Calorimetric and Structural Characterization of Thin Liquid-Crystal Films Exhibiting the Smectic- A –Hexatic- B –Crystal- B Transitions

High-resolution heat-capacity and electron-diffraction measurements have been conducted on thin free-standing films of a liquid-crystal compound exhibiting the smectic- A--hexatic- B--crystal- B transitions. Despite the absence of herringbone order, the liquid-hexatic transition in extremely thin films has nevertheless been found to show a pronounced pretransitional heat-capacity anomaly, in disagreement with the predictions of two-dimensional melting theory.