Study of Interfacial Tension of Distilled Water Using Pendant Drop Method

The pendant drop tensiometry is a preferred primary method for measuring interfacial tension (IFT) or surface tension. In a typical experimental setup, Gravitational pull opposes an interfacial tension forces to cause a liquid drop to develop into a pendant-like shape. The process comprises quantitatively modifying a theoretical profile generated through calculating the Young–Laplace capillarity formula to such an experimental pendant drop analysis and information by performing digital image analysis. However, specific parameters of this method lead to uncertainty in the obtained value of IFT. The present work aims to determine the role of factors such as evaporation of the hanging drop and its changing volume in interfacial tension, which is acting as major source of error in determining IFT of distilled water. This study details the measurement process and evaluation of standard errors with interfacial tension readings of distilled water by using pendant drop method with three calibrated needles of diameters, 0.9 mm (20 G), 1.27 mm (18 G) and 1.65 (16 G) mm. The needle’s diameter influenced the evaporation rate and the value of IFT. Also, it is essential to consider these factors for further evaluating measurement uncertainties when determining the IFT of biological fluids. In addition, the present study makes an effort to determine the measurement error associated with drop volume and evaporation rate of drop in study. The distilled water used in the measurement had an absolute Interfacial tension of 72 mN/m, and the enlarged measurement errors were predicted to be in the range of 0.4–0.6%. It is critical to consider these associated measurement errors when determining the IFT of liquids for metrological application such as establishing primary standards for measurement pertaining to biological fluids.