Dielectric studies and critical behaviour in the vicinity of nematic-isotropic phase transition of a smectogenic binary mixture showing induced nematic phase

The phase diagram of a binary mixture composed of compounds, one having NCS terminal group (4DBT, showing smectic A(1) phase) and the other with CN terminal group (11OCB, showing smectic A(d) phase), exhibiting induced nematic phase in a certain concentration range (0.100 < x(4DBT) < 0.951) is reported here. Results of the static dielectric parameters measurement on this binary system within the entire mesomorphic range are presented. Evidence of strong pretransitional behaviour near the nematic-isotropic (N-I) phase transition, indicating the influence of tricritical behaviour, is observed. Precise determination of discontinuity (Delta T) and the critical exponent (alpha) of N-I phase transition have been carried out. Moreover, the order parameter critical exponent beta is correctly predicted by the tricritical hypothesis through the dielectric anisotropy data for all the investigated mixtures.