The spectral densities obtained from the measured relaxation times are discussed in terms of internal and overall molecular motions. A small step rotational diffusion model for the overall molecular motions, superimposed on a free rotational model for internal motions, allowed diffusion coefficients for molecular spinning and tumbling and for phenyl ring rotations to be derived for HL; the same models were used in describing the dynamics of Azpac. 
  Reference    Z. Naturforsch. 53a, 427—435 (1998); received October 31 1997 
  Published    1998 
  Keywords    Liquid Crystals, Deuterium Relaxation, Molecular Dynamics, Metallomesogens, NMR 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0427.pdf 
 Identifier    ZNA-1998-53a-0427 
 Volume    53 
11Author    A. Würflinger, S. UrbanRequires cookie*
 Title    Relations between Nematic Potential and Order Parameters (P 2 ) and (P 4 >  
 Abstract    The Maier-Saupe theory is employed in order to calculate order parameters (P 2), (P 4) from the nema-tic potential q. The relation between <r=q/(RT) and S = (P 2) corresponds well with a recently establis-hed formula by Kalmykov. The relation between the order parameters is in accordance with the analy-tic expression (P 4)=5/l (P 2) 2 proposed by Zanonni, but deviates significantly from the Faber model, according to which log (P 4)=(10/3) log (P 2). Experimental results for 5 CB obtained from Raman mea-surements, however, are in better agreement with the Faber model. 
  Reference    Z. Naturforsch. 53a, 883—886 (1998); received September 12 1998 
  Published    1998 
  Keywords    Liquid Crystals, Nematic Potential, Order Parameters 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0883.pdf 
 Identifier    ZNA-1998-53a-0883 
 Volume    53 
12Author    A. Kapanowski, K. SokalskiRequires cookie*
 Title    Elastic Constants of Binary Liquid Crystalline Mixtures  
 Abstract    Microscopic expressions for the elastic constants of binary liquid crystalline mixtures composed of short rigid uniaxial molecules are derived in the thermodynamic limit at small distorsions and a small density. Uniaxial and biaxial nematic phases are considered. The expressions involve the one-particle distribution functions and the potential energy of two-body short-range interactions. The theory is used to calculate the phase diagram of a mixture of rigid prolate and oblate molecules. The concentration dependence of the order parameters and the elastic constants are obtained. The possibility of phase separation is not investigated. 
  Reference    Z. Naturforsch. 53a, 963—976 (1998); received September 24 1998 
  Published    1998 
  Keywords    Liquid Crystals, Nematics, Elastic Constants, Mixtures 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0963.pdf 
 Identifier    ZNA-1998-53a-0963 
 Volume    53 
13Author    M. Massalska-Arodź, A. Würflinger, D. BüsingRequires cookie*
 Title    High-pressure DTA Studies of the Phase Behaviors of 4-n -butyl-thiocyanobiphenyl (4TCB) and 4-w-pentyl-4'-n-phenyl-cyanocyclohexane (5HCP)  
 Abstract    DTA measurements of 4-/i-butyl-thiocyanobiphenyl (4TCB) and/?-cyano-/?'-pentylphenyl-cyclohex-ane (5HCP) have been performed in the temperature range 220 K-390 K and pressures up to 400 MPa. For 4TCP a transition from a crystalline to a liquid crystal phase (probably smectic E) could be detect-ed at higher pressures > 90 MPa. The pressure dependence of the transition temperature has been estab-lished. At pressures lower than 88.7 MPa no transition of SmE into a crystal or into a glass has been found. For 5HCP only the melting curve was observed, in contrast to 5PCH, which displays a liquid crystalline nematic phase. 
  Reference    Z. Naturforsch. 54a, 675—678 (1999); received November 5 1999 
  Published    1999 
  Keywords    DTA, High Pressures, Phase Transitions, Liquid Crystals 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0675.pdf 
 Identifier    ZNA-1999-54a-0675 
 Volume    54 
14Author    H. Schmalfuss, W. Weissflog, A. Würflinger3, S. Masberg3, G. M. Schneider3Requires cookie*
 Title    Thermodynamic Measurements on Selected Liquid Crystals at Normal and Elevated Pressures  
 Abstract    Densities have been determined for two 5-n-alkyl-2-(4-isothiocyanatophenyl)-l,3-dioxanes (6DBT, 10DBT), 4-n-tetradecyl-4'-cyanobiphenyl (14CB), 4-n-octyl-4'-thiocyanatobiphenyl (8BT) and two laterally aryl-branched mesogens 4-cyanobenzyl 5-(4-n-octyloxybenzoyloxy)-2-undecyloxybenzoate (4CNOUB), 3-cyanobenzyl 2,5-bis(4-n-octyloxybenzoyloxy)benzoate (3CN-BOB). The densities have been measured in the isotropic, nematic (only 3CNBOB) and smectic phases with a vibrating tube densimeter. The densities decrease with increasing alkyl chain length within a homologous series. Furthermore the enthalpy changes accompanying the phase transitions have been determined by DSC. 
