Some Aspects of Spinning Drop Tensiometry

The spinning drop technique is used routinely for measuring surface and interfacial tensions of and between fluids. This report aims to investigate the cause of—and to provide solutions to—some commonly encountered problems that have to do with the difficulty of releasing the drop from the tube wall. It is concluded that such problems are caused by inadequate maximum rotational speeds and/or tube diameters that are typical of commercial instruments. Clear criteria are developed for the optimum design and successful operation of the instrument. In the process, we have discovered the existence of unusual and novel drop shapes that could be used to advantage.