Experimental studies of the surface tension of nematic liquid crystals

Abstract

Equilibrium measurements of surface tension have been carried out on nematic compounds using the pendant drop method. A drop of the liquid crystal is suspended at the tip of a capillary tube inside a completely enclosed thermostatic chamber filled with an inert gas and is maintained in equilibrium with its saturated vapour throughout the experiment. The surface tensiontemperature characteristic for all the compounds studied show anomalous behaviour. The slope in the nematic phase is initially negative but changes sign near the nematic-isotropic transition for p-azoxyanisole, p-anisaldazine and p-methoxy benzylidene-p'-n-butylaniline, whereas for p-azoxyphenetole the change of slope occurs in the isotropic phase. The original monotonically decreasing trend is regained in all the cases at higher temperatures in the isotropic phase. The data on p-azoxyanisole, p-azoxyphenetole and p-anisaldazine confirm the earlier measurements of Ferguson and Kennedy1 on the same compounds. The observed features are in qualitative agreement with the theoretical predictions of Croxton and Chandrasekhar.6