Surface tensions of smectic liquid crystals

We determine surface tensions sigma of smectic liquid crystals from the curvature pressure of smectic films. A new technique is introduced for the comparison of surface tensions of different smectic materials. The method is based on the relation of curvatures of smectic films drawn on communicating vessels. The measurement of the temperature dependence of sigma reveals anomalies in the vicinity of phase transitions to low temperature smectic modifications. This anomalous slope d sigma /dT can be related to the surface excess entropy of the material in the corresponding temperature range. The surface tension values determined for a number of mesogens fit well into the classification proposed by Mach et al.