Buoyancy effects in the spinning-drop interfacial tensiometer

Abstract

Interfacial tension measurements for the n-butanol/water system at 25.0°C were performed with a spinning-drop apparatus. At rotational frequencies above 5000 rpm the measured interfacial tension is found to be constant, independent of frequency and drop volume. At lower frequencies, the drop is displaced away from the rotation axis of the system by a combination of Coriolis and buoyancy forces. Measured displacements are in good agreement with a theoretical model, in which Ekman layers play a dominant role in the description of the drop behavior. However, the model is not capable of explaining the observed falloff in the apparent values of interfacial tension at low frequency.