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'Liquid Crystals' in keywords Facet   Publication Year 1989  [X]
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1989[X]
1Author    K. H. Schweikert, F. NoackRequires cookie*
 Title      
 Abstract    The frequency dependence of the longitudinal proton spin relaxation time Tx was measured by field-cycling and standard NMR techniques in the nematic, smectic and reentrant nematic mesophases of the reentrant liquid crystal 6OCB-8OCB. The results clearly demonstrate that, in contrast to conclusions reported in the literature, the underlying relaxation mechanisms are the same for the nematic and reentrant nematic order, but different in the nematic and smectic phase. In particular, at low frequencies the nematic and reentrant samples reveal a square-root dispersion profile (T, ~ v1 2) characteristic for nematic director fluctuations, whereas the smectic samples show a dissimilar and only very narrow dispersion step. It can be attributed to a linear relaxation time increase (Tx ~ v1) expected for smectic-type order fluctuations. The experimental data are described and discussed in terms of four molecular processes, namely nematic or smectic order fluctuations, self-diffusion, rotational motions, and a resonant proton nitrogen coupling. 
  Reference    Z. Naturforsch. 44a, 597 (1989); received April 19 1989 
  Published    1989 
  Keywords    Spin relaxation Field-cycling, Liquid crystals, Reentrant nematic 
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 TEI-XML for    default:Reihe_A/44/ZNA-1989-44a-0597.pdf 
 Identifier    ZNA-1989-44a-0597 
 Volume    44 
2Author    Jan Böm, G. Erd, Heppke, A. Ndreas RanftRequires cookie*
 Title    Synthese und ferroelektrische Eigenschaften chiraler Ester von 2,5-Diphenylpyrimidinen mit a-Fluorcarbonsäuren Synthesis and Ferroelectric Properties of 2,5-Diphenylpyrimidines with Different a-Fluorocarboxylic Acids  
 Abstract    Chiral esters of 2-[4-/?-hexylphenyl]-5-[4-hydroxyphenyl]pyrimidine and 2-[4-w-hexyloxy-phenyl]-5-[4-hydroxyphenyl]pyrimidine with four different a-fluorocarboxylic acids have been synthesized. The spontaneous polarization and the tilt angles in the smectic C* phase were m easured as a function of tem perature. All compounds exhibit wide range smectic C* phases, the highest values of the spontaneous polarization being about 400 nC/cm: . Additionally the spon­ taneous polarization in a higher ordered smectic phase was determ ined, the values ranging up to about 600 nC/cm2. The spontaneous polarization/tilt angle ratio strongly increases with decreasing tem perature. 
  Reference    Z. Naturforsch. 44b, 1127—1131 (1989); eingegangen am 6. März 1989 
  Published    1989 
  Keywords    Liquid Crystals, Smectic Liquid Crystals, Ferroelectric Properties, Chiral cc-Fluorocarboxylic Acid E sters, 2, 5-Diphenylpyrim idines 
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 TEI-XML for    default:Reihe_B/44/ZNB-1989-44b-1127.pdf 
 Identifier    ZNB-1989-44b-1127 
 Volume    44