A novel fast technique for measuring dynamic surface and interfacial tension of surfactant solutions at constant interfacial area

A novel, fast formed drop technique is developed for measuring dynamic surface and interfacial tension of surfactant solutions. It employs the basis of the capillary pressure methods. A new way of formation of a fresh interface is the key point in the proposed technique. It is based on the fact that a jet of liquid flowing out of a capillary breaks very fast after a sudden stop of the how, but a small drop with a fresh interface remains at the capillary tip. Once the drop is formed, its size (and thereby its area) remains constant, while the capillary pressure is measured with a pressure transducer, The dynamic surface (or interfacial) tension is calculated by means of the Laplace equation for capillarity. In this way, measurements under constant interfacial area in a time domain from about 50 ms up to several minutes or more can be made. The measurements with pure liquids give constant values of the dynamic surface and interfacial tension equal to the corresponding equilibrium values reported in literature. The dynamic surface tension of Triton X 100 and Triton X 405 solutions measured by the new technique are in a good agreement with those obtained by the static drop weight method. The applicability of the new technique for measuring the dynamic interfacial tension is demonstrated. (C) 1999 Academic Press.