The re-entrant nematic phase in some pure compounds and their mixtures at atmospheric pressure

Abstract

Recently we reported the occurrence of the re-entrant nematic phase in three pure compounds at atmospheric pressure: (i) trans-p-n-decyloxy-a-methyl-p'- cyanophenyl cinnamate (10 OMCPC), (ii) 4-cyanophenyl-3-methyl-4(4-n-undecyl- benzoyloxy) benzoate (11CPMBB) and (iii) 4-cyanophenyi-3-methyl-4 (4-n-dodecyl- benzoy loxy) benzoate (12CPMBB) . We have now studied the light scattering arising from twist fluctuations as a function of temperature in these compounds which again confirms the formation of the re-entrant nematic phase. We also present in this paper, phase diagrams of binary mixtures involving these compounds. In addition, we have determined the orientational order parameter in the nematic, smectic A and re-entrant nematic phases using (a) infrared dichroic studies on homeotropically aligned samples, and (b) optical birefringence studies again on homeotropically aligned samples employing a new technique.