Rotating field induced torque on ferrofluid emulsion with deformable dispersed phase microdrops

Abstract

The application of ferrofluids for actuation purposes is a very active research area and the development of advanced techniques in this field is of great interest. In this work the macroscopic mechanical effects in a ferrofluid emulsion associated with internal rotations of dispersed phase microdrops are studied experimentally. The studied emulsion microdrops are easily deformed under the action of a rotating magnetic field due to a low interfacial tension and take the flattened shape in a plane of field rotation. The rotations of microdrops produce a macroscopic torque in a restricted volume of an emulsion. Particularly the magnetic torque induced rotations of a spherical cavity filled with a ferrofluid emulsion and a nonmagnetic sphere floating on the surface of a ferrofluid emulsion were observed. The value of the magnetic torque has been measured as a function of the magnetic field strength and rotation frequency. The magnitude of the resulting torque in ferrofluid emulsions is higher than that in pure ferrofluids of equal magnetic content. The translatory motion of a spherical cavity filled with a ferrofluid emulsion and a nonmagnetic sphere floating on the surface of a ferrofluid emulsion was observed, and the translation velocity was measured. The studied actuation mechanism can be used for intensification of delivery process in biomedical and engineering applications