Measurement of Dynamic Interfacial Tension by an Expanding Drop Tensiometer

Abstract

An accurate, nonintrusive method is described to measure the dynamic tension of dilated liquid-liquid interfaces. In this method, the time-dependent pressure difference across the curved interface of an expanding spherical drop, immersed in the second immiscible phase, was measured as a function of time. A sensitive apparatus employing this principle was constructed. Experiments were performed with a drop of dodecane expanding in an aqueous solution of a nonionic surfactant. In such a system, the dynamic interfacial tension depends upon the adsorption kinetics of the surfactant. A diffusion/adsorption model was formulated to describe the transport and exchange of surfactant species with the interface and the bulk phases. The analytical solution for this model was in good agreement with experimental data. The experiment also provided a direct value of the Gibbs elasticity. The noninvasiveness and the direct measurement of the capillary pressure make this technique an attractive and powerful tool.