The experimental study of ferrocolloid surface tension in a magnetic field

Direct measurements of surface tension, viscosity and surface elasticity under the action of external forces are often impossible. In many tasks, the magnetic fluid surface tension is considered to be independent of the magnitude of the applied magnetic field and is determined by the properties of the base fluid. The anisotropy of the magnetic properties at the interface due to the jump in the fluid’s magnetization suggests the dependence of the surface tension tensor on the magnetic field. In this paper, we propose a new experimental method for studying the surface tension of a magnetic fluid in an external uniform magnetic field, depending on the orientation of the magnetic field intensity towards the liquid-gas interface. The study was carried out with the help of modified capillary wave method in a magnetic field orthogonal to the liquid surface and with the ring detachment method in the case of a longitudinal field. It was shown experimentally that the surface tension of a ferrocolloid fluid base (kerosene) does not depend either on the frequency of capillary waves excitation or on intensity of an applied external magnetic field, and corresponds to the value determined with the help of a commercial tensiometer by the standard method of ring detachment. The surface tension of the ferrofluid decreases with increasing intensity of the orthogonal magnetic field interface and with increasing frequency of acoustic vibrations. However, an increase in the field strength longitudinally directed to the interface, provokes an increase in the surface tension of the magnetic fluid. The experimental results are in qualitative agreement with theoretical predictions by A. V. Zhukov: the eigenvalues of the surface tension tensor monotonically increase with the tangential magnetic field component and monotonically decrease with an increase in its normal component.