Nature of the smectic-A–smectic-Ctransition of a partially perfluorinated compound

The smectic-A--smectic-C phase transition of one partially perfluorinated liquid-crystal compound has been investigated by performing detailed calorimetric studies of both bulk samples and free-standing films. The heat-capacity data from thin free-standing films demonstrate the importance of fluctuations due to reduced dimensionality. Moreover, the data from bulk samples and thick films cannot be adequately described by the customary extended mean-field model. Discussions of other fitting schemes are presented. The free-standing film and bulk data are most consistent with a functional form based on the extended mean-field model but including Gaussian fluctuations. Moreover, the inclusion of Gaussian fluctuation terms adequately accounts for the observed film thickness dependence of smectic-A--smectic-C heat-capacity anomaly exhibited by this partially perfluorinated compound. {} 1996 The American Physical Society.