AN EXAMINATION ON THE ACCURACY OF INTERFACIAL-TENSION MEASUREMENT FROM PENDANT DROP PROFILES

Interfacial tension (IFT) gamma of a fluid-fluid interface is determin ed by using a video-enhanced pendant drop tensiometry. Fitting the ima ge data of the x and z coordinates of a drop edge to the theoretical d rop profile of the Young-Laplace equation yields four parameters: the location of the apex X(0) and Z(0), the radius of curvature at the ape x R(0), and the capillary constant B. The IFT is then determined by ga mma = Delta rho gR(0)(2)/B, where Delta rho is the density difference between fluids. The accuracy of IFT measurements using the pendant dro p shape technique is carefully studied by examining two systems: air-w ater and n-tetradecane-water-diethylene glycol monohexyl ether, corres ponding to air-liquid and liquid-liquid interfaces, respectively. It i s found that the measured IFT is drop size dependent. The results of a nalysis show that a drop or bubble with a smaller absolute value of ca pillary constant may have larger measurement error due to the limitati on of accuracy on the edge detection of a drop image. Three ways of im provement for accurate measurement of interfacial tension are recommen ded.