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'Nematic liquid crystals' in keywords
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1Author    Z. NaturforschRequires cookie*
 Abstract    The pressure-dependence of the dielectric anisotropy, Ae = e0||— e0±, of two nematogens, n-pentyl-and n-hexyl-cyanobiphenyl (5CB and 6CB) has been measured at constant temperature. For this purpose a high pressure chamber made of non-magnetic materials was constructed, allowing for the orientation of the samples by a magnetic field. The pressure dependencies of Aex were analyzed in the frame of the Maier-Meier equations for the principal permittivity components in the nematic phase. It was found that the relation between Ae and the order parameter S is not properly described by these equations. The Kirkwood correlation factor calculated on the basis of the present results and the Maier-Meier equations is smaller than 0.5, whereas it increases to a more realistic value (~0.7) if the electronic polarization is incorporated in the equations. P r e s s u r e D e p e n d e n c e o f th e D ie le c tric A n is o tr o p y o f 5 C B a n d 6 C B 
  Reference    Z. Naturforsch. 50a, 826—830 (1995); received April 28 1995 
  Published    1995 
  Keywords    Nematic liquid crystals, Cyanobiphenyls, High pressure, Dielectric anisotropy 
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 TEI-XML for    default:Reihe_A/50/ZNA-1995-50a-0826.pdf 
 Identifier    ZNA-1995-50a-0826 
 Volume    50 
2Author    Stanisław Urban, Jerzy Kędzierski, Roman DąbrowskiRequires cookie*
 Title    Analysis of the Dielectric Anisotropy of Typical Nematics with the Aid of the Maier-Meier Equations  
 Abstract    Using the experimental data on the dielectric anisotropy, density, polarizability, dipole moment, and order parameter in the nematic phase of seven typical liquid crystalline substances, the applicability of the Maier-Meier theory for the description of the dielectric properties of nematics is checked. Substanc-es with different polarity and different tendency to form associates in the nematic phase were studied. It is found that the Maier-Meier equations describe fairly well the dielectric permittivity components of nematics. The estimated values of the angle ß formed by the dipole moment with the long molecular axis are compared with those obtained in other studies. 
  Reference    Z. Naturforsch. 55a, 449—456 (2000); received December 9 1999 
  Published    2000 
  Keywords    Nematic Liquid Crystals, Dielectric Anisotropy, Maier-Meier Equations 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0449.pdf 
 Identifier    ZNA-2000-55a-0449 
 Volume    55 
3Author    S. UrbanRequires cookie*
 Title    Dielectric Studies of 4-w-Hexyloxy-4'-Cyanobiphenyl (60CB) at Elevated Pressure  
 Abstract    The principal dielectric permittivity components in the nematic phase of 4-rc-hexyloxy-4'-cyanobiph-enyl (60CB) were measured as functions of temperature at ambient pressure and as functions of pres-sure up to 100 MPa at several constant temperatures. The dielectric anisotropy is analized in the frame of the Maier-Meier equations. The pressure dependence of the order parameter is deduced. Preliminary results for the activation volume and activation enthalpy from the pressure and temperature dependenc-es of the longitudinal relaxation times are obtained. 
  Reference    Z. Naturforsch. 54a, 365—369 (1999); received March 29 1999 
  Published    1999 
  Keywords    Nematic Liquid Crystal, 60CB, Dielectric Anisotropy, Order Parameter, High Pressure 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0365.pdf 
 Identifier    ZNA-1999-54a-0365 
 Volume    54 
4Author    Siegfried Hess, Bin SuRequires cookie*
 Title    Pressure and Isotropic-Nematic Transition Temperature of Model Liquid Crystals  
 Abstract    The pressure in the gaseous, the isotropic liquid and nematic liquid crystalline states, as well as the isotropic-nematic transition temperature are calculated for a model system composed of non-spherical particles. The potential is a generalization of the Lennard-Jones interaction where the attractive part depends on the relative orientations of the particles and the vector joining their centers of mass. Point of departure is an augmented van der Waals approach. It involves a modified Carnahan-Starling expression associated with the repulsive part of the interaction, and an orientation dependent second virial coefficient, as well as the orientational distribution functions of a pair of particles, linked with the attractive part of the potential. In a high temperature approximation, and for a special choice of model parameters, results are presented and displayed graphically. 
  Reference    Z. Naturforsch. 54a, 559—569 (1999); received June 1 1999 
  Published    1999 
  Keywords    Nematic Liquid Crystal, Interaction Potential, Equation of State 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0559.pdf 
 Identifier    ZNA-1999-54a-0559 
 Volume    54 
5Author    A. Scharkowski, H. Schmiedel, R. Stannarius, E. WeißhuhnRequires cookie*
 Title    Elastic Constants of Nematic Phenylpyrimidines Determined by Two Different Methods  
 Abstract    A survey of various methods to measure the elastic constants K, of nematic liquid crystals is given. To determine K 3 and the anisotropy of the diamagnetic susceptibility Ax of two members of the 5n-hexyl-2-[4n-alkyloxy-phenyl]-pyrimidines and a mixture of both, we used a combined electro-magneto-optical method, consisting in independent measurements of the optical phase difference in electric and magnetic fields acting on the same cell. The temperature dependence of the K r and K 3 -values for these phenylpyrimidines can be explained by common theories. The Ax data show the same temperature dependence as the values of the orientational order parameter S obtained by 'H-NMR. 
  Reference    Z. Naturforsch. 45a, 37—42 (1990); received June 23 1989 
  Published    1990 
  Keywords    Nematic liquid crystals, elastic constants, diamagnetic susceptibility, electro-optic, magneto-optic 
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 TEI-XML for    default:Reihe_A/45/ZNA-1990-45a-0037.pdf 
 Identifier    ZNA-1990-45a-0037 
 Volume    45