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'liquid crystals' in keywords Facet   Publication Year 1995  [X]
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Publication Year
1995[X]
1Author    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 
2Author    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 
3Author    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 
4Author    V.Salas Reyes3, C. AguilerabRequires cookie*
 Title    Synthesis and Characterization of Copper(II) and Nickel(II) Complexes Derived from «-Substituted Malondialdehydes  
 Abstract    The synthesis and characterization of two series of novel bis(4'-alkyloxyphenyl)m alondi-aldehydes of copper(II) and nickel(II), (R=C"H2"+1, n = 9, 10, 11, 12) from 2-(4'-hydroxy-phenyl)-3-dimethylamino acrolein is described. 
  Reference    Z. Naturforsch. 50b, 205 (1995); received September 28 1994 
  Published    1995 
  Keywords    M alondialdehyde, Acroleins, Formylation, M etallom esogen, Liquid Crystal 
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 TEI-XML for    default:Reihe_B/50/ZNB-1995-50b-0205.pdf 
 Identifier    ZNB-1995-50b-0205 
 Volume    50