A new method of interface tension measurement of a magnetic fluid drop

Abstract

A new method for determining the interfacial tension of a magnetic fluid (MF) is proposed on the basis of deformation of a MF drop lying on a liquid substrate and subjected to a vertical uniform magnetic field. 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 were 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. The magnetic field causes the drop to elongate till the peak instability. The critical values of the field strength respond to the ferrofluid initial magnetic susceptibility. The ratio of the critical magnetic field values is determined by the ratio of the interfacial tension.

Magnetowetting dynamics of sessile ferrofluid droplets: a review

“…Khokhryakova et al 109 (and also ref. 183) showed that both the peak-formation instabilities occur at different magnetic fields and that the ratio of these two critical field intensities was correlated to the measurement of the surface/interfacial tensions. We have previously explained the deformation dynamics of an FF droplet in this configuration 109 in relation to Fig.…”

“…For all the systems studied in both ref. 109 and 183, the first peak was formed at the submerged part of the FF droplet dispensed atop a liquid substrate, i.e. , deformation of the liquid–liquid interface, and followed by peak formation at the upper part, i.e.…”

“…The surface tension or interfacial tension is either measured by calculating the wavelength of the peak instability in a perpendicular magnetic field 179,181 or via comparing the shape of the stretched magnetic fluid droplet to that of the modeled drop in a longitudinal field, 79,182 or using the capillary rise method. 179 Most recently, a fascinating method was proposed, 109,183 wherein the peak-formation instability on both the free surface in contact with air as well as the oil-water interface was considered for measuring the surface tension (see Fig. 8), after subjecting an FF droplet, dispensed atop a deformable liquid surface to a homogeneous perpendicular magnetic field.…”

Does Magnetic Field Influence the Surface Tension of Ferrofluid?

“…12 Indirectly, surface tension can be estimated by analyzing the spatial scale of this relief. 10,13,14 Another class of techniques is based on the analysis of the shape of a FF droplet suspended in a nonmagnetic liquid, or drop-like aggregates being a condensed phase of the surrounding FF. These droplets elongate in the external MF.…”

“…In a transversely homogeneous MF this phenomenon results in the emergence of Rosensweig surface instability and the formation of a stationary topography . Indirectly, surface tension can be estimated by analyzing the spatial scale of this relief. ,, …”