THEORETICAL-STUDY OF THE ANOMALOUS SURFACE-TENSION PROPERTIES OF LIQUID-CRYSTALS

We study the surface properties of a molecular model of a liquid cryst al using a density functional theory. The intermolecular interaction i ncludes a Maier-Saupe term as well as terms which break the orientatio nal symmetry at the interface. These latter contributions prove to pla y an essential role in the explanation of some of the anomalous surfac e-tension features observed in experimental systems. In particular, a dramatic surface tension maximum above the clearing point T-NI is Seen to be associated with increased nematic order close to the nematic-va por interface. In addition, further reduction of the surface tension w ith decreasing temperature below T-NI is observed to be related either with rapidly increasing surface-enhanced order, in which case there i s a surface tension minimum, or with growing surface smectic order abo ve the nematic-smectic transition temperature. (C) 1998 American Insti tute of Physics.