A method for measuring the interfacial tension for density-matched liquids.

We propose a method to measure the interfacial tension characterizing the interface between two immiscible liquids of practically the same density. In this method, a cylindrical liquid bridge made of one the liquids is vibrated laterally inside a tank filled with the other. The first resonance frequency is determined and equated to the first eigenfrequency of the m=1 linear mode to infer the interfacial tension value. The method does not involve the density jump across the interface. Therefore, its accuracy is affected neither by the smallness of the Bond number nor by errors of the density difference. The experimental setup is relatively simple, and the procedure does not use image processing techniques. The results satisfactorily agree with those measured by TIFA-AI (Theoretical Fitting Image Analysis-Axisymmetric Interfaces) for the same liquid bridges when the density difference is sufficiently large for TIFA-AI to be valid. We conduct numerical simulations of the Navier-Stokes equations to determine the best parameter conditions for the proposed method. The transfer function characterizing the frequency response of the fluid configuration is measured in some experiments to quantify non-linear effects and to study the role played by the outer bath vibration.

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Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.