A new technique for the measurement of the dynamic evolution of surface tension.

We develop a novel technique which deduces the surface tension in air of a fluid as a function of surface age, beginning at age zero. The technique utilizes pointwise measurements of perpendicular free surface profiles of a steady oscillating jet corresponding to a discretization interval on the order of 0.1 ms. We implement the technique on constant-surface-tension test fluids (100% ethanol and 15% ethanol/85% water by volume) to demonstrate the extent to which the technique can qualitatively capture that the surface tensions of these fluids are constant in time, and quantitatively produce values of these constants consistent with static measurements. We then implement the technique on jets of two agricultural surfactant mixtures, Triton X-405 and Triton X-100, and quantitatively deduce the decay of surface tension as a function of surfactant concentration.