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1Author    R. Dąbrowski, J. Jadżyn, J. Dziaduszek, Z. Stolarz, G. Czechowski, M. KasprzykRequires cookie*
 Title    The Physical and Molecular Properties of New Low Melting Nematics with Negative Dielectric Anisotropy  
 Abstract    The paper presents some basic physical properties (static electric permittivities, refraction indices, density and viscosity) of 2-chloro-4-n'-alkylphenyl esters of 4-/r-alkylbicyclo[2,2,2] octane-1-carbox-ylic acids (n'=l, n = 5 and 7) which are, at room temperature, nematics with a negative dielectric an-isotropy. On the basis of temperature dependence of the principal static permittivities £ H (T) and e±(T) of the nematics, using the Maier-Meier equations, the angle between the dipole moment vector and the long axis of mesogenic molecules, the apparent molecular dipole moment square pl P[) {T), and the ne-matic order parameter S(T) were determined. 
  Reference    Z. Naturforsch. 54a, 448—452 (1999); received May 8 1999 
  Published    1999 
  Keywords    Nematics, Dielectric Anisotropy, Density, Viscosity 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0448.pdf 
 Identifier    ZNA-1999-54a-0448 
 Volume    54 
2Author    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 
3Author    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 
4Author    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 
5Author    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