A spinning-drop technique was used to study the thermal variation in the surface tension at a liquid crystal-isotropic liquid interface. A polymesomorphic liquid crystal with nematic and smectic A phases bounded by an isotropic liquid (glycerine) was used for the present study. The surface tension-temperature characteristics, unlike the monotonically decreasing dependence found in most isotropic liquids, showed regions with a positive slope for both the smectic A and the nematic phases. A sharp increase in slope of the surface tension-temperature characteristic was observed near the smectic A-nematic and nematic-isotropic transition temperatures, indicating that excess surface order is developing near these transitions. The observed results are in compliance with the available theoretical predictions.
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