  Reference    Z. Naturforsch. 56a, 262—266 (2001); received December 5 2000 
  Published    2001 
  Keywords    Specific Volumes, Density, DSC, Liquid Crystals, Thermodynamics 
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 TEI-XML for    default:Reihe_A/56/ZNA-2001-56a-0262.pdf 
 Identifier    ZNA-2001-56a-0262 
 Volume    56 
15Author    V. Villa, F. Fischer3, J. ThiembRequires cookie*
 Title     
 Abstract    o le k u la r e s V e rd rillu n g s v e rm ö g e n von K o h le n h y d ra t-D e riv a te n Helical Twisting Power of Carbohydrate Derivatives For the first time carbohydrate derivatives were systematically studied as doping material for a liquid crystalline phase. These compounds can exhibit a large twisting power. It may be controlled by the configurations of single chiral centers. Thus, a series of phenomena are realized in the cholesteric phase such as helix inversion, large or small temperature dependencies of the pitch, as well as broad blue phases. Durch Zugabe einer chiralen, löslichen Substanz zu einer nematischen Phase läßt sich die cholesterische Phase erzeugen [1], Neben neu synthetisierten Ver­ bindungen wurden auch zahlreiche Naturstoffe, vor­ nehmlich Isoprenoide eingesetzt. Kohlenhydratderi-vate wurden dagegen vermutlich aufgrund ihrer er­ heblichen Polarität bisher nicht in Betracht gezogen. Diese chemisch robusten und leicht zugänglichen Ver­ bindungen erscheinen ideal geeignet zu sein, da sich mit ihnen in einmaliger Weise alle stereochemischen Möglichkeiten realisieren lassen. Zur Überprüfung der Eignung von Kohlenhydrat-Derivaten als chirale Zusätze zu nematischen Phasen wurden 22 Mischungen untersucht. Als Wirtssubstanz diente jeweils 4-n-Butyloxy-phenyl-4'-n-hexyloxybenzoat (1, ZLI 1792). Als chirale Zusätze wurden gewählt (s. Tab. 1): 
  Reference    Z. Naturforsch. 43a, 1119—1125 (1988); eingegangen am 30. September 1988 
  Published    1988 
  Keywords    Helical twisting power, carbohydrates, induced cholesteric phase, diastereomers, liquid crystals 
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 TEI-XML for    default:Reihe_A/43/ZNA-1988-43a-1119.pdf 
 Identifier    ZNA-1988-43a-1119 
 Volume    43 
16Author    Ingo Dierking, Frank Gießelmann, Peter ZugenmaierRequires cookie*
 Title     
 Abstract    n O p tic a l M e th o d f o r th e D e te r m in a tio n o f th e C h o le s te r ic P itc h in L iq u id C r y s ta ls Preparation of a cholesteric liquid crystalline phase in planar orienting liquid crystal cells exhibits discontinuous colour changes with temperature when viewed between crossed polarizers. The trans­ mission spectra of such a system can be described by a modified de Vries equation, with the bire­ fringence dispersion included in a simplified single-band model. With a suitable choice of the cell gap as compared to the cholesteric pitch, the procedure can be used as a new method to determine the temperature dependence of the cholesteric pitch. 
  Reference    Z. Naturforsch. 50a, 589—594 (1995); received December 17 1994 
  Published    1995 
  Keywords    Liquid crystal, cholesteric mesophase, pitch determination, birefringence dispersion, twist inversion 
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 TEI-XML for    default:Reihe_A/50/ZNA-1995-50a-0589.pdf 
 Identifier    ZNA-1995-50a-0589 
 Volume    50 
17Author    T. Brückert, D. Büsing, A. Würflinger, S. UrbanRequires cookie*
 Title      
 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 
18Author    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 
19Author    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 
20Author    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 
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