Influence of drop volume on surface tension evaluated using the pendant drop method

The pendant drop technique is one of the most accurate methods to measure surface tension of liquids. Recently, it has been found that the value of the surface/interfacial tension found using the pendant drop method might be drop-volume dependent. In this work, the surface tension of glycerol at a 25 °C and the surface tension of polypropylene at 240 °C were measured using the pendant drop method for different drop volumes. It was shown that the values of the surface tension depend on the drop size if no calibration to take into account the anisotropy in the optical enlargement is performed. However, when a calibration procedure for optical anisotropy correction is performed, the values of the surface tension obtained do not depend on the volume drop size and they corroborate the values in the literature.