Langmuir, Vol.10, No.12, 4703-4709, 1994
Measurement of Low Interfacial-Tension by Pendant Drop Digitization
Pendant drop tensiometry enhanced by video-image digitization is shown to be a useful tool for the experimental measurement of ultralow dynamic interfacial tension (IFT). Pendant drops of ultralow IFT usually do not have a clear equator due to the low value of capillary constant. A new technique, replacing the classical selected plane method, is developed to obtain the values of capillary constant and the radius of curvature at apex. The IFT is computed from the best-fit between the coordinates of digitized drop profile and the theoretical curve obtained from the Laplace equation. The technique works well for pendant drops with or without an equator. Dynamic interfacial tensions of water + n-tetradecane + C(6)E(2) ternary system and water + AOT + NaCl + heptane two-phase system are reported. The deviation of the IFT measurement is only a few percent.