The temperature variation of surface tension in free standing films of three liquid-crystal compounds was measured, using a curvature-pressure tensiometer. The tensiometer used a feedback loop to hold constant the curvature of a film, while the temperature of the system was smoothly ramped. A choped intensity-stabilized He-Ne laser beam was reflected from the bubble to a position-sensitive photodiode. Using the tensiometer, the temperature variation of surface tension was obtained in a continuous manner with resolution in surface tension of ∼0.2%.
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