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1Author    S. A. Markarian, M. StockhausenRequires cookie*
 Title    Dielectric Relaxation of Diethylsulfoxide  
 Abstract    The dielectric loss spectrum of the title substance has been measured in its pure liquid state between 10 MHz and 72 GHz at 20°C. In comparison to the Debye function, it is slightly broadened towards the high frequency side. The maximum cor-responds to a relaxation time of 51 ps. In view of the molecu-lar size and viscosity, this is relatively long and thus indicative of associative intermolecular effects as in the case of the homol-ogous compound dimethylsulfoxide. 
  Reference    Z. Naturforsch. 55a, 667—668 (2000); received April 25 2000 
  Published    2000 
  Keywords    Association, Dielectric Relaxation, Liquids 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0667_n.pdf 
 Identifier    ZNA-2000-55a-0667_n 
 Volume    55 
2Author    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 
3Author    J. Barthel, K. Bachhuber, R. BüchnerRequires cookie*
 Abstract    ie le c tr ic R e la x a tio n o f N a C 1 0 4 S o lu tio n s in F o r m a m id e , N -M e th y lf o r m a m id e , a n d N ,N -D im e th y lf o rm a m id e Dedicated to Prof. Hitoshi Ohtaki on the occasion of his 60th birthday Complex permittivity spectra in the frequency range 0.95 < v/[GHz] < 89 for N,N-dimethylform-amide (DMF), N-methylformamide (NMF), formamide (FA) and their solutions of NaC104 are investigated to study the change of liquid structure and dynamics arising from the availability of one hydrogen-bond acceptor site together with no (DMF), one (NMF), or two (FA) donor sites on the same molecule. Three solvent relaxation processes are observed for NMF and two for FA and DMF. The relaxation parameters are used to determine solvation numbers. They show that ion-solvent interactions lead to a reduction of the average length of the H-bonded NMF chains but have only moderate influence on the FA structure. An additional solute relaxation process in DMF solutions is due to the diffusion-controlled formation and decomposition of solvent-shared ion pairs. 
  Reference    Z. Naturforsch. 50a, 65—74 (1995); received October 22 1994 
  Published    1995 
  Keywords    Dielectric relaxation, Formamides, Solvation, Solvent dynamics, Ion association 
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 TEI-XML for    default:Reihe_A/50/ZNA-1995-50a-0065.pdf 
 Identifier    ZNA-1995-50a-0065 
 Volume    50 
4Author    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 
5Author    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 
6Author    R. Elsebrock, M. StockhausenRequires cookie*
 Title    Dielectric Spectroscopy of Solutions of Some Alkylammonium Salts in Chloroform and 1-Octanol  
 Abstract    Dielectric loss spectra between 1 MHz and 36 GHz have been measured at 20°C for solutions of hexadecyl trimethylammonium bromide and chloride, tetrahexylammonium bromide and tetrabutylam-monium bromide in chloroform and 1-octanol (three solutes per solvent) at moderate and high concen-trations. The discussion is aimed at identifying relaxation processes involving ions. Describing the relax -ational part of the spectra (after subtraction of the conductivity contribution) by a sum of spectral com-ponents, the lowest frequency component can be attributed to the solute in all cases. Its concentration dependence is indicative of two ionic relaxation processes differing in physical nature. The solvent is partly involved in those processes; moreover a structure breaking effect is likely to occur in case of the alcoholic solvent. The results are also discussed in comparison with a molten alkylammonium salt and with solutions of this and of inorganic salts. 
  Reference    Z. Naturforsch. 55a, 629—636 (2000); received April 13 2000 
  Published    2000 
  Keywords    Dielectric Relaxation, Electrolyte Solutions, Ionic Aggregation 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0629.pdf 
 Identifier    ZNA-2000-55a-0629 
 Volume    55 
7Author    Jan Jadżyn, Grzegorz Czechowski, Danuta BaumanRequires cookie*
 Title    Static and Dynamic Dielectric Polarization and Viscosity of AZ-Hexylcyanobiphenyl in the Isotropic and Nematic Phases  
 Abstract    On the basis of the temperature dependence of the static principal permittivities, £y and e x , measured for the nematic phase of «-hexylcyanobiphenyl (C 6 H 13 -Ph-Ph-C=N, 6CB), a value of the angle ß between the long molecular axis and the direction of the dipole moment /iof 6CB, as well as the order parameter S{T), were obtained by use of the Maier-Meier equations. From the dielectric relaxation and viscosity data, the contribution of the nematic potential to the molecular dynamics was estimated. In the isotropic phase the dielectric and viscosity data allow one, in the framework of the Debye model, to estimate the effective length of 6CB molecule. 
  Reference    Z. Naturforsch. 55a, 810—816 (2000); received June 24 2000 
  Published    2000 
  Keywords    Electric Permittivity, Dielectric Relaxation, Viscosity, 6CB 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0810.pdf 
 Identifier    ZNA-2000-55a-0810 
 Volume    55 
8Author    J. Jadżyn, G. Czechowski, B. Żywucki, C. Legrand, P. Bonnet, R. DąbrowskiRequires cookie*
 Title    Dielectric Properties of Mesomorphic n-TPEB's in Isotropic Phase  
 Abstract    Dielectric relaxation studies have been performed for the isotropic phase of a series of mesogenic molecules of l-[3-n-alkyl-biphenyl]-2-[4-isothiocyanatophenyl]ethane, CnH 2n+ 1 -(f)-(t>-CH 2 CH 2 -<p-NCS (n-TPEB), for n = 7, 8 and 9. Two Debye-type dielectric absorption bands have been interpreted as corresponding to the rotation around the short and long molecular axis. 
  Reference    Z. Naturforsch. 48a, 871—874 (1993); received May 29 1993 
  Published    1993 
  Keywords    Dielectric relaxation, Molecular dynamics, Mesomorphic molecules, Relaxation time, Activation energy 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0871.pdf 
 Identifier    ZNA-1993-48a-0871 
 Volume    48 
9Author    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 
10Author    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