Heat capacity near the smectic-A hexatic-B and hexatic-BE transitions of n-hexyl-4-n-pentyloxybiphenyl-4-carboxylate (65OBC)

High-resolution ac calorimetry was used to measure the heat capacity of n-hexyl-4-n-pentyloxybiphenyl-4-carboxylate in the vicinity of the smectic-A (SmA)hexatic-B and hexatic-B-E transitions. The SmA hexatic-B transition was found to be continuous with critical exponents -=+=0.610.02 and amplitude ratio A+A-=0.840.03. The addition of a crystalline-B material [N-(4-n- butyloxybenzylidene)-4-octylaniline (4O.8), 10 wt.%] produced a weakly-first-order SmA hexatic-B phase transition. The data with | T-Tc |100 mK can be fitted by a power law with =0.490.02 and A+A-=0.820.03. The large values for the critical exponents and the theoretical suggestion that the Sm Ahexatic-B transition may be near tricritical point (t=0.5) are discussed. The hexatic-B-E transition was found to be first order in nature.