Deformation of ferrofluid floating drop under the action of magnetic field as method of interface tension measurement

The deformation of a kerosene-based ferrofluid drop lying on a liquid substrate and subjected to a vertical uniform magnetic field has been studied experimentally. In the absence of magnetic field the drop has a shape of two vertical axisymmetric semi-ellipsoids of different height which are joined at the plane of the interface between air and liquid substrate. The results show that the drop elongates in the direction of the field with an increase of its intensity. As soon as the field strength reaches a certain value, the interface and the free surface of the drop become unstable, which causes the peaks of different height to form. It has been found that the ratio of the corresponding critical values of magnetic field intensity is determined by the ratio of surface tension at the interface to that on the free boundary of the drop. Surface and interfacial tension of liquids used in the experiment was measured with the help of tensiometer by the ring detachment method to verify the experimental data. The presented results on the ferrofluid interface tension measurements can be of interest for the specialists in the field of ferrohydrodynamics.