کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
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5222440 | 1383454 | 2009 | 7 صفحه PDF | دانلود رایگان |
The synthesis and mesomorphism of a series of liquid crystal trimers made by covalently linking two cyanobiphenyl moieties with a central salicylaldimine core through two flexible spacers are reported. Nine different oxyalkyleneoxy spacers varying in the number of carbon atoms and thus, methylene units from 3 to 11 were used to understand structure-mesomorphic property correlations. The optical microscope and differential scanning calorimeter were employed to evaluate their phase transitional behavior. All the trimers exhibit an enantiotropic uniaxial nematic phase over a wide thermal range (>80 °C) while a homolog comprising an octamethylene (even-parity) spacer displays, additionally, a metastable smectic phase. The nematic-isotropic transition temperatures critically depend on the parity of the spacer with the values for the odd-parity spacer containing homologs being lower than those of the even members, a feature generally observed in oligomesogens.
Journal: Tetrahedron - Volume 65, Issue 32, 8 August 2009, Pages 6403-6409