Temperature variation of film tension measured by a vibrating membrane tensiometer

We have constructed a vibrating membrane tensiometer that utilizes a phase lock-in technique to track a resonant peak. This experimental apparatus enables us to obtain the temperature variation of the film tension in a continuous manner. The film tension of two different liquid crystal compounds has been measured with resolution better than 0.2%. The results from a 126 nm-thick film in the crystal-B phase of one compound yield a bulk tension value of 2.5 dyn/cm. We interpret several reproducible features of our tensiometer data in the context of surface and bulk phase transitions.