Definitive evidence for the existence of an effective interfacial tension between miscible fluids: Isobutyric acid and water in a spinning drop tensiometer

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Conference Proceeding

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For over one hundred years, there have been reports that miscible fluids could exhibit an effective interfacial tension (EIT). However, the results were only suggestive. Light scattering data has provided the most compelling evidence to date. We report here definitive evidence for an effective interfacial tension between two miscible fluids using spinning drop tensiometry. Isobutyric acid and water have an Upper Critical Solution Temperature (UCST) of 26.3°C. We create a drop of IBA in water below the UCST and then increase the temperature above it. Long after the fluids have reached thermal equilibrium, the drop persists. The drop contracts when the rotation rate is decreased, indicating an interfacial tension exists. When the rotation rate is dropped from 7000 rpm to 1500 rpm, the drop breaks up via the Rayleigh-Tomotika instability. We calculate the interfacial tension from the Vonnegut formula.

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43rd AIAA Aerospace Sciences Meeting and Exhibit - Meeting Papers

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