Experimental determination of the surface tension of nematic liquid crystals

Abstract

Equilibrium measurements of surface tension have been carried out on p-anisaldazine and p-azoxyanisole in the nematic and isotropic phases using the pendaot drop method. The drop was completely enclosed in a chamber filled with inert atmosphere and maintained at all times in equilibrium with its saturated vapour. The surface tension-temperature characteristic shows a marked anomaly for both compounds ; the slope in the nematic phase is initially negative and then reverses sign as the temperature approaches the nematic-isotropic transition point. For p-anisaldazine the slope again becomes negative immediately after the transition whereas for p-azoxyanisole the positive slope extends for a few degrees in the isotropic phase before changing sign at higher temperatures. The observed features are in qualitative agreement with the theoretical predictions of Croxton and Chandrasekhar.