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'induced cholesteric phase' in keywords
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1999 (1)
1988 (1)
1Author    V. Villa, F. Fischer3, J. ThiembRequires cookie*
 Title     
 Abstract    o le k u la r e s V e rd rillu n g s v e rm ö g e n von K o h le n h y d ra t-D e riv a te n Helical Twisting Power of Carbohydrate Derivatives For the first time carbohydrate derivatives were systematically studied as doping material for a liquid crystalline phase. These compounds can exhibit a large twisting power. It may be controlled by the configurations of single chiral centers. Thus, a series of phenomena are realized in the cholesteric phase such as helix inversion, large or small temperature dependencies of the pitch, as well as broad blue phases. Durch Zugabe einer chiralen, löslichen Substanz zu einer nematischen Phase läßt sich die cholesterische Phase erzeugen [1], Neben neu synthetisierten Ver­ bindungen wurden auch zahlreiche Naturstoffe, vor­ nehmlich Isoprenoide eingesetzt. Kohlenhydratderi-vate wurden dagegen vermutlich aufgrund ihrer er­ heblichen Polarität bisher nicht in Betracht gezogen. Diese chemisch robusten und leicht zugänglichen Ver­ bindungen erscheinen ideal geeignet zu sein, da sich mit ihnen in einmaliger Weise alle stereochemischen Möglichkeiten realisieren lassen. Zur Überprüfung der Eignung von Kohlenhydrat-Derivaten als chirale Zusätze zu nematischen Phasen wurden 22 Mischungen untersucht. Als Wirtssubstanz diente jeweils 4-n-Butyloxy-phenyl-4'-n-hexyloxybenzoat (1, ZLI 1792). Als chirale Zusätze wurden gewählt (s. Tab. 1): 
  Reference    Z. Naturforsch. 43a, 1119—1125 (1988); eingegangen am 30. September 1988 
  Published    1988 
  Keywords    Helical twisting power, carbohydrates, induced cholesteric phase, diastereomers, liquid crystals 
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 TEI-XML for    default:Reihe_A/43/ZNA-1988-43a-1119.pdf 
 Identifier    ZNA-1988-43a-1119 
 Volume    43 
2Author    Reiner Memmer, Folkert JanssenRequires cookie*
 Title    Computer Simulation of Chiral Liquid Crystal Phases IX. Chiral Induction in Guest-host Systems - Calculation of the Helical Twisting Power  
 Abstract    The chiral induction in liquid crystalline phases was studied by Monte Carlo simulation of the chiral Lebwohl-Lasher model. Binary guest-host systems composed of achiral and chiral molecules as well as of different chiral molecules were investigated in dependence on the composition. A cholesteric phase was induced by dissolving a small fraction of chiral molecules in a nematic phase. For dilute solutions the equilibrium pitch was found to be a linear function of the chiral dopant concentration. Independent of system size effects the application of self-determined boundary conditions enabled the determination of the symmetry adapted quantities for the chiral induction, the helical twisting power (HTP) and the achiral helical twisting power (AHTP). Additionally, a different orientational behaviour of enantiomer-ic dopants in the chiral surroundings of a cholesteric host phase has been determined. 
  Reference    Z. Naturforsch. 54a, 747—754 (1999); received October 29 1999 
  Published    1999 
  Keywords    Chirality, Liquid Crystals, Computer Simulation, Induced Cholesteric Phases, Helical Twisting Power 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0747.pdf 
 Identifier    ZNA-1999-54a-0747 
 Volume    54