Phase Transitions in p-(Phenyl Benzylidene)-p¹-Alkylaniline Compounds: A Dilatometric Study

Abstract

Dilatometric studies are carried out on liquid crystals (LCs), viz., p-(phenyl benzylidene)-p 1 - alkylanilines (PBnA for n = 7 - 10, 12, 14 and 16). LC PBnA compounds are found to exhibit four different types of phase variants. The lower homologues (for n = 3 - 6) exhibit an NBE trivariant, intermediate homologues (with n = 7 - 9) exhibit an NABE tetravariant, higher homologues (for n = 10 - 12) exhibit an ABE tetravariant, and long higher homologues (for n = 14 and 16) exhibit an AB bivariant phase sequence. Dilatometry studies in PBnA compounds infer the first order nature for IN (for n = 7, 8 and 9), IA (for n = 10, 12, 14 and 16), NA (for n = 8 and 9) and AB (for n = 14 and 16) phase transitions. Phase transitions involving the growth of the 3D smectic-B phase in PBnAs are found to be tuned by squeezing of orientational disorder. A comparative study of phase transitions exhibited by PBnA compounds is presented along with the data in other Schiff base compounds.