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'Dielectric relaxation' in keywords Facet   Publication Year 1995  [X]
Facet   section ZfN Section A  [X]
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1995[X]
1Author    J. Barthel, K. Bachhuber, R. BüchnerRequires cookie*
 Title     
 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 
2Author    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