Critical behavior of thermal parameters at the smectic-A-hexatic-B and smectic-A-smectic-C phase transitions in liquid crystals.

High temperature resolution measurements of thermal conductivity, thermal diffusivity, and specific heat, with simultaneous polarized light visual inspection of the sample, have been performed at two different liquid crystal phase transitions: the SmA-SmC (Smectic-A-Smectic-C) and the SmA-HexB (Smectic-A-hexatic-B) in racemic A7 [4-(3-methyl-2-chlorobutanoyloxy)-4(')-heptyloxybiphenyl] and 65OBC (n-hexyl-4(')-n-pentyloxybiphenyl-4-carboxylate) compounds, respectively. In the past, anomalies in the thermal conductivity at the transitions have been reported. Our results indicate a nonsingular behavior of the thermal conductivity at both transitions, similarly to what has been previously reported for the smectic-A-nematic phase transition. It is also shown how, in several cases, the nature of the transition can be affected by the sample thermal history due to the presence of strain annealing phenomena.