Miscibility Studies Indicating a Low Temperature Smectic A Phase in Biaromatic Liquid Crystals with Re-entrant Behaviour
Recent reports [1] have shown that compounds of the homologous series of the 4(4-n-alkyloxy- benzoyloxy)-4′-cyanoazobenzenes (Cn; n = 1 - 12), all have a low temperature smectic A phase (SA″). The homologues with alkyl chain length n≧9 exhibit in addition a high temperature smectic A phase (SA′), separated from the first one by a re-entrant nematic phase (N(re)). Homologues of this series were used for miscibility studies with some compounds of the biaromatic liquid crystal series of the 4-cyano-4′-n-alkyloxybiphenyls (n̄ CBP) and of the 4-cyanobenzylidene- 4′-n-alkyloxyanilines (CN · n̄). The phase diagrams studied show that the smectic A phases of biaromatic liquid crystalline nitrile compounds correspond to the high temperature smectic SA′ type and are not miscible with the low temperature SA″ phase. Moreover, the shapes of the transition temperature curves to the SA″ phase indicate a low temperature smectic A phase (SA″) for the biaromatic compounds. This suggests that for biaromatic compounds with re-entrant behaviour, the dependence of liquid crystalline phase sequences on the alkyl chain length is very similar to that of triaromatic compounds.