Critical heat capacity at the smectic A smectic C transition in a partially fluorinated liquid crystal

A high resolution a.c. calorimetric study of a phenyl pyrimidine derivative with one alkyl and one perfluorinated end group shows that the excess heat capacity associated with the smectic A-smectic C transition exhibits critical fluctuation behaviour that is consistent with the three-dimensional XY universality class. This is in contrast to the usual mean-field SmA-SmC behaviour and the near tricritical fluctuation behaviour reported recently in several other compounds. It is speculated that smaller than usual correlation lengths are the cause for the wide fluctuation region in this compound.