Dilatometric Studies across Intra-Smectic Transitions in Some Homologues of N-(p-n-octyloxybenzylidene)p-n-alkylanilines

Abstract

The variation of density with temperature in four homologues of N-(p-n-octyloxy benzylidene)p-n-alkylanilines, 8O.m's, viz., N-(p-n-octyloxybenzylidene)p-n-pentylaniline, 8O.5, N-(p-n-octyloxy-benzylidene)p-n-hexylaniline, 8O.6, N-(p-n-octyloxybenzylidene)p-n-heptylaniline, 8O.7, and N-(p-n-octyloxybenzylidene)p-n-nonylaniline,8O.9, is reported. Results infer first order nature of isotropic to smectic-A (IA), smectic-A to smectic-B (AB) and smectic-C to smectic-B (CB) transitions, while smectic-A to smectic-C (AC) transition is found to be second order. The pressure dependence of the transition temperatures is estimated from the Clausius-Clapeyron equation using density and enthalpy data. Pre-transitional effects are estimated in the vicinity of fluctuation dominated non-linear regions of isotropic to smectic-A phase transition in all the compounds and the results are discussed in the light of the available data on other nO.m compounds.