A high-sensitivity ac calorimeter system has been developed to investigate the temperature variation of the heat capacity from free-standing liquid-crystal films. We have observed a clear evolution of the heat-capacity anomaly from films of the liquid-crystal compound 650 BC as the films are reduced in thickness from 10 to 4 molecular layers near their bulk smectic-A–hexatic-B transition. Here 650BC refers to n-hexyl-4’-n-pentyloxybiphenyl-4-carboxylate. The four-layer films show a single, sharp, and cusplike heat-capacity peak without thermal hysteresis.

• Received 15 May 1989

DOI:https://doi.org/10.1103/PhysRevLett.63.540