Tricritical behavior of the smectic-hexatic phase transitions in binary mixtures using the landau mean field theory

The smectic-hexatic phase transitions are studied by the Landau mean field theory in binary mixtures, particularly, THI-14 + MPR-6 liquid crystalline system. By considering the phase lines of SmA-Hex B, SmC-SmF (Hex F) and SmF-Hex B as the first order; SmA-SmC and SmC-SmF as the second order, in the presence of the two tricritical points (C-F-B and A-C-B), we calculate the T-X phase diagram of the binary mixture studied. The phase line equations obtained from the free energies of the smectic and hexatic phases, are fitted to the experimental data given in the literature.We find that the Landau mean field theory explains satisfactorily the observed T-X phase diagram for the smectic-hexatic transitions in the binary mixture of THI-14 + MPR-6.