Odd–even effects at the nematic–isotropic and intercalated smectic A–nematic transitions of the non-symmetric α-(4′-cyanobiphenyl-4-yloxy)-ω-(4-alkylanilinebenzylidene-4′-oxy) alkane dimers An experimental study

Abstract

Liquid crystal dimers, in which two mesogenic groups are linked by a flexible spacer, exhibit a rich smectic polymorphism for both symmetric and non-symmetric dimers with their differing mesogenic groups. For example, dimers with smectic phases having monolayer, interdigitated and intercalated structures have been discovered. We have used DSC to determine the smectic A–nematic transition entropies for non-symmetric dimers having intercalated phases. In addition we have employed EPR and ²H NMR spectroscopy to investigate the orientational order of the nematic and intercalated smectic phases. We have observed a marked reduction in the odd–even effect at the intercalated smectic A–nematic phase transition. This is revealed by an unexpectedly large change in the entropy and increase in the orientational order for the odd spacer dimers at the transition, after allowance is made for the length of the preceding nematic range.